全文获取类型
收费全文 | 4242篇 |
免费 | 364篇 |
国内免费 | 2篇 |
出版年
2023年 | 14篇 |
2022年 | 20篇 |
2021年 | 84篇 |
2020年 | 45篇 |
2019年 | 49篇 |
2018年 | 58篇 |
2017年 | 60篇 |
2016年 | 99篇 |
2015年 | 219篇 |
2014年 | 185篇 |
2013年 | 248篇 |
2012年 | 365篇 |
2011年 | 297篇 |
2010年 | 204篇 |
2009年 | 134篇 |
2008年 | 239篇 |
2007年 | 259篇 |
2006年 | 214篇 |
2005年 | 220篇 |
2004年 | 230篇 |
2003年 | 212篇 |
2002年 | 195篇 |
2001年 | 43篇 |
2000年 | 31篇 |
1999年 | 40篇 |
1998年 | 88篇 |
1997年 | 35篇 |
1996年 | 45篇 |
1995年 | 34篇 |
1994年 | 42篇 |
1993年 | 30篇 |
1992年 | 34篇 |
1991年 | 24篇 |
1990年 | 41篇 |
1989年 | 35篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 33篇 |
1983年 | 33篇 |
1982年 | 40篇 |
1981年 | 27篇 |
1980年 | 33篇 |
1979年 | 22篇 |
1978年 | 13篇 |
1977年 | 23篇 |
1976年 | 17篇 |
1974年 | 16篇 |
1971年 | 10篇 |
排序方式: 共有4608条查询结果,搜索用时 15 毫秒
91.
Jacqueline S. Weinman Claude L. Gallien Dominique P. Rainteau Michèle Guyot Serge J. Weinman Jacques G. Demaille 《Developmental biology》1984,101(1):73-85
Calmodulin isolated and purified to homogeneity from young larvae is very similar to that obtained from adult Pleurodeles waltlii and these proteins are almost identical to previously described vertebrate calmodulins. During P. waltlii development, an increase in total individual calmodulin content is observed after the heart beating stage. In dorsal axial muscle, calmodulin level which is very high at the beginning of larval life (premetamorphosis) decreases strikingly in the first part of prometamorphosis. Such an evolution is observed in Ambystoma mexicanum too. Then, a significant increase occurs during metamorphosis. In contrast, calmodulin level in P. waltlii cardiac ventricular muscle increases continuously from hatching to the end of metamorphic climax. Thyroxine treatment which promotes precocious metamorphosis in P. waltlii and experimental metamorphosis in neotenic A. mexicanum, induces a rapid and significant increase in muscle calmodulin concentration. 相似文献
92.
What's new in lysozyme research? 总被引:49,自引:0,他引:49
The present review is focused on the main achievements realized in the lysozyme research field since the meeting held in 1972 to commemorate the fiftieth anniversary of the discovery of this enzyme. Despite of extensive structural, physico-chemical, crystallographic, genetic, immunological and evolutionary studies devoted to lysozymes, their biological role is still not exactly known. 相似文献
93.
94.
It was found that genetic recombination occurs if two marked strains of Streptomyces griseus (leukaemomycin-producing strains IMET JA 3933 and IMET JA 5142) are grown together in mixed cultures on semisolid media. The crossing techniques used and the method for carrying out selective analysis were essentially the same as those described by HOPWOOD (1967, 1972). The parent strains used for crosses were marked with single or double nutritional requirements and with mutations for drug resistance. The crosses are quite self-sterile, yielding only in one combination stable prototrophic recombinants at a low frequency (10(-5) to 10(-6)). The majority of recombinants behaved as stable haploid genotypes. A series of four-point crosses of different types of auxotrophs was carried out. The results of these experiments do not provide sufficient data for constructing a chromosome map, but provide basic information on the possibilities of genetic analysis of the production of anthracycline antibiotics. The majority of crosses performed were not fertile at 28 degrees C but, surprisingly, in some crosses carried out at 34 degrees C viable colonies were detected on minimal media at frequencies from 10(-3) to 10(-2). 相似文献
95.
The products synthesized in vitro by messenger RNA (mRNA) extracted from Nicotiana sylvestris were analyzed by electrophoresis on polyacrylamide slab gels. Only three of the major polypeptides synthesized are considered here: P55, P32, and P20. P55 and P32 were translated from chloroplast mRNA. P55 corresponds to the large subunit of ribulose-1,5-bisphosphate (RuP2) carboxylase; P32 is probably a chloroplast membrane protein. P20, the polypeptide synthesized from cytoplasmic poly(A)+ RNA, is the precursor of the small subunit of RuP2 carboxylase. The balance between P20 and P32, in which their relative proportions varied inversely, was regulated by the age of the leaves and the time of illumination; we took advantage of this phenomenon to isolate the mRNA from the small subunit in relatively large amounts. This mRNA has a molecular weight of 350,000.Abbreviations RuP2
ribulose-1,5-bisphosphate
- mRNA
messenger RNA
- SDS
sodium dodecyl sulfate 相似文献
96.
W F Fleck 《Zeitschrift für allgemeine Mikrobiologie》1980,20(2):105-112
In order to obtain high-producing mutants of the lambdamycin producer Streptomyces glaucoachromogenes IMET 31 118, a new selection technique using the thermophilic phage-host system Tal/Thermoactinomyces vulgaris, was developed. Lambdamycin is a yellow-green pigment antibiotic of the chromoglycoside type with antimicrobial, antiviral, cancerostatic, and ergotropic activity in vitro and in vivo. The physicochemical properties of lambdamycin resemble those of chartreusin. By means of the selection technique developed the determination of the concentration-dependent influence of lambdamycin on bacterial growth inhibition and Tal-phage development in the agar diffusion sphere of mutagen-treated colonies is possible without time and material-consuming pre-tests. A positive correlation exists between the biosynthetic capacity of mutants on solid media and in fermentation liquors. Using this new selection technique, the titres of lambdamycin in fermentation liquors of mutants could be increased by 10 to 20 fold in comparison to the wild type strain. 相似文献
97.
The reduction of cytochrome c by beef liver sulfite oxidase was found to be strongly inhibited by high ionic strength, indicating the importance of electrostatic interactions to the reaction. The reaction rates of sulfite oxidase with singly trifluoroacetylated or trifluoromethylphenylcarbamylated cytochrome c derivatives were studied to determine the role of individual lysines in the reaction. The reaction rate was decreased by modification of the lysines immediately surrounding the heme crevice, the decreases following the order: Lys 13 > Lys 25 Lys 79 ≈ Lys 87 > Lys 8 ≈ Lys 27 ≈ Lys 72. Modification of lysines 22, 55, 88, 99, and 100 had no effect on the reaction rate. These results indicate that the interaction site on cytochrome c for sulfite oxidase is at the heme crevice region, and overlaps considerable with that for cytochrome oxidase. 相似文献
98.
David E. Moody Jacqueline L. James Edward A. Smuckler 《Biochemical and biophysical research communications》1980,97(2):673-679
Treatment of male rats with carbon tetrachloride, bromotrichloromethane, chloroform, 1,2-dibromoethane, 1-bromo-2-chloroethane, and 1,2-dibromo-3-chloropropane results in a decrease in cytochrome P-450 content and alterations in the relative content of fatty acids in hepatic microsomes. A high correlation was found between the loss of cytochrome P-450, the decrease in arachidonic acid (r=0.93), and the increases in linoleic (r=?0.91) and oleic acids (r=?0.89). 相似文献
99.
Summary The effect of aging on the morphology and function of the thyroid gland of the cream hamster was studied by light and electron microscopy coupled with autoradiography or histochemistry.Morphologically, aging induces an accumulation of lysosomal dense bodies and a loss of the phagocytosis of colloid droplets after stimulation with TSH. Iodine uptake and organification occur normally and thyroglobulin synthesis, estimated by autoradiography with 3H-leucine, is not different from that observed in young animals. The basal T4 and T3 plasma levels are lower in the old animals. A low iodine diet administered for several months prevents the age related accumulation of lysosomal dense bodies. Hormone secretion seems to proceed by two different mechanisms; phagocytosis of colloid droplets, the classical mechanism that decreases with age, and an additional mechanism, probably micropinocytosis, that is maintained during the whole lifespan.Presented at the First French Congress of Endocrinology, Montpellier, September 1980Work was performed under contracts n 3.4523.79 and n 3.4512.80 of the Fonds de la Recherche Scientifique Médicale, thanks to a grant of the Ministère Belge de la Politique Scientifique (Action concertée) and with the help of the Fondation Interuniversitaire pour la Recherche du Processus du Vieillissement, Belgium 相似文献
100.