全文获取类型
收费全文 | 2456篇 |
免费 | 165篇 |
国内免费 | 1篇 |
专业分类
2622篇 |
出版年
2023年 | 10篇 |
2022年 | 38篇 |
2021年 | 46篇 |
2020年 | 25篇 |
2019年 | 41篇 |
2018年 | 44篇 |
2017年 | 48篇 |
2016年 | 62篇 |
2015年 | 111篇 |
2014年 | 143篇 |
2013年 | 151篇 |
2012年 | 224篇 |
2011年 | 194篇 |
2010年 | 139篇 |
2009年 | 103篇 |
2008年 | 148篇 |
2007年 | 117篇 |
2006年 | 131篇 |
2005年 | 138篇 |
2004年 | 121篇 |
2003年 | 106篇 |
2002年 | 80篇 |
2001年 | 56篇 |
2000年 | 79篇 |
1999年 | 44篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有2622条查询结果,搜索用时 15 毫秒
101.
KpnBI is the prototype of a new family (IE) of bacterial type I restriction-modification system 总被引:1,自引:0,他引:1
KpnBI is a restriction-modification (R-M) system recognized in the GM236 strain of Klebsiella pneumoniae. Here, the KpnBI modification genes were cloned into a plasmid using a modification expression screening method. The modification genes that consist of both hsdM (2631 bp) and hsdS (1344 bp) genes were identified on an 8.2 kb EcoRI chromosomal fragment. These two genes overlap by one base and share the same promoter located upstream of the hsdM gene. Using recently developed plasmid R-M tests and a computer program RM Search, the DNA recognition sequence for the KpnBI enzymes was identified as a new 8 nt sequence containing one degenerate base with a 6 nt spacer, CAAANNNNNNRTCA. From Dam methylation and HindIII sensitivity tests, the methylation loci were predicted to be the italicized third adenine in the 5′ specific region and the adenine opposite the italicized thymine in the 3′ specific region. Combined with previous sequence data for hsdR, we concluded that the KpnBI system is a typical type I R-M system. The deduced amino acid sequences of the three subunits of the KpnBI system show only limited homologies (25 to 33% identity) at best, to the four previously categorized type I families (IA, IB, IC, and ID). Furthermore, their identity scores to other uncharacterized putative genome type I sequences were 53% at maximum. Therefore, we propose that KpnBI is the prototype of a new ‘type IE’ family. 相似文献
102.
103.
104.
Kim JH Brown SL Kolozsvary A Jenrow KA Ryu S Rosenblum ML Carretero OA 《Radiation research》2004,161(2):137-142
Inhibitors of angiotensin-converting enzyme (ACE) have been used to reduce radiation-induced normal tissue injury. The present study was carried out to determine whether ramipril, one of the inhibitors of ACE, would ameliorate radiation-induced brain damage, using a well-characterized optic neuropathy model in the rat, one of the most critical and radiosensitive structures in the brain. The brains of adult Fischer rats were irradiated stereotactically with 30 Gy using a single collimated beam. Six months after irradiation and 1.5 mg/kg day(-1) ramipril (started 2 weeks after irradiation), rats were assessed for optic nerve damage functionally, using visual evoked potential, and histologically. Results show that ramipril conferred significant modification of radiation injury, since rats receiving radiation alone showed a threefold lengthening in the mean peak latency in the visual evoked potential, whereas 75% of rats receiving radiation followed by ramipril had evoked potentials that resembled those of normal untreated control rats. The histology of irradiated and ramipril-treated optic nerves appeared nearly normal, while there was significant demyelination in both optic nerves of irradiated rats. The study represents the first demonstration of prophylaxis of radiation injury by a carboxyl-containing ACE inhibitor, providing a pharmacological strategy designed to reduce radiation-induced normal tissue damage. 相似文献
105.
Characterization of a novel amylolytic enzyme encoded by a gene from a soil-derived metagenomic library 总被引:16,自引:0,他引:16
Yun J Kang S Park S Yoon H Kim MJ Heu S Ryu S 《Applied and environmental microbiology》2004,70(12):7229-7235
It has been estimated that less than 1% of the microorganisms in nature can be cultivated by conventional techniques. Thus, the classical approach of isolating enzymes from pure cultures allows the analysis of only a subset of the total naturally occurring microbiota in environmental samples enriched in microorganisms. To isolate useful microbial enzymes from uncultured soil microorganisms, a metagenome was isolated from soil samples, and a metagenomic library was constructed by using the pUC19 vector. The library was screened for amylase activity, and one clone from among approximately 30,000 recombinant Escherichia coli clones showed amylase activity. Sequencing of the clone revealed a novel amylolytic enzyme expressed from a novel gene. The putative amylase gene (amyM) was overexpressed and purified for characterization. Optimal conditions for the enzyme activity of the AmyM protein were 42 degrees C and pH 9.0; Ca2+ stabilized the activity. The amylase hydrolyzed soluble starch and cyclodextrins to produce high levels of maltose and hydrolyzed pullulan to panose. The enzyme showed a high transglycosylation activity, making alpha-(1, 4) linkages exclusively. The hydrolysis and transglycosylation properties of AmyM suggest that it has novel characteristics and can be regarded as an intermediate type of maltogenic amylase, alpha-amylase, and 4-alpha-glucanotransferase. 相似文献
106.
Hong SY Chung KH You HJ Choi IH Chae MJ Han JY Jung OJ Kang SJ Ryu CK 《Bioorganic & medicinal chemistry letters》2004,14(13):3563-3566
A series of 6-arylamino-5-chloro-benzimidazole-4,7-diones were synthesized and tested for their inhibitory activity on the rat aortic smooth muscle cell (RAoSMC) proliferation. Among them, 6-arylamino-5-chloro-2-methyl-benzimidazole-4,7-diones exhibited potent antiproliferative activity. Benzimidazole-4,7-dione 2c activated SAPK/JNK signaling pathway in the RAoSMCs. 相似文献
107.
A halophilic bacterium was isolated from fermented seafood. The 16S rDNA sequence identity between the isolate and Halomonas subglaciescola AJ306801 was above 95%. The isolate that did not grow in the condition without NaCl or in the condition with other sodium (Na+) or chloride ions (Cl-) instead of NaCl was named H. subglaciescola DH-1. Two mutants capable of growing without NaCl were obtained by random mutagenesis, of which their total soluble protein profiles were compared with those of the wild type by two-dimensional electrophoresis. The external compatible solutes (betaine and choline) and cell extract of the wild type did not function as osmoprotectants, and these parameters within the mutants did not enhance their growth in the saline environment. In the proton translocation test, rapid acidification of the reactant was not detected for the wild type, but it was detected for the mutant in the condition without NaCl. From these results, we derived the hypothesis that NaCl may be absolutely required for the energy metabolism of H. subglaciescola DH-1 but not for its osmoregulation, and the mutants may have another modified proton translocation system that is independent of NaCl, except for those mutants with an NaCl-dependent system. 相似文献
108.
Jin-Ha?Lee Mi-Hwa?Choi Ji-Young?Park Hee-Kyoung?Kang Hwa-Won?Ryu Chang-Sin?Sunwo Young-Jung?Wee Ki-Deok?Park Do-Won?Kim Doman?KimEmail author 《Biotechnology and Bioprocess Engineering》2004,9(4):318-322
Lactic acid is an environmentally benign organic acid that could be used as a raw material for biodegradable plastics if it
can be inexpensively produced by fermentation. Two genes (IdhL andIdhD) encoding the L-(+) and D-(−) lactate dehydrogenases (L-LDH and D-LDH) were cloned fromLactobacillus sp., RKY2, which is a lactic acid hyper-producing bacterium isolated from Kimchi. Open reading frames ofIdhL for andIdhD for the L and D-LDH genes were 962 and 998 bp, respectively. Both the L(+)- and D(−)-LDH proteins showed the highest degree
of homology with the L- and D-lactate dehydrogenase genes ofLactobacillus plantarum. The conserved residues in the catalytic activity and substrate binding of both LDHs were identified in both enzymes. 相似文献
109.
The phylogenetic relationships of all 16 genera (plus Psenes pellucidus) of the suborder Stromateoidei were estimated cladistically based on 43 osteological, myological, and external characters. Thirty equally parsimonious trees were obtained. Based on the strict consensus tree, Centrolophidae was nonmonophyletic, Psenopsis being placed as a sister group of a clade comprising Amarsipus, Ariomma, nomeids, Tetragonurus, and stromateids. Schedophilus formed a sister group relationship with Seriolella. The relationships among the Centrolophus, Hyperoglyphe, Icichthys, Tubbia, Schedophilus+Seriolella clade, and Psenopsis+Amarsipus+Ariomma+nomeids+Tetragonurus+stromateids clade were unresolved. Amarsipus, which is unique within the suborder in lacking a pharyngeal sac, was nested within the stromateoid clade, being a sister group of the clade including Ariomma, nomeids, Tetragonurus, and stromateids. The absence of a pharyngeal sac in Amarsipus was interpreted as a reversal, its presence in the Stromateoidei therefore being considered as a synapomorphy. Ariomma was placed as the sister group of a clade comprising nomeids, Tetragonurus, and stromateids. Monophyly of the Nomeidae and Stromateidae were supported by 2 and 11 synapomorphies, respectively. 相似文献
110.
Park SY Ryu SH Jang IC Kwon SY Kim JG Kwak SS 《Molecular genetics and genomics : MGG》2004,271(3):339-346
A cDNA encoding a cytosolic ascorbate peroxidase (APX), swAPX1 , was isolated from cell cultures of sweetpotato (Ipomoea batatas) by cDNA library screening, and its expression in the context of various environmental stresses was investigated. swAPX1 contains an ORF of 250 amino acids (27.5 kDa) encoding a protein with a pI value of 5.32. The swAPX1 ORF does not code for a transit peptide, suggesting that the product is a cytosolic isoform. RNA blot analysis showed that swAPX1 gene is expressed in cultured cells and mature leaves, but not in stems, non-storage or storage roots of sweetpotato. The level of swAPX1 RNA progressively increased during cell growth in suspension cultures. In leaf tissues, the gene responded differentially to various abiotic stresses, as revealed by RT-PCR analysis. swAPX1 was highly induced in leaves by wounding, and treatment with methyl viologen (50 M), hydrogen peroxide (440 mM), abscisic acid (ABA; 100 M) or exposure to high temperature (37°C). In addition, the gene was strongly induced in the leaves following inoculation with a bacterial pathogen (Pectobacterium chrysanthemi). These results indicate that swAPX1 may be involved in hydrogen peroxide-detoxification and thus help to overcome the oxidative stress induced by abiotic and biotic stresses.Communicated by G. Jürgens 相似文献