全文获取类型
收费全文 | 167769篇 |
免费 | 407篇 |
国内免费 | 428篇 |
专业分类
化学 | 54273篇 |
晶体学 | 2034篇 |
力学 | 12565篇 |
数学 | 52148篇 |
物理学 | 47584篇 |
出版年
2020年 | 60篇 |
2019年 | 68篇 |
2018年 | 17745篇 |
2017年 | 18406篇 |
2016年 | 9148篇 |
2015年 | 1698篇 |
2014年 | 494篇 |
2013年 | 651篇 |
2012年 | 7526篇 |
2011年 | 21343篇 |
2010年 | 12065篇 |
2009年 | 12548篇 |
2008年 | 16520篇 |
2007年 | 21932篇 |
2006年 | 452篇 |
2005年 | 8554篇 |
2004年 | 5032篇 |
2003年 | 5364篇 |
2002年 | 2433篇 |
2001年 | 412篇 |
2000年 | 617篇 |
1999年 | 208篇 |
1998年 | 244篇 |
1997年 | 167篇 |
1996年 | 324篇 |
1995年 | 202篇 |
1994年 | 158篇 |
1993年 | 164篇 |
1992年 | 117篇 |
1991年 | 131篇 |
1990年 | 118篇 |
1989年 | 130篇 |
1988年 | 147篇 |
1987年 | 137篇 |
1986年 | 129篇 |
1985年 | 140篇 |
1984年 | 146篇 |
1983年 | 139篇 |
1982年 | 137篇 |
1981年 | 128篇 |
1980年 | 134篇 |
1979年 | 145篇 |
1978年 | 154篇 |
1976年 | 80篇 |
1975年 | 68篇 |
1974年 | 61篇 |
1973年 | 113篇 |
1969年 | 84篇 |
1968年 | 114篇 |
1966年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
A tomographic reconstruction method based on Monte Carlo random searching guided by the information contained in the projections
of radiographed objects is presented. In order to solve the optimization problem, a multiscale algorithm is proposed to reduce
computation. The reconstruction is performed in a coarse-to-fine multigrid scale that initializes each resolution level with
the reconstruction of the previous coarser level, which substantially improves the performance. The method was applied to
a real case reconstructing the internal structure of a small metallic object with internal components, showing excellent results. 相似文献
152.
Ya. I. Kurys’ N. S. Netyaga V. G. Koshechko V. D. Pokhodenko 《Theoretical and Experimental Chemistry》2007,43(5):334-342
A guest-host nanocomposite based on electroconducting polyaniline doped with 12-phosphotungstic acid and V2O5 as well as its bifunctional analog containing not more than 5 mass% nanosized platinum were obtained. A study was carried
out on the structure of these nanocomposites, their redox characteristics, and electrocatalytic activity in the reduction
of oxygen. These nanocomposites were found to display catalytic properties in the electrochemical reduction of oxygen, while
the presence of even a slight amount of nanosized platinum in the bifunctional composite leads to a significant increase in
its electrocatalytic activity.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 307–314, September–October, 2007. 相似文献
153.
A new stochastic method of reconstructing porous media 总被引:1,自引:0,他引:1
We present a new stochastic method of reconstructing porous medium from limited morphological information obtained from two-dimensional
micro- images of real porous medium. The method is similar to simulated annealing method in the capability of reconstructing
both isotropic and anisotropic structures of multi-phase but differs from the latter in that voxels for exchange are not selected
completely randomly as their neighborhood will also be checked and this new method is much simpler to implement and program.
We applied it to reconstruct real sandstone utilizing morphological information contained in porosity, two-point probability
function and linear-path function. Good agreement of those references verifies our developed method’s powerful capability.
The existing isolated regions of both pore phase and matrix phase do quite minor harm to their good connectivity. The lattice
Boltzmann method (LBM) is used to compute the permeability of the reconstructed system and the results show its good isotropy
and conductivity. However, due to the disadvantage of this method that the connectivity of the reconstructed system’s pore
space will decrease when porosity becomes small, we suggest the porosity of the system to be reconstructed be no less than
0.2 to ensure its connectivity and conductivity. 相似文献
154.
Pascal Noble 《Archive for Rational Mechanics and Analysis》2007,186(1):53-76
The phenomenon of roll-waves occurs when shallow water flows down open inclined channels. This flow is described by the Saint
Venant’s equations with a friction term due to Chezy. In the case of a flat bottom, their existence (as entropic and periodic
travelling waves) follows from a classical work due to DRESSLER [6].
The aim of this paper is to prove the existence of roll-waves when the bottom is modulated by a small periodic perturbation.
Following JIN and KATSOULAKIS [15], we first compute a Burgers-type equation which possesses “pulsating” roll-waves (the wave
speed oscillates around an average velocity). We prove, in a mathematically rigorous fashion, the existence of these solutions. 相似文献
155.
A switching of the S-type in the 20–200 μm thick polycrystalline n-CdTe:In layers with resistance of 103–106 Ω·cm is studied. The electric instability in the layers is found to be due to the electron-thermal breakdown mechanism. The
dependence of the switching threshold parameters on the intensity of exposure can be used for fabrication of infrared-radiation
controlled electric switches on the basis of n-CdTe:In layers.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 28–30, June, 2005. 相似文献
156.
157.
158.
Michael Struwe 《Calculus of Variations and Partial Differential Equations》2003,16(4):431-437
Extending our previous work [5] on this subject we show global existence of smooth solutions to the Cauchy problem for wave
maps from the (1 + 2)-dimensional Minkowski space to an arbitrary smooth, compact Riemannian manifold without boundary, for
arbitrary smooth, radially symmetric data.
Received: 14 December 2001 / Accepted: 1 March 2002 / Published online: 6 August 2002 相似文献
159.
We consider the differential operators Ψ
k
, defined by Ψ1(y) =y and Ψ
k+1(y)=yΨ
k
y+d/dz(Ψ
k
(y)) fork ∈ ℕ fork∈ ℕ. We show that ifF is meromorphic in ℂ and Ψ
k
F has no zeros for somek≥3, and if the residues at the simple poles ofF are not positive integers, thenF has the formF(z)=((k-1)z+a)/(z
2+β
z+γ) orF(z)=1/(az+β) where α, β, γ ∈ ℂ. If the residues at the simple poles ofF are bounded away from zero, then this also holds fork=2. We further show that, under suitable additional conditions, a family of meromorphic functionsF is normal if each Ψ
k
(F) has no zeros. These conditions are satisfied, in particular, if there exists δ>0 such that Re (Res(F, a)) <−δ for all polea of eachF in the family. Using the fact that Ψ
k
(f
′/f) =f
(k)/f, we deduce in particular that iff andf
(k) have no zeros for allf in some familyF of meromorphic functions, wherek≥2, then {f
′/f :f ∈F} is normal.
The first author is supported by the German-Israeli Foundation for Scientific Research and Development G.I.F., G-643-117.6/1999,
and INTAS-99-00089. The second author thanks the DAAD for supporting a visit to Kiel in June–July 2002. Both authors thank
Günter Frank for helpful discussions. 相似文献
160.
Results of studying electro-optic size effects and nonlinear electro-optic effects in ferroelectric PLZT ceramics are presented. It is established that the presence of electro-optic size effects makes microvolume samples of PLZT ceramics promising for designing efficient modulating devices. 相似文献