全文获取类型
收费全文 | 701篇 |
免费 | 79篇 |
专业分类
780篇 |
出版年
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 23篇 |
2015年 | 35篇 |
2014年 | 46篇 |
2013年 | 36篇 |
2012年 | 48篇 |
2011年 | 40篇 |
2010年 | 39篇 |
2009年 | 14篇 |
2008年 | 38篇 |
2007年 | 33篇 |
2006年 | 36篇 |
2005年 | 29篇 |
2004年 | 33篇 |
2003年 | 20篇 |
2002年 | 25篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 17篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 3篇 |
1967年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有780条查询结果,搜索用时 15 毫秒
1.
2.
Antti Huunan-Seppälä 《Journal of bioenergetics and biomembranes》1971,2(3-4):197-207
The effect of the polybasic substances Polybrene and spermine on the passive and active transport of monovalent cations in mitochondria was studied. These agents were found to stimulate the low amplitude swelling of mitochondria. Volume oscillations were induced by addition of substrate in the presence of spermine. In conditions where weak oscillations were obtained without these substances, oscillations were stimulated and their frequencies increased in the presence of Polybrene and spermine. Their effects were maximal with 100–300 moles spermine per litre and 3–5 mg Polybrene per litre. These results are discussed in relation to an interaction of the agents studied with membrane negative charges which may be important regulators of ion transport. 相似文献
3.
4.
Factors Influencing the Enhancement of the Infectivity of Poliovirus Ribonucleic Acid by Diethylaminoethyl-Dextran 总被引:22,自引:9,他引:13 下载免费PDF全文
The enhancement by diethylaminoethyl-dextran (DEAE-D) of the infectivity of poliovirus ribonucleic acid (RNA) for cell cultures was demonstrated by infective-center as well as by plaque assays, both in nonprimate (L) and primate cell systems (MK, HeLa, LLC-MK(2)). The sensitivity of plaque assays was greatly improved by using a tris (hydroxymethyl)aminomethane-buffered synthetic medium (basal medium Eagle) and freshly confluent cell monolayers. Enhancement of nucleic acid infectivity was directly dependent on the molecular weight of the DEAE-D. Two observations bearing on the action of DEAE-D appeared important: ribonuclease activity was reduced by DEAE-D, and cells pretreated with DEAE-D remained susceptible to infection with RNA in isotonic medium. Appreciable susceptibility of the treated cells persisted for at least 2 hr; the susceptible state could be reversed at will by an application of heparin. Enhancement of nucleic acid infectivity was independent of an effect of DEAE-D on intact virus and agar inhibitors. 相似文献
5.
6.
7.
Stability constants for the calcium-ion complexes of several methyl aldo-furanosides have been determined in aqueous solution by using a potentiostatic technique with an electrode that is selective for calcium ions. The results obtained have been verified by examining the chromatographic behaviour of the compounds on a strong cation-exchange resin in the Ca2+ form. The rate constants for the acid-catalyzed hydrolysis and methanolysis of a few 4-chlorophenyl aldofuranosides having different complexing abilities have been determined at various concentrations of calcium chloride. The dependences of the observed salt effects on the complexing ability of the substrate are discussed. 相似文献
8.
Siv Osterman-Golkar Antti Kautiainen Emma Bergmark Krystyna Hkansson Jorma Mki-Paakkanen 《Chemico-biological interactions》1991,80(3):291-302
Binding of 1,2-epoxy-3-butene, the primary metabolite of butadiene, to hemoglobin (Hb) and excretion of its mercapturic acid in urine were studies as potential indicators of butadiene exposure. Four groups of Wistar rats were exposed to butadiene at 0, 250, 500 and 1000 ppm 6 h/day, 5 days/week, during 2 weeks. Blood was collected at the end of exposure and 17 days later for analysis of hemoglobin adducts and adduct stability. Urine was collected each day during exposure (afternoon samples) and in between exposures (morning samples). Adducts of 1,2-epoxy-3-butene to N-terminal valine in Hb were measured using the N-alkyl Edman procedure and GC/MS of the thiohydantoin derivatives. The corresponding mercapturic acid was analysed, after deacetylation, through derivatization with phthaldialdehyde and HPLC with fluorescence detection. The Hb adducts proved to be stable and are therefore useful for dosimetry of long-term exposure to butadiene. The adduct levels increased linearly with exposure dose up to 1000 ppm (3 nmol/g Hb at 1000 ppm). The increase with exposure dose of the mercapturic acid concentration in urine was also compatible with a linear does response up to 1000 ppm. The sensitivity of both analytical methods needs to be improved for their application to human samples. 相似文献
9.
The Bacillus subtilis cytochrome-c oxidase. Variations on a conserved protein theme. 总被引:16,自引:0,他引:16
M Saraste T Metso T Nakari T Jalli M Lauraeus J Van der Oost 《European journal of biochemistry》1991,195(2):517-525
The structural genes of cytochrome-c oxidase in Bacillus subtilis have been isolated and sequenced. Five genes, ctaB-F, are closely spaced. ctaC, ctaD, ctaE and ctaF are the genes for subunits II, I, III and IVB, respectively, ctaB, which may encode an assembly factor, is separated and upstream from the others. In comparison to its mitochondrial counterparts, subunit I has an extended C-terminus with two additional transmembrane segments, whereas subunit III has lost two such segments from its N-terminus. The C-terminal extension in subunit II is a covalent cytochrome-c domain, previously characterized only in the thermophilic oxidases. Subunit IVB, a small hydrophobic protein, is a novel subunit. These predictions suggest that the B. subtilis cytochrome-c oxidase is structurally more related to the four-subunit Escherichia coli cytochrome-bo complex than, for instance, to the Paracoccus denitrificans enzyme. Cytochrome aa3, which was previously isolated from B. subtilis [de Vrij, W., Azzi, A. & Konings, W. N. (1983) Eur. J. Biochem. 131, 97-103] is not encoded by the ctaC-F genes; thus, there seems to be two different cytochrome-aa3-type oxidases in this Gram-positive bacterium. 相似文献
10.
We have used a gene replacement strategy to delete the previously isolated gene [(1987) EMBO J. 6, 2825-2833] for the cytochrome c oxidase subunit I from Paracoccus denitrificans. The resulting mutant was still able to synthesize active cytochrome c oxidase. This led us to look for another locus which could completely suppress the mutation. In this study we report the isolation of a second gene encoding subunit I. An open reading frame coding for cytochrome c 550 was found upstream from this gene. We suggest that there are isoenzymes of cytochrome c oxidase (cytochrome aa3) in this bacterium. 相似文献