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131.
132.
Communicated by
C. Dafermos 相似文献
133.
Summary We provide an alternate proof of McMullen's theorem on contractive properties of the Poincaré series operator in the special case of the universal covering. This case includes in particular Kra's Theta Conjecture.Oblatum 16-X-1991 & 14-IV-1992First author supported in part by a grant from the National Science Foundation 相似文献
134.
An overview is given on the stepwise learning programmes undertaken to identify the main sources of error associated with the determination of the mandatory organic contaminants in the marine monitoring programmes. Details are given on the preparation and use of LRMs and CRMs to maintain analytical control and quantify the laboratory errors in relation to the measurement of changes in the environment. 相似文献
135.
Manju Rajeswaran Thomas N. Blanton David R. Whitcomb Nicholas Zumbulyadis Brian J. Antalek Scott T. Misture 《Journal of solid state chemistry》2006,179(4):1053-1059
In continuation of our interest in solid-state structures of silver complexes of photographic importance, the structure for silver benzotriazole (AgBZT), has now been obtained. The preferred method for solving crystal structures is via single-crystal X-ray diffraction (XRD). However, for some materials, growing single crystals of appropriate size and quality is often difficult or even impossible. AgBZT is an example of such a silver complex with poor solubility. The usual routes to preparing single crystals using recrystallization from a cooperating solvent resulted in polycrystalline powder samples. We propose a crystal structure for AgBZT, solved from synchrotron X-ray powder diffraction data, using a direct-space Monte Carlo simulated annealing approach. AgBZT crystals are monoclinic, (P21/c), with unit cell dimensions, a=14.8052(3) Å, b=3.7498(4) Å, c=12.3495(12) Å, and β=114.200(6)°. The AgBZT complex is constructed from all three of the Benzotriazole (BZT) nitrogens bonding to a separate silver atom. As a consequence of this bonding mode, the structure is a highly cross-linked, coordination polymer. 相似文献
136.
Li Changjun; Li Zheng; Evans David J.; Zhang Tie 《IMA Journal of Numerical Analysis》2003,23(4):581-592
Golub et al. (2001, BIT, 41, 7185) gave a generalizedsuccessive over-relaxation method for the augmented systems.In this paper, the connection between the SOR-like method andthe preconditioned conjugate gradient (PCG) method for the augmentedsystems is investigated. It is shown that the PCG method isat least as accurate (fast) as the SOR-like method. Numericalexamples demonstrate that the PCG method is much faster thanthe SOR-like method. 相似文献
137.
InAs/GaSb/AlSb resonant tunneling spin device concepts 总被引:1,自引:0,他引:1
David Z. -Y. Ting Xavier Cartoix 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):350
We discuss device concepts for creating spin-polarized current sources without external magnetic fields, using non-magnetic 6.1 Å semiconductor resonant tunneling structures. Spin filters, spin pumps, and spin transistors that exploit structural and bulk inversion asymmetries will be examined. 相似文献
138.
Functionalised hydroxylamine derivatives of (S)-prolinol prepared by a Cope elimination have been found to undergo oxidation to the nitrone either in the presence of air or a catalytic quantity of TPAP. These undergo intramolecular cycloaddition to give tricyclic isoxazolidines with high diastereoselectivity. 相似文献
139.
Yi Liu David D. Díaz Adrian A. Accurso K. Barry Sharpless Valery V. Fokin M. G. Finn 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5182-5189
1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007 相似文献
140.
The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means of sensitive 174 nm VUV absorption (CH2O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH2O + M → HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1.2 bar, k1a = 5.0 × 1015 exp(‐308 kJ mol?1/RT) cm3 mol?1 s?1. The pressure dependence, the rate of the competing molecular channel (1b), CH2O + M → H2 + CO + M, and the branching fraction β = k1a/(kA1a + k1b) was characterized by a two‐channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1–50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended, which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH2O, CO, and H atom measurements at temperatures of 1200–3200 K, with mixtures of 7 ppm to 5% formaldehyde, and pressures up to 15 bar. Some evidence was found for a self‐reaction of two CH2O molecules. At high initial CH2O mole fractions the reverse of reaction (6), CH2OH + HCO ? CH2O + CH2O becomes noticeable. The rate of the forward reaction was roughly measured to be k6 = 1.5 × 1013 cm3 mol?1 s?1. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 157–169 2004 相似文献