全文获取类型
收费全文 | 5403篇 |
免费 | 471篇 |
国内免费 | 1篇 |
专业分类
5875篇 |
出版年
2022年 | 38篇 |
2021年 | 64篇 |
2020年 | 69篇 |
2019年 | 67篇 |
2018年 | 99篇 |
2017年 | 73篇 |
2016年 | 106篇 |
2015年 | 186篇 |
2014年 | 189篇 |
2013年 | 308篇 |
2012年 | 317篇 |
2011年 | 321篇 |
2010年 | 230篇 |
2009年 | 181篇 |
2008年 | 247篇 |
2007年 | 262篇 |
2006年 | 268篇 |
2005年 | 228篇 |
2004年 | 228篇 |
2003年 | 243篇 |
2002年 | 242篇 |
2001年 | 70篇 |
2000年 | 59篇 |
1999年 | 92篇 |
1998年 | 76篇 |
1997年 | 48篇 |
1996年 | 58篇 |
1995年 | 60篇 |
1994年 | 56篇 |
1993年 | 54篇 |
1992年 | 57篇 |
1991年 | 39篇 |
1990年 | 46篇 |
1989年 | 47篇 |
1988年 | 41篇 |
1987年 | 47篇 |
1986年 | 40篇 |
1985年 | 49篇 |
1984年 | 62篇 |
1983年 | 41篇 |
1982年 | 60篇 |
1981年 | 43篇 |
1980年 | 60篇 |
1979年 | 42篇 |
1978年 | 41篇 |
1977年 | 36篇 |
1976年 | 34篇 |
1975年 | 31篇 |
1974年 | 31篇 |
1973年 | 30篇 |
排序方式: 共有5875条查询结果,搜索用时 0 毫秒
61.
Summary Inward-rectifier channels in cardiac cells (I
K1) stabilize the resting membrane potential near the K equilibrium potential. Here we investigate the role ofI
K1 in the regulation of action potentials and link this to the influx of Ca during beating. Inward Ca current alters the open-channel probability of outwardI
K1 current. Thus Ca ions depolarize cells not only by carrying an inward current but also by blocking an outward current. 相似文献
62.
Synopsis Recent sampling programs conducted in the estuaries of the Eastmain and La Grande rivers (James Bay) and the Great Whale, Little Whale, Innuksuac and Povungnituk rivers (Hudson Bay) revealed patterns of coregonine fish distribution that differ from previous observations. The relative abundance of cisco, Coregonus artedii, and lake whitefish, C. clupeaformis, varied among rivers but did not reveal a latitudinal cline. Previous sampling programs underestimated the abundance of cisco in the Little Whale River. In addition, cisco was the third most abundant species captured in the Povungnituk River, situated 200 km to the north of the previously proposed northern limit at Innuksuac River. As such, the low abundances of cisco in the Great Whale and Innuksuac rivers cannot be attributed to a physiological inability to cope with a reduced growing season. Immature cisco were almost totally absent from the estuaries of the Hudson Bay rivers following spring breakup whereas immature lake whitefish made up 100% of the catch in the Innuksuac River at the same time of year. Species-specific migration patterns in Hudson Bay that differ from those observed in James Bay and the existence of unique juvenile overwintering rivers are 2 hypotheses proposed to explain the discontinuous age-class distribution of cisco and lake whitefish observed in Hudson Bay.Contribution to the program of GIROQ (Groupe Interuniversitaire de Recherche Océanographique du Québec). 相似文献
63.
Full-length sequence and mosaic structure of a human immunodeficiency virus type 1 isolate from Thailand. 总被引:15,自引:9,他引:6
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J K Carr M O Salminen C Koch D Gotte A W Artenstein P A Hegerich D St Louis D S Burke F E McCutchan 《Journal of virology》1996,70(9):5935-5943
Human immunodeficiency virus type 1 isolates of envelope genotype E are contributing substantially to the global pandemic. These strains appear to be mosaics, with the gag gene from clade A and the envelope from clade E; the parental clade E strain has not been found. Here we report the first full genomic sequence of one such mosaic virus, isolate CM240 from Thailand. Multiple breakpoints between the two parental genotypes have been found in a CM240 virus. The entire gag-pol region and most, if not all, of the accessory genes vif, vpr, tat, rev, and vpu appear to derive from clade A. The genotype switches to E shortly after the signal peptide of the envelope and back to clade A near the middle of gp41; thus, the portion of the envelope that lies on the cytoplasmic side of the membrane appears to be principally derived not from clade E, as previously thought, but from clade A. Another small segment not belonging to any recognized clade and presumably also contributed by the parental E strain has been found in the long terminal repeat. It may be significant that the implied virion structure resembles a pseudotype virus with the matrix and core from one clade and the outer envelope from another. In the long terminal repeat, differences were observed between CM240 and other clades in the number of NF-kappa B binding sites, the sequence of the TATA box, and the putative secondary structure of the transactivation response region stem-loop. The mosaic structure of a CM240 virion is suggestive of phenotypic differences which might have contributed to the emergence of this variant. 相似文献
64.
Integrated Genetic Map of Anopheles Gambiae: Use of Rapd Polymorphisms for Genetic, Cytogenetic and Sts Landmarks 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Randomly amplified polymorphic DNA (RAPD) markers have been integrated in the genetic and cytogenetic maps of the malaria vector mosquito, Anopheles gambiae. Fifteen of these markers were mapped by recombination, relative to microsatellite markers that had been mapped previously. Thirty-four gel-purified RAPD bands were cloned and sequenced, generating sequence tagged sites (STSs) that can be used as entry points to the A. gambiae genome. Thirty one of these STSs were localized on nurse cell polytene chromosomes through their unique hybridization signal in in situ hybridization experiments. Five STSs map close to the breakpoints of polymorphic inversions, which are notable features of the Anopheles genome. The usefulness and limitations of this integrated mosquito map are discussed. 相似文献
65.
Olivier Cohen Christine Cans Jean Louis Gilardi Hubert Roth Marie-Ange Mermet Pierre Jalbert Jacques Demongeot Martine Cuillel 《Human genetics》1996,97(5):659-667
Reciprocal translocations (rcp) are among the most common constitutional chromosomal aberrations in man. Using a European
database of 1574 families carrying autosomal rcp, a cartographic study was done on the breakpoints involved. The breakpoints
are non-randomly distributed along the different chromosomes, indicating “hot spots”. Breakpoints of rcp that result in descendants
that are unbalanced chromosomally at birth are more frequent in a distal position on chromosomal arms, and 65% of them are
localised in R-bands. Among the R-bands, bands rich in GC islands and poor in Alu repetitive sequences are more frequently
the site of breakpoints, as well as bands that include a fragile site. This result suggests that the variation in degree of
methylation in GC islands could be involved in chromosomal breakage and hence in chromosomal rearrangements.
Received: 10 April 1995 / Revised: 1 July 1995 相似文献
66.
67.
Frenette Jean-Jacques; Demers Serge; Legendre Louis; Boule Michel 《Journal of plankton research》1996,18(1):45-61
Phytoplankton photosynthetic responses were studied in two basinsof an oligotrophic lake (Québec, Canada). which are characterizedby the absence (shallow Basin 1) and presence (deeper Basin2) of seasonal thermal stratification. Size-fractionated photosynthesiswas used to characterize changes in phytoplankton characteristicsduring periods of seasonal mixing and stratification. Seasonalvariations of P max showed size-related differences, with maximumvalues in July for the picoplankton and in November for thenanoplankton. Similar patterns of variability in 相似文献
68.
Conserved function of anopheles gambiae midgut-specific promoters in the fruitfly. 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Control of malaria by a methodology that would permit the effective blockage of the Anopheles gambiae midgut wall penetration by Plasmodium parasites requires a detailed understanding of both the physiology of the mosquito's digestion, and of the interactions between the parasite and its host. We have transformed Drosophila melanogaster with several constructs that allow the study of the promoter region of two of the major late trypsin genes of A. gambiae. Using several deletions, we have identified, for both genes, small genomic segments that are sufficient to confer tissue specificity to the promoter in a species that is far away in evolution from the mosquito. This will allow further studies that will enable both the understanding of the blood meal digestion, and may potentially be useful for the design of anti-plasmodial constructs at a later stage. 相似文献
69.
Louis I. Dublin 《Obesity (Silver Spring, Md.)》1995,3(1):107-112
The very expression “well built” has become a part of our language. It implies that persons of a particular build or structure are better coordinated or somehow can function better than other people and may, therefore, be expected to have a greater life span. Variations in the structure of individuals are marked and serve to distinguish fairly definite types. Insurance experience has crystallized into a number of fairly definite conclusions with regard to the relative longevity of certain of these types. Extremes of stature, for example, are decided handicaps. Extreme overweight and underweight carry with them increased mortality and correspondingly shorter life. Very heavy people are more likely to succumb prematurely to such conditions as diabetes, organic heart disease, renal impairment, hardening of the arteries, and very light persons, particularly at the younger ages, are more likely to develop tuberculosis. Insurance experience has confirmed the popular judgment that the individuals who approach the mean of these body measures are better able to withstand the hazards of life and to round out a fairly full expectation. 相似文献
70.
Pradip Bhatnagar William Huffman Andrew King Louis Pelus William Potts et al. 《Journal of Ornithology》1994,135(1):61-71