全文获取类型
收费全文 | 430281篇 |
免费 | 3557篇 |
国内免费 | 1124篇 |
专业分类
化学 | 224147篇 |
晶体学 | 6727篇 |
力学 | 19835篇 |
综合类 | 13篇 |
数学 | 49954篇 |
物理学 | 134286篇 |
出版年
2020年 | 3513篇 |
2019年 | 3889篇 |
2018年 | 5252篇 |
2017年 | 5146篇 |
2016年 | 7513篇 |
2015年 | 4544篇 |
2014年 | 7241篇 |
2013年 | 18097篇 |
2012年 | 13974篇 |
2011年 | 16901篇 |
2010年 | 11950篇 |
2009年 | 11662篇 |
2008年 | 15629篇 |
2007年 | 15915篇 |
2006年 | 15006篇 |
2005年 | 13523篇 |
2004年 | 12487篇 |
2003年 | 11235篇 |
2002年 | 11015篇 |
2001年 | 12258篇 |
2000年 | 9486篇 |
1999年 | 7339篇 |
1998年 | 6274篇 |
1997年 | 6222篇 |
1996年 | 5808篇 |
1995年 | 5423篇 |
1994年 | 5436篇 |
1993年 | 5085篇 |
1992年 | 5754篇 |
1991年 | 5827篇 |
1990年 | 5641篇 |
1989年 | 5325篇 |
1988年 | 5458篇 |
1987年 | 5398篇 |
1986年 | 5087篇 |
1985年 | 6762篇 |
1984年 | 7152篇 |
1983年 | 5945篇 |
1982年 | 6248篇 |
1981年 | 6141篇 |
1980年 | 6001篇 |
1979年 | 6057篇 |
1978年 | 6405篇 |
1977年 | 6349篇 |
1976年 | 6436篇 |
1975年 | 5941篇 |
1974年 | 6007篇 |
1973年 | 6252篇 |
1972年 | 4281篇 |
1971年 | 3502篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Rajiv Manohar G. Tripathi A.K. Srivastava A.K. Prajapati 《Journal of Physics and Chemistry of Solids》2006,67(11):2300-2304
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared. 相似文献
23.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
24.
M. V. Kartikeyan G. Singh E. Borie B. Piosczyk M. Thumm 《International Journal of Infrared and Millimeter Waves》2006,27(5):657-670
The feasibility of an 84 GHz, 500 kW, CW gyrotron for ECRH on an experimental tokamak will be presented in this paper. Mode
competition and mode selection procedures are carefully investigated by considering various candidate modes and the TE10,4 mode is chosen as the operating mode. A conventional cylindrical cavity resonator with weak input and output tapers and parabolic
roundings is considered for interaction studies. Self-consistent, both single mode and time-dependent, calculations are carried
out and power and efficiencies are computed for a typical set of beam parameters. The results show that an output power of
well over 500 kW, CW and efficiency around 40% can be reached without a depressed collector. 相似文献
25.
The interferometric intensity patterns from a 2D shearing interferometer are shown and discussed. The intensity patterns can be obtained in two different approaches incorporating differential and extended wavefront controlled displacements. The reliable directional sensitivity of this interferometer allows the optimization of the measurement parameters to estimate the wavefront of the intensity patterns by regularization techniques. 相似文献
26.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 815–819, May, 1991. 相似文献
27.
28.
A. L. Apanasenko A. V. Kuznichenko Yu. B. Govyadovskii V. G. Yakunin 《Journal of Applied Spectroscopy》1991,54(3):271-276
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 1991. 相似文献
29.
A new geometrical method to determine the surface damage threshold for ultrashort pulses is presented. It consists in the formation of a surface damage profile by a movement of the sample across the laser beam focus. A single measurement of the maximum transversal dimension of this damage profile, which depends solely on the laser beam power, is used to calculate the local damage threshold intensity. It is also theoretically shown that the damage in the transverse dimension can be controlled under the diffraction-limited spot. 相似文献
30.
The dynamics of multiphoton transitions in a two-level spin system excited by transverse microwave and longitudinal RF fields with the frequencies ωmw and ωrf, respectively, is analyzed. The effective time-independent Hamiltonian describing the “dressed” spin states of the “spin + bichromatic field” system is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The direct detection of the time behavior of the spin system by the method of nonstationary nutations makes it possible to identify the multiphoton transitions for resonances ω0 = ωmw + rωrf (ω0 is the central frequency of the EPR line, r = 1, 2), to measure the amplitudes of the effective fields of these transitions, and to determine the features generated by the inhomogeneous broadening of the EPR line. It is shown that the Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening of spectral lines reduce only the nutation amplitude but do not change their frequencies. 相似文献