全文获取类型
收费全文 | 1224篇 |
免费 | 74篇 |
国内免费 | 73篇 |
专业分类
化学 | 1217篇 |
晶体学 | 8篇 |
综合类 | 1篇 |
物理学 | 145篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 19篇 |
2021年 | 20篇 |
2020年 | 34篇 |
2019年 | 34篇 |
2018年 | 32篇 |
2017年 | 23篇 |
2016年 | 27篇 |
2015年 | 23篇 |
2014年 | 50篇 |
2013年 | 155篇 |
2012年 | 45篇 |
2011年 | 61篇 |
2010年 | 46篇 |
2009年 | 47篇 |
2008年 | 53篇 |
2007年 | 74篇 |
2006年 | 64篇 |
2005年 | 66篇 |
2004年 | 94篇 |
2003年 | 62篇 |
2002年 | 35篇 |
2001年 | 25篇 |
2000年 | 29篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 31篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有1371条查询结果,搜索用时 15 毫秒
1.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
2.
We show that using ionic liquids as reagents in conjunction with microwave heating it is possible to prepare primary alkyl halides from the corresponding alcohols rapidly. Using ionic liquids as solvents in conjunction with microwave heating it is possible to prepare aryl nitriles from the corresponding aryl bromides or iodides. The scope and limitations of using microwave-promotion as a tool in these reactions is discussed. 相似文献
3.
A variety of aryl nitriles were prepared in excellent yields from the palladium acetate catalyzed coupling of aryl halides with Zn(CN)2 using polymer-supported triphenyl phosphine as the ligand and dimethylformamide as solvent under microwave irradiation conditions. 相似文献
4.
Small amounts of certain halogenated compounds are found to have, at most, only a slight enhancing effect on the radiolytic decay rates of added poly-unsaturated compounds in polyethylene, but significantly increase the elastic modulus at 433 K (melt modulus) obtained thereby. Experiments with model chlorine-containing additives suggest that this increase is due to a more random distribution of polymer and monomer mediated crosslinks in the polymer, that it does not result from a significant increase in crosslinking and that it is mediated by chlorine atoms, in a similar manner to radiolytic hydrogen atoms, through facilitation of long range free radical migration. Although low molecular weight chloro-paraffins inhibit radiolytically induced growth of melt modulus in monomer containing polyethylenes, even very small additions of chlorinated polyethylenes, which form a separate phase, increase the melt modulus. This again indicates that the active species is the chlorine radical. 相似文献
5.
In the present paper, a new two-parameter inverted equation of state (EOS) is developed which is found to be working very
well in the high-pressure region. To check its success and validity, this EOS has been applied in a number of solids. The
computed volume compression is found to be in very good agreement with the experimental data in the whole range of pressure
in all the solids. The minimum and the maximum pressure range used in the present study is 0–320 kbar and 0–3000 kbar, respectively. 相似文献
6.
Adriana Tudose 《Tetrahedron letters》2006,47(48):8529-8533
Simple catalysts formed in situ from palladium acetate and a variety of imidazolium and imidazolinium carboxylates and dithiocarboxylates have been screened in the coupling of aryl halides with trans-2-phenylvinylboronic acid. Imidazol(in)ium carboxylates show an excellent activity, which compares to that displayed by the parent imidazol(in)ium chlorides, whereas imidazol(in)ium dithiocarboxylates are poorly efficient. Interestingly, the base employed exerts a profound influence on the trans/cis stereochemistry of the coupling product. 相似文献
7.
A new hydrophilic copolymer having three kinds of hydroxyl groups, i.e. primary OH on -hydroxy allyl alcohol component, secondary OH on cyclic hemiacetal component and tertiary OH on -hydroxy acrylate component, was prepared by reducing a ‘polylactone’, poly(1-oxa-2-oxobutane-1,4:3,3-tetrayl), with NaBH4 in mixed solvents containing an alcohol. The structural analyses were performed by the solution 1H NMR and the solid state 13C NMR spectroscopies of the reduced samples. The composition of the three components turned out to be variable to the alcohol species used for the mixed solvent. 相似文献
8.
Bobonich F. M. Yaroshenko N. A. Solomakha V. N. Strelko V. V. Il'in V. G. 《Theoretical and Experimental Chemistry》2004,40(4):254-259
Under the conditions studied for the synthesis of mesophase materials with alkylpyridinium halides an increase in the density of packing of these molecules in the encapsulated micelles was observed with an increase in the length of the alkyl radicals. The difference in the density of packing of these surface active reagents (SAR) depended to a considerable extent on the perfection of the hexagonal structure and the characteristic absorption properties of the mesophase materials of MCM-41 type. 相似文献
9.
含活性基团的醛可与烯丙碘和锡粉直接进行亲核加成反应,得到高烯丙基的醇,水的存在不利于此反应的进行,与烯丙基溴相比,烯丙基碘反应活性更强,可在短时间内得较高的产率。 相似文献
10.
Lyudmila V. Chernykh Jitka Eysseltova Mikhail Y. Skripkin 《Monatshefte für Chemie / Chemical Monthly》2003,134(5):751-761
Summary. Solubility isotherms in the CuBr2−MBr−H2O (M
+ = Li+, Na+, Cs+) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide
systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated
solutions was performed.
Corresponding author. E-mail: jitka@prfdec.natur.cuni.cz
Received August 6, 2002; accepted (revised) November 29, 2002
Published online April 3, 2003 相似文献