首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5082篇
  免费   138篇
  2024年   15篇
  2023年   64篇
  2022年   89篇
  2021年   90篇
  2020年   200篇
  2019年   167篇
  2018年   219篇
  2017年   219篇
  2016年   240篇
  2015年   144篇
  2014年   141篇
  2013年   659篇
  2012年   304篇
  2011年   292篇
  2010年   208篇
  2009年   260篇
  2008年   263篇
  2007年   307篇
  2006年   271篇
  2005年   276篇
  2004年   174篇
  2003年   148篇
  2002年   158篇
  2001年   77篇
  2000年   102篇
  1999年   26篇
  1998年   14篇
  1997年   15篇
  1996年   14篇
  1995年   8篇
  1994年   14篇
  1993年   13篇
  1992年   5篇
  1991年   8篇
  1990年   4篇
  1986年   1篇
  1983年   4篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1978年   2篇
排序方式: 共有5220条查询结果,搜索用时 203 毫秒
61.
北京大学入藏的秦代水陆里程简册中记载秦代有"阳"县存在,关于这一新出现的秦县,前辈学者认为可能是位于今河南省方城县的秦汉"阳城"。然而,从简册中记载的"阳"县下属各乡到其他地区的距离来看,"阳县"不太可能在今方城附近,而更有可能是位于先秦"唐"国故地的"唐"县。其他出土材料所见的"唐"县一般写作"阳",清华简《系年》中还有楚国曾灭"唐(阳)"置县的明确记载。秦代的阳县应该就是继承了楚灭唐国之后所设的阳县。  相似文献   
62.
Critics have been uncertain as to the genre of Catalan writer Jaume Cabré's 2000 book, Viatge d’hivern. The confusion, I argue, is due to the fact that the volume is a short story cycle, a literary form situated midway between the novel and the short story collection. Forrest Ingram differentiates among composed, arranged, and completed cycles, and Cabré's comments in his Epilogue to Viatge d’hivern indicate that the book is an example of the third category. While he composed its fourteen narratives over a period of years, when he revised them for inclusion in a single volume he discovered that various threads, some secret and others more obvious, connected the stories. In this essay I examine ways in which theme, structure, and motifs, as well as recurrent imagery and wording, form a web of associations among the individual units of Viatge d’hivern.  相似文献   
63.
64.
The Hui-style residence is an important architectural heritage of China. The hollow wall structures are widely used to build its exterior wall system. However, the thermal performance of the hollow wall is no longer able to meet the new energy-saving and environmental requirement. This article describes a laboratory study of the development of foamed mortar (FM), with the potential for use in thermal upgrading of the Hui-style hollow wall system without dramatically changing its traditional structure. The key early age, physical, mechanical and thermal properties were systematically measured. Two extended models were respectively developed to calculate compressive strength and thermal conductivity, as a function of porosity. Environment chamber test was also employed to investigate the effectiveness of this novel thermal upgrading approach and the results show that filling the voids with FM can effectively improve the overall thermal resistance of the hollow wall system by 44%, which is almost equal to the overall thermal resistance when using the more expensive commercial inorganic stucco system. In addition, the combination of these two methods yielded an overall thermal resistance of 0.701 m2·K/W, which is even higher than 0.67 m2·K/W for the code required in the hot summer/cold winter climate zone.  相似文献   
65.
66.
Smoking bans have recently expanded to private vehicles in which children are present. This study considers the place of children's rights and children's voices in this policy initiative, with respect to the Canadian context, where vehicular smoking bans have been widely adopted. First, we examine print media reports, finding children's right to health was acknowledged less frequently than an array of competing adult rights. Children's voices were largely absent from the record. Second, we report on focus groups involving 23 young people in Edmonton, Alberta, highlighting participants' strong support for bans, based on their knowledge of health harms, aversion to smoke, and awareness that children have limited ability to contest adult authority in vehicles. We conclude that vehicular smoking bans may address the situation whereby children are forced to share an unhealthy environment, in breach of their rights.  相似文献   
67.
This paper presents a review of services sector development in China. It is found that China’s services have recently emerged as the dominant contributor to economic growth and job creation. Trade in services has also increased dramatically, although China maintains a huge deficit. In comparison with economies at a similar stage of development, however, China’s services sector is lagging behind. Both GDP and employment shares of the services sector are relatively small. Services trade also accounts for a relatively small share of China’s total trade. In particular, China’s new services are underdeveloped. As per capita income rises and resultant urbanization accelerates, the country’s services sector is expected to expand further and hence play a key role in rebalancing China’s economy away from its over-reliance on manufacturing and exporting. To reach this goal, further reforms and prudent government policies are needed.  相似文献   
68.
Historical towers, in particular medieval towers, are an important part of cultural heritage, and their preservation mandates monitoring and detailed analyses of vulnerability under seismic actions as well as of their long-term performance. Certain aspects of structural nature are linked to the masonry behavior as a unilateral material, and other are aspects related to the interaction with soft soil conditions. This study aims to contribute to the aspects of preservation by exploring the role of the soil-structure interaction in predicting the behavior of the structures, with specific reference to the well-documented case history of the medieval Ghirlandina Tower (Modena, Italy). A significant contribution comes from an experimental identification analysis, performed in the presence of ambient vibration. A novel finding is that the soil structure interaction cannot be neglected, in contrast to most published identification analyses that usually assume the structure to have rigid constraint at base.  相似文献   
69.
The long established distinction between civic nationalism and ethnonationalism is useful heuristically to understand different dimensions of nationalism and perhaps track a movement from ethnic forms to civic allegiances, though some have challenged its empirical veracity and others question the normative implications of such a distinction. This paper demonstrates the ways in which the two are elided in everyday discourses about migrants in Australia. We argue suspicion of cultural difference, identified more than three decades ago as the new racism, has given way to talk of the need for migrants to ‘follow the law’. This serves rhetorically to reinforce the notion that migrants, often implied to overlap with the category ‘Muslims’, are insisting on breaking the law and/or changing it and are therefore culturally incompatible with a modern liberal democracy. We argue that since ethnic nationalism, like racism, is out of favour normatively, ethnic nationalist arguments are now superficially concealed beneath the acceptable language of civic nationalism. The manner in which this occurs is mapped discursively using data from a corpus of twenty seven focus groups conducted around Australia.  相似文献   
70.
CO2 injected into rock formations for deep geological storage must not leak to surface, since this would be economically and environmentally unfavourable, and could present a human health hazard. In Italy natural CO2 degassing to the surface via seeps is widespread, providing an insight into the various styles of subsurface ‘plumbing’ as well as surface expression of CO2 fluids. Here we investigate surface controls on the distribution of CO2 seep characteristics (type, flux and temperature) using a large geographical and historical data set. When the locations of documented seeps are compared to a synthetic statistically random data set, we find that the nature of the CO2 seeps is most strongly governed by the flow properties of the outcropping rocks, and local topography. Where low‐permeability rocks outcrop, numerous dry seeps occur and have a range of fluxes. Aqueous fluid flow will be limited in these low‐permeability rocks, and so relative permeability effects may enable preferential CO2 flow. CO2 vents typically occur along faults in rocks that are located above the water table or are low permeability. Diffuse seeps develop where CO2 (laterally supplied by these faults) emerges from the vadose zone and where CO2 degassing from groundwater follows a different flow path due to flow differences for water and CO2 gas. Bubbling water seeps (characterized by water bubbling with CO2) arise where CO2 supply enters the phreatic zone or an aquifer. CO2‐rich springs often emerge where valleys erode into CO2 aquifers, and these are typically high flux seeps. Seep type is known to influence human health risk at CO2 seeps in Italy, as well as the topography surrounding the seep which affects the rate of gas dispersion by wind. Identifying the physical controls on potential seep locations and seep type above engineered CO2 storage operations is therefore crucial to targeted site monitoring strategy and risk assessment. The surface geology and topography above a CO2 store must therefore be characterized in order to design the most effective monitoring strategy.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号