全文获取类型
收费全文 | 4527篇 |
免费 | 323篇 |
国内免费 | 1篇 |
专业分类
4851篇 |
出版年
2024年 | 3篇 |
2023年 | 33篇 |
2022年 | 77篇 |
2021年 | 127篇 |
2020年 | 52篇 |
2019年 | 83篇 |
2018年 | 113篇 |
2017年 | 133篇 |
2016年 | 173篇 |
2015年 | 230篇 |
2014年 | 276篇 |
2013年 | 333篇 |
2012年 | 417篇 |
2011年 | 426篇 |
2010年 | 230篇 |
2009年 | 170篇 |
2008年 | 249篇 |
2007年 | 272篇 |
2006年 | 254篇 |
2005年 | 267篇 |
2004年 | 226篇 |
2003年 | 192篇 |
2002年 | 172篇 |
2001年 | 52篇 |
2000年 | 19篇 |
1999年 | 28篇 |
1998年 | 44篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有4851条查询结果,搜索用时 15 毫秒
11.
12.
13.
David J. Evans Gerald B. Pier Michael J. Coyne Jr Joanna B. Goldberg 《Molecular microbiology》1994,13(3):427-434
Summary
Strains of Pseudomonas aeruginosa initially isolated from patients with cystic fibrosis (CF) often express a smooth lipopolysaccharide (LPS) containing many long O side-chain antigens, but once a chronic infection is established, strains recovered from these patients express little or no LPS O antigen. The genetic basis for this loss of O antigen expression by P. aeruginosa CF isolates is unknown. We report here that 20 CF isoiates of P. aeruginosa , 13 of which are LPS-rough, were each capable of expressing serogroup 011 antigen when provided with the rfb iocus from P. aeruginosa serogroup 011 strain PA103 on the recombinant plasmid pLPS2. Eight of the thirteen LPS-rough isolates co-expressed another, presumably endogenous, O antigen when they contained pLPS2. Different subcloned regions of pLPS2 complemented distinct strains to restore endogenous O antigen expression. These data suggest that the loss of O antigen expression by P. aeruginosa CF isolates results from alterations specific to the rfb region, and is not due to mutations involving other loci or ancillary LPS genes. 相似文献
Strains of Pseudomonas aeruginosa initially isolated from patients with cystic fibrosis (CF) often express a smooth lipopolysaccharide (LPS) containing many long O side-chain antigens, but once a chronic infection is established, strains recovered from these patients express little or no LPS O antigen. The genetic basis for this loss of O antigen expression by P. aeruginosa CF isolates is unknown. We report here that 20 CF isoiates of P. aeruginosa , 13 of which are LPS-rough, were each capable of expressing serogroup 011 antigen when provided with the rfb iocus from P. aeruginosa serogroup 011 strain PA103 on the recombinant plasmid pLPS2. Eight of the thirteen LPS-rough isolates co-expressed another, presumably endogenous, O antigen when they contained pLPS2. Different subcloned regions of pLPS2 complemented distinct strains to restore endogenous O antigen expression. These data suggest that the loss of O antigen expression by P. aeruginosa CF isolates results from alterations specific to the rfb region, and is not due to mutations involving other loci or ancillary LPS genes. 相似文献
14.
Irving W. Wainer John C. Chen Heli Parenteau Sami Abdullah Julie Ducharme Hiltrude Fieger Joanna Iredale 《Chirality》1994,6(4):347-354
The disposition of the enantiomers of hydroxychloroquine (HCQ) and its major metabolites in ocular tissues of rabbits has been studied. Both albino, New Zealand White (NZW), and pigmented animals were administered daily oral doses of rac-HCQ, (S)-HCQ or (R)-HCQ (20 mg/kg) over 1, 6, or 8 day periods or for 8 days followed by a 7-day washout period. At the end of the study periods, plasma and whole blood samples were collected and the rabbits were sacrificed. The eyes were collected, the aqueous humor removed with a syringe, and the eyes separated into the cornea, lens, vitreous body, iris, choroid-retina, sclera, and conjunctiva. The concentrations of (R)-HCQ, (S)-HCQ, and their respective metabolites were determined using a validated enantioselective liquid chromatographic assay. The data from these studies indicate that HCQ accumulated in both pigmented and nonpigmented ocular tissues. In the pigmented tissues, HCQ and its metabolites were bound to melanin and the binding was not enantiospecific. In the nonpigmented tissues and in the iris and retina-choroid of the NZW rabbits, the accumulation appeared to be the result of a reversible and enantioselective binding of HCQ and its metabolites to an unidentified biopolymer present in these ocular tissues. © 1994 Wiley-liss, Inc. 相似文献
15.
Nichola A. Strandberg Mary Edwards Joanna C. Ellison Manuel J. Steinbauer Anna Walentowitz Patricia L. Fall David Sear Peter Langdon Shane Cronin Alvaro Castilla-Beltrán Ian W. Croudace Matiu Prebble William D. Gosling Sandra Nogué 《Biotropica》2023,55(4):816-827
Here, we investigate Mid- to Late-Holocene vegetation changes in low-lying coastal areas in Tonga and how changing sea levels and recurrent volcanic eruptions have influenced vegetation dynamics on four islands of the Tongan archipelago (South Pacific). To investigate past vegetation and environmental change at Ngofe Marsh (‘Uta Vava’u), we examined palynomorphs (pollen and spores), charcoal (fire), and sediment characteristics (volcanic activity) from a 6.7-m-long sediment core. Radiocarbon dating indicated the sediments were deposited over the last 7700 years. We integrated the Ngofe Marsh data with similar previously published data from Avai’o’vuna Swamp on Pangaimotu Island, Lotofoa Swamp on Foa Island, and Finemui Swamp on Ha’afeva Island. Plant taxa were categorized as littoral, mangrove, rainforest, successional/ disturbance, and wetland groups, and linear models were used to examine relationships between vegetation, relative sea level change, and volcanic eruptions (tephra). We found that relative sea level change has impacted vegetation on three of the four islands investigated. Volcanic eruptions were not identified as a driver of vegetation change. Rainforest decline does not appear to be driven by sea level changes or volcanic eruptions. From all sites analyzed, vegetation at Finemui Swamp was most sensitive to changes in relative sea level. While vegetation on low-lying Pacific islands is sensitive to changing sea levels, island characteristics, such as area and elevation, are also likely to be important factors that mediate specific island responses to drivers of change. 相似文献
16.
Bernhard Koppenhoefer Andreas Nothdurft Joanna Pierrot-Sanders Patrick Piras Cristina Popescu Christian Roussel Matthias Stiebler Ulrich Trettin 《Chirality》1993,5(4):213-219
In order to cope with the increasing number of publications on the separation of enantiomers by chromatography on a chiral stationary phase, the graphical molecular database CHIRBASE was created. In the present state, the database package covers information (structural, bibiographic, and chromatographic data) on liquid-, supercritical fluid-, and gas chromatography; other methods will follow. CHIRBASE, running on the MDL software Chembase®, meets the requirements of contemporary information management in the chemical and pharmaceutical industry. (Detailed information including a demo-version of each part of CHIRBASE can be obtained from the authors on request.) © 1993 Wiley-Liss, Inc. 相似文献
17.
18.
19.
Beata Bartodziejska Joanna Radziejewska-Lebrecht Maria Lipinska Yuriy A. Knirel Leonid O. Kononov Anatoly Y. Chernyak Hubert Mayer Antoni Rozalski 《FEMS immunology and medical microbiology》1996,13(2):113-121
Abstract In DOC-PAGE, lipopolysaccharide (LPS) of Proteus mirabilis R14/1959 (Rb-type) mutant showed a ladder-like migration pattern indicating the presence of a high molecular weight polysaccharide chain. The isolated polysaccharide, called T-antigen because of similarity with the T1 chain of Salmonella friedenau LPS, contained d -glucose, d -galacturonic acid ( d -GalA), and d -GlcNAc in molar ratios 2:1:1 and was structurally different from the O-antigen of the parental S-strain P. mirabilis S1959 but identical to the O-antigen of another S-strain Proteus penneri 42. The importance of a d -GalA( l -Lys)-containing epitope, most likely present in the core region of LPS, and of GalA present in the T-antigen chain in manifesting the serological specificity of P. mirabilis R14/1959 were revealed using rabbit polyclonal homologous and heterologous R- and O-specific antisera and the appropriate antigens, including synthetic antigens which represent partial structures of various Proteus LPS. 相似文献
20.
Comparative mapping in Arabidopsis and Brassica, fine scale genome collinearity and congruence of genes controlling flowering time 总被引:6,自引:0,他引:6
Ulf Lagercrantz Joanna Putterill George Coupland Derek Lydiate 《The Plant journal : for cell and molecular biology》1996,9(1):13-20
The model dicotyledonous plant, Arabidopsis thaliana , is closely related to Brassica crop species. It is intended that information concerning the genetic control of basic biological processes in Arabidopsis will be transferable to other species. Genome collinearity and its potential to facilitate the identification of candidate genes in Arabidopsis homologous to genes controlling important agronomic traits in Brassica was investigated. Genetic mapping in B. nigra identified two loci influencing flowering time (FT), with loci on linkage groups 2 and 8 explaining 53% and 12% of the total variation in FT, respectively. The CO gene exerts an important control over FT in A. thaliana , and B. nigra homologues of CO probably also play an important role in regulating FT. B. nigra homologues of CO were identified on linkage groups 2 and 8, the homologue on group 2 was coincident with the major locus controlling FT while the homologue on group 8 was within the 90% confidence interval of the weaker FT gene. The CO homologue on group 2 exhibits abundant allelic variation suggesting that it naturally controls a wide range of flowering times. Fine-scale A. thaliana/B. nigra comparative mapping demonstrated short-range collinearity between the genomes of Arabidopsis and Brassica . Eleven DNA fragments spaced over a 1.5 Mb contig in A. thaliana were used as RFLP probes in B. nigra . Three collinear representations of the A. thaliana contig were identified in B. nigra , with one interrupted by a large chromosomal inversion. Collinearity over this range will allow the resources generated by the Arabidopsis genome project to facilitate map-based cloning in Brassica crops. 相似文献