全文获取类型
收费全文 | 5186篇 |
免费 | 329篇 |
国内免费 | 2篇 |
专业分类
5517篇 |
出版年
2023年 | 33篇 |
2022年 | 56篇 |
2021年 | 96篇 |
2020年 | 63篇 |
2019年 | 91篇 |
2018年 | 118篇 |
2017年 | 107篇 |
2016年 | 137篇 |
2015年 | 262篇 |
2014年 | 258篇 |
2013年 | 414篇 |
2012年 | 432篇 |
2011年 | 416篇 |
2010年 | 246篇 |
2009年 | 208篇 |
2008年 | 347篇 |
2007年 | 320篇 |
2006年 | 275篇 |
2005年 | 268篇 |
2004年 | 232篇 |
2003年 | 232篇 |
2002年 | 212篇 |
2001年 | 34篇 |
2000年 | 25篇 |
1999年 | 49篇 |
1998年 | 57篇 |
1997年 | 36篇 |
1996年 | 39篇 |
1995年 | 38篇 |
1994年 | 36篇 |
1993年 | 21篇 |
1992年 | 25篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 25篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 21篇 |
1985年 | 12篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 15篇 |
1974年 | 8篇 |
1971年 | 9篇 |
排序方式: 共有5517条查询结果,搜索用时 0 毫秒
51.
De Giovanni C Nicoletti G Galli MC Nanni P 《Bollettino della Società italiana di biologia sperimentale》1979,55(2):117-121
A method for determining cytoplasmic progesterone receptor was standardized in normal human endometrium comparing two different tracers, 3H-progesterone (3H-P) and 3H-medroxyprogesterone acetate (3H-MAP), a synthetic progestin which does not bind to Corticosteroid Binding Globulin (CBG). Receptor assays were performed as previously reported for 17beta-estradiol receptor, with slight modifications: incubation lasted 1 hr at 0 degree C, followed by 5 min DCC exposure under the same conditions. When 3H-P was employed as tracer, blanks performed with cold MAP gave similar results as using cortisol in incubation tubes and progesterone and cortisol in blanks. 3H-MAP was a good tracer for progesterone receptor because it neither bound to CBG nor to androgen or cortisol receptors; it had very high affinity and specificity for P-R; it was not metabolized by cytosol at 0 degree C and, finally, it detected receptor amounts quite comparable to those obtained using 3H-P. 相似文献
52.
Pasquale Petrilli Pietro Pucci Anna Maria Garzillo Giovanni Sannia Dr. Gennaro Marino 《Molecular and cellular biochemistry》1981,35(2):121-128
Summary Reactivity of sulphydryl groups of cytosolic and mitochondrial aspartate aminotransferases from ox heart has been studied.
A total of 5 and 7 cysteine residues per monomer are present in cAATo and mAATo, respectively. In native conditions only a
single sulphydryl group can be titrated by Nbs2 while the catalytic activity remains unchanged, however in the mitochondrial isozyme the reactivity depends on the functional
state of the enzyme. Reactivity toward NEM reveals the existence of a syncatalytic sulphydryl group in the cytosolic isozyme.
Titration of cAATo with pMB at pH 8 and pH 5 confirms the existence of two exposed sulphydryl groups with a different reactivity.
The results compared with those reported on the corresponding isozymes from pig and chicken heart show that syncatalytic sulphydryl
groups are of general occurrence in these enzymes. 相似文献
53.
Giovanni Felice Azzone Stefano Massari Tullio Pozzan 《Molecular and cellular biochemistry》1977,17(2):101-112
Summary The evidence that all energy transducing membranes can generate a proton electrochemical potential difference,
H, across the membrane and that this potential can be used to transfer energy among energy transducing units and to generate ATP, has increased the interest for the view that
H plays an obligatory role in energy transduction and ATP synthesis. In the present article we shall concentrate on two experimental questions related with the generation and role of
H: (a) the charge/site ratio; (b) the relation between the proton electrochemical potential on one side and the cation electrochemical potential, the phosphate potential and the redox potential on the other. We shall then discuss the view that energy transduction corresponds to a molecular energy machine rather than to a fuel cell. 相似文献
54.
Giovanni Romeo 《Human genetics》1977,39(3):261-276
Summary In four of the five autosomal dominant porphyrias four different partial enzymatic defects of the porphyrin biosynthetic pathway have been discovered in the last few years. With the exception of protoporphyria, the residual enzymatic activity in carriers of these defects is approximately equal to 50% of that found in controls. In each case the pattern of excretion of porphyrin and/or porphyrin precursors reflects the site of the partial metabolic block. There are indications, at least in intermittent acute porphyria, that the degree of penetrance of the disorder varies according to the level of phenotypic expression, being highest for the enzyme deficiency, lower for the excretion of precursors and lowest for the clinical symptoms. It is proposed that environmental factors, and probably also gene interaction, are the cause of the different degrees of penetrance.On leave from the University of Naples, Italy 相似文献
55.
Alessandro Zuddas Germano Oberto Francesca Vaglini Flavia Fascetti Francesco Fornai Giovanni U. Corsini 《Journal of neurochemistry》1992,59(2):733-739
In cynomologus monkeys, systemic administration of MK-801, a noncompetitive antagonist for the N-methyl-D-aspartate receptor, prevented the development of the parkinsonian syndrome induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MK-801 also attenuated dopamine depletion in the caudate and putamen and protected dopaminergic neurons in the substantia nigra from the degeneration induced by the neurotoxin. Nevertheless, 7 days after MPTP administration in the caudate and putamen of monkeys also receiving MK-801, the levels of toxic 1-methyl-4-phenylpyridinium were even higher than those measured in monkeys receiving MPTP alone. This indicates that the protective action of MK-801 is not related to MPTP metabolism and strongly suggests that, in primates, the excitatory amino acids could play a crucial role in the mechanism of the selective neuronal death induced by MPTP. 相似文献
56.
Giovanni Spinelli Marialuisa Melli Eva Arnold Caterina Casano Fabrizio Gianguzza Mirella Ciaccio 《Journal of molecular biology》1980,139(2):111-122
Sea urchin RNA extracted from early and mesenchyme blastula embryos and oocytes and fractionated on denaturing sucrose density gradients, was hybridized with histone DNA recombinants of Psammechinus miliaris (clone λh22) and of Paracentrotus lividus (clone pPH70). Histone sequences are found in the 9 S and larger than 9 S regions of the formamide/sucrose density gradients. The melting of the RNA-DNA duplexes obtained by hybridization of polysomal and high molecular weight RNA of embryos of P. lividus at the stage of early blastula, suggests a degree of heterogeneity in the high Mr RNA. The high Mr RNA contains at least four of the five histone gene sequences covalently linked. 相似文献
57.
Carmen Attolini Giorgio Mazza Adriana Fortunato Giovanni Ciarrocchi Giorgio Mastromei Silvano Riva Arturo Falaschi 《Molecular & general genetics : MGG》1976,148(1):9-17
Summary The dnaP strains of Bacillus subtilis are altered in the initiation of DNA replication at high temperature (Riva et al., 1975). Fine mapping of the gene shows that it is located very close to the dnaF gene, described by Karamata and Gross (1970) and mapped by Love et al. (1976) in the polC region. The phenotype of both mutants is indistinguishable: the DNA synthesis stops at non permissive temperature after synthesizing an amount of DNA equivalent to the completion of the rounds of replication already initiated; at permissive temperature they are abnormally sensitive to MMS and are reduced in the ability to be transformed. Both mutants are to be considered as belonging to the dnaF locus.The dnaF gene is very close to the polC gene, which specifies the DNA polymerase III of B. subtilis. The DNA polymerase III of the dnaF mutants is not temperature sensitive in vitro, however, the level of this enzyme is lower by a factor of 4 or 5 in the dnaF mutants, at the permissive temperature. Following shift of dnaF cultures to the non permissive temperature, the level of DNA polymerase III activity specifically decreases further by a factor of at least 10 in the mutant, whereas the DNA polymerase I level is unaffected.The possible roles of the dnaF gene in the control of the cellular level of the DNA polymerase III, and the possibility of a regulatory role of DNA polymerase III in the initiation of DNA replication in bacteria are discussed.Abbreviations and symbols HPUra
6-(p-hydroxyphenylazo)-uracil; mic, minimum inhibitory concentration
- MMS
methyl-methanesufonate
- Pol I
Pol II and Pol III: DNA polymerase I, II and III respectively
- PCMB
parachloro-mercuri-benzoate 相似文献
58.
Giovanni Vidari Maria De Bernardi Paola Vita-Finzi Giovanni Fronza 《Phytochemistry》1976,15(12):1953-1955
Six sesquiterpene lactones were isolated from Lactarius blennius. The structures of two new sesquiterpenes, blennin A and blennin B were determinated by spectroscopic methods and the structure of the seco-compound, blennin C, is revised. The two known furan sesquiterpenes and lactarorufin A were also identified. 相似文献
59.
Umberto Tomati Giovanni Giovannozzi-Sermanni Silvestro Duprè Carlo Cannella 《Phytochemistry》1976,15(5):597-598
The NADH: nitrate reductase from durum wheat leaves was inactivated by cyanide and its activity restored by thiosulphate and beef kidney rhodanese. Rhodanese and thiosulphate, added to NADH-nitrate reductase before cyanide treatment protected NADH-nitrate reductase activity. No oxidizing agent was required for the protection or restoration of cyanide treated NADH-nitrate reductase. 相似文献
60.