全文获取类型
收费全文 | 169385篇 |
免费 | 16329篇 |
国内免费 | 534篇 |
专业分类
化学 | 122194篇 |
晶体学 | 2087篇 |
力学 | 6782篇 |
综合类 | 5篇 |
数学 | 14781篇 |
物理学 | 40399篇 |
出版年
2023年 | 4198篇 |
2022年 | 1810篇 |
2021年 | 2901篇 |
2020年 | 5096篇 |
2019年 | 2853篇 |
2018年 | 2830篇 |
2016年 | 6611篇 |
2015年 | 6287篇 |
2014年 | 6072篇 |
2013年 | 9740篇 |
2012年 | 6515篇 |
2011年 | 5467篇 |
2010年 | 6005篇 |
2009年 | 5760篇 |
2008年 | 4994篇 |
2007年 | 4766篇 |
2006年 | 4243篇 |
2005年 | 4113篇 |
2004年 | 3564篇 |
2003年 | 3235篇 |
2002年 | 3147篇 |
2001年 | 3620篇 |
2000年 | 2708篇 |
1999年 | 2228篇 |
1998年 | 1912篇 |
1997年 | 1956篇 |
1996年 | 1881篇 |
1995年 | 1900篇 |
1993年 | 1735篇 |
1992年 | 1843篇 |
1991年 | 1809篇 |
1990年 | 1729篇 |
1989年 | 1749篇 |
1988年 | 1793篇 |
1987年 | 1764篇 |
1986年 | 1664篇 |
1985年 | 2229篇 |
1984年 | 2364篇 |
1983年 | 1979篇 |
1982年 | 2323篇 |
1981年 | 2170篇 |
1980年 | 2248篇 |
1979年 | 2223篇 |
1978年 | 2363篇 |
1977年 | 2389篇 |
1976年 | 2453篇 |
1975年 | 2468篇 |
1974年 | 2319篇 |
1973年 | 2367篇 |
1972年 | 1631篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
A. Ferreira da Silva I. Pepe S.A. Tomás W.M. de Azevedo R. Ahuja 《Applied Surface Science》2006,252(15):5365-5367
In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed. 相似文献
92.
Daniel W. Stroock 《Journal of Functional Analysis》2007,242(1):295-303
The purpose of this note is to describe a procedure for transferring familiar estimates for transition probabilities on RN to transition probabilities on compact manifolds. 相似文献
93.
Z.G. Xiao R.J. HuH.Y. Wu G.M. JinZ.Y. Li L.M. DuanH.W. Wang B.G. ZhangS.F. Wang Z.Y. WeiH.S. Xu Y.T. ZhuS.L. Li F. FuX.H. Yuan Z.Q. Feng 《Physics letters. [Part B]》2006
The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of 36Ar + 112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in 36Ar + 124Sn system than that in 36Ar + 112Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in 36Ar + 112Sn and 120 fm/c in the 36Ar + 124Sn, respectively. 相似文献
94.
95.
D. Fong J. H. Hamilton A. V. Ramayya J. K. Hwang C. Goodin K. Li J. Kormicki J. O. Rasmussen Y. X. Luo S. C. Wu I. Y. Lee A. V. Daniel G. M. Ter-Akopian G. S. Popeko A. S. Fomichev A. M. Rodin Yu. Ts. Oganessian M. Jandel J. Kliman L. Krupa J. D. Cole M. A. Stoyer R. Donangelo W. C. Ma 《Physics of Atomic Nuclei》2006,69(7):1161-1167
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be
Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the
“hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.
The text was submitted by the authors in English. 相似文献
96.
The major goal of this paper is to examine the hypothesis that stock returns and return volatility are asymmetric, threshold nonlinear, functions of change in trading volume. A minor goal is to examine whether return spillover effects also display such asymmetry. Employing a double-threshold GARCH model with trading volume as a threshold variable, we find strong evidence supporting this hypothesis in five international market return series. Asymmetric causality tests lend further support to our trading volume threshold model and conclusions. Specifically, an increase in volume is positively associated, while decreasing volume is negatively associated, with the major price index in four of the five markets. The volatility of each series also displays an asymmetric reaction, four of the markets display higher volatility following increases in trading volume. Using posterior odds ratio, the proposed threshold model is strongly favored in three of the five markets, compared to a US news double threshold GARCH model and a symmetric GARCH model. We also find significant nonlinear asymmetric return spillover effects from the US market. 相似文献
97.
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
98.
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
99.
100.
We propose a new approach towards proving that the fixed point property for ordered sets is preserved by products. This approach uses a characterization of fixed points in products via isotone relations. First explorations of classes of isotone relations are presented. These first explorations give us hope that this approach could lead to advances on the Product Problem. 相似文献