全文获取类型
收费全文 | 444篇 |
免费 | 13篇 |
国内免费 | 109篇 |
专业分类
化学 | 550篇 |
晶体学 | 6篇 |
综合类 | 5篇 |
物理学 | 5篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 16篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 28篇 |
2013年 | 67篇 |
2012年 | 23篇 |
2011年 | 33篇 |
2010年 | 12篇 |
2009年 | 22篇 |
2008年 | 16篇 |
2007年 | 24篇 |
2006年 | 16篇 |
2005年 | 29篇 |
2004年 | 22篇 |
2003年 | 16篇 |
2002年 | 61篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有566条查询结果,搜索用时 15 毫秒
461.
462.
Reactions of 6-Amino-5-Cyano-3-Methyl-1,4-Diphenyl-1H 4H-Pyrano[2,3-C]Pyrazole and its Methanimidate
Reaction of 6-amino-5-cyano-3-methyl-1,4-diphenyl- 1H,4H-pyrano[2,3-c]pyrazole 1 with triethyl orthoformate in acetic anhydride gave its methanimidate 2, which reacts with primary aliphatic and aromatic amines to give 4,6-dihydro-3-methyl-1,4-diphenyl-6- (alkyl)pyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5(lH)- imine 3 and the starting compound 1 , respectively. Treatment of 1 with o-aminophenol gave 5-(2-benzoxalyl)- 1,4-dihydro-3-methyl-1,4-diphenylpyrano[2,3-c]pyrazol- 6-amine 9. 相似文献
463.
AbstractThe high functionality compound namely 2-cyano-3-(1,3-diphenyl-1H-pyrazol-4-yl)acryloyl chloride (1) was utilized as a building block synthon via reactions with some nitrogen and sulfur nucleophilic reagents. The present work was planned to study the effect of 2-cyano group on the reactivity and stability of C2–C3 double bond toward different strong-to-weak nucleophiles, in addition to its facility of nucleophilic addition at C2–C3 double bond to construct new heterocyclic derivatives. The proclivity toward some mono-, 1,2-, 1,3-, 1,4-, and 1,5-binucleophiles was investigated. The reaction with 2-cyanoacetohydrazide was mainly dependent on the reaction conditions. Some new heterocycles integrated with pyrazole scaffold were successfully synthesized, such as benzoxazinone, indoline, isoindoline, pyrazolone, chromene, and pyrimidopyrimidine derivatives. Some of the newly synthesized compounds were screened for their antioxidant activity using ABTS method, and the results revealed that some compounds exhibited promising inhibitory antioxidant activity. 相似文献
464.
Tarak Nath Mandal Somnath Roy Anil Kumar Barik Samik Gupta Ray J. Butcher Susanta Kumar Kar 《Polyhedron》2008
Two mononuclear copper(II) complexes [Cu(L1)ClO4] (1), [Cu(L2)ClO4] (3) and two mononuclear vanadium(V) complexes [{VO(L1)(OCH3)(CH3OH)}{VO(L1)(OCH3)}] (2) and [VO(L2) (OCH3)(CH3OH)] (4) have been synthesized using two Schiff base ligands HL1 [N′-(2-hydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazide] and HL2 [1-(4,6-dimethylpyrimidin-2-yl)-N′-(2-hydroxybenzylidene)-5-methyl-1H-pyrazole-3-carbohydrazide]. These two similar ligands HL1 and HL2 in their ‘ketoimine’ form function as mononegative NNNO tetradentate ones towards the Cu(II) centre forming square planar part of the square pyramidal geometry. Where as the same ligands in their ‘imineol’ form behave as binegative ONO tridentate ones to form their V(V) analogues. In the asymmetric unit of 2, there are two independent V(V) complex molecules differing in their conformations as well as in coordination environment – octahedral V(V) in ‘unit A’ is hexa-coordinated while that in ‘unit B’ being penta-coordinated is square pyramidal. Vanadium atom in 4 is in octahedral geometry with NO5 chromophore. The ligands HL1 and HL2 have been synthesized for the first time in our laboratory and characterized by X-ray crystallography and spectroscopy. The complexes (1, 2 and 4) are also characterized by X-ray crystallography, spectroscopic and electrochemical studies. 相似文献
465.
Summary N-substituted imides (RSIs) were synthesized from the reactions of alkylbromides (RX) and potassium salts of imides (KSIs) under
solid-liquid phase-transfer catalytic conditions (SL-PTC). No water is required in the reaction system. In this work, serious
hydration of KSIs is avoided using SL-PTC to synthesize RSIs. The reaction catalyzed by quaternary ammonium salts is greatly
enhanced in the solid-liquid solution 相似文献
466.
新型含吡唑基的查尔酮的合成、表征及晶体结构 总被引:2,自引:0,他引:2
以2种1-苯基-3-甲基-5-对甲苯氧基-吡唑-4-甲醛为原料, 在强碱条件下与苯乙酮(取代苯乙酮)发生羟醛缩合, 高产率地合成出10种新型含吡唑基的查尔酮. 化合物的结构经元素分析, IR和1H NMR确认. 并用X射线衍射法测定了化合物4c的晶体结构. 化合物4c属三斜晶系, 空间群P-1, 晶胞参数: a=1.0225(2) nm, b=1.4263(3) nm, c=1.6718(3) nm, α=110.32(3)°, β=106.30(3)°, γ=98.11(3)°, Mr=428.90, V=2.1159(7) nm3, Dc=1.346 Mg/m3, Z=2, F(000)=896. 相似文献
467.
468.
新型含吡啶环取代的吡唑肟醚类化合物的合成及生物活性研究 总被引:1,自引:0,他引:1
为了寻找新型高效低毒的农药先导化合物,通过N-吡啶基吡唑肟与2-氯-5-氯甲基吡啶的缩合反应,合成了一系列含吡啶环取代的吡唑肟醚类化合物.目标化合物的结构均经1H NMR,13C NMR和元素分析确证.初步生物活性试验结果表明,部分化合物具有一定的杀菌、杀虫和植物生长调节活性.如化合物5e在浓度为50 μtg/mL时对番茄早疫的抑制率为61.4%;化合物5j在浓度为50 μg/mL时对花生褐斑的抑制率为60.2%;化合物5i在浓度为500 μg/mL时对蚜虫表现出50.3%的杀死率;化合物5f在浓度为10 μg/mL时对黄瓜子叶生根表现出71.0%的促进生长作用. 相似文献
469.
以乙酰丙酮为起始原料,经三步反应制得了w-溴代-1-苯基-5-甲基吡唑-4-乙酮(5).中间体5在超声波辐射下与芳基乙酮缩氨基硫脲类化合物(1a-1g)反应生成了新型的N-(1-芳基乙酮)-N1-[(1-苯基-5-甲基吡唑-4-基)噻唑-2-基]腙(6a-6g).以1H NMR,IR,MS和元素分析对产物进行了确证及表... 相似文献
470.
膦酰三胺类化合物具有优良的杀菌、抗病毒作用,其中部分还有抗肿瘤活性。脲和硫脲类化合物及其衍生物既具有优良的杀菌、除草等活性,又是一种重要的有机合成中间体。它的糖基衍生物是生物体内重要的代谢产物,具有维持代谢水平,提高机体耐受力等生理活性。糖基的多羟基特点,有利于增加这些化合物的水溶性, 相似文献