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   42885篇
  免费   2895篇
  国内免费   2784篇
  2023年   429篇
  2022年   548篇
  2021年   828篇
  2020年   861篇
  2019年   1064篇
  2018年   1061篇
  2017年   978篇
  2016年   984篇
  2015年   1434篇
  2014年   2538篇
  2013年   2893篇
  2012年   2419篇
  2011年   3345篇
  2010年   2946篇
  2009年   2325篇
  2008年   2240篇
  2007年   2216篇
  2006年   2093篇
  2005年   1992篇
  2004年   1801篇
  2003年   1612篇
  2002年   1285篇
  2001年   802篇
  2000年   785篇
  1999年   823篇
  1998年   764篇
  1997年   631篇
  1996年   593篇
  1995年   700篇
  1994年   614篇
  1993年   503篇
  1992年   460篇
  1991年   395篇
  1990年   358篇
  1989年   353篇
  1988年   281篇
  1987年   278篇
  1986年   198篇
  1985年   305篇
  1984年   351篇
  1983年   268篇
  1982年   301篇
  1981年   163篇
  1980年   205篇
  1979年   135篇
  1978年   78篇
  1977年   64篇
  1976年   60篇
  1973年   48篇
  1972年   35篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Volatile organic compounds (VOCs) are secondary metabolites acting as a language for the communication of plants with the environment. In orange fruits, the monoterpene D-limonene accumulates at very high levels in oil glands from the peel. Drastic down-regulation of D-limonene synthase gene expression in the peel of transgenic oranges harboring a D-limonene synthase transgene in antisense (AS) configuration altered the monoterpene profile in oil glands, mainly resulting in reduced accumulation of D-limonene. This led to fruit resistance against Penicillium digitatum (Pd), Xanthomonas citri subsp. citri (Xcc) and other specialized pathogens. Here, we analyze resistance to pathogens in independent AS and empty vector (EV) lines, which have low, medium or high D-limonene concentrations and show that the level of resistance is inversely related to the accumulation of D-limonene in orange peels, thus explaining the need of high D-limonene accumulation in mature oranges in nature for the efficient attraction of specialized microorganism frugivores.  相似文献   
2.
Cardiac stem cells are described in a number of mammalian species including humans. Cardiac stem cell clusters consisting of both lineage-negative and partially committed cells are generally identified between contracting cardiac myocytes. In the present study, c-kit+, Sca+, and Isl1+ stem cells were revealed to be located inside the sarcoplasm of cardiac myocytes in myocardial cell cultures derived from newborn, 20-, and 40-day-old rats. Intracellularly localized cardiac stem cells had a coating or capsule with a few pores that opened into the host cell sarcoplasm. The similar structures were also identified in the suspension of freshly isolated myocardial cells (ex vivo) of 20- and 40-day-old rats. The results from this study provide direct evidence for the replicative division of encapsulated stem cells, followed by their partial cardiomyogenic differentiation. The latter is substantiated by the release of multiple transient amplifying cells following the capsule rupture. In conclusion, functional cardiac stem cells can reside not only exterior to but also within cardiomyocytes.  相似文献   
3.
A series of 1-aryl-2-(((6-aryl)pyrimidin-4-yl)amino)ethanols have been found to be competitive inhibitors of fatty acid amide hydrolase (FAAH). One member of this class, JNJ-40413269, was found to have excellent pharmacokinetic properties, demonstrated robust central target engagement, and was efficacious in a rat model of neuropathic pain.  相似文献   
4.
Abstract The gene-protein database was used to obtain the two-dimensional polyacrylamide gel coordinates of proteins phosphorylated in extracts of Escherichia coli including those phosphorylated by eukaryotic-like kinase activities. These suggest that the phosphoproteins correspond to, or co-migrate with, the product of an open reading frame at 1.3 min (Orf80), Enzyme 1 of the phosphoenolpyruvate-dependent phosphotransferase system (Ptsl), the tRNA synthetase for histidine (HisS), and proteins involved in the response to carbon starvation and quinone treatment.  相似文献   
5.
The analysis of the membrane proteins and their antigenic properties in a group of 14 geographically diverse strains of Renibacterium salmoninarum revealed the existence of antigenic diversity within this species. Eleven isolates, including the type strain ATCC 33209, shared a similar protein profile with a major component of 57 kDa whereas three strains showed a common pattern with a major protein of 30 kDa. The quantitative agglutination tests and Western blotting assays seem to indicate the existence of serological heterogeneity, with two distinct groups being detected.  相似文献   
6.
Evidence of differential renal dysfunctions during exercise in men   总被引:1,自引:0,他引:1  
Post-exercise proteinuria is a common phenomenon in healthy subjects. Previous studies have used albumin (Alb) and β2-microglobulin (β2-m) molecules as representatives of high- and low-molecular-weight proteins. Recently, more specific markers of the human kidney proximal tubule have been used to identify the precise site of alterations. Active male subjects underwent two strenuous runs, one 400-m run and one 3000-m run. Urine was collected from the subjects before and after each event. Total protein (TP), Alb, α1-microglobulin (α1-m), β2-m, intestinal alkaline phosphatase (IAP), tissue-nonspecific alkaline phosphatase (TNAP) and N-acetyl-β-d-glucosaminidase (NAG) were determined for each sample. The short-distance run (400 m) resulted in the largest increases (P ≤ 0.05) in TP (31-fold), Alb (100-fold) and β2-m (164-fold) as compared to the long-distance run (3000-m). The α1-m excretion rates were increased to a lesser extent by the exercises. The IAP activity was slightly increased (+90%) by the 400-m run while the TNAP and NAG activities showed a 6.8-fold and a 3.6-fold increase, respectively, after this event. Smaller increases were recorded for the long-distance run (P = 0.05). To conclude, the present investigation showed that: (1) post-exercise proteinuria is related to the absolute intensity of exercise; (2) the impairment of protein reabsorption is revealed better by changes in Alb and β2-m; (3) changes in TNAP and NAG activities could reveal biochemical modifications that occur in the proximal tubule, particularly at the S1-S2 segment. Accepted: 31 January 1997  相似文献   
7.
Protein secretion in streptomycetes   总被引:1,自引:0,他引:1  
  相似文献   
8.
Structural properties of carbohydrate surface binding sites (SBSs) were investigated with computational methods. Eighty‐five SBSs of 44 enzymes in 119 Protein Data Bank (PDB) files were collected as a dataset. On the basis of SBSs shape, they were divided into 3 categories: flat surfaces, clefts, and cavities (types A, B, and C, respectively). Ligand varieties showed the correlation between shape of SBSs and ligands size. To reduce cut‐off differences in each SBSs with different ligand size, molecular docking were performed. Molecular docking results were used to refine SBSs classification and binding sites cut‐off. Docking results predicted putative ligands positions and displayed dependence of the ligands binding mode to the structural type of SBSs. Physicochemical properties of SBSs were calculated for all docking results with YASARA Structure. The results showed that all SBSs are hydrophilic, while their charges could vary and depended to ligand size and defined cut‐off. Surface binding sites type B had highest average values of solvent accessible surface area. Analysis of interactions showed that hydrophobic interactions occur more than hydrogen bonds, which is related to the presence of aromatic residues and carbohydrates interactions.  相似文献   
9.
10.
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