全文获取类型
收费全文 | 4086篇 |
免费 | 329篇 |
学科分类
生物科学 | 4415篇 |
出版年
2023年 | 18篇 |
2022年 | 43篇 |
2021年 | 73篇 |
2020年 | 36篇 |
2019年 | 50篇 |
2018年 | 62篇 |
2017年 | 58篇 |
2016年 | 93篇 |
2015年 | 151篇 |
2014年 | 229篇 |
2013年 | 244篇 |
2012年 | 298篇 |
2011年 | 301篇 |
2010年 | 232篇 |
2009年 | 190篇 |
2008年 | 246篇 |
2007年 | 267篇 |
2006年 | 248篇 |
2005年 | 171篇 |
2004年 | 217篇 |
2003年 | 182篇 |
2002年 | 189篇 |
2001年 | 61篇 |
2000年 | 62篇 |
1999年 | 60篇 |
1998年 | 48篇 |
1997年 | 36篇 |
1996年 | 36篇 |
1995年 | 20篇 |
1994年 | 26篇 |
1993年 | 26篇 |
1992年 | 39篇 |
1991年 | 26篇 |
1990年 | 31篇 |
1989年 | 30篇 |
1988年 | 26篇 |
1987年 | 19篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1974年 | 6篇 |
1972年 | 11篇 |
排序方式: 共有4415条查询结果,搜索用时 15 毫秒
41.
In 234 copulations, male and female behavioural patterns were collected, especially the vocal pattern for the female. Moreover
quantitative structural analysis was performed on 38 of these female copulatory vocalizations. A multifactorial analysis,
ANAFAC, was performed to seek relations between (1) utterance of female copulatory call and male and female copulatory behaviour
and (2) these patterns and the great variability of female calls. Utterance of female copulatory vocalizations is essentially
due to the female’s own copulatory behaviour in periods of intense sexual activity. Long female calls are related to male
ejaculation, and those “rich” in harmonics are related to visual and tactile communicatory signals exchanged by the male and
the female during a mount. This analysis strongly confirms the tied bond between quality of a call and internal state of the
emitter. Long calls, rich in harmonics, may serve as signals maintaining or strengthening the possibly temporary preferential
relation between male and sexually receptive female. 相似文献
42.
43.
Analysis of Escherichia coli TonB membrane topology by use of PhoA fusions. 总被引:14,自引:8,他引:6 下载免费PDF全文
Alkaline phosphatase (PhoA) fusions to TonB amino acids 32, 60, 125, 207, and 239 (the carboxy terminus) all showed high PhoA activity; a PhoA fusion to TonB amino acid 12 was inactive. The full-length TonB-PhoA fusion protein was associated with the cytoplasmic membrane and retained partial TonB function. These results support a model in which TonB is anchored in the cytoplasmic membrane by its hydrophobic amino terminus, with the remainder of the protein, including its hydrophobic carboxy terminus, extending into the periplasm. 相似文献
44.
M J Gauthier B Lafay R Christen L Fernandez M Acquaviva P Bonin J C Bertrand 《International journal of systematic bacteriology》1992,42(4):568-576
On the basis of phenotypical characteristics and analysis of 16S rRNA sequence, a new species belonging to a new genus is described, and the name Marinobacter hydrocarbonoclasticus is proposed. This organism, isolated from Mediterranean seawater near a petroleum refinery, is a gram-negative, aerobic, rod-shaped bacterium. It grows at NaCl concentrations of 0.08 to 3.5 M and uses various hydrocarbons as the sole source of carbon and energy. Its DNA has a guanine-plus-cytosine content of 52.7 mol%. The 16S rRNA analysis shows a clear affiliation between M. hydrocarbonoclasticus and the gamma group of the phylum Proteobacteria. A close phylogenetic relationship appears among the species Marinomonas vaga, Oceanospirillum linum, Halomonas elongata, and Pseudomonas aeruginosa. Because of the impossibility of finding a single most closely related species, we suggest that this bacterium be assigned to a new genus, at least temporarily. The possibility of a revision of this status when new data appear is, however, not excluded. The type strain is M. hydrocarbonoclasticus SP.17 (= ATCC 49840). 相似文献
45.
Incorporation of radiolabeled thymidine is commonly used to investigate DNA damage. Using a filter-binding assay, we observed that the addition of various doses of [methyl-3H]thymidine (0.2 and 2 microCi/ml) or [2-14C]thymidine (0.02 and 0.2 microCi/ml) in the culture medium for 2 days, a standard method for cell-labeling, induces DNA fragmentation in HL-60 human promyelocytic cells. This effect was dose- and time-dependent and the DNA fragments were not protein-linked since the levels of DNA fragmentation were identical in the presence and in the absence of proteinase K (0.5 mg/ml). Radiolabeled thymidine-induced DNA fragmentation was associated with an inhibition of cell growth, but cells remained able to exclude trypan blue, suggesting that plasma membrane integrity was conserved, except at very high doses of [methyl-3H]thymidine (2 microCi/ml). By agarose-gel electrophoresis, the DNA-fragmentation was demonstrated to be internucleosomal with a typical ladder pattern. Addition of unlabeled thymidine to the culture medium prevented DNA fragmentation in a dose-dependent manner, indicating that radiolabeled thymidine incorporation in DNA was directly responsible for DNA fragmentation. We conclude that radiolabeling of DNA using thymidine incorporation can induce DNA fragmentation in some cell lines such as HL-60. This observation must be taken into account in methods using radiolabeling to study DNA damage in these cells. 相似文献
46.
Claire Zehnacker Thomas W. Becker Akira Suzuki Elisa Carrayol Michel Caboche Bertrand Hirel 《Planta》1992,187(2):266-274
Ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) was purified to electrophoretic homogeneity from leaves of tobacco (Nicotiana tabacum L.). The holoenzyme is a monomeric flavoprotein with a molecular weight of 164 kDa. Polyclonal rabbit antibodies against the purified enzyme were used to isolate a 450-bp Fd-GOGAT cDNA clone (C16) from a tobacco gt11 expression library. A longer Fd-GOGAT cDNA clone (C35) encoding about 70% of the amino acids of tobacco Fd-GOGAT was isolated from a tobacco gt10 cDNA library using C16 as the probe. The amino-acid sequence of the protein encoded by the Fd-GOGAT cDNA clone C35 was delineated. It is very likely that Fd-GOGAT is encoded by two genes in the amphidiploid genome of tobacco while only a single Fd-GOGAT gene appears to be present in the diploid genome of Nicotiana sylvestris. Two Fd-GOGAT isoenzymes could be distinguished in extracts of tobacco leaf protein. In contrast, a single Fd-GOGAT protein species was detected in leaves of Nicotiana sylvestris speg. et Comes. In tobacco leaves, the 6-kb Fd-GOGAT mRNA is about 50-fold less abundant than chloroplastic glutamine synthetase (EC 6.3.1.2) mRNA. Both Fd-GOGAT mRNA and Fd-GOGAT protein accumulated during greening of etiolated tobacco leaves, and a concomitant increase in Fd-GOGAT activity was observed. These results indicate that tobacco Fd-GOGAT gene expression is light-inducible. Levels of Fd-GOGAT mRNA in tobacco organs other than leaves were below the detection limit of our Northern-blot analysis. Polypeptides of Fd-GOGAT were present in tobacco leaves and, to a lesser extent, in pistils and anthers, but not in corollas, stems and roots. These results support organ specificity in tobacco Fd-GOGAT gene expression.Abbreviations bp
base pairs
- Fd-GOGAT
ferredoxin-dependent glutamate synthase
- GS
glutamine synthetase
- PAGE
polyacrylamide gel electrophoresis
- SDS
sodium dodecyl sulfate
The authors wish to thank Juan Luis Gómez Pinchetti (Marine Plant Biotechnology Laboratory) for his assistance during the experiments. This study was supported by grants received from SAREC (Swedish Agency for Research Cooperation with Developing Countries), Carl Tryggers Fund for Scientific Research (K. Haglund), SJFR (Swedish Council for Forestry and Agricultural Research) (M. Björk, M. Pedersén), CITYT Spain (SAB 89-0091 and MAR 91-1237, M. Pedersén) and CICYT Spain (Z. Ramazanov, invited professor of Ministerio de Educatión y Ciencia, Spain). The planning of this cooperation was facilitated by COST-48. 相似文献
47.
Thomas W. Becker Michel Caboche Elisa Carrayol Bertrand Hirel 《Plant molecular biology》1992,19(3):367-379
48.
49.
Cytochrome b5 from Candida tropicalis grown on alkane has been solubilized in three different ways (sodium cholate, trypsin, osmotic wash). After solubilization of the microsomal membrane with sodium cholate, the purification of cytochrome b5 was achieved by DEAE-cellulose chromatography, hydroxylapatite chromatography, a second DEAE-cellulose chromatography and a Sephadex G-75 gel filtration. The purified protein had an apparent molecular weight of 16 000 ± 1 000. After solubilization by trypsin treatment or osmotic wash, the purification procedure yielded a protein with an apparent molecular weight of 12 000 ± 1 000. Though the purified proteins presented molecular weights depending on the technique of solubilization, they exhibited identical optical properties, a great stability with respect to temperature and pH, and were all autooxidable. Redox titrations revealed differences in their midpoint potential values, which were 35 ± 5 mV for the b5 purified after cholate solubilization, —59 ± 5 mV for the b5 purified after trypsin treatment and —65 ± 5 mV for the b5 purified after osmotic wash. 相似文献
50.