全文获取类型
收费全文 | 749篇 |
免费 | 48篇 |
出版年
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 16篇 |
2015年 | 26篇 |
2014年 | 26篇 |
2013年 | 42篇 |
2012年 | 38篇 |
2011年 | 45篇 |
2010年 | 30篇 |
2009年 | 30篇 |
2008年 | 29篇 |
2007年 | 29篇 |
2006年 | 25篇 |
2005年 | 36篇 |
2004年 | 15篇 |
2003年 | 22篇 |
2002年 | 28篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1997年 | 5篇 |
1995年 | 4篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 19篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1971年 | 7篇 |
1970年 | 7篇 |
1968年 | 6篇 |
排序方式: 共有797条查询结果,搜索用时 15 毫秒
41.
Exogenous phage recombinase-independent inactivation of chromosomal genes in Yersinia enterocolitica
Characterization of newly identified genes is necessary to understand their functions. Phenotypic characterization of isogenic mutants provides good understanding of the functions of the genes in wild type strains. In the present study, we report the use of linear dsDNA as a substrate for homologous recombination in Yersinia enterocolitica. A double-stranded linear recombinant DNA (LRD) containing an antibiotic resistance gene flanked by homologous regions to the target gene was created. Transformation of this LRD into Y. enterocolitica led to the replacement of targeted loci with antibiotic resistance gene. Using this strategy, two chromosomal genes namely urease C (ureC) and hemophore A (hasA) were disrupted in three strains of Y. enterocolitica. These recombinations were independent of the EPR functions. This is the first report of EPR-independent inactivation of chromosomal genes in Y. enterocolitica strains. 相似文献
42.
Shailendra Kumar Dhar Dwivedi Krishnananda Samanta Manisha Yadav Amit Kumar Jana Abhishek Kumar Singh Bandana Chakravarti Sankalan Mondal Rituraj Konwar Arun Kumar Trivedi Naibedya Chattopadhyay Sabyasachi Sanyal Gautam Panda 《Bioorganic & medicinal chemistry letters》2013,23(24):6816-6821
Two series of new benzoxazepines substituted with different alkyl amino ethyl chains were synthesized comprising synthetic steps of inter and intramolecular Mitsunobu reaction, lithium aluminium hydride (LAH) reduction, debenzylation, bimolecular nucleophilic substitution (SN2) reaction. The present study investigates the effect of a tyrosine-based benzoxazepine derivative in human breast cancer cells MCF-7 and MDA-MB-231 and in breast cancer animal model. The anti-proliferative effect of 15a on MCF-7 cells was associated with G1 cell-cycle arrest. This G1 growth arrest was followed by apoptosis as 15a dose dependently increased phosphatidylserine exposure, PARP cleavage and DNA fragmentation that are hallmarks of apoptotic cell death. Interestingly, 15a activated components of both intrinsic and extrinsic pathways of apoptosis characterized by activation of caspase-8 and -9, mitochondrial membrane depolarization and increase in Bax/Bcl2 ratio. However, use of selective caspase inhibitors revealed that the caspase-8-dependent pathway is the major contributor to 15a-induced apoptosis. Compound 15a also significantly reduced the growth of MCF-7 xenograft tumors in athymic nude mice. Together, 15a could serve as a base for the development of a new group of effective breast cancer therapeutics. 相似文献
43.
Mohammad Ali Amanda K. Debes Francisco J. Luquero Deok Ryun Kim Je Yeon Park Laura Digilio Byomkesh Manna Suman Kanungo Shanta Dutta Dipika Sur Sujit K. Bhattacharya David A. Sack 《PLoS medicine》2016,13(9)
IntroductionVaccinating a buffer of individuals around a case (ring vaccination) has the potential to target those who are at highest risk of infection, reducing the number of doses needed to control a disease. We explored the potential vaccine effectiveness (VE) of oral cholera vaccines (OCVs) for such a strategy.ConclusionsThese findings suggest that high-level protection can be achieved if individuals living close to cholera cases are living in a high coverage ring. Since this was an observational study including participants who had received two doses of vaccine (or placebo) in the clinical trial, further studies are needed to determine whether a ring vaccination strategy, in which vaccine is given quickly to those living close to a case, is feasible and effective.
Trial registration
ClinicalTrials.gov NCT00289224相似文献44.
Effects of cover soil stockpiling on plant community development following reclamation of oil sands sites in Alberta 总被引:1,自引:0,他引:1
Stockpiling of cover soil can influence vegetation development following reclamation. Cover soil, comprising the upper 15–30 cm of the surface material on sites scheduled for mining, is commonly salvaged prior to mining and used directly or stockpiled for various lengths of time until it is needed. Salvaging and stockpiling causes physical, chemical, and biological changes in cover soils. In particular, stockpiling reduces the availability and vigor of vegetative propagules and seed, and can lead to increases in the abundance of some weedy species. This study uses data from monitoring plots to assess how stockpiling of cover soil impacts plant community development on reclaimed oil sands mine sites in northern Alberta. Development of plant communities differed distinctly between directly placed and stockpiled cover soil treatments even 18 years after reclamation. Direct placement of cover soil resulted in higher percent cover, species richness, and diversity. Nonmetric multidimensional scaling and multiresponse permutation procedure revealed compositional differentiation between the treatments. Indicator species analysis showed that direct placement treatment was dominated by perennial species while grasses and annual forb species dominated sites where stockpiled soil was used. Results indicate that stockpiling leads to slower vegetation recovery while direct placement of cover soil supports more rapid succession (from ruderal and annual communities to perennial communities). In addition, direct placement may be less costly than stockpiling. However, scheduling of salvage and placement remains a challenge. 相似文献
45.
46.
Adiki Shanta Kumari Perla Chandra Kiran Saha Gargi Katakam Prakash Theendra Vinaykumar 《Biological trace element research》2019,190(1):150-156
Biological Trace Element Research - This research article aims to establish the intake ratio of probiotic Lactobacillus plantarum 299v with iron supplement pearl millet by central composite design... 相似文献
47.
Giuliani Rita Karki Shanta Covshoff Sarah Lin Hsiang-Chun Coe Robert A. Koteyeva Nuria K. Evans Marc A. Quick W. Paul von Caemmerer Susanne Furbank Robert T. Hibberd Julian M. Edwards Gerald E. Cousins Asaph B. 《Photosynthesis research》2019,142(2):153-167
Photosynthesis Research - The engineering process of C4 photosynthesis into C3 plants requires an increased activity of phosphoenolpyruvate carboxylase (PEPC) in the cytosol of leaf mesophyll... 相似文献
48.
Neeraj Kumar Aditi Singh Sonam Grover Anchala Kumari Pawan Kumar Dhar Ramesh Chandra 《Journal of biomolecular structure & dynamics》2019,37(8):2098-2109
Outbreak of Human Herpes virus-5 (HHV-5) infection in emerging countries has raised worldwide health concern owing to prevalence of congenital impairments and life threatening consequences in immunocompromised individuals. Thus, there lies an impending need to develop vaccine against HHV-5. HHV-5 enters into host cells with the help of necessary components glycoprotein B (gB) and H/L. In this study, the conformational linear B-cell and T-cell epitopes for gB of HHV-5 have been predicted using conformational approaches, for their possible collective use as vaccine candidates. We examined epitope’s interactions with major histocompatibility complexes using molecular docking and also investigated their stable binding with specific toll like receptor-2 (TLR2), present on host cells during HHV-5 infection. Predicted MHC-I epitope ‘LVAIAVVII’ with high antigenicity and large coverage of HLA alleles was found to superimpose on MHC-II epitope (Rank 1) and was also identified to be the core sequence of putative B cell epitope ‘ILVAIAVVIITYLI’. Resulting epitope was found to have consistent interaction with TLR2 during long term (100?ns) MD run. We also validated this nonamer epitope for its dissimilarity with human genome and high population coverage, suggesting it to be a potential vaccine candidate with higher coverage for both the MHC alleles of Indian population.
Communicated by Ramaswamy H. Sarma 相似文献
49.
Two different protein kinase activities phosphorylate Ras2 protein in Saccharomyces cerevisiae 总被引:1,自引:0,他引:1
T L Sreenath D Breviario N Ahmed R Dhar 《Biochemical and biophysical research communications》1988,157(3):1182-1189
In this report, we show that Ras2 protein in the yeast Saccharomyces cerevisiae is phosphorylated in vivo by protein kinase(s) and the phosphorylation is stable. Ras2 protein is phosphorylated by cAMP dependent protein kinase and by an additional protein kinase activity which is independent of cAMP levels. 相似文献
50.
B Dhar B D Singh R B Singh J S Srivastava V P Singh R M Singh 《Acta microbiologica Polonica》1979,28(4):319-324
Soil samples from 30 fields in neighbouring districts of Varanasi were screened for rhizobiophages on 60 Rhizobium strains. Plaques were observed on five strains: P1, P5, SU391 (R. leguminosarum), CB756 and 32H1 (Rhizobium sp.). Rhizobiophages infective on one or more of the five strains were present in all fields. There seems to be no correlation between presence of phage and the standing crop or the pH (7.1-8.2) of the soil. Eight distinct rhizobiophages have been isolated and characterized for host specificity, plaque morphology and maximum titer in broth. 相似文献