全文获取类型
收费全文 | 4668篇 |
免费 | 128篇 |
国内免费 | 29篇 |
专业分类
化学 | 3013篇 |
晶体学 | 50篇 |
力学 | 81篇 |
数学 | 911篇 |
物理学 | 770篇 |
出版年
2023年 | 41篇 |
2022年 | 98篇 |
2021年 | 127篇 |
2020年 | 99篇 |
2019年 | 125篇 |
2018年 | 133篇 |
2017年 | 118篇 |
2016年 | 157篇 |
2015年 | 126篇 |
2014年 | 129篇 |
2013年 | 300篇 |
2012年 | 245篇 |
2011年 | 315篇 |
2010年 | 209篇 |
2009年 | 208篇 |
2008年 | 254篇 |
2007年 | 241篇 |
2006年 | 238篇 |
2005年 | 230篇 |
2004年 | 185篇 |
2003年 | 150篇 |
2002年 | 122篇 |
2001年 | 76篇 |
2000年 | 58篇 |
1999年 | 43篇 |
1998年 | 46篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 25篇 |
1994年 | 28篇 |
1993年 | 34篇 |
1992年 | 19篇 |
1991年 | 34篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1987年 | 18篇 |
1986年 | 24篇 |
1985年 | 25篇 |
1984年 | 32篇 |
1983年 | 26篇 |
1982年 | 27篇 |
1981年 | 32篇 |
1980年 | 28篇 |
1979年 | 30篇 |
1978年 | 30篇 |
1977年 | 31篇 |
1976年 | 19篇 |
1975年 | 23篇 |
1974年 | 20篇 |
1955年 | 15篇 |
排序方式: 共有4825条查询结果,搜索用时 484 毫秒
11.
Andrew Mills Anne Lepre Nicholas Elliott Sharan Bhopal Ivan P. Parkin S. A. ONeill 《Journal of photochemistry and photobiology. A, Chemistry》2003,160(3):213-224
Pilkington Glass Activ™ represents a possible suitable successor to P25 TiO2, especially as a benchmark photocatalyst film for comparing other photocatalyst or PSH self-cleaning films. Activ™ is a glass product with a clear, colourless, effectively invisible, photocatalytic coating of titania that also exhibits PSH. Although not as active as a film of P25 TiO2, Activ™ vastly superior mechanical stability, very reproducible activity and widespread commercial availability makes it highly attractive as a reference photocatalytic film. The photocatalytic and photo-induced superhydrophilitic (PSH) properties of Activ™ are studied in some detail and the results reported. Thus, the kinetics of stearic acid destruction (a 104 electron process) are zero order over the stearic acid range 4–129 monolayers and exhibit formal quantum efficiencies (FQE) of 0.7×10−5 and 10.2×10−5 molecules per photon when irradiated with light of 365±20 and 254 nm, respectively; the latter appears also to be the quantum yield for Activ™ at 254 nm. The kinetics of stearic acid destruction exhibit Langmuir–Hinshelwood-like saturation type kinetics as a function of oxygen partial pressure, with no destruction occurring in the absence of oxygen and the rate of destruction appearing the same in air and oxygen atmospheres. Further kinetic work revealed a Langmuir adsorption type constant for oxygen of 0.45±0.16 kPa−1 and an activation energy of 19±1 kJ mol−1. A study of the PSH properties of Activ™ reveals a high water contact angle (67°) before ultra-bandgap irradiation reduced to 0° after prolonged irradiation. The kinetics of PSH are similar to those reported by others for sol–gel films using a low level of UV light. The kinetics of contact angle recovery in the dark appear monophasic and different to the biphasic kinetics reported recently by others for sol–gel films [J. Phys. Chem. B 107 (2003) 1028]. Overall, Activ™ appears a very suitable reference material for semiconductor film photocatalysis. 相似文献
12.
Anelia Achanova Ivan Zhelyazkov Tsvetelina Petrova 《Czechoslovak Journal of Physics》2004,54(2):211-223
Microwave discharges produced by travelling/standing electromagnetic waves have drawn considerable attention in recent years
due to their wide application in microelectronic industry. Here are presented the axial distributions of the electrons and
ions as well as those of excited atoms in an argon microwave discharge at a low gas pressure (400 mTorr) sustained by a 2.45
GHz travelling dipolar electromagnetic wave. The numerical calculations are based on a self-consistent kinetic-electrodynamic
model and the results obtained are in a good agreement with the experimental data. The model yields also the magnitude of
the wave power sustaining the discharge and the axial profiles of all electromagnetic-wave characteristics and the axial distribution
of the neutral gas temperature. 相似文献
13.
This paper presents a few novel results, and collects together what is known and conjectured about the branching graph of a polyhex. 相似文献
14.
Ivan Nunes da Silva Wagner Caradori do AmaralLucia Valeria de Arruda 《Applied Mathematical Modelling》2007
This paper presents an efficient approach based on recurrent neural network for solving nonlinear optimization. More specifically, a modified Hopfield network is developed and its internal parameters are computed using the valid subspace technique. These parameters guarantee the convergence of the network to the equilibrium points that represent an optimal feasible solution. The main advantage of the developed network is that it treats optimization and constraint terms in different stages with no interference with each other. Moreover, the proposed approach does not require specification of penalty and weighting parameters for its initialization. A study of the modified Hopfield model is also developed to analyze its stability and convergence. Simulation results are provided to demonstrate the performance of the proposed neural network. 相似文献
15.
The primary resource for quantum computation is Hilbert-space dimension. Whereas Hilbert space itself is an abstract construction, the number of dimensions available to a system is a physical quantity that requires physical resources. Avoiding a demand for an exponential amount of these resources places a fundamental constraint on the systems that are suitable for scalable quantum computation. To be scalable, the effective number of degrees of freedom in the computer must grow nearly linearly with the number of qubits in an equivalent qubit-based quantum computer. 相似文献
16.
17.
The covering graph of a lattice which is contained in an ordered set with a planar covering graph is itself planar.Presented by R. W. Quackenbush. 相似文献
18.
On the numerical solution of axisymmetric domain optimization problems by dual finite element method
Shape optimization of an axisymmetric three-dimensional domain with an elliptic boundary value state problem is solved. Since the cost functional is given in terms of the cogradient of the solution, a dual finite element method based on the minimum of complementary energy principle is used. © 1994 John Wiley & Sons, Inc. 相似文献
19.
We analyze the polarization changes introduced by a rotated Dove prism on the linearly polarized light, using the Jones calculus and the exact ray trace analysis. The state of polarization changes from the linear to a mildly elliptical one when a plane wave front passes through a rotated Dove prism: its semi-major axis is nearly parallel to the input plane of polarization, for any angle of prism rotation. The interferogram contrast remains high for all shearing angles in spite of polarization changes when the Dove prism is incorporated into a rotational shearing interferometer. These results are confirmed experimentally. 相似文献
20.