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   49801篇
  免费   116篇
  国内免费   206篇
系统科学   269篇
丛书文集   1078篇
教育与普及   107篇
理论与方法论   281篇
现状及发展   22759篇
研究方法   1897篇
综合类   23040篇
自然研究   692篇
  2013年   385篇
  2012年   654篇
  2011年   1380篇
  2010年   285篇
  2008年   860篇
  2007年   915篇
  2006年   942篇
  2005年   919篇
  2004年   873篇
  2003年   860篇
  2002年   883篇
  2001年   1447篇
  2000年   1336篇
  1999年   915篇
  1992年   884篇
  1991年   704篇
  1990年   760篇
  1989年   780篇
  1988年   751篇
  1987年   806篇
  1986年   776篇
  1985年   944篇
  1984年   744篇
  1983年   637篇
  1982年   568篇
  1981年   580篇
  1980年   744篇
  1979年   1537篇
  1978年   1331篇
  1977年   1313篇
  1976年   997篇
  1975年   1065篇
  1974年   1482篇
  1973年   1291篇
  1972年   1342篇
  1971年   1576篇
  1970年   2048篇
  1969年   1546篇
  1968年   1514篇
  1967年   1540篇
  1966年   1304篇
  1965年   940篇
  1964年   275篇
  1959年   535篇
  1958年   870篇
  1957年   656篇
  1956年   561篇
  1955年   488篇
  1954年   545篇
  1948年   326篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
871.
The developmental dynamics of the maize leaf transcriptome   总被引:5,自引:0,他引:5  
  相似文献   
872.
873.
Psoriatic arthritis (PsA) is an inflammatory joint disease that is distinct from other chronic arthritides and which is frequently accompanied by psoriasis vulgaris (PsV) and seronegativity for rheumatoid factor. We conducted a genome-wide association study in 609 German individuals with PsA (cases) and 990 controls with replication in 6 European cohorts including a total of 5,488 individuals. We replicated PsA associations at HLA-C and IL12B and identified a new association at TRAF3IP2 (rs13190932, P = 8.56 × 10?1?). TRAF3IP2 was also associated with PsV in a German cohort including 2,040 individuals (rs13190932, P = 1.95 × 10?3). Sequencing of the exons of TRAF3IP2 identified a coding variant (p.Asp10Asn, rs33980500) as the most significantly associated SNP (P = 1.13 × 10?2?, odds ratio = 1.95). Functional assays showed reduced binding of this TRAF3IP2 variant to TRAF6, suggesting altered modulation of immunoregulatory signals through altered TRAF interactions as a new and shared pathway for PsA and PsV.  相似文献   
874.
In this paper I identify a tension between the two sets of works by Kuhn regarding the genesis of the "new historiography of science". In the first, it could be said that the change from the traditional to the new historiography is strictly endogenous (referring to internal causes or reasons). In the second, the change is predominantly exogenous. To address this question, I draw on a text that is considered to be less important among Kuhn's works, but which, as shall be argued, allows some contact between Kuhn's two approaches via Koyré. I seek to point out and differentiate the roles of Koyré and Kuhn--from Kuhn's point of view--in the development of the historiography of science and, as a complement, present some reflections regarding the justification of the new historiography.  相似文献   
875.
876.
This review focuses on the recent advances in functions of spectrins in non-erythroid cells. We discuss new data concerning the commonly known role of the spectrin-based skeleton in control of membrane organization, stability and shape, and tethering protein mosaics to the cellular motors and to all major filament systems. Particular effort has been undertaken to highlight recent advances linking spectrin to cell signaling phenomena and its participation in signal transduction pathways in many cell types.  相似文献   
877.
Protein intrinsic disorder as a flexible armor and a weapon of HIV-1   总被引:2,自引:2,他引:0  
Many proteins and protein regions are disordered in their native, biologically active states. These proteins/regions are abundant in different organisms and carry out important biological functions that complement the functional repertoire of ordered proteins. Viruses, with their highly compact genomes, small proteomes, and high adaptability for fast change in their biological and physical environment utilize many of the advantages of intrinsic disorder. In fact, viral proteins are generally rich in intrinsic disorder, and intrinsically disordered regions are commonly used by viruses to invade the host organisms, to hijack various host systems, and to help viruses in accommodation to their hostile habitats and to manage their economic usage of genetic material. In this review, we focus on the structural peculiarities of HIV-1 proteins, on the abundance of intrinsic disorder in viral proteins, and on the role of intrinsic disorder in their functions.  相似文献   
878.
Age is an important risk for autoimmunity, and many autoimmune diseases preferentially occur in the second half of adulthood when immune competence has declined and thymic T cell generation has ceased. Many tolerance checkpoints have to fail for an autoimmune disease to develop, and several of those are susceptible to the immune aging process. Homeostatic T cell proliferation which is mainly responsible for T cell replenishment during adulthood can lead to the selection of T cells with increased affinity to self- or neoantigens and enhanced growth and survival properties. These cells can acquire a memory-like phenotype, in particular under lymphopenic conditions. Accumulation of end-differentiated effector T cells, either specific for self-antigen or for latent viruses, have a low activation threshold due to the expression of signaling and regulatory molecules and generate an inflammatory environment with their ability to be cytotoxic and to produce excessive amounts of cytokines and thereby inducing or amplifying autoimmune responses.  相似文献   
879.
Over the last two decades the molecular and cellular mechanisms underlying T cell activation, expansion, differentiation, and memory formation have been intensively investigated. These studies revealed that the generation of memory T cells is critically impacted by a number of factors, including the magnitude of the inflammatory response and cytokine production, the type of dendritic cell [DC] that presents the pathogen derived antigen, their maturation status, and the concomitant provision of costimulation. Nevertheless, the primary stimulus leading to T cell activation is generated through the T cell receptor [TCR] following its engagement with a peptide MHC ligand [pMHC]. The purpose of this review is to highlight classical and recent findings on how antigen recognition, the degree of TCR stimulation, and intracellular signal transduction pathways impact the formation of effector and memory T cells.  相似文献   
880.
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