全文获取类型
收费全文 | 1767篇 |
免费 | 144篇 |
国内免费 | 3篇 |
出版年
2022年 | 8篇 |
2021年 | 27篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 19篇 |
2017年 | 18篇 |
2016年 | 30篇 |
2015年 | 40篇 |
2014年 | 61篇 |
2013年 | 103篇 |
2012年 | 83篇 |
2011年 | 69篇 |
2010年 | 63篇 |
2009年 | 47篇 |
2008年 | 77篇 |
2007年 | 87篇 |
2006年 | 71篇 |
2005年 | 79篇 |
2004年 | 81篇 |
2003年 | 69篇 |
2002年 | 73篇 |
2001年 | 65篇 |
2000年 | 75篇 |
1999年 | 49篇 |
1998年 | 27篇 |
1997年 | 23篇 |
1996年 | 24篇 |
1995年 | 25篇 |
1994年 | 21篇 |
1993年 | 10篇 |
1992年 | 33篇 |
1991年 | 37篇 |
1990年 | 45篇 |
1989年 | 24篇 |
1988年 | 42篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1982年 | 19篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1972年 | 7篇 |
1969年 | 8篇 |
排序方式: 共有1914条查询结果,搜索用时 15 毫秒
81.
Most of the heat-labile enterotoxin (LT) synthesized by Escherichia coli is cell associated; however, a small portion of LT (approximately 10%) is released by bacterial cells into the culture supernatant. The LT subunit B (LT-B) produced by a cloned LT-B gene (tox B) was released in amounts equal to the parent LT release. In contrast, no release of LT subunit A (LT-A) or its smaller derivatives was observed in strains containing cloned toxA genes. The data suggest that LT-B is necessary for the release of LT-A across the bacterial membrane. 相似文献
82.
Transfer of the phosphatidyl moiety of phosphatidylglycerol to phosphatidylethanolamine in Escherichia coli 总被引:1,自引:1,他引:0 下载免费PDF全文
Phosphatidylglycerol was pulse-labeled with radioactive lipid precursors in a serine auxotroph of Escherichia coli. Most of the radioactivity of phosphatidylglycerol labeled in a serine-depleted medium was transferred to phosphatidylethanolamine during a chase in the presence of L-serine, but not in its absence. Metabolism of fatty acyl moieties labeled with [1-14C]acetate, acylated glycerol moieties labeled with [2-3H]glycerol, and phosphate moieties labeled with 32Pi, followed by a chase in the presence of cerulenin, showed that the intact phosphatidyl moiety of phosphatidylglycerol was transferred to phosphatidylethanolamine. The composition of phosphatidylethanolamine molecular species was unaltered and not perturbed by the transfer of the phosphatidyl moiety of phosphatidylglycerol. The increase of phosphatidylethanolamine with a concomitant decrease of phosphatidylglycerol was not coupled with the postulated turnover of phosphatidylglycerol to membrane-derived oligosaccharides and lipoprotein. It is suggested that phosphatidylglycerol is capable of providing its phosphatidyl moiety for the production of phosphatidylethanolamine in response to the relief of serine limitation by addition of L-serine. 相似文献
83.
Soyasaponin I, a triterpenoid saponin isolated from etiolated pea (Pisum sativum cv. Alaska) shoots and identified as Pfr killer, was examined for its effects on spectral properties of undegraded pea phytochrome. When soyasaponin I in concentrations of 100 micromolar or lower was added to Pr in the dark, the spectrum of Pr was not significantly affected, whereas in the presence of 120 micromolar or higher concentrations the absorption maximum of Pr shifted from 666 to 658 nanometer with slight decrease of absorbance. After a brief exposure of the mixture to red light, the increase in absorbance at 666 nanometers that occurs in the dark was inhibited at 26 micromolar and higher soyasaponin I concentrations; the maximum effect being reached at about 180 micromolar. The decrease in absorbance at 724 nanometers in the dark after red light irradiation was somewhat inhibited by 60 micromolar and totally prevented by 410 micromolar soyasaponin I. When P658 was irradiated with red light in the presence of 220 micromolar or higher soyasaponin I concentrations, a bleached form (Pbl) was produced instead of Pfr. Pbl showed no dark spectral changes, and the phototransformation of Pbl to P658 required a significantly high irradiance of far-red light. When the saponin was added to Pfr in the dark, none of the above-described spectral changes occurred, although the same effects were observed after the mixture was exposed briefly to far-red light followed by red light. 相似文献
84.
Construction of a physical map of a kanamycin (Km) transposon, Tn5, and a comparison to another km transposon, Tn903 总被引:6,自引:0,他引:6
Summary A cleavage map of Tn5, a kanamycin (Km) transposon from plasmid JR67, was constructed from pMKI, a composite plasmid of ColE1 and Tn5, and compared to that of Tn903, a Km transposon from plasmid R6-5. The two transposons showed marked heterogeneity in both the structural gene for Km resistance and the inverted repeat regions as evidenced by their distinctly different restriction maps. This result suggests separate paths of evolution for the two Km transposons. 相似文献
85.
Takao Yokota Kunikazu Hiraga Hisakazu Yamane Nobutaka Takai-Iashi 《Phytochemistry》1975,14(7):1569-1574
The mass spectra of trimethylsilyl ethers of six gibberellin-β-d-glucopyranosyl ethers and five gibberellin-β-d-glucopyranosyl esters are discussed. The fragmentation patterns are shown to be affected by the structural variations of the aglycones. 相似文献
86.
87.
Role of salicylic acid glucosyltransferase in balancing growth and defence for optimum plant fitness
88.
Yasuhiro Iwao Chihiro Kimoto Ayaka Fujimoto Asuka Suda Yuki Hara 《Molecular reproduction and development》2020,87(3):358-369
The union between a sperm and an egg nucleus in egg fertilization is necessary to mix genetic materials to create a new diploid genome for the next generation. In most animals, only one sperm is incorporated into the egg (monospermy), but several animals exhibit physiological polyspermy in which several sperms enter the egg during normal fertilization. However, only one sperm nucleus forms the zygote nucleus with the egg nucleus, even in a polyspermic egg. The cellular and molecular mechanisms involved in the selection of sperm nuclei in the egg cytoplasm have been well investigated in urodele amphibians. The principal sperm nucleus develops a larger sperm aster and contacts the egg nucleus to form a zygote nucleus, whereas other accessory sperm nuclei are unable to approach the egg nucleus. The diploid zygote nucleus induces cleavage and participates in embryonic development, whereas the accessory sperm nuclei undergo pyknosis and degenerate. We propose several models to account for the mechanisms of the selection of one sperm nucleus and the degeneration of accessory sperm nuclei. The roles of physiological polyspermy in animal reproduction are discussed by comparison with other polyspermic species. 相似文献
89.
Kazuki Yuzuriha Ayaka Yoshida Shunyi Li Akihiro Kishimura Takeshi Mori Yoshiki Katayama 《Journal of peptide science》2020,26(10)
In this report, we designed conjugates of an antigen peptide with the immunosuppressive vitamins all‐trans retinoic acid (ATRA) and vitamin D3 for efficient induction of antigen‐specific immunotolerance. We established a synthetic scheme for the preparation of the peptide‐vitamin conjugates, which the chemically unstable vitamins tolerated. Among the obtained conjugates, the ATRA conjugate successfully suppressed inflammatory effects in macrophages and dendritic cells and induced antigen presentation in dendritic cells. This synthetic method of conjugate is conceivably applicable to other antigen peptides for induction of antigen‐specific immunotolerance. 相似文献