全文获取类型
收费全文 | 12555篇 |
免费 | 668篇 |
国内免费 | 1142篇 |
出版年
2023年 | 107篇 |
2022年 | 173篇 |
2021年 | 231篇 |
2020年 | 265篇 |
2019年 | 366篇 |
2018年 | 330篇 |
2017年 | 297篇 |
2016年 | 338篇 |
2015年 | 301篇 |
2014年 | 567篇 |
2013年 | 763篇 |
2012年 | 479篇 |
2011年 | 594篇 |
2010年 | 514篇 |
2009年 | 641篇 |
2008年 | 767篇 |
2007年 | 748篇 |
2006年 | 675篇 |
2005年 | 576篇 |
2004年 | 558篇 |
2003年 | 490篇 |
2002年 | 476篇 |
2001年 | 354篇 |
2000年 | 344篇 |
1999年 | 296篇 |
1998年 | 237篇 |
1997年 | 242篇 |
1996年 | 187篇 |
1995年 | 187篇 |
1994年 | 165篇 |
1993年 | 144篇 |
1992年 | 138篇 |
1991年 | 118篇 |
1990年 | 98篇 |
1989年 | 75篇 |
1988年 | 69篇 |
1987年 | 61篇 |
1986年 | 66篇 |
1985年 | 148篇 |
1984年 | 202篇 |
1983年 | 129篇 |
1982年 | 134篇 |
1981年 | 114篇 |
1980年 | 117篇 |
1979年 | 97篇 |
1978年 | 82篇 |
1977年 | 72篇 |
1976年 | 66篇 |
1975年 | 57篇 |
1974年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
RegB is involved in the control of the phage T4 life cycle. It inactivates the phage early mRNAs when their translation is
no more required. We determined its structure and identified residues involved in substrate binding. For this, all backbone
and 90% of side-chain resonance frequencies were assigned. 相似文献
12.
13.
A. Korte I. Ribera R. G. Beutel D. Bernhard 《Journal of Zoological Systematics and Evolutionary Research》2004,42(4):281-288
The series Staphyliniformia is one of the mega‐diverse groups of Coleoptera, but the relationships among the main families are still poorly understood. In this paper we address the interrelationships of staphyliniform groups, with special emphasis on Hydrophiloidea and Hydraenidae, based on partial sequences of the ribosomal genes 18S rDNA and 28S rDNA. Sequence data were analysed with parsimony and Bayesian posterior probabilities, in an attempt to overcome the likely effect of some branches longer than the 95% cumulative probability of the estimated normal distribution of the path lengths of the species. The inter‐family relationships in the trees obtained with both methods were in general poorly supported, although most of the results based on the sequence data are in good agreement with morphological studies. In none of our analyses a close relationship between Hydraenidae and Hydrophiloidea was supported, contrary to the traditional view but in agreement with recent morphological investigations. Hydraenidae form a clade with Ptiliidae and Scydmaenidae in the tree obtained with Bayesian probabilities, but are placed as basal group of Staphyliniformia (with Silphidae as subordinate group) in the parsimony tree. Based on the analysed data with a limited set of outgroups Scarabaeoidea are nested within Staphyliniformia. However, this needs further support. Hydrophiloidea s.str., Sphaeridiinae, Histeroidea (Histeridae + Sphaeritidae), and all staphylinoid families included are confirmed as monophyletic, with the exception of Hydraenidae in the parsimony tree. Spercheidae are not a basal group within Hydrophiloidea, as has been previously suggested, but included in a polytomy with other Hydrophilidae in the Bayesian analyses, or its sistergroup (with the inclusion of Epimetopidae) in the parsimony tree. Helophorus is placed at the base of Hydrophiloidea in the parsimony tree. The monophyly of Hydrophiloidea s.l. (including the histeroid families) and Staphylinoidea could not be confirmed by the analysed data. Some results, such as a placement of Silphidae as subordinate group of Hydraenidae (parsimony tree), or a sistergroup relationship between Ptiliidae and Scydmaenidae, appear unlikely from a morphological point of view. 相似文献
14.
15.
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
16.
We isolated a Zea mays cDNA encoding the 40S subunit cytoplasmic ribosomal protein S11. The nucleotide sequence was determined and the derived amino acid sequence compared to the corresponding Arabidopsis thaliana protein showing an homology of 90%. This ribosomal protein is encoded by a small multigene family of at least two members. The mRNA steady-state level is about one order of magnitude higher in rapidly growing parts of the plant such as the roots and shoots of seedlings compared to fully expanded leaf tissue. 相似文献
17.
B. K. Pierson S. J. Giovannoni D. A. Stahl R. W. Castenholz 《Archives of microbiology》1985,142(2):164-167
An unusual filamentous, gliding bacterium was found in a few hot springs in Oregon where it formed a nearly unispecific top layer of microbial mats. It contained a bacteriochlorophyll a-like pigment and an abundance of carotenoids. There were no chlorosomes or additional chlorophylls. The organism was aerotolerant and appeared to be photoheterotrophic. It was successfully co-cultured with an aerobic chemoheterotroph in a medium containing glucose and casamino acids. Although it has many characteristics in common with the genus Chloroflexus, the lack of chlorosomes and bacteriochlorophyll c and the aerobic nature of this organism indicate that it should be placed in a new genus. This conclusion is supported by 5S rRNA nucleotide sequence data. 相似文献
18.
Karl-D. Entian Kai-U. Fröhlich Dieter Mecke 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,799(2):181-186
An electrophoretic method has been devised to investigate the changes in the enzymes and isoenzymes of carbohydrate metabolism, upon adding glucose to derepressed yeast cell. (i) Of the glycolytic enzymes tested, enolase II, pyruvate kinase and pyruvate decarboxylase were markedly increased. This increase was accompanied by an overall increase in glycolytic activity and was prevented by cycloheximide, an inhibitor of protein synthesis. (ii) In contrast, respiratory activity decreased after adding glucose. This decrease was clearly shown to be the result of repression of respiratory enzymes. A rapid decrease within a few minutes of adding glucose, by analogy with the so-called ‘Crabtree effect’, was not observed in yeast. (iii) The gluconeogenic enzymes, fructose-1,6-bisphosphatase and malate dehydrogenase, which are inactivated after adding glucose, showed no significant changes in electrophoretic mobilities. Hence, there was no evidence of enzyme modifications, which were postulated as initiating degradation. However, it was possible to investigate cytoplasmic and mitochondrial malate dehydrogenase isoenzymes separately. Synthesis of the mitochondrial isoenzyme was repressed, whereas only cytoplasmic malate hydrogenase was subject to glucose inactivation. 相似文献
19.
Margarita Burguera-Pascu Alberto Rodríguez-Archilla Pilar Baca 《Journal of trace elements in medicine and biology》2007,21(2):92-101
The antimicrobial efficacy of zinc (Zn) salts (sulfate and acetate) against Streptococcus mutans (S. mutans) present in the oral cavity was tested in this study. The substantivity of Zn salts was assessed by determining the concentration of Zn in whole, unstimulated saliva and by measuring the magnitude of suppression of salivary S. mutans, 2h after rinsing. The concentration of Zn was measured by atomic absorption spectrometry (AAS) with electrothermal atomization (ET AAS) in saliva sampled before (basal) and 24h after mouth rinsing with different concentrations of Zn (0.1%, 0.5% and 1%) administrated as sulfate and acetate. The estimation of Zn levels in samples collected 30, 60, 90 and 120 min after rinsing was carried out by AAS with flame atomization (FAAS). Immediately after rinsing, the concentration of Zn in saliva sharply increased with respect to the baseline values (0.055+/-0.017 mg/L), followed by a sustained decrease, probably due to clearance of salivary flow or swallowing during sampling. A significant reduction (>87%) in the total mean S. mutans counts was found 2h after rinsing either with sulfate or acetate solutions, as evidence of the high substantivity and effectiveness of the Zn salts tested. A statistically significant inverse relationship (p<0.001 and the Pearson correlation coefficients between -34% and -50%) was found between Zn levels and the respective pH values measured in the samples collected 60 and 120 min after rinsing, sustaining the theory of bacterial glycolysis inhibition. 相似文献
20.