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排序方式: 共有9477条查询结果,搜索用时 312 毫秒
971.
α,α'-二氧代烯酮环二硫代缩醛的NMR研究 总被引:4,自引:3,他引:1
报道了7种新的α,α'-二氧代烯酮环二硫代缩醛化合物的NMR谱.应用1H、13C NMR谱等确定了这7种新化合物的分子结构,并对全部谱峰进行了归属,初步探讨了分子结构对化学位移的影响. 相似文献
972.
The polycondensation of p-aminobenzoic acid by the use of triphenylphospine and hexachloroethane is described. One way to obtain a mixed solution of rigid rod and flexible coil polymers is the polycondensation of the rigid chains in a solution of a flexible polymer matrix. Results on matrix polycondensation of poly(p-benzamide) in solutions of poly(methyl methacrylate), poly(methyl methacrylate-co-styrene), polystyrene and polyacrylonitrile are reported. It is shown that there exists an interrelation between the phase behavior of the mixed polymer solutions and the influence of the matrix polymer on the synthesis of poly(1.4.-benzamide). The ternary phase diagrams of the rigid rod/flexible coil polymer solutions were determined. 相似文献
973.
M. Kajita 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):55-59
Collisions between linear polar molecules that were electrostatically trapped were investigated. The collisional transition
from a low to a high field seeking state (inelastic collision) causes trap loss. The efficiency of evaporative cooling is
improved at higher elastic collision rates. We calculated cross-sections of inelastic and elastic collision using a semi-classical
treatment.
Received 6 December 2001 / Received in final form 26 February 2002 Published
online 28 June 2002 相似文献
974.
Paul D. Beer Christopher G. Crane Jonathan P. Danks Philip A. Gale Jerome F. McAleer 《Journal of organometallic chemistry》1995,490(1-2):143-148
New polyferrocene bis benzo-15-crown-5 ligands have been prepared and shown to form 1:1 intramolecular sandwich complexes with the potassium cation. Electrochemical investigations reveal that both receptors undergo small anodic perturbations of the respective ferrocene-ferrocenium redox couples in the presence of alkali metal cations. 相似文献
975.
An asymmetric molecular sieve carbon membrane is obtained by conventional pyrolysis of a thermosetting polymeric film, followed by unequal oxidation. Morphology, pore size distribution, and gas separation characteristics of the membrane are discussed. The transport mechanism for gas permeation is clearly non-Knudsen diffusion since heavier oxygen permeates faster than lighter nitrogen. The proposed mass transfer mechanism is that of a molecular sieve. 相似文献
976.
We generalize previous stochastic classical trajectory-ghost atom calculations for describing palladium deposition onto the Ni(111) surface between 0.1 and 0.5 monolayers. The growth evolves through two-dimensional islands. The islands are formed following the downward funneling mechanism. Surface temperature does not affect the island growth. 相似文献
977.
Y. Kangawa T. Ito A. Taguchi K. Shiraishi T. Irisawa T. Ohachi 《Applied Surface Science》2002,190(1-4):517-520
Diffusion length of Ga on the GaAs(0 0 1)-(2×4)β2 is investigated by a newly developed Monte Carlo-based computational method. The new computational method incorporates chemical potential of Ga in the vapor phase and Ga migration potential on the reconstructed surface obtained by ab initio calculations; therefore we can investigate the adsorption, diffusion and desorption kinetics of adsorbate atoms on the surface. The calculated results imply that Ga diffusion length before desorption decreases exponentially with temperature because Ga surface lifetime decreases exponentially. Furthermore, Ga diffusion length L along
and [1 1 0] on the GaAs(0 0 1)-(2×4)β2 are estimated to be
and L[110]200 nm, respectively, at the incorporation–desorption transition temperature (T860 K). 相似文献
978.
979.
A model electrochemical ion-transfer reaction is investigated by molecular dynamics simulations. Non-equilibrium solvation effects can lead to barrier recrossings when the ion passes the transition state. The resulting transmission coefficient, which measures the deviation of the rate from the predictions of the transition state theory, is in good agreement with the Grote–Hynes theory. By contrast, Kramers theory predicts a much lower rate constant. The reaction occurs in the polarization caging regime of Grote–Hynes theory, in which the solvent motion controls the advance of the reaction. Furthermore, the molecular friction depends strongly on the distance from the electrode. 相似文献
980.
Yonggang Zhang Yi Gu Cheng Zhu Guoqiang Hao Aizhen Li Tiandong Liu 《Infrared Physics & Technology》2006,47(3):257-262
Using homo-junction structure and relative thin linear graded InxGa1−xAs as the buffer layer, extended wavelength InGaAs PIN photodetectors with cut-off wavelength of 2.2 and 2.5 μm at room temperature have been grown by using GSMBE, and their performance over a wide temperature range have been extensively investigated. For those 2.2 or 2.5 μm detectors with 100 μm diameter, the typical dark current (VR = 10 mV) and R0A are 57 nA/10.3 Ω cm2 or 67 nA/12.7 Ω cm2 at 290 K, and 84 pA/4.70 kΩ cm2 or 161 pA/3.12 kΩ cm2 at 210 K respectively. The thermal activation energies of the dark current are 0.447 eV or 0.404 eV for 2.2 or 2.5 μm detectors respectively. 相似文献