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   638篇
  免费   38篇
  国内免费   2篇
  2023年   10篇
  2022年   12篇
  2021年   17篇
  2020年   10篇
  2019年   10篇
  2018年   14篇
  2017年   8篇
  2016年   23篇
  2015年   28篇
  2014年   26篇
  2013年   42篇
  2012年   48篇
  2011年   74篇
  2010年   46篇
  2009年   31篇
  2008年   50篇
  2007年   53篇
  2006年   31篇
  2005年   36篇
  2004年   33篇
  2003年   14篇
  2002年   21篇
  2001年   4篇
  2000年   2篇
  1999年   1篇
  1998年   3篇
  1997年   3篇
  1996年   4篇
  1995年   6篇
  1994年   2篇
  1993年   4篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1988年   2篇
  1981年   2篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1963年   1篇
排序方式: 共有678条查询结果,搜索用时 31 毫秒
531.
532.
533.

Background  

Grafting is a widely used technique contributing to sustainable and ecological production of many vegetables, but important fruit quality characters such as taste, aroma, texture and shape are known for years to be affected by grafting in important vegetables species including pepper. From all the characters affected, fruit shape is the most easily observed and measured. From research in tomato, fruit shape is known to be controlled by many QTLs but only few of them have larger effect on fruit shape variance. In this study we used pepper cultivars with different fruit shape to study the role of a pepper Ovate-like gene, CaOvate, which encodes a negative regulator protein that brings significant changes in tomato fruit shape.  相似文献   
534.

Introduction

To assess the efficacy and safety of the interleukin-1 receptor (IL-1R) inhibitor anakinra in adult patients with refractory Still's disease.

Methods

Twenty-five patients (13 males and 12 females, median age 32 years, median disease duration seven months) with Still's disease were treated with subcutaneous injections of anakinra (100 mg/day). Treatment was given as adjunct therapy in 16 patients and as standalone in 9 patients for a median time of 15 months (range 1.5-71). The clinical and laboratory parameters during follow-up were recorded.

Results

In 84% of patients the clinical activity resolved completely within a few days (median time 0.2 months), and response was maintained until the last visit in all but one patient. A complete response of all disease-related symptoms (clinical and laboratory) occurred subsequently within a median time of three months in 80% of patients. A partial clinical and laboratory improvement was shown in 12% and 16% of patients, respectively. The Visualized Analogue Scale and Health Assessment Questionnaire scores significantly decreased during treatment. The proportion of patients achieving the American College of Rheumatology 20 (ACR20) score (20% improvement) was 82% at one month and improved to 100% at one year. The mean oral corticosteroid dose was significantly reduced at each visit. Anakinra was discontinued due to unresponsiveness in one patient and due to relapsing disease in another. Treatment was also withdrawn in three patients with severe skin reactions (urticaria). Seven patients experienced an infection during follow-up.

Conclusions

The rapid and sustained response in the majority of our patients encourages the use of anakinra in adults with Still's disease.  相似文献   
535.
During the past two decades, evidence has accumulated of adaptive evolution within protein-coding genes in a variety of species. However, with the exception of Drosophila and humans, little is known about the extent of adaptive evolution in noncoding DNA. Here, we study regions upstream and downstream of protein-coding genes in the house mouse Mus musculus castaneus, a species that has a much larger effective population size (N(e)) than humans. We analyze polymorphism data for 78 genes from 15 wild-caught M. m. castaneus individuals and divergence to a closely related species, Mus famulus. We find high levels of nucleotide diversity and moderate levels of selective constraint in upstream and downstream regions compared with nonsynonymous sites of protein-coding genes. From the polymorphism data, we estimate the distribution of fitness effects (DFE) of new mutations and infer that most new mutations in upstream and downstream regions behave as effectively neutral and that only a small fraction is strongly negatively selected. We also estimate the fraction of substitutions that have been driven to fixation by positive selection (α) and the ratio of adaptive to neutral divergence (ω(α)). We find that α for upstream and downstream regions (~ 10%) is much lower than α for nonsynonymous sites (~ 50%). However, ω(α) estimates are very similar for nonsynonymous sites (~ 10%) and upstream and downstream regions (~ 5%). We conclude that negative selection operating in upstream and downstream regions of M. m. castaneus is weak and that the low values of α for upstream and downstream regions relative to nonsynonymous sites are most likely due to the presence of a higher proportion of neutrally evolving sites and not due to lower absolute rates of adaptive substitution.  相似文献   
536.
537.
High energy prices, depletion of crude oil supplies, and price imbalance created by the increasing demand of plant oils or animal fat for biodiesel and specific lipid derivatives such as lubricants, adhesives, and plastics have given rise to heated debates on land-use practices and to environmental concerns about oil production strategies. However, commercialization of microbial oils with similar composition and energy value to plant and animal oils could have many advantages, such as being non-competitive with food, having shorter process cycle and being independent of season and climate factors. This review focuses on the ongoing research on different oleaginous yeasts producing high added value lipids and on the prospects of such microbial oils to be used in different biotechnological processes and applications. It covers the basic biochemical mechanisms of lipid synthesis and accumulation in these organisms, along with the latest insights on the metabolic processes involved. The key elements of lipid accumulation, the mechanisms suspected to confer the oleaginous character of the cell, and the potential metabolic routes enhancing lipid production are also extensively discussed.  相似文献   
538.
Based on the crystal structure of the extracellular domain (ECD) of the mouse nicotinic acetylcholine receptor (nAChR) alpha1 subunit bound to α-bungarotoxin (α-Btx) we have generated in silico models of the human nAChR α1 bound to α-Btx and α-cobratoxin (α-Cbtx), both in the presence and in the absence of the N-linked carbohydrate chain. To gain further insight into the structural role of glycosylation molecular dynamics (MD) simulations were carried out in explicit solvent so as to compare the conformational dynamics of the binding interface between nAChR α1 and the two toxins. An interesting observation during the course of the MD simulations is the strengthening of the receptor-toxin interaction in the presence of the carbohydrate chain, mediated through a shift in the position of the sugars towards the bound toxin. Critical protein-sugar interactions implicate residues Ser187 and Trp184 of nAChR and Thr6, Ser9, and Thr15 of α-Btx, as well as Thr6 and Pro7 of α-Cbtx. Analysis of the predicted residue-specific intermolecular interactions is intended to inspire biophysical studies on the functional role of glycosylation in the gating mechanism.  相似文献   
539.
The Drosophila Gene Disruption Project (GDP) has created a public collection of mutant strains containing single transposon insertions associated with different genes. These strains often disrupt gene function directly, allow production of new alleles, and have many other applications for analyzing gene function. Here we describe the addition of ~7600 new strains, which were selected from >140,000 additional P or piggyBac element integrations and 12,500 newly generated insertions of the Minos transposon. These additions nearly double the size of the collection and increase the number of tagged genes to at least 9440, approximately two-thirds of all annotated protein-coding genes. We also compare the site specificity of the three major transposons used in the project. All three elements insert only rarely within many Polycomb-regulated regions, a property that may contribute to the origin of "transposon-free regions" (TFRs) in metazoan genomes. Within other genomic regions, Minos transposes essentially at random, whereas P or piggyBac elements display distinctive hotspots and coldspots. P elements, as previously shown, have a strong preference for promoters. In contrast, piggyBac site selectivity suggests that it has evolved to reduce deleterious and increase adaptive changes in host gene expression. The propensity of Minos to integrate broadly makes possible a hybrid finishing strategy for the project that will bring >95% of Drosophila genes under experimental control within their native genomic contexts.  相似文献   
540.

Objective

The aim of this study was to evaluate the effects of intensive physical exercise and acute psychological stress during high level athletic competition as reflected on the levels of salivary cortisol in elite artistic gymnasts (AGs).

Design

The study included 239 AGs (142 females-97 males) who participated in the European Championship of Gymnastics in 2006 and 81 adolescents (40 females-41 males), matched for age, as controls. All athletes participated voluntarily in all or parts of the study, providing samples or data for each of the variables measured. Height, weight, body fat, lean body mass (LBM), bone age and Tanner stage of puberty were assessed and data concerning the time of thelarche, adrenarche and menarche as well as, the onset and the intensity (hours per week) of training were obtained.

Methods

Saliva samples were collected, the morning before training and in the afternoon shortly after the competition. From controls, the saliva samples were collected in the morning. Cortisol concentrations were measured using a chemiluminescence method. Acute stress was assessed using a questionnaire designed for the study.

Results

No difference was found between morning and afternoon salivary cortisol levels in both male and female AGs (females: AM: 15.45 ± 7.45 nmol/l vs PM: 15.73 ± 9.38 nmol/l; males: AM: 10.21 ± 5.52 nmol/l vs PM: 9.93 ± 13.8 nmol/l, p > 0.05).Female AGs presented higher levels of morning salivary cortisol than female controls (p < 0.05). Both male and female AGs had higher degree of psychological stress in comparison with controls (p < 0.001, p < 0.013, respectively). Female AGs had higher morning and afternoon salivary cortisol levels (p < 0.01, p < 0.01, respectively) and higher degree of stress (p < 0.003) than males.

Conclusions

In elite AGs the diurnal rhythm of salivary cortisol has been abolished, probably due to the strenuous training and competition conditions. Female AGs presented higher levels of morning salivary cortisol and psychological stress compared to both male AGs and female controls. The long term consequences of these modifications of the HPA axis remain to be elucidated.  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