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   462篇
  免费   52篇
  2022年   3篇
  2021年   5篇
  2020年   2篇
  2019年   9篇
  2018年   7篇
  2017年   8篇
  2016年   12篇
  2015年   16篇
  2014年   25篇
  2013年   23篇
  2012年   27篇
  2011年   39篇
  2010年   20篇
  2009年   12篇
  2008年   27篇
  2007年   18篇
  2006年   23篇
  2005年   18篇
  2004年   20篇
  2003年   13篇
  2002年   20篇
  2001年   14篇
  2000年   10篇
  1999年   13篇
  1998年   11篇
  1997年   8篇
  1996年   2篇
  1995年   7篇
  1994年   7篇
  1992年   7篇
  1991年   10篇
  1990年   19篇
  1989年   13篇
  1988年   8篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1983年   5篇
  1981年   3篇
  1980年   2篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1969年   2篇
  1967年   1篇
  1966年   2篇
  1965年   1篇
  1963年   1篇
  1961年   1篇
排序方式: 共有514条查询结果,搜索用时 46 毫秒
91.
92.
A total of 1500 environmental strains of Vibrio parahaemolyticus, isolated from the aquatic environment of Bangladesh, were screened for the presence of a major V. parahaemolyticus virulence factor, the thermostable direct haemolysin (tdh) gene, by the colony blot hybridization method using a digoxigenin-labeled tdh gene probe. Of 1500 strains, 5 carried the tdh sequence, which was further confirmed by PCR using primers specific for the tdh gene. Examination by PCR confirmed that the 5 strains were V. parahaemolyticus and lacked the thermostable direct haemolysin-related haemolysin (trh) gene, the alternative major virulence gene known to be absent in pandemic strains. All 5 strains gave positive Kanagawa phenomenon reaction with characteristic beta-haemolysis on Wagatsuma agar medium. Southern blot analysis of the HindIII-digested chromosomal DNA demonstrated, in all 5 strains, the presence of 2 tdh genes common to strains positive for Kanagawa phenomenon. However, the 5 strains were found to belong to 3 different serotypes (O3:K29, O4:K37, and O3:K6). The 2 with pandemic serotype O3:K6 gave positive results in group-specific PCR and ORF8 PCR assays, characteristics unique to the pandemic clone. Clonal variations among the 5 isolates were analyzed by comparing RAPD and ribotyping patterns. Results showed different patterns for the 3 serotypes, but the pattern was identical among the O3:K6 strains. This is the first report on the isolation of pandemic O3:K6 strains of V. parahaemolyticus from the aquatic environment of Bangladesh.  相似文献   
93.
Normal cellular function is dependent on a number of highly regulated homeostatic mechanisms, which act in concert to maintain conditions suitable for life. During periods of nutritional deficit, cells initiate a number of recycling programs which break down complex intracellular structures, thus allowing them to utilize the energy stored within. These recycling systems, broadly named “autophagy”, enable the cell to maintain the flow of nutritional substrates until they can be replenished from external sources. Recent research has shown that a number of regulatory components of the autophagy program are controlled by lysine acetylation. Lysine acetylation is a reversible post-translational modification that can alter the activity of enzymes in a number of cellular compartments. Strikingly, the main substrate for this modification is a product of cellular energy metabolism: acetyl-CoA. This suggests a direct and intricate link between fuel metabolites and the systems which regulate nutritional homeostasis. In this review, we examine how acetylation regulates the systems that control cellular autophagy, and how global protein acetylation status may act as a trigger for recycling of cellular components in a nutrient-dependent fashion. In particular, we focus on how acetylation may control the degradation and turnover of mitochondria, the major source of fuel-derived acetyl-CoA.  相似文献   
94.
(22S,23S)-Homobrassinolide was tested for its effect on the electric cell potential, proton extrusion, ferricyanide reduction, and amino acid and sucrose uptake of leaves of Egeria densa Planchon. In the light, (22S,23S)-homobrassinolide and its derivative, 2α-3α-dihydroxy-5α-stigmast-22-en-6-one, were similar to each other and similar to fusicoccin in causing hyperpolarization and proton extrusion, whereas stigmasterol was less effective. In darkness, the three sterols showed comparable effects. (22S,23S)-Homobrassinolide slightly stimulated ferricyanide reduction and promoted uptake of sucrose and α-aminoisobutyric acid. The results are compatible with a stimulation of an electrogenic proton pump mechanism at the plasmalemma by (22S,23S)-homobrassinolide.  相似文献   
95.
Vibrio cholerae O1 in plankton samples collected from ponds and rivers between February 1987 and January 1990 in Matlab, Bangladesh, was detected by the fluorescent-monoclonal antibody (FA) technique. Samples were collected at sites which were monitored fortnightly (fixed sites) as well as at sites that were part of a case-control study. FA results were compared with those obtained by conventional culture methods (CM). A total of 876 samples were collected; V. cholerae O1 was detected in 563 samples (64.27%) by the FA method and in 3 samples (0.34%) by CM. Of the fixed-site plankton samples, 439 (63.62%) were positive by FA and none were positive by CM. Of the 93 case sites sampled on the day after the occurrence of a case of cholera, 73 (78.49%) were positive for V. cholerae O1 by FA and 3 (3.2%) were positive by CM. In comparison, of the 93 first-day sample collections at control sites at the time a case of cholera occurred, only 51 (54.83%) were positive by FA and none were positive by CM. From the data, it is concluded that V. cholerae O1 is present throughout the year in the ponds and rivers of Bangladesh that were examined in this study and that V. cholerae can be detected by FA but not always by CM. The FA procedure was found to be very useful in detecting V. cholerae in plankton, with which it was associated and often occurred in large numbers in the nonculturable stage. Thus, studies investigating the significance of the role of environmental factors in the epidemiology of cholera can be performed effectively by using FA. Such studies are in progress.  相似文献   
96.
The growth characteristics of known strains of Plesiomonas shigelloides were compared with those of Aeromonas species (the major competing species in environmental waters) on plesiomonas differential agar, inositol brilliant green bile salt, and modified salmonella-shigella agar at incubation temperatures of 37, 42, and 44 degrees C. Using local isolates from clinical and environmental sources, optimal growth conditions, as determined by colony counts and the colony characteristics, plesiomonas differential agar proved to be ideal when incubated at 44 degrees C. Contrary to earlier recommendations for 48 h incubation, the colonies could be recognized readily after an incubation of 24 h.  相似文献   
97.
Within the artery intima, endothelial cells respond to mechanical cues and changes in subendothelial matrix stiffness. Recently, we found that the aging subendothelial matrix stiffens heterogeneously and that stiffness heterogeneities are present on the scale of one cell length. However, the impacts of these complex mechanical micro-heterogeneities on endothelial cells have not been fully understood. Here, we simulate the effects of matrices that mimic young and aged vessels on single- and multi-cell endothelial cell models and examine the resulting cell basal strain profiles. Although there are limitations to the model which prohibit the prediction of intracellular strain distributions in alive cells, this model does introduce mechanical complexities to the subendothelial matrix material. More heterogeneous basal strain distributions are present in the single- and multi-cell models on the matrix mimicking an aged artery over those exhibited on the young artery. Overall, our data indicate that increased heterogeneous strain profiles in endothelial cells are displayed in silico when there is an increased presence of microscale arterial mechanical heterogeneities in the matrix.  相似文献   
98.
Aspergillus niger, isolated from hydrocarbon-contaminated soil, was examined for its potential to degrade phenanthrene and pyrene. Two novel metabolites, 1-methoxyphenanthrene and 1-methoxypyrene, were identified by conventional chemical techniques. Minor metabolites identified were 1- and 2-phenanthrol and 1-pyrenol. No 14CO2 evolution was observed in either [14C]phenanthrene or [14C]pyrene cultures.  相似文献   
99.
BACKGROUND: Neonatal screening for congenital adrenal hyperplasia was introduced in 1977. However, even today only a few national screening programs exist and their cost effectiveness is still debatable. This study was conducted in order to evaluate the advisability of a national or regional screening program in Israel. METHODS: From June 1987 until December 1992 we screened a countrywide random sample of 113,846 newborns for 21-hydroxylase (21-OH) deficiency measuring 17alpha-OH progesterone (17-OHP) from blood spotted on filter paper. Between January 1993 and August 1995 we continued the screening program concentrating on the population of northern Israel. A total of 56,958 newborns were screened. We compared these findings with the incidence of 21-OH deficiency in the total population born in Israel during the years 1986-1991. RESULTS: In the countrywide screening program, 4 newborns (2 Arabs and 2 Jews) were found to have levels of 17-OHP between 409 and 2,049 nmol/l (2 males and 2 females). This constitutes a low incidence of 1 in 28,462 live births. In the north-Israel screening program 4 newborns (all Arabs) were detected (2 males and 2 females) constituting a much higher incidence of 1 in 14,240 live births. The data obtained from the archives revealed that the incidence of 21-OH deficiency nationwide during the years 1986-1991 was 1:19,000 live births, 1:30,000 for Jews and 1:8,000 for Arabs. The incidence of 21-OH deficiency among Arab newborns in the northern part of the country was as high as 1:5,000 (14:71,130). The female to male (F:M) ratio was 2.6:1 and the ratio of the salt-losing to the simple virilizing variant was 5:1. Two male patients were diagnosed prenatally, 21 patients (17 F and 4 M) during the first month after birth and 6 others subsequently. CONCLUSIONS: The high F:M ratio of 21-OH deficiency in the total population compared to a 1:1 ratio in our random screening programs suggests that 21-OH-deficient male patients in the general population might have been missed or died early due to a salt-losing crisis. The high incidence of this disease in the northern part of the country and especially among the Arabs, suggests that screening in this part of the country, especially among the Arab population, is warranted and might save the lives of some male patients.  相似文献   
100.
Water plays a central role in plant biology and the efficiency of water transport throughout the plant affects both photosynthetic rate and growth, an influence that scales up deterministically to the productivity of terrestrial ecosystems. Moreover, hydraulic traits mediate the ways in which plants interact with their abiotic and biotic environment. At landscape to global scale, plant hydraulic traits are important in describing the function of ecological communities and ecosystems. Plant hydraulics is increasingly recognized as a central hub within a network by which plant biology is connected to palaeobiology, agronomy, climatology, forestry, community and ecosystem ecology and earth‐system science. Such grand challenges as anticipating and mitigating the impacts of climate change, and improving the security and sustainability of our food supply rely on our fundamental knowledge of how water behaves in the cells, tissues, organs, bodies and diverse communities of plants. A workshop, ‘Emerging Frontiers in Plant Hydraulics’ supported by the National Science Foundation, was held in Washington DC, 2015 to promote open discussion of new ideas, controversies regarding measurements and analyses, and especially, the potential for expansion of up‐scaled and down‐scaled inter‐disciplinary research, and the strengthening of connections between plant hydraulic research, allied fields and global modelling efforts.  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