全文获取类型
收费全文 | 8333篇 |
免费 | 302篇 |
国内免费 | 322篇 |
出版年
2023年 | 59篇 |
2022年 | 72篇 |
2021年 | 86篇 |
2020年 | 108篇 |
2019年 | 159篇 |
2018年 | 202篇 |
2017年 | 110篇 |
2016年 | 133篇 |
2015年 | 152篇 |
2014年 | 734篇 |
2013年 | 834篇 |
2012年 | 614篇 |
2011年 | 550篇 |
2010年 | 350篇 |
2009年 | 400篇 |
2008年 | 402篇 |
2007年 | 426篇 |
2006年 | 377篇 |
2005年 | 364篇 |
2004年 | 252篇 |
2003年 | 285篇 |
2002年 | 227篇 |
2001年 | 201篇 |
2000年 | 149篇 |
1999年 | 164篇 |
1998年 | 166篇 |
1997年 | 136篇 |
1996年 | 124篇 |
1995年 | 183篇 |
1994年 | 178篇 |
1993年 | 140篇 |
1992年 | 130篇 |
1991年 | 69篇 |
1990年 | 65篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 24篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 49篇 |
1981年 | 32篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 16篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1973年 | 8篇 |
排序方式: 共有8957条查询结果,搜索用时 15 毫秒
101.
The use of PCR to monitor the population abundance of six human intestinal bacterial species in an in vitro semicontinuous culture system 总被引:2,自引:0,他引:2
Rong-Fu Wang Wei-Wen Cao Warren L. Campbell Latrina Hairston Wirt Franklin Carl E. Cerniglia 《FEMS microbiology letters》1994,124(2):229-237
Abstract Six PCR primer sets complementary to the 16S rDNAs (rRNA genes) were developed and shown to be specific for the following anaerobic bacteria: Clostridium clostridiiforme, C. perfringens, C. leptum, Bacteroides vulgatus, B. distasonis , and B. thetaiotaomicron , respectively. These primers were used for PCR to detect and monitor the bacteria in a semicontinuous culture system designed to mimic intestinal microflora in the human gastrointestinal tract. Except for C. perfringens , the five species of Bacteroides and Clostridia present in the in vitro culture system were detected by the PCR, and the titers varied from 10−2 to 10−6 dilutions. The role of azo dye reduction by these bacterial species in the system was examined and discussed. 相似文献
102.
Jeffrey A. Banas Daniel Simon Lisa K. Williams Joseph J. Ferretti Roy R.B. Russell 《FEMS microbiology letters》1994,123(3):349-354
Abstract A glucosyltransferase (GTF) gene, designated gtfL , from Streptococcus salivarius was cloned and expressed in Escherichia coli and its nucleotide sequence determined. The GTF-L enzyme catalysed the synthesis of water-insoluble glucan in a primer-independent manner. The nucleotide sequence and derived amino acid sequence of GTF-L were similar in size and domain structure to previously sequenced glucosyltransferases. However, a 464-bp region of high variability was identified which could be selectively amplified from strains of S. salivarius by the polymerase chain reaction and could therefore form the basis for species identification. No sequence-specific motifs related to the solubility and linkage of the glucan product or its need for a dextran primer could be ascertained. 相似文献
103.
Detection of Nitrosomonas spp. by polymerase chain reaction 总被引:2,自引:0,他引:2
Abstract A unique genomic DNA fragment was isolated from Nitrosomonas europaea ATCC 19718. Based on the sequence of this fragment, oligonucleotide primers for polymerase chain reaction amplification were prepared which amplify sequences of 775 and 658 bp. The predicted DNA fragments were both amplified from the genome of N. europaea and a Nitrosomonas spp. isolated from a local oxidation pond. The primers failed to amplify DNA from the genomes of the ammonia oxidiser Nitrosolobous multiformis , the nitrite oxidiser Nitrococcus mobilis as well as from the genomes of other unrelated heterotrophic bacteria. These DNA sequences could be amplified from 0.01 ng of N. europaea genomic DNA or from 100 intact cells, and it was possible to detect Nitrosomonas DNA in a DNA mixture extracted from water samples drawn from a local oxidation pond. 相似文献
104.
A full-length cDNA encoding a human homolog of the 15-kDa subunit (p15) of RNA polymerase II elongation factor SIII was isolated and sequenced. Comparison of the open reading frames of the human p15 cDNA and the previously characterized rat p15 cDNA [Garrett et al., Proc. Natl. Acad. Sci. USA 91 (1994) 5237-5241] indicates that they encode identical proteins and are 93% conserved in nucleotide sequence. 相似文献
105.
106.
The sensitivity and specificity of the polymerase chain reaction (PCR) test kit, AMPLICOR Chlamydia trachomatis, were examined by the use of purified elementary bodies (EBs), cells having inclusions containing reticulate bodies alone and 20 clinical isolates. The numbers of EB and inclusion of C. trachomatis at the detection limit were determined to be approximately 2 to 4 EBs and one inclusion per assay, respectively. No reaction occurred for C. psittaci and C. pneumoniae. All clinical isolates were positively reacted in the PCR assay. 相似文献
107.
双价外壳蛋白基因植物表达载体的构建及马铃薯转基因植株的鉴定 总被引:10,自引:0,他引:10
在克隆了马铃薯X病毒(PVX)、马铃薯Y 病毒(PVY)和马铃薯卷叶病毒(PLRV)的外壳蛋白基因的基础上,构建同时包含PVX和PVY 与PVY 和PLRV 两个外壳蛋白基因植物表达框架的表达载体,通过农杆菌(Agrobacterium tumefaciens)介导转化烟草(Nicotianatabacum )和生产上常用的几个马铃薯(Solanum tuberosum )优良品种:“Favorita”、“虎头”、“克4”。经PCR检测证明外源基因已整合到植物的染色体上,得到批量转基因植株。在转PVX+PVY 外壳蛋白基因的烟草上接种PVX (5 μg/m L)、PVY(20 μg/m L)病毒,得到有一定抗性的植株 相似文献
108.
109.
人脑髓鞘碱性蛋白cDNA体外扩增、克隆和鉴定 总被引:3,自引:0,他引:3
采用聚合酶链反应(PCR)从人脑cDNA文库中扩增出600bp的髓鞘碱性蛋白(MBP)cDNA片段,与载体pGEM-3Zf(+)平端连接.重组质粒DNA转化宿主菌JM109,在含X-gal和IPTG的平板上直接筛选阳性克隆.限制性内切酶分析和成套引物扩增鉴定证明,该克隆含有7个外显子的21.5kD人脑MBP全长编码序列. 相似文献
110.
Francisco F. Roberto Debby F. Bruhn Anna M. Wilhite Thomas E. Ward 《FEMS microbiology reviews》1993,11(1-3):31-35
Abstract: In the course of our studies to determine appropriate conditions to transform Thiobacillus ferrooxidans , we have adopted a tetrathionate-containing medium. A number of different, apparently stable colony morphologies have arisen from cultures presumed to be pure while grown on iron-containing medium. In an effort to assess whether these different morphologies are indicative of previously undetected contamination, or simply manifestations of physiological variability within a strain, we have applied a number of biochemical and genetic techniques, including cellular fatty acid analysis and 16S rRNA sequence determination. These data should allow us to unequivocally characterize and compare the organisms present in our cultures. 相似文献