全文获取类型
收费全文 | 88422篇 |
免费 | 776篇 |
国内免费 | 475篇 |
专业分类
化学 | 31425篇 |
晶体学 | 885篇 |
力学 | 6961篇 |
综合类 | 1篇 |
数学 | 33722篇 |
物理学 | 16679篇 |
出版年
2023年 | 78篇 |
2022年 | 98篇 |
2021年 | 212篇 |
2020年 | 216篇 |
2019年 | 263篇 |
2018年 | 10536篇 |
2017年 | 10359篇 |
2016年 | 6416篇 |
2015年 | 1141篇 |
2014年 | 641篇 |
2013年 | 965篇 |
2012年 | 4386篇 |
2011年 | 11117篇 |
2010年 | 6072篇 |
2009年 | 6418篇 |
2008年 | 7159篇 |
2007年 | 9337篇 |
2006年 | 725篇 |
2005年 | 1869篇 |
2004年 | 1975篇 |
2003年 | 2322篇 |
2002年 | 1365篇 |
2001年 | 417篇 |
2000年 | 436篇 |
1999年 | 257篇 |
1998年 | 296篇 |
1997年 | 270篇 |
1996年 | 319篇 |
1995年 | 225篇 |
1994年 | 174篇 |
1993年 | 204篇 |
1992年 | 141篇 |
1991年 | 149篇 |
1990年 | 135篇 |
1989年 | 133篇 |
1988年 | 115篇 |
1987年 | 121篇 |
1986年 | 134篇 |
1985年 | 163篇 |
1984年 | 154篇 |
1983年 | 123篇 |
1982年 | 122篇 |
1981年 | 122篇 |
1980年 | 120篇 |
1979年 | 116篇 |
1978年 | 108篇 |
1977年 | 66篇 |
1975年 | 73篇 |
1974年 | 70篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Jeong Hwan Kim Ji Hoon Ko Byeong-Soo Bae 《Journal of Sol-Gel Science and Technology》2007,41(3):249-255
Multi-scale hybrid nanocomposites containing both ∼15 nm silica colloids and ∼2 nm oligosiloxanes in a methacryl polymer matrix
were newly designed and fabricated. Colloidal silica sols were dispersed in methacryl oligosiloxanes nano-hybrid resins synthesized
by sol-gel reaction of methacryloxypropylmethoxysilane and diphenylsilanediol. On the basis of TEM and SANS analyses, it was
confirmed that the silica colloids were compatibly dispersed and different sizes of colloidal silica and oligosiloxanes co-exist
in the solutions. Multi-scale hybrid nanocomposites fabricated by UV and thermal curing with incorporation of silica colloids
in the nano-hybrid materials show enhanced mechanical and thermal characteristics. 相似文献
992.
Stassen AF Kooijman H Spek AL de Jongh LJ Haasnoot JG Reedijk J 《Inorganic chemistry》2002,41(24):6468-6473
Two new isostructural compounds, dichlorobis(1-(2-chloroethyl)tetrazole)copper(II) (1) and dibromobis(1-(2-chloroethyl)tetrazole)copper(II) (2), have been prepared. The synthesis, characterization, and spectral and magnetic properties as well as the crystal and molecular structures of 1 and 2 have been studied. Both complexes form two-dimensional, distorted square grid planes of copper and halides, distinctly separated by layers of tetrazole ligands. The differential (ac) magnetic susceptibility, chi = (deltaM/deltaH)(T), and magnetization M(H) of both complexes have been studied as a function of temperature and field. The compounds possess a ferromagnetic interaction within the isolated copper-halide layers (J/k(B) = 8.0 K, J/k(B) = 10.2 K, respectively, for the chloride and the bromide, and T(c) = 4.75 K, T(c) = 8.01 K). The magnetic coupling J'/k(B) between the different layers is found to be very weak (|J'/J| 相似文献
993.
The geometry of the 4′-cyano-(4′-CNPTB) and the 4′-methoxy-(4′-MePTB) phenylthiolbenzoates were obtained by ab initio calculations
employing 6–31G basis set at Hartee-Fock level of theory. The results predict an extended form of the molecules and torsional
angle between the phenyl rings at 90.85(6)0 and 90.87(3)0, respectively. On the basis of vibrational analysis the frequency assignment was carried out. The calculated frequencies
were compared with the experimental IR spectral data in carbon tetrachloride, carbon disulfide solutions and in solid state. 相似文献
994.
Jan L. M. Dillen 《Journal of computational chemistry》1995,16(5):610-619
The EFF'93 force field is used to study crystalline alkanes. In addition to detailed molecular geometries, the sublimation enthalpy, heat capacity, and lattice vibrations for a number of saturated hydrocarbons are reported and compared with experiment. © 1995 by John Wiley & Sons, Inc. 相似文献
995.
František Kvasnička Rudolf Ševčík Michal Voldřich Jana Krátká 《Central European Journal of Chemistry》2004,2(3):417-424
A simple and rapid capillary zone electrophoresis (CZE) method for the determination of aristolochic acid (AA) in dietary
supplements and selected herbs is described. A clear separation of AA from other sample constituents was achieved within 5
minutes without any sample clean up. A mixture of 20 mM-morpholinethanesulphonic acid+10 mM-BisTrisPropane+0.2% hydroxyethylcelullose
in 10% methanol serves as a background electrolyte. The linearity, accuracy, intra-assay and detection limit of the developed
method are 200–6000 ng/mL, 95–103%, 3.5%, and 50 ng/ml, respectively. Ease of use, sufficient sensitivity and low running
cost are the most important attributes of the CZE method. The proposed CZE method was compared with HPLC. 相似文献
996.
Robert Pietrzak Mieczysław Kozłowski Helena Wachowska Jan Yperman 《Central European Journal of Chemistry》2004,2(2):278-289
Soluble products obtained from the oxidation of four types of coal, each characterised by different degree of coalification
and different degree of sulphur content, are studied. The coals are oxidised with peracetic acid (PAA) and nitric acid. Analyses
are performed by Atmospheric Pressure-Temperature Programmed Reduction (AP-TPR) and Fourier Transform Infrared Spectroscopy
(FTIR). The soluble products contain much more sulphur than the insoluble products of oxidation. The products obtained from
the reaction with HNO3 contain higher amounts of inorganic sulphur compounds, while those obtained from the reaction with PAA are characterised
by an increased content of organic sulphur species. 相似文献
997.
EPR study has shown that the anticancer agent vanadocene dichloride (Cp2VCl2) interacts with carbonate contained in physiological solutions. Chelate complex Cp2VO2CO (|A(iso)(51V)| = 175.1 MHz, g(iso) = 1.9861) is the only paramagnetic species formed in the range about the physiological pH (5.5-11.0). The super-hyperfine coupling (|a(iso)(13C)| = 24.1 MHz) was evidenced at measurements using 13C labelled carbonate. The structure of carbonate complex was validated by comparison of observed and theoretical calculated HFC tensors (at the density functional level of theory). 相似文献
998.
Melinda Fekete Pál Kolonits Ngo Thi Hien Lajos Novák 《Central European Journal of Chemistry》2005,3(4):792-802
New tryptamine 5, 7 and β-carboline derivatives 3 were preparated by palladium-catalyzed coupling reaction of 5-bromotryptamine 1 with aryl boronic acids.
Dedicated to Professor András Lipták on his 70th birthday. 相似文献
999.
Xiongyu Wu Xiaohong Liu Guangce Jiang Yongcheng Lin Willy Chan L. L. P. Vrijmoed 《Chemistry of Natural Compounds》2005,41(1):27-29
A novel metabolite 1, named xyloketal G, was isolated from cultures of marine derived mangrove fungus Xylaria sp. 2508. Its structure was elucidated by analysis of spectroscopic data.__________Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 22–23, January–February, 2005. 相似文献
1000.
Marie-Noelle Avettand-Fènoël N. David G. Reumont J. -M. Fiorani M. Vilasi P. Perrot 《Journal of Thermal Analysis and Calorimetry》2007,90(2):329-332
The Fe-Sn-Zn system is of interest because Sn is one element added to the Zn galvanizing bath to overcome the drawbacks due
to the presence of Si in semi-killed steels. This work has been undertaken with the aim to understand the tin effect on the
microstructure and the layers growth in batch galvanized coatings on low alloyed steels.
Various experimental techniques such as metallography, scanning electron microscopy (SEM) coupled with X-ray energy dispersive
spectroscopy (EDX) are used in order to characterize the microstructure and the properties of such coatings elaborated in
a zinc bath enriched with tin.
Solidification phenomena and layers growth mechanisms during galvanization are explained by means of the ternary phase diagram
Fe-Sn-Zn at 450°C. The Calphad method allows to obtain this phase diagram from the three optimized binary phase diagrams Fe-Sn,
Fe-Zn and Sn-Zn and some experimental data inside the ternary Fe-Sn-Zn system. 相似文献