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   6281篇
  免费   590篇
  国内免费   3篇
  2024年   4篇
  2023年   40篇
  2022年   108篇
  2021年   206篇
  2020年   114篇
  2019年   126篇
  2018年   165篇
  2017年   122篇
  2016年   215篇
  2015年   396篇
  2014年   415篇
  2013年   485篇
  2012年   631篇
  2011年   565篇
  2010年   325篇
  2009年   284篇
  2008年   410篇
  2007年   394篇
  2006年   382篇
  2005年   309篇
  2004年   280篇
  2003年   241篇
  2002年   203篇
  2001年   48篇
  2000年   30篇
  1999年   33篇
  1998年   61篇
  1997年   35篇
  1996年   23篇
  1995年   18篇
  1994年   22篇
  1993年   15篇
  1992年   22篇
  1991年   15篇
  1990年   11篇
  1989年   5篇
  1988年   8篇
  1987年   10篇
  1986年   8篇
  1985年   4篇
  1984年   11篇
  1983年   5篇
  1982年   9篇
  1981年   11篇
  1980年   8篇
  1979年   8篇
  1977年   4篇
  1976年   4篇
  1973年   5篇
  1968年   3篇
排序方式: 共有6874条查询结果,搜索用时 31 毫秒
151.
RNA interference (RNAi) is a widely adopted tool for loss-of-function studies but RNAi results only have biological relevance if the reagents are appropriately mapped to genes. Several groups have designed and generated RNAi reagent libraries for studies in cells or in vivo for Drosophila and other species. At first glance, matching RNAi reagents to genes appears to be a simple problem, as each reagent is typically designed to target a single gene. In practice, however, the reagent–gene relationship is complex. Although the sequences of oligonucleotides used to generate most types of RNAi reagents are static, the reference genome and gene annotations are regularly updated. Thus, at the time a researcher chooses an RNAi reagent or analyzes RNAi data, the most current interpretation of the RNAi reagent–gene relationship, as well as related information regarding specificity (e.g., predicted off-target effects), can be different from the original interpretation. Here, we describe a set of strategies and an accompanying online tool, UP-TORR (for Updated Targets of RNAi Reagents; www.flyrnai.org/up-torr), useful for accurate and up-to-date annotation of cell-based and in vivo RNAi reagents. Importantly, UP-TORR automatically synchronizes with gene annotations daily, retrieving the most current information available, and for Drosophila, also synchronizes with the major reagent collections. Thus, UP-TORR allows users to choose the most appropriate RNAi reagents at the onset of a study, as well as to perform the most appropriate analyses of results of RNAi-based studies.  相似文献   
152.
153.
154.
Interest is increasing in developing fluorescent ligands for characterization of adenosine receptors (ARs), which hold a promise of usefulness in the drug discovery process. The size of a strategically labeled AR ligand can be greatly increased after the attachment of a fluorophore. The choice of dye moiety (e.g. Alexa Fluor 488), attachment point and linker length can alter the selectivity and potency of the parent molecule. Fluorescent derivatives of adenosine agonists and antagonists (e.g. XAC and other heterocyclic antagonist scaffolds) have been synthesized and characterized pharmacologically. Some are useful AR probes for flow cytometry, fluorescence correlation spectroscopy, fluorescence microscopy, fluorescence polarization, fluorescence resonance energy transfer, and scanning confocal microscopy. Thus, the approach of fluorescent labeled GPCR ligands, including those for ARs, is a growing dynamic research field.  相似文献   
155.
Here we report the biosynthetic pathway for the neoantimycin and present three novel neoantimycin analogues, neoantimycin D (1), E (2) and F (3), from this assembly system from Streptoverticillium orinoci. Identification of these novel neoantimycin variants was achieved by selective MS/MS interrogation of natural product extracts using diagnostic fragments of the known neoantimycins. Their structures, including the absolute configurations, were elucidated using a combination of NMR experiments, detailed MS/MS experiments and the advanced Marfey’s method. The biosynthetic pathway of neoantimycin was dissected by genome sequencing data analysis for the first time, which includes a hybrid nonribosomal peptide synthetase (NRPS) and polyketide synthetase (PKS) assembly lines.  相似文献   
156.
This study aims at substituting the essential functions of photoreceptors in patients who are blind owing to untreatable forms of hereditary retinal degenerations. A microelectronic neuroprosthetic device, powered via transdermal inductive transmission, carrying 1500 independent microphotodiode-amplifier-electrode elements on a 9 mm2 chip, was subretinally implanted in nine blind patients. Light perception (8/9), light localization (7/9), motion detection (5/9, angular speed up to 35 deg s−1), grating acuity measurement (6/9, up to 3.3 cycles per degree) and visual acuity measurement with Landolt C-rings (2/9) up to Snellen visual acuity of 20/546 (corresponding to decimal 0.037 or corresponding to 1.43 logMAR (minimum angle of resolution)) were restored via the subretinal implant. Additionally, the identification, localization and discrimination of objects improved significantly (n = 8; p < 0.05 for each subtest) in repeated tests over a nine-month period. Three subjects were able to read letters spontaneously and one subject was able to read letters after training in an alternative-force choice test. Five subjects reported implant-mediated visual perceptions in daily life within a field of 15° of visual angle. Control tests were performed each time with the implant''s power source switched off. These data show that subretinal implants can restore visual functions that are useful for daily life.  相似文献   
157.
158.
We studied the colonization of the paunch wall of three lower termites, Reticulitermes flavipes, Incisitermes tabogae, and Incisitermes marginipennis, by light and electron microscopy. In addition to various prokaryotes, oxymonad flagellates were attached to the wall of the paunch in all three species. The prokaryotic layer found in R. flavipes is relatively thin, since most organisms are attached laterally. Large members of the flagellate genus Pyrsonympha protrude into the gut lumen. The prokaryotes are very abundant on the gut wall in I. tabogae and I. marginipennis, forming a thick carpet of mostly vertically attached rods and wavy spirochetes. The adhering oxymonads are relatively small and almost hidden in the thick bacterial biofilm. Three small morphotypes were seen in I. tabogae; two possessing a short rostellum and one amoeboid. The only oxymonad found in I. tabogae so far, Oxymonas clevelandi, is not identical to any of the present oxymonads. I. marginipennis contains a mid-sized oxymonad with ectobiotic spirochetes, probably identical to Oxymonas hubbardi, and a tiny unknown morphotype. The spatial organization of the pro- and eukaryotic microorganisms on the gut wall of the three termites is described and discussed concerning oxygen stress.  相似文献   
159.
Recent studies suggest that the combination of caffeine-containing drinks together with alcohol might reduce the subjective feelings of alcohol intoxication—the so-called “masking effect”. In this study, we aimed to review the effects of alcohol in combination with caffeine or energy drink with special focus on the “masking effect”. Fifty-two healthy male volunteers were analysed concerning breath alcohol concentration and subjective sensations of intoxication using a 18 item Visual Analogue Scale in a randomised, double-blinded, controlled, four treatments cross-over trial after consumption of (A) placebo, (B) alcohol (vodka 37.5 % at a dose of 46.5 g ethanol), (C) alcohol in combination with caffeine at a dose of 80 mg (equivalent to one 250 ml can of energy drink) and (D) alcohol in combination with energy drink at a dose of 250 ml (one can). Primary variables were headache, weakness, salivation and motor coordination. Out of four primary variables, weakness and motor coordination showed a statistically significant difference between alcohol and non-alcohol group, out of 14 secondary variables, five more variables (dizziness, alterations in sight, alterations in walking, agitation and alterations in speech) also showed significant differences due mainly to contrasts with the non-alcohol group. In none of these end points, could a statistically significant effect be found for the additional ingestion of energy drink or caffeine on the subjective feelings of alcohol intoxication. This within-subjects study does not confirm the presence of a “masking effect” when combining caffeine or energy drink with alcohol.  相似文献   
160.
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