全文获取类型
收费全文 | 1265653篇 |
免费 | 25542篇 |
国内免费 | 7659篇 |
专业分类
化学 | 620504篇 |
晶体学 | 19906篇 |
力学 | 73321篇 |
综合类 | 101篇 |
数学 | 236618篇 |
物理学 | 348404篇 |
出版年
2021年 | 13428篇 |
2020年 | 15847篇 |
2019年 | 15973篇 |
2016年 | 26874篇 |
2015年 | 20437篇 |
2014年 | 30214篇 |
2013年 | 73994篇 |
2012年 | 33838篇 |
2011年 | 27566篇 |
2010年 | 34559篇 |
2009年 | 37612篇 |
2008年 | 28088篇 |
2007年 | 22836篇 |
2006年 | 31345篇 |
2005年 | 22650篇 |
2004年 | 25308篇 |
2003年 | 24715篇 |
2002年 | 26312篇 |
2001年 | 24058篇 |
2000年 | 22101篇 |
1999年 | 21262篇 |
1998年 | 20524篇 |
1997年 | 20587篇 |
1996年 | 20869篇 |
1995年 | 19007篇 |
1994年 | 18421篇 |
1993年 | 17952篇 |
1992年 | 17452篇 |
1991年 | 17800篇 |
1990年 | 17032篇 |
1989年 | 17141篇 |
1988年 | 16681篇 |
1987年 | 16732篇 |
1986年 | 15612篇 |
1985年 | 22089篇 |
1984年 | 23477篇 |
1983年 | 19749篇 |
1982年 | 21497篇 |
1981年 | 20750篇 |
1980年 | 20079篇 |
1979年 | 20084篇 |
1978年 | 21506篇 |
1977年 | 21055篇 |
1976年 | 20715篇 |
1975年 | 19382篇 |
1974年 | 19011篇 |
1973年 | 19489篇 |
1972年 | 14014篇 |
1968年 | 11889篇 |
1967年 | 12269篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
O. Fülöp 《Discrete Mathematics》2005,294(3):285-290
We give a short proof for the Mixed Connectivity Certificate Theorem of Even, Itkis and Rajsbaum and provide an upper bound on the edge number of a certificate of local T-mixed connectivity up to k. 相似文献
992.
R. Chitra Pascal Roussel R. R. Choudhury 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):o547-o549
The title complex, 2CH4N2S·C4H6O4, is a host–guest system. The asymmetric unit consists of one complete thiourea molecule and one‐half of a dimethyl oxalate molecule lying on an inversion centre. The host thiourea molecules are connected to form zigzag chains by N—H⋯S hydrogen bonds. The guest dimethyl oxalate molecules provide O‐atom acceptors for N—H⋯O hydrogen bonds, thus interconnecting the chains of thiourea molecules to form completely connected sheets. The reduction in temperature from 300 to 100 K leaves the structure unchanged and still isostructural with that previously determined for the analogous thiourea–diethyl oxalate (2/1) complex. It does, however, induce closer packing of the molecules, general shrinkage of the unit cell and shortening of the hydrogen bonds, these last two to the extent of 1–2%. 相似文献
993.
K. C. Kumara Swamy E. Balaraman M. Phani Pavan N. N. Bhuvan Kumar K. Praveen Kumar N. Satish Kumar 《Journal of Chemical Sciences》2006,118(6):495-501
The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated
acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature
of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction. 相似文献
994.
995.
Kristian Hougaard Frederik D. Nielsen 《Journal of Optical and Fiber Communications Reports》2004,1(1):63-83
In this paper we will present an overview of the use
of photonic crystal fibers as fiber amplifiers. We
will describe the basic concepts of optical
amplification, and how to do numerical modelling of
such components. We will then identify advantages
and disadvantages of amplifiers based on PCF
technology compared to conventional fibers, and then
go into greater detail on some of these specific
applications, such as low pump power amplifiers, and
high-power double-clad amplifiers and lasers. 相似文献
996.
Stress-Strain State in the Zone of Load Transfer in a Composite Specimen under Uniaxial Tension 总被引:2,自引:2,他引:0
Kulakov V. L. Tarnopol'skii Yu. M. Arnautov A. K. Rytter J. 《Mechanics of Composite Materials》2004,40(2):91-100
The stress-strain state in the zone of load transfer in a uniaxially stretched specimen made of a unidirectional epoxy carbon-fiber-reinforced plastic (CFRP) is investigated. A parametric analysis of the influence of geometric and mechanical characteristics of the specimen on its stress-strain state is performed by means of finite-element modeling. The parameters allowing us to significantly reduce the dangerous concentration of transverse and tangential stresses are revealed. The mechanical tensile characteristics of a high-strength pultruded unidirectional CFRP are determined experimentally, and the size effect of its strength is estimated. 相似文献
997.
M. Lashkarizadeh Bami 《Semigroup Forum》2004,69(2):219-229
In the present paper it is shown that if S1 and S2 are two
Clifford topological semigroups satisfying certain conditions
and T is an isometric isomorphism of LUC(S1*) onto LUC(S2*), then T
maps S1 topologically isomorphically onto S2. Furthermore, T
maps M
l
n(S1) (M(S1), respectively) isometrically
isomorphically onto M
l
n(S2) (M(S2), respectively). Indeed,
we have obtained a generalization of a well-known result of
Ghahramani, Lau and Losert for locally compact groups to a more
general setting of Clifford topological semigroups. 相似文献
998.
We obtain expressions for the energy spectrum widths of Rayleigh waves corresponding to their deformational coupling to Fermi and Boltzmann electrons in a two-dimensional layer near the surface of a semibounded solid. We evaluate the nonequilibrium energy of Rayleigh waves that depends on these widths and is caused by the same coupling to the corresponding hot electrons. We show that this energy is independent of the degeneracy degree of the electrons and is given by the mean energy of free Rayleigh waves heated up to temperature of the electrons. We find conditions under which the thermodynamics is determined by this nonequilibrium energy of Rayleigh waves in films of a certain thickness with Fermi electrons near the surface and by the equilibrium energy of bulk phonons in thicker samples. All the results are obtained using the Keldysh diagram technique applied to the case of semibounded media. 相似文献
999.
We propose a unified method for deducing recursive relations for the canonical partition function of a system of noninteracting particles with charge conservation if the particles follow the Bose–Einstein, Fermi–Dirac, or Maxwell–Boltzmann statistics or parastatistics. For all these types of statistics, we find recursive relations for the partition function of a new statistical model of nuclear multifragmentation with electric charge and baryon number conservation, accounting for the internal degrees of freedom of the nuclear fragments. 相似文献
1000.
We establish a relation between stable distributions in probability theory and the fractional integral. Moreover, it turns out that the parameter of the stable distribution coincides with the exponent of the fractional integral. It follows from an analysis of the obtained results that equations with the fractional time derivative describe the evolution of some physical system whose time degree of freedom becomes stochastic, i.e., presents a sum of random time intervals subject to a stable probability distribution. We discuss relations between the fractal Cantor set (Cantor strips) and the fractional integral. We show that the possibility to use this relation as an approximation of the fractional integral is rather limited. 相似文献