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   4777篇
  免费   201篇
  2020年   81篇
  2019年   100篇
  2018年   138篇
  2017年   141篇
  2016年   173篇
  2015年   109篇
  2014年   129篇
  2013年   1428篇
  2012年   147篇
  2011年   181篇
  2010年   174篇
  2009年   133篇
  2008年   113篇
  2007年   120篇
  2006年   113篇
  2005年   74篇
  2004年   61篇
  2003年   56篇
  2002年   64篇
  2001年   68篇
  2000年   63篇
  1999年   78篇
  1998年   59篇
  1997年   42篇
  1996年   34篇
  1995年   44篇
  1994年   33篇
  1993年   41篇
  1992年   28篇
  1991年   36篇
  1990年   40篇
  1989年   39篇
  1988年   29篇
  1987年   40篇
  1986年   41篇
  1985年   46篇
  1984年   53篇
  1983年   47篇
  1982年   38篇
  1981年   45篇
  1980年   42篇
  1979年   39篇
  1978年   36篇
  1977年   36篇
  1976年   27篇
  1975年   28篇
  1974年   27篇
  1973年   31篇
  1972年   30篇
  1970年   27篇
排序方式: 共有4978条查询结果,搜索用时 15 毫秒
991.
Detailed compositional and technological analysis of a large assemblage of prehistoric ceramics from numerous sites situated within the Peak District National Park has been used to explore the settlement patterns, societal structure, mobility and interaction of the populations that inhabited this area during the Early Bronze Age to Early Iron Age. A surprising pattern emerges of the widespread dominance of a single, geographically restricted temper type, which appears to have been transported and mixed with locally procured clay and used to produce pottery at numerous different sites. The distribution of this and several other compositional groups are defined via thin‐section petrography and compared to raw material field samples. The resulting patterns are used to assess the validity of previous theories about prehistoric life in this region during the third to first millennia bc .  相似文献   
992.
Lead analysis of tooth enamel from individuals recovered from a Viking Age burial pit in southern England provides further evidence for their childhood origins outside Britain. All except one of the men have very low Pb concentrations that exclude anthropogenic Pb exposure. Strontium and oxygen isotope compositions identify a core group of men who have Pb isotope compositions of 208Pb/206Pb = 2.065 ± 0.021 (n = 20, 2SD) that, when compared with data from European soils, appear to exclude a childhood in the Scandinavian countries of Norway, Sweden and Finland, whereas areas of Northern continental Europe cannot be excluded.  相似文献   
993.
Archaeological excavations carried out in Early Iron Age Vetulonia (northern Tuscany, Italy) brought to light a funerary urn particularly noteworthy for the presence of an unusual decoration obtained by plastering the vase surface with an organic dark grey substance, on which metal strips were originally fixed. In order to reveal the origin of such coating, it was chemically studied by gas chromatography coupled with mass spectrometry (GC/MS). Chemical analysis not only revealed that birch bark tar was used as coating/adhesive material for the manufacture of the urn, but also allowed us to discuss the significance of the vessel in terms of eco‐technological knowledge and possible cultural connections on a large geographical scale.  相似文献   
994.
We estimate the impact of internal migration on job‐match quality for recent Dutch university and college graduates. We find positive yet modest wage returns. After controlling for the self‐selection of migrants with an IV approach, this effect is no longer significant for university graduates and all graduates from peripheral areas. We also find that, for our alternative job‐match measures, where there is evidence of migrant self‐selection, controlling for self‐selection strongly reduces the effect of internal migration on job‐match quality. In some cases, the returns on internal migration are found to be negative, which may signal forced migration.  相似文献   
995.
996.
997.
An analysis of Forest Service-related legislative activity found that increasingly Congress is becoming involved in agency activities and decisionmaking. Congress's growing scrutiny and management of the Forest Service is indicated by rising trends in requests for agency testimony at congressional hearings, in the number of Forest Service-related bills and amendments introduced in Congress, and in the amount of Forest Service-related legislation enacted. Anecdotal evidence of direct political pressure imposed upon agency personnel by congressional members also indicates that much congressional influence occurs outside of these legislative activities. An examination of activities such as these and directives attached to annual appropriation bills also shows that not all congressional actions are productive in fostering positive agency change. The results of this study indicate the likelihood that Congress has been playing a major role in instigating change within the agency.  相似文献   
998.
Interest groups involved in the Forest Service's 1990 Resources Planning Act (RPA) forest planning process and representatives from accredited forestry schools were surveyed via a written questionnaire on their perceptions of change within the Forest Service since 1976. Respondents felt that the agency had changed, particularly during the late 1980s and early 1990s. Consumptive users perceived the change to be negative, while non-consumptive user groups and forestry schools felt it was somewhat positive, although they still felt the Forest Service had much further to go in this direction before achieving these groups' desired priorities for National Forest management. These results indicate that the agency is undergoing a net shift in direction towards increased emphasis on non-commodity forest uses. In general, external forces, such as Congress and the courts, were seen as having a greater impact on agency change than were sources of change within the agency itself. Forestry schools agreed most often with non-consumptive users, indicating that these programs may be undergoing a change away from their traditional focus on timber production. In addition to providing valuable insights on the subject of change in the Forest Service, these survey results locate areas of agreement and disagreement, and provide valuable feedback to the agency regarding its constituent groups' views about its performance in managing the National Forests.  相似文献   
999.
Lipid residues from two Late Saxon/early medieval ceramic vessels recovered from excavations at West Cotton, Raunds, Northamptonshire, U.K., have been investigated by high-temperature gas chromatography (GC) and GC/mass spectrometry (GC/MS). The solvent extracts of sherds sampled from different points on each vessel (i.e., base, body and rim) were analysed quantitatively and qualitatively and compounds were identified which were characteristic of beeswax and animal fat. Furthermore, by determining the sites of accumulation of the specific lipid types and their concentrations in different parts of the vessels it can be inferred that the beeswax was added to the vessels prior to the addition of the fat. It was concluded that the two vessels performed different functions in antiquity.  相似文献   
1000.
The expression 'Information is power' is widely used, particularly with reference to the imminent 'Information Age'. Yet women must ask, 'Whose information?' and 'Whose power?' if, as a large body of scholarly literature has suggested, women's relationship to information technologies is somehow problematic. In this article, I argue that electronic networks, bulletin boards, online conferences and other computer-mediated communications emphasizing women's issues can recast traditional notions of the computer and its relationship with women. While historically, the dominant groups in many societies have used their command of communications technologies as a means to consolidate their power, new communications technologies escaping centralised political or legal control can diversify information and offer alternative courses of action. Computer-mediated communications on the Internet currently offer these options, yet their future is uncertain. Women who engage with information technologies as the technology and the regulatory framework develop have the opportunity to influence the deployment of this medium, which in turn may have consequences for their sociopolitical status.  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