全文获取类型
收费全文 | 1536899篇 |
免费 | 143704篇 |
国内免费 | 1488篇 |
出版年
2021年 | 18091篇 |
2019年 | 16215篇 |
2018年 | 18747篇 |
2017年 | 17570篇 |
2016年 | 28824篇 |
2015年 | 42840篇 |
2014年 | 50891篇 |
2013年 | 77059篇 |
2012年 | 42739篇 |
2011年 | 32952篇 |
2010年 | 45933篇 |
2009年 | 46526篇 |
2008年 | 30870篇 |
2007年 | 29517篇 |
2006年 | 33349篇 |
2005年 | 34409篇 |
2004年 | 33654篇 |
2003年 | 30970篇 |
2002年 | 29112篇 |
2001年 | 42811篇 |
2000年 | 40544篇 |
1999年 | 38253篇 |
1998年 | 26602篇 |
1997年 | 26480篇 |
1996年 | 25787篇 |
1995年 | 24029篇 |
1994年 | 23753篇 |
1993年 | 22921篇 |
1992年 | 33354篇 |
1991年 | 31716篇 |
1990年 | 30352篇 |
1989年 | 30829篇 |
1988年 | 28666篇 |
1987年 | 27364篇 |
1986年 | 25734篇 |
1985年 | 27514篇 |
1984年 | 26223篇 |
1983年 | 23181篇 |
1982年 | 22448篇 |
1981年 | 21372篇 |
1980年 | 20109篇 |
1979年 | 22897篇 |
1978年 | 20457篇 |
1977年 | 19609篇 |
1976年 | 18617篇 |
1975年 | 18573篇 |
1974年 | 19558篇 |
1973年 | 19900篇 |
1972年 | 17338篇 |
1971年 | 15926篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
211.
Ryanodine was found to initially inhibit calcium uptake by cardiac sarcoplasmic reticulum. This initial depression was followed by a later marked stimulation of calcium uptake. These effects were noted when calcium uptake was measured in the presence or absence of oxalate. The requirement for preincubation with ryanodine was highly dependent on ryanodine concentration and temperature. The mechanism of action of ryanodine clearly was not an effect on oxalate entry or calcium oxalate precipitation because the effects were also observed in the absence of oxalate. Ryanodine also had no effect on passive calcium efflux from actively loaded vesicles. Because ryanodine had no effect on Ca2+-ATPase activity under defined conditions of an ATP-regenerating system and no calcium gradient, we suggest ryanodine does not change the stoichiometry of the pump. Our results are consistent with the hypothesis that ryanodine closes a calcium channel in a subpopulation of the vesicles. 相似文献
212.
213.
A. Knob C. R. F. Terrasan E. C. Carmona 《World journal of microbiology & biotechnology》2010,26(3):389-407
β-Xylosidases are hydrolytic enzymes which play an important role in xylan degradation, hydrolyzing xylobiose and xylooligosaccharides to xylose from the non-reducing end. Filamentous fungi are particularly interesting producers of this enzyme from an industrial point of view, due to the fact that they secrete β-xylosidases into the medium. Besides, fungal β-xylosidases are highly advantageous for their elevated activity levels and specificity. Interest in xylanolytic enzymes has been increasing, for their possible application in many biotechnological processes. This fact has driven the isolation, purification and characterization of several β-xylosidases. In this review, the mechanisms of action, substrate specificities, physicochemical characteristics, regulation at molecular level, molecular cloning and classification of filamentous fungal β-xylosidases are described. The potential industrial applications of fungal β-xylosidases will also be presented. 相似文献
214.
The linkage of the Phi, Pgd, Po2, S, H and halothane sensitivity loci was followed in a Belgian Landrace family, heterozygous for these systems over 6 generations. Recombination next to the S locus occurred mainly in pigs belonging to this particular family. From this investigation the position of the S locus is proved to be outwith the Phi-Pgd region, next to Phi . Therefore the gene sequence S - Phi - Hal -H- Po2 -Pgd is proposed. Higher recombination rates were observed in the female parental line of the multiheterozygous family when compared to the male parental line. Additional data from animals, unrelated to this strain, confirm the evidence of close linkage of the S system to the nearest marker loci. 相似文献
215.
Fumaria capreolata was taken into cell suspension culture. The culture yielded a biomass of about 12 g dry weight per liter of medium; the dried cells contained ca. 0.1% of alkaloids. Besides choline, the following ten known isoquinoline alkaloids were isolated from the cell extract in crystalline form: coptisine, dehydrocheilanthifoline; (+)-isoboldine; magnoflorine; N-methylcoclaurine; (+)-reticuline; (–)-pallidine; protopine; sanguinarine; (–)-scoulerine. This is the most diverse isoquinoline alkaloid spectrum thus far published for a cell suspension culture. 相似文献
216.
EEG activity was recorded in rats submitted to osmotic opening of the BBB by intracarotid mannitol infusion.This procedure produced an immediate short-lasting depression of the EEG and a tardive paroxysmal EEG activity. Both these phenomena were more relevant on the ipsilateral hemisphere. In some instances a tonico-clonic seizure was recorded.Pre-treatment with diazepam abolished the occurrence of the tardive EEG and behavioral modifications.In accord with previous findings, focal seizure activity is likely to be responsible for the metabolic abnormalities associated with osmotic opening of the BBB. This preparation therefore produces in the brain unphysiological states in respect to local metabolism and electrical function. 相似文献
217.
218.
219.
N. V. Ozolina E. V. Kolesnikova V. N. Nurminsky I. S. Nesterkina L. V. Dudareva L. I. Donskaya R. K. Salyaev 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2010,4(3):297-301
The changes in transport activity of tonoplast proton pumps under the influence of exogenous NO donator and modulation of
Ca2+ concentration jointly and separately were investigated at different stages of ontogenesis and under hyperosmotic stress.
The results suggest that both exogenous NO donator and Ca2+ ions can influence the activity of transport processes related to tonoplast and this influence is especially evident in the
period of growth and accumulation of metabolites. Under hyperosmotic stress, H+-pyrophosphatase plays a more important role than H+-ATPase: the activity of the former increases 2.3-fold compared to the control osmotic conditions, whereas the activity of
H+-ATPase is practically unchanged. H+-pyrophosphatase was more responsive to the presence of exogenous NO donator and to variations in Ca2+ concentration. The effects of exogenous NO donator on tonoplast proton pumps depended on the concentration of Ca2+, which apparently can mediate NO action. 相似文献
220.
K. Ferrazzoli Devienne M.S. Gonalves Raddi R. Gomes Coelho W. Vilegas 《Phytomedicine》2005,12(5):378-381
Three naturally occurring isocoumarins (paepalantine, paepalantine 9-O-beta-D-glucopyranoside and paepalantine 9-O-beta-D-allopyranosyl(1 --> 6) glucopyranoside) and two semi-synthetic analogues, 9,10-acylated compound and 9-OH-10-methylated compound, structurally similar to paepalantine, were evaluated for antimicrobial activity using a spectrophotometric microdilution technique. The paepalantine was active against S. aureus, S. epidermidis, and E. faecalis while the other four compounds proved ineffective against all microorganisms tested at concentrations of 500 microg/ml. Variations in phenolic substitution at OH-9 and/or OH-10 in the paepalantine molecule resulted in compounds without antimicrobial activity. A combination of structural features, two phenolic groups as cathecolic system, forms an oxygenated system arrangement that may reflect the potentially antimicrobial properties of paepalantine. 相似文献