全文获取类型
收费全文 | 23693篇 |
免费 | 1775篇 |
国内免费 | 676篇 |
专业分类
26144篇 |
出版年
2024年 | 38篇 |
2023年 | 234篇 |
2022年 | 507篇 |
2021年 | 854篇 |
2020年 | 565篇 |
2019年 | 722篇 |
2018年 | 799篇 |
2017年 | 625篇 |
2016年 | 908篇 |
2015年 | 1332篇 |
2014年 | 1431篇 |
2013年 | 1674篇 |
2012年 | 1973篇 |
2011年 | 1953篇 |
2010年 | 1218篇 |
2009年 | 1001篇 |
2008年 | 1303篇 |
2007年 | 1190篇 |
2006年 | 1141篇 |
2005年 | 990篇 |
2004年 | 895篇 |
2003年 | 776篇 |
2002年 | 722篇 |
2001年 | 319篇 |
2000年 | 245篇 |
1999年 | 286篇 |
1998年 | 196篇 |
1997年 | 211篇 |
1996年 | 171篇 |
1995年 | 159篇 |
1994年 | 153篇 |
1993年 | 123篇 |
1992年 | 150篇 |
1991年 | 128篇 |
1990年 | 115篇 |
1989年 | 85篇 |
1988年 | 104篇 |
1987年 | 69篇 |
1986年 | 72篇 |
1985年 | 91篇 |
1984年 | 70篇 |
1983年 | 57篇 |
1982年 | 68篇 |
1981年 | 57篇 |
1980年 | 43篇 |
1979年 | 36篇 |
1978年 | 30篇 |
1977年 | 38篇 |
1976年 | 29篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Changling Zhang Haifeng Pan Lingli Yao Wenna Bao Jinxin Wang Zhipeng Xie Jianguo Zhang 《Biotechnology letters》2016,38(8):1301-1306
Objectives
To enhance activity of cis-epoxysuccinate hydrolase from Klebsiella sp. BK-58 for converting cis-epoxysuccinate to tartrate.Results
By semi-saturation mutagenesis, all the mutants of the six important conserved residues almost completely lost activity. Then random mutation by error-prone PCR and high throughput screening were further performed to screen higher activity enzyme. We obtained a positive mutant F10D after screening 6000 mutations. Saturation mutagenesis on residues Phe10 showed that most of mutants exhibited higher activity than the wild-type, and the highest mutant was F10Q with activity of 812 U mg?1 (k cat /K m , 9.8 ± 0.1 mM?1 s?1), which was 230 % higher than that of wild-type enzyme 355 U mg?1 (k cat /K m , 5.3 ± 0.1 mM?1 s?1). However, the thermostability of the mutant F10Q slightly decreased.Conclusions
The catalytic activity of a cis-epoxysuccinate hydrolase was efficient improved by a single mutation F10Q and Phe10 might play an important role in the catalysis.992.
993.
Yufeng Yuan Kehan Huang Mengfang Chang Cuifang Qin Sanjun Zhang Haifeng Pan Yan Chen Jianhua Xu 《Analytical biochemistry》2016
Fluorescent silver nanoclusters (Ag NCs) displaying dual-excitation and dual-emission properties have been developed for the specific detection of NAD+ (nicotinamide adenine dinucleotide, oxidized form). With the increase of NAD+ concentrations, the longer wavelength emission (with the peak at 550 nm) was gradually quenched due to the strong interactions between the NAD+ and Ag NCs, whereas the shorter wavelength emission (peaking at 395 nm) was linearly enhanced. More important, the dual-emission intensity ratio (I395/I550), fitting by a single-exponential decay function, can efficiently detect various NAD+ levels from 100 to 4000 μM, as well as label NAD+/NADH (reduced form of NAD) ratios in the range of 1–50. 相似文献
994.
995.
996.
997.
用RT-PCR法从一名抗-HCV阳性献血员血清中扩增到约900bp的DNA片段,经EcoRI酶切后插入pET17Xb表达质粒。SDS-PAGE表明重组质粒在约65kD处有融合蛋白表达,表达蛋白含量约为24%。对其插入片段进行序列分析:核着酸长度为945bp,A:T:G:C比例为18.6:21.9:30.5:29.0,G/C含量占59%,与其它一些HCV殊比较,核着酸同源性Ⅰ型为77.1%.Ⅲ、Ⅳ、Ⅴ、Ⅵ型均<70%.Ⅱ型各株均>90%;氨基酸序列比较的同源性Ⅰ型为857%,Ⅲ、Ⅳ、ⅤⅥ型各株均>70%,Ⅱ型各株均>93%。NS4基因的克隆和表达为其基因和产物作用的进一步研究奠定了基础。 相似文献
998.
Dexuan Wang Shufang Pan Yixiao Xu Xiaohua Ye Xiaobi Ren Qiyi Zeng 《中国科学:生命科学英文版》2016,59(11):1189-1191
正Dear Editor,NCC(Na-Cl cotransporter)is a cotransporter mainly distributed in the distal tubule of the kidney,functioning to reabsorb sodium and chloride ions from the tubular fluid into the cells of the renal distal convoluted tubule.It is a 相似文献
999.
1000.
Tonin AA Da Silva AS Costa MM Otto MA Thomé GR Tavares KS Miletti LC Leal MR Lopes ST Mazzanti CM Monteiro SG de La Rue ML 《Experimental parasitology》2011,128(3):243-249
The aim of this study was to evaluate the utilization of a standard treatment with diminazene aceturate against the infection caused by Trypanosoma evansi, associated to sodium selenite and vitamin E. In vitro tests showed trypanocidal effect related to the treatment with diminazene aceturate and sodium selenite, but vitamin E had no harmful effect on the trypanosomes. In vivo experiments utilized a total of 72 adult outbreed females rats, separated into 9 groups (A, B, C, D, E, F, G, H and I), 8 animals each. Group A was the uninfected group; groups B to I were infected with 0.2 mL of blood containing 106 trypanosomes. Parasitemia was estimated daily by microscopic examination of blood smears. Group B served as positive control; group C was treated with diminazene aceturate; group D with sodium selenite; group E with vitamin E; group F received an association of diminazene aceturate and sodium selenite; group G received an association of diminazene aceturate and vitamin E; group H received an association of diminazene aceturate, sodium selenite and vitamin E, and group I received an association of sodium selenite and vitamin E. Diminazene aceturate was administrated in a single dose on the 3rd day post infection (PI). Sodium selenite and vitamin E were administered at the 3rd and 23rd day PI. In vivo tests showed increase of longevity in groups treated with diminazene aceturate associated with sodium selenite (groups F and H). No difference was found between groups C and E, thus the vitamin E did not increase the efficacy of treatment against T. evansi when associated to diminazene aceturate. The curative efficacy of treatments was 37.5, 87.7, 37.7 and 75% to the groups C, F, G and H, respectively. Other treatments showed no efficacy. The sodium selenite when combined with chemotherapy may represent an alternative in the treatment of trypanosomosis. 相似文献