全文获取类型
收费全文 | 3101篇 |
免费 | 321篇 |
国内免费 | 104篇 |
出版年
2023年 | 27篇 |
2022年 | 40篇 |
2021年 | 74篇 |
2020年 | 85篇 |
2019年 | 112篇 |
2018年 | 139篇 |
2017年 | 101篇 |
2016年 | 95篇 |
2015年 | 124篇 |
2014年 | 228篇 |
2013年 | 248篇 |
2012年 | 194篇 |
2011年 | 222篇 |
2010年 | 193篇 |
2009年 | 208篇 |
2008年 | 204篇 |
2007年 | 164篇 |
2006年 | 153篇 |
2005年 | 150篇 |
2004年 | 89篇 |
2003年 | 108篇 |
2002年 | 88篇 |
2001年 | 65篇 |
2000年 | 44篇 |
1999年 | 29篇 |
1998年 | 40篇 |
1997年 | 27篇 |
1996年 | 23篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 21篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 17篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 16篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 5篇 |
排序方式: 共有3526条查询结果,搜索用时 93 毫秒
31.
32.
J H Miller M P Calos D Galas M Hofer D E Büchel B Müller-Hill 《Journal of molecular biology》1980,144(1):1-18
The lac region of Escherichia coli, carried on an F′ lacproB episome, was used as a target for the transposition of several transposable elements. Tn9 shows a preferential integration (by a factor of 50) into a region extending from the end of the Z gene through the Y gene. Throughout the remainder of the lacI, Z and Y genes one other short region, located in the middle of the I gene, is favored for integration. Within these favored regions many different integration points are evident. Inspection of the DNA sequence for the I and Y genes, and parts of the Z gene, shows a strong correlation between A + T richness and regions of preferential integration. Tn5 insertions follow a similar pattern, although with less preference; whereas Tn10 insertions (provided by T. J. Foster), also favor the Y gene and the end of Z, but are distributed among fewer integration points. Most of the Tn3 insertions into the episome are accompanied by a nearby or adjacent deletion. 相似文献
33.
An electrophoretic variant of the X-linked enzyme phosphoglycerate kinase (PGK-1) has been used to study regulation of X chromosome expression in the diploid derivatives of the trophectoderm at 8–8.5 days post coitum in the mouse. These derivatives included the chorionic ectoderm and the polar trophoblast. The biochemical analysis suggests that only the maternally derived X chromosome (Xm) is expressed in the diploid trophectoderm derivatives. Cell selection and maternal tissue contamination were ruled out as possible causes of the observed Xm expression. From these and other results, we conclude that all derivatives of the trophectoderm, along with the primitive endoderm, express only Xm, whereas derivatives of the primitive ectoderm show random X chromosome expression. 相似文献
34.
The content of cytochrome c-420 in Rhodospirillum rubrum chromatophores prepared by grinding with alumina is 5–10% of that in whole cells, and 20–40% in chromatophores by ‘French’ pressing.Flash-induced phosphorylation of various chromatophores which varied in cytochrome content from 7 to 40% is proportional to the cytochrome content. Extrapolating the cytochrome c-420 content to that observed in whole cells, a ratio near 1 is calculated. At low flash intensity the phosphorylation per flash is proportional to flash energy.Photophosphorylation in flashes given after a time of several minutes is only slightly dependent on the number of flashes. If the flashes are spaced from 0.1 to 10 s, relative phosphorylation in the first flash is about 70% and in the second 90% of that observed in the following flashes. Proton binding is not affected by the cytochrome c-420 content and a ratio of of 2.3 was found.These results can be explained by a working hypothesis in which charge separation occurring at one reaction centre and the resulting electron transport mediated amongst others by c-420, results in the injection of two protons into an ATPase, this in contrast to a chemiosmotic mechanism, where the protons are released in the chromatophore inner space. 相似文献
35.
J.-P. Villeneuve P. Mavier J.-G. Joly 《Biochemical and biophysical research communications》1976,70(3):723-728
Cytochrome P-450 was partially purified from liver microsomes obtained from control, ethanol, phenobarbital, and 3-methylcholanthrene-treated rats. Benzphetamine demethylation, benzpyrene hydroxylation and aniline hydroxylation activities were assayed in a reconstituted system using fixed amounts of reductase and lipids, and increasing amounts of cytochrome P-450 from each source. Cytochrome P-450 from ethanol-fed rats showed substrate specificity differing from cytochrome P-450 obtained from control, phenobarbital and 3-methylcholanthrene-treated rats. 相似文献
36.
A mutant form of erythrocyte hypoxanthine-guanine phosphoribosyltransferase with an abnormal isoenzyme pattern was found in a patient with a partial enzyme deficiency and X-linked gout. This abnormal pattern was a marker for the mutant enzyme in hemolysate from the heterozygote for the enzyme deficiency.These studies were generously supported by the Medical Research Council of Canada (MRC # MA4758) and the Canadian Arthritis and Rheumatism Society. 相似文献
37.
Delayed fluorescence from Rhodopseudomonas viridis membrane fragments has been studied using a phosphoroscope employing single, short actinic flashes, under conditions of controlled redox potential and temperature. The emission spectrum shows that delayed fluorescence is emitted by the bulk, antenna bacteriochlorophyll. The energy for delayed fluorescence, however, must be stored in a reaction-center complex including the photooxidized form (P+) of the primary electron-donor (P) and the photoreduced form (X?) of the primary electron-acceptor. This is shown by the following observations: (1) Delayed luminescence is quenched (a) at low redox potentials which allow cytochromes to reduce P+ rapidly after the flash, (b) at higher redox potentials which, by oxidizing P chemically, prevent the photochemical formation of P+X?, and (c) upon transfer of an electron from X? to a secondary acceptor, Y. (2) Under conditions that prevent the reduction of P+ by cytochromes and the oxidation of X? by Y, the decay kinetics of delayed fluorescence are identical with those of P+X?, as measured from optical absorbance changes.The main decay route for P+X? under these conditions has a rate-constant of approximately 103 s?1. In contrast, a comparison of the intensities of delayed and prompt fluorescence indicates that the process in which P+X? returns energy to the bulk bacteriochlorophyll has a rate-constant of 3.7 s?1, at 295 °K and pH 7.8. The decay kinetics of P+X? and delayed fluorescence change little with temperature, whereas the intensity of delayed fluorescence increases with increasing temperature, having an activation energy of 12.5 kcal · mol?1. We conclude that the main decay route involves tunneling of an electron from X? to P+, without the promotion of P to an excited state. Delayed fluorescence requires such a promotion, followed by transfer of energy to the bulk bacteriochlorophyll, and this combination of events is rare. The activation energy, taken with potentiometric data, indicates that the photochemical conversion of PX to P+X? results in increases of both the energy and the entropy of the system, by 16.6 kcal · mol?1 and 8.8 cal · mol?1 · deg?1. The intensity of delayed fluorescence depends strongly on the pH; the origin of this effect remains unclear. 相似文献
38.
39.
苏林娜刘向强吕丽芬聂勇战时永全 《现代生物医学进展》2014,14(10):1875-1878
目的:研究FXR在胃炎,胃粘膜肠化生及胃癌组织中的表达,分析其在胃癌发生中的意义。方法:采用免疫组化方法检测FXR在55例胃炎组织,61例胃黏膜肠化生组织及61例胃癌组织中的表达,利用统计学方法 SPSS17.0软件分析其在三种组织中的表达变化,结合文献回顾,分析FXR在胃癌发生中的意义。结果:FXR在胃黏膜肠化生中的表达明显高于胃炎组织(P0.05),而在胃癌组织中,FXR的表达显著低于胃粘膜肠化生组织(P0.05)。结论:FXR是一个潜在的胃癌发生生物标记物,其具体机制有待于进一步探索。 相似文献
40.