全文获取类型
收费全文 | 2799篇 |
免费 | 186篇 |
国内免费 | 1篇 |
专业分类
2986篇 |
出版年
2022年 | 31篇 |
2021年 | 40篇 |
2020年 | 31篇 |
2019年 | 41篇 |
2018年 | 49篇 |
2017年 | 36篇 |
2016年 | 54篇 |
2015年 | 90篇 |
2014年 | 109篇 |
2013年 | 170篇 |
2012年 | 167篇 |
2011年 | 147篇 |
2010年 | 96篇 |
2009年 | 81篇 |
2008年 | 153篇 |
2007年 | 149篇 |
2006年 | 155篇 |
2005年 | 125篇 |
2004年 | 141篇 |
2003年 | 116篇 |
2002年 | 118篇 |
2001年 | 77篇 |
2000年 | 69篇 |
1999年 | 76篇 |
1997年 | 17篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 47篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 39篇 |
1988年 | 24篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1979年 | 18篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1975年 | 15篇 |
1974年 | 21篇 |
1973年 | 15篇 |
1972年 | 23篇 |
1970年 | 15篇 |
1966年 | 15篇 |
排序方式: 共有2986条查询结果,搜索用时 15 毫秒
11.
A cDNA clone for muscle adenylate kinase was isolated from a cDNA library of chick skeletal muscle poly(A)+ RNA, and the DNA sequence was determined. The cDNA insert had 854 nucleotides, which consisted of the 5'-untranslated sequence of 57 nucleotides, the sequence of 582 nucleotides coding for 194 amino acids, and the 3'-untranslated sequence of 163 nucleotides and the poly(A) tail of 52 nucleotides. The amino acid sequence predicted from the nucleotide sequence was highly homologous with the reported sequences of human, calf, porcine, and rabbit muscle adenylate kinases. RNA blot analysis of poly(A)+ RNA from various chicken tissues revealed a single species of mRNA of approximately 850 nucleotides and its tissue-specific distribution. The induction of muscle adenylate kinase mRNA synthesis during the chick embryogenesis was also demonstrated by the blot analysis. Southern blot analysis indicated a single gene for muscle adenylate kinase in the chicken genome. 相似文献
12.
Occurrence of Yersinia enterocolitica in wild-living birds and Japanese serows. 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yersinia spp. were isolated from 34 of 500 birds representing nine species. The highest isolation rate, 5 of 21 (23.8%), was found in blue magpies (Cyanopia cyanus), followed by pheasants (Phasianus colchicus tohkaidi), 5 of 33 (15.2%); gray starlings (Sturnus cineraceus), 6 of 57 (10.5%); tree sparrows (Passer montanus), 1 of 14 (7.1%); bulbuls (Hypsipetes amaurotis), 4 of 57 (7.0%); crows (Corvus levailantii or Corvus corone), 7 of 117 (6.0%); eastern turtledoves (Streptopelia orientalis), 4 of 118 (3.4%); Chinese bamboo pheasants (Bumbusicola thoracica thoracica), 1 of 36 (2.8%); and domestic pigeons (Columba livia domestica), 1 of 47 (2.1%). The isolates were identified as Yersinia enterocolitica O:3, O:4, O:4,32, O:5A, O:6,30, O:7,8, and O:14, Yersinia frederiksenii, Yersinia intermedia, and Yersinia kristensenii. Yersinia spp. were isolated from 35 of 157 wild-living Japanese serows (Capricornis cripus). The isolates were identified as Y. enterocolitica O:4, O:4,32, O:5A, O:7, O:7,8, O:9, O:14, O:18, and O:34, Y. frederiksenii, Y. intermedia, and Y. kristensenii. 相似文献
13.
Distinctions between the multiple cationic forms of rat liver glutathione S-transferase 总被引:3,自引:0,他引:3
Three cationic glutathione S-transferase forms isolated from rat liver were characterized as dimers that originated from different combinations of two subunit types, Ya and Yc. The cationic forms were purified using lysyl glutathione affinity matrices and were chromatographically resolved from anionic glutathione S-transferases that contain Yb subunits. The three classes of cationic transferase exhibited similar specific activities with 1-chloro-2,4-dinitrobenzene as a substrate, all forms cross-reacted with antibodies to glutathione S-transferase B, and all had comparable secondary structures and tryptophan fluorescence properties. In spite of those similarities, the Yc-containing forms were clearly distinguishable from Ya forms on the basis of characteristic differences in circular dichroic patterns associated with their aromatic side chains. All cationic transferases bound bilirubin with stoichiometric ratios of 1 mol/dimeric protein molecule, but discrete differences in mode of binding were ascribed to forms containing Ya subunits as compared to Yc dimers. Binding to Yc forms was of lower affinity and may be associated with the catalytic region of the protein since glutathione effectively displaced bilirubin from the Yc component. 相似文献
14.
Summary The effect of cholecystokinin (CCK) and internal Ca2+ on outward K+ current in isolated pig pancreatic acinar cells has been investigated using the patch-clamp method for whole-cell current recording under voltage-clamp conditions. CCK (2 × 10–10
M) applied to the bath evoked a marked increase in the outward K+ current associated with depolarizing voltage steps, and this effect was fully reversible and acutely dependent on the presence of external Ca2+. When strongly buffered Ca2+-EGTA solutions were used inside the cells CCK failed to evoke an effect. Increasing the internal Ca2+ concentration ([Ca2+]
i
) from 5 × 10–10
M to 10–7 and 5 × 10–7
M mimicked the effect of CCK. It would appear therefore that CCK controls K+ conductance in the acinar cells via changes in the internal free ionized Ca2+ concentration. 相似文献
15.
Models of Evolution of Reproductive Isolation 总被引:12,自引:3,他引:9
Mathematical models are presented for the evolution of postmating and premating reproductive isolation. In the case of postmating isolation it is assumed that hybrid sterility or inviability is caused by incompatibility of alleles at one or two loci, and evolution of reproductive isolation occurs by random fixation of different incompatibility alleles in different populations. Mutations are assumed to occur following either the stepwise mutation model or the infinite-allele model. Computer simulations by using It?'s stochastic differential equations have shown that in the model used the reproductive isolation mechanism evolves faster in small populations than in large populations when the mutation rate remains the same. In populations of a given size it evolves faster when the number of loci involved is large than when this is small. In general, however, evolution of isolation mechanisms is a very slow process, and it would take thousands to millions of generations if the mutation rate is of the order of 10(-5) per generation. Since gene substitution occurs as a stochastic process, the time required for the establishment of reproductive isolation has a large variance. Although the average time of evolution of isolation mechanisms is very long, substitution of incompatibility genes in a population occurs rather quickly once it starts. The intrapopulational fertility or viability is always very high. In the model of premating isolation it is assumed that mating preference or compatibility is determined by male- and female-limited characters, each of which is controlled by a single locus with multiple alleles, and mating occurs only when the male and female characters are compatible with each other. Computer simulations have shown that the dynamics of evolution of premating isolation mechanism is very similar to that of postmating isolation mechanism, and the mean and variance of the time required for establishment of premating isolation are very large. Theoretical predictions obtained from the present study about the speed of evolution of reproductive isolation are consistent with empirical data available from vertebrate organisms. 相似文献
16.
Expression of adenovirus type 12 early region 1 in KB cells transformed by recombinants containing the gene. 总被引:10,自引:4,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)
K Shiroki I Saito K Maruyama Y Fukui Y Imatani K I Oda H Shimojo 《Journal of virology》1983,45(3):1074-1082
The adenovirus type 12 (Ad12) early region 1 (E1) gene was introduced into KB cells by using a dominant selection vector, pSV2-gpt, and over 80 Gpt+ KB cell clones were established. Three types of recombinant DNAs (gAE1A, gARC, and gABA) were constructed. They contained the AccI-H, EcoRI-C, and BamHI-A fragments, respectively, of Ad12 DNA in pSV2-gpt. Five of 50 (10%) gABA-transformed cell clones, 12 of 18 (67%) gAE1A-transformed cell clones, and 10 of 18 (56%) gARC-transformed cell clones complemented the growth of Ad5 dl312 (deletion in E1A) and were designated as Gpt+ Ad+ cell clones. In these cell clones at their early passages, recombinant genome sequences were detected in cellular DNA and were expressed. T antigen g (the E1A gene product) was detected by immunofluorescence. The Gpt+ Ad+ cell clones supported the growth of Ad5 deletion mutants in parallel with the expression of Ad12 E1A or E1A plus E1B genes. After infection of Gpt+ Ad+ cell clones with Ad5 dl312, the early genes of dl312 were efficiently transcribed, indicating the expression of the pre-early function of the Ad12 E1A gene. Two clones each from gAE1A-,gARC-, and gABA-transformed cells were subcultured for a long period to determine the stability of the transfecting DNAs. Subculture in a nonselective medium resulted in cells which lost the transfecting DNAs. Subculture in a selective medium resulted in the selection of cells which maintained the gpt gene expression but lost the Ad12 gene expression. These results indicate that the transfecting DNA is present in an unstable state in KB cells. 相似文献
17.
18.
19.
Physiological role of malic enzymes in the liver 总被引:2,自引:0,他引:2
20.