全文获取类型
收费全文 | 1602篇 |
免费 | 176篇 |
国内免费 | 1篇 |
出版年
2023年 | 10篇 |
2022年 | 8篇 |
2021年 | 24篇 |
2020年 | 24篇 |
2019年 | 22篇 |
2018年 | 37篇 |
2017年 | 17篇 |
2016年 | 51篇 |
2015年 | 55篇 |
2014年 | 84篇 |
2013年 | 99篇 |
2012年 | 140篇 |
2011年 | 108篇 |
2010年 | 63篇 |
2009年 | 76篇 |
2008年 | 72篇 |
2007年 | 69篇 |
2006年 | 55篇 |
2005年 | 47篇 |
2004年 | 60篇 |
2003年 | 50篇 |
2002年 | 44篇 |
2001年 | 53篇 |
2000年 | 40篇 |
1999年 | 44篇 |
1998年 | 29篇 |
1997年 | 32篇 |
1996年 | 22篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 44篇 |
1991年 | 28篇 |
1990年 | 24篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1970年 | 7篇 |
排序方式: 共有1779条查询结果,搜索用时 437 毫秒
31.
Characterization of the Erwinia chrysanthemi osmoprotectant transporter gene ousA. 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Growth of Erwinia chrysanthemi in media of elevated osmolarity can be achieved by the uptake and accumulation of various osmoprotectants. This study deals with the cloning and sequencing of the ousA gene-encoded osmoprotectant uptake system A from E. chrysanthemi 3937. OusA belongs to the superfamily of solute ion cotransporters. This osmotically inducible system allows the uptake of glycine betaine, proline, ectoine, and pipecolic acid and presents strong similarities in nucleotide sequence and protein function with the proline/betaine porter of Escherichia coli encoded by proP. The control of ousA expression is clearly different from that of proP. It is induced by osmotic strength and repressed by osmoprotectants. Its expression in E. coli is controlled by H-NS and is rpoS dependent in the exponential phase but unaffected by the stationary phase. 相似文献
32.
Recombinant Treponema pallidum rare outer membrane protein 1 (Tromp1) expressed in Escherichia coli has porin activity and surface antigenic exposure. 总被引:3,自引:2,他引:1
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
D R Blanco C I Champion M M Exner E S Shang J T Skare R E Hancock J N Miller M A Lovett 《Journal of bacteriology》1996,178(23):6685-6692
We recently reported the cloning and sequencing of the gene encoding a 31-kDa Treponema pallidum subsp. pallidum rare outer membrane porin protein, designated Tromp1 (D. R. Blanco, C. I. Champion, M. M. Exner, H. Erdjument-Bromage, R. E. W. Hancock, P. Tempst, J. N. Miller, and M. A. Lovett, J. Bacteriol. 177:3556-3562, 1995). Here, we report the stable expression of recombinant Tromp1 (rTromp1) in Escherichia coli. rTromp1 expressed without its signal peptide and containing a 22-residue N-terminal fusion resulted in high-level accumulation of a nonexported soluble protein that was purified to homogeneity by fast protein liquid chromatography (FPLC). Specific antiserum generated to the FPLC-purified rTromp1 fusion identified on immunoblots of T. pallidum the native 31-kDa Tromp1 protein and two higher-molecular-mass oligomeric forms of Tromp1 at 55 and 80 kDa. rTromp1 was also expressed with its native signal peptide by using an inducible T7 promoter. Under these conditions, rTromp1 fractionated predominantly with the E. coli soluble and outer membrane fractions, but not with the inner membrane fraction. rTromp1 isolated from the E. coli outer membrane and reconstituted into planar lipid bilayers showed porin activity based on average single-channel conductances of 0.4 and 0.8 nS in 1 M KCl. Whole-mount immunoelectron microscopy using infection-derived immune serum against T. pallidum indicated that rTromp1 was surface exposed when expressed in E. coli. These findings demonstrate that rTromp1 can be targeted to the E. coli outer membrane, where it has both porin activity and surface antigenic exposure. 相似文献
33.
J.F. Fernández-Garayzábal C. Delgado M.M. Blanco G. Suáiez L. Domínguez 《Letters in applied microbiology》1996,22(3):249-252
J.F. FERNÁNDEZ-GARAYZÁBAL, C. DELGADO, M.M. BLANCO, G. SUÁREZ AND L. DOMÍNGUEZ. 1996. The CAMP reaction between Listeria monocytogenes and Rhodococcus equi was studied by a diffusion assay. Listeria monocytogenes displayed identical cooperative haemolytic effect with supernatant cultures of equi or with commercial cholesterol oxidase (COX). This result, even with enzymes of different sources (commercial COX is obtained from Pseudomonas spp.) suggests that this enzyme secreted by R. equi has a crucial role in the synergistic haemolytic (CAMP) reaction with L. monocytogenes . The mechanism of the cooperative lytic process between L. monocytogenes and R. equi may represent a different and novel mechanism reaction, in which the COX may not act as a conventional second-step factor, and a reaction different to the direct interaction with the cholesterol of the erythrocyte membrane may be involved. 相似文献
34.
The functional significance of the conserved motif ''YxGG/A'', located between the 3''-5'' exonuclease and polymerization domains of eukaryotic-type DNA polymerases, has been studied by site-directed mutagenesis in phi29 DNA polymerase. Single substitutions at this region were obtained, and 11 phi29 DNA polymerase mutant derivatives were overproduced in Escherichia coli and purified to homogeneity. Nine mutants showed an altered polymerase/3''-5'' exonuclease balance on a template/primer DNA structure, giving rise to three different mutant phenotypes: (i) favored polymerization (high pol/exo ratio); (ii) favored exonucleolysis (low pol/exo ratio); and (iii) favored exonucleolysis and null polymerization. Interestingly, these three different phenotypes could be obtained by mutating a single amino acid at the ''YxGG/A'' motif. All different phenotypes could be directly related to defects in DNA binding at a particular active site. Thus, a high pol/exo ratio was related to a poor stability at the 3''-5'' exonuclease active site. On the contrary, a low pol/exo ratio or null polymerization capacity was related to a poor stability at the polymerization active site and either a normal or an increased accessibility to the exonuclease active site. These results allow us to propose that this motif, located in the connecting region between the N-terminal and C-terminal domains, has a primary role in DNA binding, playing a critical role in the coordination or cross-talk between synthesis and degradation. 相似文献
35.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
36.
Mycotoxin Research - In the present work we studied the ability of phosphate buffer to solubize sterigmatocystin (ST) at different pH values. We observed a higher solubility of ST at acid pH... 相似文献
37.
Guerrero Francisco; Blanco Jose M; Rodriguez Valeriano 《Journal of plankton research》1994,16(1):95-103
A comparative analysis was carried out on the several equationsmost commonly used to describe the dependence of the developmentof organisms on temperature. Goodness of fit, number of parameters,ease of fitting data and biological significance were compared. 相似文献
38.
In vitro replication of bacteriophage PRD1 DNA. Characterization of the protein-primed initiation site. 总被引:5,自引:0,他引:5
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)
Bacteriophage PRD1 replicates its DNA by means of a protein-primed replication mechanism. Using single-stranded oligonucleotide templates carrying the sequence corresponding to the 25 first bases of the 3' end of PRD1 DNA, and Mg2+ as the activating metal ion of the phage DNA polymerase, we show that the fourth base from the 3' end of the template directs, by base complementarity, the dNMP to be linked to the phage terminal protein (TP) in the initiation reaction. This result suggests that phage PRD1 maintains its 3' end DNA sequences via a sliding-back mechanism. The single-stranded DNA templates could not be replicated by the PRD1 DNA polymerase, much in contrast to the natural TP-DNA. Nevertheless, the analysis of the transition products obtained with TP-DNA and origin-containing oligonucleotides suggests that sliding-back occurs stepwise, the fourth base being the directing position during the entire process. 相似文献
39.
Estaras Matias Ortiz-Placin Candido Castillejo-Rufo Alba Fernandez-Bermejo Miguel Blanco Gerardo Mateos Jose M. Vara Daniel Gonzalez-Cordero Pedro L. Chamizo Sandra Lopez Diego Rojas Adela Jaen Isabel de Armas Noelia Salido Gines M. Iovanna Juan L. Santofimia-Castaño Patricia Gonzalez Antonio 《Journal of physiology and biochemistry》2023,79(1):235-249
Journal of Physiology and Biochemistry - We have investigated the effects of melatonin on major pathways related with cellular proliferation and energetic metabolism in pancreatic stellate cells.... 相似文献
40.
Franco M. Valdez Ovallez Rodrigo Gómez Alés Vanesa Astudillo Mariela Córdoba Gustavo Fava Rodrigo Acosta Graciela Blanco José Villavicencio Juan Carlos Acosta 《Acta zoologica》2023,104(4):561-574
Ectotherms thermoregulate to maintain their body temperature within the optimal range needed for performing vital functions. The effect of climate change on lizards has been studied as regards the sensitivity of locomotor performance to environmental temperatures. We studied thermoregulatory efficiency and locomotor performance for Liolaemus fitzgeraldi in the Central Andes of Argentina. We determined body temperature, micro-environmental temperatures and operative temperatures in the field. In the laboratory, we measured preferred temperatures and calculated the index of thermoregulatory efficiency. We estimated the thermal sensitivity of locomotion by measuring sprint speed (initial velocity and long sprint) and endurance at five different body temperatures. Body temperature was not associated with either micro-environmental temperature, nor did it show differences with preferred temperatures. Thermoregulatory efficiency was moderate (0.61). Initial velocity and long sprint trials showed differences at different temperatures; however, endurance did not. Moreover, the optimal temperatures for the performance trials showed no significant differences among themselves. We conclude that Liolaemus fitzgeraldi has thermal sensitivity in locomotor performance with respect to body temperature and that it is an eurythermic lizard that experiences a large variation in body temperature and that has thermal flexibility in the cold. 相似文献