全文获取类型
收费全文 | 8656篇 |
免费 | 390篇 |
出版年
2023年 | 38篇 |
2020年 | 121篇 |
2019年 | 177篇 |
2018年 | 493篇 |
2017年 | 394篇 |
2016年 | 495篇 |
2015年 | 187篇 |
2014年 | 170篇 |
2013年 | 2017篇 |
2012年 | 248篇 |
2011年 | 397篇 |
2010年 | 400篇 |
2009年 | 262篇 |
2008年 | 266篇 |
2007年 | 325篇 |
2006年 | 169篇 |
2005年 | 139篇 |
2004年 | 105篇 |
2003年 | 103篇 |
2002年 | 113篇 |
2001年 | 144篇 |
2000年 | 105篇 |
1999年 | 113篇 |
1998年 | 92篇 |
1997年 | 80篇 |
1996年 | 84篇 |
1995年 | 69篇 |
1994年 | 60篇 |
1993年 | 73篇 |
1992年 | 71篇 |
1991年 | 60篇 |
1990年 | 63篇 |
1989年 | 57篇 |
1988年 | 54篇 |
1987年 | 63篇 |
1986年 | 62篇 |
1985年 | 69篇 |
1984年 | 79篇 |
1983年 | 84篇 |
1982年 | 69篇 |
1981年 | 69篇 |
1980年 | 67篇 |
1979年 | 62篇 |
1978年 | 66篇 |
1977年 | 67篇 |
1976年 | 63篇 |
1975年 | 72篇 |
1974年 | 44篇 |
1973年 | 39篇 |
1972年 | 43篇 |
排序方式: 共有9046条查询结果,搜索用时 31 毫秒
131.
This paper introduces a pattern recognizer, similar to weighting schemes used in combining time series forecasts, for use in spatial adaptive filtering applied to estimating multivariate cross-sectional models. The pattern recognizer enhances the ability to automatically detect and estimate parameters with discontinuous or sharp gradient changes over geographic contexts. Results from Monte Carlo studies suggest that the weighted spatial adaptive filter is at least as accurate as the unweighted filter for cases having smoothly changing parameters, but superior for cases having discontinuous, step-jump parameters. A case study on illicit drug-market activities using census tract-level data from Pittsburgh, Pennsylvania, further illustrates the advantages of the weighted filter. 相似文献
132.
133.
Jack Vowdes 《Australian journal of political science》1994,29(1):96-114
New Zealand has had a reputation for high voting participation, but age‐eligible turnout has declined since 1938 and, despite a brief recovery between 1975 and 1984, continued to fall subsequently. By 1990 it was far closer to the average turnout of Western democracies. Brief analysis of aggregate data since 1938 sets the scene for more specific study of individual‐level data from the 1963, 1981, and 1990 elections, which indicates effects which are minimal for institutional factors, small for social and demographic variables, and substantial for changes in public attitudes. In particular, dealignment of the party system and voter demobilisation are associated with declining interest in politics, political efficacy, and party identification. While also associated with extra‐parliamentary mass action to the partial detriment of voting among the university‐educated in 1981, a more general mobilisation of postmaterialist issues was probably responsible for the post‐1975 turnout recovery. After 1984 the longer‐term trend was reestablished. 相似文献
134.
Fifty-three copper-based metal fragments, recovered from the Robitaille site in southcentral Ontario, were analysed by neutron activation to establish their chemical make-up and to sort them by their trace elemental chemistries. Three different European copper samples, one brassy copper and 48 brass samples with five different chemistries were found. As few as eight trading actions may account for all of the recovered European metal fragments. 相似文献
135.
136.
The possibility of lead isotope fractionation in ancient lead production is examined. Kinetic theory relating to isotopic fractionation in non-equilibrium evaporation is considered and the feasibility of the alteration of lead isotope abundance ratios in ore roasting and smelting is assessed. Previous experimental work is shown to have been inconclusive and conclusions are drawn on the need for further research to quantify the possible extent of fractionation in practice. 相似文献
137.
D. E. NELSON G. CHALOUPKA C. CHIPPINDALE M. S. ALDERSON J. R. SOUTHON 《Archaeometry》1995,37(1):151-156
Accelerator mass spectrometry radiocarbon ages have been taken for a test suite of small samples of material removed from some of the ‘beeswax’art figures found in rock shelters in northern Australia. The results indicate that we can reliably date this unique form of rock art with no noticeable damage. We had not expected to find figures of any great antiquity, and so we were surprised to find that the ages obtained spanned the time period from the recent past to about 4000 BP. 相似文献
138.
A Roman archaeological site in northern Spain (La Maja, province of La Rioja) includes pottery workshops, part of an important ceramic industry that developed from about the first century BC to the first century AD. A geophysical study was planned to determine the extent of the industrial complex in the vicinity of an excavated kiln. Magnetic observations were done on a grid of 30 × 36m, with a sampling interval of 1m. Two dipolar-shaped anomalies were found: one in the north-east and the other in the south-west of the area. Low-pass and band-pass filters were used in the Fourier domain to enhance the characteristics of the magnetic data and to remove noise and undesirable shallow features. Three-dimensional polygonal prisms were used to model the magnetic anomalies based on palaeomagnetic measurements performed over an uncovered kiln that helped to constrain the induced and remanent parameters of the magnetizing fields. 相似文献
139.
In recent decades, many Appalachian households have experienced declining incomes due to the loss of traditional male jobs in the mining and manufacturing sectors. One response to this decline has been an increase in female employment in formal sector activities. Another response is homework, or the home-based production of goods and services for sale in the formal and informal sectors. In rural Appalachia, where formal jobs are often unavailable or inadequate to support a household, many women are engaging in homework as an economic strategy. Consequently, economic restructuring cannot be fully understood without analyzing household strategies and gender relations. This paper examines the intersection of gender, households, and economic restructuring as it relates to women's homework and employment shifts in rural Appalachia. Research for this paper entailed qualitative interviews with 50 West Virginia women who are engaged in the home-based production of goods and services. The study analyzes the variety of homework activities done by rural women, their contribution to household incomes, and the effect of these activities on gender relations and divisions of labor in the home. The research forwarded in this study advances a conceptual understanding of household economic strategies and has some practical applications for women and economic development in underdeveloped regions . 相似文献
140.
Shields MP 《Journal of regional science》1995,35(1):117-134
"A hedonic migration model is developed where regional amenities are viewed as influencing household production within the framework of the new demand theory. The inputs to household production are goods, time and housing. It is shown that economic growth in the economy as a whole will increase the relative attractiveness of regions that are relatively time-saving, in the sense that they have a lower time elasticity of household production. Hence, migration will flow into time saving regions and housing costs in those regions will rise as real GDP grows." The implied geographical focus is on the United States. 相似文献