全文获取类型
收费全文 | 101332篇 |
免费 | 1040篇 |
国内免费 | 815篇 |
出版年
2023年 | 41篇 |
2022年 | 72篇 |
2021年 | 157篇 |
2020年 | 120篇 |
2019年 | 166篇 |
2018年 | 11959篇 |
2017年 | 10779篇 |
2016年 | 7664篇 |
2015年 | 1057篇 |
2014年 | 736篇 |
2013年 | 803篇 |
2012年 | 4938篇 |
2011年 | 13490篇 |
2010年 | 12344篇 |
2009年 | 8591篇 |
2008年 | 10295篇 |
2007年 | 11820篇 |
2006年 | 769篇 |
2005年 | 998篇 |
2004年 | 1439篇 |
2003年 | 1434篇 |
2002年 | 1152篇 |
2001年 | 368篇 |
2000年 | 232篇 |
1999年 | 118篇 |
1998年 | 103篇 |
1997年 | 94篇 |
1996年 | 75篇 |
1995年 | 57篇 |
1994年 | 69篇 |
1993年 | 68篇 |
1992年 | 61篇 |
1991年 | 69篇 |
1990年 | 44篇 |
1989年 | 30篇 |
1988年 | 49篇 |
1987年 | 40篇 |
1986年 | 24篇 |
1985年 | 19篇 |
1984年 | 33篇 |
1983年 | 33篇 |
1982年 | 26篇 |
1981年 | 15篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1975年 | 13篇 |
1972年 | 252篇 |
1971年 | 277篇 |
1965年 | 17篇 |
1962年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Objective
To develop a new expression system regulated by a ferric uptake regulator in which silicic acid is used as an inducer.Results
Fur box (binding site for Fur) was substituted for the lac operator to regulate the expression of GFP with the lac promoter. Since the addition of supersaturated silicic acid invokes iron deficiency, supersaturated silicic acids were used as an inducer. GFP expression was dependent on silica concentration, and the expression level without silica was negligible. Basal expression level of this lac-Fur system was extremely low and, hence, lytic enzyme gene E from bacteriophage ?X174 could be retained in this system. Furthermore, the expression of genes of interest was spontaneously initiated as the cell density increased and the costs of the inducer are considerably less than IPTG.Conclusion
The combination of lac promoter and Ferric uptake repressor allowed the protein expression by supersaturated silicic acid as an inducer in an easy and cost-effective way.993.
Ryosuke Fujiwara Shuhei Noda Yoshifumi Kawai Tsutomu Tanaka Akihiko Kondo 《Biotechnology letters》2016,38(9):1543-1549
Objectives
To find a novel host for the production of 4-vinylphenol (4VPh) by screening Streptomyces species.Results
The conversion of p-coumaric acid (pHCA) to 4VPh in Streptomyces mobaraense was evaluated using a medium containing pHCA. S. mobaraense readily assimilated pHCA after 24 h of cultivation to produce 4VPh. A phenolic acid decarboxylase, derived from S. mobaraense (SmPAD), was purified following heterologous expression in Escherichia coli. SmPAD was evaluated under various conditions, and the enzyme’s kcat/Km value was 0.54 mM ?1 s?1. Using intergenetic conjugation, a gene from Rhodobacter sphaeroides encoding a tyrosine ammonia lyase, which catalyzes the conversion of l-tyrosine to p-coumaric acid, was introduced into S. mobaraense. The resulting S. mobaraense transformant produced 273 mg 4VPh l?1 from 10 g glucose l?1.Conclusion
A novel strain suitable for the production of 4VPh and potentially other aromatic compounds was isolated.994.
Objectives
To investigate the mode of action of leucocin K7 against Listeria monocytogenes and to assess its inhibitory effect on Lis. monocytogenes in refrigerated milk.Results
A bacteriocin-producing strain, Leuconostoc mesenteroides K7, was isolated from a fermented pickle. The bacteriocin, leucocin K7, exhibited antagonistic activity against Lis. monocytogenes with an MIC of 28 µg/ml. It was sensitive to proteaseS and displayed good thermal stability and broad active pH range. Leucocin K7 had no effect on the efflux of ATP from Lis. monocytogenes but triggered the efflux of K+ and the intracellular hydrolysis of ATP. It also dissipated the transmembrane electrical potential completely and transmembrane pH gradient partially. It 80 AU/ml inhibited the growth of Lis. monocytogenes by 2.3–3.9 log units in milk; when combined with glycine (5 mg/ml), it completely eliminated viable Lis. monocytogenes over 7 daysConclusion
Leucocin K7 shows different mode of action from nisin and may have potential application in milk preservation.995.
Objectives
To investigate the contribution of direct electron transfer mechanisms to electricity production in microbial fuel cells by physically retaining Shewanella oneidensis cells close to or away from the anode electrode.Results
A maximum power output of 114 ± 6 mWm?2 was obtained when cells were retained close to the anode using a dialysis membrane. This was 3.5 times more than when the cells were separated away from the anode. Without the membrane the maximum power output was 129 ± 6 mWm?2. The direct mechanisms of electron transfer contributed significantly to overall electron transfer from S. oneidensis to electrodes, a result that was corroborated by another experiment where S. oneidensis cells were entrapped in alginate gels.Conclusion
S. oneidensis transfers electrons primarily by direct electron transfer as opposed to mediated electron transfer.996.
Jiandong Zhang Zhimei Cui Honghong Chang Xiaojun Fan Qiuyong Zhao Wenlong Wei 《Biotechnology letters》2016,38(9):1559-1564
Objectives
To investigate the efficiency of a cofactor regeneration enzyme co-expressed with a glycerol dehydrogenase for the production of 1,3-dihydroxyacetone (DHA).Results
In vitro biotransformation of glycerol was achieved with the cell-free extracts containing recombinant GlyDH (glycerol dehydrogenase from Escherichia coli), LDH (lactate dehydrogenase form Bacillus subtilis) or LpNox1 (NADH oxidase from Lactobacillus pentosus), giving DHA at 1.3 g l?1 (GlyDH/LDH) and 2.2 g l?1 (GlyDH/LpNox1) with total turnover number (TTN) of NAD+ recycling of 6039 and 11100, respectively. Whole cells of E. coli (GlyDH–LpNox1) co-expressing both GlyDH and LpNox1 were constructed and converted 10 g glycerol l?1 to DHA at 0.2–0.5 g l?1 in the presence of zero to 2 mM exogenous NAD+. The cell free extract of E. coli (GlyDH–LpNox) converted glycerol (2–50 g l?1) to DHA from 0.5 to 4.0 g l?1 (8–25 % conversion) without exogenous NAD+.Conclusions
The disadvantage of the expensive consumption of NAD+ for the production of DHA has been overcome.997.
Objectives
To improve the production and activity of an alkaline zinc metalloprotease from Salinivibrio proteolyticus in response to ZnSO4 (ionic and nanoparticle forms) and low intensity direct electric current (LIDC).Results
A DC of 50 µA for 10 min increased enzyme production from 35 to 53 U ml?1 when applied to the stationary phase bacterial cells. Zn2+ improved enzyme production better than zinc nanoparticles (52 vs. 43.5 U ml?1). Zinc nanoparticles (0.5 mM) added to an enzyme reaction mixture containing casein (0.65 %) and 20 mM Tris/HCl buffer (pH 8) improved enzyme activity more than Zn2+ (42 vs. 36 U ml?1).Conclusion
LIDC exposure (50 µA, 10 min) to the stationary phase bacterial cells increases metalloprotease production in Salinivibrio. A low concentration of zinc nanoparticles (0.5 mM) increases maximum enzyme activity.998.
999.
Pegah Amiri Azar Shahpiri Mohammad Ali Asadollahi Fariborz Momenbeik Siavash Partow 《Biotechnology letters》2016,38(3):503-508
Objectives
To engineer the yeast Saccharomyces cerevisiae for the heterologous production of linalool.Results
Expression of linalool synthase gene from Lavandula angustifolia enabled heterologous production of linalool in S. cerevisiae. Downregulation of ERG9 gene, that encodes squalene synthase, by replacing its native promoter with the repressible MET3 promoter in the presence of methionine resulted in accumulation of 78 µg linalool l?1 in the culture medium. This was more than twice that produced by the control strain. The highest linalool titer was obtained by combined repression of ERG9 and overexpression of tHMG1. The yeast strain harboring both modifications produced 95 μg linalool l?1.Conclusions
Although overexpression of tHMG1 and downregulation of ERG9 enhanced linalool titers threefold in the engineered yeast strain, alleviating linalool toxicity is necessary for further improvement of linalool biosynthesis in yeast.1000.
Sheng Zhang Fang Wang Congli Fan Bo Tang Xueming Zhang Ziyi Li 《Biotechnology letters》2016,38(3):395-402