全文获取类型
收费全文 | 1559篇 |
免费 | 193篇 |
国内免费 | 1篇 |
出版年
2021年 | 25篇 |
2020年 | 14篇 |
2019年 | 17篇 |
2018年 | 22篇 |
2017年 | 23篇 |
2016年 | 30篇 |
2015年 | 49篇 |
2014年 | 60篇 |
2013年 | 77篇 |
2012年 | 81篇 |
2011年 | 80篇 |
2010年 | 66篇 |
2009年 | 45篇 |
2008年 | 76篇 |
2007年 | 53篇 |
2006年 | 59篇 |
2005年 | 64篇 |
2004年 | 55篇 |
2003年 | 57篇 |
2002年 | 46篇 |
2001年 | 52篇 |
2000年 | 41篇 |
1999年 | 29篇 |
1998年 | 30篇 |
1997年 | 17篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 11篇 |
1992年 | 36篇 |
1991年 | 37篇 |
1990年 | 22篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 18篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1974年 | 14篇 |
1973年 | 15篇 |
1972年 | 22篇 |
1970年 | 9篇 |
1966年 | 13篇 |
排序方式: 共有1753条查询结果,搜索用时 562 毫秒
51.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
52.
53.
A. L. Archibald C. S. Haley J. F. Brown S. Couperwhite H. A. McQueen D. Nicholson W. Coppieters A. Van de Weghe A. Stratil A. K. Winterø M. Fredholm N. J. Larsen V. H. Nielsen D. Milan N. Woloszyn A. Robic M. Dalens J. Riquet J. Gellin J. -C. Caritez G. Burgaud L. Ollivier J. -P. Bidanel M. Vaiman C. Renard H. Geldermann R. Davoli D. Ruyter E. J. M. Verstege M. A. M. Groenen W. Davies B. Høyheim A. Keiserud L. Andersson H. Ellegren M. Johansson L. Marklund J. R. Miller D. V. Anderson Dear E. Signer A. J. Jeffreys C. Moran P. Le Tissier Muladno M. F. Rothschild C. K. Tuggle D. Vaske J. Helm H. -C. Liu A. Rahman T. -P. Yu R. G. Larson C. B. Schmitz 《Mammalian genome》1995,6(3):157-175
A linkage map of the porcine genome has been developed by segregation analysis of 239 genetic markers. Eighty-one of these markers correspond to known genes. Linkage groups have been assigned to all 18 autosomes plus the X Chromosome (Chr). As 69 of the markers on the linkage map have also been mapped physically (by others), there is significant integration of linkage and physical map data. Six informative markers failed to show linkage to these maps. As in other species, the genetic map of the heterogametic sex (male) was significantly shorter (16.5 Morgans) than the genetic map of the homogametic sex (female) (21.5 Morgans). The sex-averaged genetic map of the pig was estimated to be 18 Morgans in length. Mapping information for 61 Type I loci (genes) enhances the contribution of the pig gene map to comparative gene mapping. Because the linkage map incorporates both highly polymorphic Type II loci, predominantly microsatellites, and Type I loci, it will be useful both for large experiments to map quantitative trait loci and for the subsequent isolation of trait genes following a comparative and candidate gene approach. 相似文献
54.
55.
The topologic arrangement of petiolar bundles varies within the length of the cottonwood petiole. Each petiolar bundle is formed by the subdivision and aggregation of acropetally differentiating subsidiary bundles in a predictable pattern. The subsidiary bundles provide vascular continuity between the stem and specific portions of the leaf lamina. Spot-labeling of individual veins with 14CO2, freeze substitution, and microautoradiography were used to establish the relation between the secondary veins of the lamina and the vasculature of the petiole. Within the petiole vasculature each subsidiary bundle was continuous with a specific portion of the lamina and seemed to have a separate function. Subsidiary bundles continuous with the central leaf trace were closely related functionally to the tip region of the lamina, while the subsidiary bundles continuous with the lateral leaf traces were functionally related to the middle and basal portions of the lamina. 相似文献
56.
Brent R. Larson 《Life sciences》1982,30(12):1003-1012
Presented is a pilot project describing a new strategy for mass spectrometric peptide sequencing. Using orthophthalaldehyde (OPA), two peptides were derivatized and their fluorescent adducts isolated using reversed phase high performance liquid chromatography. The OPA-peptides were permethylated and the derivatized molecules subjected to direct probe mass spectral analysis. The spectra obtained from the OPA-peptides was analogous to those observed for standard -acyl permethyl derivatives enabling the complete sequence of the peptides to be determined. 相似文献
57.
A mature medusa of Velella velella (Linnaeus, 1758) is reportedfor the first time from the North Atlantic; previously adultmedusae were known only from the Mediterranean. This specimen,collected by SCUBA divers, is the largest specimen recordedto date. Distinctive features are: two opposite adaxial-axialpairs of perradial capitate tentacles; two marginal bulbs lackingtentacles; conical manubrium with 4 perradial longitudinal gonads;perradial exumbrellar cnidae tracts; cnidome of stenoteles andmacrobasic euryteles; and zooxanthellae within the subumbrella.Since this specimen was collected near the surface and has zooxanthellae,it is likely that V. velella medusae are epipelagic. 相似文献
58.
The antigen used in an immunodiffusion test to diagnose infectious bovine rhinotracheitis has been purified by affinity chromatography. The homogeneity of the antigen was indicated by sedimentation rate and sedimentation equilibrium experiments. A So20,w of 0.749 was determined and a molecular weight of 8900 was calculated from sedimentation equilibrium analysis. The purified antigen formed precipitin lines of identity with crude diagnostic antigen. Purified antigen remained serologically active in the immunodiffusion test after lyophilization and subsequent reconstitution. 相似文献
59.
H E Larson J V Parry A B Price D R Davies J Dolby D A Tyrrell 《BMJ (Clinical research ed.)》1977,1(6071):1246-1248
A girl aged 12 developed pseudomembranous colitis after a short course of oral penicillin. She had no history of adverse reaction to penicillin before or after the illness. No pathogenic bacteria, mycoplasmas, or viruses were found in her faeces, but they did contain a toxin. Toxin was also found in four of five other patients with pseudomembranous colitis but not in six specimens obtained from patients with diarrhoea caused by other disorders. Further studies may show that pseudomembranous colitis is caused by a bacterial toxin. 相似文献
60.