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   31318篇
  免费   46篇
  国内免费   68篇
系统科学   154篇
丛书文集   717篇
教育与普及   79篇
理论与方法论   200篇
现状及发展   13501篇
研究方法   1347篇
综合类   15065篇
自然研究   369篇
  2013年   174篇
  2012年   419篇
  2011年   832篇
  2010年   180篇
  2008年   552篇
  2007年   539篇
  2006年   596篇
  2005年   591篇
  2004年   517篇
  2003年   567篇
  2002年   566篇
  2001年   978篇
  2000年   896篇
  1999年   598篇
  1992年   569篇
  1991年   462篇
  1990年   486篇
  1989年   489篇
  1988年   490篇
  1987年   498篇
  1986年   490篇
  1985年   599篇
  1984年   494篇
  1983年   404篇
  1982年   346篇
  1981年   340篇
  1980年   448篇
  1979年   967篇
  1978年   855篇
  1977年   846篇
  1976年   580篇
  1975年   630篇
  1974年   931篇
  1973年   785篇
  1972年   804篇
  1971年   1017篇
  1970年   1339篇
  1969年   1004篇
  1968年   945篇
  1967年   988篇
  1966年   829篇
  1965年   609篇
  1964年   148篇
  1959年   360篇
  1958年   522篇
  1957年   443篇
  1956年   366篇
  1955年   316篇
  1954年   363篇
  1948年   193篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
631.
632.
633.
Genome-wide association (GWA) studies have identified multiple loci at which common variants modestly but reproducibly influence risk of type 2 diabetes (T2D). Established associations to common and rare variants explain only a small proportion of the heritability of T2D. As previously published analyses had limited power to identify variants with modest effects, we carried out meta-analysis of three T2D GWA scans comprising 10,128 individuals of European descent and approximately 2.2 million SNPs (directly genotyped and imputed), followed by replication testing in an independent sample with an effective sample size of up to 53,975. We detected at least six previously unknown loci with robust evidence for association, including the JAZF1 (P = 5.0 x 10(-14)), CDC123-CAMK1D (P = 1.2 x 10(-10)), TSPAN8-LGR5 (P = 1.1 x 10(-9)), THADA (P = 1.1 x 10(-9)), ADAMTS9 (P = 1.2 x 10(-8)) and NOTCH2 (P = 4.1 x 10(-8)) gene regions. Our results illustrate the value of large discovery and follow-up samples for gaining further insights into the inherited basis of T2D.  相似文献   
634.
We identified a SNP in the DPP6 gene that is consistently strongly associated with susceptibility to amyotrophic lateral sclerosis (ALS) in different populations of European ancestry, with an overall P value of 5.04 x 10(-8) in 1,767 cases and 1,916 healthy controls and with an odds ratio of 1.30 (95% confidence interval (CI) of 1.18-1.43). Our finding is the first report of a genome-wide significant association with sporadic ALS and may be a target for future functional studies.  相似文献   
635.
To identify renally expressed genes that influence risk for hypertension, we integrated expression quantitative trait locus (QTL) analysis of the kidney with genome-wide correlation analysis of renal expression profiles and blood pressure in recombinant inbred strains derived from the spontaneously hypertensive rat (SHR). This strategy, together with renal transplantation studies in SHR progenitor, transgenic and congenic strains, identified deficient renal expression of Cd36 encoding fatty acid translocase as a genetically determined risk factor for spontaneous hypertension.  相似文献   
636.
This review discusses the state-of-the-art in molecular research on the most prominent and widely applied lantibiotic, i.e., nisin. The developments in understanding its complex biosynthesis and mode of action are highlighted. Moreover, novel applications arising from engineering either nisin itself, or from the construction of totally novel dehydrated and/or lanthionine-containing peptides with desired bioactivities are described. Several challenges still exist in understanding the immunity system and the unique multiple reactions occurring on a single substrate molecule, carried out by the dehydratase NisB and the cyclization enzyme NisC. The recent elucidation of the 3-D structure of NisC forms the exciting beginning of further 3-D-structure determinations of the other biosynthetic enzymes, transporters and immunity proteins. Advances in achieving in vitro activities of lanthionine-forming enzymes will greatly enhance our understanding of the molecular characteristics of the biosynthesis process, opening up new avenues for developing unique and novel biocatalytic processes. Received 9 April 2007; received after revision 31 August 2007; accepted 28 September 2007  相似文献   
637.
638.
639.
Human eosinophil cationic protein (ECP)/ ribonuclease 3 (RNase 3) is a protein secreted from the secondary granules of activated eosinophils. Specific properties of ECP contribute to its cytotoxic activities associated with defense mechanisms. In this work the ECP cytotoxic activity on eukaryotic cell lines is analyzed. The ECP effects begin with its binding and aggregation to the cell surface, altering the cell membrane permeability and modifying the cell ionic equilibrium. No internalization of the protein is observed. These signals induce cell-specific morphological and biochemical changes such as chromatin condensation, reversion of membrane asymmetry, reactive oxygen species production and activation of caspase-3-like activity and, eventually, cell death. However, the ribonuclease activity component of ECP is not involved in this process as no RNA degradation is observed. In summary, the cytotoxic effect of ECP is attained through a mechanism different from that of other cytotoxic RNases and may be related with the ECP accumulation associated with the inflammatory processes, in which eosinophils are present. Received 26 October 2007; accepted 23 November 2007  相似文献   
640.
Inhibition of gastric acid secretion is the mainstay of the treatment of gastroesophageal reflux disease and peptic ulceration; therapies to inhibit acid are among the best-selling drugs worldwide. Highly effective agents targeting the histamine H2 receptor were first identified in the 1970s. These were followed by the development of irreversible inhibitors of the parietal cell hydrogen-potassium ATPase (the proton pump inhibitors) that inhibit acid secretion much more effectively. Reviewed here are the chemistry, biological targets and pharmacology of these drugs, with reference to their current and evolving clinical utilities. Future directions in the development of acid inhibitory drugs include modifications of current agents and the emergence of a novel class of agents, the acid pump antagonists. Received 30 May 2007; received after revision 15 August 2007; accepted 13 September 2007  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