全文获取类型
收费全文 | 5396篇 |
免费 | 36篇 |
国内免费 | 15篇 |
专业分类
化学 | 2298篇 |
晶体学 | 72篇 |
力学 | 250篇 |
数学 | 697篇 |
物理学 | 2130篇 |
出版年
2022年 | 48篇 |
2021年 | 80篇 |
2020年 | 86篇 |
2019年 | 103篇 |
2018年 | 131篇 |
2017年 | 127篇 |
2016年 | 160篇 |
2015年 | 58篇 |
2014年 | 123篇 |
2013年 | 238篇 |
2012年 | 203篇 |
2011年 | 192篇 |
2010年 | 208篇 |
2009年 | 194篇 |
2008年 | 225篇 |
2007年 | 185篇 |
2006年 | 212篇 |
2005年 | 171篇 |
2004年 | 149篇 |
2003年 | 126篇 |
2002年 | 141篇 |
2001年 | 141篇 |
2000年 | 129篇 |
1999年 | 81篇 |
1998年 | 98篇 |
1997年 | 73篇 |
1996年 | 78篇 |
1995年 | 53篇 |
1994年 | 56篇 |
1993年 | 53篇 |
1992年 | 67篇 |
1991年 | 56篇 |
1990年 | 85篇 |
1989年 | 53篇 |
1988年 | 55篇 |
1987年 | 68篇 |
1986年 | 59篇 |
1985年 | 58篇 |
1984年 | 67篇 |
1983年 | 55篇 |
1982年 | 68篇 |
1980年 | 55篇 |
1979年 | 48篇 |
1978年 | 49篇 |
1977年 | 60篇 |
1976年 | 60篇 |
1975年 | 57篇 |
1974年 | 61篇 |
1973年 | 73篇 |
1969年 | 45篇 |
排序方式: 共有5447条查询结果,搜索用时 203 毫秒
131.
132.
The effect of stirring a vanadium-titanium-tellurium catalyst on the yield of the selective oxidation products for oxidation of o-xylene in fluidized bed reactors has been studied. It is shown that the stirring of catalyst pellets increases the yield of phthalic anhydride.
-- - . , .相似文献
133.
B. A. Ivanov 《Journal of Mathematical Sciences》1980,13(2):216-217
A method is indicated for the approximate determination of the positive eigenvalue of the problem x–Qx=0, >0, xK, x0, whereK is a cone in Banach space and Q is an operator-valued function positive relative toK.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 58, pp. 37–39, 1976. 相似文献
134.
Nekrasov A. A. Ivanov V. F. Gribkova O. L. Vannikov A. V. 《Russian Journal of Electrochemistry》2004,40(3):249-258
The electrochemical oxidation–reduction of films of polyaniline is studied in the presence of various counteranions. The differential cyclic voltabsorptometric (DCVA) curves (dA/dt relative to potential, where A is the optical absorption) are recorded at characteristic wavelengths corresponding to individual spectrum components previously isolated with the Alentsev–Fok method. The DCVA curves for aqueous solutions of HCl, HClO4, and H2SO4 at different potential scan rates are compared to traditional cyclic voltammograms. For the DCVA curves obtained at 665 nm discovered is one broad peak of dA/dt in the region of potentials between the first and second stages of polyaniline oxidation (0.6 V vs. Ag/AgCl). An assumption is made about a chemical nature of the process of generation of absorption in this spectral region, which, more likely than not, is connected with the emergence of dimers of radical cations of polyaniline. It is discovered that the electrochemical processes in the region of potentials that correspond to the first stage of oxidation give rise to variations in the absorption inside several regions of spectrum: 435 nm (radical cations) and 755 nm (localized polarons). An assumption is made that the first peak of the current corresponds to several successive processes that occur in a polyaniline molecule in the course of oxidation as well as to the existence of heterogeneous regions where the generation of localized polarons proceeds at different rates. 相似文献
135.
Dobrikova AG Ivanov AG Morgan R Petkanchin IB Taneva SG 《Journal of photochemistry and photobiology. B, Biology》2000,57(1):33-40
Electric light scattering measurements demonstrate a strong decline in the permanent electric dipole moment and electric polarizability of both thylakoid membranes and photosystem II-enriched particles of the Chlorina f2 mutant which has severely reduced levels of light-harvesting chlorophyll a/b-binding proteins compared to the wild type barley chloroplasts. The shift in the electric polarizability relaxation to higher frequencies in thylakoids and photosystem II particles from Chlorina f2 reflects higher mobility of the interfacial charges of the mutant than that of the wild type membranes. The experimental data strongly suggest that the major light-harvesting complex of photosystem II directly contribute to the electric properties of thylakoid membranes. 相似文献
136.
Krayushkin M. M. Ivanov S. N. Martynkin A. Yu. Lichitsky B. V. Dudinov A. A. Uzhinov B. M. 《Russian Chemical Bulletin》2001,50(12):2424-2427
Procedures were developed for the synthesis of substituted bis(2,5-dimethyl-3-thienyl)furans based on 1,2-bis(2,5-dimethyl-3-thienyl)-2-hydroxyethanone. Dithienylethene structures in which the ethene fragment is involved in the furan or furopyrimidine system possess photochromic properties and their open forms exhibit fluorescence. 相似文献
137.
I. N. Ivanov O. K. Nikolaenko A. S. Shtan 《Journal of Radioanalytical and Nuclear Chemistry》1985,90(1):189-196
Expanding application of activation analysis in industry resulted in exposure of features related to higher requirements to productivity, reliability, automation level, metrological support of analytical methods and equipment. Based on the application of neutron generators, radioisotope neutron sources, nuclear reactors, electron accelerators as activating radiation sources, high-productivity activation analytical systems used directly in analytical laboratories and plants were constructed. Level of development of the above works makes it possible to conclude that industrial activation analysis has formed as an independent trend of nuclear analytics and has considerable prospects. 相似文献
138.
S. V. Trepalin A. V. Yarkov V. B. Sokolov A. N. Ivanov 《Russian Chemical Bulletin》1990,39(3):476-480
The potential function has been constructed for internal rotation of the NO-group in (CH3)2CClNO, CH3CCl2NO, and their deuterium analogs. It has been established that the N=O bond in the cisCl conformer of CH3CCl2NO does not eclipse the C-Cl bond, rather forming an angle of approximately 30. It has been shown that a change in substitutent on the -carbon atom may produce a substantial change in the form of the potential function of internal rotation (PFIR) of the NO group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 550–555, March, 1990. 相似文献
139.
Ivanov A. V. Bredyuk O. A. Antzutkin O. N. Forsling W. 《Russian Journal of Coordination Chemistry》2004,30(7):480-485
Alkylxanthate complexes of the general formula [M{S(S)COR}2] (M = Ni, 63Cu, and 65Cu; R = C2H5, i-C3H7, i-C4H9, s-C4H9, and C5H11) were synthesized and studied by EPR and high-resolution solid-state 13C CP/MAS NMR. In the copper(II) complexes stabilized in the matrix of nickel(II) compounds, square planar chromophores [CuS4] are characterized by rhombic distortion (EPR data). Experimental EPR spectra were simulated at the second order of perturbation theory. Nickel(II) complexes were characterized by 13C NMR spectra. In all cases, the –OC(S)S– groups were found to exhibit intramolecular structural equivalence. 相似文献
140.