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   1792篇
  免费   158篇
  国内免费   1篇
  1951篇
  2023年   5篇
  2022年   15篇
  2021年   17篇
  2020年   9篇
  2019年   10篇
  2018年   13篇
  2017年   17篇
  2016年   36篇
  2015年   58篇
  2014年   66篇
  2013年   92篇
  2012年   120篇
  2011年   124篇
  2010年   81篇
  2009年   78篇
  2008年   110篇
  2007年   125篇
  2006年   85篇
  2005年   113篇
  2004年   129篇
  2003年   97篇
  2002年   117篇
  2001年   26篇
  2000年   12篇
  1999年   17篇
  1998年   31篇
  1997年   26篇
  1996年   23篇
  1995年   19篇
  1994年   18篇
  1993年   20篇
  1992年   13篇
  1991年   14篇
  1990年   14篇
  1989年   10篇
  1988年   8篇
  1987年   11篇
  1986年   6篇
  1985年   19篇
  1984年   15篇
  1983年   18篇
  1982年   15篇
  1981年   8篇
  1980年   8篇
  1979年   6篇
  1978年   10篇
  1977年   13篇
  1976年   11篇
  1974年   7篇
  1967年   5篇
排序方式: 共有1951条查询结果,搜索用时 0 毫秒
991.
The 25th anniversary of the Antibody Engineering & Therapeutics Conference, the Annual Meeting of The Antibody Society, will be held in Huntington Beach, CA, December 7–11, 2014. Organized by IBC Life Sciences, the event will celebrate past successes, educate participants on current activities and offer a vision of future progress in the field. Keynote addresses will be given by academic and industry experts Douglas Lauffenburger (Massachusetts Institute of Technology), Ira Pastan (National Cancer Institute), James Wells (University of California, San Francisco), Ian Tomlinson (GlaxoSmithKline) and Anthony Rees (Rees Consulting AB and Emeritus Professor, University of Bath). These speakers will provide updates of their work, placed in the context of the substantial growth of the industry over the past 25 years.  相似文献   
992.
Endosomes are one of the major membrane sorting checkpoints in eukaryotic cells and they regulate recycling or destruction of proteins mostly from the plasma membrane and the Golgi. As a result the endosomal system plays a central role in maintaining cell homeostasis, and mutations in genes belonging to this network of organelles interconnected by vesicular transport, cause severe pathologies including cancer and neurobiological disorders. It is therefore of prime relevance to understand the mechanisms underlying the biogenesis and organization of the endosomal system. The yeast Saccharomyces cerevisiae has been pivotal in this task. To specifically label and analyze at the ultrastructural level the endosomal system of this model organism, we present here a detailed protocol for the positively charged nanogold uptake by spheroplasts followed by the visualization of these particles through a silver enhancement reaction. This method is also a valuable tool for the morphological examination of mutants with defects in endosomal trafficking. Moreover, it is not only applicable for ultrastructural examinations but it can also be combined with immunogold labelings for protein localization investigations.  相似文献   
993.
Although substantial upper extremity (U/E) muscular efforts are required when individuals with spinal cord injury (SCI) perform sitting pivot transfers, little is known about the electromyographic (EMG) activation patterns of key shoulder and elbow muscles solicited during the performance of this functional task. The aims of this study were to examine the EMG activation patterns of U/E muscles in 10 males with SCI, and to compare them across sitting pivot transfers performed toward seats of different heights (low, same, high). EMG data from the biceps, triceps, deltoid, pectoralis major and latissimus dorsi were recorded bilaterally. Transfers were divided into pre-lift, lift, and post-lift phases. Each phase was time- and amplitude-normalized using a mean dynamic EMG approach. Similar EMG activation patterns were found across the different transfers for all muscles (rmean = 0.942–0.991), whereas moderate to high inter-subject variability (CV: 20.9–70.6%) was reported for the different muscles and transfers. Peak EMG occurred earlier at the trailing U/E compared to the leading one, and was observed around seat-off for most of the muscles. When transfer to a high target seat was compared to transfer to one of the same height, significantly higher relative EMG values were observed at the biceps (mean: 1.64 vs. 1.00) of the leading U/E as well as the deltoid (mean: 1.20 vs. 1.00) and pectoralis major (mean: 1.20 vs. 1.00; peak: 2.27 vs. 1.79) of the trailing U/E. Transferring to a low target seat did not lead to lower muscular demand than transferring to one of the same height (P > 0.05). These results indicate that coordinated and higher muscular efforts were generated at the trailing deltoid and pectoralis major when transferring to a high target seat compared to one of similar height. Higher muscular efforts were also developed at the leading biceps when transferring to a high target seat compared to a leveled one. Lowering the target seat with respect to the initial seat had no favorable effect on muscular demand.  相似文献   
994.
A previously undescribed plant-microbe interaction between a root-colonizing Streptomyces species, S. lydicus WYEC108, and the legume Pisum sativum is described. The interaction is potentially of great importance to the health and growth in nature of this nodulating legume. The root-colonizing soil actinomycete S. lydicus WYEC108 influences pea root nodulation by increasing root nodulation frequency, possibly at the level of infection by Rhizobium spp. S. lydicus also colonizes and then sporulates within the surface cell layers of the nodules. Colonization leads to an increase in the average size of the nodules that form and improves the vigor of bacteroids within the nodules by enhancing nodular assimilation of iron and possibly other soil nutrients. Bacteroid accumulation of the carbon storage polymer, poly-β-hydroxybutyrate, is reduced in colonized nodules. Root nodules of peas taken from agricultural fields in the Palouse hills of northern Idaho were also found to be colonized by actinomycete hyphae. We hypothesize that root and nodule colonization is one of several mechanisms by which Streptomyces acts as a naturally occurring plant growth-promoting bacterium in pea and possibly other leguminous plants.  相似文献   
995.
Glucose is absolutely essential for the survival and function of the brain. In our current understanding, there is no endogenous glucose production in the brain, and it is totally dependent upon blood glucose. This glucose is generated between meals by the hydrolysis of glucose-6-phosphate (Glc-6-P) in the liver and the kidney. Recently, we reported a ubiquitously expressed Glc-6-P hydrolase, glucose-6-phosphatase-beta (Glc-6-Pase-beta), that can couple with the Glc-6-P transporter to hydrolyze Glc-6-P to glucose in the terminal stages of glycogenolysis and gluconeogenesis. Here we show that astrocytes, the main reservoir of brain glycogen, express both the Glc-6-Pase-beta and Glc-6-P transporter activities and that these activities can couple to form an active Glc-6-Pase complex, suggesting that astrocytes may provide an endogenous source of brain glucose.  相似文献   
996.
B cell hybridomas are an important source of monoclonal antibodies. In this paper, we developed a high-throughput method to characterize mouse IgG antibodies using surface plasmon resonance technology. This assay rapidly determines their sub-isotypes, whether they bind native antigen and their approximate affinities for the antigen using only 50 μl of hybridoma cell culture supernatant. Moreover, we found that mouse hybridomas secreting IgG antibodies also have membrane form IgG expression without Igα. Based on this surface IgG, we used flow cytometry to isolate rare γ2a isotype switched variants from a γ2b antibody secreting hybridoma cell line. Also, we used fluorescent antigen to single cell sort antigen binding hybridoma cells from bulk mixture of fused hybridoma cells instead of the traditional multi-microwell plate screening and limiting dilution sub-cloning thus saving time and labor. The IgG monoclonal antibodies specific for the native antigen identified with these methods are suitable for in vivo therapeutic uses, but also for sandwich ELISA assays, histology, flow cytometry, immune precipitation and x-ray crystallography.  相似文献   
997.
Hybridisations between related species with divergent ontogenies can provide insights into the bases for evolutionary change in development. One example of such hybridisations involves sea urchin species that exhibit either standard larval (pluteal) stages or those that develop directly from embryo to adult without an intervening feeding larval stage. In such crosses, pluteal features were found to be restored in fertilisations of the eggs of some direct developing sea urchins (Heliocidaris erythrogramma) with the sperm of closely (Heliocidaris tuberculata) and distantly (Pseudoboletia maculata) related species with feeding larvae. Such results can be argued to support the punctuated equilibrium model—conservation in pluteal regulatory systems and a comparatively rapid switch to direct development in evolution. 1 , 1 Generation of hybrids between distantly related direct developers may, however, indicate evolutionary convergence. The ‘rescue’ of pluteal features by paternal genomes may require maternal factors from H. erythrogramma because the larva of this species has pluteal features. In contrast, pluteal features were not restored in hybridisations with the eggs of Holopneustes purpurescens, which lacks pluteal features. How much of pluteal development can be lost before it cannot be rescued in such crosses? The answer awaits hybridisations among indirect and direct developing sea urchins differing in developmental phenotype, in parallel with investigations of the genetic programs involved. BioEssays 26:343–347, 2004. © 2004 Wiley Periodicals, Inc.  相似文献   
998.
Intensive longitudinal behavior observations of male chimpanzees in stable mixed-sex social groups in a semi-natural environment were analyzed by state of development as defined by dental, growth and hormonal signals. Initial increase of sexual behaviors preceded adolescent hormonal changes. Peak prevalence of sexual behaviors coincided with the adolescent period. This period is also characterized by peak activity level and feeding. The major increase in aggression and stabilization of submissive behavior at adult level occurred concomitant with achievement of adult hormone levels and body size, and these were accompanied by increase of grooming affiliative behaviors.  相似文献   
999.
Our aim was to examine the docosahexaenoic acid (DHA; 22:6n-3) status of pregnant African-American women reporting to the antenatal clinic at Wayne State University in a longitudinal study design. Fatty acid compositions of plasma and erythrocyte total lipid extracts were determined and food frequency surveys were administered at 24 weeks of gestation, delivery, and 3 months postpartum for participants (n = 157). DHA (mean +/- SD) in the estimated total circulating plasma was similar at gestation (384 +/- 162 mg) and delivery (372 +/- 155 mg) but was significantly lower at 3 months postpartum (178 +/- 81 mg). The relative weight percentage of DHA and docosapentaenoic acid n-6 (DPAn-6; 22:5n-6) decreased postpartum, whereas their respective metabolic precursors, eicosapentaenoic acid (EPA; 20:5n-3) and arachidonic acid (AA; 20:4n-6), increased. Similar results were found in erythrocytes. Dietary intake of DHA throughout the study was estimated at 68 +/- 75 mg/day. The relative amounts of circulating DHA and DPAn-6 were increased during pregnancy compared with 3 months postpartum, possibly via increased synthesis from EPA and AA. The low dietary intake and blood levels of DHA in this population compared with others may not support optimal fetal DHA accretion and subsequent neural development.  相似文献   
1000.
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