全文获取类型
收费全文 | 2153篇 |
免费 | 53篇 |
国内免费 | 14篇 |
专业分类
化学 | 1226篇 |
晶体学 | 10篇 |
力学 | 47篇 |
数学 | 225篇 |
物理学 | 712篇 |
出版年
2022年 | 13篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 28篇 |
2018年 | 18篇 |
2017年 | 13篇 |
2016年 | 35篇 |
2015年 | 27篇 |
2014年 | 40篇 |
2013年 | 88篇 |
2012年 | 100篇 |
2011年 | 129篇 |
2010年 | 54篇 |
2009年 | 39篇 |
2008年 | 97篇 |
2007年 | 108篇 |
2006年 | 117篇 |
2005年 | 79篇 |
2004年 | 83篇 |
2003年 | 67篇 |
2002年 | 77篇 |
2001年 | 53篇 |
2000年 | 64篇 |
1999年 | 35篇 |
1998年 | 17篇 |
1997年 | 37篇 |
1996年 | 40篇 |
1995年 | 20篇 |
1994年 | 18篇 |
1993年 | 40篇 |
1992年 | 40篇 |
1991年 | 21篇 |
1990年 | 29篇 |
1989年 | 22篇 |
1988年 | 37篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 27篇 |
1984年 | 27篇 |
1983年 | 25篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 25篇 |
1977年 | 23篇 |
1976年 | 29篇 |
1975年 | 27篇 |
1974年 | 23篇 |
1973年 | 29篇 |
排序方式: 共有2220条查询结果,搜索用时 578 毫秒
151.
Moore BC Peters RW Glasberg BR 《The Journal of the Acoustical Society of America》1999,106(6):3539-3552
Psychometric functions for detecting increments or decrements in level of sinusoidal pedestals were measured for increment and decrement durations of 5, 10, 20, 50, 100, and 200 ms and for frequencies of 250, 1000, and 4000 Hz. The sinusoids were presented in background noise intended to mask spectral splatter. A three-interval, three-alternative procedure was used. The results indicated that, for increments, the detectability index d' was approximately proportional to delta I/I. For decrements, d' was approximately proportional to delta L. The slopes of the psychometric functions increased (indicating better performance) with increasing frequency for both increments and decrements. For increments, the slopes increased with increasing increment duration up to 200 ms at 250 and 1000 Hz, but at 4000 Hz they increased only up to 50 ms. For decrements, the slopes increased for durations up to 50 ms, and then remained roughly constant, for all frequencies. For a center frequency of 250 Hz, the slopes of the psychometric functions for increment detection increased with duration more rapidly than predicted by a "multiple-looks" hypothesis, i.e., more rapidly than the square root of duration, for durations up to 50 ms. For center frequencies of 1000 and 4000 Hz, the slopes increased less rapidly than predicted by a multiple-looks hypothesis, for durations greater than about 20 ms. The slopes of the psychometric functions for decrement detection increased with decrement duration at a rate slightly greater than the square root of duration, for durations up to 50 ms, at all three frequencies. For greater durations, the increase in slope was less than proportional to the square root of duration. The results were analyzed using a model incorporating a simulated auditory filter, a compressive nonlinearity, a sliding temporal integrator, and a decision device based on a template mechanism. The model took into account the effects of both the external noise and an assumed internal noise. The model was able to account for the major features of the data for both increment and decrement detection. 相似文献
152.
David J. Kennedy Paul Todd Sam Logan Matthew Becker Klearchos K. Papas Lee R. Moore 《Journal of magnetism and magnetic materials》2007
Quadrupole magnetic flow sorting (QMS) is being adapted from the separation of suspensions of single cells (<15 μm) to the isolation of pancreatic islets (150–350 μm) for transplant. To achieve this goal, the critical QMS components have been modeled and engineered to optimize the separation process. A flow channel has been designed, manufactured, and tested. The quadrupole magnet assembly has been designed and verified by finite element analysis. Pumps have been selected and verified by test. Test data generated from the pumps and flow channel demonstrate that the fabricated channel and peristaltic pumps fulfill the requirements of successful QMS separation. 相似文献
153.
We describe an adaptive mesh refinement finite element method-of-lines procedure for solving one-dimensional parabolic partial differential equations. Solutions are calculated using Galerkin's method with a piecewise hierarchical polynomial basis in space and singly implicit Runge-Kutta (SIRK) methods in time. A modified SIRK formulation eliminates a linear systems solution that is required by the traditional SIRK formulation and leads to a new reduced-order interpolation formula. Stability and temporal error estimation techniques allow acceptance of approximate solutions at intermediate stages, yielding increased efficiency when solving partial differential equations. A priori energy estimates of the local discretization error are obtained for a nonlinear scalar problem. A posteriori estimates of local spatial discretization errors, obtained by order variation, are used with the a priori error estimates to control the adaptive mesh refinement strategy. Computational results suggest convergence of the a posteriori error estimate to the exact discretization error and verify the utility of the adaptive technique.This research was partially supported by the U.S. Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant Number AFOSR-90-0194; the U.S. Army Research Office under Contract Number DAAL 03-91-G-0215; by the National Science Foundation under Grant Number CDA-8805910; and by a grant from the Committee on Research, Tulane University. 相似文献
154.
155.
The γ-decays of the states in 47Ti at 157 keV and 1547 keV have been studied following the 46Ti(d, p)47Ti reaction at 5.0 MeV incident energy. Protons were detected at 0° with a semiconductor detector. The angular correlations of the γ-rays with the reaction protons were measured. The E2/M1 mixing ratios of the γ-decays and the population ratios of the
to the
substates were deduced. From the non-zero population of the
substate it was concluded that a spin-flip mechanism exists in the 46Ti(d, p)47Ti stripping reaction. 相似文献
156.
157.
The paper reports the results of work on the construction of LISP programs for various symbolic operations in complex analysis, including the evaluation of integrals around closed contours by the use of Cauchy's Theorem. It is concluded that the only difficulty in the way of the preparation of programs for all of the important and useful textbook calculations in complex analysis is that large amounts of fast storage in the computer are needed. 相似文献
158.
This case-based article arose out of a decision tree analysis carried out by the authors in an industrial firm. The company's identity and the actual product manufactured have both been altered for reasons of confidentiality. The various discussions outlined in the case are reported in the same order as they occurred within the firm whilst the problem was originally under study. The work reported was first carried out in 1971 and has been the subject of regular "follow-up" analyses since that date. A much simplified and restricted version of Parts I and II of this case was originally published in two articles appearing in the Financial Times during January 1972. 相似文献
159.
The reaction 125Te(d, p)126Te has been studied at a bombarding energy of 7.5 MeV in order to get information about the 126Te nuclear level scheme. Forty-two levels were observed below an excitation energy of 5.1 MeV. The angular distributions of 25 of the emitted proton groups were compared with DWBA calculations to determine the angular momentum of the captured neutrons. Contributions from more than one ln value were observed for two of the transitions. Transition strengths were extracted and compared to pairing-theory calculations. 相似文献
160.