全文获取类型
收费全文 | 276388篇 |
免费 | 2916篇 |
国内免费 | 970篇 |
专业分类
化学 | 155603篇 |
晶体学 | 4272篇 |
力学 | 10915篇 |
综合类 | 8篇 |
数学 | 28245篇 |
物理学 | 81231篇 |
出版年
2020年 | 1985篇 |
2019年 | 2008篇 |
2018年 | 2358篇 |
2017年 | 2346篇 |
2016年 | 3976篇 |
2015年 | 2778篇 |
2014年 | 3871篇 |
2013年 | 11148篇 |
2012年 | 8646篇 |
2011年 | 10819篇 |
2010年 | 7087篇 |
2009年 | 6909篇 |
2008年 | 10099篇 |
2007年 | 9929篇 |
2006年 | 9901篇 |
2005年 | 9393篇 |
2004年 | 8324篇 |
2003年 | 7558篇 |
2002年 | 7404篇 |
2001年 | 8723篇 |
2000年 | 6471篇 |
1999年 | 5110篇 |
1998年 | 3952篇 |
1997年 | 4038篇 |
1996年 | 3943篇 |
1995年 | 3660篇 |
1994年 | 3461篇 |
1993年 | 3243篇 |
1992年 | 3917篇 |
1991年 | 3968篇 |
1990年 | 3756篇 |
1989年 | 3758篇 |
1988年 | 3694篇 |
1987年 | 3731篇 |
1986年 | 3424篇 |
1985年 | 4566篇 |
1984年 | 4687篇 |
1983年 | 3829篇 |
1982年 | 4125篇 |
1981年 | 3810篇 |
1980年 | 3899篇 |
1979年 | 4123篇 |
1978年 | 4327篇 |
1977年 | 4187篇 |
1976年 | 4112篇 |
1975年 | 3900篇 |
1974年 | 3730篇 |
1973年 | 3952篇 |
1972年 | 2492篇 |
1971年 | 1974篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
O.G. Kosareva N.A. Panov N. Akozbek V.P. Kandidov Q. Luo S.A. Hosseini W. Liu J.-F. Gravel G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2006,82(1):111-122
We demonstrate a three orders of magnitude increase and stability in the backscattered fluorescence signal from nitrogen molecules
by terawatt femtosecond laser pulse induced air filaments using a new method. The method is based on squeezing the initial
beam diameter using a telescope. The effect of laser shot-to-shot fluctuations was included in numerical simulations by a
random distribution of the initial intensity in both squeezed and non-squeezed beams. Statistical processing of the simulation
results shows that the average diameter of plasma channels as well as the total amount of free electrons generated in a bunch
of multiple filaments in air is larger in the squeezed beam. Shot-to-shot stability of the simulated plasma density increases
in the squeezed beam. The change of this plasma density with propagation distance is in good qualitative agreement with the
change of the range-corrected nitrogen fluorescence signal with distance.
PACS 42.65.Jx; 42.60.Jf; 42.68.Ay; 42.68.Wt 相似文献
203.
V. S. Bilanych I. I. Makauz T. D. Mel’nichenko I. M. Rizak V. M. Rizak 《Physics of the Solid State》2006,48(11):2060-2064
The internal friction in Ge x As40 ? x S60 glasses is investigated in the temperature range 100 K-T g at infralow frequencies (10?3?10?1 Hz). It is shown that the concentration dependence of the internal friction of these materials changes as a result of the transformation of the dominant kinetic unit in dissipative processes of the relaxation and nonrelaxation types. It is established tha the change in the mechanism of internal friction in the Ge x As40 ? x S60 glasses leads to a jump in the activation energy of the α relaxation and to a local minimum in the frequency factor τ0. 相似文献
204.
We discuss the spectral lineshapes of reflectance and modulated reflectance (MR) measurements on optoelectronic device structures such as epi-layers, quantum wells (QWs), vertical-cavity surface emitting-lasers (VCSELs) and resonant-cavity light-emitting diodes (RCLEDs). We consider the various methods for the extraction of built-in electric fields and band-gap energies from Franz-Keldysh oscillations (FKO), using the example of a tensilely strained InGaAs QW system, whose InGaAsP barriers yield strong FKO. We describe how critical point transition energies can be easily obtained by eye from Kramers-Kronig (KK) transforms of low field or QW modulation spectra, using the example of the modulated transmittance spectra of dilute-nitrogen InGaAsN p-i-n structures. We also discuss how the ordinary reflectivity spectrum, usually acquired at the same time as the MR signal, may also be exploited to extract layer thicknesses and compositions, and information about the active QW absorption spectrum in VCSEL and RCLED structures. 相似文献
205.
The q-Catalan numbers studied by Carlitz and Riordan are polynomials in q with nonnegative coefficients. They evaluate, at q = 1, to the Catalan numbers: 1, 1, 2, 5, 14,…, a log-convex sequence. We use a combinatorial interpretation of these polynomials
to prove a q-log-convexity result. The sequence of q-Catalan numbers is not q-log-convex in the narrow sense used by other authors, so our work suggests a more flexible definition of q-log convex be adopted.
Received January 2, 2007 相似文献
206.
207.
Hyperfine Interactions - In this paper, the conditions for which three-dimensional crystalline ion beams were attained in the rf quadrupole storage ring PALLAS at a velocity of around 2800 m/s are... 相似文献
208.
Precise measurement of magnetic moment of short-lived β-emitting nuclei12B ( I π=1+, T 1/2=20.18 ms)
Zhou Dongmei Zheng Yongnan Du Enpeng Xu Yongjun Zhu Jiazheng Yuan Daqing Wang Zhiqiang Luo Hailong Zuo Yi Ma Ruigang Duan Xiao M. Mihara M. Fukuda K. Matsuta T. Minamisono Zhu Shengyun 《中国科学G辑(英文版)》2004,47(5):531-539
The spin polarized β-emitting nuclei12B (I
π=1+,T
1/2=20.18 ms) were produced by the nuclear reaction11B(d, p)12B and by the selection technique of the incident deuteron energy and the12B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei12B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment
of12B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift. 相似文献
209.
Curtis T. McMullen 《Journal of the American Mathematical Society》2003,16(4):857-885
This paper exhibits an infinite collection of algebraic curves isometrically embedded in the moduli space of Riemann surfaces of genus two. These Teichmüller curves lie on Hilbert modular surfaces parameterizing Abelian varieties with real multiplication. Explicit examples, constructed from L-shaped polygons, give billiard tables with optimal dynamical properties.
210.
The Li oxides species formed on Li over-deposited V2O5 thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V2O5 system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li2O and Li2O2 compounds on the surface. The formation of Li2O2 causes to arise an emission line at about 11.3 eV in the valence band spectra. 相似文献