全文获取类型
收费全文 | 13520篇 |
免费 | 1243篇 |
国内免费 | 4346篇 |
专业分类
化学 | 14127篇 |
晶体学 | 412篇 |
力学 | 493篇 |
综合类 | 142篇 |
数学 | 1672篇 |
物理学 | 2263篇 |
出版年
2024年 | 22篇 |
2023年 | 124篇 |
2022年 | 307篇 |
2021年 | 333篇 |
2020年 | 374篇 |
2019年 | 310篇 |
2018年 | 331篇 |
2017年 | 405篇 |
2016年 | 471篇 |
2015年 | 392篇 |
2014年 | 626篇 |
2013年 | 1058篇 |
2012年 | 1400篇 |
2011年 | 753篇 |
2010年 | 629篇 |
2009年 | 845篇 |
2008年 | 974篇 |
2007年 | 1048篇 |
2006年 | 969篇 |
2005年 | 952篇 |
2004年 | 865篇 |
2003年 | 719篇 |
2002年 | 628篇 |
2001年 | 497篇 |
2000年 | 500篇 |
1999年 | 470篇 |
1998年 | 406篇 |
1997年 | 360篇 |
1996年 | 350篇 |
1995年 | 340篇 |
1994年 | 302篇 |
1993年 | 217篇 |
1992年 | 273篇 |
1991年 | 201篇 |
1990年 | 159篇 |
1989年 | 117篇 |
1988年 | 88篇 |
1987年 | 64篇 |
1986年 | 67篇 |
1985年 | 48篇 |
1984年 | 34篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1972年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Piano‐stool ([(p‐cymene)Ru(thz)Cl], 2 ) and six‐coordinated ([Ru(thz)2(PPh3)2], 3 ) ruthenium complexes derived from 2‐phenylthiazoline‐4‐carboxylic acid (Hthz, 1 ) were synthesized for the first time, and fully characterized using conventional methods. Also, the molecular structure of complex 3 was determined using X‐ray analysis. These complexes were evaluated as catalysts for transfer hydrogenation of carbonyl compounds in the presence of isopropyl alcohol and KOtBu. Complex 2 was found to be more active than 3 in transfer hydrogenation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
992.
《Journal of Coordination Chemistry》2012,65(18):2966-2973
The complex of 2,6-diacetylpyridinedihydrazone (L) with lead(II) and azide has been characterized by elemental analyses, FTIR, and single-crystal X-ray analysis. The Pb(C9H13N11) (1) crystallized in the monoclinic space group C2/c. The coordination of 1 exhibits a gap around the lead(II), possibly occupied by a stereochemically active electron lone pair on lead(II) resulting in a hemidirected complex. Antimicrobial activity of the complex is higher than the free ligand. 相似文献
993.
Magnetic‐based picolinaldehyde–melamine copper complex for the one‐pot synthesis of hexahydroquinolines via Hantzsch four‐component reactions
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A picolinaldehyde–melamine copper complex was loaded on a magnetic Fe3O4 core, so that it contained 0.33 mmol of Cu per gram, and was used as an efficient catalyst. The as‐synthesized catalyst was characterized using various techniques, including Fourier transform infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry and thermogravimetric analysis. The catalyst was used to activate the raw materials in the synthesis of hexahydroquinoline derivatives in one‐pot four‐component reactions. Low reaction time (minutes versus half an hour), solvent‐free condition and magnetically separable catalyst are some salient features of the developed catalyst. Also, the optimum amount of catalyst and temperature were determined as 0.07 g and 87.6 °C, respectively, which were obtained using response surface methodology and optimization techniques. 相似文献
994.
In the present paper, we deal with the complex Szász-Durrmeyer operators and study Voronovskaja type results with quantitative estimates for these operators attached to analytic functions of exponential growth on compact disks. Also, the exact order of approximation is found. 相似文献
995.
《应用有机金属化学》2017,31(10)
A simple and effective strategy is described for the synthesis of Pd–CdS nanopowder by the reduction of an organopalladium(II) complex, [PdCl2(cod)] (cod = cis ,cis ‐1,5‐cyclooctadiene), in the presence of CdS quantum dots (QDs) at a toluene–water interface. We investigated the impact of addition of CdS QDs on catalytic activity of Pd nanoparticles (NPs). The Pd–CdS nanopowder functions as an efficient catalyst for Suzuki–Miyaura reactions for the formation of carbon–carbon bonds. There is a high electron density on Pd NPs and due to their high electron affinity they behave as an electron scavenger from CdS increasing the rate of oxidative addition, which is the rate‐determining step of the catalytic cycle, and, just as we expect, the C─C coupling reaction with the Pd–CdS nanopowder is faster and occurs in less time than that with Pd nanocatalysts. Compared to classical reactions, this method consistently has the advantages of short reaction times, high yields in a green solvent, reusability of the catalyst without considerable loss of catalytic activity and low cost, and is a facile method for the preparation of the catalyst. 相似文献
996.
《应用有机金属化学》2017,31(8)
We have prepared two chiral Schiff base ligands, H2L1 and H2L2, and one achiral Schiff base ligand, H2L3, by treating 2,6‐diformyl‐4‐methylphenol separately with (R )‐1,2‐diaminopropane, (R )‐1,2‐diaminocyclohexane and 1,1′‐dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL1ClO4 ( 1 ), MnL2ClO4 ( 2 ), MnL3ClO4 ( 3 ), FeL1ClO4 ( 4 ), FeL2ClO4 ( 5 ) and FeL3ClO4 ( 6 ) have been obtained by reacting the ligands H2L1, H2L2 and H2L3 with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H2L1 and H2L2 and their corresponding complexes have asymmetric character. Complexes 1 – 6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4 , so they were attached to surface‐modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe3O4@dopa@MnL1 and Fe3O4@dopa@FeL4. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused. 相似文献
997.
《应用有机金属化学》2017,31(9)
A β‐diketimine ligand with vinylidene substitution at γ‐carbon, CH2C(CH3CNAr)2 (Ar = 2,6‐diisopropylphenyl) ( L 2 ), was synthesized by treating β‐diketimine H2C(CH3CNAr)2 with n ‐BuLi followed by paraformaldehyde. L 2 formed the homobimetallic ether‐bridged β‐diketiminate complex [O{(CH2‐β‐diketiminate)Pd(OAc)}2] ( 1 ) with (PdOAc)2. It also gave complexes [L2PdCl2] ( 2 ) and [L2NiBr2] ( 3 ) when treated with PdCl2(CH3CN)2 and NiBr2(dimethoxyethane), respectively. All the compounds were characterized using 1H/13C NMR spectroscopy and single‐crystal X‐ray diffraction studies. The catalytic activity of Pd and Ni complexes 1 , 2 and 3 was explored in Heck coupling and alkyne trimerization reactions and it was found that they are very good catalysts. The results are reported in detail. 相似文献
998.
《应用有机金属化学》2017,31(9)
Because of the side effects and drug resistance of cisplatin, a basic clinically approved chemotherapeutic drug, a new attempt is reported to develop a novel antitumor drug based on complexation of iron metal ion with organic moiety that may be effective and safer. A newly synthesized iron(III) diacetylmonoxime‐2‐hydrazinopyridine complex was tested firstly for its cytotoxicity and superoxide dismutase (SOD)‐mimic activity in vitro then for its antitumor activity against Ehrlich ascites carcinoma (EAC) and the related biochemical alterations in vivo in comparison with cisplatin. The complex showed 80.88% SOD‐mimic activity and IC50 of 2.6 μg ml−1. In EAC‐bearing mice, in a dose‐dependent manner, Fe(III) complex treatment exhibited significant hematological profile improvements, tumor volume, viable cell count and hepatic lipid peroxidation level decreases, life span extension, hepatic glutathione and total antioxidant capacity levels enhancements, hepatic SOD and catalase activities augmentations, liver function tests alterations attenuations, and hepatocyte nucleic acids content normalization. Thus, the Fe(III) diacetylmonoxime‐2‐hydrazinopyridine complex is a novel, promising, less toxic antitumor agent. Its killing of tumor cells may be via a reactive oxygen species scavenging mechanism. 相似文献
999.
《Analytical letters》2012,45(17):1497-1512
Abstract Hexamethylphosphoramide (HMPA) gives, in aqueous solutions in the presence of SCN? ions, complexes with many metal ions, which absorb in the visible region of spectrum. The spectra have been studied in function of ligand concentration and pH for Co, Ni and Fe complexes. For the Co complex an equation was found that describes the behaviour of the absorption vs. SCN? and HMPA concentration. Absorption follows Lambert-Beer law and can be used for analytical determinations. Analysis of solutions containing Ni and Co in various ratios of concentration has been performed and results are discussed. Co, Ni and Fe content of an alloy has been measured by this way. 相似文献
1000.
C. Jandl S. Stegbauer A. Pthig 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(7):509-513
In the coordination chemistry of palladium, dimers bridged via halides are a common motif. Higher oligomers, however, are still rare. We report the structure of an alternating eight‐membered [Pd4Br4]4− ring framed by cycloheptatrienide ligands, which was obtained by cocrystallization of dimers and tetramers of the complex salt bromido{η3‐[3‐(2,6‐diisopropylphenyl)imidazolium‐1‐yl]cycloheptatrienido}palladium(II) tetrafluoroborate, namely bis[di‐μ‐bromido‐bis({η3‐[3‐(2,6‐diisopropylphenyl)imidazolium‐1‐yl]cycloheptatrienido}palladium(II))] cyclo‐tetra‐μ‐bromido‐tetrakis({η3‐[3‐(2,6‐diisopropylphenyl)imidazolium‐1‐yl]cycloheptatrienido}palladium(II)) octakis(tetrafluoroborate) dichloromethane octasolvate, [Pd4Br4(C22H26N2)4][Pd2Br2(C22H26N2)2]2(BF4)8·8CH2Cl2. These dimers and tetramers form a highly dynamic equilibrium in solution which was studied by low‐temperature NMR spectroscopy. In the light of the presented results, tetrameric PdII species can be assumed to co‐exist as a second species in many cases where by current knowledge only a dimeric compound would be expected. 相似文献