全文获取类型
收费全文 | 722075篇 |
免费 | 28657篇 |
国内免费 | 18660篇 |
专业分类
化学 | 363190篇 |
晶体学 | 10837篇 |
力学 | 39684篇 |
综合类 | 35篇 |
数学 | 100187篇 |
物理学 | 255459篇 |
出版年
2021年 | 6726篇 |
2020年 | 7467篇 |
2019年 | 9029篇 |
2018年 | 11805篇 |
2017年 | 12594篇 |
2016年 | 16628篇 |
2015年 | 10402篇 |
2014年 | 15942篇 |
2013年 | 34284篇 |
2012年 | 27785篇 |
2011年 | 33141篇 |
2010年 | 26786篇 |
2009年 | 27200篇 |
2008年 | 28964篇 |
2007年 | 28343篇 |
2006年 | 26241篇 |
2005年 | 23526篇 |
2004年 | 23069篇 |
2003年 | 20334篇 |
2002年 | 20198篇 |
2001年 | 21824篇 |
2000年 | 16858篇 |
1999年 | 13550篇 |
1998年 | 11701篇 |
1997年 | 11264篇 |
1996年 | 10884篇 |
1995年 | 10126篇 |
1994年 | 10230篇 |
1993年 | 10062篇 |
1992年 | 10245篇 |
1991年 | 10350篇 |
1990年 | 9771篇 |
1989年 | 9582篇 |
1988年 | 9286篇 |
1987年 | 8864篇 |
1986年 | 8392篇 |
1985年 | 10014篇 |
1984年 | 10493篇 |
1983年 | 8545篇 |
1982年 | 9187篇 |
1981年 | 8679篇 |
1980年 | 8382篇 |
1979年 | 8833篇 |
1978年 | 9032篇 |
1977年 | 9057篇 |
1976年 | 9402篇 |
1975年 | 8345篇 |
1974年 | 8163篇 |
1973年 | 8542篇 |
1972年 | 6422篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
We study oscillation in a gyrotron with allowance for reflections from an output horn. Regions with different system behaviors,
such as stationary oscillation, self-modulation, and complex-dynamics regimes are found in the parameter plane. The scenarios
of appearance of chaotic oscillations are considered. It is shown that they can emerge via either a sequence of period-doubling
bifurcations or destruction of quasiperiodic motion. For chaotic attractors, Lyapunov exponents are calculated and their dimensions
are estimated on the basis of the Kaplan-Yorke formula. The dimension values turn out to be anomalously large, which is stipulated
by the presence of a large number of high-Q eigenmodes in the gyrotron cavity due to operation near the cutoff frequency of
an electrodynamic system.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 10, pp. 887–899, October 2006. 相似文献
132.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献
133.
134.
The quantitative rainbow schlieren deflectometry (RSD) technique was applied to measure temperature and oxygen concentration in an axisymmetric hydrogen gas-jet diffusion flame burning in quiescent air at fuel jet exit Reynolds number of 70. Schlieren measurements were compared with conventional measurements using a thermocouple and a gas-sampling probe. Good agreement between the two measurement techniques was achieved on the fuel-lean side of the flame. 相似文献
135.
A successful application of ultrasound Doppler velocimetry in liquid sodium flows is described. To obtain sufficient Doppler
signals, different problems had to be solved: the transmission of the ultrasonic beam through the channel wall made of stainless
steel, the acoustic coupling between the transducer and the channel wall, and the wetting of the inner surface of the wall
by the liquid metal, respectively. A sodium flow in a square duct exposed to a transverse magnetic field is investigated.
In accordance with the existing knowledge about MHD channel flows, we found that the velocity profiles modified to a M-shape
owing to the effect of an inhomogeneous magnetic field.
Received: 12 June 2001/Accepted: 27 October 2001 相似文献
136.
137.
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained. 相似文献
138.
Mathematical Notes - 相似文献
139.
140.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献