全文获取类型
收费全文 | 1380427篇 |
免费 | 25938篇 |
国内免费 | 7756篇 |
专业分类
化学 | 695993篇 |
晶体学 | 20331篇 |
力学 | 75253篇 |
综合类 | 110篇 |
数学 | 243241篇 |
物理学 | 379193篇 |
出版年
2021年 | 13582篇 |
2020年 | 15972篇 |
2019年 | 16101篇 |
2018年 | 12700篇 |
2016年 | 27974篇 |
2015年 | 20823篇 |
2014年 | 30497篇 |
2013年 | 74619篇 |
2012年 | 39628篇 |
2011年 | 37342篇 |
2010年 | 37508篇 |
2009年 | 39562篇 |
2008年 | 36297篇 |
2007年 | 32138篇 |
2006年 | 38422篇 |
2005年 | 30364篇 |
2004年 | 31524篇 |
2003年 | 29653篇 |
2002年 | 30650篇 |
2001年 | 31847篇 |
2000年 | 26784篇 |
1999年 | 23499篇 |
1998年 | 21437篇 |
1997年 | 21430篇 |
1996年 | 21254篇 |
1995年 | 19308篇 |
1994年 | 18762篇 |
1993年 | 18318篇 |
1992年 | 18802篇 |
1991年 | 19019篇 |
1990年 | 18303篇 |
1989年 | 18297篇 |
1988年 | 17854篇 |
1987年 | 17799篇 |
1986年 | 16757篇 |
1985年 | 23118篇 |
1984年 | 24185篇 |
1983年 | 20232篇 |
1982年 | 21802篇 |
1981年 | 21024篇 |
1980年 | 20366篇 |
1979年 | 20836篇 |
1978年 | 21938篇 |
1977年 | 21657篇 |
1976年 | 21425篇 |
1975年 | 20117篇 |
1974年 | 19833篇 |
1973年 | 20276篇 |
1972年 | 14721篇 |
1967年 | 12932篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
981.
Erich Miersemann Hans D. Mittelmann W. Trnig 《Mathematical Methods in the Applied Sciences》1989,11(1):95-104
In this paper we generalize recent theoretical results on the local continuation of parameter-dependent non-linear variational inequalities. The variational inequalities are rather general and describe, for example, the buckling of beams, plates or shells subject to obstacles. Under a technical hypothesis that is satisfied by the simply supported beam, we obtain the existence of a continuation of both the solution and the eigenvalue with respect to a local parameter. A numerical continuation method is presented that easily overcomes turning points. Numerical results are presented for the non-linear beam. 相似文献
982.
本文提出从高分辨电子显微像中,利用光学、全息和部分相干等方法,提取传递函数,制作相位和振幅滤波器,实现解卷,提高高分辨电子显微像的分辨率. 相似文献
983.
In recent years there has been tremendous progress in lithium niobate-based photonic switches. The various switch configurations proposed and implemented, and their characteristics, are reviewed. A summary of the device technology is given. Performance analysis based on different architecture and the size of arrays that can be relalized are discussed.Indian Institute of Science, Bangalore, India 相似文献
984.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1132–1136, September, 1989. 相似文献
985.
P. Kolář 《Czechoslovak Journal of Physics》1989,39(11):1317-1320
Conclusions The sets (3) and (4) of condensates have been compared using the QCD sum rules (2) with indefinite weight functions. A bad matching between both sets of condensates and experimental data has been obtained. The standard values (3) appear to be closer to data but some increase ofQ is necessary to improve the agreement. Only higher values ofm
0
2
could change the results of this analysis. It is interesting that negative values ofm
0
2
considerably improve the agreement with data; note that this quantity cannot be determined with a sufficient accuracy. We conclude that the QCD sum rules (2) cannot definitely determine a privileged set of condensates.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday. 相似文献
986.
987.
988.
This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated 3-dB modulation bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of conventional electrode structures that are limited by phase velocity mismatch.This work was supported by the U.S. Army Research Office under contract DAAL-03-88-K-0005 and the Texas Advanced Technology Program. 相似文献
989.
R A Altes 《The Journal of the Acoustical Society of America》1989,85(2):934-942
Target parameters such as reflectivity, range, velocity, and angular position are represented by ordered maps of tuned cortical neurons in insectivorous bats. It is suggested that the response of each neuron in such a map is determined by a hypothesis test conditioned on a particular value of the mapped parameter. The excitation of each neuron is then interpreted as a sample value of a conditional log-likelihood ratio or a log-likelihood function. Interpolation between the samples, which is needed to find the parameter that maximizes the mapped function (e.g., the maximum likelihood parameter estimate), can be accomplished with overlapped tuning curves. An attempt to portray a sharp peak by a weighted sum of relatively broad neuronal tuning curves or interpolation functions results in excitatory center/inhibitory surround behavior. Facilitation or antifacilitation of neurons that are likely to be excited by succeeding observations can be used for sequential detection and tracking. Interpolation and pulse-to-pulse data storage capability are required to explain range jitter sensitivity and to allow for moving target indication in bat sonar. If a cortical map represents an ordered array of hypothesis tests, then many such tests are implemented in parallel when target parameters are unknown. Detection performance is then degraded relative to the idealized situation in which all parameters are specified. Performance in noise may thus appear to be much worse than that of an ideal detector, even if each hypothesis test is optimally implemented. 相似文献
990.
Time structure of iodine laser pulse in the free running mode of operation was studied using the power amplifier of laser system PERUN as the laser oscillator. Two characteristic shapes of laser pulse correspond to different regimes of laser operation, the existence of which is ascribed to the critical concentration of I2 molecules. Simultaneously an additional chemical pumping was proved at least in the initial phase of photodissociation and in a late-time lasing after the end of flashlamps pumping light. 相似文献