全文获取类型
收费全文 | 1429763篇 |
免费 | 125208篇 |
国内免费 | 1404篇 |
出版年
2021年 | 17910篇 |
2019年 | 16154篇 |
2018年 | 18316篇 |
2017年 | 17108篇 |
2016年 | 28499篇 |
2015年 | 42505篇 |
2014年 | 50576篇 |
2013年 | 76833篇 |
2012年 | 38205篇 |
2011年 | 27357篇 |
2010年 | 44619篇 |
2009年 | 45616篇 |
2008年 | 25762篇 |
2007年 | 24250篇 |
2006年 | 28637篇 |
2005年 | 29906篇 |
2004年 | 28831篇 |
2003年 | 26517篇 |
2002年 | 24818篇 |
2001年 | 40309篇 |
2000年 | 38032篇 |
1999年 | 36008篇 |
1998年 | 25888篇 |
1997年 | 25746篇 |
1996年 | 25175篇 |
1995年 | 23317篇 |
1994年 | 23080篇 |
1993年 | 22182篇 |
1992年 | 31072篇 |
1991年 | 29591篇 |
1990年 | 27905篇 |
1989年 | 28691篇 |
1988年 | 26427篇 |
1987年 | 24839篇 |
1986年 | 23324篇 |
1985年 | 25264篇 |
1984年 | 24352篇 |
1983年 | 21563篇 |
1982年 | 21175篇 |
1981年 | 20239篇 |
1980年 | 18963篇 |
1979年 | 20361篇 |
1978年 | 18901篇 |
1977年 | 17922篇 |
1976年 | 16992篇 |
1975年 | 16970篇 |
1974年 | 17509篇 |
1973年 | 17820篇 |
1972年 | 15368篇 |
1971年 | 13806篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
K I Savitskaia A A Vorob'ev G G Sinitsina 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(12):24-31
The results of the inoculation of material taken from the anterior section of the nasal cavity and from the pharyngeal mucosa of 50 healthy young children and 298 acute pneumonia patients were analyzed. 23 microbial species were isolated. In the samples taken from the anterior section of the nasal cavity, monocultures were detected in 86 samples and 54 variants of associations including 2-4 species, in 139 samples. In the samples taken from the pharynx, monocultures were detected in 59 samples and 180 variants of associations including 2-6 species, in 282 samples. Differences in the contamination of the nasal cavity and the pharynx in healthy children and in pneumonia patients were revealed. These differences were manifested in the structure of the microflora (monocultures, associations, their composition), the assortment of microbial species and their concentration. In young children with pneumonia the microflora of the upper respiratory tract was found to reflect the severity of acute pneumonia and the intensity of the pathological process in the lungs (uncomplicated, pyodestructive pneumonia, pyodestructive pneumonia with fatal termination, acute purulent pleurisy). 相似文献
62.
63.
64.
Comparison of statistics for candidate-gene association studies using cases and parents. 总被引:17,自引:5,他引:12
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Studies of association between candidate genes and disease can be designed to use cases with disease, and in place of nonrelated controls, their parents. The advantage of this design is the elimination of spurious differences due to ethnic differences between cases and nonrelated controls. However, several statistical methods of analysis have been proposed in the literature, and the choice of analysis is not always clear. We review some of the statistical methods currently developed and present two new statistical methods aimed at specific genetic hypotheses of dominance and recessivity of the candidate gene. These new methods can be more powerful than other current methods, as demonstrated by simulations. The basis of these new statistical methods is a likelihood approach. The advantage of the likelihood framework is that regression models can be developed to assess genotype-environment interactions, as well as the relative contribution that alleles at the candidate-gene locus make to the relative risk (RR) of disease. This latter development allows testing of (1) whether interactions between alleles exist, on the scale of log RR, and (2) whether alleles originating from the mother or father of a case impart different risks, i.e., genomic imprinting. 相似文献
65.
The Fis protein: it''s not just for DNA inversion anymore 总被引:36,自引:0,他引:36
66.
Transcriptional control, translation and function of the products of the five open reading frames of the Escherichia coli nir operon 总被引:3,自引:0,他引:3
Nerina R. Harborne Lesley Griffiths Stephen J. W. Busby Jeffrey A. Cole 《Molecular microbiology》1992,6(19):2805-2813
Five open reading frames designated nirB, nirD, nirE, nirC and cysG have been identified from the DNA sequence of the Escherichia coli nir operon. Complementation experiments established that the NirB, NirD and CysG polypeptides are essential and sufficient for NADH-dependent nitrite reductase activity (EC 1.6.6.4). A series of plasmids has been constructed in which each of the open reading frames has been fused in-phase with the beta-galactosidase gene, lacZ. Rates of beta-galactosidase synthesis during growth in different media revealed that nirB, -D, -E and -C are transcribed from the FNR-dependent promoter, p-nirB, located just upstream of the nirB gene: expression is co-ordinately repressed by oxygen and induced during anaerobic growth. Although the nirB, -D and -C open reading frames are translated into protein, no translation of nirE mRNA was detected. The cysG gene product is expressed from both p-nirB and a second, FNR-independent promoter, p-cysG, located within the nirC gene. No NADH-dependent nitrite reductase activity was detected in extracts from bacteria lacking either NirB or NirD, but a mixture of the two was as active as an extract from wild-type bacteria. Reconstitution of enzyme activity in vitro required stoichiometric quantities of NirB and NirD and was rapid and independent of the temperature during mixing. NirD remained associated with NirB during the initial stages of purification of the active enzyme, suggesting that NirD is a second structural subunit of the enzyme. 相似文献
67.
M S Bortnik A V Skurat I R Eshba T V Bulargina E S Severin 《Biokhimii?a (Moscow, Russia)》1985,50(4):589-594
Changes in the properties of adenylate cyclase from the lungs of tuberculotic guinea pigs were revealed. The number of beta-adrenergic receptors in the lungs was found to be reduced by 30% at the second and by 70% at the third stage of the disease. The degree and the value of Ka for adenylate cyclase activation by isoproterenol remained thereby unchanged. The basal activity of adenylate cyclase was increased by 20% against the control level at the second stage and decreased by 20% at the third stage of the disease. At these periods, the stimulating effects of guanylyl imidodiphosphate, NaF and forskolin on lung adenylate cyclase were diminished. The experimental results point to the significant role of the enzymes of cAMP metabolism and reflect the course of the tuberculosis process in experimental animals. 相似文献
68.
69.
This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982). 相似文献
70.
Purification of smooth-muscle myosin free of calmodulin and myosin light-chain kinase. Susceptibility to oxidation.
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Smooth-muscle myosin purified as described by Persechini & Hartshorne [(1983) Biochemistry 22, 470-476] contains trace amounts of calmodulin and myosin light-chain kinase, which can be removed by Ca2+-dependent hydrophobic-interaction chromatography followed by calmodulin-Sepharose affinity chromatography. The resultant column-purified myosin exhibits properties similar to those of the non-purified myosin, e.g. actin activation of the Mg2+-ATPase requires Ca2+/calmodulin-dependent phosphorylation of the two 20 kDa light chains. However, unlike the non-purified myosin, the column-purified myosin undergoes a time-dependent transition to a form which no longer requires phosphorylation for actin activation of the myosin Mg2+-ATPase. This transition is identified as a time-dependent change in conformation of the column-purified myosin from a 10 S to 6 S form and is caused by slow oxidation of the column-purified myosin, since it could be prevented by storage under N2 and reversed by 5 mM-dithiothreitol. 相似文献