全文获取类型
收费全文 | 5635篇 |
免费 | 283篇 |
国内免费 | 594篇 |
出版年
2024年 | 5篇 |
2023年 | 45篇 |
2022年 | 74篇 |
2021年 | 115篇 |
2020年 | 129篇 |
2019年 | 124篇 |
2018年 | 99篇 |
2017年 | 109篇 |
2016年 | 130篇 |
2015年 | 115篇 |
2014年 | 182篇 |
2013年 | 379篇 |
2012年 | 219篇 |
2011年 | 243篇 |
2010年 | 214篇 |
2009年 | 295篇 |
2008年 | 356篇 |
2007年 | 323篇 |
2006年 | 291篇 |
2005年 | 263篇 |
2004年 | 249篇 |
2003年 | 233篇 |
2002年 | 163篇 |
2001年 | 153篇 |
2000年 | 134篇 |
1999年 | 160篇 |
1998年 | 151篇 |
1997年 | 126篇 |
1996年 | 114篇 |
1995年 | 140篇 |
1994年 | 149篇 |
1993年 | 138篇 |
1992年 | 128篇 |
1991年 | 107篇 |
1990年 | 82篇 |
1989年 | 84篇 |
1988年 | 99篇 |
1987年 | 100篇 |
1986年 | 65篇 |
1985年 | 37篇 |
1984年 | 53篇 |
1983年 | 28篇 |
1982年 | 31篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1972年 | 3篇 |
排序方式: 共有6512条查询结果,搜索用时 31 毫秒
371.
Kadioglu A Sharpe JA Lazou I Svanborg C Ockleford C Mitchell TJ Andrew PW 《FEMS microbiology letters》2001,204(1):105-110
The pneumococcus is the principle cause of bacterial pneumonia and also a major cause of bacterial meningitis. The mechanisms and sites of pneumococcal adherence and invasion of the respiratory tract in vivo are not clear however. We have made pneumococci expressing green fluorescent protein (GFP) and used it to trace pneumococcal adherence and invasion in vivo. By using GFP pneumococci we have shown bacterial adherence and invasion of broncho-epithelial cells in vivo by 4 h post-infection, with increases in pneumococcal invasiveness by 24 h. Using confocal image analysis we have shown varying levels of pneumococcal penetration and internalisation into host cells, as well as translocation through epithelial layers. To our knowledge this is the first report of pneumococcal invasion and cellular translocation in vivo. 相似文献
372.
Heat-stable enterotoxin II of Escherichia coli (STII) is synthesized as a precursor form consisting of pre- and mature regions. The pre-region is cleaved off from the mature region during translocation across the inner membrane, and the mature region emerges in the periplasm. The mature region, composed of 48 amino acid residues, is processed in the periplasm by DsbA to form an intramolecular disulfide bond between Cys-10 and Cys-48 and between Cys-21 and Cys-36. STII formed with these disulfide bonds is efficiently secreted out of the cell through the secretory system, including TolC. However, it remains unknown which regions of STII are involved in interaction with TolC. In this study, we mutated the STII gene and examined the secretion of these STIIs into the culture supernatant. A deletion of the part covering from amino acid residue 37 to the carboxy terminal end did not markedly reduce the efficiency of secretion of STII into the culture supernatant. On the other hand, the efficiency of secretion of the peptide covering from the amino terminal end to position 18 to the culture supernatant was significantly low. These observations indicated that the central region of STII from amino acid residue 19 to that at position 36 is involved in the secretion of STII into the milieu. The experiment using a dsbA-deficient strain of E. coli showed that the disulfide bond between Cys-21 and Cys-36 by DsbA is necessary for STII to adapt to the structure that can cross the outer membrane. 相似文献
373.
Kaneko A Fujino T Sugawara C Kagami Y Miyadai H Kirikae T Kawahara K 《Microbiology and immunology》2001,45(6):433-438
Escherichia coli O25 strains that produce heat-stable toxin (ST) have been recently isolated in Japan, and epidemiological study of this type of enterotoxigenic E. coli is required. In this study the heterogeneity of 16 ST-producing and non-producing strains of E. coli O25 was investigated. All eight ST-producing strains were shown to have STIb gene, and seven of them had similar profiles of plasmids, ladder-banding of LPS in SDS-polyacrylamide gel electrophoresis, and chromosomal DNA digestions in pulsed-field gel electrophoresis (PFGE). In contrast, ST-non-producing strains were more heterogeneous in all parameters examined. PFGE of the digested chromosomal DNA with several restriction enzymes was proved to be an effective procedure to compare the closely related strains of E. coli O25. 相似文献
374.
Escherichia coli genes involved in resistance to pyrazinoic acid,the active component of the tuberculosis drug pyrazinamide 总被引:1,自引:0,他引:1
The natural resistance of Escherichia coli to pyrazinoic acid (POA), the active derivative of pyrazinamide, was investigated. The TolC mutant was found to be more susceptible to POA and other weak acids than the wild-type strain. Mutation in EmrB but not AcrB efflux protein slightly increased POA susceptibility. Two transposon mutants with increased susceptibility to POA were found to harbor mutations in acnA encoding aconitase-1 and ygiY encoding a putative two-component sensor protein. Complementation of the AcnA and YgiY mutants conferred resistance to POA, whereas the complemented TolC mutant became resistant to POA and other weak acids. 相似文献
375.
Nakao H Kataoka C Kiyokawa N Fujimoto J Yamasaki S Takeda T 《Microbiology and immunology》2002,46(11):777-780
A monoclonal antibody, 5-5B, which neutralizes Shiga toxin 1 (Stx1) cytotoxicity of Escherichia coli, was constructed. An epitope analysis indicated that Asn55 in Stx1 B subunit was an important residue. This result and our previous results using an anti-Stx2 monoclonal antibody indicate that the region around the cysteine residue of the disulfide bond might be important for the neutralization of Stx cytotoxicity, making it a potential vaccination candidate. 相似文献
376.
Use of at-line and in-situ near-infrared spectroscopy to monitor biomass in an industrial fed-batch Escherichia coli process 总被引:1,自引:0,他引:1
One of the key goals in bioprocess monitoring is to achieve real-time knowledge of conditions within the bioreactor, i.e., in-situ. Near-infrared spectroscopy (NIRS), with its ability to carry out multi-analyte quantification rapidly with little sample presentation, is potentially applicable in this role. In the present study, the application of NIRS to a complex, fed-batch industrial E. coli (RV308/PHKY531) process was investigated. This process undergoes a series of temperature changes and is vigorously agitated and aerated. These conditions can pose added challenges to in-situ NIRS. Using the measurement of a key analyte (biomass) as an illustration, the details of the relationship between the at-line and in-situ use of NIRS are considered from the viewpoint of both theory and practical application. This study shows that NIRS can be used both at-line and in-situ in order to achieve good predictive models for biomass. There are particular challenges imposed by in-situ operation (loss of wavelength regions and noise) which meant the need for signal optimisation studies. This showed that whilst the at-line modelling process may provide some useful information for the in-situ process, there were distinct differences. This study shows that the in-situ use of NIRS in a highly challenging matrix (similar to those encountered in current industrial practice) is possible, and thus extends previous works in the area. 相似文献
377.
378.
Jeremy S Edwards Ramprasad Ramakrishna Bernhard O Palsson 《Biotechnology and bioengineering》2002,77(1):27-36
Genome-scale metabolic maps can be reconstructed from annotated genome sequence data, biochemical literature, bioinformatic analysis, and strain-specific information. Flux-balance analysis has been useful for qualitative and quantitative analysis of metabolic reconstructions. In the past, FBA has typically been performed in one growth condition at a time, thus giving a limited view of the metabolic capabilities of a metabolic network. We have broadened the use of FBA to map the optimal metabolic flux distribution onto a single plane, which is defined by the availability of two key substrates. A finite number of qualitatively distinct patterns of metabolic pathway utilization were identified in this plane, dividing it into discrete phases. The characteristics of these distinct phases are interpreted using ratios of shadow prices in the form of isoclines. The isoclines can be used to classify the state of the metabolic network. This methodology gives rise to a "phase plane" analysis of the metabolic genotype-phenotype relation relevant for a range of growth conditions. Phenotype phase planes (PhPPs) were generated for Escherichia coli growth on two carbon sources (acetate and glucose) at all levels of oxygenation, and the resulting optimal metabolic phenotypes were studied. Supplementary information can be downloaded from our website (http://epicurus.che.udel.edu). 相似文献
379.
Our results show that experimental evolution mimics evolution in nature. In particular, only 1000 generations of periodic
recombination with immigrant genotypes is enough for linkage disequilibrium values in experimental populations to change from
a maximum linkage value to a value similar to the one observed in wild strains of E. coli. Our analysis suggests an analogy between the recombination experiment and the evolutionary history of E. coli; the E. coligenome is a patchwork of genes laterally inserted in a common backbone, and the experimental E. coli chromosome is a patchwork where some sites are highly prone to recombination and others are very clonal. In addition, we
propose a population model for wild E. coli where gene flow (recombination and migration) are an important source of genetic variation, and where certain hosts act as
selective sieves; i.e., the host digestive system allows only certain strains to adhere and prosper as resident strains generating
a particular microbiota in each host. Therefore we suggest that the strains from a wide range of wild hosts from different
regions of the world may present an ecotypic structure where adaptation to the host may play an important role in the population
structure.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
380.
Escherichia coli, lacking cytoplasmic superoxide dismutases, exhibits a variety of oxygen-dependent phenotypic deficits. Enrichment of the growth medium with Mn(II) relieved those deficits. Extracts of cells grown on Mn(II)-rich medium exhibited superoxide dismutase-like activity that was due partially to low-molecular-weight and partially to high-molecular-weight complexes. The high-molecular-weight activity was sensitive to proteolysis. Hence this activity is likely associated with low-affinity binding of Mn to proteins. 相似文献