全文获取类型
收费全文 | 8925篇 |
免费 | 947篇 |
国内免费 | 659篇 |
专业分类
化学 | 1366篇 |
晶体学 | 21篇 |
力学 | 689篇 |
综合类 | 157篇 |
数学 | 6417篇 |
物理学 | 1881篇 |
出版年
2024年 | 17篇 |
2023年 | 59篇 |
2022年 | 108篇 |
2021年 | 153篇 |
2020年 | 160篇 |
2019年 | 192篇 |
2018年 | 187篇 |
2017年 | 249篇 |
2016年 | 295篇 |
2015年 | 203篇 |
2014年 | 389篇 |
2013年 | 672篇 |
2012年 | 460篇 |
2011年 | 433篇 |
2010年 | 407篇 |
2009年 | 489篇 |
2008年 | 542篇 |
2007年 | 564篇 |
2006年 | 526篇 |
2005年 | 488篇 |
2004年 | 420篇 |
2003年 | 363篇 |
2002年 | 394篇 |
2001年 | 367篇 |
2000年 | 314篇 |
1999年 | 320篇 |
1998年 | 247篇 |
1997年 | 219篇 |
1996年 | 189篇 |
1995年 | 160篇 |
1994年 | 127篇 |
1993年 | 103篇 |
1992年 | 100篇 |
1991年 | 86篇 |
1990年 | 63篇 |
1989年 | 54篇 |
1988年 | 43篇 |
1987年 | 47篇 |
1986年 | 42篇 |
1985年 | 49篇 |
1984年 | 53篇 |
1983年 | 17篇 |
1982年 | 34篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
161.
We use the topological tool of Nielsen fixed-point theory to study the controllability of perturbed linear control processes whose control space can be reduced to a finite-dimensional one. These methods produce a lower bound on the number of controls that achieve a given target. We concentrate particularly on the case where the perturbation has sublinear growth, and we exhibit examples of multiple controls of various types that are detected by the Nielsen theory method.This research was partly supported by the Research Grant Teoria del Controllo dei Sistemi Dinamici, Ministero della Pubblica Istruzione, Roma, Italy. 相似文献
162.
For one-dimensional expanding mapsT with an invariant measure we consider, in a parameter space, the envelope
n
of the real lines associated to any couple of points of the orbit, connected byn iterations ofT. If the map hass inverses and is piecewise linear, then the sets
n
are just the union ofs
n
points and converge to the invariant Cantor set ofT. A correspondence between all the sets and their measures is established and allows one to associate the atomic measure on 1 to the completly continuous measure on the Cantor set. If the map is nonlinear, hyperbolic, and hass inverses, the sets
n
are homeomorphic to the Cantor set; they converge to the Cantor set ofT and their measures converge to the measure of the Cantor set whenn. The correspondence between the sets
n
allows one to define converging approximation schemes for the map an its measure: one replaces each of thes
n
disjoint sets with a point in a convenient neighborhood and a probability equal to its measure and transforms it back to the original set 1. All the approximations with linear Cantor systems previously proposed are recovered, the converging proprties being straightforward in the present scheme. Moreover, extensions to higher dimensionality and to nondisconnected repellers arte possible and are briefly examined. 相似文献
163.
In his celebrated paper, Polya has considered the random walk in the three-dimensional (cubic) lattice and showed that the probability of return to the origin is less than 1. Subsequent authors have shown that the probability is %34.053.... Here we consider the same random walk, with the restriction that the drunkard is only allowed to stay inxyz. It is shown that his probability of returning to the originand staying in the allowed region is %6.4844.... 相似文献
164.
165.
Skuban S. J. Skuban F. Lukić S. R. Cvejić ž 《Journal of Thermal Analysis and Calorimetry》2003,71(2):439-444
The object of the paper is an investigation of the glasses of the (As2S3)x(AsSe0.5Te0.5I)100-x. type for 65≤;x≤;95, using methods of thermomechanical analysis. Values of the thermal coefficients of linear expansion in solid and visco-plastic
phase were determined. it was shown that introducing arsenic-sulfide in glass-matrix AsChI, i.e. (AsSe0.5Te0.5I), leads to an increasing stability of these glasses. The characteristic temperatures of softening Tg and the temperature of the beginning of deformation tw increase by increasing content of As2S3. The analytical forms of dependence of four significant physical values αg, αl, Tg, Tw, as a function of As2S3 content in the structure of glasses were fitted.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
166.
菁是一类很重要的离子型染料和感光材料,也有极少数可用作激光染料,绝大部价菁染料为直链分子。我们最近合成了一系列带有五员桥环的菁,并研究了这些桥环菁化合物的质子化平衡和荧光性质。 相似文献
167.
硅杂环丁烷在有机硅化学中是一类非常重要的小分子环系化合物。由于硅杂环丁烷和环丁烷的环张力相似,因而显示出较高的反应活性。例如能与某些试剂作用,生成开环产物;在光解或热解条件下,产生具有Si=C结构的高活性中间体,可用以合成多种有机硅化合物。 相似文献
168.
M Riedel 《Journal of multivariate analysis》1985,16(2):241-252
Let X1, X2,…, be independent, identically distributed random variables. Suppose that the linear forms L1 = Σj=1∞ajXj and L2 = Σj=1∞bjXj exist with probability one and are identically distributed; necessary and sufficient conditions assuring that X1 is normally distributed are presented. The result is an extension of a theorem of Linnik (Ukrainian Math. J.5 (1953), 207–243, 247–290) concerning the case that the linear forms L1 and L2 have a finite number of nonvanishing components. This proof only makes use of elementary properties of characteristic functions and of meromorphic functions. 相似文献
169.
Minkin V. I. Gribanova T. N. Starikov A. G. Minyaev R. M. 《Russian Chemical Bulletin》2003,52(3):519-525
The electronic and molecular structure of planar (cyclic and linear) tetra- and hexaatomic clusters (XY)
n
(XY = CC, BN, BeO, LiF; n = 2, 3) was studied using the ab initio CCD(full)/6-311+G** method and density functional approach (B3LYP/6-311+G**). The stability of cyclic clusters C6, B3N3, and Be3O3 with D3h
symmetry is mainly determined by the aromaticity of their -electron systems. 相似文献
170.
L. F. Kosyanchuk N. V. Kozak O. I. Antonenko G. Ya. Menzheres Yu. S. Lipatov 《Theoretical and Experimental Chemistry》2006,42(6):357-363
For semi-interpenetrating polymer networks (semi-IPNs) based on an incompatible polyurethane network/linear polymethylmethacrylate
pair formed in situ in the presence of 3d metal chelates, we have studied the effect of the system composition on the kinetics
of formation of the components and the nature of complex formation between the metal compound and the polymer matrix. The
ratio of the system components has been shown to have an effect on the selection of the macroligand in formation of complexes
of the metal chelate with the polar groups of the semi-IPN, where the general character of the kinetic behavior for the formation
of the network and the linear polymer is preserved.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 6, pp. 351–356, November–December, 2006. 相似文献