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   6321篇
  免费   246篇
  国内免费   3篇
  6570篇
  2024年   41篇
  2023年   36篇
  2022年   30篇
  2021年   79篇
  2020年   53篇
  2019年   64篇
  2018年   171篇
  2017年   129篇
  2016年   193篇
  2015年   330篇
  2014年   341篇
  2013年   438篇
  2012年   504篇
  2011年   483篇
  2010年   327篇
  2009年   241篇
  2008年   399篇
  2007年   397篇
  2006年   382篇
  2005年   379篇
  2004年   322篇
  2003年   309篇
  2002年   271篇
  2001年   41篇
  2000年   47篇
  1999年   48篇
  1998年   40篇
  1997年   37篇
  1996年   26篇
  1995年   24篇
  1994年   17篇
  1993年   27篇
  1992年   24篇
  1991年   17篇
  1990年   26篇
  1989年   15篇
  1988年   23篇
  1987年   14篇
  1986年   25篇
  1985年   12篇
  1984年   19篇
  1983年   11篇
  1982年   11篇
  1981年   10篇
  1979年   13篇
  1978年   15篇
  1977年   9篇
  1974年   11篇
  1973年   9篇
  1968年   9篇
排序方式: 共有6570条查询结果,搜索用时 15 毫秒
1.
The yeast Snf1, animal AMPK, and plant SnRK1 protein kinases constitute a family of related proteins that have been proposed to serve as metabolic sensors of the eukaryotic cell. We have previously reported the characterization of two redundant SnRK1 encoding genes (PpSNF1a and PpSNF1b) in the moss Physcomitrella patens. Phenotypic analysis of the snf1a snf1b double knockout mutant suggested that SnRK1 is important for the plant’s ability to recognize and adapt to conditions of limited energy supply, and also suggested a possible role of SnRK1 in the control of plant development. We have now used a yeast two-hybrid system to screen for PpSnf1a interacting proteins. Two new moss genes were found, PpSKI1 and PpSKI2, which encode highly similar proteins with homologues in vascular plants. Fusions of the two encoded proteins to the green fluorescent protein localize to the nucleus. Knockout mutants for either gene have an excess of gametophores under low light conditions, and exhibit reduced gametophore stem lengths. Possible functions of the new proteins and their connection to the SnRK1 kinase are discussed.  相似文献   
2.
Post-breeding habitats of nine passerine species were studied in the permanently flooded reed beds of ponds near the village Pusté úlany (SW Slovakia) in 2002. Structural features of reed beds and the abundance of all birds studied were sampled at two sites and eight study plots. The reed bed structure and abundance of four passerines differed considerably between the individual study plots. The variations in vegetation structure were also caused by winter reed burning in the SE part of study area. Stems in burnt reed beds were smaller and thinner than unburnt. Abundance of the reed warbler and to a lesser extent sedge warbler was higher in tall reed beds, while the bearded tit preferred thick reed stems. Position of reed beds along the shore — open water gradient was an important factor in terms of abundance at the study plots in the case of the reed bunting. This species showed a strong preference for the reed bed edge with open water. Horizontal distribution of other species seems to be random, however, the birds with the exception of Savi’s warbler preferred the upper stratum of reed bed in vertical distribution. Our field data corroborate with those found in experimental studies concerning with ecomorphological characteristics of birds. Some inconsistencies, however, could also be caused by other factors (e.g. foraging preferences). Comparison of breeding and post-breeding habitat requirements of the studied bird species confirmed a more or less random distribution of the majority of species in the post-breeding period. Some variation was found in the cases of only the reed warbler and bearded tit.  相似文献   
3.
We examine the relationship of the inbreeding coefficient (f) and molecular estimates of inbreeding (IR, sMLH) in the Icelandic sheepdog. The breed experienced a severe genetic bottleneck and near extinction in the last century. Molecular estimates and the inbreeding coefficient are significantly correlated despite the moderate number of markers and individuals used in this study. This is most likely an effect of the extreme relatedness and relatively high variance in individual inbreeding coefficients in the population. There is a significant relationship between inbreeding (f) and the occurrence of hip dysplasia. However, the molecular measures did not detect hip dysplasia as an inbreeding effect.  相似文献   
4.
Biological autotrophic sulfur oxidation processes have been proposed to remove heavy metals from wastewater treatment sludge by bioleaching. We made a characterization of the microbial population in batch and continuous sludge bioleaching reactors using fluorescent in situ hybridization of fluorescently-labeled oligonucleotidic probes targeting rRNA in a ‚top to bottom approach’. Batch incubations of sludge with 0.2% (w/v) elemental sulfur resulted in a pH value of 5. Alpha-Proteobacteria hybridizing with probe ALF1b were dominant in this incubation. Members of the Acidophilium-group (hybridizing with probe Acdp821) of Nitrospira/Leptospirillum phylum (Ntspa712 probe) and from the archaeal domain (ARCH915) were also detected. When sludge was incubated with 1% elemental sulfur in batch or continuous reactor experiments, final pH values were always below 2. Active microbial communities consisted almost exclusively of gamma-Proteobacteria (hybridizing with probe GAM42a). However, further hybridization experiments with probe Thio820 targeting Acidithiobacillus ferroxidans and Acidithiobacillus thioxidans gave negative results. A new probe, named THIO181, encompassing all known members of the genus was designed. Hybridization perfomed with THIO181 and GAM42a showed a perfect co-localization of the hybridization signals. Further hybridization experiments with probe THIO181 and THC642, specific for the species Acidithiobacillus caldus, confirmed that this bacteria was largely responsible for the sulfur oxidation reaction in our acidophilic sludge bioleaching reactors.  相似文献   
5.
6.
The main goals of this work were to produce the fusion protein of the Trichoderma reesei swollenin I (SWOI) and Aspergillus niger feruloyl esterase A (FAEA) and to study the effect of the physical association of the fusion partners on the efficiency of the enzyme. The fusion protein was produced up to 25 mg l−1 in the T. reesei strains Rut-C30 and CL847. In parallel, FAEA alone was produced for use as a control protein in application tests. Recombinant FAEA and SWOI–FAEA were purified to homogeneity and characterized. The biochemical and kinetic characteristics of the two recombinant proteins were found to be similar to those of native FAEA, except for the temperature stability and specific activity of the SWOI–FAEA. Finally, the SWOI–FAEA protein was tested for release of ferulic acid from wheat bran. A period of 24 h of enzymatic hydrolysis with the SWOI–FAEA improved the efficiency of ferulic acid release by 50% compared with the results obtained using the free FAEA and SWOI. Ferulic acid is used as an antioxidant and flavor precursor in the food and pharmaceutical industries. This is the first report of a potential application of the SWOI protein fused with an enzyme of industrial interest.  相似文献   
7.
8.
9.
The case of the Northern spotted owl (Strix occidentalis caurina) has now become a classic case study in conservation biology, characterized by a harsh social battle but also by the quantity and quality of the research performed. Based on this example, I study the way the research-management interface was organized. The main lessons I have learned were: 1. laws that involve science in management are crucial but should be more precise; 2. scientific ad-hoc groups are useful reviewers of management plans and interpreters of the best scientific data available, even if more transparent scientific argumentation is needed on some points; 3. in such applied cases, even science that has not been strongly integrated with management can produce results that are useful for management; 4. stronger links between science and management appear necessary, but difficult to implement. This last point makes me wonder whether environmental laws should not more frequently target the incorporation of science into the management process itself rather than “only” basing management on the best scientific data available. On a more ecological level, perhaps the habitat issue has been underrated during the last few years compared to other emerging threats such as the invasion of the spotted owl range by barred owls.  相似文献   
10.
    
Among the different types of small RNAs, microRNAs (miRNAs) are key players in controlling gene expression at the mRNA level. To be active, they must associate with an Argonaute protein to form the miRNA induced silencing complex (miRISC) and binds to specific mRNA through complementarity sequences. The miRISC binding to an mRNA can lead to multiple outcomes, the most frequent being inhibition of the translation and/or deadenylation followed by decapping and mRNA decay. In the last years, several studies described different mechanisms modulating miRISC functions in animals. For instance, the regulation of the Argonaute protein through post-translational modifications can change the miRISC gene regulatory activity as well as modulate its binding to proteins, mRNA targets and miRISC stability. Furthermore, the presence of RNA binding proteins and multiple miRISCs at the targeted mRNA 3′ untranslated region (3′UTR) can also affect its function through cooperation or competition mechanisms, underlying the importance of the 3′UTR environment in miRNA-mediated repression. Another way to regulate the miRISC function is by modulation of its interactors, forming different types of miRNA silencing complexes that affect gene regulation differently. It is also reported that the subcellular localization of several components of the miRNA pathway can modulate miRISC function, suggesting an important role for vesicular trafficking in the regulation of this essential silencing complex. This article is categorized under:
  • RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes
  • Regulatory RNAs/RNAi/Riboswitches > RNAi: Mechanisms of Action
  • Regulatory RNAs/RNAi/Riboswitches > Biogenesis of Effector Small RNAs
  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