全文获取类型
收费全文 | 1767篇 |
免费 | 123篇 |
国内免费 | 1篇 |
专业分类
1891篇 |
出版年
2022年 | 9篇 |
2021年 | 20篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 26篇 |
2017年 | 21篇 |
2016年 | 35篇 |
2015年 | 52篇 |
2014年 | 53篇 |
2013年 | 141篇 |
2012年 | 87篇 |
2011年 | 98篇 |
2010年 | 62篇 |
2009年 | 49篇 |
2008年 | 84篇 |
2007年 | 81篇 |
2006年 | 81篇 |
2005年 | 86篇 |
2004年 | 83篇 |
2003年 | 86篇 |
2002年 | 86篇 |
2001年 | 59篇 |
2000年 | 54篇 |
1999年 | 62篇 |
1998年 | 15篇 |
1997年 | 17篇 |
1996年 | 8篇 |
1995年 | 17篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 25篇 |
1991年 | 30篇 |
1990年 | 32篇 |
1989年 | 27篇 |
1988年 | 32篇 |
1987年 | 28篇 |
1986年 | 28篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 16篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1970年 | 9篇 |
1969年 | 8篇 |
1968年 | 14篇 |
1967年 | 8篇 |
排序方式: 共有1891条查询结果,搜索用时 11 毫秒
31.
Crystallization and main-chain structure of neutral protease from Streptomyces caespitosus 总被引:1,自引:0,他引:1
A neutral protease, i.e., a zinc-containing metalloendoprotease from Streptomyces caespitosus, has been crystallized using acetone as a precipitating agent. The crystals diffract to better than 1.5 A resolution when a rotating anode X-ray generator is used as an X-ray source. Protein phase angles were calculated by the multiple isomorphous replacement method using two heavy-atom derivatives (HgCl2 and CH3HgCl). A 6 A resolution electron density map clearly showed molecular boundaries. Although its amino acid sequence is not known, the folding pattern of the polypeptide chain could be traced on a 2.5 A resolution electron density map. A large cleft, which is located on the molecular surface, was proved to be the active site of the enzyme by structure analyses of inhibitor-complex crystals. The highest electron density peak, which corresponds to the cleft, was assigned to a catalytically essential zinc atom on difference Fourier synthesis between native and EDTA-soaked crystals. 相似文献
32.
M Kawaichi C Oka R Reeves M Kinoshita T Honjo 《The Journal of biological chemistry》1991,266(27):18387-18394
We have constructed a plasmid, pLTR100, which contains human interleukin 2 receptor light (IL-2R L) chain cDNA in the inverted orientation relative to the upstream SV40 promoter. The cDNA segment is flanked by the immunoglobulin gene recombination signal sequences so that the cDNA segment can invert and the human IL-2R L chain is subsequently expressed under the control of the SV40 promoter. A murine pre-B cell line, 38B9, transfected with pLTR100 began to express the human IL-2R L chain on the cell surface. The frequency of human IL-2R L chain positive cells increased almost linearly up to 50% for 60 days of culture after transfection. Southern blot analysis and sequencing of the DNA fragments at the recombination junction confirmed that the cDNA segment was inverted in a signal sequence-dependent manner by the variable-diversity-joining recombination process. Transgenic mice bearing the recombination substrate DNA similar to pLTR100 expressed the human IL-2 L chain in the spleen, thymus, and bone marrow, but not in the other tissues examined at the detectable level. Both IgM- and CD3-positive cells expressed the human IL-2R L chain, indicating that this artificial DNA can serve as a substrate for recombination both in B- and T-cells and that another DNA segment may be necessary to confer the cell-type specificity on the substrate DNA. 相似文献
33.
Enhancement of DNA synthesis in rat thymocytes by stimulating their muscarinic acetylcholine receptors. 总被引:2,自引:0,他引:2
K Tominaga F Hato Y Kinoshita M Tominaga M Yamada 《Cellular and molecular biology, including cyto-enzymology》1992,38(8):815-822
The binding of 3H-acetylcholine (ACh) to acetylcholine receptors (AChRs) on rat thymocytes was examined and found to be inhibited by the treatment with several antagonists against nicotinic and muscarinic AChRs. This result suggested that thymocytes have AChRs with different affinity, and bear both nicotinic and muscarinic AChRs on their surfaces. To make clear the functional significance of the AChRs, DNA synthesis of the thymocytes stimulated with ACh was examined. 3H-thymidine uptake of thymocytes was significantly increased when the cells were stimulated with ACh or another cholinergic agonist. The increment of DNA synthesis caused by ACh in thymocytes was not reduced by treatment with nicotinic antagonists, but was decreased by treatment with any of the muscarinic antagonists. Concentration of the intracellular second messengers, inositol 1,4,5-triphosphate (IP3) and guanosine 3',5'-cyclic monophosphate (cGMP) was also made higher by ACh stimulation. It is discussed that the enhancement of intracellular IP3 and cGMP concentrations after stimulation of muscarinic AChRs appears to be related with the increment of thymocyte DNA synthesis. 相似文献
34.
N Arima Y Yamashita H Nakata A Nakamura Y Kinoshita T Chiba 《Biochemical and biophysical research communications》1991,176(3):1027-1032
Histamine dose-dependently stimulated cyclic AMP production in human gastric carcinoma cell line MKN-45, and this effect was inhibited by cimetidine but not by pyrilamine. Moreover, not only histamine but also cimetidine displaced the specific binding of [3H]tiotidine to these cells, whereas pyrilamine had no effect. On the other hand, pretreatment of MKN-45 cells with retinoic acid (RA) significantly enhanced histamine-induced increase of cyclic AMP production, although the cyclic AMP response to either forskolin or NaF was not affected. Finally, RA treatment increased the number of histamine receptor without altering its affinity. Thus, it appears that histamine H2-receptors are present on MKN-45 cells, and that RA treatment enhances the action of histamine on these cells by increasing the number of H2-receptors. 相似文献
35.
36.
Negative ion fast atom bombardment-tandem mass spectrometry for structural analysis of isoprenoid diphosphates 总被引:1,自引:0,他引:1
M Kitaoka H Nagaki T Kinoshita M Kurabayashi T Koyama K Ogura 《Analytical biochemistry》1990,185(1):182-186
Applicability of negative ion fast atom bombardment (FAB)-tandem mass spectrometry (MS/MS) was examined in trace mixture analyses and structural assignments of some isoprenoid diphosphates. Negative ion FAB-MS spectra using a glycerol matrix of these isoprenoid diphosphates showed predominantly molecular ions (M-H)- together with fragment ions at m/z 177 (H3P2O7)-, 176 (H2P2O7)-, 159 (HP2O6)-, and 79 (PO3)- which were characteristic of the diphosphate ester moiety. The molecular ions did not overlap with peaks arising from any impurities even when crude sample such as butanol extracts from enzymatic reaction mixtures were directly analyzed without any purification. Moreover, collisionally activated dissociation spectra of the molecular ion showed many structurally significant fragment ions which enabled us to elucidate the structures of such irregular alkyl chain moieties as those having a homoisoprenoid skeleton or substituted structures. These studies indicate that negative ion FAB-MS/MS is a simple and useful technique for trace mixture analysis and structure elucidation of isoprenoid diphosphates. 相似文献
37.
Cartilage-derived factor (CDF) : II. Somatomedin-like action on cultured chondrocytes 总被引:2,自引:0,他引:2
Yukio Kato Yoshio Nomura Mitsuko Tsuji Hiroaki Ohmae Masahiko Kinoshita Shinji Hamamoto Fujio Suzuki 《Experimental cell research》1981,132(2):339-347
Previously, we showed that fetal bovine cartilage contains a polypeptide that stimulates the incorporation of [35S]sulfate into proteoglycans synthesized by rat and rabbit costal chondrocytes in culture. In this paper, we report that the cartilage-derived factor (CDF) increases not only [35S]sulfate incorporation but also [3H]thymidine incorporation into rabbit chondrocytes in monolayer culture. The dose-response curve of CDF stimulation of DNA synthesis was similar in profile to that of CDF stimulation of proteoglycan synthesis. In addition, CDF markedly enhanced [3H]uridine incorporation into rabbit chondrocytes and significantly enhanced [3H]serine incorporation into total protein. These findings indicate that fetal bovine cartilage contains a factor that shows somatomedin-like activity in monolayer cultures of rabbit chondrocytes. 相似文献
38.
39.
40.
Yasuhiro Yamada Hirobumi Motoi Shinichi Kinoshita Nobuo Takada Hirosuke Okada 《Applied microbiology》1975,29(3):400-404
An organism isolated from soil and identified as Arthrobacter sp. was studied for its squalene degradation. The degradation product from squalene, which accumulated in the culture broth, was isolated and identified as trans-geranylacetone by mass spectrometry, gas chromatography, infrared spectrometry, and nuclear magnetic resonance spectrometry. Addition of a high concentration of K2HPO4 to the culture medium resulted in accumulation of fairly large amounts of carboxylic acids in addition to geranylacetone. These carboxylic acids were identified as isovaleric, β,β′-dimethylacrylic, geranic, and (+)-(R)-citronellic acids. Among these acids, α,β-saturated carboxylic acids were found to be predominant in quantity. 相似文献