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121.
Experimental evidence for surface segregation of Pt at (1 1 1) surfaces of ternary (Pt, Ni)3Al alloys is presented, based upon Auger electron spectroscopy, low energy ion scattering, and angle-resolved X-ray photoelectron spectroscopy. Density functional calculations in the dilute limit confirm that Pt segregation is energetically favored. 相似文献
122.
Jay E. Taylor 《Journal of Physical Organic Chemistry》2007,20(12):1088-1092
Periodate oxidations of ethanediol and pinacol each occur in two phases; these are (1) formation and (2) decomposition of the intermediate complex. In phase (1), an increase in acidity gives . The rate of oxidation of ethanediol decreases with increasing acidity, whereas the rate of oxidation of pinacol maximizes with H5IO6. For both glycols, the activation energy increases and ΔSact decreases with increasing acidity. In phase (2), the energy of activation is essentially constant with pH, whereas the rate decreases, and the entropy of activation decreases modestly as pH decreases. The latter correlates with the nonhomogeniuty of product formation. Rates for 3‐chloro‐1,2‐propanediol are also listed. Pentaerythritol forms an inactive complex with or H5IO6 indicating the importance of chelation in the formation of the intermediate complex. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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124.
Global optimization is one of the key challenges in computational physics as several problems, e.g. protein structure prediction, the low-energy landscape of atomic clusters, detection of community structures in networks, or model-parameter fitting can be formulated as global optimization problems. Extremal optimization (EO) has become in recent years one particular, successful approach to the global optimization problem. As with almost all other global optimization approaches, EO is driven by an internal dynamics that depends crucially on one or more parameters. Recently, the existence of an optimal scheme for this internal parameter of EO was proven, so as to maximize the performance of the algorithm. However, this proof was not constructive, that is, one cannot use it to deduce the optimal parameter itself a priori. In this study we analyze the dynamics of EO for a test problem (spin glasses). Based on the results we propose an online measure of the performance of EO and a way to use this insight to reformulate the EO algorithm in order to construct optimal values of the internal parameter online without any input by the user. This approach will ultimately allow us to make EO parameter free and thus its application in general global optimization problems much more efficient. 相似文献
125.
Within the framework of the effective-mass approximation, the exciton states and interband optical transitions in InxGa1−xN/GaN strained quantum dot (QD) nanowire heterostructures are investigated using a variational method, in which the important built-in electric field (BEF) effects, dielectric-constant mismatch and three-dimensional confinement of the electron and hole in InxGa1−xN QDs are considered. We find that the strong BEF gives rise to an obvious reduction of the effective band gap of QDs and leads to a remarkable electron-hole spatial separation. The BEF, QD height and radius, and dielectric mismatch effects have a significant influence on exciton binding energy, electron interband optical transitions, and the exciton oscillator strength. 相似文献
126.
127.
With the progress of LSI technology, the electronic device size is scaled down to the sub 0.1μ m region. In such an ultrasmall device, it is indispensable to take quantum mechanical effects into account in device modeling. In this paper, we present a newly developed quantum Monte Carlo device simulation applicable to ultrasmall semiconductor devices. In this model, the quantum effects are represented in terms of quantum mechanically corrected potential in the classical Boltzmann equation. It is demonstrated that the quantum transport effects such as tunneling and energy quantization in ultrasmall semiconductor devices are obtained for the first time by using the standard Monte Carlo techniques. 相似文献
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129.
M.N. Mineva M. Hellström M. Bernas J. Gerl H. Grawe M. Pfützner P.H. Regan M. Rejmund D. Rudolph F. Becker C.R. Bingham T. Enqvist B. Fogelberg H. Gausemel H. Geissel J. Genevey M. Górska R. Grzywacz K. Hauschild Z. Janas I. Kojouharov Y. Kopatch A. Korgul W. Korten J. Kurcewicz M. Lewitowicz R. Lucas H. Mach S. Mandal P. Mayet C. Mazzocchi J.A. Pinston Zs. Podolyàk H. Schaffner Ch. Schlegel K. Schmidt K. Sümmerer H.J. Wollersheim 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):9-13
Rapidity correlations in 800 GeV proton interactions with emulsion nuclei are investigated for different targets and multiplicity
regions. To study the energy dependence, the results have been compared with proton interactions at 200 GeV and 400 GeV. A
common feature of all the interactions is the existence of strong, short-range correlations. However, no dependence of cluster
parameters on primary energy or target mass is found. A marginal increase of correlation strength with multiplicity is observed.
Received: 30 March 2001 / Accepted: 18 September 2001 相似文献
130.