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   4184篇
  免费   14篇
  国内免费   15篇
系统科学   87篇
丛书文集   24篇
教育与普及   11篇
理论与方法论   12篇
现状及发展   1787篇
研究方法   275篇
综合类   1959篇
自然研究   58篇
  2016年   32篇
  2014年   28篇
  2012年   109篇
  2011年   172篇
  2010年   45篇
  2008年   121篇
  2007年   122篇
  2006年   114篇
  2005年   124篇
  2004年   138篇
  2003年   116篇
  2002年   117篇
  2001年   115篇
  2000年   113篇
  1999年   82篇
  1992年   90篇
  1991年   54篇
  1990年   49篇
  1989年   46篇
  1988年   30篇
  1987年   47篇
  1986年   54篇
  1985年   57篇
  1984年   60篇
  1983年   35篇
  1982年   37篇
  1981年   28篇
  1980年   47篇
  1979年   108篇
  1978年   73篇
  1977年   91篇
  1976年   59篇
  1975年   60篇
  1974年   112篇
  1973年   98篇
  1972年   82篇
  1971年   97篇
  1970年   135篇
  1969年   117篇
  1968年   121篇
  1967年   114篇
  1966年   112篇
  1965年   79篇
  1964年   31篇
  1959年   28篇
  1958年   50篇
  1957年   39篇
  1956年   45篇
  1955年   31篇
  1948年   32篇
排序方式: 共有4213条查询结果,搜索用时 4 毫秒
31.
The iron-chalcogenide high temperature superconductor Fe(Se,Te) (FST) has been reported to exhibit complex magnetic ordering and nontrivial band topology which ...  相似文献   
32.
We tested 310,605 SNPs for association in 778 individuals with celiac disease and 1,422 controls. Outside the HLA region, the most significant finding (rs13119723; P = 2.0 x 10(-7)) was in the KIAA1109-TENR-IL2-IL21 linkage disequilibrium block. We independently confirmed association in two further collections (strongest association at rs6822844, 24 kb 5' of IL21; meta-analysis P = 1.3 x 10(-14), odds ratio = 0.63), suggesting that genetic variation in this region predisposes to celiac disease.  相似文献   
33.
We have genotyped 14,436 nonsynonymous SNPs (nsSNPs) and 897 major histocompatibility complex (MHC) tag SNPs from 1,000 independent cases of ankylosing spondylitis (AS), autoimmune thyroid disease (AITD), multiple sclerosis (MS) and breast cancer (BC). Comparing these data against a common control dataset derived from 1,500 randomly selected healthy British individuals, we report initial association and independent replication in a North American sample of two new loci related to ankylosing spondylitis, ARTS1 and IL23R, and confirmation of the previously reported association of AITD with TSHR and FCRL3. These findings, enabled in part by increased statistical power resulting from the expansion of the control reference group to include individuals from the other disease groups, highlight notable new possibilities for autoimmune regulation and suggest that IL23R may be a common susceptibility factor for the major 'seronegative' diseases.  相似文献   
34.
5-Methylcytosine localised in mammalian constitutive heterochromatin   总被引:26,自引:0,他引:26  
O J Miller  W Schnedl  J Allen  B F Erlanger 《Nature》1974,251(5476):636-637
  相似文献   
35.
My research examines the performance of natural resource-use information systems. I question why such systems, despite receiving substantial financial and human investment, appear to have a weak impact on projects, programs, and policy intended for rural poverty alleviation in developing countries. Drawing on my understanding of the process of unfolding introduced by C. West Churchman, and its particular relationship to Habermasian constitutive interests, I reflect on my experiences of using the concept during fieldwork undertaken in Botswana. The concept is found useful on two fronts: first, it provides a purposeful guide for gathering and processing information/knowledge—what I have termed an epistemological intent; second, it provides a useful template for evaluating other information systems; in particular, the role of expertise—what I have termed an ontological intent. The process of unfolding, as I understand it, also provides an invitation for constructive (rather than self-indulgent) personal reflection: what might be termed a constitutive reflexive intent. By making information gathering and knowledge generation less mystical and a more transparent social activity, the conceptual and practical application of the process of unfolding can help toward retrieving inquiry as being a purposeful, openly political, and thereby less deceptive engagement: features which I believe are found particularly wanting in the business of rural development information gathering.  相似文献   
36.
Agent-oriented Aid-modeling for the Distributed Activity Network   总被引:6,自引:0,他引:6  
1  IntroductionModern system characters distributed problem solving from the view of new generation ofDSS.Thus,traditional DSS(P.Sage,1 992 ) will separate the system into4 main parts atdifferent allocation,so that it needs an environment of information technologies (R.Blanning,1 995) and the supportoforganizational connectivity(M.Jeusfeld,1 997) .Atthesame time,distributed decision processing requires coalescent problem modeling andcollaborated decision.The distributed problem solves in…  相似文献   
37.
38.
消失场荧光技术已被广泛应用在工业、生物和医学等领域的研究工作中.本文给出各种分层结构中消失场分布的严密电磁理论.在生物和医学上,利用受激荧光强度正比于局部电场能量的规律,可根据测得的相对荧光强度算出细胞和基板的间距.文中还给出一些消失场荧光测量的应用.  相似文献   
39.
Epitopes presented by major histocompatibility complex (MHC) class I molecules are selected by a multi-step process. Here we present the first computational prediction of this process based on in vitro experiments characterizing proteasomal cleavage, transport by the transporter associated with antigen processing (TAP) and MHC class I binding. Our novel prediction method for proteasomal cleavages outperforms existing methods when tested on in vitro cleavage data. The analysis of our predictions for a new dataset consisting of 390 endogenously processed MHC class I ligands from cells with known proteasome composition shows that the immunological advantage of switching from constitutive to immunoproteasomes is mainly to suppress the creation of peptides in the cytosol that TAP cannot transport. Furthermore, we show that proteasomes are unlikely to generate MHC class I ligands with a C-terminal lysine residue, suggesting processing of these ligands by a different protease that may be tripeptidyl-peptidase II (TPPII).Received 26 November 2004; received after revision 4 February 2005; accepted 4 March 2005S. Tenzer and B. Peters contributed equally to this work.  相似文献   
40.
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