全文获取类型
收费全文 | 38128篇 |
免费 | 66篇 |
国内免费 | 100篇 |
专业分类
系统科学 | 175篇 |
丛书文集 | 757篇 |
教育与普及 | 102篇 |
理论与方法论 | 221篇 |
现状及发展 | 16552篇 |
研究方法 | 1570篇 |
综合类 | 18406篇 |
自然研究 | 511篇 |
出版年
2013年 | 200篇 |
2012年 | 502篇 |
2011年 | 1050篇 |
2010年 | 211篇 |
2008年 | 641篇 |
2007年 | 669篇 |
2006年 | 697篇 |
2005年 | 708篇 |
2004年 | 653篇 |
2003年 | 683篇 |
2002年 | 691篇 |
2001年 | 1193篇 |
2000年 | 1113篇 |
1999年 | 755篇 |
1994年 | 341篇 |
1992年 | 720篇 |
1991年 | 572篇 |
1990年 | 624篇 |
1989年 | 598篇 |
1988年 | 584篇 |
1987年 | 621篇 |
1986年 | 629篇 |
1985年 | 775篇 |
1984年 | 626篇 |
1983年 | 511篇 |
1982年 | 445篇 |
1981年 | 450篇 |
1980年 | 551篇 |
1979年 | 1225篇 |
1978年 | 1046篇 |
1977年 | 993篇 |
1976年 | 720篇 |
1975年 | 771篇 |
1974年 | 1070篇 |
1973年 | 914篇 |
1972年 | 966篇 |
1971年 | 1195篇 |
1970年 | 1538篇 |
1969年 | 1169篇 |
1968年 | 1118篇 |
1967年 | 1135篇 |
1966年 | 983篇 |
1965年 | 721篇 |
1959年 | 417篇 |
1958年 | 622篇 |
1957年 | 500篇 |
1956年 | 412篇 |
1955年 | 355篇 |
1954年 | 403篇 |
1948年 | 236篇 |
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
401.
Community indicators have been a frequent focus of the scholarly literature. There has been little exploration, however, in relation to rural communities, especially in developing countries. This reflects the special challenges associated with the complexity of rural systems, and the difficulties involved in developing appropriate and systemic indicators for rural communities. Identifying indicators that help the community to monitor progress towards sustainable outcomes requires a framework that is both practical and holistic. This paper introduces a participatory systemic framework for identifying community indicators, which respects the principles of complexity and honours the sense of ownership present in the communities. This framework is an iterative, sharing, co-learning engagement process that extends from creating a shared vision and extracting its core messages, to identifying indicators of progress and determining what actions to try. Importantly, this framework enables us to rank the indicators identified by communities with reference to ‘leverage points’, the best places to intervene in the social-environmental system for transformational change. This framework provides a potential pathway for sustainable rural development and perhaps also for organisations and urban communities. 相似文献
402.
403.
404.
405.
406.
407.
408.
Matthew D. Hitchings Philip Townsend Ehmke Pohl Paul D. Facey D. Hugh Jones Paul J. Dyson Ricardo Del Sol 《Cellular and molecular life sciences : CMLS》2014,71(24):4911-4926
Dps proteins are members of an extensive family of proteins that oxidise and deposit iron in the form of ferric oxide, and are also able to bind DNA. Ferroxidation centres are formed at the interface of anti-parallel dimers, which further assemble into dodecameric nanocages with a hollow core where ferric oxide is deposited. Streptomyces coelicolor encodes three Dps-like proteins (DpsA, B and C). Despite sharing the conserved four-helix bundle organisation observed in members of the Dps family, they display significant differences in the length of terminal extensions, or tails. DpsA possess both N- and C-terminal tails of different lengths, and their removal affects quaternary structure assembly to varying degrees. DpsC quaternary structure, on the other hand, is heavily dependent on its N-terminal tail as its removal abolishes correct protein folding. Analysis of the crystal structure of dodecamers from both proteins revealed remarkable differences in the position of tails and interface surface area; and provides insight to explain the differences in biochemical behaviour observed while comparing DpsA and DpsC. 相似文献
409.
Molla R. Islam Yongfeng Gao Xue Li Qiang Matthew Zhang Menglian Wei Michael J. Serpe 《科学通报(英文版)》2014,59(32):4237-4255
Stimuli-responsive polymers have the extraor- dinary ability to change their physical and/or chemical state after they "detect" a change in their environment; their response depends dramatically on their chemical compo- sition. This property has been used for a plethora of applications; this review highlights their utility for human health. Specifically, this review will highlight efforts in the areas of sensing and biosensing, antimicrobial/antifouling coatings, tissue engineering and regenerative medicine, and drug delivery. Specific examples are given in each of these areas, with some focus on our work engineering poly(N- isopropylacrylamide)-based microgels and other respon- sive systems. 相似文献
410.
Shachi P. Patel Suzanne J. Randle Sarah Gibbs Anne Cooke Heike Laman 《Cellular and molecular life sciences : CMLS》2017,74(8):1553-1566
G1 phase cell cycle proteins, such as cyclin-dependent kinase 6 (Cdk6) and its activating partners, the D-type cyclins, are important regulators of T-cell development and function. An F-box protein, called F-box only protein 7 (Fbxo7), acts as a cell cycle regulator by enhancing cyclin D-Cdk6 complex formation and stabilising levels of p27, a cyclin-dependent kinase inhibitor. We generated a murine model of reduced Fbxo7 expression to test its physiological role in multiple tissues and found that these mice displayed a pronounced thymic hypoplasia. Further analysis revealed that Fbxo7 differentially affected proliferation and apoptosis of thymocytes at various stages of differentiation in the thymus and also mature T-cell function and proliferation in the periphery. Paradoxically, Fbxo7-deficient immature thymocytes failed to undergo expansion in the thymus due to a lack of Cdk6 activity, while mature T cells showed enhanced proliferative capacity upon T-cell receptor engagement due to reduced p27 levels. Our studies reveal differential cell cycle regulation by Fbxo7 at different stages in T-cell development. 相似文献