全文获取类型
收费全文 | 4363篇 |
免费 | 360篇 |
国内免费 | 110篇 |
出版年
2023年 | 25篇 |
2022年 | 76篇 |
2021年 | 175篇 |
2020年 | 100篇 |
2019年 | 141篇 |
2018年 | 185篇 |
2017年 | 133篇 |
2016年 | 165篇 |
2015年 | 230篇 |
2014年 | 269篇 |
2013年 | 327篇 |
2012年 | 369篇 |
2011年 | 311篇 |
2010年 | 214篇 |
2009年 | 174篇 |
2008年 | 198篇 |
2007年 | 191篇 |
2006年 | 208篇 |
2005年 | 173篇 |
2004年 | 166篇 |
2003年 | 152篇 |
2002年 | 131篇 |
2001年 | 91篇 |
2000年 | 82篇 |
1999年 | 75篇 |
1998年 | 44篇 |
1997年 | 40篇 |
1996年 | 24篇 |
1995年 | 31篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 24篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1979年 | 14篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1972年 | 9篇 |
1971年 | 10篇 |
排序方式: 共有4833条查询结果,搜索用时 650 毫秒
1.
2.
3.
4.
The Escherichia coli dnaW mutation is an allele of the adk gene 总被引:3,自引:0,他引:3
Joan M. Henson Aleksandra Blinkowa James R. Walker 《Molecular & general genetics : MGG》1982,186(4):488-492
Summary A dnaW mutant, isolated on the basis of inability to effect conjugal DNA transfer at high temperature, has been shown by complementation and enzyme assay to be defective in the adk (adenylate kinase; EC 2.7.4.3) locus. The adk mutant, known to have reduced ATP concentration at the nonpermissive temperature (Cousin and Belaich 1966), was used to demonstrate a donor energy requirement for stable aggregate formation and for chromosome transfer in conjugation. 相似文献
5.
Leandro Neves Faria Marlon Gomes Da Rocha Quirijn De Jong Van Lier Derblai Casaroli 《Plant and Soil》2010,331(1-2):299-311
Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality. 相似文献
6.
7.
Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect. 相似文献
8.
N C Leal A T De Sá C A Solari S J Da Silva E Hofer 《Memórias do Instituto Oswaldo Cruz》1987,82(1):43-49
From 13,196 faecal cultures made in Recife-Pernambuco during the period from 1978 to 1980, 1,720 strains of Salmonella were isolated. Serological typing on 1,387 of the isolates recognized 63 serotypes, 73.18% of which belonged to group B. The prevalent serotypes adding up to 1,231 strains (88.75% of the total of the isolates) were: S. typhimurium, S. saint-paul, S. poona, S. derby, S. agona, S. newport, S. oranienburg, S. infantis, S. tshiongwe and S. ndolo. 相似文献
9.
M Roghani C Da Silva M Castagna 《Biochemical and biophysical research communications》1987,142(3):738-744
The major interaction site for tumor-promoting phorbol esters is the calcium-activated, phospholipid-dependent protein kinase (protein kinase C), a key-element in signal transduction. Binding of phorbol esters results in enzyme activation which mediates, at least in part, the action of these agents. We have investigated the effects of tumor promoter chloroform on protein kinase C activity. Like thrombin and 12-O-tetradecanoylphorbol-13-acetate (TPA), chloroform was able to activate protein kinase C in intact rabbit platelets. In addition, chloroform stimulated enzyme activity as well as TPA binding capacity in cell-free system. Scatchard analysis of the data has shown that chloroform increased the number of phorbol ester binding sites. Structurally related compounds, carbon tetrachloride and methylene chloride, activated the enzyme similarly. 相似文献
10.
Lidija Simova Carolyn Williams Georgi D. Efremov Aleksandra Gordova-Muratovska Stojka Suštić Eila K. Watson Robert Williamson 《Human genetics》1990,85(4):432-433
Summary Chromosomes from 19 unrelated Southern Yugoslav families in which cystic fibrosis (CF) occurs were analysed for the presence
of the ΔF508 mutation, using polymerase chain reaction amplification followed by dot blot and polyacrylamide gel analysis.
Of the 38 CF chromosomes, 15 (39.5%) carry the ΔF508 deletion. Restriction fragment length polymorphism haplotypes for KM19/PstI, XV2c/TaqI and J3.11/PstI marker loci were determined and are compared for a total of 34 N and 37 CF chromosomes. 相似文献