全文获取类型
收费全文 | 816篇 |
免费 | 97篇 |
国内免费 | 2篇 |
出版年
2021年 | 10篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 31篇 |
2014年 | 35篇 |
2013年 | 43篇 |
2012年 | 57篇 |
2011年 | 50篇 |
2010年 | 28篇 |
2009年 | 30篇 |
2008年 | 57篇 |
2007年 | 47篇 |
2006年 | 43篇 |
2005年 | 40篇 |
2004年 | 60篇 |
2003年 | 39篇 |
2002年 | 40篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 17篇 |
1998年 | 22篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1970年 | 5篇 |
1969年 | 3篇 |
1965年 | 4篇 |
排序方式: 共有915条查询结果,搜索用时 15 毫秒
851.
Anders Folkesson Abdolreza Advani Soila Sukupolvi John D. Pfeifer Staffan Normark & Sven Löfdahl 《Molecular microbiology》1999,33(3):612-622
On centisome 7, Salmonella spp. contain a large region not present in the corresponding region of Escherichia coli. This region is flanked by sequences with significant homology to the E. coli tRNA gene aspV and the hypothetical E. coli open reading frame yafV. The locus consists of a mosaic of differentially acquired inserts forming a dynamic cs7 region of horizontally transferred inserts. Salmonella enterica subspecies I, responsible for most Salmonella infections in warm-blooded animals, carries a fimbrial gene cluster (saf) in this region as well as a regulatory gene (sinR). These genes are flanked by inverted repeats and are inserted in another laterally transferred region present in most members of Salmonella spp. encoding a putative invasin (pagN ). S. enterica subspecies I serovar Typhi, the Salmonella serovar that causes the most severe form of human salmonellosis, contains an additional insert of at least 8 kb in the sinR-pagN intergenic region harbouring a novel fimbrial operon (tcf ) similar to the coo operon encoding the CS1 fimbrial adhesin expressed by human-specific enterotoxigenic E. coli. It is suggested that the multiple insertions of fimbrial genes that have occurred in the cs7 region have contributed to phylogenetic diversity and host adaptation of Salmonella spp. 相似文献
852.
High- and low-altitude ecotypes of mountain birch (Betula pubescens ssp. czerepanovii) showed clear differences in their responses to various experimental conditions, including two temperature regimes and four
fertilisation rates. There was, however, no simple way to characterise the elevational ecotypes in terms of relative growth
rate, nitrogen (N) productivity, or root N uptake rate. The leaf N concentration was generally higher in the high-altitude
seedlings than in the low-altitude seedlings. At low temperature, high-altitude mountain birch maintained a relatively high
growth rate by combining high root N uptake rate and high leaf N concentration with high N productivity. An increase in temperature
and/or fertiliser rate resulted in a marginal increase in N productivity in the high-altitude seedlings but resulted in a
strong increase in N productivity in the low-altitude seedlings. In parallel, increased temperature resulted in a pronounced
decrease in leaf N concentration only in the low-altitude seedlings. Our results suggest that the weak growth response to
increased temperature in high-altitude mountain birch is functionally related to high leaf N concentration. The high leaf
N concentration of high-altitude mountain birch is genetically determined and has an adaptive value in a cold environment.
This suggests that there is a trade-off between high N productivity at low temperature and a strong response of N productivity
to temperature.
Received: 21 March 1998 / Accepted: 1 December 1998 相似文献
853.
Margareta Bielenstein Leif Astner Staffan Ekberg 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1999,730(2):671-182
The chemical substance 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) is in clinical use for the treatment of hereditary tyrosinemia type 1. In the present study, the plasma concentration of NTBC was determined by a coupled column liquid chromatographic method. A 20-μl volume of plasma was diluted with phosphate buffer, pH 2, and injected into a small precolumn (BioTrapAcid C18) with a mobile phase containing sulfuric acid. The precolumn was based on the restricted access principle, i.e., retention of NTBC within the lipophilic pores, while polar and large endogenous compounds were eluted with the void volume. NTBC was transferred to the analytical column using a mobile phase with a high content of acetonitrile. The compound was monitored by UV detection at 278 nm. The standard curve was linear between 0.3 and 69 μM, and the between-day precision (RSD) was 3% (n=6 days) at 13.8 μM and 14% (n=6 days) at 0.3 μM NTBC in plasma. The quantitation limit was approximately 0.3 μM using 20 μl of plasma. 相似文献
854.
The four stereoisomers of the antimuscarinic 3-(2,3-dihydrobenzofuran-2-yl)quinuclidine have been prepared by a method involving chromatographic separation of the racemic diastereoisomers as borane complexes. The relative and absolute configurations of the stereoisomers were determined by X-ray crystallographic methods. The crystal structure of (2′R,3R)-3-(2,3-dihydrobenzofuran-2-yl)quinuclidine · HCl · H2O contains two independent molecules with different conformations of both the quinuclidine moiety and the dihydrofuran ring. Chirality 10:813–820, 1998. © 1998 Wiley-Liss, Inc. 相似文献
855.
K Graham J E Fleming R Young K G Bensch 《The International journal of biochemistry》1989,21(7):715-722
1. Human xanthine oxidase [XO; EC 1.2.3.2.] was isolated by a non-proteolytic method from fresh human milk. Final purification of the protein was achieved by hydroxyapatite chromatography. Most (less than 95%) of the enzyme was released in the 0.40 M phosphate fraction at pH 6.8. 2. The specific activity of this preparation was found to be 0.047 microM min-1 mg-1 with xanthine as substrate. 3. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) separated two subunits, each with a mol. wt approximately 122 kDa. 4. On non-denaturing acrylamide gels both of these subunits exhibited oxidase-like activity with xanthine as substrate in the presence of nitroblue tetrazolium and molecular oxygen. 5. Immunoconjugates of XO were prepared by the keyhole limpet hemocyanin (KLH)- and glutaraldehyde-crosslinking techniques. 6. Polyclonal antibodies to XO were raised by i.m. injection of these conjugates into female New Zealand rabbits. 7. Western blot analysis using the semi-dry technique was employed to confirm the specificity of the antibody. 相似文献
856.
Tom Bjrnheden Bozena Jakubowicz Max Levin Birgitta Odn Staffan Edn Lars Sjstrm Malin Lnn 《Obesity (Silver Spring, Md.)》2004,12(1):95-105
Objective: Fat cell size is a fundamental parameter in the study of adipose tissue metabolism, because it markedly influences the cellular rates of metabolism. Previous techniques for the sizing of adipocytes are often complicated or time‐consuming. The aim of this study was to develop a new, computerized method for rapid and accurate determination of adipocyte size in a cell suspension obtained by incubating human or rat adipose tissue biopsies with collagenase. Research Methods and Procedures: The cell suspension was placed between a siliconized glass slide and a cover slip. Using the reference method [designated as (R)], the cell diameters were determined manually using a microscope with a calibrated ocular. The new method presented here [designated as (C)] was based on computerized image analysis. Results: After two well‐defined corrective adjustments, measurements with (R) and (C) agreed very well. The small remaining differences seemed, in fact, to depend on inconsistencies in (R). Discussion: We propose that (C) constitutes a valuable tool to study fat cell size, because this method is fast and allows the assessment of a sufficient number of cells to get reliable data on size distribution. Furthermore, images of cell preparations may be stored for future reference. 相似文献
857.
Isolation and long-term serial cultivation of endothelial cells from the microvessels of the adult human dermis 总被引:1,自引:0,他引:1
P. M. Davison K. Bensch M. A. Karasek 《In vitro cellular & developmental biology. Plant》1983,19(12):937-945
Sumamry A method to isolate and maintain microvascular endothelial cells from the cutaneous vessels of adult human skin in long-term
culture has been developed. Endothelial cells lining the microvessels of the papillary dermis are released from surrounding
tissue during a brief trypsin incubation (0.3% trypsin, 1% EDTA). Cells are plated onto a fibronectin substrate and maintained
in Leibovitz (L15) culture medium containing pooled human serum (50%) and antibiotics. Proliferation is dependent upon the
presence of several additional growth factors, cholera enterotoxin (1×10−9
M), isobutyl methylxanthine (3.3×10−5
M), and medium conditioned by explant culture of the mouse EHS sarcoma. Using this supplemented medium, cells proliferate readily
and can be cultivated serially for more than 6 passages (3 months in vitro). These cells retain their characteristic endothelial
cell morphology, stain positively for Factor VIII antigen, and contain Weibel-Palade bodies.
This research was supported by grant AG 01312 from the U.S. Public Health Service, Washington, D.C. 相似文献
858.
859.
860.
Nan H. Albertson Serina Stretton Somchai Pongpattanakitshote Jörgen Östling Kevin C. Marshall Amanda E. Goodman Staffan Kjelleberg 《FEMS microbiology letters》1996,140(2-3):287-294
Abstract The previously described pLOFKm transposon delivery plasmid (J. Bacteriol. (1990) 172, 6557–6567) was engineered such that a promoterless lacZ gene was cloned within the transposon cassette, generating the vector pLBT. Using pLBT, stable insertion mutations were generated at high frequencies in Vibrio sp. S141 and Pseudomonas sp. S91, and the interrupted genes could be monitored for their pattern of regulation. Genetic screens isolated mutants defective in a variety of activities. We describe the construction and use of pLBT as a tool for reporter gene mutant analysis in bacteria other than well-characterized laboratory strains. 相似文献