全文获取类型
收费全文 | 10534篇 |
免费 | 863篇 |
国内免费 | 951篇 |
出版年
2024年 | 29篇 |
2023年 | 182篇 |
2022年 | 371篇 |
2021年 | 601篇 |
2020年 | 433篇 |
2019年 | 486篇 |
2018年 | 473篇 |
2017年 | 310篇 |
2016年 | 458篇 |
2015年 | 710篇 |
2014年 | 790篇 |
2013年 | 829篇 |
2012年 | 937篇 |
2011年 | 807篇 |
2010年 | 541篇 |
2009年 | 450篇 |
2008年 | 553篇 |
2007年 | 475篇 |
2006年 | 424篇 |
2005年 | 346篇 |
2004年 | 284篇 |
2003年 | 264篇 |
2002年 | 205篇 |
2001年 | 177篇 |
2000年 | 153篇 |
1999年 | 168篇 |
1998年 | 94篇 |
1997年 | 82篇 |
1996年 | 75篇 |
1995年 | 75篇 |
1994年 | 101篇 |
1993年 | 48篇 |
1992年 | 53篇 |
1991年 | 67篇 |
1990年 | 42篇 |
1989年 | 48篇 |
1988年 | 32篇 |
1987年 | 27篇 |
1986年 | 34篇 |
1985年 | 27篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1973年 | 4篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
The effects of procedures which diminish Ca2+ influx into myocardial cells on responses of isolated cardiac preparations to cAMP-independent histamine H1 receptor stimulation and cAMP-generating beta-receptor stimulation were measured. The histamine response of guinea pig left atria, which appears to be primarily mediated by H1 receptors, was depressed to a greater extent than was the response of this preparation to isoproterenol by decreasing the extracellular Ca2+ concentration, and by the Ca2+ influx blocker D-600. Similarly, while the H1 agonist 2-pyridylethylamine dihydrochloride (PEA) produced increases in tension of a similar magnitude as the partial beta-agonist salbutamol in both left atria and in papillary muscles, responses of both preparations to PEA were depressed to a significantly greater extent by decreasing the extracellular Ca2+ concentration than were responses to salbutamol. Overall, both the basal developed force of papillary muscles and the responses of these preparations to H1 and beta-receptor stimulation appeared to be less depressed by decreasing the extracellular Ca2+ concentration than were those of left atria. These results indicate that responses mediated via cAMP-independent H1 receptors, like those arising from alpha-receptor stimulation, are more sensitive to procedures which diminish Ca2+ influx than are responses arising from stimulation of cAMP-generating beta-receptors. This may reflect differences in the mechanisms by which stimulation of H1, alpha-, and beta-receptors give rise to positive inotropic responses. In addition, left atria may be more dependent than papillary muscles on extracellular Ca2+ for the support of contraction. 相似文献
36.
T-cell-mediated regression of "spontaneous" and of Epstein-Barr virus-induced B-cell transformation in vitro: studies with cyclosporin A 总被引:15,自引:0,他引:15
A B Rickinson M Rowe I J Hart Q Y Yao L E Henderson H Rabin M A Epstein 《Cellular immunology》1984,87(2):646-658
The regression of Epstein-Barr (EB) virus-transformed B-cell outgrowth which is seen in experimentally-infected cultures of blood mononuclear (UM) cells from healthy seropositive donors can be abolished in medium containing the T-cell-suppressive agent cyclosporin A (CSA) at concentrations of 0.05 microgram/ml and above. CSA mediates its effect within the first 4 days post-infection of the UM cells and this prevents subsequent in vitro generation of the EB virus-specific cytotoxic-T-cell response which normally brings about regression. Regression can be fully restored by supplementing the CSA-treated culture with interleukin 2 (IL-2)-containing culture supernatants or indeed with purified IL-2 itself, suggesting that CSA mediates its effect in this system through inhibiting the endogenous production of IL-2 which is required to amplify the virus-specific cytotoxic response. "Spontaneous transformation" to EB virus genome-positive lymphoblastoid cell lines in noninfected cultures of UM cells from healthy seropositive donors, though rare in normal medium, is enhanced to such a degree in the presence of CSA that, for many donors, the phenomenon becomes titratable against input cell dose across the 2.0 X 10(6)-2.5 X 10(5) cells/culture range. Cell mixing experiments suggest that the spontaneously transformed cell lines which arise with such efficiency under these conditions do so not by direct in vitro outgrowth of progenitor cells transformed by the virus in vivo, but by a two-step mechanism involving virus release and secondary infection in vitro. 相似文献
37.
R M Kamp Z J Yao B Wittmann-Liebold 《Hoppe-Seyler's Zeitschrift für physiologische Chemie》1983,364(2):141-155
Tryptic peptides of the ribosomal proteins S11, L9 and L29 were separated by reversed phase chromatography under conditions which enabled direct micro-sequencing with the 4-(dimethylamino)azobenzene-4'-isothiocyanate/phenylisothiocyanate double coupling method [Chang, Brauer, Wittmann-Liebold (1978) FEBS Lett. 93, 205-214]. The peptides were separated on a RP-18 column employing volatile buffers at pH 2.0, 4.1 and 7.8. Depending on the different chromatographic behaviour of the peptide mixture, the elution gradient was optimised for each hydrolysate using 20 micrograms of the hydrolysed protein. Preparative separations were made with 150-250 micrograms. At least 80% of the peptides could be isolated by these techniques and used for direct micro-sequencing without further purification or desalting. The results show that the high-performance liquid chromatographic method employed allows easy isolation and sequencing with minute amounts of peptides. 相似文献
38.
Purification of Escherichia coli 30S ribosomal proteins by high performance liquid chromatography 总被引:1,自引:0,他引:1
R M Kamp Z J Yao A Bosserhoff B Wittmann-Liebold 《Hoppe-Seyler's Zeitschrift für physiologische Chemie》1983,364(12):1777-1793
High performance liquid chromatography was applied to the separation of proteins derived from the Escherichia coli 30S ribosomal subunit. Several methods of separating this protein mixture has been tested: size-exclusion chromatography on hydrophilic phases; ion exchange and reversed phase chromatography (on C2 to C18 hydrocarbon-bonded supports). Various elution systems were examined in order to obtain pure proteins suitable for micro-sequence analysis. The resolution and yields of the proteins varied considerably, depending on the type of support and gradient system used. The best results were achieved with uniformly globular-shaped supports of large pore size, and by combining high performance size exclusion with rechromatography on reversed phase columns. Purification conditions for the individual proteins are listed. The methods employed avoid any precipitation step and allow easy identification of the proteins by one or two-dimensional gel electrophoresis, amino-acid analysis or direct manual or automatic micro-sequencing. Since the isolation time is much reduced compared with conventional purification procedures, the proteins obtained by the techniques described here are well suited for topographical and immunological studies or reconstitution assays. Ribosomal proteins of other organisms can be separated under similar conditions. 相似文献
39.
14C-Sterigmatocystin isolated from cultures of supplemented with (1-14C)acetate was shown to be efficiently converted to aflatoxin B1 by the resting mycelium of . The experimental results may indicate a biosynthetic pathway leading from 5-hydroxysterigmatocystin to sterigmatocystin and then to aflatoxin B1. 相似文献
40.