全文获取类型
收费全文 | 282842篇 |
免费 | 30877篇 |
国内免费 | 264篇 |
专业分类
313983篇 |
出版年
2018年 | 2422篇 |
2016年 | 3272篇 |
2015年 | 4627篇 |
2014年 | 5204篇 |
2013年 | 7803篇 |
2012年 | 8434篇 |
2011年 | 8677篇 |
2010年 | 5727篇 |
2009年 | 5263篇 |
2008年 | 7777篇 |
2007年 | 7884篇 |
2006年 | 7459篇 |
2005年 | 7220篇 |
2004年 | 7111篇 |
2003年 | 6849篇 |
2002年 | 6639篇 |
2001年 | 11811篇 |
2000年 | 11833篇 |
1999年 | 9386篇 |
1998年 | 3471篇 |
1997年 | 3658篇 |
1996年 | 3551篇 |
1995年 | 3163篇 |
1994年 | 3141篇 |
1993年 | 3144篇 |
1992年 | 7906篇 |
1991年 | 7880篇 |
1990年 | 7543篇 |
1989年 | 7511篇 |
1988年 | 6878篇 |
1987年 | 6638篇 |
1986年 | 6054篇 |
1985年 | 6235篇 |
1984年 | 5181篇 |
1983年 | 4359篇 |
1982年 | 3415篇 |
1981年 | 3186篇 |
1980年 | 2982篇 |
1979年 | 4972篇 |
1978年 | 3847篇 |
1977年 | 3750篇 |
1976年 | 3451篇 |
1975年 | 3817篇 |
1974年 | 4206篇 |
1973年 | 4120篇 |
1972年 | 3684篇 |
1971年 | 3451篇 |
1970年 | 3104篇 |
1969年 | 3007篇 |
1968年 | 2763篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
Summary The ability of microorganisms to produce hydantoinase and L-N-carbamoylase could be established by an overlay assay. Enzyme producing strains form clear areas around their colonies caused by the cleavage of D,L-indolylmethylhydantoin. A second overlayer with a tryptophan-auxotroph yeast enables us to detect microorganisms which are able to produce L-tryptophan from D,L-indolylmethylhydantoin. 相似文献
182.
F L Golladay B H Liese 《Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)》1980,209(1174):173-180
Experimental projects have demonstrated the technical feasibility of systems of accessible, affordable health care. These projects have relied extensively on non-professional community health workers. However, large-scale implementation of these schemes will require new management procedures that are both responsive to rural health needs and congruent with national institutions. This paper identifies the need to establish institutional mechanisms to mobilize essential inputs, promote acceptance by beneficiaries, maintain quality standards, recruit and retain field staff, and achieve accountability for resources. It then outlines methods for developing these institutions. It stresses the need for both formal, bureaucratic organizations and informal organizations of clients. It also identifies the need to consider administrative and institutional resources in determining the appropriateness of a health care technology. 相似文献
183.
Chemotactic responses by motile bacteria 总被引:3,自引:0,他引:3
184.
185.
186.
187.
188.
189.
190.
P Kischel L Stevens V Montel F Picquet Y Mounier 《Journal of applied physiology》2001,90(5):1825-1832
We examined the changes in functional properties of triceps brachii skinned fibers from monkeys flown aboard the BION 11 satellite for 14 days and after ground-based arm immobilization. The composition of myosin heavy chain (MHC) isoforms allowed the identification of pure fibers containing type I (slow) or type IIa (fast) MHC isoforms or hybrid fibers coexpressing predominantly slow (hybrid slow; HS) or fast (hybrid fast) MHC isoforms. The ratio of HS fibers to the whole slow population was higher after flight (28%) than in the control population (7%), and the number of fast fibers was increased (up to 86% in flight vs. 12% in control). Diameters and maximal tensions of slow fibers were decreased after flight. The tension-pCa curves of slow and fast fibers were modified, with a decrease in pCa threshold and an increase in steepness. The proper effect of microgravity was distinguishable from that of immobilization, which induced less marked slow-to-fast transitions (only 59% of fast fibers) and changed the tension-pCa relationships. 相似文献