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   3653篇
  免费   303篇
  国内免费   3篇
  2021年   34篇
  2020年   31篇
  2019年   51篇
  2018年   53篇
  2017年   40篇
  2016年   68篇
  2015年   106篇
  2014年   168篇
  2013年   171篇
  2012年   226篇
  2011年   215篇
  2010年   162篇
  2009年   148篇
  2008年   218篇
  2007年   234篇
  2006年   213篇
  2005年   219篇
  2004年   192篇
  2003年   166篇
  2002年   191篇
  2001年   66篇
  2000年   50篇
  1999年   57篇
  1998年   48篇
  1997年   38篇
  1996年   34篇
  1995年   43篇
  1994年   36篇
  1993年   41篇
  1992年   40篇
  1991年   43篇
  1990年   39篇
  1989年   30篇
  1988年   29篇
  1987年   24篇
  1986年   16篇
  1985年   36篇
  1984年   27篇
  1983年   21篇
  1982年   30篇
  1981年   20篇
  1980年   26篇
  1979年   20篇
  1978年   22篇
  1977年   19篇
  1976年   17篇
  1975年   15篇
  1974年   21篇
  1973年   16篇
  1969年   15篇
排序方式: 共有3959条查询结果,搜索用时 31 毫秒
1.
2.

Backgound  

It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT).  相似文献   
3.

Extracting biomedical information from large metabolomic datasets by multivariate data analysis is of considerable complexity. Common challenges include among others screening for differentially produced metabolites, estimation of fold changes, and sample classification. Prior to these analysis steps, it is important to minimize contributions from unwanted biases and experimental variance. This is the goal of data preprocessing. In this work, different data normalization methods were compared systematically employing two different datasets generated by means of nuclear magnetic resonance (NMR) spectroscopy. To this end, two different types of normalization methods were used, one aiming to remove unwanted sample-to-sample variation while the other adjusts the variance of the different metabolites by variable scaling and variance stabilization methods. The impact of all methods tested on sample classification was evaluated on urinary NMR fingerprints obtained from healthy volunteers and patients suffering from autosomal polycystic kidney disease (ADPKD). Performance in terms of screening for differentially produced metabolites was investigated on a dataset following a Latin-square design, where varied amounts of 8 different metabolites were spiked into a human urine matrix while keeping the total spike-in amount constant. In addition, specific tests were conducted to systematically investigate the influence of the different preprocessing methods on the structure of the analyzed data. In conclusion, preprocessing methods originally developed for DNA microarray analysis, in particular, Quantile and Cubic-Spline Normalization, performed best in reducing bias, accurately detecting fold changes, and classifying samples.

  相似文献   
4.
Mono- and sesqui-terpenes of individual oil glands of Citrus latipes fruits were analyzed for their homogeneity. The effect of oleocellosis, desiccation, Penicillium and Phytophthora infection upon the individual terpene components was investigated and expressed in a discriminant analysis and in canonical variables. Each oil gland contained the entire spectrum of terpenes specific for each species, and the biggest difference in affected glands was due to Penicillium infection.  相似文献   
5.
GCAC1 is a strongly voltage-dependent anion channel in the guard-cell plasma membrane of Vicia faba . In patch–clamp experiments, we have investigated the permeation and gating properties of GCAC1 with respect to its anion dependence in the whole-cell and excised-patch configuration. The relative permeability followed the order SCN > NO3 > Br > Cl, while the single-channel conductances in symmetrical anionic solutions exhibited a nearly inverse sequence. The Cl dependence of inward currents (Cl release) is characterized by a maximum single-channel conductance of 89 pS half-saturating at 87 mM cytoplasmic chloride. In addition to this substrate saturation, anion release was also dependent on the external Cl activity ( K m = 16 mM). In the presence of SCN and Cl, the single-channel conductance exhibited an anomalous mole-fraction dependence, identifying GCAC1 as a multi-ion single-file pore. Using anions with increasing ionic size, a minimum pore diameter of 0.5 nm was assumed from their relative permeabilities. In line with an anion-selective channel, a tenfold increase in the extracellular anion activity shifted the reversal potential by –59.8 mV. Simultaneously, the half-activation potential shifted negatively by about 23 mV. A further analysis of the anion dependence revealed that extracellular rather than cytosolic anions affect the gating process of GCAC1. From anion substitution experiments, we conclude that anion concentration and species determines both permeation and gating of the plant anion channel GCAC1.  相似文献   
6.
Abstract

Combined UV- and liquid scintillation-HPLC has been applied to study the complexing of purine nucleosides with Pt(II)-diamine ions, and the effect of the complex formation on the acidic depurination.  相似文献   
7.
Assay of reducing sugars in the nanomole range with 2,2'-bicinchoninate   总被引:7,自引:0,他引:7  
The photometric assay of reducing sugars with 2,2'-bicinchoninate was improved and its conditions were optimized. Optical density is linear between 1 and 25 nmol sugar/sample, and the assay is not affected by borate, phosphate, or other buffer anions. The molar extinction coefficients produced by the standard procedure with the 12 most common monosaccharides occurring in carbohydrates and conjugated glycocompounds are listed.  相似文献   
8.

Background  

Identifying essential genes in bacteria supports to identify potential drug targets and an understanding of minimal requirements for a synthetic cell. However, experimentally assaying the essentiality of their coding genes is resource intensive and not feasible for all bacterial organisms, in particular if they are infective.  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