全文获取类型
收费全文 | 6151篇 |
免费 | 537篇 |
国内免费 | 3篇 |
出版年
2023年 | 26篇 |
2022年 | 78篇 |
2021年 | 149篇 |
2020年 | 91篇 |
2019年 | 121篇 |
2018年 | 131篇 |
2017年 | 117篇 |
2016年 | 193篇 |
2015年 | 354篇 |
2014年 | 362篇 |
2013年 | 446篇 |
2012年 | 545篇 |
2011年 | 525篇 |
2010年 | 311篇 |
2009年 | 280篇 |
2008年 | 397篇 |
2007年 | 366篇 |
2006年 | 329篇 |
2005年 | 367篇 |
2004年 | 328篇 |
2003年 | 279篇 |
2002年 | 239篇 |
2001年 | 57篇 |
2000年 | 48篇 |
1999年 | 53篇 |
1998年 | 50篇 |
1997年 | 33篇 |
1996年 | 33篇 |
1995年 | 22篇 |
1994年 | 40篇 |
1993年 | 22篇 |
1992年 | 28篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 20篇 |
1985年 | 10篇 |
1984年 | 22篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 25篇 |
1976年 | 12篇 |
1974年 | 6篇 |
1972年 | 8篇 |
1971年 | 7篇 |
排序方式: 共有6691条查询结果,搜索用时 114 毫秒
911.
Phylogenetic analyses inferred from rbcL sequences indicates that specimens of Caloglossa (Harvey) G. Martens collected from Vermilion Bay, Louisiana and Galveston, Texas, reported as C. leprieurii (Montagne) G. Martens (1869) constitutes a separate taxon. Studies are presently being conducted to compare this northwestern Gulf of Mexico taxon with material of C. intermedia Kamiya et West in Kamiya et al. (2000, J. Phycol. 36:411-420) from the Western Atlantic coast and with C. apomeiotica West et Zuccarello in West et al. (1994, Bot. Mar. 37:381–390) from Baja California, Mexico. 相似文献
912.
913.
Cross-Presentation of Human Cytomegalovirus pp65 (UL83) to CD8+ T Cells Is Regulated by Virus-Induced, Soluble-Mediator-Dependent Maturation of Dendritic Cells 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Graldine Arrode Claire Boccaccio Jean-Pierre Abastado Christian Davrinche 《Journal of virology》2002,76(1):142-150
Cytotoxic CD8+ T lymphocytes (CTL) directed against the matrix protein pp65 are major effectors in controlling infection against human cytomegalovirus (HCMV), a persistent virus of the Betaherpesvirus family. We previously suggested that cross-presentation of pp65 by nonpermissive dendritic cells (DCs) could overcome viral strategies that interfere with activation of CTL (G. Arrode, C. Boccaccio, J. Lule, S. Allart, N. Moinard, J. Abastado, A. Alam, and C. Davrinche, J. Virol. 74:10018-10024, 2000). It is well established that mature DCs are very potent in initiating T-cell-mediated immunity. Consequently, the DC maturation process is a key step targeted by viruses in order to avoid an immune response. Here, we report that immature DCs maintained in coculture with infected human (MRC5) fibroblasts acquired pp65 from early-infected cells for cross-presentation to specific HLA-A2-restricted CTL. In contrast, coculture of DCs in the presence of late-infected cells decreased their capacity to stimulate CTL. Analyses of DC maturation after either coculture with infected MRC5 cells or incubation with infected-cell-conditioned medium revealed that acquisition of a mature phenotype was a prerequisite for efficient stimulation of CTL and that soluble factors secreted by infected cells were responsible for both up and down regulation of CD83 expression on DCs. We identified transforming growth factor beta1 secreted by late HCMV-infected cells as one of these down regulating mediators. These findings suggest that HCMV has devised another means to compromise immune surveillance mechanisms. Together, our data indicate that recognition of HCMV-infected cells by DCs has to occur early after infection to avoid immune evasion and to allow generation of anti-HCMV CTL. 相似文献
914.
Byung-Ki Hur Dae-Won Cho Ho-Jung Kim Chun-Ik Park Hyung-Joon Suh 《Biotechnology and Bioprocess Engineering》2002,7(1):10-15
Environmental and medium factors were investigated as basic data for optimizing DHA production when usingThraustochytrium aureum. To study the effect of environmental conditions, the rotation speed and culture temperature were, changed. Plus the trend
of the growth characteristics, lipid content in the biomass, and DHA content in lipids were evaluated according to various
initial glucose concentrations. The biomass, lipid, and DHA analyses showed that the physiological characteristics ofT. aureum were closely related with the environmental and medium conditions, as in the case of other marine microorganisms. For example,
a low rotation speed of 50 rpm lowered the cell growth rate as well as the DHA content in the lipids. A low temperature had
a negative effect on the cell growth, yet a positive effect on the lipid content in the biomass. Different initial glucose
concentrations had no effect on the lipid content in the biomass or DHA content in the lipids, yet did affect the cell growth.
Accordingly, these results show that environmental and medium factors must be synthetically considered in order to optimize
DHA production when usingT. aureum. 相似文献
915.
Claire Gaillard Luda S Shlyakhtenko Yuri L Lyubchenko Fran?ois Strauss 《BMC structural biology》2002,2(1):7-13
Background
We have previously isolated a stable alternative DNA structure, which was formed in vitro by reassociation of the strands of DNA fragments containing a 62 bp tract of the CA-microsatellite poly(CA)·poly(TG). In the model which was proposed for this structure the double helix is folded into a loop, the base of the loop consists of a DNA junction in which one of the strands of one duplex passes between the two strands of the other duplex, forming a DNA hemicatenane in a hemiknot structure. The hemiknot DNA structures obtained with long CA/TG inserts have been imaged by AFM allowing us to directly visualize the loops. 相似文献916.
Robert Wilson Karin Lyall Louise Smyth Claire E Fernie Rudolph A Riemersma 《Free radical biology & medicine》2002,32(2):162-168
Lipid peroxidation products formed in vivo or originating from the diet may lead to atherosclerosis. However, little is known about the absorption of these products in man. We studied the absorption of fat (30 g) containing 14-15 mg [U-13C]-labeled hydroxy or dihydroxy triglycerides in two groups of six apparently healthy women aged 40 +/- 2 years. Post-prandial 13C-labeled hydroxy fatty acid concentration increased in a pattern somewhat different from that of plasma triglycerides, with peak levels being reached between 4 and 6 h. However, the amount of 13C-labeled oxidized fat absorbed (area under the curve of plasma concentrations from 0 to 8 h) was related to that of plasma triglycerides: 13C hydroxy vs TG (r = 0.88, p <.02), and 13C dihydroxy vs TG (r = 0.85, p <.05). 13C monohydroxy triglycerides appeared to be absorbed to a greater extent than those of 13C dihydroxy triglycerides. Although low levels of 13C hydroxy lipids could be detected in fasting plasma after 24 h, concentrations were very low. Dietary lipid oxidation products are absorbed. The measurement of hydroxy fatty acids in plasma total lipids may not be a valid marker of lipid peroxidation in vivo when subjects are not fasting. 相似文献
917.
Claire R. Quilter Sarah C. Blott Alan J. Mileham Nabeel A. Affara Carole A. Sargent Darren K. Griffin 《Mammalian genome》2002,13(10):588-594
A combination of FISH and RH mapping was used to study the evolution of sex chromosome genes in the pig. In total, 19 genes
were identified, including 3 PAR genes (STS, KAL, PRK). The gene order of the porcine X Chromosome (Chr) closely resembled
the human X Chr (PRK/STS/KAL–AMELX–EIF2s3X/ZFX–USP9X–DBX–SMCX), suggesting that the porcine X has undergone very little rearrangement
during evolution. For the porcine Y Chr, two linkage groups of 10 NRY genes were found, and the following order was established:
Ypter–(AMELY–EIF2S3Y/ZFY–USP9Y–DBY/UTY)–(TSPY–SMCY–UBE1Y–SRY)–CEN. This gene order showed greater conservation with the murine
Y than with the human Y Chr. In addition, all porcine Y Chr genes mapped to Yp, which is similar to the mouse and included
EIF2s3Y and UBE1Y, which are not present in humans. Interestingly, complete conservation of X/Y homologous gene order was
found between the pig X and Y Chrs, indicating that the porcine Y Chr has not undergone extensive reorganisation with respect
to the X. This suggests that the order of the X/Y homologous genes of the porcine X and Y Chrs may closely resemble the ancestral
gene order of the eutherian sex chromosomes. 相似文献
918.
Xuejun Cao XingYan Wu Tong Wu Keming Jin Byung Ki Hur 《Biotechnology and Bioprocess Engineering》2001,6(3):200-204
In this study, nanofiltration was applied to the concentration of the 6-aminopenicillinic acid (6-APA) from bioconverted penicillin
solution and also to its mother liquor. The 6-APA in the solution was concentrated from 0.211 mol/L to 0.746 mol/L by nanofiltration.
The final maximum concentration was 3.6 times higher than the initial concentration and the recovery yield was 97% to 99%
of the original 6-APA. The concentrated solution was crystallized with the yields of 88.9–90.2% and the purity of the crystallized
product was about 98%. The concentration of 6-APA in the mother liquor after crystallization was 0.014 mol/L and thus was
concentrated 20–30 fold by nanofiltration and crystallization. The recovery of 6-APA was over 98%. The salts contained in
the mother liquor, such as NH4Cl and KCl, could be removed by allowing them to permeate through the membrane. 相似文献
919.
This paper demonstrates the use of phenology models mapped over the landscape as a tool in support of risk assessments for nonindigenous plant pests. Drawing on the relationship between pest development and temperature, the approach uses gridded sequential interpolated temperatures at a resolution of 1 km, linked with phenology models, to predict the potential for a pest to develop throughout the landscape. The potential for establishment of Colorado beetle (Leptinotarsa decemlineata) in England and Wales was used as an illustration. The likelihood of the pest completing a single generation during a 30‐year period (1961–90) was computed. Summaries of phenology, based firstly upon point temperature series from weather stations and secondly upon temperatures interpolated across the landscape, were compared. The results revealed that the use of point data led to a 70% likelihood of over‐estimating the area at risk from year to year. In the case of average long‐term risk however, the point‐based and landscape‐wide distributions of establishment potential were similar. We demonstrate how the use of phenology models running on a daily time scale provides date based results, so allowing outputs to be tied in with periods in the cropping cycle. The application of daily data in computing the phenological results, unlike the main body of published work on pest risk assessment which uses averaged monthly data, reflects more fully the underlying variability and degrees of sensitivity of the pest to changes in weather. 相似文献
920.
Quantitative amplification of single-stranded DNA (QAOS) demonstrates that cdc13-1 mutants generate ssDNA in a telomere to centromere direction 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We have developed a method that allows quantitative amplification of single-stranded DNA (QAOS) in a sample that is primarily double-stranded DNA (dsDNA). Single-stranded DNA (ssDNA) is first captured by annealing a tagging primer at low temperature. Primer extension follows to create a novel, ssDNA-dependent, tagged molecule that can be detected by PCR. Using QAOS levels of between 0.2 and 100% ssDNA can be accurately quantified. We have used QAOS to characterise ssDNA levels at three loci near the right telomere of chromosome V in budding yeast cdc13-1 mutants. Our results confirm and extend previous studies which demonstrate that when Cdc13p, a telomere-binding protein, is disabled, loci close to the telomere become single stranded whereas centromere proximal sequences do not. In contrast to an earlier model, our new results are consistent with a model in which a RAD24-dependent, 5′ to 3′ exonuclease moves from the telomere toward the centromere in cdc13-1 mutants. QAOS has been adapted, using degenerate tagging primers, to preferentially amplify all ssDNA sequences within samples that are primarily dsDNA. This approach may be useful for identifying ssDNA sequences associated with physiological or pathological states in other organisms. 相似文献