全文获取类型
收费全文 | 2966篇 |
免费 | 181篇 |
专业分类
3147篇 |
出版年
2023年 | 14篇 |
2022年 | 39篇 |
2021年 | 56篇 |
2020年 | 35篇 |
2019年 | 75篇 |
2018年 | 70篇 |
2017年 | 53篇 |
2016年 | 89篇 |
2015年 | 164篇 |
2014年 | 140篇 |
2013年 | 208篇 |
2012年 | 243篇 |
2011年 | 210篇 |
2010年 | 136篇 |
2009年 | 102篇 |
2008年 | 173篇 |
2007年 | 180篇 |
2006年 | 169篇 |
2005年 | 162篇 |
2004年 | 158篇 |
2003年 | 132篇 |
2002年 | 151篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 28篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 20篇 |
1994年 | 16篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 19篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 21篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有3147条查询结果,搜索用时 0 毫秒
941.
Mustacchi R Knowles CJ Li H Dalrymple I Sunderland G Skibar W Jackman SA 《Biotechnology and bioengineering》2005,89(1):18-23
The simultaneous enhancement of biotransformation coupled to product recovery, purification and concentration is presented. The nitrilase of Rhodococcus rhodochrous LL100-21 catalyses the single-step hydrolytic biotransformation of benzonitrile to benzoic acid and ammonia. When a direct electric current is applied across a bioreactor containing the bacterium and benzonitrile, the charged product (benzoic acid) can be removed in situ across an anion exchange membrane and recovered in a separate compartment. Over the course of a 24-hour biotransformation, benzonitrile was converted to benzoic acid which was completely removed from the bioreactor chamber and concentrated 3-fold in a separate chamber. The rate of production of benzoic acid increased by 42% when the current was applied (0.044 mmol/min/g dry cell weight in the presence of current as compared to 0.03 mmol/min/g dry cell weight in its absence). The enhanced reaction rate was achieved irrespective of product separation and therefore appears to be a direct effect upon the bacterial cells. This process has potential for enhanced productivity from biotransformations through a simultaneous increase in metabolic activity and in situ product recovery. 相似文献
942.
943.
944.
945.
Detection of a polymorphism in exon 8 of the human CD86 gene 总被引:1,自引:0,他引:1
946.
Mac Sweeney A Lange R Fernandes RP Schulz H Dale GE Douangamath A Proteau PJ Oefner C 《Journal of molecular biology》2005,345(1):115-127
The key enzyme in the non-mevalonate pathway of isoprenoid biosynthesis, 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) has been shown to be the target enzyme of fosmidomycin, an antimalarial, antibacterial and herbicidal compound. Here we report the crystal structure of selenomethionine-labelled Escherichia coli DXR in a ternary complex with NADPH and fosmidomycin at 2.2 A resolution. The structure reveals a considerable conformational rearrangement upon fosmidomycin binding and provides insights into the slow, tight binding inhibition mode of the inhibitor. Although the inhibitor displays an unusual non-metal mediated mode of inhibition, which is an artefact most likely due to the low metal affinity of DXR at the pH used for crystallization, the structural data add valuable information for the rational design of novel DXR inhibitors. Using this structure together with the published structural data and the 1.9 A crystal structure of DXR in a ternary complex with NADPH and the substrate 1-deoxy-D-xylulose 5-phosphate, a model for the physiologically relevant tight-binding mode of inhibition is proposed. The structure of the substrate complex must be interpreted with caution due to the presence of a second diastereomer in the active site. 相似文献
947.
McKean-Cowdin R Spencer Feigelson H Xia LY Pearce CL Thomas DC Stram DO Henderson BE 《Human genetics》2005,116(6):497-506
We sequenced the entire coding region of BRCA1 to improve our understanding of the frequency and nature of BRCA1 variants in African-American and Latina women identified from a multiethnic cohort in Los Angeles, California. The study included 109 African-American and 140 Latina sibships from families with two or more cases of breast or ovarian cancer among first-degree relatives. BRCA1 was sequenced in 278 breast or ovarian cancer cases and 229 unaffected sisters. The proportion of cases with known disease-causing mutations was low (0.72, 95% confidence interval: 0–1.7%). In total, 33 sequence variants were identified, including two protein truncation mutations, one deletion, and six silent and 24 missense variants. Two novel rare variants were identified that appeared to act as benign polymorphisms. Four rare variants may be unique to women of African descent based on existing literature, and three have been described exclusively in Latina women. The frequency of common variants was similar for cases and controls, but the frequency of common variants for African-American women significantly differed from those previously described for Caucasian women. We believe this to be the largest study of high-risk African-American and Latina women sequenced for variants in the BRCA1 gene to date. 相似文献
948.
Barbieri E Bertini L Rossi I Ceccaroli P Saltarelli R Guidi C Zambonelli A Stocchi V 《FEMS microbiology letters》2005,247(1):23-35
The microbial community associated with ascocarps of the ectomycorrhizal fungus Tuber borchii Vittad. was studied by both cultivation and direct extraction of bacterial 16S rRNA gene (rDNA) sequence approaches. The inner part of six T. borchii ascoma collected in North-Central Italy was used to establish a bacterial culture collection and to extract the total genomic DNA to obtain a library of 16S rDNAs representative of the truffle bacterial community. Most of the isolates were affiliated to the gamma-Proteobacteria, mainly Fluorescent pseudomonads; some isolates were members of the Bacteroidetes group and Gram-positive bacteria, mostly Bacillaceae. The majority of the clones from the library were alpha-Proteobacteria showing significant similarity values, of greater than 97%, with members of the Sinorhizobium/Ensifer Group, Rhizobium and Bradyrhizobium spp. not previously identified as Tuber-associated bacteria. Only a few bacterial strains belonging to this bacterial subclass were found in the culture collection and isolated on a medium specific for Rhizobium-like organisms. A few clones were members of the beta- and gamma-Proteobacteria; as well as low and high G+C Gram-positive bacteria. Our findings clearly indicate that a dual approach increases the information obtained on the structural composition of a truffle bacterial community as compared to that derived via cultivation or direct recovery of 16S rDNA sequences alone. 相似文献
949.
Mitochondria and plasma membrane as targets of UVA-induced toxicity of neuroleptic drugs fluphenazine, perphenazine and thioridazine 总被引:1,自引:0,他引:1
Bastianon C Zanoni R Miolo G Caffieri S Reddi E 《The international journal of biochemistry & cell biology》2005,37(4):901-908
In order to gain insights into the mechanism of phototoxicity of the neuroleptic drugs fluphenazine, perphenazine and thioridazine in cultured cells, studies were performed with murine 3T3 fibroblasts, aimed at identifying some cellular targets responsible for photoinduced cell death and possible cytotoxic reactive species involved in the photosensitization process. 3T3 fibroblasts incubated with 5 microM drugs and irradiated with UVA light (up to 8 J/cm2) underwent cell death, the extent of which depended on light dose. Of the three drugs, fluphenazine exhibited the highest phototoxicity and 100% cell death was achieved with a light dose of 5 J/cm2. Superoxide dismutase and alpha-tocopherol exerted a dose-dependent protective effect against drug phototoxicity, whereas N-acetylcysteine failed to do so. These findings indicate that superoxide anion and other free radical intermediates, generated in lipophilic cellular environments, play a role in photoinduced toxicity. Phototreatment of drug-loaded cells induces release of the cytosolic enzyme lactate dehydrogenase and causes loss of activity of mitochondrial NADH dehydrogenase, indicating that plasma membrane and mitochondria are among the targets of the phototoxicity of these drugs. 相似文献
950.
The evolutionary origin of cardiac chambers 总被引:3,自引:0,他引:3