全文获取类型
收费全文 | 57601篇 |
免费 | 3194篇 |
国内免费 | 6863篇 |
专业分类
化学 | 40290篇 |
晶体学 | 809篇 |
力学 | 1529篇 |
综合类 | 431篇 |
数学 | 13651篇 |
物理学 | 10948篇 |
出版年
2024年 | 74篇 |
2023年 | 512篇 |
2022年 | 1099篇 |
2021年 | 1105篇 |
2020年 | 1433篇 |
2019年 | 1353篇 |
2018年 | 1220篇 |
2017年 | 1728篇 |
2016年 | 1632篇 |
2015年 | 1426篇 |
2014年 | 2128篇 |
2013年 | 4895篇 |
2012年 | 3928篇 |
2011年 | 2890篇 |
2010年 | 2329篇 |
2009年 | 3513篇 |
2008年 | 3659篇 |
2007年 | 3589篇 |
2006年 | 3208篇 |
2005年 | 2877篇 |
2004年 | 2668篇 |
2003年 | 2117篇 |
2002年 | 2954篇 |
2001年 | 1902篇 |
2000年 | 1765篇 |
1999年 | 1751篇 |
1998年 | 1445篇 |
1997年 | 1118篇 |
1996年 | 912篇 |
1995年 | 871篇 |
1994年 | 773篇 |
1993年 | 623篇 |
1992年 | 654篇 |
1991年 | 408篇 |
1990年 | 366篇 |
1989年 | 380篇 |
1988年 | 257篇 |
1987年 | 216篇 |
1986年 | 229篇 |
1985年 | 209篇 |
1984年 | 225篇 |
1983年 | 107篇 |
1982年 | 178篇 |
1981年 | 148篇 |
1980年 | 169篇 |
1979年 | 156篇 |
1978年 | 146篇 |
1977年 | 98篇 |
1976年 | 82篇 |
1973年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Chun Chun ZHANG Wei ZENG Jian Zhang LI Sheng Ying QIN* Department of Chemistry Sichuan University Chengdu 《中国化学快报》2003,(6)
It is well known that the study on biomimetic oxygen carriers not only has important theoretic significance to discover the mechanism of reversible bonding, activating oxygen as well as the oxidation reaction in organism, but also has potential application in separating oxygen from air and realizing the high efficiency and selectivity of catalytic oxidation reaction under a mild condition1. Metal- porphyrin and metal- phthalol- gaunine have been extensively used as biomimetic oxygen carriers u… 相似文献
942.
Phenols are deprotected with weak bases from their tert-butoxycarbonyl (Boc) derivatives. Boc deprotection with bases can avoid side reactions during the deprotection with acids. We note the lability of the Boc to bases and are able to utilize it as a new cleavage condition for synthetic studies. 相似文献
943.
A. A. Balandina V. A. Mamedov E. A. Khafizova Sh. K. Latypov 《Russian Chemical Bulletin》2006,55(12):2256-2264
The combined use of 2D NMR correlation methods and ab initio chemical shift calculations is efficient and, in some cases, virtually the only way to determine the structures of new organic
compounds. This approach enabled us to establish the structure of the major unusual product of the three-component reaction
of imidazo[1,5-a]quinoxalin-4-one, bis(2-chloroethyl)amine hydrochloride, and potassium carbonate in DMF.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2172–2179, December, 2006.
Dedicated to Professor A. V. Il’yasov on the occasion of his 70th birthday. 相似文献
944.
Traceability of the measurement of analytical parameters capable of evaluating the performance of methods is an important
concept for the assessment of quality for the routine control, especially for residue monitoring of non-authorized medicinal
substances in food from animal origin. The European Decision no. 657/2002/EC recommends to calculate two statistical limits,
CCα and CCβ, which allow to evaluate the critical concentrations above which the method reliably distinguish and quantify
a substance taking into account the variability of the method and the statistical risk to take a wrong decision. The calculation,
which can be derived from the ISO standard no. 11843 is applied on a routine basis. An example displays a very simple way
for evaluating the performance of an LC-MSMS method which has been validated a few years ago and is qualified onto a Micromass
Quattro LCZ tandem mass spectrometer to monitor and confirm the nitrofuran metabolite residues in food from animal origin.
Community Reference Laboratory for Antimicrobial Veterinary Drug Residue Control in Food from Animal Origin 相似文献
945.
Takeshi Takeda Koutaro Arai Hirohisa Shimokawa Akira Tsubouchi 《Tetrahedron letters》2005,46(5):775-778
Cyclopropanes were obtained by the titanocene(II)-promoted reaction of thioacetals with vinyl pivalate. It was also found that vinycyclopropanes were produced by a similar treatment of thioacetals with the titanocene(II) species in the presence of 1,3-dienes. 相似文献
946.
Rubén A. Machado David Rivillo Lindora D’Ornelas Reinaldo Atencio Esperanza Galarza 《Journal of organometallic chemistry》2004,689(15):2486-2493
The reaction of the labile compound [Re2(CO)8(CH3CN)2] with trans-1,2-bis(2-pyridyl)ethene (C12H10N2) at room temperature in tetrahydrofuran affords the compounds [Re2(μ:η3-C12H10N2)(CO)8] (1) and the oxidative addition product [Re2(μ-H)(μ:η3-C12H9N2)(CO)7] (2). When the reaction is carried out at temperatures of refluxing tetrahydrofuran, besides compounds 1 and 2, the oxidative addition product [Re2(μ-H)(μ:η4-C12H9N2)(CO)6] (3), the insertion product [Re2(μ:η4-C12H10N2)(CO)8] (4) and [Re2(μ:η6-C24H18N4)(CO)6] (5) are obtained. Compound 5 contains the organic ligand rtct-tetrakis(2-pyridyl)cyclobutandiyl which is derived from a [2 + 2] cycloaddition of 1,2-bis(2-pyridyl)ethene mediated by its coordination to the bimetallic framework. The molecular structures of 1, 2, 4 and 5 were confirmed by X-ray crystallographic studies. 相似文献
947.
Ming Z. Gao 《Tetrahedron letters》2004,45(29):5649-5652
The novel structures of sulfur-containing chiral bis(oxazoline) compounds which have been synthesized have been determined by X-ray crystal diffraction analyses. A high enantioselectivity (ee >99%) in the asymmetric cyclopropanation of diphenylethene with diazoester using the bis(oxazoline)-Ru(II) catalyst was obtained. 相似文献
948.
Anna Kowalska Zygmunt Kowalski Andrzej Kotarba Andrzej Barański 《Mikrochimica acta》1990,100(5-6):349-353
The analytical procedure of determination of Fe(II) in the presence of Fe(III) in milligram samples is proposed. A solid sample is dissolved in hydrochloric acid in argon atmosphere. Subsequently, the pH-value of the solution is fixed and Fe(III) complexed by phosphoric buffer. At the next step Fe(II) is oxidized by -molybdosilicic acid. Finally, the intensity of colouring caused by the reduced form of the acid is measured at the wavelength 770 nm. The proper treatment of the sample during oxidation, and immediately before, is decisive for the accuracy of the analysis. The method was verified by means of the analysis of synthetic magnetite. The theoretical content of Fe(II) was 24.12%, the determined one was 24.02 ± 0.10%. The method was applied to the determination of the homogeneity of an iron catalyst for ammonia synthesis. 相似文献
949.
The principles underlying a novel method intended for analyzing experimental data obtained when studying fluctuation processes are considered. The method in question is Chebyshev’s spectroscopy. The application of this method allows one to determine statistic characteristics of steady-state electrochemical noise against the background of severe deterministic interference without invoking the procedure of the fitting of the initial data. The potentialities of this novel method, which is intended for treating noise experiment, are demonstrated by examining model examples and analyzing the electrochemical noise generated by a lithium electrode placed in an aprotic organic electrolyte. 相似文献
950.