首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   384篇
  免费   19篇
  国内免费   41篇
化学   391篇
晶体学   7篇
综合类   8篇
数学   11篇
物理学   27篇
  2023年   4篇
  2022年   7篇
  2021年   7篇
  2020年   8篇
  2019年   12篇
  2018年   10篇
  2017年   13篇
  2016年   17篇
  2015年   11篇
  2014年   24篇
  2013年   25篇
  2012年   20篇
  2011年   24篇
  2010年   17篇
  2009年   22篇
  2008年   20篇
  2007年   18篇
  2006年   17篇
  2005年   18篇
  2004年   17篇
  2003年   8篇
  2002年   15篇
  2001年   10篇
  2000年   10篇
  1999年   11篇
  1998年   1篇
  1997年   9篇
  1996年   3篇
  1995年   3篇
  1994年   5篇
  1993年   5篇
  1992年   1篇
  1991年   6篇
  1990年   8篇
  1989年   2篇
  1988年   8篇
  1987年   2篇
  1986年   4篇
  1985年   5篇
  1984年   5篇
  1983年   2篇
  1982年   1篇
  1980年   3篇
  1979年   3篇
  1978年   1篇
  1973年   1篇
  1966年   1篇
排序方式: 共有444条查询结果,搜索用时 15 毫秒
1.
We describe identification of seven components from Antrodia cinnamomea. Their structures were determined on the basis of spectral analysis and comparison with authentic samples. These compounds include two steroids (1, 2) (β-sitosterol and eburicol), two new steroids (3, 4) [methyl-4α-methylergost-8,24(28)-dien-3,7,11-trion-26-oate and methyl-4α-methylergost-8,24(28)-dien-3,11-dion-26-oate], two lignans (5, 6) [(+)-sesamin and 4-hydroxysesamin], and one long chain methyl ester (7) (methyl oleate). Among them, compounds 3 and 4 are first isolated from nature.  相似文献   
2.
大多数鳞翅目昆虫性信息素是不饱和长碳链(C_(12)~C_(16))醇、乙酸酯或醛,双键位置一般在5、7、8、9、10和11位。它们的差别主  相似文献   
3.
粘虫是一种多食性害虫,分布极广。它的危害对象包括麦类、水稻、玉米等十多种粮食和经济作物。1979年Takahashi等首先确定粘虫雄蛾(Mythimna Separata male)的性信息素,这是由8:1比例混合的(Z)-11-十六碳烯-1-醇乙酸酯3和(Z)-11-十六碳烯-1-醇4组  相似文献   
4.
通过二苯基烯丙基型叶立德与8-氧辛酸甲酯进行的Wittig反应,合成苹果蠹蛾性信息素,E,E-8,10-十二碳二烯-1-醇(5)。这个反应的特点是反式选择性高,产物中E,E-异构体的含量可达95%以上。  相似文献   
5.
A simple method for the synthesis of (±)-2,6-dimethylocta-5(Z),7-diene-4-ol possessing a high pheromone activity for the bark beetle Ips typographus was developed.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2245–2247, October, 2004.  相似文献   
6.
Sexing Bovine Embryos Using PCR Amplification of Bovine SRY Sequence   总被引:2,自引:0,他引:2  
This study analyses the bovine SRY DNA sequence by direct sequencing procedure, followed by the designation of the PCR primers specific for bovine SRY. Using PCR amplification of bovine SRY gene, the embryo sex was determined. The results of the embryo sex identification were confirmed after the embryo transfer and pregnancies.  相似文献   
7.
本文采用TLC、GC、微量臭氧化和GC-MS等分析方法,从茄黄斑螟雌蛾性腺体提取物中,分离和鉴定出性信息素反-11-十六碳烯醇乙酸酯(1a)。触角电位和田间试验证明,天然提取物和合成样品均有强烈的生物活性。  相似文献   
8.
We have established a method for separation and characterization of a series of peptide hormones of pharmaceutical interest and wide therapeutical use by capillary electrophoresis-electrospray-mass spectrometry (CE-ES-MS) using a sheath flow interface. Several parameters were systematically investigated, such as concentration of the electrolyte, organic solvent and sheath liquid composition, gas flow rates and capillary position. Moreover, limits of detection, linearity, repeatability and day-to-day reproducibility of the proposed method were studied in order to obtain the main quality parameters.  相似文献   
9.
Due to anatomic barriers and lacrimal drainage it is difficult to obtain therapeutic drug concentrations in the posterior part of the eye after topical drug administrations. Lipophilic cyclodextrins, such as randomly methylated β-cyclodextrin (RMβCD), are known to act both as solubilizers of water-insoluble drugs in aqueous solutions and as penetration enhancers that reduce the barrier function of lipophilic membranes. The purpose of this study was to investigate the effects of RMβCD on dexamethasone delivery from aqueous eye drop solution into rabbit eyes. Dexamethasone (0.5 and 1.5% w/v) drops (50 μl) were administered to the left eye of rabbits (n = 6) and the drug levels measured in different eye tissues 2 h after administration. In aqueous humor dexamethasone levels were 1,190 ± 110 and 1,670 ± 630 ng/g (mean ± SD) after administration of the 0.5 and 1.5% dexamethasone eye drops, respectively. In the retina the levels were 33 ± 7 and 66 ± 49 ng/g, and in optic nerve 41 ± 12 and 130 ± 50 ng/g, respectively. In a previous study the dexamethasone concentration in aqueous humor after topical administration of 1.3% (w/v) dexamethasone eye drops in aqueous 2-hydroxypropyl-β-cyclodextrin (HPβCD) solution was determined to be 320 ± 230 ng/g and 66 ± 20 ng/g after administration of Maxidex® eye drops. Both the hydrophilic HPβCD and the lipophilic RMβCD enhance topical dexamethasone delivery into the eye, but of the two, the lipophilic RMβCD results in higher dexamethasone concentrations.  相似文献   
10.
A new and efficient route has been developed to synthesize 17β-(1-methyl-3-perfluoroalkyl)propyl-3β-androsterol (1) in nine steps from hyodeoxycholic acid via selective addition of 1-perfluoroalkyl iodide to 24-norchola-5,22-dien-3β-ol. From (1), the first series of steroidal liquid crystalline aliphatic esters (smectic A) with fluorocarbon side chains has been prepared.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号