全文获取类型
收费全文 | 51591篇 |
免费 | 17120篇 |
国内免费 | 10篇 |
专业分类
68721篇 |
出版年
2023年 | 178篇 |
2022年 | 273篇 |
2021年 | 777篇 |
2020年 | 2448篇 |
2019年 | 3984篇 |
2018年 | 4275篇 |
2017年 | 4496篇 |
2016年 | 4660篇 |
2015年 | 4886篇 |
2014年 | 4617篇 |
2013年 | 5487篇 |
2012年 | 3573篇 |
2011年 | 3277篇 |
2010年 | 4143篇 |
2009年 | 2726篇 |
2008年 | 2210篇 |
2007年 | 1878篇 |
2006年 | 1804篇 |
2005年 | 1787篇 |
2004年 | 1721篇 |
2003年 | 1692篇 |
2002年 | 1589篇 |
2001年 | 530篇 |
2000年 | 512篇 |
1999年 | 446篇 |
1998年 | 349篇 |
1997年 | 233篇 |
1996年 | 244篇 |
1995年 | 253篇 |
1994年 | 214篇 |
1993年 | 172篇 |
1992年 | 219篇 |
1991年 | 177篇 |
1990年 | 147篇 |
1989年 | 147篇 |
1988年 | 122篇 |
1987年 | 132篇 |
1986年 | 113篇 |
1985年 | 139篇 |
1984年 | 157篇 |
1983年 | 121篇 |
1982年 | 158篇 |
1981年 | 168篇 |
1980年 | 143篇 |
1979年 | 135篇 |
1978年 | 135篇 |
1977年 | 117篇 |
1976年 | 119篇 |
1975年 | 91篇 |
1974年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
P. Cruz C. H. Mejia‐Ruiz R. Perez‐Enriquez A. M. Ibarra 《Molecular ecology resources》2002,2(3):239-241
Five polymorphic microsatellite loci were characterized for Penaeus (Litopenaeus) vannamei. Loci were isolated using a partial Sau3A1 genomic library by the sequencing of randomly selected clones and by a biotinylated (CT)10 and (GT)10 probes screening procedure. The last strategy resulted in the most useful data. About 40% of the clones showed a previously reported satellite/microsatellite (PVS1), reducing the chance of finding new microsatellite regions. Whereas two of the microsatellite loci with more than 10 alleles will be useful for mating analysis in a breeding program, the others might prove useful for population genetic studies. 相似文献
22.
Location within a tree was analyzed as a source of variation in Sequoia sempervirens leaf monoterpenes. No differences were found for quantitative composition or total yield/dry wt among lower, middle and upper canopy positions. The awlshaped, spirally arranged leaves of vigorous upper shoots showed small quantitative compositional differences, but not differences in total yield. The intermediate leaf form of young sprouts had the most different monoterpene quantitative composition and about three times the total yield of the above two leaf forms. Analysis of a clonal ring of 17 adult trees resulted in coefficients of variation similar to those for samples collected from different canopy levels of the same shoot. Results revealed the sources and magnitudes of experimental error in comparative studies of this species' leaf monoterpenes, and did not support the concept that somatic mutation provides an important source of variation in a large, long-lived organism such as coast redwood. 相似文献
23.
Antoine Sioufi Françoise Pommier 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1980,181(2):161-168
A method for the determination of benzoic acid down to concentrations of 10 ng/ml in plasma or urine is described. After addition of an internal standard, benzoic acid is extracted at acid pH into diethyl ether. Both compounds are derivatized with pentafluorobenzyl bromide. The derivatives are determined by gas chromatography using a 43Ni electron-capture detector. Hippuric acid is hydrolysed in plasma and urine and total benzoic acid is determined by the same technique. 相似文献
24.
Neurosecretory granules from the rat and bovine neurohypophysis were isolated and some of their biochemical and biophysical properties studied. Neurosecretory granules (NSG) from rat neurohypophysis were labeled, in vivo, with [35S]cysteine and isolated on isoosmotic gradients. Whereas 1 day after labeling most of the radioactivity was found in the lower part of the gradient, 35 days later the isotope was also located in the lighter NSG-containing fraction. Different analytical procedures showed that the lighter fraction, both in bovine and rat NSG, contain more subpopulations of neurophysin-like material than the heavier fraction. The first material to be released during stimulation of secretion, in vivo or in vitro, is mobilized from the heavy NSG. Isolation of rat NSG, at different times during and after dehydration of the animals, reveals that the newly synthesized material is found in the heavy NSG-containing fraction. Furthermore, the results indicate that the newly synthesized NSG are more resistant to lysis than the lighter granules. The results are discussed in relation to the maturation and degradation processes of the granule content and to the functional state of the NSG. 相似文献
25.
26.
Jean-Marie Delaissé Philippe Martin Marie-Françoise Verheyen-Bouvy Edmond-Jacques Nyns 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,676(1):77-90
The subcellular localization of the ω-hydroxylase of Saccharomycopsis lipolytica was assessed by the analytical fractionation technique, originally described by de Duve C., Pressman, B.C., Gianetto, R., Wattiaux, R. and Appelmans, F., and hitherto little, if at all, applied to yeast. Protoplasts were separated in six fractions by differential centrifugation. Some of these fractions were further fractioned by density gradient centrifugation. The distribution of ω-hydroxylase and 15 other constituents chosen as possible markers of its subcellular membranes has been established. ω-Hydroxylase resulted in being bound to a membrane that containes also cytochrome P-450 and NADPH-cytochrome c reductase. This membrane clearly differs from five other subcellular entities. (1) Mitochondria were characterized by particulate malate dehydrogenase, particulate Antimycin A-insensitive NADH-cytochrome c reductase, oligomycin-sensitive and K+-stimulated ATPase pH 9. (2) Most if not all of the catalase and urate oxidase is peroxisomal. (3) Free ribosomes account for most RNA. (4) Nucleoside diphosphatase is for the first time reported in a yeast and appears to belong to an homogeneous population of small membranes. (5) The soluble compartment contains magnesium pyrophosphatase, alkaline phosphatase, 5′-nucleotidase and part of the NADH-cytochrome c reductase. Latent arylesterase and ATPase pH7 have an unspecific distribution. Alkaline phosphodiesterase I has not been detected. 相似文献
27.
28.
29.
30.