全文获取类型
收费全文 | 2102篇 |
免费 | 213篇 |
国内免费 | 2篇 |
专业分类
2317篇 |
出版年
2023年 | 17篇 |
2022年 | 26篇 |
2021年 | 50篇 |
2020年 | 42篇 |
2019年 | 34篇 |
2018年 | 46篇 |
2017年 | 43篇 |
2016年 | 71篇 |
2015年 | 132篇 |
2014年 | 122篇 |
2013年 | 153篇 |
2012年 | 179篇 |
2011年 | 170篇 |
2010年 | 119篇 |
2009年 | 92篇 |
2008年 | 139篇 |
2007年 | 150篇 |
2006年 | 111篇 |
2005年 | 80篇 |
2004年 | 93篇 |
2003年 | 80篇 |
2002年 | 63篇 |
2001年 | 37篇 |
2000年 | 18篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1971年 | 8篇 |
1969年 | 4篇 |
排序方式: 共有2317条查询结果,搜索用时 12 毫秒
11.
Charles Coudray Sylvie Pucheu François Boucher Josiane Arnaud Joël de Leiris Alain Favier 《Biological trace element research》1994,41(1-2):69-75
The hypothesis that oxygen-derived free radicals play an important role in myocardial ischemic and reperfusion injury has received a lot of support. In the presence of catalytic amounts of transition metals such as iron, superoxide anions, and hydrogen peroxide can be transformed into a highly reactive hydroxyl radical °OH (Haber-Weiss reaction). In view of this, we have undertaken this study to investigate whether iron is involved in the reperfusion syndrome and therefore could aggravate free radicals injury. Coronary effluent iron concentrations and cardiac cytosolic iron levels were evaluated in rat hearts subjected to an ischemia/reperfusion sequences. In the case of total ischemia, iron concentration in coronary effluents peaked immediately in the first sample collected upon reperfusion. However, in the case of partial ischemia, iron concentration in coronary effluents peaked rather exclusively during ischemia period. Cardiac cytosolic iron level augmented significantly after 30 min of total ischemia and non significantly in the other ischemia protocols compared to perfused control hearts. It also appears that the iron released is not protein-bound, and could therefore have a marked catalytic activity. The results of the present study suggest that in the oxygen paradox, iron plays an important role in inducing alterations during reoxygenation. 相似文献
12.
Marie J. Richard Veronique Ducros Michel Rorêt Josiane Arnaud Charles Coudray Michèle Fusselier Alain Favier 《Biological trace element research》1993,39(2-3):149-159
In six chronic dialyzed uremic patients, an intravenous sodium selenite (Se 50 μg during 5 wk and then 100 μg) and zinc gluconate
(Zn 5 mg) supplementation was performed during 20 wk at each dialysis session three times weekly. Before supplementation,
plasma Se and Zn, plasma and erythrocytes (RBC) antioxidant metalloenzymes glutathione peroxidase (GPX), and superoxide dismutase
(SOD) were significantly decreased, whereas lipid peroxidation (as thiobarbituric acid reactants TBARs) was increased. To
obtain a significative change in plasma selenium, we had to use an Se dose of 100 μg/dialysis session. Then, treatment-increased
plasma Se (from 0.58 ±0.09 to 0.89±0.16 μmol/L) led to a repletion of RBC-GPX (from 29.6±6 to 43±5.8 U/g Hb) and increased
plasma GPX levels (from 62±13 to 151±43 U/L). Plasma Zn and RBC-SOD did not vary significantly. The change of TBARs was not
observed between wk 1 and 4. They decreased significantly between wk 4 (4.80±0.21μmol/L) and wk 20 (4.16±0.26 μmol/L). We
noted a low correlation between TBARs and plasma GPX. A strong correlation was observed between Se and plasma GPX. The reversal
of Se deficiencies should reduce oxidative damage observed in these patients. 相似文献
13.
Marie Arnaud Stefan Krause Richard J. Norby Thuong Huyen Dang Nezha Acil Nicholas Kettridge Vincent Gauci Sami Ullah 《Global Change Biology》2023,29(12):3256-3270
Mangroves are among the most carbon-dense ecosystems worldwide. Most of the carbon in mangroves is found belowground, and root production might be an important control of carbon accumulation, but has been rarely quantified and understood at the global scale. Here, we determined the global mangrove root production rate and its controls using a systematic review and a recently formalised, spatially explicit mangrove typology framework based on geomorphological settings. We found that global mangrove root production averaged ~770 ± 202 g of dry biomass m−2 year−1 globally, which is much higher than previously reported and close to the root production of the most productive tropical forests. Geomorphological settings exerted marked control over root production together with air temperature and precipitation (r2 ≈ 30%, p < .001). Our review shows that individual global changes (e.g. warming, eutrophication, drought) have antagonist effects on root production, but they have rarely been studied in combination. Based on this newly established root production rate, root-derived carbon might account for most of the total carbon buried in mangroves, and 19 Tg C lost in mangroves each year (e.g. as CO2). Inclusion of root production measurements in understudied geomorphological settings (i.e. deltas), regions (Indonesia, South America and Africa) and soil depth (>40 cm), as well as the creation of a mangrove root trait database will push forward our understanding of the global mangrove carbon cycle for now and the future. Overall, this review presents a comprehensive analysis of root production in mangroves, and highlights the central role of root production in the global mangrove carbon budget. 相似文献
14.
Bacillus subtilis genome project: cloning and sequencing of the 97 kb region from 325° to 333deg; 总被引:2,自引:2,他引:0
P. Glaser F. Kunst M. Arnaud M.-P. Coudart W. Gonzales M.-F. Hullo M. Ionescu B. Lubochinsicy L. Marcelino I. Moszer E. Presecan M. Santana E. Schneider J. Schwelzer A. Vertes G. Rapoport A. Danchin 《Molecular microbiology》1993,10(2):371-384
In the framework of the European project aimed at the sequencing of the Bacillus subtilis genome the DNA region located between gerB (314°) and sacXV (333°) was assigned to the Institut Pasteur. In this paper we describe the cloning and sequencing of a segment of 97 kb of contiguous DNA. Ninety-two open reading frames were predicted to encode putative proteins among which only forty-two were found to display significant similarities to known proteins present in databanks, e.g. amino acid permeases, proteins involved in cell wall or antibiotic biosynthesis, various regulatory proteins, proteins of several dehydrogenase families and enzymes II of the phosphotransferase system involved in sugar transport. Additional experiments led to the identification of the products of new B. subtilis genes, e.g. galactokinase and an operon involved in thiamine biosynthesis. 相似文献
15.
Brice Maxime Nkouayeb Nangmou Hermine Laure Maza Djomkam Georges Bellier Tabekoueng Willifred Dongmo Tékapi Tsopgni Gabin Thierry Mbahbou Bitchagno Michel Arnaud Mbock Raceline Gounoue Kamkumo Marcel Frese Bruno Ndjakou Lenta Silvère Augustin Ngouela Nobert Sewald Anatole Guy Blaise Azebaze 《化学与生物多样性》2023,20(4):e202200271
The root extract of Nauclea xanthoxylon (A.Chev.) Aubrév. displayed significant 50 % inhibition concentration (IC50s) of 0.57 and 1.26 μg/mL against chloroquine resistant and sensitive Plasmodium falciparum (Pf) Dd2 and 3D7 strains, respectively. Bio-guided fractionation led to an ethyl acetate fraction with IC50s of 2.68 and 1.85 μg/mL and subsequently, to the new quinovic acid saponin named xanthoxyloside ( 1 ) with IC50s of 0.33 and 1.30 μM, respectively against the tested strains. Further compounds obtained from ethyl acetate and hexane fractions were the known clethric acid ( 2 ), ursolic acid ( 3 ), quafrinoic acid ( 4 ), quinovic acid ( 5 ), quinovic acid 3-O-β-D-fucopyranoside ( 6 ), oleanolic acid ( 7 ), oleanolic acid 3-acetate ( 8 ), friedelin ( 9 ), β-sitosterol ( 10a ), stigmasterol ( 10b ) and stigmasterol 3-O-β-D-glucopyranoside ( 11 ). Their structures were characterised with the aid of comprehensive spectroscopic methods (1 and 2D NMR, Mass). Bio-assays were performed using nucleic acid gel stain (SYBR green I)-based fluorescence assay with chloroquine as reference. Extracts and compounds exhibited good selectivity indices (SIs) of >10. Significant antiplasmodial activities measured for the crude extract, the ethyl acetate fraction and xanthoxyloside ( 1 ) from that fraction can justify the use of the root of N. xanthoxylon in ethnomedicine to treat malaria. 相似文献
16.
17.
Andrea Robitzki Alexandra Mack Arnaud Chatonnet Paul G. Layer 《Journal of neurochemistry》1997,69(2):823-833
Abstract: The function of the enzyme butyrylcholinesterase (BChE) in the developing and mature brain is still unclear. We have inserted 577 bp of the 5' upstream region plus 106 bp of the exon 1 of the rabbit BChE gene in reverse orientation under control of an SV40 early promoter derivative in an expression vector. This vector was introduced by calcium phosphate-mediated transfection into embryonic chicken retina cells during the first days of reaggregation culture. Depending on the retinal origin, the transfected cell population forms histotypic retina-like spheres, so-called rosetted or stratified retinospheroids. We show that antisense 5'-BChE gene expression decreased the steady-state mRNA level of BChE and the translation of the BChE protein, inhibited proliferation, and accelerated histogenesis in both cellular systems. The pronounced effects of antisense 5'-BChE transfection of spheroids document a key role of BChE during the early reaggregation process of retinal cells, most likely by regulating their growth and differentiation. 相似文献
18.
Muriel Bost Mary Berkaw O. Wesley McBride Guy Chazot Philippe Arnaud 《Human genetics》1995,96(2):239-240
Using a probe isolated from a human liver cDNA library, polymorphisms were observed in the human ceruloplasmin gene with the enzymes PstI and MspI. The PstI polymorphism was frequent (allele frequencies, 0.46 and 0.54) whereas the polymorphisms found with MspI were rare. 相似文献
19.
alpha 1-Acid glycoprotein (AGP) was purified to homogeneity by a 3-step procedure using pseudo-ligand affinity chromatography on immobilized Cibacron blue F3GA, Procion red HE3B, and preparative column isoelectric focusing. The overall yield of the combined techniques was 88%. Analysis of the purified AGP by lectin affinity chromatography on immobilized Con A and immunoaffino-electrophoresis indicated that the most acidic form did not interact with the lectin, while the two more basic fractions possessed different affinities for Con A. In addition, 3 different populations of AGP were clearly separated by Con A affinity chromatography. 相似文献
20.