全文获取类型
收费全文 | 458357篇 |
免费 | 51657篇 |
国内免费 | 523篇 |
出版年
2018年 | 4537篇 |
2017年 | 4320篇 |
2016年 | 6204篇 |
2015年 | 8587篇 |
2014年 | 10144篇 |
2013年 | 13530篇 |
2012年 | 15706篇 |
2011年 | 15679篇 |
2010年 | 10410篇 |
2009年 | 9548篇 |
2008年 | 13385篇 |
2007年 | 13682篇 |
2006年 | 12698篇 |
2005年 | 12109篇 |
2004年 | 11940篇 |
2003年 | 11457篇 |
2002年 | 11103篇 |
2001年 | 23205篇 |
2000年 | 23142篇 |
1999年 | 18238篇 |
1998年 | 5783篇 |
1997年 | 5963篇 |
1996年 | 5509篇 |
1995年 | 5190篇 |
1994年 | 5107篇 |
1993年 | 4913篇 |
1992年 | 14240篇 |
1991年 | 13615篇 |
1990年 | 12962篇 |
1989年 | 12738篇 |
1988年 | 11781篇 |
1987年 | 10896篇 |
1986年 | 9835篇 |
1985年 | 9826篇 |
1984年 | 7926篇 |
1983年 | 6953篇 |
1982年 | 5352篇 |
1981年 | 4631篇 |
1980年 | 4384篇 |
1979年 | 7740篇 |
1978年 | 5814篇 |
1977年 | 5412篇 |
1976年 | 4938篇 |
1975年 | 5383篇 |
1974年 | 5774篇 |
1973年 | 5834篇 |
1972年 | 5344篇 |
1971年 | 4977篇 |
1970年 | 4222篇 |
1969年 | 4067篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
21.
F F Dias M K Shaikh Y B Bhatt D C Modi V R Subramanyam 《The Journal of applied bacteriology》1986,60(4):271-275
Mutants of Bacillus amyloliquefaciens resistant to at least 10 micrograms/ml of tunicamycin were isolated and shown to be pleiotropic. The mutants were more resistant to streptomycin, chloramphenicol, kanamycin and neomycin than was the parent strain but less resistant to penicillin G and tetracycline. They were more autolytic, presumably due to an altered cell wall. The mutants produced reduced levels of amylase, penicillinase and both metal and serine protease besides having an enhanced sporulation frequency and being more motile. 相似文献
22.
23.
All plant cells are provided with the necessary rigidity to withstand the turgor by an exterior cell wall. This wall is composed
of long crystalline cellulose microfibrils embedded in a matrix of other polysaccharides. The cellulose microfibrils are deposited
by mobile membrane bound protein complexes in remarkably ordered lamellar textures. The mechanism by which these ordered textures
arise, however, is still under debate. The geometrical model for cell wall deposition proposed by Emons and Mulder (Proc.
Natl. Acad. Sci. 95, 7215–7219, 1998) provides a detailed approach to the case of cell wall deposition in non-growing cells, where there is no evidence for the
direct influence of other cellular components such as microtubules. The model successfully reproduces even the so-called helicoidal
wall; the most intricate texture observed. However, a number of simplifying assumptions were made in the original calculations.
The present work addresses the issue of the robustness of the model to relaxation of these assumptions, by considering whether
the helicoidal solutions survive when three aspects of the model are varied. These are: (i) the shape of the insertion domain,
(ii) the distribution of lifetimes of individual CSCs, and (iii) fluctuations and overcrowding. Although details of the solutions
do change, we find that in all cases the overall character of the helicoidal solutions is preserved. 相似文献
24.
Cristian A. Acevedo Elizabeth Y. Sanchez Juan G. Reyes Manuel E. Young 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(3-4):449-455
It is known that skin releases volatile organic compounds to the environment, and also that its emission pattern changes with aging of the skin. It could be considered, that these compounds are intermediaries in cell metabolism, since many intermediaries of metabolic pathways have a volatile potential. In this work, a simple and non-destructive method consisting of SPME sampling and GC/MS analysis was developed to identify volatile organic emanations from cell cultures. This technique, applied to skin cells culture, indicates that the cells or cell metabolism produce several skin emissions. Chemometric analysis was performed in order to explore the relationship between a volatile profile and the senescence of cell cultures. Volatile profiles were different for cell cultures in different degrees of senescence, indicating that volatile compound patterns could be used to provide information about the age of skin cells. 相似文献
25.
26.
27.
28.
29.
30.
T. B. Lapirova V. R. Mikryakova A. S. Mavrin G. A. Yinogradova 《Journal of Evolutionary Biochemistry and Physiology》2000,36(1):47-51
The paper presents data on a change in lysozyme content in tissues of spleen, liver and heart in fry of the Lena River sturgeon
exposed to the presence of sublethal concentrations of Hg2+, Cd2+, and Cu2+ under conditions of chronic experiment. It has been shown that the lysozyme content in fish tissues varies and has a phasic
character. The amplitude of fluctuations of this parameter depends on the moment of sampling, nature of the toxicant, and
structural-functional organization of the studied organs. 相似文献