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   2715篇
  免费   132篇
  2021年   15篇
  2020年   17篇
  2019年   29篇
  2018年   30篇
  2017年   24篇
  2016年   43篇
  2015年   68篇
  2014年   70篇
  2013年   252篇
  2012年   170篇
  2011年   165篇
  2010年   88篇
  2009年   122篇
  2008年   164篇
  2007年   149篇
  2006年   146篇
  2005年   146篇
  2004年   167篇
  2003年   158篇
  2002年   141篇
  2001年   34篇
  2000年   40篇
  1999年   39篇
  1998年   35篇
  1997年   37篇
  1996年   27篇
  1995年   35篇
  1994年   31篇
  1993年   26篇
  1992年   30篇
  1991年   19篇
  1990年   14篇
  1989年   22篇
  1988年   23篇
  1987年   18篇
  1986年   9篇
  1985年   14篇
  1984年   21篇
  1983年   10篇
  1982年   13篇
  1981年   24篇
  1980年   13篇
  1979年   11篇
  1978年   10篇
  1977年   17篇
  1976年   11篇
  1975年   10篇
  1974年   16篇
  1973年   13篇
  1970年   8篇
排序方式: 共有2847条查询结果,搜索用时 15 毫秒
121.
Indoleamine 2,3-dioxygenase (IDO) plays a significant role in several disorders such as Alzheimer’s disease, age-related cataracts and tumors. A series of novel tryptoline derivatives were synthesized and evaluated for their inhibitory activity against IDO. Substituted tryptoline derivatives (11a, 11c, 11e, 12b and 12c) were demonstrated to be more potent than known inhibitor MTH-Trp. Suzuki–Miyaura cross-coupling reaction of 11ad with phenylboronic acid proceeded in high yields. In most cases, C5 and C6 substitutions on the corresponding indole ring were well tolerated. The tryptoline derivative 11c is a promising chemical lead for the discovery of novel IDO inhibitors.  相似文献   
122.
123.
DNA-synthesis stimulatory activity was found in some tryptic fragments of human /¡-casein by using BALB/c3T3 cells, and two of them were identified as the /¡-casein fragments of Arg[l] to Lys[18] (/¡-CN(f 1 -18)) and of Gln[105] to Lys[l 17] (/¡-CN(fl05 -117)).  相似文献   
124.
Synthesis of β-tubanol (VIa) was achieved by the bromination of dihydro-β-tubanol acetate (VIIb) followed by dehydrobromination and the subsequent hydrolysis. 2,2-Dimethyl-5-hydroxy-chromanone as well as its derivatives (IV) and the corresponding chromanols (V) and chromans (VII) were also prepared.  相似文献   
125.
Macrosporin monoluethylether was synthesized by means of condensation between α-resorcylic acid (I) and 3-methoxy-p-toluic acid (II) with the use of conc. sulfuric acid and boric anhydride.

From this result macrosporin C16H12O5, a metabolic product of Macrosporium Porri Elliott, was established to be 3,5-dihydroxy-7-methoxy-2-methyl anthraquinone (A).  相似文献   
126.
Paromamine and its related compounds were synthesized by a modified Königs-Knorr reaction of 3,4,6-tri-O-acetyl-2-(2′,4′-dinitroanilno)-α-d-glucopyranosyl bromide with isopropylidene derivatives of 2-deoxystreptamine, streptamine and dihydroconduramine F–4. The condensed products were isolated as their poly N-acetyl derivatives and proved to have α-configuration by PMR spectroscopy in D2O.  相似文献   
127.
β-BTC(3, 4/5, 6),1) γ-BTC(3, 4, 6/5), and ε-BTC(3, 4, 5/6) were synthesized from α-BTC (3, 6/4, 5) by stepwise routes.  相似文献   
128.
A purple non-sulfur bacterium, Rhodopseudomonas sp. No. 7, was isolated from n-propanol–enrichment cultures under anaerobic-light conditions. Strain No. 7 can produce hydrogen from alcohols. The rate of hydrogen production from n-propanol was 34 μl/hr/mg dry cells. Strain No. 7 showed multiplication by budding and the best growth on n-propanol among other organic compounds tested. But its growth on n-propanol was poor under aerobic-dark conditions. NAD-linked alcohol dehydrogenase, NAD-linked aldehyde dehydrogenase, acyl-CoA synthetase and malate synthetase were found in strain No. 7. These enzymes were constitutive. On the other hand, isocitrate lyase was induced in cells grown on ethanol but not on n-propanol. No activity of phenazine methosulfate-linked alcohol dehydrogenase was detected in strain No. 7.  相似文献   
129.
Steam distilled oil of quince fruit (Cydonia oblonga Mill.=C. vulgaris Pers., marmelo in Japanese) was analyzed by gas chromatography and gas chromatography-mass spectrometry. Sixty-two compounds, 2 hydrocarbons, 13 esters, 11 alcohols, 11 aldehydes, 11 ketones, 5 lactones and 9 miscellaneous compounds, were identified. Of them, the chemical structures of two new oxide compounds, trans- and cis-3-methyl-5-[(E)-3′-methyl-13′-butadien-1′-yl]tetrahydrofuran, were elucidated by instrumental analyses.  相似文献   
130.
The electronic and hydrophobic substituent parameters of a number of o-, m- and p- substituted phenyl N-methylcarbamates were estimated by measuring the alkaline catalyzed hydrolysis rate constant and 1-octanol/water partition coefficient. Since some o-substituted derivatives are very potent insecticides, emphasis was placed on determining the ortho substituent effects in terms of the existing free-energy related parameters. The information obtained should be useful in structure-activity studies of carbamate insecticides.  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