全文获取类型
收费全文 | 5289篇 |
免费 | 350篇 |
专业分类
5639篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 66篇 |
2021年 | 97篇 |
2020年 | 45篇 |
2019年 | 79篇 |
2018年 | 116篇 |
2017年 | 94篇 |
2016年 | 152篇 |
2015年 | 218篇 |
2014年 | 273篇 |
2013年 | 408篇 |
2012年 | 452篇 |
2011年 | 436篇 |
2010年 | 274篇 |
2009年 | 205篇 |
2008年 | 341篇 |
2007年 | 340篇 |
2006年 | 319篇 |
2005年 | 318篇 |
2004年 | 280篇 |
2003年 | 229篇 |
2002年 | 244篇 |
2001年 | 52篇 |
2000年 | 46篇 |
1999年 | 54篇 |
1998年 | 50篇 |
1997年 | 37篇 |
1996年 | 43篇 |
1995年 | 39篇 |
1994年 | 30篇 |
1993年 | 41篇 |
1992年 | 28篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1973年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有5639条查询结果,搜索用时 0 毫秒
1.
Fabrizio Villani Milena Galimberti Elena Monti Francesco Piccinini Enrica Lanza Annalinda Rozza Luigia Favalli Paola Poggi Franco Zunino 《Free radical research》1990,11(1):145-151
The effects of two sulfhydryl compounds, glutathione (GSH) and N-acetylcysteine (NAC), on the cardiotoxicity of doxorubicin (DXR) were tested on in vitro and in vivo models. DXR was administered to rats as 4 weekly i.v. doses of 3mg/kg. GSH (1.5 mmoles/kg), given i.v. 10 min before and 1 hr after DXR, was found to prevent the development of the delayed cardiotoxic effects of DXR, as assessed by electrocardiographic and mechanical parameters, as well as by histological examination of left ventricular preparations. In contrast, equimolar oral doses of NAC (1 hr before and 2hrs after DXR) were found to be ineffective. Both GSH and NAC prevented the negative inotropic effect produced by DXR on isolated rat atria. A good correlation exists between the cardioprotective effects of the two agents and their ability to enhance the non-protein sulfhydryl group content of the myocardium. Differences observed in vivo between GSH and NAC might be accounted for by pharmacokinetic factors. 相似文献
2.
3.
1-Methyl-, 1-ethyl-2-phenylindoles react with nitrogen monoxide, forming mainly 3,3(')-azo-bis-indoles, nitrosoindoles together with traces of nitroindoles. 2-Phenylindole, under the same experimental conditions, forms isonitrosoindole in good yields. The formation mechanism of azo-bis-indoles has been demonstrated to occur through 1,2-disubstituted nitrosoindoles by the intermediate formation of a diazonium salt. 相似文献
4.
Paola Villa 《Evolutionary anthropology》1992,1(3):93-104
The key argument for the identification of prehistoric cannibalism is provided by analysis of close similarities in the treatment of human and animal remains. Such analysis requires precise data on depositional context, meticulous excavation records, detailed bone modification studies, a relatively large sample of human and animal postcranial bones, and data on local mortuary practices. With the exception of Fontbrégoua Cave, these necessary conditions are lacking at all Stone Age European sites where it has been hypothesized that cannibalism occurred. The alternative hypothesis of secondary burial practices has been proposed informally for some sites and, in a more formal and detailed way, for Krapina and Fontbrégoua. However, this hypothesis does not have a higher probability, is not justified by current data, and uses ethnographic analogies to prop up interpretations of materials for which contextual data are missing or have been neglected. At Fontbrégoua, cannibalism remains the simplest and most plausible explanation of the evidence; at Krapina and other sites the available evidence is insufficient to prove either secondary burial or cannibalism. 相似文献
5.
6.
Purification, Characterization, and Functional Role of a Novel Extracellular Protease from Pleurotus ostreatus 总被引:3,自引:0,他引:3 下载免费PDF全文
Gianna Palmieri Carmen Bianco Giovanna Cennamo Paola Giardina Gennaro Marino Maria Monti Giovanni Sannia 《Applied microbiology》2001,67(6):2754-2759
A new extracellular protease (PoSl; Pleurotus ostreatus subtilisin-like protease) from P. ostreatus culture broth has been purified and characterized. PoSl is a monomeric glycoprotein with a molecular mass of 75 kDa, a pI of 4.5, and an optimum pH in the alkaline range. The inhibitory profile indicates that PoSl is a serine protease. The N-terminal and three tryptic peptide sequences of PoSl have been determined. The homology of one internal peptide with conserved sequence around the Asp residue of the catalytic triad in the subtilase family suggests that PoSl is a subtilisin-like protease. This hypothesis is further supported by the finding that PoSl hydrolysis sites of the insulin B chain match those of subtilisin. PoSl activity is positively affected by calcium. A 10-fold decrease in the Km value in the presence of calcium ions can reflect an induced structural change in the substrate recognition site region. Furthermore, Ca2+ binding slows PoSl autolysis, triggering the protein to form a more compact structure. These effects have already been observed for subtilisin and other serine proteases. Moreover, PoSl protease seems to play a key role in the regulation of P. ostreatus laccase activity by degrading and/or activating different isoenzymes. 相似文献
7.
Algara-Suárez P Espinosa-Tanguma R 《Biochemical and biophysical research communications》2004,314(2):597-601
In this study, guinea pig tracheal smooth muscle pre-contracted with histamine was relaxed by the addition of 100microM 8Br-cGMP, a non-hydrolyzable and cell-permeable analog for cGMP. This effect was not sensitive to cGMP-dependent protein kinase (PKG) inhibitors, whereas it was partially blocked by cAMP-dependent protein kinase (PKA) inhibitors. The relaxation observed was also reverted up to 50+/-8.5% by iberiotoxin, a selective inhibitor of large conductance, calcium-activated potassium channels (BK(Ca)). Our results indicate that there exists a crosstalk mechanism between cAMP and cGMP signaling pathways which lead to relaxation of guinea pig tracheal smooth muscle and also that BK(Ca) channels are involved to a certain extent in this phenomenon. 相似文献
8.
Maria Assunta Piano Lisa Gianesello Angela Grassi Paola Del Bianco Adriana Mattiolo Anna Maria Cattelan Lolita Sasset Paola Zanovello Maria Luisa Calabr 《Journal of cellular and molecular medicine》2019,23(2):1486-1494
The aim of this study was to identify circulating microRNAs (miRNAs) that could be used as biomarkers in patients at risk for or affected by AIDS‐Kaposi's sarcoma (KS). Screening of 377 miRNAs was performed using low‐density arrays in pooled plasma samples of 10 HIV/human herpesvirus 8 (HHV8)‐infected asymptomatic and 10 AIDS‐KS patients before and after successful combined antiretroviral therapy (cART). MiR‐375 was identified as a potential marker of active KS, being the most down‐regulated in AIDS‐KS patients after cART and the most up‐regulated in naïve AIDS‐KS patients compared to naïve asymptomatic subjects. Validation on individual plasma samples confirmed that miR‐375 levels were higher in AIDS‐KS compared to asymptomatic patients, decreased after cART‐induced remission in most AIDS‐KS patients and increased in patients with active KS. In asymptomatic patients miR‐375 was up‐regulated after cART in both screening and validation. Statistical analyses revealed an association between miR‐375 changes and CD4 cell counts, which could explain the discordant cases and the opposite trend between asymptomatic and AIDS‐KS patients. These data suggest that circulating miR‐375 might be a good indicator of active AIDS‐KS. Moreover, changes in miR‐375 levels may have a prognostic value in HIV/HHV8‐infected patients undergoing treatment. Further large‐scale validation is needed. 相似文献
9.
Radice F Orlandi V Massa V Battini V Bertoni G Reineke W Barbieri P 《Applied microbiology and biotechnology》2007,75(5):1111-1118
An Arthrobacter strain, able to utilize 4-chlorobenzoic acid as the sole carbon and energy source, was isolated and characterized. The first step of the catabolic pathway was found to proceed via a hydrolytic dehalogenation that leads to the formation of 4-hydroxybenzoic acid. The dehalogenase encoding genes (fcb) were sequenced and found highly homologous to and organized as those of other 4-chlorobenzoic acid degrading Arthrobacter strains. The fcb genes were cloned and successfully expressed in the heterologous host Pseudomonas putida PaW340 and P. putida KT2442 upper TOL, which acquired the ability to grow on 4-chlorobenzoic acid and 4-chlorotoluene, respectively. The cloned dehalogenase displayed a high specificity for para-substituted haloaromatics with affinity Cl > Br > I > F, in the order. 相似文献
10.
Rodrigo Scheihing Leyla Cardenas Roberto F. Nespolo Paola Krall Katherina Walz Shiro Kohshima Pedro Labarca 《Hydrobiologia》2010,637(1):45-52
In small metazoan invertebrates classical taxonomic analyses can be ambiguous due to the limited number of morphological characters
available. This difficulty can yield incorrect estimates of species richness or taxa distribution. The Boeckella genus has been described as the dominant taxon of zooplankton assemblages in the Andean biogeographical region. In this genus,
taxonomic classification and delimitation of boundaries between species has long been problematic and controversial. Among
South American centropagids Boeckella gracilipes has been regarded as one of the most broadly distributed species, its presence having been reported from Ecuador to Tierra
del Fuego. However, in the high Andean plateau some centropagid populations identified as Boeckella gracilipes have also been considered as B. gracilipes titicacae or even identified as a different species, namely Boeckella titicacae. In an attempt to resolve the taxonomic status of the Centropagidae family from the high Andean plateau, we combined traditional
and multivariate morphological analyses (integral approach) with the molecular phylogenetic approach. The results obtained
allow us to conclude that centropagids collected from the high Andean plateau actually represent a different species, B. titicacae, not B. gracilipes. The phylogenetic reconstruction of the South American Centropagidae family indicated that B. gracilipes represents a sister taxon to B. titicacae. The present study stresses the usefulness of integrating alfa-taxonomy with morphometric and molecular approaches in order
to resolve species boundaries, to determine geographical distributions and to investigate evolutionary processes. 相似文献