全文获取类型
收费全文 | 451367篇 |
免费 | 3118篇 |
国内免费 | 1046篇 |
专业分类
化学 | 222148篇 |
晶体学 | 6774篇 |
力学 | 23366篇 |
综合类 | 16篇 |
数学 | 64014篇 |
物理学 | 139213篇 |
出版年
2020年 | 3497篇 |
2019年 | 4180篇 |
2018年 | 11992篇 |
2017年 | 12497篇 |
2016年 | 10892篇 |
2015年 | 4779篇 |
2014年 | 7278篇 |
2013年 | 16315篇 |
2012年 | 15599篇 |
2011年 | 24058篇 |
2010年 | 16310篇 |
2009年 | 16551篇 |
2008年 | 22106篇 |
2007年 | 24705篇 |
2006年 | 13019篇 |
2005年 | 16092篇 |
2004年 | 12993篇 |
2003年 | 12373篇 |
2002年 | 10710篇 |
2001年 | 10544篇 |
2000年 | 8344篇 |
1999年 | 6115篇 |
1998年 | 5253篇 |
1997年 | 5346篇 |
1996年 | 5085篇 |
1995年 | 4302篇 |
1994年 | 4473篇 |
1993年 | 4421篇 |
1992年 | 4830篇 |
1991年 | 4961篇 |
1990年 | 4752篇 |
1989年 | 4813篇 |
1988年 | 4686篇 |
1987年 | 4660篇 |
1986年 | 4450篇 |
1985年 | 5724篇 |
1984年 | 5924篇 |
1983年 | 4851篇 |
1982年 | 5109篇 |
1981年 | 4969篇 |
1980年 | 4576篇 |
1979年 | 5144篇 |
1978年 | 5256篇 |
1977年 | 5323篇 |
1976年 | 5368篇 |
1975年 | 5019篇 |
1974年 | 4933篇 |
1973年 | 5197篇 |
1972年 | 3702篇 |
1971年 | 3363篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
A classification has been obtained for spaces which admit complete sets of motion integrals of the (3.1)-type and are spatially homogeneous. The metrics and Killing vectors have been found in explicit form for all types of these spaces. A classification by Bianchi is given for the spaces obtained. 相似文献
892.
N.-K. Lee T.A. Vilgis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):451-465
We study the elastic properties of single A/B random copolymer chains, with a specific sequence and use them as theoretical
model for so called HP proteins. HP proteins carry hydrophilic (P) and hydrophobic (H) monomers. We predict a rich structure
in the force-extension relations which can be attributed to the information in the sequence. The variational method is used
to probe local minima on the path of stretching and releasing for the chain molecules. At a given force, we find multiple
configurations which are separated by energy barriers. A collapsed globular configuration consists of several domains which
unravel cooperatively. Upon stretching, the unfolding path shows a stepwise pattern corresponding to the unfolding of each
domain. While releasing, several cores can be created simultaneously in the middle of the chain, resulting in a different
path of collapse. The long-range interactions and stiffness of the chain simplify the potential landscape given by the disorder
in sequence.
Received 5 March 2002 / Received in final form 16 May 2002 Published online 13 August 2002 相似文献
893.
Ying Zhang Gang Hu Shigang Chen H.A. Cerdeira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):381-384
A method of controlling global stochasticity in Hamiltonian systems by applying nonlinear perturbation is proposed. With the
well-known standard map we demonstrate that this control method can convert global stochasticity into regular motion in a
wide chaotic region for arbitrary initial condition, in which the control signal remains very weak after a few kicks. The
system in which chaos has been controlled approximates to the original Hamiltonian system, and this approach appears robust
against small external noise. The mechanism underlying this high control efficiency is intuitively explained.
Received 15 January 2002 Published online 6 June 2002 相似文献
894.
D.A. Garanin E.M. Chudnovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):3-7
We compute the width and shape of the EPR and tunneling resonances due to dislocations in Mn12 acetate crystals. Uncorrelated dislocations produce the Gaussian shape of resonances while dislocations bound in pairs produce
the Lorentzian shape. We stress that the uniaxial spin Hamiltonian together with crystal defects can explain the totality
of experimental data on Mn12.
Received 2 August 2001 / Received in final form 15 March 2002 Published online 17 September 2002 相似文献
895.
R. Adhikari A. Sil A. Raychaudhuri 《The European Physical Journal C - Particles and Fields》2002,25(1):125-130
We present a solution of the solar neutrino deficit using three flavors of neutrinos and R-parity non-conserving supersymmetry. In this model, in vacuum, the is massless and unmixed, mass and mixing being restricted to the - sector only, which we choose in consistency with the requirements of the atmospheric neutrino anomaly. The flavor changing
and flavor diagonal neutral currents present in the model and the three-flavor picture together produce an energy dependent
resonance-induced - mixing in the sun. This mixing plays a key role in the new solution to the solar neutrino problem. The best fit to the solar
neutrino rates and spectrum (1258-day SK and 241-day SNO data) requires a mass square difference of eV2 in vacuum between the two lightest neutrinos. This solution cannot accommodate a significant day-night effect for solar neutrinos
nor CP violation in terrestrial neutrino experiments.
Received: 26 December 2001 / Revised version: 16 February 2002 / Published online: 26 July 2002 相似文献
896.
The maximum likely and optimal (Bayesian) algorithms for detecting an arbitrary-shaped signal observed against the background of Gaussian white noise and for measuring the duration are synthesized. Exact expressions for the characteristics of the maximum likely algorithms are found. The characteristics of the Bayesian algorithms are obtained using computer simulations. 相似文献
897.
N. S. Smirnova 《Journal of Mathematical Sciences》1991,55(3):1741-1746
We consider theoretical seismographs of a wave field passing through an elastic layer with high propagation velocity. We note the presence of a low-frequency part of the seismogram for longitudinal waves. It is shown that the propagation time of low-frequency vibrations is equal to that of longitudinal disturbances screened by the layer.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, AN SSSR, Vol. 173, pp. 134–141, 1988. 相似文献
898.
N. L. Vekshin 《Journal of Applied Spectroscopy》1991,54(1):17-22
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 1, pp. 26–32, January, 1991. 相似文献
899.
Velislava A Ignatova Sven Van Den Berghe Steven Van Dyck Vladimir N Popok 《Microscopy and microanalysis》2006,12(5):432-437
The oxide scales of AISI 304 formed in boric acid solutions at 300 degrees C and pH = 4.5 have been studied using X-ray photoelectron spectroscopy (XPS) depth profiling. The present focus is depth profile quantification both in depth and chemical composition on a molecular level. The roughness of the samples is studied by atomic force microscopy before and after sputtering, and the erosion rate is determined by measuring the crater depth with a surface profilometer and vertical scanning interferometry. The resulting roughness (20-30 nm), being an order of magnitude lower than the crater depth (0.2-0.5 microm), allows layer-by-layer profiling, although the ion-induced effects result in an uncertainty of the depth calibration of a factor of 2. The XPS spectrum deconvolution and data evaluation applying target factor analysis allows chemical speciation on a molecular level. The elemental distribution as a function of the sputtering time is obtained, and the formation of two layers is observed-one hydroxide (mainly iron-nickel based) on top and a second one deeper, mainly consisting of iron-chromium oxides. 相似文献
900.
Summary We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most
finitely additive integration theories. 相似文献