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   253篇
  免费   22篇
  2022年   2篇
  2021年   3篇
  2019年   1篇
  2018年   1篇
  2017年   6篇
  2016年   3篇
  2015年   13篇
  2014年   16篇
  2013年   19篇
  2012年   17篇
  2011年   9篇
  2010年   8篇
  2009年   13篇
  2008年   16篇
  2007年   10篇
  2006年   18篇
  2005年   12篇
  2004年   8篇
  2003年   7篇
  2002年   6篇
  2001年   15篇
  2000年   12篇
  1999年   6篇
  1998年   12篇
  1997年   5篇
  1996年   3篇
  1995年   4篇
  1994年   2篇
  1993年   1篇
  1992年   4篇
  1991年   1篇
  1989年   3篇
  1988年   2篇
  1987年   3篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1979年   1篇
  1976年   2篇
  1975年   2篇
  1971年   1篇
  1969年   1篇
  1967年   1篇
排序方式: 共有275条查询结果,搜索用时 15 毫秒
1.
The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.  相似文献   
2.
The antihypertensive effect of atenolol, a new beta-1-receptor blocking agent, was studied in a double-blind trial in which 45 patients with essential hypertension were randomly assigned to placebo or atenolol treatment. Atenolol caused a statistically significant and clinically relevant reduction of blood pressure. The optimum daily dose for moderately severe hypertension was considered to be 200 mg. Several irrelevant side effects were collected by the use of a check list, but there was no difference in the number of complaints during placebo and active treatment. Atenolol has a useful antihypertensive effect and, at least theoretically, has advantages over other beta-adrenergic blocking agents.  相似文献   
3.
4.
5.

Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight.  相似文献   
6.
7.
8.
The development of TCR alphabeta(+), CD8alphabeta(+) intestinal intraepithelial lymphocytes (IEL) is dependent on MHC class I molecules expressed in the thymus, while some CD8alphaalpha(+) IEL may arise independently of MHC class I. We examined the influence of MHC I allele dosage on the development CD8(+) T cells in RAG 2(-/-) mice expressing the H-2D(b)-restricted transgenic TCR specific for the male, Smcy-derived H-Y Ag (H-Y TCR). IEL in male mice heterozygous for the restricting (H-2D(b)) and nonrestricting (H-2D(d)) MHC class I alleles (MHC F(1)) were composed of a mixture of CD8alphabeta(+) and CD8alphaalpha(+) T cells, while T cells in the spleen were mostly CD8alphabeta(+). This was unlike IEL in male mice homozygous for H-2D(b), which had predominantly CD8alphaalpha(+) IEL and few mostly CD8(-) T cells in the spleen. Our results demonstrate that deletion of CD8alphabeta(+) cells in H-Y TCR male mice is dependent on two copies of H-2D(b), whereas the generation of CD8alphaalpha(+) IEL requires only one copy. The existence of CD8alphabeta(+) and CD8alphaalpha(+) IEL in MHC F(1) mice suggests that their generation is not mutually exclusive in cells with identical TCR. Furthermore, our data imply that the level of the restricting MHC class I allele determines a threshold for conventional CD8alphabeta(+) T cell selection in the thymus of H-Y TCR-transgenic mice, whereas the development of CD8alphaalpha(+) IEL is dependent on, but less sensitive to, this MHC class I allele.  相似文献   
9.
The hydrolysis of starch to low-molecular-weight products (normally characterised by their dextrose equivalent (DE), which is directly related to the number-average molecular mass) was studied at different temperatures. Amylopectin potato starch, lacking amylose, was selected because of its low tendency towards retrogradation at lower temperatures. Bacillus licheniformis alpha-amylase was added to 10% [w/w] gelatinised starch solutions. The hydrolysis experiments were done at 50, 70, and 90 degrees C. Samples were taken at defined DE values and these were analysed with respect to their saccharide composition. At the same DE the oligosaccharide composition depended on the hydrolysis temperature. This implies that at the same net number of bonds hydrolysed by the enzyme, the saccharide composition was different. The hydrolysis temperature also influenced the initial overall molecular-weight distribution. Higher temperatures led to a more homogenous molecular weight distribution. Similar effects were observed for alpha-amylases from other microbial sources such as Bacillus amyloliquefaciens and Bacillus stearothermophilus. Varying the pH (5.1, 6.2, and 7.6) at 70 degrees C did not significantly influence the saccharide composition obtained during B. licheniformis alpha-amylase hydrolysis. The underlying mechanisms for B. licheniformis alpha-amylase were studied using pure linear oligosaccharides, ranging from maltotriose to maltoheptaose as substrates. Activation energies for the hydrolysis of individual oligosaccharides were calculated from Arrhenius plots at 60, 70, 80, and 90 degrees C. Oligosaccharides with a degree of polymerisation exceeding that of the substrate could be detected. The contribution of these oligosaccharides increased as the degree of polymerisation of the substrate decreased and the temperature of hydrolysis increased. The product specificity decreased with increasing temperature of hydrolysis, which led to a more equal distribution between the possible products formed. Calculations with the subsite map as determined for the closely related alpha-amylase from B. amyloliquefaciens reconfirmed this finding of a decreased substrate specificity with increased temperature of hydrolysis. Copyright 1999 John Wiley & Sons, Inc.  相似文献   
10.
We have investigated protein-protein interactions among the respiratory syncytial virus (RSV) RNA polymerase subunits using affinity chromatography. Here we demonstrate a novel interaction of P and M2-1 proteins. Phosphorylation of either M2-1 or P appears to be dispensable for this interaction. Internal deletions within P mapped the M2-1-binding domain to a region between residues 100 and 120. Alanine-scanning mutagenesis within this region of P revealed that substitution of any one of the three residues, L101, Y102, and F109, prevented both M2-1 and P binding and expression of an M2-1-dependent luciferase reporter gene. However, these same mutations did not prevent the activity of an M2-1-independent chloramphenicol acetyltransferase minigenome, suggesting that these residues of P specifically affect M2-1-P interaction. On the basis of these observations, it is possible that the interaction between RSV M2-1 and P proteins is important for viral replication.  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