全文获取类型
收费全文 | 13257篇 |
免费 | 479篇 |
国内免费 | 901篇 |
出版年
2024年 | 13篇 |
2023年 | 137篇 |
2022年 | 208篇 |
2021年 | 206篇 |
2020年 | 244篇 |
2019年 | 323篇 |
2018年 | 340篇 |
2017年 | 257篇 |
2016年 | 297篇 |
2015年 | 329篇 |
2014年 | 912篇 |
2013年 | 1109篇 |
2012年 | 752篇 |
2011年 | 662篇 |
2010年 | 456篇 |
2009年 | 639篇 |
2008年 | 660篇 |
2007年 | 658篇 |
2006年 | 601篇 |
2005年 | 572篇 |
2004年 | 453篇 |
2003年 | 500篇 |
2002年 | 427篇 |
2001年 | 355篇 |
2000年 | 277篇 |
1999年 | 266篇 |
1998年 | 288篇 |
1997年 | 249篇 |
1996年 | 239篇 |
1995年 | 298篇 |
1994年 | 285篇 |
1993年 | 240篇 |
1992年 | 208篇 |
1991年 | 151篇 |
1990年 | 156篇 |
1989年 | 92篇 |
1988年 | 80篇 |
1987年 | 72篇 |
1986年 | 49篇 |
1985年 | 81篇 |
1984年 | 89篇 |
1983年 | 68篇 |
1982年 | 114篇 |
1981年 | 54篇 |
1980年 | 45篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 28篇 |
1976年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
201.
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
202.
203.
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
204.
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
205.
206.
207.
Sites polluted with organic compounds frequently contain inorganic pollutants such as heavy metals. The latter might inhibit the biodegradation of the organics and impair bioremediation. Chromosomally located polychlorinated biphenyl (PCB) catabolic genes ofAlcaligenes eutrophus A5,Achromobacter sp. LBS1C1 andAlcaligenes denitrificans JB1 were introduced into the heavy metal resistantAlcaligenes eutrophus strain CH34 and related strains by means of natural conjugation. Mobile elements containing the PCB catabolic genes were transferred fromA. eutrophus A5 andAchromobacter sp. LB51C1 intoA. eutrophus CH34 after transposition onto their endogenous IncP plasmids pSS50 and pSS60, respectively. The PCB catabolic genes ofA. denitrificans JB1 were transferred intoA. eutrophus CH34 by means of RP4::Mu3A mediated prime plasmid formation. TheA. eutrophus CH34 transconjugant strains expressed both catabolic and metal resistance markers. Such constructs may be useful for the decontamination of sites polluted by both organics and heavy metals. 相似文献
208.
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
209.
210.
The influence of chromium concentration on ethylene production in bean plants ( Phaseolus vulgaris L. cv. Contender) was investigated. A Cr ion-induced inhibition of ethylene synthesis from endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) was observed within both leaf discs floated on 2 m M CrO2− 4 or Cr3+ and leaf discs from plants cultured in nutrient solutions containing 10, 20 or 40 μ M CrO2− 4 . However, Cr ions supplied either to plants with the nutrient solution or to discs with the incubation medium rather increased the conversion of exogenous ACC to ethylene. Primary leaves of plants exposed to CrO2− 4 -containing nutrient solutions showed a statistically insignificant decrease of ACC-synthase activity. In the trifoliolate leaves of plants exposed to 10 μ M CrO2− 4 , in which a significant decrease of ethylene production from endogenous ACC was observed, a substantial increase of ACC synthase was found. These results indicate that Cr ion-induced inhibition of ethylene production is not due to a breakdown of membrane integrity, which is necessary for ethylene forming enzyme activity, but caused by metabolic alterations leading to decreased ACC availability. Chromium ions may act by inhibiting ACC synthase activity or by diverting a metabolic step prior to the ACC synthase catalyzed reaction. 相似文献