全文获取类型
收费全文 | 2137篇 |
免费 | 40篇 |
国内免费 | 3篇 |
专业分类
化学 | 1439篇 |
晶体学 | 24篇 |
力学 | 60篇 |
数学 | 237篇 |
物理学 | 420篇 |
出版年
2023年 | 16篇 |
2022年 | 65篇 |
2021年 | 65篇 |
2020年 | 40篇 |
2019年 | 43篇 |
2018年 | 43篇 |
2017年 | 31篇 |
2016年 | 56篇 |
2015年 | 49篇 |
2014年 | 65篇 |
2013年 | 150篇 |
2012年 | 147篇 |
2011年 | 168篇 |
2010年 | 103篇 |
2009年 | 132篇 |
2008年 | 153篇 |
2007年 | 141篇 |
2006年 | 91篇 |
2005年 | 85篇 |
2004年 | 64篇 |
2003年 | 52篇 |
2002年 | 45篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 21篇 |
1995年 | 7篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 8篇 |
1981年 | 22篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 16篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有2180条查询结果,搜索用时 15 毫秒
1.
Fátima Nunes Serralha José Madeira Lopes Francisco Lemos Duarte Prazeres Maria Aires-Barros Joo Rocha Joaquim Cabral Fernando Ramôa Ribeiro 《Reaction Kinetics and Catalysis Letters》2000,69(2):217-222
Novel [CrIII(amp)(bipy)(Cl)] (1) (H2amp = N-(hydroxyphenyl)salicyldimine; bipy = 2,2-bipyridyl) and [CrIII(app)(bipy)(Cl)]+ (2) (H2app = N-(hydroxyphenyl)pyridine-2-carboxaldimine; bipy = 2,2-bipyridyl) complexes have been synthesized and characterized by physico-chemical methods. Complexes 1 and 2 have been employed as catalysts in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). The significance of the results with respect to oxo-functionalization of C-H bonds both in unsaturated and saturated hydrocarbons is noted. 相似文献
2.
Maria Merces Marques C. Costa F. Lemos F. Ram?a Ribeiro A. R. Dias 《Reaction Kinetics and Catalysis Letters》1997,62(1):9-15
In this paper we present a kinetic approach to the analysis of steady-state homogeneous Ziegler-Natta polymerization activity
data. The influence of the number of monomeric species that are coordinated to the active site on the apparent rate law is
discussed and the equations are fitted to the experimental results. 相似文献
3.
Gian Paolo Chiusoli Mirco Costa Luciano Pallini Giuliana Terenghi 《Transition Metal Chemistry》1982,7(6):304-306
Summary In presence of nickel or palladium catalysts, nucleophiles can attack vinylcyclopropanes with concomitant ring cleavage. With palladium catalysts in presence of appropriate substituents the terminal carbon atom of the resulting open chain is able to add to two molecules of a conjugated diene giving rise to long-chain unsaturated compounds. 相似文献
4.
D. T. Ribeiro C. Madzak A. Sarasin P. DI Mascio H. Sies C. F. M. Menck † 《Photochemistry and photobiology》1992,55(1):39-45
The effects of singlet oxygen (1O2), generated by the thermal decomposition of water soluble NDPO2 (endoperoxide of the disodium 3,3'-(1,4-naphthylidene) dipropionate), on a single-stranded shuttle vector were analysed. 1O2 induces a much higher level of breaks in the phosphodiester backbone of single-stranded than double-stranded DNA. This may be due to a higher accessibility of guanine residue, primarily damaged by 1O2. The damaged vector was transfected into monkey COS7 cells where single-stranded DNA was converted to the double-stranded replicative form DNA. After 3 days, extrachromosomal DNA was extracted and the plasmids rescued in E. coli to study mutagenesis. There is a significant increase in mutation frequency of damaged single-stranded DNA in comparison to untreated DNA. It is concluded that 1O2 induces breaks in the backbone of single-stranded DNA and that the 1O2-damaged molecules are mutated after passage through mammalian cells. 相似文献
5.
Pier G. Desideri Luciano Lepri Roberto Udisti Leonardo Checchini Massimo Del Bubba Renato Cini 《International journal of environmental analytical chemistry》2013,93(3-4):331-351
Abstract Organic compounds extractable with n-hexane were identified and quantitatively determined in pack, surface and deep snow samples taken at different depths and collected at several altitudes above sea level from Antarctica during the 1993/94 Italian expedition. The comparison between the composition of organic compounds in snow and the ones in pack and sea-water samples pointed out that the three matrices substantially contain the same biogenic and anthropogenic organic compounds. The contribution of marine aerosol to organic content in the snow is confirmed by the enrichment ratios calculated for the more representative classes of identified compounds (n-alkanes, phthalates and low molecular weight alkylbenzenes). The changes in the composition of organic compounds in snow as the altitude increases seem to depend on the dimensional spectrum of the aerosol. Thus, smallest particles, richest in surfactant material, reach the highest altitudes. 相似文献
6.
Manuel A. V. Ribeiro da Silva 《Journal of Thermal Analysis and Calorimetry》2012,108(2):533-535
7.
Carolina Resmini Melo Elidio Angioletto Humberto Gracher Riella Michael Peterson Márcio Roberto Rocha Aline Resmini Melo Luciano Silva Susane Strugale 《Journal of Thermal Analysis and Calorimetry》2012,109(3):1341-1345
Research focused on the transformation and utilization of industrial wastes into products of commercial interest plays an increasingly important role. Residual pulp can become useful in the manufacture of different materials, providing high value to this waste and reducing its environmental impact when disposed of improperly in the environment. The main constituents of this waste are kaolin and calcium carbonate (CaCO3). Starting from kaolin, metakaolin can be produced by calcination of the residue at 630?°C for 2?h in a rotary reactor with air flow, followed by solubilization with hydrochloric acid to remove the CaCO3. The development of technological alternatives aimed at the reuse of certain wastes can result in applications of real economic interest to the chemical industry and ceramics and glass, which is the case in this study. The raw material and metakaolin obtained were analyzed by thermogravimetric analysis and derivative thermogravimetric analysis, X-ray diffraction, and X-ray fluorescence spectroscopy with promising results. This is because metakaolin was obtained free of contamination by other materials. 相似文献
8.
9.
Sebastião PJ Simeão Carvalho P Chaves MR Nguyen HT Ribeiro AC 《The European physical journal. E, Soft matter》2006,20(1):55-61
We present a polarising optical microscopy study of the low-temperature anticlinic-like tilted mesophase of the liquid-crystal
compound octylphenyl-2-chloro-4-(p-cyano-benzoyloxy) (DB8Cl). This mesophase has been described as a bilayer smectic structure in which the molecules within each layer are organised
in an anticlinic way. The optical textures observed in samples with planar orientation show a double stripe pattern, with
the lines aligned parallel to the rubbing direction, characteristic of a double periodic modulation of the refractive index
of the material. The long-period modulation is temperature dependent and disappears for thin sample cells (< 5μm). The short-period
modulation is nearly independent of the thickness of the cells. The experimental results are analysed in terms of a model
which considers that there is a special distribution of the principal optical axis which may be in or out of the polariser-analyser
plane. The observed periodic variation of the principal optical axis could not be interpreted in terms of the original structure
proposed for this phase. DB8Cl presents a structure formed by dimers that can be viewed as flexible bent-core-like molecules, showing similarities with
phases found in banana-like systems, but exhibiting a much more complex structure. 相似文献