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   404篇
  免费   47篇
  2023年   2篇
  2022年   2篇
  2021年   12篇
  2020年   15篇
  2019年   10篇
  2018年   7篇
  2017年   7篇
  2016年   14篇
  2015年   27篇
  2014年   20篇
  2013年   28篇
  2012年   31篇
  2011年   36篇
  2010年   18篇
  2009年   19篇
  2008年   30篇
  2007年   31篇
  2006年   23篇
  2005年   20篇
  2004年   13篇
  2003年   9篇
  2002年   12篇
  2001年   3篇
  2000年   4篇
  1999年   8篇
  1998年   4篇
  1997年   3篇
  1996年   6篇
  1995年   1篇
  1994年   1篇
  1993年   2篇
  1992年   4篇
  1991年   4篇
  1990年   2篇
  1989年   2篇
  1988年   2篇
  1986年   4篇
  1985年   2篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1979年   1篇
  1978年   1篇
  1973年   1篇
  1971年   2篇
  1970年   1篇
  1968年   1篇
  1959年   1篇
  1931年   1篇
排序方式: 共有451条查询结果,搜索用时 15 毫秒
51.
52.
53.
As neoliberalism continues to influence environmental governance, it affects notions about the appropriate level of community involvement in resource management. Under more recent iterations, hybrid forms of governance are emphasized, including government–civil society partnerships and approaches geared towards harnessing the strengths of local communities. Here we explore the characteristics of different resource management rights, strategies, and tools through which communities can find political space to assert their own agendas within a neoliberalized policy environment. We examine the successful use of some of these approaches by communities during the initial development of community forests policy and practice in British Columbia, Canada. While we confirm the complex, contingent and case-specific nature of opportunities for comanagement created through neoliberal policy elements, we suggest that space does exist for community forest bodies to assert local values, goals and strategies, demonstrating the creativity, ingenuity and determination of communities to attain a real voice in management.
Evelyn PinkertonEmail:
  相似文献   
54.

   

Intracellular vesicle traffic that enables delivery of proteins between the endoplasmic reticulum, Golgi and various endosomal subcompartments is one of the hallmarks of the eukaryotic cell. Its evolutionary history is not well understood but the process itself and the core vesicle traffic machinery are believed to be ancient. We show here that the 4-vinyl reductase (V4R) protein domain present in bacteria and archaea is homologous to the Bet3 subunit of the TRAPP1 vesicle-tethering complex that is conserved in all eukaryotes. This suggests, for the first time, a prokaryotic origin for one of the key eukaryotic trafficking proteins.  相似文献   
55.
Clustered regularly interspaced short palindromic repeats (CRISPRs) together with the associated CAS proteins protect microbial cells from invasion by foreign genetic elements using presently unknown molecular mechanisms. All CRISPR systems contain proteins of the CAS2 family, suggesting that these uncharacterized proteins play a central role in this process. Here we show that the CAS2 proteins represent a novel family of endoribonucleases. Six purified CAS2 proteins from diverse organisms cleaved single-stranded RNAs preferentially within U-rich regions. A representative CAS2 enzyme, SSO1404 from Sulfolobus solfataricus, cleaved the phosphodiester linkage on the 3'-side and generated 5'-phosphate- and 3'-hydroxyl-terminated oligonucleotides. The crystal structure of SSO1404 was solved at 1.6A resolution revealing the first ribonuclease with a ferredoxin-like fold. Mutagenesis of SSO1404 identified six residues (Tyr-9, Asp-10, Arg-17, Arg-19, Arg-31, and Phe-37) that are important for enzymatic activity and suggested that Asp-10 might be the principal catalytic residue. Thus, CAS2 proteins are sequence-specific endoribonucleases, and we propose that their role in the CRISPR-mediated anti-phage defense might involve degradation of phage or cellular mRNAs.  相似文献   
56.
We characterized recombinant d-hydantoin hydrolase (DHHase) and N-carbamoyl-d-amino acid amidohydrolase (DCHase) from Flavobacterium sp. AJ11199 and Pasteurella sp. AJ11221. The DHHases from these two strains showed a wide range of hydrolytic activity for various 5-monosubstituted d-hydantoin compounds, including a very high level activity for d-hydantoin compounds corresponding to d-aromatic amino acids such as d-tryptophan d-phenylalanine and d-tyrosine. The DCHases, in turn, were capable of catalyzing the hydrolysis of various N-carbamoyl-d-amino acids (NCD-A.A.) corresponding to d-aliphatic and d-aromatic amino acids. The combination of these enzymes was found to be applicable for the production of various d-amino acids.  相似文献   
57.
Three genes respectively encoding d-specific hydantoinase (DHHase), N-carbamoyl-d-amino acid amidohydrolase (DCHase) and hydantoin racemase (HRase) were co-expressed in E. coli in a system designed for the efficient enzymatic production of d-amino acids via a combination of hydantoin hydrolysis and hydantoin racemization. With the use of whole cells, the d-forms of eight amino acids – d-phenylalanine, d-tyrosine, d-tryptophan, O-benzyl-d-serine, d-valine, d-norvaline, d-leucine and d-norleucine – were efficiently converted from the corresponding dl-5-monosubtituted hydantoin compounds.  相似文献   
58.
Ott V  Koch J  Späte K  Morbach S  Krämer R 《Biochemistry》2008,47(46):12208-12218
The glycine betaine carrier BetP from Corynebacterium glutamicum responds to changes in external osmolality by regulation of its transport activity, and the C-terminal domain was previously identified to be involved in this process. Here we investigate the structural requirements of the C-terminal domain for osmoregulation as well as interacting domains that are relevant for intramolecular signal transduction in response to osmotic stress. For this purpose, we applied a proline scanning approach and amino acid replacements other than proline in selected positions. To analyze the impact of the surrounding membrane, BetP mutants were studied in both C. glutamicum and Escherichia coli, which strongly differ in their phospholipid composition. A region of approximately 25 amino acid residues within the C-terminal domain with a high propensity for alpha-helical structure was found to be essential in terms of its conformational properties for osmodependent regulation. The size of this region was larger in E. coli membranes than in the highly negatively charged C. glutamicum membranes. As a novel aspect of BetP regulation, interaction of the C-terminal domain with one of the cytoplasmic loops as well as with the N-terminal domain was shown to be involved in osmosensing and/or osmoregulation. These results support a functional model of BetP activation that involves the C-terminal domain shifting from interaction with the membrane to interaction with intramolecular domains in response to osmotic stress.  相似文献   
59.
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