全文获取类型
收费全文 | 28435篇 |
免费 | 82篇 |
国内免费 | 271篇 |
专业分类
化学 | 10166篇 |
晶体学 | 259篇 |
力学 | 1373篇 |
综合类 | 12篇 |
数学 | 8943篇 |
物理学 | 8035篇 |
出版年
2021年 | 30篇 |
2018年 | 1186篇 |
2017年 | 1441篇 |
2016年 | 699篇 |
2015年 | 541篇 |
2014年 | 462篇 |
2013年 | 628篇 |
2012年 | 3088篇 |
2011年 | 2273篇 |
2010年 | 1782篇 |
2009年 | 1515篇 |
2008年 | 522篇 |
2007年 | 573篇 |
2006年 | 569篇 |
2005年 | 4408篇 |
2004年 | 3889篇 |
2003年 | 2279篇 |
2002年 | 465篇 |
2001年 | 281篇 |
2000年 | 86篇 |
1999年 | 169篇 |
1998年 | 107篇 |
1997年 | 66篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 42篇 |
1992年 | 168篇 |
1991年 | 152篇 |
1990年 | 135篇 |
1989年 | 106篇 |
1988年 | 99篇 |
1987年 | 56篇 |
1986年 | 41篇 |
1985年 | 37篇 |
1984年 | 29篇 |
1983年 | 26篇 |
1979年 | 29篇 |
1978年 | 25篇 |
1976年 | 79篇 |
1975年 | 37篇 |
1974年 | 40篇 |
1973年 | 48篇 |
1972年 | 39篇 |
1971年 | 25篇 |
1970年 | 34篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1967年 | 30篇 |
1966年 | 37篇 |
1923年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
S. Petrovi? B. Gakovi? D. Peru?ko T. Desai D. Batani M. ?ekada B. Radak M. Trtica 《Laser Physics》2009,19(8):1844-1849
Interaction of an Nd:YAG laser, operating at 532 nm wavelength and pulse duration of 40 ps, with tungsten-titanium (WTi) thin film (thickness, 190 nm) deposited on single silicon (100) substrate was studied. Laser fluences of 10.5 and 13.4 J/cm2 were found to be sufficient for modification of the WTi/silicon target system. The energy absorbed from the Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following WTi/silicon surface morphological changes were observed: (i) ablation of the thin film during the first laser pulse. The boundary of damage area was relatively sharp after action of one pulse whereas it was quite diffuse after irradiation with more than 10 pulses; (ii) appearance of some nano-structures (e.g., nano-ripples) in the irradiated region; (iii) appearance of the micro-cracking. The process of the laser interaction with WTi/silicon target was accompanied by formation of plasma. 相似文献
992.
Set-valued dynamic systems and random iterations of set-valued weaker contractions in uniform spaces
K. W?odarczyk C. Obczyński D. Wardowski 《Journal of Mathematical Analysis and Applications》2006,318(2):772-780
Set-valued weaker contractions in uniform, locally convex and metric spaces are defined and dynamic systems of such weaker contractions are studied. Conditions guaranteeing the convergence of generalized sequences of random iterations and iterations and the existence and uniqueness of endpoints of set-valued weaker contractions are established. Our definitions and results are new for set-valued maps in uniform, locally convex and metric spaces and even for single-valued maps. 相似文献
993.
Dragana S. Cvetkovi?-Ili? Dragan S. Djordjevi? Yimin Wei 《Linear algebra and its applications》2006,418(1):53-61
In this paper we investigate additive properties of the generalized Drazin inverse in a Banach algebra. We find some new conditions under which the generalized Drazin inverse of the sum a + b could be explicitly expressed in terms of a, ad, b, bd. Also, some recent results of Castro and Koliha [New additive results for the g-Drazin inverse, Proc. Roy. Soc. Edinburgh Sect. A 134 (2004) 1085-1097] are extended. 相似文献
994.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart. 相似文献
995.
FLAIR will be the next-generation facility for physics with low-energy antiprotons, providing antiprotons at energies from tens of MeV down to rest. It will also offer unique possibilities for physics with highly charged ions at very low energies. The FLAIR facility will have two deceleration rings, the LSR which will decelerate antiprotons to 300 keV and the USR which will bring them down further to 20 keV. The LSR will consist of the present CRYRING at the Manne Siegbahn Laboratory. During the next few years, CRYRING will be modified with respect to injection and extraction, to allow injection of 30 MeV antiprotons and to provide it with both fast (single-turn) and slow (resonant) extraction at a variable energy. We here describe plans and preparations for the transfer of CRYRING to FLAIR, giving, in particular, an overview of new components for injection and extraction. 相似文献
996.
Jan Kyn?l 《Discrete Mathematics》2008,308(19):4315-4321
Given n red and n blue points in convex position in the plane, we show that there exists a noncrossing alternating path of length . We disprove a conjecture of Erd?s by constructing an example without any such path of length greater than . 相似文献
997.
Donatas Surgailis Gilles Teyssière Marijus Vai?iulis 《Journal of multivariate analysis》2008,99(3):510-541
We introduce a new statistic written as a sum of certain ratios of second-order increments of partial sums process of observations, which we call the increment ratio (IR) statistic. The IR statistic can be used for testing nonparametric hypotheses for d-integrated () behavior of time series Xt, including short memory (d=0), (stationary) long-memory and unit roots (d=1). If Sn behaves asymptotically as an (integrated) fractional Brownian motion with parameter , the IR statistic converges to a monotone function Λ(d) of as both the sample size N and the window parameter m increase so that N/m→∞. For Gaussian observations Xt, we obtain a rate of decay of the bias EIR-Λ(d) and a central limit theorem (N/m)1/2(IR-EIR)→N(0,σ2(d)), in the region . Graphs of the functions Λ(d) and σ(d) are included. A simulation study shows that the IR test for short memory (d=0) against stationary long-memory alternatives has good size and power properties and is robust against changes in mean, slowly varying trends and nonstationarities. We apply this statistic to sequences of squares of returns on financial assets and obtain a nuanced picture of the presence of long-memory in asset price volatility. 相似文献
998.
In this note we prove that the game chromatic index χ
g
′(G) of a graph G of arboricity k is at most Δ + 3k − 1. This improves a bound obtained by Cai and Zhu [J. Graph Theory 36 (2001), 144–155] for k-degenerate graphs.
Tomasz Bartnicki: Research of the first author is supported by a PhD grant from Polish Ministry of Science and Higher Education
N201 2128 33.
Received: November 1, 2006. Final version received: December 22, 2007. 相似文献
999.
Lafon C Murillo-Rincon A Goldenstedt C Chapelon JY Mithieux F Owen NR Cathignol D 《Ultrasonics》2009,49(2):172-178
Miniature flat ultrasound transducers have shown to be effective for a large variety of thermal therapies, but the associated superficial heating implicates developing original strategies in order to extend therapeutic depth. The goal of the present paper is to use ultrasound contrast agents (UCA) to increase remote attenuation and heating. Theoretical simulations demonstrated that increasing attenuation from 0.27 to 0.8 Np/cm at 10 MHz beyond a distance of 18 mm from the transducer should result in longer thermal damages due to protein coagulation in a tissue mimicking phantom. Contrast agents (BR14, Bracco, Plan-les-Ouates, Switzerland) were embedded in thermo-sensitive gel and attenuations ranging from 0.27 to 1.33 Np/cm were measured at 10 MHz for concentrations of BR14 between 0 and 4.8%. Thermal damages were then induced in several gels, which had different layering configurations. Thermal damages, 12.8 mm in length, were obtained in homogeneous gels. When mixing contrast agents at a concentration of 3.2% beyond a first 18 mm-thick layer of homogeneous gel, the thermal damages reached 21.5 mm in length. This work demonstrated that contrast agents can be used for increasing attenuation remotely and extending therapeutic depth induced by a non-focused transducer. Additional work must be done in vivo in order to verify the remote-only distribution of bubbles and associated increase in attenuation. 相似文献
1000.
Sergei Gukov Amer Iqbal Can Koz?az Cumrun Vafa 《Communications in Mathematical Physics》2010,298(3):757-785
We establish a direct map between refined topological vertex and sl(N) homological invariants of the of Hopf link, which include Khovanov-Rozansky homology as a special case. This relation provides
an exact answer for homological invariants of the Hopf link, whose components are colored by arbitrary representations of
sl(N). At present, the mathematical formulation of such homological invariants is available only for the fundamental representation
(the Khovanov-Rozansky theory) and the relation with the refined topological vertex should be useful for categorizing quantum
group invariants associated with other representations (R
1, R
2). Our result is a first direct verification of a series of conjectures which identifies link homologies with the Hilbert
space of BPS states in the presence of branes, where the physical interpretation of gradings is in terms of charges of the
branes ending on Lagrangian branes. 相似文献