全文获取类型
收费全文 | 294100篇 |
免费 | 14615篇 |
国内免费 | 864篇 |
出版年
2018年 | 15281篇 |
2017年 | 14284篇 |
2016年 | 10774篇 |
2015年 | 2805篇 |
2014年 | 3213篇 |
2013年 | 4488篇 |
2012年 | 9786篇 |
2011年 | 20312篇 |
2010年 | 17704篇 |
2009年 | 13582篇 |
2008年 | 16675篇 |
2007年 | 19162篇 |
2006年 | 5125篇 |
2005年 | 5817篇 |
2004年 | 5948篇 |
2003年 | 6172篇 |
2002年 | 5859篇 |
2001年 | 8695篇 |
2000年 | 8862篇 |
1999年 | 6334篇 |
1998年 | 1996篇 |
1997年 | 2056篇 |
1996年 | 1824篇 |
1993年 | 1709篇 |
1992年 | 5218篇 |
1991年 | 5417篇 |
1990年 | 5147篇 |
1989年 | 5133篇 |
1988年 | 4749篇 |
1987年 | 4503篇 |
1986年 | 4076篇 |
1985年 | 4235篇 |
1984年 | 3421篇 |
1983年 | 2937篇 |
1982年 | 1943篇 |
1981年 | 1728篇 |
1980年 | 1719篇 |
1979年 | 3211篇 |
1978年 | 2545篇 |
1977年 | 2278篇 |
1976年 | 2081篇 |
1975年 | 2558篇 |
1974年 | 2884篇 |
1973年 | 2804篇 |
1972年 | 3339篇 |
1971年 | 3045篇 |
1970年 | 2124篇 |
1969年 | 2022篇 |
1968年 | 1906篇 |
1967年 | 1743篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
V. V. Smirnov L. N. Churkina A. N. Kravets V. I. Perepnikhatka 《Applied Biochemistry and Microbiology》2000,36(3):262-265
Various plasmids carrying transposon Tn5 were used to generate insertion mutants synthesizing batumin, a unique antibiotic
with a selective antistaphylococcal effect. One of the plasmids used provided a sufficient yield of the clones in question.
An analysis of over 7000 clones allowed us to select the mutant clones with increased and decreased levels of batumin synthesis
and the mutants that lost the ability to synthesize this antibiotic. 相似文献
232.
233.
The probability that protected areas will deliver their potential for maintaining or enhancing biodiversity is likely to be
maximised if they are appropriately and effectively managed. As a result, governments and conservation agencies are devoting
much attention to the management of protected areas. In the U.K., the demand for performance accountability has resulted in
Public Service Agreements (PSA) that set out targets for government departments to deliver results in return for investments
being made. One such target for England is to ensure that all nationally important wildlife sites are in favourable condition
by 2010. Here, we tested the hypothesis, of potential strategic importance, that the ecological condition of these sites is
predictable from relationships with a range of physical, environmental and demographic variables. We used binary logistic
regression to investigate these relationships, using the results of English Nature’s 1997–2003 condition assessment exercise.
Generally, sites in unfavourable condition tend to be larger in area, located at higher elevations, but with higher human
population density and are more spatially isolated from units of the same habitat. However, despite the range of different
parameters included in our models, the extent to which the condition of any given site could be predicted was low. Our results
have implications for the delivery of PSA targets, funding allocation, and the location of new protected areas. 相似文献
234.
P S Simavorian D A Gevorkian I L Saakian A B Iordanian 《Biulleten' eksperimental'no? biologii i meditsiny》1987,103(3):310-312
It has been experimentally and clinically established that the determination of leucine-aminotransferase activity in the blood serum and abdominal exudate may serve as a marker for the early determination of pancreonecrosis and edematous (serous) pancreatitis. 相似文献
235.
236.
G T Sukhikh I V Bogdashin L V Van'ko 《Biulleten' eksperimental'no? biologii i meditsiny》1985,99(4):399-401
It has been shown that at late periods after immobilization stress there is an essential reduction in the cytostatic activity of CBA mice splenocytes detected by inhibition of mastocytoma P 815 cell proliferation in the test with 3H-uridine incorporation. The cytostatic activity returns to normal 5 to 14 days after stress. The changes in the cytolytic and cytostatic activity of mouse splenocytes following stress are correlated and a possible biological value of changes in the immunoassays for the host are discussed. 相似文献
237.
The processes of the cultivation of N. meningitidis, serogroups A, B and C, in a liquid synthetic culture medium have been studied. Strictly group-specific biomass has been obtained. The maximum productivity at all stages of the batch cultivation of N. meningitidis strains 125 and 133 in this medium does not differ from that at similar stages of cultivation in modified Cohen-Wheller semisynthetic medium. In the serotype antigen preparations obtained from N. meningitidis strain 125 grown in the above-mentioned liquid synthetic culture medium basic polypeptides with a molecular weight of 33000, 36000 and 41000 D have been detected. Their presence in N. meningitidis cells is linked with the growth phase of the population. 相似文献
238.
239.
240.
Daren Lee Seth Ruffins Queenie Ng Nikhil Sane Steve Anderson Arthur Toga 《BMC bioinformatics》2010,11(1):608