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   7414篇
  免费   485篇
  国内免费   1篇
  7900篇
  2023年   34篇
  2022年   84篇
  2021年   150篇
  2020年   95篇
  2019年   126篇
  2018年   192篇
  2017年   160篇
  2016年   236篇
  2015年   375篇
  2014年   443篇
  2013年   569篇
  2012年   643篇
  2011年   645篇
  2010年   373篇
  2009年   391篇
  2008年   495篇
  2007年   448篇
  2006年   457篇
  2005年   362篇
  2004年   393篇
  2003年   323篇
  2002年   326篇
  2001年   52篇
  2000年   45篇
  1999年   52篇
  1998年   59篇
  1997年   44篇
  1996年   40篇
  1995年   32篇
  1994年   23篇
  1993年   24篇
  1992年   27篇
  1991年   23篇
  1990年   24篇
  1989年   15篇
  1988年   18篇
  1987年   8篇
  1986年   7篇
  1985年   17篇
  1984年   13篇
  1983年   7篇
  1982年   12篇
  1981年   7篇
  1979年   4篇
  1978年   3篇
  1977年   4篇
  1975年   3篇
  1974年   3篇
  1973年   2篇
  1967年   2篇
排序方式: 共有7900条查询结果,搜索用时 14 毫秒
51.
A psychrotolerant marine bacterial strain, designated JUB59(T), was isolated from Antarctic surface seawater and classified as a new species of the genus Bizionia. Here, we present the first draft genome sequence for this genus, which suggests interesting features such as UV resistance, hydrolytic exoenzymes, and nitrogen metabolism.  相似文献   
52.
The soil fungus Trichoderma harzianum is a mycoparasitic fungus known for its use as a biocontrol agent of phytopathogenic fungi. Among other factors, Trichoderma produces a series of antibiotics and fungal cell wall-degrading enzymes. These enzymes are believed to play an important role in mycoparasitism. Among the hydrolytic enzymes, we have identified a basic proteinase (Prb1) which is induced by either autoclaved mycelia, fungal cell wall preparation or chitin; however, the induction does not occur in the presence of glucose. The proteinase was purified and biochemically characterized as a serine proteinase of 31 kDa and pl 9.2. Based on the sequence of three internal peptides, synthetic oligonudeotide probes were designed. These probes allowed subsequent isolation of a cDNA and its corresponding genomic clone. The deduced amino acid sequence indicates that the proteinase is synthesized as a pre-proenzyme and allows its classification as a serine proteinase. Northen analysis shows that the induction of this enzyme is due to an increase in the corresponding mRNA level.  相似文献   
53.
54.
This study seeks to explore whether neuroticism, agreeableness, and conscientiousness moderate the influence of relationship conflict experienced in groups on changes in group members'' evaluative cognitions related to teamwork quality (teamwork-related mental models). Data from 216 students, nested in 48 groups were analyzed using a multilevel modeling approach. Our results show that the experience of relationship conflict leads to a negative shift from the pre-task to the post-task teamwork-related mental models. Moreover, the results indicate that conscientiousness buffered the negative association between relationship conflict and the change in teamwork-related mental models. Our results did not support the hypothesized moderating effect of agreeableness and show that the detrimental effect of relationship conflict on the shift in teamwork-related mental models is accentuated for group members scoring low rather than high on neuroticism. These findings open new research venues for exploring the association between personality, coping styles and change in teamwork-related mental models.  相似文献   
55.
Cells derived from the amniotic foetal membrane of human term placenta have drawn particular attention mainly for their plasticity and immunological properties, which render them interesting for stem-cell research and cell-based therapeutic applications. In particular, we have previously demonstrated that amniotic mesenchymal tissue cells (AMTC) inhibit lymphocyte proliferation in vitro and suppress the generation and maturation of monocyte-derived dendritic cells. Here, we show that AMTC also significantly reduce the proliferation of cancer cell lines of haematopoietic and non-haematopoietic origin, in both cell-cell contact and transwell co-cultures, therefore suggesting the involvement of yet-unknown inhibitory soluble factor(s) in this 'cell growth restraint'. Importantly, we provide evidence that the anti-proliferative effect of AMTC is associated with induction of cell cycle arrest in G0/G1 phase. Gene expression analyses demonstrate that AMTC can down-regulate cancer cells' mRNA expression of genes associated with cell cycle progression, such as cyclins (cyclin D2, cyclin E1, cyclin H) and cyclin-dependent kinase (CDK4, CDK6 and CDK2), whilst they up-regulate cell cycle negative regulator such as p15 and p21, consistent with a block in G0/G1 phase with no progression to S phase. Taken together, these findings warrant further studies to investigate the applicability of these cells for controlling cancer cell proliferation in vivo.  相似文献   
56.
We describe structure-based optimization of a series of novel 2,4-diaminopyrimidine MK2 inhibitors. Co-crystal structures (see accompanying Letter) demonstrated a unique inhibitor binding mode. Resulting inhibitors had IC50 values as low as 19 nM and moderate selectivity against a kinase panel. Compounds 15, 31a, and 31b inhibit TNFα production in peripheral human monocytes.  相似文献   
57.
Dyes belonging to the mono-, di-, tri- and poly-azo as well as anthraquinonic and mono-azo Cr-complexed classes, chosen among the most utilized in textile applications, were employed for a comparative enzymatic decolorization study using the extracellular crude culture extracts from the white rot fungus Funalia (Trametes) trogii grown on different culture media and activators able to trigger different levels of expression of oxidizing enzymes: laccase and cellobiose dehydrogenase. Laccase containing extracts were capable to decolorize some dyes from all the different classes analyzed, whereas the recalcitrant dyes were subjected to the combined action of laccase and the chemical mediator HBT, or laccase plus cellobiose dehydrogenase. Correlations among the decolorization degree of the various dyes and their electronic and structural diversities were rationalized and discussed. The utilization of cellobiose dehydrogenase in support to the activity of laccase for the decolorization of azo textile dyes resulted in substantial increases in decolorization for all the refractory dyes proving to be a valid alternative to more expensive and less environmentally friendly chemical treatments of textile dyes wastes.  相似文献   
58.

Purpose

Organizational life cycle assessment (O-LCA) is still a rather young proposal, but moving towards becoming more broadly accepted as a scientifically mature and practical method. The UNEP/SETAC flagship project “LCA of organizations” concluded its “road-testing” phase and is glad to announce the publication of the final report “Road testing organizational life cycle assessment around the world: applications, experiences and lessons learned.” The full report can be accessed at http://www.lifecycleinitiative.org/download/6060. This article shortly summarizes the flagship project phases and main outcomes, particularly the report recently launched, and pinpoints future actions.

Methods

In 2015, the “Guidance on Organizational Life Cycle Assessment” was published. During the following 2 years, the flagship project accompanied 12 organizations in the road testing of that O-LCA Guidance. They represent four world regions, different sectors and sizes. The road testers’ case studies and their feedback are the basis of the Road-testing Report.

Results and discussion

The Road-testing Report aims to complement the O-LCA Guidance through the road testers’ experience, thus delivering advice for future practitioners and inspiration to method developers. It includes executive summaries of the O-LCA road testers’ case studies and the main results of a comprehensive survey through which the road testers share their experience, feedback, and lessons learned. The road testing confirmed the application potential of the O-LCA method and the positive outcomes of the road testing have shown that no immediate updates to the O-LCA Guidance are needed, but some priority actions were identified in order to further ease the application of O-LCA.

Conclusions

Three main tasks for the coming years are identified by the authors: firstly, the challenges highlighted during the road testing should be addressed in the future by the LCA community; specific methodological difficulties of certain kinds of organizations, like the service sector, should be targeted; and finally, the potential revealed by the organizational perspective can be deployed in adjacent LCA fields. The flagship project team hopes that this second publication, together with the great acceptance of the O-LCA Guidance and the contribution of third parties, will pave the way to make O-LCA a mainstream tool.
  相似文献   
59.
TAR DNA ‐binding protein 43 (TDP ‐43) is an RNA ‐binding protein and a major component of protein aggregates found in amyotrophic lateral sclerosis and several other neurodegenerative diseases. TDP ‐43 exists as a full‐length protein and as two shorter forms of 25 and 35 kD a. Full‐length mutant TDP ‐43s found in amyotrophic lateral sclerosis patients re‐localize from the nucleus to the cytoplasm and in part to mitochondria, where they exert a toxic role associated with neurodegeneration. However, induction of mitochondrial damage by TDP ‐43 fragments is yet to be clarified. In this work, we show that the mitochondrial 35 kD a truncated form of TDP ‐43 is restricted to the intermembrane space, while the full‐length forms also localize in the mitochondrial matrix in cultured neuronal NSC ‐34 cells. Interestingly, the full‐length forms clearly affect mitochondrial metabolism and morphology, possibly via their ability to inhibit the expression of Complex I subunits encoded by the mitochondrial‐transcribed mRNA s, while the 35 kD a form does not. In the light of the known differential contribution of the full‐length and short isoforms to generate toxic aggregates, we propose that the presence of full‐length TDP ‐43s in the matrix is a primary cause of mitochondrial damage. This in turn may cause oxidative stress inducing toxic oligomers formation, in which short TDP ‐43 forms play a major role.

  相似文献   
60.
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