全文获取类型
收费全文 | 8210篇 |
免费 | 703篇 |
国内免费 | 7篇 |
出版年
2023年 | 19篇 |
2022年 | 60篇 |
2021年 | 187篇 |
2020年 | 104篇 |
2019年 | 118篇 |
2018年 | 192篇 |
2017年 | 159篇 |
2016年 | 276篇 |
2015年 | 468篇 |
2014年 | 496篇 |
2013年 | 578篇 |
2012年 | 707篇 |
2011年 | 656篇 |
2010年 | 405篇 |
2009年 | 325篇 |
2008年 | 499篇 |
2007年 | 498篇 |
2006年 | 410篇 |
2005年 | 407篇 |
2004年 | 412篇 |
2003年 | 287篇 |
2002年 | 290篇 |
2001年 | 219篇 |
2000年 | 156篇 |
1999年 | 127篇 |
1998年 | 66篇 |
1997年 | 41篇 |
1996年 | 54篇 |
1995年 | 35篇 |
1994年 | 35篇 |
1993年 | 25篇 |
1992年 | 63篇 |
1991年 | 38篇 |
1990年 | 43篇 |
1989年 | 36篇 |
1988年 | 34篇 |
1987年 | 38篇 |
1986年 | 26篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 21篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1977年 | 23篇 |
1976年 | 21篇 |
1974年 | 17篇 |
1969年 | 15篇 |
排序方式: 共有8920条查询结果,搜索用时 27 毫秒
21.
22.
Determination of the optimal feed rate for fed-batch fermentation is normally a problem in singular control with a state inequality constraint and as such is, in general, difficult to solve, especially for those described by a large number of dynamic mass balance equations. In this article we use a new set of state variables and the culture volume as the control variable. In this way the problem is converted to one of nonsingular control with the magnitude and rate constraints on the manipulated variable and can be numerically solved by a gradient-based technique, thus avoiding the difficulty associated with singular control problems. Examples are given to illustrate the method. 相似文献
23.
Beta-thalassemia mutations in Indonesia and their linkage to beta haplotypes. 总被引:2,自引:1,他引:1
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)
L E Lie-Injo S P Cai I Wahidijat S Moeslichan M L Lim L Evangelista M Doherty Y W Kan 《American journal of human genetics》1989,45(6):971-975
A total of 72 chromosomes from 36 Indonesian patients, 23 with beta-thalassemia major and 13 with Hb E-beta-thalassemia, were analyzed by specific oligonucleotide hybridization after DNA amplification. Thirteen had the beta E mutation (codon 26 GAG----AAG). Of the 59-beta-thalassemic chromosomes, 32 were of the variant IVS-1 nt5 (G----C). Seven had the mutation IVS-2 nt654 (C----T), one had the mutation codon 41/42 (deletion CTTT), and one had the mutation codon 17 (AAG----TAG). Another six with the mutation IVS-1 nt1 (G----T), one with the mutation IVS-1 nt1 (G----A), four with the mutation codon 15 (TGG----TAG), one with a mutation codon 30 (AGG----ACG), and one with a mutation codon 35 (deletion C) were first identified by direct sequencing of a patient's genomic DNA followed by further hybridizing other patients' DNA with the appropriate oligonucleotide probes. Five did not carry the common mutations previously described in Asian populations. The four most prevalent mutations encountered made up 83% of the total number of beta-thalassemic chromosomes studied. The most common mutation, IVS-1 nt5 (G----C), was mostly associated with two different haplotypes. 相似文献
24.
Novel yeast protein kinase (YPK1 gene product) is a 40-kilodalton phosphotyrosyl protein associated with protein-tyrosine kinase activity. 总被引:23,自引:8,他引:15
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D Dailey G L Schieven M Y Lim H Marquardt T Gilmore J Thorner G S Martin 《Molecular and cellular biology》1990,10(12):6244-6256
Extracts of bakers' yeast (Saccharomyces cerevisiae) contain protein-tyrosine kinase activity that can be detected with a synthetic Glu-Tyr copolymer as substrate (G. Schieven, J. Thorner, and G.S. Martin, Science 231:390-393, 1986). By using this assay in conjunction with ion-exchange and affinity chromatography, a soluble tyrosine kinase activity was purified over 8,000-fold from yeast extracts. The purified activity did not utilize typical substrates for mammalian protein-tyrosine kinases (enolase, casein, and histones). The level of tyrosine kinase activity at all steps of each preparation correlated with the content of a 40-kDa protein (p40). Upon incubation of the most highly purified fractions with Mn-ATP or Mg-ATP, p40 was the only protein phosphorylated on tyrosine. Immunoblotting of purified p40 or total yeast extracts with antiphosphotyrosine antibodies and phosphoamino acid analysis of 32P-labeled yeast proteins fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the 40-kDa protein is normally phosphorylated at tyrosine in vivo. 32P-labeled p40 immunoprecipitated from extracts of metabolically labeled cells by affinity-purified anti-p40 antibodies contained both phosphoserine and phosphotyrosine. The gene encoding p40 (YPK1) was cloned from a yeast genomic library by using oligonucleotide probes designed on the basis of the sequence of purified peptides. As deduced from the nucleotide sequence of YPK1, p40 is homologous to known protein kinases, with features that resemble known protein-serine kinases more than known protein-tyrosine kinases. Thus, p40 is a protein kinase which is phosphorylated in vivo and in vitro at both tyrosine and serine residues; it may be a novel type of autophosphorylating tyrosine kinase, a bifunctional (serine/tyrosine-specific) protein kinase, or a serine kinase that is a substrate for an associated tyrosine kinase. 相似文献
25.
Decarboxylation of uroporphyrinogen III by erythrocyte uroporphyrinogen decarboxylase. Evidence for a random decarboxylation mechanism.
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)
The isomeric composition of type-III heptacarboxylic porphyrinogens derived from decarbosylation of uroporphyrinogen III by erythrocyte uroporphyringogen decarboxylase was analysed by h.p.l.c. with electrochemical detection. All four possible isomers were identified, and there were little differences in the proportion of isomers formed by erythrocytes from normal subjects and from patients with sporadic porphyria cutanea tarda. The results provide conclusive evidence that the normal decarboxylation pathway is random in nature, and the fourth isomer only increases when enzyme abnormality is found. 相似文献
26.
27.
28.
29.
HSPA6 is a member of the human heat-shock protein gene family, encoding a basic 70-kDa protein, with unique induction characteristics (Leung et al., 1990, Biochem. J. 267: 125-132). Hybridization analyses with a somatic cell hybrid DNA panel localized the gene to chromosome 1q. The highly related HSPA7 DNA sequence (Voellmy et al., 1985, Proc. Natl. Acad. Sci. USA 82: 4949-4953) colocalized. Both HSPA6 and HSPA7 represent functional genes, as determined by analyses of mRNA from heat-shocked human cells using specific oligonucleotides, although their pattern of expression differed. Neither mRNA was detected in the absence of heat stress. A BamHI polymorphism in the HSPA7 gene was present in a predominantly Asian population. 相似文献
30.