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   6268篇
  免费   441篇
  国内免费   4篇
  6713篇
  2023年   23篇
  2022年   83篇
  2021年   158篇
  2020年   73篇
  2019年   98篇
  2018年   137篇
  2017年   122篇
  2016年   201篇
  2015年   290篇
  2014年   326篇
  2013年   420篇
  2012年   530篇
  2011年   603篇
  2010年   318篇
  2009年   280篇
  2008年   371篇
  2007年   435篇
  2006年   365篇
  2005年   328篇
  2004年   305篇
  2003年   315篇
  2002年   302篇
  2001年   54篇
  2000年   28篇
  1999年   42篇
  1998年   47篇
  1997年   43篇
  1996年   32篇
  1995年   31篇
  1994年   18篇
  1993年   22篇
  1992年   15篇
  1991年   14篇
  1989年   12篇
  1988年   9篇
  1987年   8篇
  1985年   8篇
  1984年   11篇
  1982年   11篇
  1981年   10篇
  1980年   12篇
  1977年   21篇
  1976年   18篇
  1975年   12篇
  1973年   9篇
  1972年   12篇
  1969年   10篇
  1968年   13篇
  1967年   7篇
  1966年   11篇
排序方式: 共有6713条查询结果,搜索用时 15 毫秒
101.
Insight into the aberrant expression of microRNAs (miRNAs) and the genes that they regulate during the progression of cancer in general and prostate cancer (PCa) in particular is one of the most important issues in current molecular biomedicine and allows for the discovery of therapeutic or diagnostic miRNA targets. The present study aimed to analyze the available data regarding the direct or indirect effects of miRNAs on the expression of the mRNAs involved in carcinogenesis and to enable updating and optimizing the selection of the corresponding targets. The present review focuses on the data related to the genes with miRNA‐dependent expression during the development of PCa. The data used in this review have been extracted from research papers and the databases STRING, PANTHER and TargetScan, with a special focus on the genes directly associated with cell transformation and the maintenance of the transformed genotype, as well as tumor invasion and spread. The search for miRNA markers of PCa and therapeutically active molecules should rely on bioinformatics resources, such as data from recent experimental studies, as well as meta‐analysis and cross‐analysis of the data on the state of the tumor, patient status, histological/immunohistological data and data on mRNA–miRNA coexpression.  相似文献   
102.
Probiotics and Antimicrobial Proteins - The study aims at elucidating the effect of bacilli probiotic preparations on the physiology of laying hens and roosters. Probiotic formulations were...  相似文献   
103.
104.
DNA polymerase mu (Polmu) is a newly discovered member of the polymerase X family with unknown cellular function. The understanding of Polmu function should be facilitated by an understanding of its biochemical activities. By using purified human Polmu for biochemical analyses, we discovered the lesion bypass activities of this polymerase in response to several types of DNA damage. When it encountered a template 8-oxoguanine, abasic site, or 1,N(6)-ethenoadenine, purified human Polmu efficiently bypassed the lesion. Even bulky DNA adducts such as N-2-acetylaminofluorene-adducted guanine, (+)- and (-)-trans-anti-benzo[a]pyrene-N(2)-dG were unable to block the polymerase activity of human Polmu. Bypass of these simple base damage and bulky adducts was predominantly achieved by human Polmu through a deletion mechanism. The Polmu specificity of nucleotide incorporation indicates that the deletion resulted from primer realignment before translesion synthesis. Purified human Polmu also effectively bypassed a template cis-syn TT dimer. However, this bypass was achieved in a mainly error-free manner with AA incorporation opposite the TT dimer. These results provide new insights into the biochemistry of human Polmu and show that efficient translesion synthesis activity is not strictly confined to the Y family polymerases.  相似文献   
105.
Plant and Soil - Clear-cut logging currently is a key factor transforming forest communities in many boreal regions. The dynamics of biogeochemical processes taking place in clear-cuts makes them a...  相似文献   
106.
An expanding capillary network is critical for several pathologic conditions. In cancer, the decrease of antiangiogenic thrombospondin-1 (TSP1) often enables an angiogenic switch, which can be reversed with exogenous TSP1 or its peptide derivative ABT510. TSP1 acts by inducing endothelial cell apoptosis via signaling cascade initiated at CD36, a TSP1 antiangiogenic receptor. Here, we show that the ligands of nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma), 15-deoxy-delta(12,14)-prostaglandin J2, troglitazone, and rosiglitazone increased PPARgamma and CD36 expression in endothelial cells and improved the efficacy of TSP1 and ABT510 in a CD36-dependent manner. The ABT510 and PPARgamma ligands cooperatively blocked angiogenic endothelial functions in vitro and neovascularization in vivo. In tumor xenografts, 15-deoxy-delta(12,14)-prostaglandin J2 and troglitazone synergistically improved antiangiogenic and antitumor effects of ABT510. Our data provide one mechanism for the in vivo angioinhibitory effect of PPARgamma ligands and show fine-tuning of the antiangiogenic efficacy via targeted up-regulation of the endothelial receptor.  相似文献   
107.
Natural attenuation can reduce contamination of tributyltin (TBT), but persistence of the xenobiotic can cause long-term issues in the environment. Biostimulation is used to accelerate biodegradation. This study investigated the ability of individual organic nutrients and growth factors to enhance TBT biodegradation by sediment microorganisms (SED) and Enterobacter cloacae strain TISTR1971 (B3). The supplements that produced high biomass yield were selected for degradation enhancement. For TBT degradation at initial concentration of 0.1 mg/l, negative or limited degradation was observed in some selected supplements indicating that increasing the biomass did not necessarily promote degradation. Consequently, the addition of nutrients was expected to increase both dioxygenase activity and the degrader population. At different concentrations of supplements, a mixture of succinate/glycerol showed the highest removal for SED which reduced TBT by 77%, 75%, and 68% for 0.1×, 1×, and 10× supplement concentration, respectively. For B3, the addition of succinate showed degradation of 49% (0.1×), 75% (1×), and 77% (10×). Most nutrients and amino acids had an inhibitory effect at 1× or 10× levels. Excess amount of the nutrients added can inhibit the initial degradation of TBT. Therefore, TBT biostimulation requires supplements that increase the capability of TBT degraders at an appropriate amount.  相似文献   
108.
A systematic study of transformation reactions of Actinomycetes with respect to the progesterone molecule was undertaken. The results obtained, i.e. the types of transformation reactions in different actinomycete species, were evaluated from the point of view of taxonomy. The actinomycetes tested were divided according to the transformation types into three groups: (1) a group of species transforming progesterone in the 16α-position; (2) a group of species transforming progesterone in the β-position; (3) a group of species in which no capacity to transform progesterone into another steroid derivative was established. From the point of view of Actinomycete classification the transformation reactions on the steroid molecule fulfil all the requirements of taxonomic features of Actinomycetes. They appear to be specific properties, independent of strictly cultivation conditions and common to all the strains of individual actinomycete species tested.  相似文献   
109.

Purpose

This article aims to analyze the role that third-party product sustainability certifications play in supply chain sustainability governance and hence the impact that they may have on facilitating corporate life cycle management (LCM). Particular emphasis is given to exploring the extent to which such schemes allow firms to outsource the work of communication, motivation, enablement, and control of sustainability-related information and performance upstream in the supply chain.

Methods

The research design is based on a comparative case study methodology. The corporate practices of sourcing the sustainability certified products in the food retailing and textile sectors are compared, to explain when third-party product sustainability certification reduces the corporate need to engage in collaborative relationships with suppliers, thereby reducing efforts associated with implementation of corporate life cycle management.

Results and discussion

In our study, we found evidence that affirms the role of third-party product sustainability certification in reducing corporate necessity to actively engage with coordination of sustainability issues upstream in the supply chain. However, we also identified a range of factors—the intention of the buying company, the supply chain context, and the design of the certification scheme—that influence the extent, to which third-party product sustainability certification replaces the corporate need for additional work to facilitate supplier compliance. Some of these factors, e.g., the design of the certification scheme, are new and have been underexplored in the supply chain management and value chain governance literature yet.

Conclusions

Our findings suggest that corporate LCM practitioners should consider third-party sustainability certification as an instrument for the transfer of significant life cycle information along the supply chain and as a tool to facilitate corporate life cycle management. The extent to which third-party product sustainability certification would be able to facilitate corporate life cycle management depends not only on whether certification requirements are based on the LCA studies but also on the market scope of the certification schemes, the scope of the certification requirements, and the architecture of the certification management services. If these parameters are aligned with corporate ambitions and allow buyers to fully outsource the work associated with communication, motivation, enablement, and control of sustainability-related information and supplier performance, the life cycle management can be exercised by companies by simply choosing to procure sustainability certified products.
  相似文献   
110.
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