全文获取类型
收费全文 | 280篇 |
免费 | 22篇 |
国内免费 | 1篇 |
出版年
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 11篇 |
2012年 | 19篇 |
2011年 | 15篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 3篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1969年 | 3篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有303条查询结果,搜索用时 359 毫秒
161.
Katie R. Tomlinson José Luis Pablo-Rodriguez Hamidun Bunawan Sarah Nanyiti Patrick Green Josie Miller Titus Alicai Susan E. Seal Andy M. Bailey Gary D. Foster 《Molecular Plant Pathology》2019,20(8):1080-1092
Cassava brown streak disease (CBSD) is a leading cause of cassava losses in East and Central Africa, and is currently having a severe impact on food security. The disease is caused by two viruses within the Potyviridae family: Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV), which both encode atypical Ham1 proteins with highly conserved inosine triphosphate (ITP) pyrophosphohydrolase (ITPase) domains. ITPase proteins are widely encoded by plant, animal, and archaea. They selectively hydrolyse mutagenic nucleotide triphosphates to prevent their incorporation into nucleic acid and thereby function to reduce mutation rates. It has previously been hypothesized that U/CBSVs encode Ham1 proteins with ITPase activity to reduce viral mutation rates during infection. In this study, we investigate the potential roles of U/CBSV Ham1 proteins. We show that both CBSV and UCBSV Ham1 proteins have ITPase activities through in vitro enzyme assays. Deep-sequencing experiments found no evidence of the U/CBSV Ham1 proteins providing mutagenic protection during infections of Nicotiana hosts. Manipulations of the CBSV_Tanza infectious clone were performed, including a Ham1 deletion, ITPase point mutations, and UCBSV Ham1 chimera. Unlike severely necrotic wild-type CBSV_Tanza infections, infections of Nicotiana benthamiana with the manipulated CBSV infectious clones do not develop necrosis, indicating that that the CBSV Ham1 is a necrosis determinant. We propose that the presence of U/CBSV Ham1 proteins with highly conserved ITPase motifs indicates that they serve highly selectable functions during infections of cassava and may represent a euphorbia host adaptation that could be targeted in antiviral strategies. 相似文献
162.
Antibodies to DNA define an important autospecificity that arises in systemic lupus erythematosus (SLE). To elucidate the molecular features that may explain the pathogenesis of SLE, a heterologous system for expression of cloned V genes is often desirable. Here, a single-chain Fv coding domain was constructed by using the heavy- and light-chain V genes of a high-affinity site-directed mutant of the murine anti-dsDNA autoantibody, 3H9. This scFv was joined in frame to the c-jun leucine zipper for dimerization, and to two affinity tags, domain B of the staphylococcal protein A and a pentahistidine peptide, for purification. Dimerization of the scFv was determined by size-exclusion chromatography. The yields of the scFv following affinity purification on IgG agarose or Ni-NTA agarose were compared, and the activities of the resulting protein fractions were determined. A two-step purification of periplasmic extracts on Ni-NTA agarose and IgG agarose, followed by elution with 3.5 M MgCl(2), yielded scFv with the highest specific activity. The final purified material bound DNA by ELISA, electrophoretic mobility shift assay, and immunofluorescence of fixed Hep-2 cells. Antibodies purified in this fashion should have applications in structure/function studies in which it is essential to generate highly purified antigen-combining sites. 相似文献
163.
164.
AIMS: The repetitive extragenic palindromic-PCR (rep-PCR) subtyping technique, which targets repetitive extragenic DNA sequences in a PCR, was optimized for Campylobacter spp. These data were then used for comparison with the established genotyping method of flaA short variable region (SVR) DNA sequence analysis as a tool for molecular epidemiology. METHODS AND RESULTS: Uprime Dt, Uprime B1 or Uprime RI primers were utilized to generate gel-based fingerprints from a set of 50 Campylobacter spp. isolates recovered from a variety of epidemiological backgrounds and sources. Analysis and phenogram tree construction, using the unweighted pair group method with arithmetic mean, of the generated fingerprints demonstrated that the Uprime Dt primers were effective in providing reproducible patterns (100% typability, 99% reproducibility) and at placing isolates into epidemiological relevant groups. Genetic stability of the rep-PCR Uprime Dt patterns under nonselective, short-term transfer conditions revealed a Pearson's correlation approaching 99%. These same 50 Campylobacter spp. isolates were analysed by flaA SVR DNA sequence analysis to obtain phylogenetic relationships. CONCLUSIONS: The Uprime Dt primer-generated rep-PCR phenogram was compared with a phenogram generated from flaA SVR DNA sequence analysis of the same isolates. Comparison of the two sets of resulting genomic relationships revealed that both methods segregated isolates into similar groups. SIGNIFICANCE AND IMPACT OF THE STUDY: These results indicate that rep-PCR analysis performed using the Mo Bio Ultra Clean Microbial Genomic DNA Isolation Kit for DNA isolation and the Uprime DT primer set for amplification is a useful and effective tool for accurate differentiation of Campylobacter spp. for subtyping and epidemiological analyses. 相似文献
165.
Introduction: The quantity and composition of seed oil affects seed viability and storability and hence the value of a species as a resource for nutrition and plant conservation. Supercritical fluid extraction with carbon dioxide (SFE‐CO2) offers a rapid, environmentally friendly alternative to traditional solvent extraction. Objective: To develop a method using SFE‐CO2 to quantify the seed oil content in a broad range of species with high to low oil contents. Methodology: Seed oil was extracted using SFE‐CO2 from four crop species representing high, medium and low oil content: Helianthus annuus, Asteraceae, with ca. 55% oil; Brassica napus, Brassicaceae, with ca. 50% oil; Glycine max, Fabaceae, with ca. 20% oil; and Pisum sativum, Fabaceae, with ca. 2% oil. Extraction pressures of 5000, 6000 and 7500 psi and temperatures of 40, 60 and 80°C were examined and a second step using 15% ethanol as a modifier included. Oil yields were compared with that achieved from Smalley Butt extraction. The optimised SFE‐CO2 method was validated on six species from taxonomically distant families and with varying oil contents: Swietenia humilis (Meliaceae), Stenocereus thurberi (Cactaceae), Sinapis alba (Brassicaceae), Robinia pseudoacacia (Fabaceae), Poa pratensis (Poaceae) and Trachycarpus fortunei (Arecaceae). Results: The two‐step extraction at 6000 psi and 80°C produced oil yields equivalent to or higher than Smalley Butt extraction for all species, including challenging species from the Brassicaceae family. Conclusion: SFE‐CO2 enables the rapid analysis of seed oils across a broad range of seed oil contents. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
166.
167.
Heavy metal transporters play a key role in regulating metal accumulation and transport in plants. These are important candidate
genes to study in metal tolerant and accumulator plants for their potential use in environmental clean up. We coupled a degenerate
primer-based RT-PCR approach with a molecular fingerprinting technique based on amplified rDNA restriction analysis (ARDRA)
to identify novel ESTs corresponding to heavy metal transporters from metal accumulator Brassica juncea. We utilized this technique to clone several family members of natural resistance-associated macrophage proteins (NRAMP) and
yellow stripe-like proteins (YSL) in a high throughput manner to distinguish between closely related isoforms and/or allelic
variants from the allopolyploid B. juncea. Partial clones of 23 Brassica juncea NRAMPs and 27 YSLs were obtained with similarity to known Arabidopsis thaliana and Noccaea (Thlaspi) caerulescens NRAMP and YSL genes. The cloned transporters showed Brassica-specific changes in domains, which can have important functional
consequences. Semi-quantitative RT-PCR-based expression analysis of chosen members indicated that even closely related isoforms/allelic
variants of BjNRAMP and BjYSL have distinct tissue-specific and metal-dependent expressions which might be essential for adaptive
fitness and heavy metal tolerance. Consistent to this, BjYSL6.1 and BjYSL5.8 were found to show elevated expressions specifically
in cadmium-treated shoots and lead-treated roots of B. juncea, respectively. 相似文献
168.
William Renthal Alexander Chamessian Michele Curatolo Steve Davidson Michael Burton Sulayman Dib-Hajj Patrick M. Dougherty Allison D. Ebert Robert W. Gereau Andre Ghetti Michael S. Gold Gwendolyn Hoben Daniela Maria Menichella Philippe Mercier Wilson Z. Ray Daniela Salvemini Rebecca P. Seal Stephen Waxman Theodore J. Price 《Neuron》2021,109(9):1426-1429
169.
Manuela Nagel Charlotte E. Seal Louise Colville Axel Rodenstein Sun Un Josefine Richter 《Free radical research》2019,53(6):641-654
To elucidate biochemical mechanisms leading to seed deterioration, we studied 23 wheat genotypes after exposure to seed bank storage for 6–16 years compared to controlled deterioration (CD) at 45?°C and 14 (CD14) and 18% (CD18) moisture content (MC) for up to 32 days. Under two seed bank storage conditions, seed viability was maintained in cold storage (CS) at 0?°C and 9% seed MC, but significantly decreased in ambient storage (AS) at 20?°C and 9% MC. Under AS and CS, organic free radicals, most likely semiquinones, accumulated, detected by electron paramagnetic resonance, while the antioxidant glutathione (GSH) was partly lost and partly converted to glutathione disulphide (GSSG), detected by HPLC. Under AS the glutathione half-cell reduction potential (EGSSG/2GSH) shifted towards more oxidising conditions, from ?186 to ?141?mV. In seeds exposed to CD14 or CD18, no accumulation of organic free radicals was observed, GSH and seed viability declined within 32 and 7 days, respectively, GSSG hardly changed (CD14) or decreased (CD18) and EGSSG/2GSH shifted to ?116?mV. The pH of extracts prepared from seeds subjected to CS, AS and CD14 decreased with viability, and remained high under CD18. Across all treatments, EGSSG/2GSH correlated significantly with seed viability (r?=?0.8, p<.001). Data are discussed with a view that the cytoplasm is in a glassy state in CS and AS, but during the CD treatments, underwent transition to a liquid state. We suggest that enzymes can be active during CD but not under the seed bank conditions tested. However, upon CD, enzyme-based repair processes were apparently outweighed by deteriorative reactions. We conclude that seed ageing by CD and under seed bank conditions are accompanied by different biochemical reactions. 相似文献
170.