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   3867篇
  免费   155篇
  2020年   62篇
  2019年   70篇
  2018年   106篇
  2017年   102篇
  2016年   128篇
  2015年   92篇
  2014年   85篇
  2013年   1184篇
  2012年   94篇
  2011年   102篇
  2010年   98篇
  2009年   91篇
  2008年   96篇
  2007年   81篇
  2006年   67篇
  2005年   63篇
  2004年   55篇
  2003年   40篇
  2002年   58篇
  2001年   59篇
  2000年   32篇
  1999年   53篇
  1998年   24篇
  1997年   34篇
  1996年   27篇
  1995年   23篇
  1994年   39篇
  1993年   33篇
  1992年   35篇
  1990年   32篇
  1989年   29篇
  1988年   32篇
  1987年   33篇
  1986年   32篇
  1985年   36篇
  1984年   52篇
  1983年   55篇
  1982年   48篇
  1981年   39篇
  1980年   34篇
  1979年   42篇
  1978年   42篇
  1977年   32篇
  1976年   32篇
  1975年   35篇
  1973年   28篇
  1972年   35篇
  1971年   21篇
  1970年   32篇
  1969年   21篇
排序方式: 共有4022条查询结果,搜索用时 15 毫秒
991.
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   
992.
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   
993.
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   
994.
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   
995.
This paper presents a pilot study designed to test the use of oxygen isotopes for investigating aspects of early herding practices in the Neolithic of western Asia, using the site of Çatalhöyük in central Anatolia as a case study. Time‐sequenced δ18O values in dental enamel of archaeological sheep are assessed for post‐depositional diagenetic effects and compared with seasonal δ18O meteoric water values in the region today. The evidence is used to indicate the environmental conditions in which individual sheep spent their first year, enabling management of breeding and birthing seasons, and movement to seasonal pastures, to be investigated.  相似文献   
996.
Biogeographical studies are often based on a statistical analysis of data sampled in a spatial context. However, in many cases standard analyses such as regression models violate the assumption of independently and identically distributed errors. In this article, we show that the theory of wavelets provides a method to remove autocorrelation in generalized linear models (GLMs). Autocorrelation can be described by smooth wavelet coefficients at small scales. Therefore, data can be decomposed into uncorrelated and correlated parts. Using an appropriate linear transformation, we are able to extend GLMs to autocorrelated data. We illustrate our new method, called the wavelet‐revised model (WRM), by applying it to multiple regression with response variables conforming to various distributions. Results are presented for simulated data and real biogeographical data (species counts of the plant genus Utricularia [bladderworts] in grid cells throughout Germany). The results of our WRM are compared with those of GLMs and models based on generalized estimating equations. We recommend WRMs, especially as a method that allows for spatial nonstationarity. The technique developed for lattice data is applicable without any prior knowledge of the real autocorrelation structure.  相似文献   
997.
Scholars in many fields have long noted the importance of social context in the development of political ideology. Recent work suggests that political ideology also has a heritable component, but no specific gene variant or combination of variants associated with political ideology have so far been identified. Here, we hypothesize that individuals with a genetic predisposition toward seeking out new experiences will tend to be more liberal, but only if they are embedded in a social context that provides them with multiple points of view. Using data from the National Longitudinal Study of Adolescent Health, we test this hypothesis by investigating an association between self-reported political ideology and the 7R variant of the dopamine receptor D4 gene (DRD4), which has previously been associated with novelty seeking. Among those with DRD4-7R, we find that the number of friendships a person has in adolescence is significantly associated with liberal political ideology. Among those without the gene variant, there is no association. This is the first study to elaborate a specific gene-environment interaction that contributes to ideological self-identification, and it highlights the importance of incorporating both nature and nurture into the study of political preferences.  相似文献   
998.
999.
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   
1000.
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