全文获取类型
收费全文 | 8950篇 |
免费 | 365篇 |
国内免费 | 42篇 |
专业分类
化学 | 6310篇 |
晶体学 | 97篇 |
力学 | 218篇 |
数学 | 642篇 |
物理学 | 2090篇 |
出版年
2024年 | 7篇 |
2023年 | 51篇 |
2022年 | 169篇 |
2021年 | 234篇 |
2020年 | 157篇 |
2019年 | 177篇 |
2018年 | 133篇 |
2017年 | 145篇 |
2016年 | 273篇 |
2015年 | 269篇 |
2014年 | 347篇 |
2013年 | 622篇 |
2012年 | 700篇 |
2011年 | 739篇 |
2010年 | 472篇 |
2009年 | 396篇 |
2008年 | 611篇 |
2007年 | 531篇 |
2006年 | 537篇 |
2005年 | 462篇 |
2004年 | 423篇 |
2003年 | 346篇 |
2002年 | 355篇 |
2001年 | 222篇 |
2000年 | 155篇 |
1999年 | 134篇 |
1998年 | 79篇 |
1997年 | 51篇 |
1996年 | 65篇 |
1995年 | 71篇 |
1994年 | 55篇 |
1993年 | 47篇 |
1992年 | 33篇 |
1991年 | 27篇 |
1990年 | 35篇 |
1989年 | 40篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1985年 | 28篇 |
1984年 | 14篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1975年 | 4篇 |
1970年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有9357条查询结果,搜索用时 15 毫秒
111.
112.
113.
Jae C. Schwartz John E. P. Syka Ian Jardine 《Journal of the American Society for Mass Spectrometry》1991,2(3):198-204
By using a modified ion trap mass spectrometer, resolution in excess of 30,000 (FWHM) at m I z 502 is demonstrated. The method of increasing resolution in the ion trap mass spectrometer operated in the mass-selective instability mode depends on decreasing the rate of scanning the primary radio frequency amplitude as well as using resonance ejection at the appropriate frequency and amplitude. A theoretical basis for the method is introduced. 相似文献
114.
Kim Y Choi YH Chin YW Jang YP Kim YC Kim J Kim JY Joung SN Noh MJ Yoo KP 《Journal of chromatographic science》1999,37(12):457-461
An investigation of the effect of plant matrix on the supercritical fluid extraction efficiency of five schisandrin derivatives is reported, exhibiting a great difference with respect to extraction efficiency depending on the matrix. Pure supercritical CO2 at 60 degrees C and 34.0 MPa cannot fully recover schisandrin derivatives from the leaves as much as from the other matrices. Only 36.9% of these compounds are extracted from leaves of Schisandra chinensis by supercritical CO2 in comparison with organic solvent extraction. However, more than 80% of schisandrin derivatives are obtained from both stem and fruit parts. Ethanol addition also shows a different effect depending on plant matrix; that is, CO2 modified with 10% ethanol could enhance the yield of schisandrin derivatives from leaves by four times when compared with that of pure CO2, but it has little effect on both stems and fruits. 相似文献
115.
A theoretical investigation of the gas-phase oxidation reaction of the saturated tert-butyl radical.
The radical-radical reaction mechanisms and dynamics of ground-state atomic oxygen [O(3P)] with the saturated tert-butyl radical (t-C4H9) are investigated using the density functional method and the complete basis set model. Two distinctive reaction pathways are predicted to be in competition: addition and abstraction. The barrierless addition of O(3P) to t-C4H9 leads to the formation of an energy-rich intermediate (OC4H9) on the lowest doublet potential energy surface, which undergoes subsequent direct elimination or isomerization-elimination leading to various products: C3H6O + CH3, iso-C4H8O + H, C3H7O + CH2, and iso-C4H8 + OH. The respective microscopic reaction processes examined with the aid of statistical calculations, predict that the major addition pathway is the formation of acetone (C3H6O) + CH3 through a low-barrier, single-step cleavage. For the direct, barrierless H-atom abstraction mechanism producing iso-C4H8 (isobutene) + OH, which was recently reported in gas-phase crossed-beam investigations, the reaction is described in terms of both an abstraction process (major) and a short-lived addition dynamic complex (minor). 相似文献
116.
H. Bruchertseifer Choi Valsek K. A. Gavrilov M. Schwarzenberg 《Journal of Radioanalytical and Nuclear Chemistry》1983,77(1):97-104
The electrolytic deposition of the hydroxides of rare earth and transplutonium elements on nickel holders from α-hydroxyisobutyrate
solutions of 10−5 M to 5·10−1 M concentrations has been investigated in the presence of ammonium chloride. It is shown that at total concentrations of
≥10−12 M of rare earth and transplutonium elements, their electrodeposition proceeds with a 90% yield. 相似文献
117.
A new synthesis of 6‐carbomethoxy‐1,2,3,5‐tetrahydroirnidazo[2,3‐b][1,3]benzodiazocines 13 by the intramolecular cycloaddition reaction of methyl 2‐(1‐aziridinylmethyl)‐3‐(2‐ureidophenyl)propenoates 10 under Appel's dehydration conditions is described. The latter were readily obtained from 2‐nitrobenzalde‐hyde with methyl acrylate through the Baylis‐Hillman reaction. 相似文献
118.
Synthesis and properties of amine‐containing poly(arylene ether sulfone) as an anion‐exchange matrix
Won‐Keun Son Hea‐Young Song Sang‐Hern Kim Hyung‐Joong Kim Whan‐Gi Kim 《Journal of polymer science. Part A, Polymer chemistry》2002,40(23):4281-4287
Poly(arylene ether sulfone) (PSF), showing good thermal stability and excellent mechanical properties, was synthesized as an anion‐exchange matrix. It was synthesized by the condensation polymerization between bisphenol A and 4,4′‐dichlorodiphenylsulfone. 1°‐Amine‐containing poly(arylene ether sulfone) (1°‐APSF) was synthesized by the reduction reaction of a nitrated PSF. Then, it was transferred to 3°‐amine‐containing poly(arylene ether sulfone) (3°‐APSF) by the alkylation of the amine of 1°‐APSF. The properties of PSF, 1°‐APSF, and 3°‐APSF were investigated by Fourier transform infrared, 1H NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The introduction of the 3°‐amine group into PSF increased the glass‐transition temperature but decreased thermooxidative stability. The ion‐exchange capacities of 1°‐APSF and 3°‐APSF were shown to be 2.24 and 2.86 mequiv/g, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4281–4287, 2002 相似文献
119.
Lee K Song H Kim B Park JT Park S Choi MG 《Journal of the American Chemical Society》2002,124(12):2872-2873
Reaction of Rh(6)(CO)(9)(dppm)(2)(mu(3)-eta(2),eta(2),eta(2)-C(60)) (1) with C(60) in refluxing chlorobenzene followed by treatment with CNR (R = CH(2)C(6)H(5)) at room temperature affords the first fullerene-metal sandwich complex Rh(6)(CO)(5)(dppm)(2)(CNR)(mu(3)-eta(2),eta(2),eta(2)-C(60))(2) (2). Compound 2 has been characterized by an X-ray diffraction study. Electrochemical study of 2 reveals six well-separated reversible redox couples localized at C(60) cages due to a strong electronic communication between the two C(60) centers via the Rh(6) cluster spacer. 相似文献
120.
Injection-molded, short-glass-fiber-reinforced high-impact polystyrene was investigated under uniaxial tension with special attention to the effects of fiber and rubber concentration on fracture behavior. According to a fracture morphology study performed by polarized optical and scanning electron microscopy, crazes were consecutively initiated from rubber-styrene composite particles and from fiber ends. The rubber particles exhibited an intra-particle failure mode which resulted from the failure manner of the matrix becoming of a more brittle character with increasing fiber fraction. Fibers were surrounded by neigh boring growing crazes. Failure at the fiber-matrix interfaces proceeded with an increase in the number of crazes. With increasing concentration of the fibers, crazing at rubber particles appeared to be suppressed and crazing occurred more preferentially at the fiber ends, which accelerated a macroscopic fracture.Dedicated to Prof. H. H. Kausch on the occasion of his 60th birthday. 相似文献