全文获取类型
收费全文 | 7137篇 |
免费 | 525篇 |
国内免费 | 1篇 |
出版年
2023年 | 56篇 |
2022年 | 116篇 |
2021年 | 226篇 |
2020年 | 154篇 |
2019年 | 190篇 |
2018年 | 238篇 |
2017年 | 228篇 |
2016年 | 340篇 |
2015年 | 413篇 |
2014年 | 453篇 |
2013年 | 506篇 |
2012年 | 644篇 |
2011年 | 551篇 |
2010年 | 330篇 |
2009年 | 294篇 |
2008年 | 406篇 |
2007年 | 339篇 |
2006年 | 331篇 |
2005年 | 297篇 |
2004年 | 286篇 |
2003年 | 245篇 |
2002年 | 222篇 |
2001年 | 72篇 |
2000年 | 55篇 |
1999年 | 75篇 |
1998年 | 63篇 |
1997年 | 52篇 |
1996年 | 43篇 |
1995年 | 36篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 33篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 21篇 |
1985年 | 25篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 12篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1970年 | 5篇 |
1968年 | 14篇 |
排序方式: 共有7663条查询结果,搜索用时 15 毫秒
31.
Nitrogen Source Regulates Glutamate Dehydrogenase NADP Synthesis in Neurospora crassa 总被引:8,自引:4,他引:4 下载免费PDF全文
Georgina Hernndez Ray Snchez-Pescador Rafael Palacios Jaime Mora 《Journal of bacteriology》1983,154(1):524-528
Neurospora crassa glutamate dehydrogenase-NADP (EC 1.3.1.3) has a higher activity when mycelium is grown on ammonium or nitrate as nitrogen source than when grown on glutamate or glutamine. Quantitative immunoelectrophoresis established that, under all conditions, enzyme activity corresponded to enzyme concentration. Isotope incorporation studies demonstrated that the nitrogen source exerts its regulation at the level of de novo enzyme synthesis. 相似文献
32.
Methylation of the Flagellin of Salmonella typhimurium 总被引:2,自引:2,他引:0
The methylation of endogenous proteins by Salmonella typhimurium SL 870 was investigated in cell-free extracts by using S-adenosylmethionine as methyl donor. Several lines of evidence are presented which suggest that one of the methylated products is the protein flagellin. Mutant strains of SL 870 (nml−fla+ and nml+fla−) were also found to synthesize epsilon-N-methyl-lysine. It is proposed that S. typhimurium possesses at least two genes specifying different methylating enzymes. One gene product is a flagellin-specific methylating enzyme, whereas the other gene(s) codes for enzymes that methylate one or more other cell proteins. 相似文献
33.
Sphaerotilus natans required calcium for the production of sheaths and probably requires calcium for growth as well, though at a lower concentration. Neither strontium nor barium substituted for calcium. S. natans grew attached to the culture vessels of the continuous-flow apparatus even when no sheaths were produced. Tentative evidence showed that the requirement for calcium is shared by the manganese-oxidizing species S. discophorus. 相似文献
34.
Growth-promoting Activity of Spent Sulfite Liquor for Sphaerotilus natans Growing in a Continuous-Flow Apparatus 下载免费PDF全文
The calcium in ammonia-base spent sulfite liquor, unlike that in calcium-base spent liquor, is not available for growth of Sphaerotilus natans. It has not been possible to obtain a mixed slime with Sphaerotilus as the dominant organism in a continuous-flow apparatus fed spent sulfite liquor. 相似文献
35.
Dr. Rafael Bonfante 《Mycopathologia》1968,34(3-4):221-224
Summary A technique for observing the reduction of potassium tellurite byCandidas was developed. Various species of these yeasts reduce it at different concentrations, but that which is most useful for differentiation is 0.02 % added to Sabouraud dextrose agar basal medium. Of the yeasts studied,C. albicans, C. parapsilosis andC. tropicalis all reduced potassium tellurite to the concentration mentioned before, while the growth ofC. krusei, C. parakrusei andC. pseudotropicalis was inhibited. Without exception,C. pseudotropicalis reduced this salt at lower concentrations. The two strains ofC. guilliermondii tested gave contradictory results: one of them grew and reduced potassium tellurite, while the growth of the other was inhibited.Professor of Microbiology. 相似文献
36.
Dias FF 《Applied microbiology》1967,15(6):1512-1513
37.
Utilization of Inorganic Nitrogen Compounds by Sphaerotilus natans Growing in a Continuous-Flow Apparatus 总被引:3,自引:3,他引:0 下载免费PDF全文
Sphaerotilus natans was grown, attached, in a continuous-flow apparatus with inorganic nitrogen compounds (NH4Cl, NaNO2, or NaNO3) as the only sources of nitrogen. The growth rate with NH4+-containing medium did not differ from that with media containing glutamate or Casitone as the nitrogen source. 相似文献
38.
39.
40.
The role of indole-3-butyric acid (IBA) in adventitious root formation was studied by analyzing the uptake and subsequent metabolism of IBA in shoots of M.26 apple (Malus pumila Mill.) rootstock grown in vitro. Roots were induced by exposing shoots to 4 M IBA and [3H]IBA for 5 days in the dark and then transferring them to plant growth regulator (PGR)-free medium in the light until roots formed. Approximately 50% of the total radioactivity applied was taken up from the agar medium by the shoots during the 5-day incubation period in IBA. Indole-3-butyric acid metabolism was studied by extraction and high-performance liquid chromatographic (HPLC) separation of [3H]IBA and metabolites from the basal sections of treated shoots. The major [3H]IBA metabolite co-eluted with authentic [14C]indole-3-acetic acid (IAA) suggesting that IBA was converted to IAA in the shoots. The proportion of newly synthesized IAA present as conjugates was higher at the end of the 5-day IBA treatment period than after 13 days in PGR-free medium. There appeared to be no conjugation of IBA at any time. 相似文献