全文获取类型
收费全文 | 407篇 |
免费 | 47篇 |
国内免费 | 3篇 |
专业分类
457篇 |
出版年
2021年 | 6篇 |
2019年 | 4篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 12篇 |
2011年 | 21篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 9篇 |
2002年 | 14篇 |
2001年 | 16篇 |
2000年 | 13篇 |
1999年 | 18篇 |
1998年 | 4篇 |
1997年 | 12篇 |
1996年 | 4篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 10篇 |
1974年 | 3篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 9篇 |
1969年 | 4篇 |
1967年 | 3篇 |
1954年 | 3篇 |
1939年 | 2篇 |
排序方式: 共有457条查询结果,搜索用时 15 毫秒
1.
2.
The ultrastructure of human spermatozoa at various stages of the freezing and thawing process was studied. In addition to conventional fixations, a freeze-substitution method was used to examine spermatozoa before they were thawed. Dilution in a glycerol-egg yolk-citrate medium caused slight swelling of the acrosome. During slow freezing, when large ice crystals grow in the diluent, the sperm plasmalemma became tighter, the mitochondria had more angular profiles and there was a reduction in electron density of the acrosomal contents. After thawing, the apical segment of the acrosome usually became swollen and the mitochondria appeared rounded. We deduce that these ultrastructural changes occur either during or after the thawing procedure. 相似文献
3.
K J Woolley 《European journal of biochemistry》1987,166(1):127-130
Two c-type cytochromes were isolated from cells of the gram-negative bacterium Aquaspirillum itersonii grown under low aeration in the presence of nitrate. The major component, cytochrome c-550, was equated with the (single) c-type cytochrome previously reported to be present in this organism [Clark-Walker, G. D. & Lascelles, J. (1970) Arch. Biochem. Biophys. 136, 153-159], although a significantly higher molecular mass was apparent in the present work. The complete amino acid sequence of this cytochrome is reported in the accompanying paper. A second soluble c-type cytochrome, designated c-556, was also isolated. The molecular mass, isoelectric point, spectrum, midpoint oxidation reduction potential and amino acid composition of this monoheam cytochrome are reported. The possible relationship of this cytochrome to other cytochromes c-556 is discussed. 相似文献
4.
PHYLOGENY OF THE SUBFAMILIES OF THE FAMILY BRACONIDAE (HYMENOPTERA: ICHNEUMONOIDEA): A REASSESSMENT 总被引:1,自引:0,他引:1
R.A. Wharton S.R. Shaw M.J. Sharkey D.B. Wahl J.B. Woolley J.B. Whitfield P.M. Marsh W. Johnson 《Cladistics : the international journal of the Willi Hennig Society》1992,8(3):199-235
Abstract— The recently published phylogeny of Braconidae by Quicke and van Achterberg is reassessed. Character-state definitions and character polarities are evaluated, and more rigorous methods are suggested. Our results indicate that there are many more parsimonious solutions to their data set, the consensus of which differs substantially from their results. Based on our reassessment, little can be said about the relationships among braconid subfamilies. Consensus trees show the cyclostomes as a largely unresolved basal grade. The two other major lineages which have been proposed, the helconoids and microgastroids, are somewhat better resolved, but not consistently so. Relationships among the helconoids vary considerably depending on the parameters used for parsimony analysis. 相似文献
5.
Susceptibility of cartilage collagens type II, IX, X, and XI to human synovial collagenase and neutrophil elastase 总被引:1,自引:0,他引:1
S J Gadher D R Eyre V C Duance S F Wotton L W Heck T M Schmid D E Woolley 《European journal of biochemistry》1988,175(1):1-7
The action of purified rheumatoid synovial collagenase and human neutrophil elastase on the cartilage collagen types II, IX, X and XI was examined. At 25 degrees C, collagenase attacked type II and type X (45-kDa pepsin-solubilized) collagens to produce specific products reflecting one and at least two cleavages respectively. At 35 degrees C, collagenase completely degraded the type II collagen molecule to small peptides whereas a large fragment of the type X molecule was resistant to further degradation. In contrast, collagen type IX (native, intact and pepsin-solubilized type M) and collagen type XI were resistant to collagenase attack at both 25 degrees C and 35 degrees C even in the presence of excess enzyme. Mixtures of type II collagen with equimolar amounts of either type IX or XI did not affect the rate at which the former was degraded by collagenase at 25 degrees C. Purified neutrophil elastase, shown to be functionally active against soluble type III collagen, had no effect on collagen type II at 25 degrees C or 35 degrees C. At 25 degrees C collagen types IX (pepsin-solubilized type M) and XI were also resistant to elastase, but at 35 degrees C both were susceptible to degradation with type IX being reduced to very small peptides. Collagen type X (45-kDa pepsin-solubilized) was susceptible to elastase attack at 25 degrees C and 35 degrees C as judged by the production of specific products that corresponded closely with those produced by collagenase. Although synovial collagenase failed to degrade collagen types IX and XI, all the cartilage collagen species examined were degraded at 35 degrees C by conditioned culture medium from IL1-activated human articular chondrocytes. Thus chondrocytes have the potential to catabolise each cartilage collagen species, but the specificity and number of the chondrocyte-derived collagenase(s) has yet to be resolved. 相似文献
6.
It is shown on the basis of the excluded-volume effect that inert macromolecules may be expected to suppress the dissociation of double-helical nucleic acids into single helices and thus to raise the melting point of the double helix. The rise in melting temperature of the ribonucleic acid [poly(I).poly(C)] caused by dextran polymers and by poly(ethylene oxide) is described and compared with the theoretical prediction. Good agreement was found in respect of the extent of the rise in melting point and in respect of its dependence upon polymer length. An additional dependence upon the identify of the polymer was attributed to detailed effects of shape in solution. 相似文献
7.
Histamine H2 receptors on chondrocytes derived from human, canine and bovine articular cartilage. 总被引:2,自引:0,他引:2 下载免费PDF全文
Histamine (1-100 microM) induced a concentration-dependent increase in intracellular cyclic AMP in monolayer cultures of human, canine and foetal-bovine articular chondrocytes. The dose-response curve for histamine in each culture was progressively displaced to the right with increasing concentrations of cimetidine, an H2-receptor antagonist. The histamine-induced cyclic AMP elevation in human articular chondrocytes was also significantly decreased by ranitidine, another H2 antagonist, but not by the H1 antagonists mepyramine and chlorpheniramine. These findings indicate that histamine activates chondrocyte adenylate cyclase through an H2 receptor. The cyclic AMP response of human chondrocytes to histamine was many times greater than that measured for synovial fibroblasts under similar conditions. Such findings suggest that mast-cell-chondrocyte interactions in vivo may contribute to changed chondrocyte metabolism in joint disease. 相似文献
8.
D W Cooper P A Woolley G M Maynes F S Sherman W E Poole 《Australian journal of biological sciences》1983,36(5-6):511-517
An investigation of genetic variation in the electrophoretic mobility of the enzyme alpha-galactosidase A (EC 3.2.1.22) has been carried out for 33 species of Australian metatherian (marsupial) mammals. The results are compatible with the enzyme being sex-linked in macropodids (kangaroos and wallabies) and probably in dasyurids (marsupial 'mice', etc.), as it is in eutherian (placental) mammals. The results also suggest that the mode of dosage compensation for this locus is the same as for other sex-linked loci in kangaroos, i.e. paternal X inactivation, rather than the random X inactivation system of eutherian mammals. The bearing of the enzyme mobility data on phylogenetic relationships among macropodid species is discussed. 相似文献
9.
Woolley JT 《Plant physiology》1971,47(5):656-662
Spectrophotometric transmittance and reflectance curves were recorded for wavelengths from 0.45 (in some cases 0.34) to 2.7 micrometers for faces and backs of leaves and for stacked leaves of several plant species. Measurements were made at different angles of illumination. Leaf spectrophotometric curves were compared with curves for leaf extracts, potato tuber tissue, glass beads in water, and frozen leaves to demonstrate the physical bases for the leaf curves. Leaves were infiltrated with liquids of different refractive indices for further comparison of spectrophotometric curves. Goniophotometric reflectance curves were recorded, giving visible reflectance and degree of polarization as functions of viewing angle for two different angles of illumination. 相似文献
10.