全文获取类型
收费全文 | 8548篇 |
免费 | 518篇 |
国内免费 | 3篇 |
出版年
2023年 | 62篇 |
2022年 | 77篇 |
2021年 | 136篇 |
2020年 | 93篇 |
2019年 | 109篇 |
2018年 | 301篇 |
2017年 | 244篇 |
2016年 | 326篇 |
2015年 | 327篇 |
2014年 | 430篇 |
2013年 | 637篇 |
2012年 | 658篇 |
2011年 | 662篇 |
2010年 | 409篇 |
2009年 | 294篇 |
2008年 | 280篇 |
2007年 | 277篇 |
2006年 | 276篇 |
2005年 | 184篇 |
2004年 | 183篇 |
2003年 | 162篇 |
2002年 | 133篇 |
2001年 | 95篇 |
2000年 | 146篇 |
1999年 | 147篇 |
1998年 | 92篇 |
1997年 | 70篇 |
1996年 | 78篇 |
1995年 | 76篇 |
1994年 | 67篇 |
1993年 | 56篇 |
1992年 | 92篇 |
1991年 | 95篇 |
1990年 | 55篇 |
1989年 | 59篇 |
1988年 | 64篇 |
1987年 | 57篇 |
1985年 | 79篇 |
1984年 | 69篇 |
1983年 | 77篇 |
1982年 | 75篇 |
1981年 | 73篇 |
1980年 | 66篇 |
1979年 | 66篇 |
1978年 | 57篇 |
1977年 | 64篇 |
1976年 | 65篇 |
1975年 | 66篇 |
1972年 | 52篇 |
1969年 | 54篇 |
排序方式: 共有9069条查询结果,搜索用时 281 毫秒
31.
Antibacterial, antifungal and antiprotozoal effects of nine mono- and bishydrazones of glycolaldehyde, glyoxal, methoxyacetaldehyde
and glutaraldehyde were studied using eight model organisms. It was found that bishydrazones are much more efficient antimicrobial
agents than monohydrazones in the case of all model microorganisms. 相似文献
32.
Mapping of the gene for anti-müllerian hormone to the short arm of human chromosome 19 总被引:3,自引:0,他引:3
O Cohen-Haguenauer J Y Picard M G Mattéi S Serero V C Nguyen M F de Tand D Guerrier M C Hors-Cayla N Josso J Frézal 《Cytogenetics and cell genetics》1987,44(1):2-6
The gene coding for human anti-Müllerian hormone (AMH) was localized to subbands p13.2----p13.3 on chromosome 19, using in situ hybridization and Southern blot analysis of a panel of man-mouse and man-hamster somatic cell hybrids. 相似文献
33.
34.
Marta Munzarová Daniela Zemanová Jan Kovařík Zdeněk Pačovský Aleš Rejthar Jiří Bártek 《Cancer immunology, immunotherapy : CII》1987,24(3):272-274
Summary Skin tests with autologous cholesteryl hemisuccinate (CHS)-treated and untreated cells were performed in ten metastatic melanoma patients. In the majority of cases evident reaction was noted with CHS-treated cells (9/10) while the reaction with untreated cells was mostly negative (7/10). Tumour cell suspensions used for skin tests were characterized for reactivity with monoclonal antibody TAL 1B5 detecting the HLA-DR alpha chain. There were no differences between CHS-treated and untreated cells with respect to HLA-DR expression and no correlation was found between grade of skin reaction to CHS-treated cells and the proportion of HLA-DR positive cells in the injected cell sample. 相似文献
35.
Summary The threonine operon fromEscherichia coli was cloned in plasmid pBR322, subcloned into the shuttle vector pCEM300 and the resulting recombinant plasmid was transferred intoBrevibacterium flavum andCorynebacterium glutamicum. The expression ofE. coli threonine genes in these coryneform bacteria was demonstrated by complementing thethrA andthrB mutations and by assaying homoserine dehydrogenase activity. 相似文献
36.
V. R. Oberbeck C. P. Mckay T. W. Scattergood G. C. Carle J. R. Valentin 《Origins of life and evolution of the biosphere》1989,19(1):39-55
Important prebiotic organic compounds might have been transported to Earth in dust or produced in vapor clouds resulting from atmospheric explosions or impacts of comets. These compounds coalesced in the upper atmosphere with particles ejected from craters formed by impacts of large objects. Coalescence during exposure to UV radiation concentrated organic monomers and enhanced formation of oligomers. Continuing coalescence added material to the growing particles and shielded prebiotic compounds from prolonged UV radiation. These particles settled into the lower atmosphere where they were scavenged by rain. Aqueous chemistry and evaporation of raindrops containing nomomers in high temperature regions near the Earth's surface also promoted continued formation of oligomers. Finally, these oligomers were deposited in the oceans where continued prebiotic evolution led to the most primitive cell. Results of our studies suggest that prebiotic chemical evolution may be an inevitable consequence of impacting comets during the late accretion of planets anywhere in the universe if oceans remained on those planetary surfaces. 相似文献
37.
38.
G. -J. A. Vidugiris A. V. Gudavičius V. J. Razumas J. J. Kulys 《European biophysics journal : EBJ》1989,17(1):19-23
Surface enhanced Raman scattering (SERS) of some enzymes (alkaline phosphatase, horseradish peroxidase and lactoperoxidase) and some amino acids (tryptophan, tyrosine and phenylalanine) on silver electrodes has been studied. The spectral band intensities of certain amino acids and amino acid residues were determined by their orientation on the surface and depended on the electrode potential (E).Abbreviations SERS
surface enhanced Raman scattering
- Trp
tryptophan
- Tyr
tyrosine
- Phe
phenylalanine
- E
electrode potential
- ORC
oxidation-reduction cycle 相似文献
39.
Aleš Vančura Ivana Vančurová Jan Kopecký Jaroslav Maršálek Daniel Cikánek Gabriela Basařová Vladimir Křišťan 《Archives of microbiology》1989,151(6):537-540
Synthesis of threonine dehydratase in Streptomyces fradiae was positively influenced by valine and negatively by isoleucine. However, these two amino acids had no effect on the activity of this enzyme. Synthesis of threonine dehydratase in -aminobutyrate resistant mutants of S. fradiae was pronouncedly less sensitive to the positive effect of valine and this change in regulation led to valine overproduction. Synthesis of acetohydroxy acid synthase is regulated in a similar manner to that of threonine dehydratase, however a lower level of expression was detected in -aminobutyrate resistant mutants. And again, no effect of branched-chain amino acids on acetohydroxy acid synthase activity was observed. It follows that in S. fradiae synthesis of threonine dehydratase is the main regulatory mechanism governing production and the mutual ratio of synthesized valine and isoleucine.Abbreviations -AB
-aminobutyrate
- AHAS
acetohydroxy acid synthase
- -KB
-ketobutyrate
- MNNG
N-methyl-N-nitro-N-nitrosoguanidine
- TD
threonine dehydratase
- Trans. B.
transaminase of branched-chain amino acids
- VDH
valine dehydrogenase 相似文献
40.
Synopsis Evidence is presented which suggests that the nonparasitic lamprey, Lampetra (Eudontomyzon) gracilis Kux, 1965, is conspecific with the parasitic lamprey Eudontomyzon danfordi Regan, 1911. The diagnostic characters of the holotype and of the non-type material of E. gracilis are features found in E. danfordi specimens in their second and final year of adult life, thereby making the former a junior synonym of the latter. 相似文献