全文获取类型
收费全文 | 9757篇 |
免费 | 1679篇 |
国内免费 | 1642篇 |
专业分类
化学 | 7497篇 |
晶体学 | 104篇 |
力学 | 671篇 |
综合类 | 105篇 |
数学 | 1130篇 |
物理学 | 3571篇 |
出版年
2024年 | 40篇 |
2023年 | 190篇 |
2022年 | 327篇 |
2021年 | 385篇 |
2020年 | 391篇 |
2019年 | 410篇 |
2018年 | 343篇 |
2017年 | 311篇 |
2016年 | 513篇 |
2015年 | 488篇 |
2014年 | 528篇 |
2013年 | 765篇 |
2012年 | 888篇 |
2011年 | 918篇 |
2010年 | 662篇 |
2009年 | 613篇 |
2008年 | 677篇 |
2007年 | 561篇 |
2006年 | 526篇 |
2005年 | 474篇 |
2004年 | 364篇 |
2003年 | 322篇 |
2002年 | 362篇 |
2001年 | 314篇 |
2000年 | 247篇 |
1999年 | 231篇 |
1998年 | 178篇 |
1997年 | 153篇 |
1996年 | 119篇 |
1995年 | 116篇 |
1994年 | 106篇 |
1993年 | 92篇 |
1992年 | 79篇 |
1991年 | 91篇 |
1990年 | 62篇 |
1989年 | 46篇 |
1988年 | 29篇 |
1987年 | 23篇 |
1986年 | 24篇 |
1985年 | 30篇 |
1984年 | 16篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1974年 | 2篇 |
1957年 | 2篇 |
1944年 | 4篇 |
1943年 | 2篇 |
1942年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
有限长通电螺线管空间的磁场分布 总被引:2,自引:0,他引:2
本文计算了有限长通电螺线管空间的磁感应强度分布,给出了解析表达式,并绘出了它们的空间分布图。 相似文献
22.
Zhong Hong YAN Chun Hao YANG Xi Han WU Yu Yuan XIEDivision of Chemistry Shanghai Second Medical University Shanghai Sate Key Laboratory of Drug Research Shanghai Institute of Materia Medica Shanghai Institutesfor Biological Sciences Shanghai 《中国化学快报》2004,(4)
The first and facile synthesis of (±)syringaresinol was described. 相似文献
23.
Zhao Fang BAI Jin Chuan HOU 《数学学报(英文版)》2005,21(5):1167-1182
Let X be a (real or complex) Banach space with dimension greater than 2 and let B0(X) be the subspace of B(X) spanned by all nilpotent operators on X. We get a complete classification of surjective additive maps Ф on B0(X) which preserve nilpotent operators in both directions. In particular, if X is infinite-dimensional, we prove that Ф has the form either Ф(T) = cATA^-1 or Ф(T) = cAT'A^-1, where A is an invertible bounded linear or conjugate linear operator, c is a scalar, T' denotes the adjoint of T. As an application of these results, we show that every additive surjective map on B(X) preserving spectral radius has a similar form to the above with |c| = 1. 相似文献
24.
HANXI'AN HUANGXILI 《高校应用数学学报(英文版)》1998,13(4):445-450
For two rational quadratic B-spline curves with same control vertexes, the cross ratio of four eollinear points are represented; which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the twocurves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Beeier curves, the value is generally related with the loeation of the ray, and the necessary and sufficient condition o5 the ratio being independent of the ray‘s loeation is showed. Alsn another cross ratio o5 the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initlal vertex intersects respectivdy with the curve segmentt the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only whh the ray‘s location, butnot with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments. 相似文献
25.
The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth. 相似文献
26.
27.
For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization
types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the
two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results
show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They
are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type
is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate
and spontaneous emission factor. 相似文献
28.
X.J. Liu E.Y. Jiang Z.Q. Li B.L. Li W.R. Li A. Yu P. Wu H.L. Bai 《Journal of magnetism and magnetic materials》2006
We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Nd0.85Na0.15MnO3 prepared by sol–gel method. A ferromagnetic–paramagnetic (FM–PM) transition is observed around 110 K, which is not accompanied by a metal–insulator transition. The sample displays the complete PM state associated with the ESR spectra fitted by single Lorentzian line shape above 130 K. Below 130 K, ESR spectra become distorted and then linewidth increases rapidly, where short-range magnetic order develops and coexists with PM phase due to the inhomogeneous magnetic state. In addition, the large difference between the activation energies obtained from the resistivity and ESR parameters (peak-to-peak linewidth and line intensity) at the frame of adiabatic small polaron hopping model is pointed out for Nd0.85Na0.15MnO3. 相似文献
29.
The paper is concerned with a two-delay singular differential system with a twin parameter. Applying fixed-point index theory, we show the relationship between the asymptotic behaviors of nonlinearities (at zero and infinity) and the open regions (eigenvalue regions) of parameters, which are correlated with delays, such that the system has zero, one and two positive solution(s). 相似文献
30.
Han-xing Wang Xi Hu Qin Zhang 《应用数学学报(英文版)》2007,23(2):235-244
In this paper,we present a random graph model with spatial reuse for a mobile ad hoc network(MANET) based on the dynamic source routing protocol.Many important performance parameters of theMANET are obtained,such as the average flooding distance (AFD),the probability generating function of theflooding distance,and the probability of a flooding route to be symmetric.Compared with the random graphmodel without spatial reuse,this model is much more effective because it has a smaller value of AFD and alarger probability for finding a symmetric valid route. 相似文献