全文获取类型
收费全文 | 874篇 |
免费 | 79篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 4篇 |
2019年 | 16篇 |
2018年 | 5篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 28篇 |
2014年 | 33篇 |
2013年 | 49篇 |
2012年 | 52篇 |
2011年 | 59篇 |
2010年 | 49篇 |
2009年 | 43篇 |
2008年 | 53篇 |
2007年 | 54篇 |
2006年 | 51篇 |
2005年 | 59篇 |
2004年 | 61篇 |
2003年 | 52篇 |
2002年 | 29篇 |
2001年 | 10篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 15篇 |
1997年 | 18篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有953条查询结果,搜索用时 15 毫秒
151.
Genetic Diversity of African and Worldwide Strains of Ralstonia solanacearum as Determined by PCR-Restriction Fragment Length Polymorphism Analysis of the hrp Gene Region 总被引:1,自引:0,他引:1 下载免费PDF全文
The genetic diversity among a worldwide collection of 120 strains of Ralstonia solanacearum was assessed by restriction fragment length polymorphism (RFLP) analysis of amplified fragments from the hrp gene region. Five amplified fragments appeared to be specific to R. solanacearum. Fifteen different profiles were identified among the 120 bacterial strains, and a hierarchical cluster analysis distributed them into eight clusters. Each cluster included strains belonging to a single biovar, except for strains of biovars 3 and 4, which could not be separated. However, the biovar 1 strains showed rather extensive diversity since they were distributed into five clusters whereas the biovar 2 and the biovar 3 and 4 strains were gathered into one and two clusters, respectively. PCR-RFLP analysis of the hrp gene region confirmed the results of previous studies which split the species into an “Americanum” division including biovar 1 and 2 strains and an “Asiaticum” division including biovar 3 and 4 strains. However, the present study showed that most of the biovar 1 strains, originating from African countries (Reunion Island, Madagascar, Zimbabwe, and Angola) and being included in a separate cluster, belong to the “Asiaticum” rather than to the “Americanum” division. These African strains could thus have evolved separately from other biovar 1 strains originating from the Americas. 相似文献
152.
José Ruiz-Herrera Alfredo D. Martínez-Espinoza Peggy Elizabeth Alvarez Beatriz Xoconostle-Cázares 《Current microbiology》1999,39(5):291-294
We analyzed the pathogenicity of chitin synthetase (chs) disruptants of Ustilago maydis obtained with the carboxin-resistant or the hygromycin-resistant cassettes. We found that only chitin synthetase (chs) mutants obtained by gene disruption with the carboxin resistance cassette lost their virulence to maize (Zea mays) seedlings. Carboxin is a systemic fungicide that inhibits respiration by preventing the oxidation of succinate. We demonstrated
that carboxin-resistant transformants were affected in the levels of succinate dehydrogenase and respiratory activities when
compared with hygromycin-resistant disruptants. We propose that loss of virulence in the carboxin-resistant transformants
is owing to loss of respiratory fitness, which probably represents an important component of virulence in this fungus.
Received: 13 May 1999 / Accepted: 26 June 1999 相似文献
153.
154.
Mining the isotopic complexity of nitrous oxide: a review of challenges and opportunities 总被引:1,自引:0,他引:1
Nitrous oxide (N2O) is an important focus of international greenhouse gas accounting agreements and mitigation of emissions will likely depend on understanding the mechanisms of its formation and reduction. Consequently, applications of stable isotope techniques to understand N2O cycling are proliferating and recent advances in technology are enabling (1) increases in the frequency of isotope analyses and (2) analyses not previously possible. The two isotopes of N and 3 isotopes of O combine to form a total of 12 possible isotopic molecules of N2O. Consequently, this remarkably simple molecule contains a wealth of isotopic information in the form of bulk (δ15N, δ18O), position dependent (site preference), mass independent (Δ17O) and multiply-substituted or clumped isotope compositions. With recent developments in high-mass resolution double sector instruments all 12 isotopic molecules will likely be resolved in the near future. Advances in spectroscopic instruments hold the promise of substantial increases in sample throughput; however, spectroscopic analyses require corrections due to interferences from other gases and frequent and accurate calibration. Mass spectrometric approaches require mass overlap corrections that are not uniform between research groups and interlaboratory comparisons remain imprecise. The continued lack of attention to calibration by both funding agencies and investigators can only perpetuate disagreement between laboratories in reported isotope values for N2O that, in turn, will compromise global assessments of N2O sources and sinks based on isotope ratios. This review discusses the challenges and opportunities offered by the isotopic complexity of N2O. 相似文献
155.
Kirst Henning Gabilly Stéphane T. Niyogi Krishna K. Lemaux Peggy G. Melis Anastasios 《Planta》2017,245(5):1009-1020
Planta - Evidence shows that decreasing the light-harvesting antenna size of the photosystems in tobacco helps to increase the photosynthetic productivity and plant canopy biomass accumulation... 相似文献
156.
157.
Collagens constitute a large family of extracellar matrix proteins in humans and mammals that provide a structural framework for tissues. A number of hereditary connective tissue diseases are associated with mutations in collagens, including Osteogenesis imperfecta (OI). Collagen-like peptides were synthesized with alterations in primary sequence to represent native and mutation states related to this disease. The peptides were self-assembled in solution and on surfaces to investigate the influence of sequence chemistry on self-organization and, subsequently, how changes in structural organization impact templating for hydroxyapatite (HA) crystallization. Bulkier and more hydrophilic amino acid side chains in the peptide sequence, representing increasing severity of the disease state, resulted in a progressive disruption of the triple helix and supramolecular assembly. These changes also resulted in alterations in the nature of the mineralization pattern and composition of the calcium phosphate deposited on assembled templates. 相似文献
158.
Kidd BA Ho PP Sharpe O Zhao X Tomooka BH Kanter JL Steinman L Robinson WH 《Arthritis research & therapy》2008,10(5):R119
Introduction
Anti-citrullinated protein antibodies have a diagnostic role in rheumatoid arthritis (RA); however, little is known about their origins and contribution to pathogenesis. Citrullination is the post-translational conversion of arginine to citrulline by peptidyl arginine deiminase, and increased citrullination of proteins is observed in the joint tissue in RA and in brain tissue in multiple sclerosis (MS). 相似文献159.
160.
Cao S Al-Rehaily AJ Brodie P Wisse JH Moniz E Malone S Kingston DG 《Phytochemistry》2008,69(2):553-557
7-(2'-Hydroxy-3'-chloroprenyloxy)-4,8-dimethoxyfuroquinoline (1) and 6-(2'-hydroxy-3'-chloroprenyloxy)-4,7-dimethoxyfuroquinoline (2), together with ten known compounds, have been isolated from the aerial parts of Ertela (Monnieria) trifolia (L.) Kuntze. All the isolates were tested for antiproliferative activity against the A2780 human ovarian cancer cell line. 相似文献