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   3578篇
  免费   127篇
  3705篇
  2020年   54篇
  2019年   64篇
  2018年   93篇
  2017年   95篇
  2016年   103篇
  2015年   78篇
  2014年   71篇
  2013年   1178篇
  2012年   82篇
  2011年   93篇
  2010年   79篇
  2009年   75篇
  2008年   80篇
  2007年   61篇
  2006年   61篇
  2005年   43篇
  2004年   36篇
  2003年   33篇
  2002年   46篇
  2001年   52篇
  2000年   29篇
  1999年   43篇
  1998年   22篇
  1997年   31篇
  1996年   26篇
  1995年   22篇
  1994年   38篇
  1993年   32篇
  1992年   34篇
  1991年   21篇
  1990年   32篇
  1989年   28篇
  1988年   30篇
  1987年   32篇
  1986年   30篇
  1985年   33篇
  1984年   52篇
  1983年   54篇
  1982年   47篇
  1981年   38篇
  1980年   34篇
  1979年   41篇
  1978年   42篇
  1977年   30篇
  1976年   32篇
  1975年   34篇
  1973年   27篇
  1972年   31篇
  1971年   21篇
  1970年   32篇
排序方式: 共有3705条查询结果,搜索用时 15 毫秒
971.
AIDS-related work and advocacy is one field that has spurred considerable activity among Chinese NGOs in the past two decades. This article explains processes leading to institutional changes that are necessary for allowing more NGOs to emerge and operate, and shows how international, domestic and local actors and influences have steered developments leading to organisational growth. The article applies new institutionalism theory and highlights differences between formal and informal institutions in explaining change and continuity for NGOs and their relations to state and government in this particular field.  相似文献   
972.
The thermoluminescence dating method was applied to 77 heated flints from the Mousterian layers of Hayonim Cave in order to provide a precise TL-based chronology for this important Levantine sequence. A detailed dosimetric study was performed by using 76 dosimeter capsules and revealed strong spatial dose-rate variations. In parallel, Fourier transform infrared spectrometry enabled the identification of various mineral assemblages in the sediments of the cave and to localize the boundaries of these assemblages. By comparing these two data sets, it is shown that low dose-rate values (∼500 μGy/a) are systematically recorded in areas where the calcite-dahllite (CD) assemblage is preserved, whereas higher values (up to 1300 μGy/a) are associated with the leucophosphite, montgomeryite, variscite and siliceous aggregates (LMVS) assemblage. The dosimetric and mineralogical information was combined in order to assess, where possible, the dose-rate experienced by each flint during its burial. Some of the flint samples analyzed were too close to mineral assemblage boundaries and were therefore discarded. This rigorous selection led to TL ages ranging from 230 to 140 ka for the lower part of the Mousterian sequence (layers F and Lower E), which contains lithic industries characterized by blade production using the laminar method.  相似文献   
973.
In recent years the pace of research on the late prehistoric Mississippian societies of eastern North America has accelerated. New data, methods, and theoretical goals are changing perspectives in Mississippian archaeology. Regional overviews and site syntheses provide unprecedented insights into the Mississippian phenomenon at local, regional, and continental scales. Traditional culture history, processualism, historical processualism, iconography, and neo-Darwinian archaeology are active theoretical orientations. Important research focuses on variability in Mississippian sociopolitical formations over time, organizational diversity among contemporaneous societies, and sources of political power. The new historicism and iconography place agency, identity, origins, factionalism, ideology, and meaning at the center of culture change, while many processualists continue to focus on developmental histories, economy, and control of material resources. Advances in physical and chemical analyses and the availability of remote sensing techniques are changing how Mississippian archaeology is conducted and expanding the kinds of data that are recovered. These diverse interests, methods, and goals have created considerable eclecticism in Mississippian archaeology.  相似文献   
974.
In May 2009, a decision of the United States Supreme Court with North Dakota roots turned fifty years old. A case unique in the annals of the law, Dick v. New York Life Insurance Company 1 still fascinates lawyers today. Factually, the case presented a strange question: could an experienced hunter accidentally shoot himself not once, but twice? Some of North Dakota's finest lawyers, including Philip Vogel, Donald Holand, and Norman Tenneson, aimed to get to the bottom of that matter. The judges were equally impressive: Judge Ronald Davies of the federal district court; Judge John Sanborn of the U.S. Court of Appeals for the Eighth Circuit; and Chief Justice Earl Warren and Justice Felix Frankfurter. Finally, as a matter of Supreme Court jurisprudence, Dick may have been the last time the High Court granted a petition for certiorari in a case that turned almost exclusively on questions of fact. In honor of its golden anniversary, this article recounts the captivating story of Dick v. New York Life.  相似文献   
975.
In one of the first quantitative designs, we explore the impact of both legalisation and flexibility on regime effectiveness, using data on international environmental institutions. One of the main implications is that ‘precision’ is an important determinant of regime performance. If the rule and norm system is well defined, well understood and clear, then a regime tends to be more effective in addressing an environmental problem. We do not find evidence, however, that ‘hard law’ is more effective than ‘soft law’ or that delegation mechanisms may be relevant. Second, flexibility in the regime structure increases regime performance – regular instead of subsidiary bodies enhance flexibility and thus have a positive effect on a regime's environmental problem management. Flexibility in states' agenda setting power, membership and decision making do not seem to have a crucial influence, though.  相似文献   
976.
The adsorption onto other minerals of charged gold nanoparticles, carried by gas ascending from the Earth’s interior, is an important component of their transport and deposition in surficial cover such as alluvial, aeolian, and glacial sediments. To simulate the adsorption of these particles, an experiment was conducted in which a flow of air that contained gold nanoparticles was passed upward through a sample of alluvium from the middle–lower reaches of the Yangtze River. These experiments showed that gold nanoparticles are adsorbed on kaolinite, halloysite, goethite, and hematite in the alluvial cover. Both the gold nanoparticles and minerals (i.e., kaolinite, halloysite, goethite, and hematite) carry surface charges that provide them with excellent adsorption properties. This study showed that the specific mineral composition of surficial alluvial cover affects the concentration of gold nanoparticles in the ascending gas. This phenomenon may plausibly be used in exploration for concealed gold, copper–gold, and silver–gold deposits in areas of thick alluvial cover. Geofluids (2010) 10 , 438–446  相似文献   
977.
This article provides an empirical evaluation of a hierarchical approach to modeling commuting flows. As the gravity family of spatial interaction models represents a benchmark for empirical evaluation, we begin by reviewing basic aspects of these models. The hierarchical modeling framework is the same that Thorsen, Ubøe, and Nævdal (1999) used. However, because some modifications are required to construct a more workable model, we undertake a relatively detailed presentation of the model, rather than merely referring to the presentation in Thorsen, Ubøe, and Nævdal (1999) . The model uses a hierarchical specification of a transportation network and the individual search procedure. Journeys to work are determined by the effects of distance deterrence and of intervening opportunities, and by the location of potential destinations relative to alternatives at subsequent levels in a transportation network. The model calibration uses commuting data from a region in western Norway. The estimated parameter values are reasonable, and the explanatory power is very satisfactory when compared with the results of a competing destinations approach.  相似文献   
978.
979.
Eight human interments were excavated in the 1990s beneath the Acropolis at the Classic Maya site of Copan in Honduras, which was the capital of a Maya kingdom from ca. AD 400 to 800. These human remains come from both royal tombs and less elaborate burials dating to the early part of this period and lie deep in the accumulated architectural layers of the Acropolis. We present a brief summary of the context, contents, and external links represented by these interments. Several lines of evidence point to connections between early Copan and Teotihuacan in the Central Highlands of Mexico, and Tikal in the central Maya lowlands of the Petén in Guatemala.  相似文献   
980.
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