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   2683篇
  免费   248篇
  国内免费   1篇
  2024年   4篇
  2023年   18篇
  2022年   16篇
  2021年   64篇
  2020年   46篇
  2019年   39篇
  2018年   60篇
  2017年   60篇
  2016年   96篇
  2015年   154篇
  2014年   147篇
  2013年   181篇
  2012年   259篇
  2011年   252篇
  2010年   145篇
  2009年   134篇
  2008年   181篇
  2007年   152篇
  2006年   168篇
  2005年   168篇
  2004年   130篇
  2003年   112篇
  2002年   110篇
  2001年   20篇
  2000年   13篇
  1999年   31篇
  1998年   17篇
  1997年   9篇
  1996年   13篇
  1995年   12篇
  1994年   11篇
  1993年   4篇
  1992年   14篇
  1991年   7篇
  1990年   8篇
  1989年   4篇
  1988年   5篇
  1987年   7篇
  1986年   5篇
  1985年   4篇
  1984年   3篇
  1983年   4篇
  1981年   3篇
  1977年   3篇
  1973年   3篇
  1971年   3篇
  1969年   3篇
  1967年   4篇
  1882年   2篇
  1878年   2篇
排序方式: 共有2932条查询结果,搜索用时 546 毫秒
131.
132.
Scabies ('Itch Mite') is truly a Great Neglected Disease that inflicts misery on millions. Molecular approaches, while still in their infancy, are providing a better understanding of the parasite and will have important implications for control and prevention. It has long been thought that dogs may act as a reservoir for human infections. However, genetic studies cast doubt over this supposition.  相似文献   
133.
Biclustering microarray data by Gibbs sampling   总被引:1,自引:0,他引:1  
MOTIVATION: Gibbs sampling has become a method of choice for the discovery of noisy patterns, known as motifs, in DNA and protein sequences. Because handling noise in microarray data presents similar challenges, we have adapted this strategy to the biclustering of discretized microarray data. RESULTS: In contrast with standard clustering that reveals genes that behave similarly over all the conditions, biclustering groups genes over only a subset of conditions for which those genes have a sharp probability distribution. We have opted for a simple probabilistic model of the biclusters because it has the key advantage of providing a transparent probabilistic interpretation of the biclusters in the form of an easily interpretable fingerprint. Furthermore, Gibbs sampling does not suffer from the problem of local minima that often characterizes Expectation-Maximization. We demonstrate the effectiveness of our approach on two synthetic data sets as well as a data set from leukemia patients.  相似文献   
134.
ssgB was identified as a novel early sporulation gene in Streptomyces coelicolor. An ssgB deletion mutant failed to sporulate, over-produced actinorhodin, and its colonies were significantly larger than those of the parental strain, suggesting an important role for the ssgB gene product in the process of growth cessation prior to sporulation-specific cell division. This places ssgB temporally before the paralogous sporulation gene ssgA. Analysis of ssgB mutant hyphae by electron microscopy and by confocal fluorescence microscopy showed that it was defective in the initiation of sporulation, as no sporulation septa could be identified, and DNA segregation had not yet been initiated in the mutant.  相似文献   
135.
Cre recombinase expression can result in phenotypic aberrations in plants   总被引:10,自引:0,他引:10  
The cre recombinase gene was stably introduced and expressed in tomato, petunia and Nicotiana tabacum. Some plants expressing the cre gene driven by a CaMV 35S promoter displayed growth retardation and a distinct pattern of chlorosis in their leaves. Although no direct relation can be proven between the phenotype and cre expression, aberrant phenotypes always co-segregate with the transgene, which strongly suggests a correlation. The severity of the phenotype does not correlate with the level of steady-state mRNA in mature leaves, but with the timing of cre expression during organogenesis. The early onset of cre expression in tomato is correlated with a more severe phenotype and with higher germinal transmission frequencies of site-specific deletions. No aberrant phenotype was observed when a tissue-specific phaseolin promoter was used to drive the cre gene. The data suggest that for the application of recombinases in plants, expression is best limited to specific tissues and a short time frame.[12pt] Abbreviations: bar, the phosphinotricin acetyltransferase gene; CAM, chloramphenicol resistance gene; Ds 5 & Ds 3, borders of the Ds transposable element from maize forming a functional transposable element that embodies the interjacent DNA; gus, the -glucoronidase gene; gus-int, the gus gene interrupted by a plant intron; hpt, the hygromycin phosphotransferase gene; nptII, the neomycin phosphotransferase gene; ORI, bacterial origin for plasmid replication in Escherichia coli of plasmid p15A  相似文献   
136.
Coucke (1998) was the first to use acoustic resonance analysis to monitor embryo development in chicken eggs. He remarked that at around 100 hours of incubation, the course of the resonant frequency and damping changed abruptly in the case of fertile eggs. He also showed that these changes were related to a physiologic event during early embryonic development. The objective of our study is to monitor the course of the vibration parameters during the early incubation of chicken eggs and to relate these changes to egg and embryo characteristics. A total of 72 Hybro eggs were incubated vertically in a small incubator at standard conditions. Several egg parameters were measured before incubation. During the early stages of incubation the vibration behavior of these eggs was monitored. The time at which the damping of the vibration suddenly changed, the diameter of the eggs and their interaction were found to be significant explanatory variables in order to predict hatching time. A correlation coefficient r of 0.72 was obtained.  相似文献   
137.
138.

Background

Body temperature is a strong predictor of outcome in acute stroke. In a previous randomized trial we observed that treatment with high-dose acetaminophen (paracetamol) led to a reduction of body temperature in patients with acute ischemic stroke, even when they had no fever. The purpose of the present trial was to study whether this effect of acetaminophen could be reproduced, and whether ibuprofen would have a similar, or even stronger effect.

Methods

Seventy-five patients with acute ischemic stroke confined to the anterior circulation were randomized to treatment with either 1000 mg acetaminophen, 400 mg ibuprofen, or placebo, given 6 times daily during 5 days. Treatment was started within 24 hours from the onset of symptoms. Body temperatures were measured at 2-hour intervals during the first 24 hours, and at 6-hour intervals thereafter.

Results

No difference in body temperature at 24 hours was observed between the three treatment groups. However, treatment with high-dose acetaminophen resulted in a 0.3°C larger reduction in body temperature from baseline than placebo treatment (95% CI: 0.0 to 0.6 °C). Acetaminophen had no significant effect on body temperature during the subsequent four days compared to placebo, and ibuprofen had no statistically significant effect on body temperature during the entire study period.

Conclusions

Treatment with a daily dose of 6000 mg acetaminophen results in a small, but potentially worthwhile decrease in body temperature after acute ischemic stroke, even in normothermic and subfebrile patients. Further large randomized clinical trials are needed to study whether early reduction of body temperature leads to improved outcome.  相似文献   
139.
The oxidation of N-hydroxylated compounds may result in production of nitrogen oxides, including nitric oxide (NO). Oxidation may be independent on NO-synthase. Production of nitrites and nitrates via NO from formaldoxime and glyceryl trinitrate was studied and compared. Superoxide ion, ions Fe2+ and Fe3+, methemoglobin and methemoglobin + NADPH + methylene blue, oxyhemoglobin and oxyhemoglobin + NADPH + methylene blue in the presence of atmospheric oxygen were used as oxidoreductive agents. Formaldoxime (triformaxime) was chosen as a newly recognized atypical cyclic oxime which can be converted to NO and glyceryl trinitrate as a well-known NO donor of quite different structure. From the oxidoreductive agents used, glyceryl trinitrate was not converted to nitrites or nitrates by Fe2+ or Fe3+ and by methemoglobin alone. Formaldoxime was resistant to the action of superoxide ion and methemoglobin alone. Importance of these possible metabolic pathways for production of NO from examined vasodilators is discussed.  相似文献   
140.
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