全文获取类型
收费全文 | 90065篇 |
免费 | 6966篇 |
国内免费 | 50篇 |
出版年
2023年 | 466篇 |
2022年 | 1032篇 |
2021年 | 1830篇 |
2020年 | 1212篇 |
2019年 | 1424篇 |
2018年 | 2041篇 |
2017年 | 1703篇 |
2016年 | 2802篇 |
2015年 | 4112篇 |
2014年 | 4213篇 |
2013年 | 5556篇 |
2012年 | 6470篇 |
2011年 | 6064篇 |
2010年 | 3723篇 |
2009年 | 3411篇 |
2008年 | 4490篇 |
2007年 | 4425篇 |
2006年 | 3970篇 |
2005年 | 4092篇 |
2004年 | 3976篇 |
2003年 | 3549篇 |
2002年 | 3010篇 |
2001年 | 1748篇 |
2000年 | 1592篇 |
1999年 | 1532篇 |
1998年 | 942篇 |
1997年 | 791篇 |
1996年 | 834篇 |
1995年 | 679篇 |
1994年 | 680篇 |
1993年 | 641篇 |
1992年 | 1063篇 |
1991年 | 977篇 |
1990年 | 918篇 |
1989年 | 867篇 |
1988年 | 856篇 |
1987年 | 777篇 |
1986年 | 713篇 |
1985年 | 713篇 |
1984年 | 674篇 |
1983年 | 512篇 |
1982年 | 417篇 |
1981年 | 414篇 |
1980年 | 392篇 |
1979年 | 509篇 |
1978年 | 401篇 |
1977年 | 348篇 |
1975年 | 335篇 |
1974年 | 334篇 |
1973年 | 342篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
M Janowski L Baugnet-Mahiec J Merregaert L de Saint-Georges A Sassen J N Ihle J R Maisin 《Comptes rendus des séances de la Société de biologie et de ses filiales》1980,174(5):832-839
Two distinct rat propagates of a radiation leukemia virus (RadLV-Rs) from the C57BL mouse respectively induced characteristic leukemogenic effects. These were found to be related with the infection titers of the isolates, but not with either their antigenic specificities or their viral and proviral genome sequences. 相似文献
43.
F. D. Miller K. F. Jorgenson R. J. Winkfein J. H. van de Sande D. A. Zarling J. Stockton 《Journal of biomolecular structure & dynamics》2013,31(3):611-620
Abstract Bacteriophage PM2 DNA, a ccc genome of high apparent superhelical density, contains left-handed (Z) regions as detected by competitive radioimmunoassay, agarose gel electrophoresis of DNA: antibody complexes and immunoelectron microscopy. The latter technique, in conjunction with partial blockage of restriction endonuclease sites by bound antibody, was used to map the left-handed regions along the DNA molecule. A cluster of four to five antibody molecules (approximately 25% of bound antibody) was located within map units 0.05–0.18 of the single Hpa II restriction site. Sequence analysis of part of this region showed the presence of several areas of high alternating purine-pyrimidine content. A strong correlation is observed between alternating pyrimidine-purine tracts of significant length and antibody binding sites. 相似文献
44.
Francisco Gutirrez‐Corchero M. Victoria Arruga Lourdes Sanz Cristina García M. Angeles Hernndez Francisco Campos 《Molecular ecology resources》2002,2(1):75-77
FTA® cards were used for long‐term storage of avian blood samples. Blood DNA was extracted by a simple method and used in PCR for sex identification of adult and nestling Great Grey Shrikes Lanius excubitor. 相似文献
45.
Carp (Cyprinus carpio) hemoglobin readily autoxidizes in blood smears. Quantification of Soret-band absorbance in individual erythrocytes by means of scanning cytophotometry therefore requires more elaborate methods of preparation of blood samples. Of the fixatives that have been tested, suspension of whole blood in isotonic salt solutions containing glutaraldehyde was most suitable. Glutaraldehyde-fixed red blood cells are totally resistant to hemolysis. In the course of fixation, hemoglobin is transformed to methemoglobin. Spectrophotometry indicated extensive similarities between glutaraldehyde-fixed carp methemoglobin and human methemoglobin. In aqueous solutions, the intensity of the Soret-peak was pH-dependent. The allosteric modifier organic polyphosphate caused an R----T transition, resulting in increased molar extinctions. Dried preparations showed Soret-spectra that were not influenced from either pH or organic polyphosphate concentration of the aqueous suspensions in which the erythrocytes had been stored. The same was true for slide preparations of cyanomethemoglobin, easily derived from methemoglobin on addition of potassium cyanide. In the absence of oxygen fresh blood cells from carp slowly transform their hemoglobin into deoxyhemoglobin. Spectra of the intermediate stages of deoxygenation, Hb4(O2)3, Hb4(O2)2 and Hb4(O2), as well as mixtures of these intermediates, could be monitored. 相似文献
46.
A González-Fernández J Sans P Aller C de la Torre 《Cell biology international reports》1985,9(3):237-243
Bromosubstitution for most of the S period in synchronous populations of Allium cepa L. meristematic cells resulted in a delay in the late S-G2 transition point where protein synthesis is needed for later mitotic entrance to occur. This retardation in the position of the transition point was not accompanied by the expected delay in the entrance into mitosis, suggesting that such protein synthesis is a requisite, but not a timer for prophase triggering. 相似文献
47.
A Levva G Schwartsmann L C Boeije H M Pinedo F de Waal 《Biochemical and biophysical research communications》1986,141(2):629-635
In the original HL-60 cells (HL-60-S) and an HL-60 subline (HL-60-R) respectively susceptible and resistant to induction of differentiation by retinoic acid or dimethyl sulfoxide, 5-aza-2'-deoxycytidine inhibited growth equally but induced differentiation to a greater extent in HL-60-S. Flow cytometry showed that 5-aza-2'-deoxycytidine produced in both HL-60 lines an increased proportion of cells in G2+M rather than G0/G1 as with retinoic acid. 5-aza-2'-deoxycytidine may have a differentiation-inducing effect in HL-60 provided cells have the competence to differentiate, indicating the importance of an alternate mechanism of action. 相似文献
48.
J. A. Roubos C. D. de Gooijer G. van Straten A. J. B. van Boxtel 《Bioprocess and biosystems engineering》1997,17(2):99-102
Two methods for the calculation of optimal trajectories for the input variables of a fed-batch culture of hybridoma cells are compared. It pointed out that a gradient method based on Pontryagins' minimum principle based yields a significant better performance with respect to computational effort and the calculated minimum than a dynamic programming approach which has been presented in a previous paper [1] as the most suitable method. 相似文献
49.
50.
Chafik Maazouzi Gérard Masson Maria Soledad Izquierdo Jean-Claude Pihan 《Journal of thermal biology》2008
The effects of the 2003 European heat wave on a freshwater plankton assemblage and its fatty acid (FA) composition were investigated. Composition and FA profiles of four size categories of planktonic organisms collected in 2003 were compared to those of the colder year 2002. 相似文献