全文获取类型
收费全文 | 2687篇 |
免费 | 339篇 |
国内免费 | 2篇 |
专业分类
3028篇 |
出版年
2021年 | 25篇 |
2018年 | 27篇 |
2017年 | 24篇 |
2016年 | 47篇 |
2015年 | 53篇 |
2014年 | 64篇 |
2013年 | 104篇 |
2012年 | 92篇 |
2011年 | 91篇 |
2010年 | 73篇 |
2009年 | 71篇 |
2008年 | 84篇 |
2007年 | 85篇 |
2006年 | 84篇 |
2005年 | 95篇 |
2004年 | 85篇 |
2003年 | 83篇 |
2002年 | 96篇 |
2001年 | 90篇 |
2000年 | 98篇 |
1999年 | 69篇 |
1998年 | 52篇 |
1997年 | 40篇 |
1996年 | 39篇 |
1995年 | 40篇 |
1994年 | 51篇 |
1993年 | 38篇 |
1992年 | 70篇 |
1991年 | 57篇 |
1990年 | 90篇 |
1989年 | 81篇 |
1988年 | 54篇 |
1987年 | 62篇 |
1986年 | 49篇 |
1985年 | 47篇 |
1984年 | 41篇 |
1983年 | 34篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 23篇 |
1979年 | 40篇 |
1978年 | 24篇 |
1977年 | 29篇 |
1976年 | 24篇 |
1973年 | 32篇 |
1972年 | 34篇 |
1971年 | 37篇 |
1970年 | 26篇 |
1969年 | 30篇 |
1968年 | 24篇 |
排序方式: 共有3028条查询结果,搜索用时 15 毫秒
1.
2.
Summary Equivalent-circuit impedance analysis experiments were performed on the urinary bladders of freshwater turtles in order to quantify membrane ionic conductances and areas, and to investigate how changes in these parameters are associated with changes in the rate of proton secretion in this tissue. In all experiments, sodium reabsorption was inhibited thereby unmasking the electrogenic proton secretion process. We report the following: (1) transepithelial impedance is represented exceptionally well by a simple equivalent-circuit model, which results in estimates of the apical and basolateral membrane ionic conductances and capacitances; (2) when sodium transport is inhibited with mucosal amiloride and serosal ouabain, the apical and basolateral membrane conductances and capacitances exhibit a continual decline with time; (3) this decline in the membrane parameters is most likely caused by subtle time-dependent changes in cell volume, resulting in changes in the areas of the apical and basolateral membranes; (4) stable membrane parameters are obtained if the tissue is not treated with ouabain, and if the oncotic pressure of the serosal solution is increased by the addition of 2% albumin; (5) inhibition of proton secretion using acetazolamide in CO2 and HCO
3
–
-free bathing solutions results in a decrease in the area of the apical membrane, with no significant change in its specific conductance; (6) stimulation of proton transport with CO2 and HCO
3
–
-containing serosal solution results in an increase in the apical membrane area and specific conductance. These results show that our methods can be used to measure changes in the membrane electrophysiological parameters that are related to changes in the rate of proton transport. Notably, they can be used to quantify in the live tissue, changes in membrane area resulting from changes in the net rates of endocytosis and exocytosis which are postulated to be intimately involved in the regulation of proton transport. 相似文献
3.
4.
R M Dixon B T Golding S Mwesigye-Kibende D N Ramakrishna Rao 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1985,311(1152):531-544
The vitamin B12 coenzyme adenosylcobalamin assists the enzymic catalysis of molecular rearrangements of the type (formula; see text) in which the migrating group X can be OH, NH2 or a suitable substituted carbon atom such as C(=CH2)CO2H. This paper discusses evidence for the participation of organic radicals as intermediates in these reactions. Theoretical and model studies supporting the intermediacy of radicals in the reactions catalysed by the enzymes diol dehydratase and alpha-methyleneglutarate mutase are described. For the model studies, alkyl radicals, alkylcobaloximes (alkyl represents, for example, ethoxycarbonyl substituted, but-3-enyl and cyclopropylmethyl) and also dihydroxyalkylcobalamins have been investigated. The Co-C alpha-C beta angle of 125 degrees in adenosylcobalamin is shown to be an 'especial' angle by analysis of the crystal structures of R- and S-2,3-dihydroxypropylcobalamin. 相似文献
5.
6.
7.
Skeletal or cardiac muscle fibers can be separated by brief (3-5 second) dissociation of formalin-fixed pieces with a Willems Polytron (Brinkmann Instrument Co.). Such separated fibers are useful for demonstration of abnormal accumulations of lipids, carbohydrates, proteins and minerals in metabolic diseases. Staining techniques for demonstration of various stored materials include: 1) toluidine blue at pH 2.8 for acid mucopolysaccharide in skeletal muscle fibers in Pompe's glycogenesis 2,2) one-step trichrome stain for nemaline myopathy and for abnormal mitochondria in X-linked infantile cardiomyopathy, 3) periodic acid-methenamine silver stain for glycolipid-containing lysosomes in I-cell disease (mucolipidosis 2), 4) Sudan black B stain for lipid in skeletal muscle fibers in Reye's syndrome, infantile lactic acidosis, Leigh's infantile subacute necrotizing encephalopathy and Jansky-Bielschowsky late infantile ceroid lipofuscinosis, 5) iron stain for iron in cardiac and skeletal muscle fibers in thalassemia with advanced hemosiderosis, and 6) autofluorescence for “ceroid” in skeletal muscle fibers in Jansky-Bielschowsky disease. 相似文献
8.
9.
S. A. Krawetz R. A. Bricker W. Connor R. B. Church G. H. Dixon 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1988,75(3):402-409
Summary We have recently cloned both the bovine protamine (Krawetz et al. 1987, DNA 6: 47–57) and high mobility group (HMG-1) cDNAs (Pentecost and Dixon 1984, Bioscience Reports 4: 49–57). They have been used as probes for Restriction Fragment Length Polymorphism analysis of male-female pairs of different species and breeds, within the genus Bos. Utilizing this approach we have studied inheritance, chromosomal location and gene copy number of the bovine protamine and HMG-1 genes. This revealed that these nuclear protein genes are highly conserved suggesting that selective pressure has maintained their gene structures during evolution. A polymorphic Taq 1 restriction fragment was identified that was shown to be a heritable marker. These genes are not sex-linked and are present in a single copy for protamine and at least two copies for the HMG-1. 相似文献
10.
Rainbow trout protamines. Amino acid sequences of six distinct proteins from a single testis 总被引:3,自引:0,他引:3
All the protamines present in detectable amounts in a single mature testis from rainbow trout have been purified to homogeneity using acid extraction, gel filtration chromatography on Bio-Gel P-10, ion-exchange chromatography on carboxymethylcellulose and reverse-phase high-pressure liquid chromatography. Each of the six purified protamines was completely sequenced using automated gas-phase Edman degradation. Each protamine is two-thirds arginine and also contains proline, serine, valine and glycine. Three protamines also contain alanine while two contain isoleucine. Four of the protamines have 32 amino acids while the remaining two have 30. The six protamines have been classified into three families on the basis of their amino acid sequences. 相似文献