全文获取类型
收费全文 | 8128篇 |
免费 | 368篇 |
出版年
2023年 | 53篇 |
2020年 | 145篇 |
2019年 | 158篇 |
2018年 | 299篇 |
2017年 | 304篇 |
2016年 | 356篇 |
2015年 | 218篇 |
2014年 | 223篇 |
2013年 | 2146篇 |
2012年 | 239篇 |
2011年 | 286篇 |
2010年 | 231篇 |
2009年 | 206篇 |
2008年 | 194篇 |
2007年 | 153篇 |
2006年 | 155篇 |
2005年 | 113篇 |
2004年 | 103篇 |
2003年 | 86篇 |
2002年 | 80篇 |
2001年 | 135篇 |
2000年 | 103篇 |
1999年 | 117篇 |
1998年 | 95篇 |
1997年 | 89篇 |
1996年 | 77篇 |
1995年 | 64篇 |
1994年 | 62篇 |
1993年 | 95篇 |
1992年 | 81篇 |
1991年 | 62篇 |
1990年 | 63篇 |
1989年 | 71篇 |
1988年 | 61篇 |
1987年 | 84篇 |
1986年 | 62篇 |
1985年 | 82篇 |
1984年 | 60篇 |
1983年 | 110篇 |
1982年 | 82篇 |
1981年 | 82篇 |
1980年 | 85篇 |
1979年 | 63篇 |
1978年 | 72篇 |
1977年 | 89篇 |
1976年 | 71篇 |
1975年 | 73篇 |
1974年 | 57篇 |
1973年 | 51篇 |
1971年 | 56篇 |
排序方式: 共有8496条查询结果,搜索用时 15 毫秒
991.
Sila Tripati G. Parthiban K. H. Vora Sundaresh S. N. Bandodker 《International Journal of Nautical Archaeology》2003,32(2):225-237
Various types of lead ingots have been reported from a number of shipwrecks from different parts of the world. In 1991 exploration of a wreck off Poompuhar, Tamil Nadu, East Coast of India, at a depth of 19 m yielded a gun, rudder gudgeon, gunpowder boxes and a variety of lead ingots. The most significant ingots are those marked W: Blackett and D with a crown symbol on the obverse and 1791, 1792 and some merchant marks on the reverse. These are similar to Blackett lead ingots found in England, the Netherlands and Sumatra. Pb-isotopic analysis has revealed their source as the North Pennine lead mines of England. Further, the lead used was of high purity -93%. Records show that Blackett was a well-known lead-exporting company in England since 1694. The wreck off Poompuhar may be a Toni type cargo ship carrying traded lead ingots of different manufacturers. 相似文献
992.
Overpressure in ‘old’ sedimentary basins that have not undergone rapid, recent sedimentation cannot be easily explained using traditional burial‐driven mechanisms. The last significant burial event in the Cooper Basin, Australia, was the Late Cretaceous deposition of the Winton Formation (98.5–90 Ma). Maximum temperature in the basin was attained during the Late Cretaceous, with cooling beginning prior to 75 Ma. Hence, overpressure related to rapid burial or palaeomaximum temperatures (e.g. hydrocarbon generation) must have developed prior to 75 Ma. Retaining overpressure for 75 Ma in ‘old’ basins such as the Cooper Basin requires extremely low seal permeabilities. An alternative explanation is that overpressure in the Cooper Basin has been generated because of an increase in mean stress associated with an increase in horizontal compressive stress since Late Cretaceous times. Structural observations and contemporary stress data indicate that there has been an increase in mean stress of approximately 50 MPa between Late Cretaceous times to that presently measured at 3780 m. The largest measured overpressure in the Cooper Basin is 14.5 MPa at 3780 m in the Kirby 1 well. Hence, disequilibrium compaction driven by increasing mean stress can explain the magnitude of the observed overpressure in the Cooper Basin. Increases in mean stress (tectonic loading) may be a feasible mechanism for overpressure generation in other ‘old’ basins that have undergone a recent increase in horizontal stress (e.g. Anadarko Basin). 相似文献
993.
ISSUES IN SPATIAL DATA ANALYSIS 总被引:2,自引:0,他引:2
Daniel P. McMillen 《Journal of regional science》2010,50(1):119-141
ABSTRACT. Misspecified functional forms tend to produce biased estimates and spatially correlated errors. Imposing less structure than standard spatial lag models while being more amenable to large datasets, nonparametric and semiparametric methods offer significant advantages for spatial modeling. Fixed effect estimators have significant advantages when spatial effects are constant within well-defined zones, but their flexibility can produce variable, inefficient estimates while failing to account adequately for smooth spatial trends. Though estimators that are designed to measure treatment effects can potentially control for unobserved variables while eliminating the need to specify a functional form, they may be biased if the variables are not constant within discrete zones. 相似文献
994.
ABSTRACT There is a strong connection between per‐worker productivity and metropolitan area population, which is commonly interpreted as evidence for the existence of agglomeration economies. This correlation is particularly strong in cities with higher levels of skill and virtually nonexistent in less skilled metropolitan areas. This fact is particularly compatible with the view that urban density is important because proximity spreads knowledge, which either makes workers more skilled or entrepreneurs more productive. Bigger cities certainly attract more skilled workers, and there is some evidence suggesting that human capital accumulates more quickly in urban areas. 相似文献
995.
From sustainable development to carbon control: eco-state restructuring and the politics of urban and regional development 总被引:2,自引:0,他引:2
Aidan While rew E G Jonas David Gibbs 《Transactions (Institute of British Geographers : 1965)》2010,35(1):76-93
The management of carbon emissions holds some prospect for challenging sustainable development as the organising principle of socio-environmental regulation. This paper explores the rise of a distinctive low-carbon polity as an ideological state project, and examines its potential ramifications for the regulation of economy–environment relations at the urban and regional scale. Carbon control would seem to introduce a new set of values into state regulation and this might open up possibilities for challenging mainstream modes of urban and regional development in a manner not possible under sustainable development. But low-carbon restructuring also portends intensified uneven development, new forms of state control and a socially uneven reworking of state–society relations. In order to explore these issues we start by setting out a framework for conceptualising environmental regulation based around the idea of eco-state restructuring. This idea is introduced to capture the conflicts, power struggles and strategic selectivities involved as governments seek to reconcile environmental protection with multiple other pressures and demands. Overall the paper seeks to make a distinctive contribution to theoretical work on state environmental regulation and the emerging spatial dimensions of climate policy. 相似文献
996.
Many indigenous populations are experiencing rural-to-urban migration. In making this transition, indigenous peoples are entering industrial societies where most income derives from wages or salaries, and formal educational achievement is crucial in determining economic prospects. This research analyzes the gap in test score results between Aboriginal and non-Aboriginal students in public schools in the Canadian province of British Columbia. It finds a strong effect of school quality, as measured by non-Aboriginal achievement, on Aboriginal achievement. It also finds a nonlinear negative relationship between Aboriginal achievement and the number of Aboriginal students in a school over the empirically observed range. It thus suggests a possible trade-off and dilemma between, on the one hand, policies that enable Aboriginal students to concentrate in a few schools able to provide a culturally sensitive curriculum and, on the other, policies to maximize Aboriginal academic achievement. 相似文献
997.
James G. Carrier 《对极》2010,42(3):672-689
Abstract: One of the ways that conservation and capitalism intersect is in ethical consumption, the shaping of purchasing decisions by an evaluation of the moral attributes of objects on offer. It is increasingly important as a way that people think that they can affect the world around them, including protecting the natural environment. This paper describes commodity fetishism in ethical consumption, and the degree to which this fetishism makes it difficult for ethical consumers to be effective both in their evaluation of objects on offer and in influencing the world around them. It looks at three forms of fetishism in ethical consumption: fetishism of objects, fetishism of the purchase and consumption of objects, fetishism of nature. 相似文献
998.
Richards et al. (2000) reconstructed the diet of the human remains found in Gough's and Sun Hole Cave through isotope analysis. They concluded that these people consumed an entirely terrestrial-based diet. Their reconstruction was based upon comparison of the results from human bones with those from a very small number of associated animals. The diets of the Gough's and Sun Hole Cave human were different from the other six Upper Palaeolithic humans from the British Isles for which dietary information has been obtained through isotope analysis. The work of Richards et al. (2000) suggests that they were the only ones for whom marine or freshwater resources did not play a significant role in their diets. We test this through further analyses of faunal remains from Gough's Cave, Sun Hole and other contemporary sites (Kent's Cavern, Aveline's Hole, Kendrick's Cave). Despite the limited faunal sample, the original palaeodietary reconstruction is broadly consistent with our findings. The isotope values of the main protein sources consumed by the humans from both sites are consistent with those of red deer and bovines, and, for a single individual, with that of horse and red deer. Reindeer was postulated in the original reconstruction as a potential food source, but this seems very unlikely based on our isotope reconstruction and the archaeological remains. 相似文献
999.
Is it possible to identify cooked, rather than burnt, bone? Mild heating (≤100 °C,1 h) – typical of cooking – does not lead to detectable changes in any biochemical parameter of bone yet measured. If it is only possible to detect charred bone, how is it possible to detect cooking in the archaeological record? In a previous paper (Koon et al., 2003, J. Arch. Sci.), we used a Transmission Electron Microscopy (TEM) based approach to investigate changes in the organization of the bone protein, collagen, as it is heated, using bone from heating experiments and short term burials. The work revealed that mineralized collagen, despite requiring aggressive treatment to gelatinise the protein (e.g. 90 °C, 240+ h), readily accumulates minor damage. We believe that the presence of mineral matrix stabilises the collagen enabling the damage to accumulate, but preventing it from causing immediate gelatinisation. Once the mineral is removed, the damage can be observed using appropriate visualization methods. 相似文献
1000.
The discovery of a Late Bronze Age trading vessel at Uluburun near Ka? off the Turkish coast offers exciting possibilities for our understanding of Bronze Age trade. On board the ship was a large consignment of glass ingots that were assumed to originate either from Mesopotamia or Egypt. This paper presents the results of major and trace elemental analyses of three deep blue and turquoise glass ingots from the Uluburun wreck, and for the first time securely demonstrates that their composition is consistent with an Egyptian origin. The compositional similarity of the glass ingots to glasses from the Mycenaean world suggests that Egypt was exporting to that region via trading ships such as that from Uluburun. 相似文献