全文获取类型
收费全文 | 58876篇 |
免费 | 775篇 |
国内免费 | 302篇 |
专业分类
化学 | 27349篇 |
晶体学 | 1026篇 |
力学 | 3199篇 |
综合类 | 8篇 |
数学 | 4652篇 |
物理学 | 23719篇 |
出版年
2022年 | 535篇 |
2021年 | 478篇 |
2020年 | 446篇 |
2019年 | 424篇 |
2018年 | 571篇 |
2017年 | 496篇 |
2016年 | 891篇 |
2015年 | 634篇 |
2014年 | 987篇 |
2013年 | 2495篇 |
2012年 | 2331篇 |
2011年 | 3009篇 |
2010年 | 2123篇 |
2009年 | 2172篇 |
2008年 | 2748篇 |
2007年 | 2585篇 |
2006年 | 2451篇 |
2005年 | 2174篇 |
2004年 | 1983篇 |
2003年 | 1752篇 |
2002年 | 1646篇 |
2001年 | 3005篇 |
2000年 | 2148篇 |
1999年 | 1554篇 |
1998年 | 1080篇 |
1997年 | 1057篇 |
1996年 | 884篇 |
1995年 | 783篇 |
1994年 | 704篇 |
1993年 | 623篇 |
1992年 | 951篇 |
1991年 | 946篇 |
1990年 | 849篇 |
1989年 | 747篇 |
1988年 | 731篇 |
1987年 | 795篇 |
1986年 | 654篇 |
1985年 | 882篇 |
1984年 | 828篇 |
1983年 | 568篇 |
1982年 | 562篇 |
1981年 | 533篇 |
1980年 | 496篇 |
1979年 | 620篇 |
1978年 | 650篇 |
1977年 | 660篇 |
1976年 | 575篇 |
1975年 | 481篇 |
1974年 | 521篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
901.
The chemistry of N2H4 on Si(100)2 × 1 and Si(111)7 × 7 has been studied using scanning tunneling microscopy. At low coverages on Si(100)2 × 1 at room temperature the adsorption sites are distributed randomly on the surface and are imaged as dark spots in the dimer row by the STM. Upon annealing the substrate at 600 K, both isolated reaction products, as well as clusters of reaction products are formed on the surface. The STM images show that the majority of the isolated reaction products are adsorbed symmetrically across the dimers. Based on previous HREELS data, these are most likely NHx groups. However, the clusters are not well resolved. Because of this we speculate that they are not simply symmetrically adsorbed NHx groups, but likely have a more complicated internal structure. At higher coverages, the STM images show that the predominant pathway for adsorption is with the N---N bond parallel to the surface, in agreement with HREELS studies of this system. On Si(111)7 × 7, the molecule behaves in a manner which is similar to NH3. That is, at low coverages the molecule adsorbs preferentially at center adatoms due to the greater reactivity of these sites, while at higher coverages it also reacts with the corner adatoms. 相似文献
902.
H.‐H. Klauß M. Hillberg W. Wagener M. Birke F.J. Litterst E. Schreier A. Kratzer G.M. Kalvius Y. Haga T. Suzuki 《Hyperfine Interactions》1997,104(1-4):177-180
We report on zero field and longitudinal field μSR experiments on a CeAs single crystal between 3.3 and 12 K. Below the antiferromagnetic
transition at 7.5 K a spontaneously precessing signal with a saturation frequency of \approx25 MHz representing the full sample
amplitude has been found. From an analysis of the field dependence of the relaxation rate of this signal in \langle 100\rangle
and \langle 110\rangle crystal orientation parallel to the muon spin and the applied longitudinal field, a \langle 100\rangle
orientation of the local field at the muon site is concluded. This supports an AF‐I single‐\veck magnetic ordering.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
903.
Doklady Physics - The mechanical properties of NWA 12370 chondrite, petrological type H5, depending on the external hydrostatic pressure were studied using ultrasonic waves. This meteorite is a... 相似文献
904.
Y. Zhang G. Hu 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):253-256
The transient process of globally coupled bistable systems from an unstable state to metastable state (i.e, quenching process) is studied analytically for small noise intensity. The influences of noise intensity and system size
on the system evolution are investigated. The problem of a large number of coupled Langevin equations is reduced to a simple
problem of a one-dimensional ordinary differential equation, subject to a white noise with intensity explicitly given. The
analytical results are fully confirmed by direct numerical computations.
Received: 3 July 1997 / Revised: 4 December 1997 / Accepted: 15 January 1998 相似文献
905.
T. Idehara I. Ogawa Y. Shimizu T. Tatsukawa 《International Journal of Infrared and Millimeter Waves》1998,19(6):803-816
Higher harmonic operation of gyrotrons is necessary to obtain high frequencies. Some gyrotrons included in the Gyrotron FU series developed at Fukui University have achieved operation at the third and even fourth harmonics of the electron cyclotron frequency. The output lies in the millimeter to submillimeter wavelength range and the output powers are several watts to several tens of watts. In this paper, the gyrotrons and the conditions under which they operate are described in detail. 相似文献
906.
We first study the basic coupling and obtain an equation between total variation norm and the basic coupling. Then by use this equation we investigate the ergodicity property of continuous time Markov processes in general state space. For an ergodic continuous-time Markov processes, adding condition π(f) < ∞, by using the coupling method, there exists the full absorption set, such that the continuous time Markov processes are f-ergodic on it. © 2022 Chinese Academy of Sciences. All rights reserved. 相似文献
907.
In this paper we give four definitions of Maslov index and show that they all satisfy the same system of axioms and hence are equivalent to each other. Moreover, relationships of several symplectic and differential geometric, analytic, and topological invariants (including triple Maslov indices, eta invariants, spectral flow and signatures of quadratic forms) to the Maslov index are developed and formulae relating them are given. The broad presentation is designed with a view to applications both in geometry and in analysis. © 1994 John Wiley & Sons, Inc. 相似文献
908.
First principles studies based on density functional theory (DFT) calculations within the generalized gradient approximations (GGA) and GGA + U approach using the full-potential, augmented plane wave + local orbitals (APW + lo) method, as implemented in the WIEN2k code, have been used to investigate the structural, electronic and magnetic properties of spinel-structure LiV2O4, in particular regarding the heavy fermion (HF) behaviour. The calculations were performed for ferromagnetic, anti-ferromagnetic, and ferrimagnetic configurations using two kinds of magnetic structures (tetragonal and rhombohedral). The GGA results showed that the Fermi energy lies in the V 3d (t2g) bands with 1.5 electrons per V atom occupying this band, and the V 3d bands are separated by a ~1.9 eV energy gap from the O 2p bands and further split into t2g and eg bands with a ~1.0 eV energy gap, which are in good agreement with the photoelectron spectra. The GGA + U method indicates that the ground state of LiV2O4 is the tetragonal anti-ferromagnetic configuration with metallic character, and ferromagnetic order character at slightly higher energy, which is consistent with experimental result. The geometric frustration and hybridization between 3d (V) and 2p (O) could induce spin fluctuation and help to explain the instability of specific heat, susceptibility and HF behaviour. 相似文献
909.
Recent experiments by Ross and co-workers proved the possibility of a mononuclear regime with heterogeneous nucleation as well as jerky growth in the vapor–liquid–solid (VLS) process for silicon nanowires. In this work, a theoretical model is presented which incorporates the effects of (i) a mononuclear regime with layer by layer growth, (i) heterogeneous nucleation of each new layer at the edge of a Au–Si droplet, (iii) drop of supersaturation after each successful nucleation and respective fast layer growth, (iv) time-dependent nucleation barrier during each new waiting period and (v) correlation between subsequent waiting periods (non-Markovian sequence of waiting periods). 相似文献
910.
Y. L. Tong 《Annals of the Institute of Statistical Mathematics》1987,39(1):289-297
Summary This paper concerns interval estimation of the critical value θ which satisfies
under the general linear model,Y
i
=μ(x
i
)+ε
i
(i=1,2,···), where
for
and the functional forms off
j
′
s are known. From an asymptotic expansion it is shown that, under reasonable conditions, the limiting distribution of
is normal. Thus in the large-sample case a confidence interval for θ can be obtained. Such a result is useful when one is
interested in carrying out a retrospective analysis rather than designing the experiment (as in the Kiefer-Wolfowitz procedure).
In Section 3 a sequential procedure is considered for confidence intervals with fixed width 2d. It is shown that, for a given stopping variableN,
is also asymptotically normal asd→0. Thus the coverage probability converges to 1−α (preassigned) asd→0. An example of application in estimating the phase parameter in circadian rhythms is given for the purpose of illustration.
Research partially supported by the NSF Grant DMS-8502346. 相似文献