全文获取类型
收费全文 | 1679篇 |
免费 | 75篇 |
国内免费 | 18篇 |
专业分类
化学 | 1182篇 |
晶体学 | 17篇 |
力学 | 98篇 |
数学 | 190篇 |
物理学 | 285篇 |
出版年
2023年 | 20篇 |
2022年 | 78篇 |
2021年 | 81篇 |
2020年 | 55篇 |
2019年 | 84篇 |
2018年 | 74篇 |
2017年 | 55篇 |
2016年 | 94篇 |
2015年 | 58篇 |
2014年 | 91篇 |
2013年 | 156篇 |
2012年 | 113篇 |
2011年 | 106篇 |
2010年 | 74篇 |
2009年 | 73篇 |
2008年 | 75篇 |
2007年 | 59篇 |
2006年 | 48篇 |
2005年 | 37篇 |
2004年 | 25篇 |
2003年 | 28篇 |
2002年 | 33篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 18篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1968年 | 2篇 |
1967年 | 3篇 |
排序方式: 共有1772条查询结果,搜索用时 15 毫秒
201.
n-Type indium antimonide-Au hybrid macro-structure was successfully fabricated on p-GaAs substrate by a simple and economic
flash evaporation technique. The elemental composition of the prepared InSb film was confirmed by energy dispersive X-ray
spectroscopy microanalysis (EDX). The surface topography and crystal structure of the InSb film was characterized by scanning
electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The magnetoresistance of the prepared hybrid macro-structure
was measured and discussed in terms of the model of current redistribution. 相似文献
202.
203.
We study poissonized triangular (reducible) urns on two colors, which we take to be white and blue. We analyze the number of white and blue balls after a certain period of time has elapsed. We show that for balanced processes in this class, a different scaling is needed for each color to produce nontrivial limits, contrary to the distributions in the usual irreducible urns which only require the same scaling for both colors. The limit distributions (of the scaled variables) underlying triangular urns are Gamma. The technique we use couples partial differential equations with the method of moments applied in a bootstrapped manner to produce exact and asymptotic moments. For the dominant color, we get exact moments, while relaxing the balance condition. The exact moments include alternating signs and Stirling numbers of the second kind. 相似文献
204.
In this research paper, we examine a novel method called the Natural Decomposition Method (NDM). We use the NDM to obtain exact solutions for three different types of nonlinear ordinary differential equations (NLODEs). The NDM is based on the Natural transform method (NTM) and the Adomian decomposition method (ADM). By using the new method, we successfully handle some class of nonlinear ordinary differential equations in a simple and elegant way. The proposed method gives exact solutions in the form of a rapid convergence series. Hence, the Natural Decomposition Method (NDM) is an excellent mathematical tool for solving linear and nonlinear differential equation. One can conclude that the NDM is efficient and easy to use. 相似文献
205.
Ali Y. Al-Rayyah Magdi S. Mahmoud 《Journal of Optimization Theory and Applications》2010,147(2):318-336
In this paper, we study the problem of designing decentralized reliable feedback control methods under a class of control
failures for a class of linear interconnected continuous-time systems having internal subsystem time-delays and additional
time-delay couplings. These failures are described by a model that takes into consideration possible outages or partial failures
in every single actuator of each decentralized controller. The decentralized control design is performed through two steps.
First, a decentralized stabilizing reliable feedback control set is derived at the subsystem level through the construction
of appropriate Lyapunov-Krasovskii functional and, second, a feasible linear matrix inequalities procedure is then established
for the effective construction of the control set under different feedback schemes. Two schemes are considered: the first
is based on state-measurement and the second utilizes static output-feedback. The decentralized feedback gains in both schemes
are determined by convex optimization over linear matrix inequalities. We characterize decentralized linear matrix inequality-based
feasibility conditions such that every local closed-loop subsystem of the linear interconnected delay system is delay-dependent
robustly asymptotically stable with an γ-level ℒ2-gain. The developed results are tested on a representative example. 相似文献
206.
Hosam M. Mahmoud 《Methodology and Computing in Applied Probability》2010,12(4):763-773
The power of choice is known to change the character of random structures and produce desirable optimization effects. We discuss
generalizations of random recursive trees, grown under the choice to meet optimization criteria. Specifically, we discuss
the random k-minimal (k-maximal) label recursive tree, where a set of k candidate parents, instead of one as in the usual recursive tree, is selected and the node with minimal (maximal) label among
them is assigned as parent for the next node. These models are proposed as alternatives for D’Souza et al. (Eur Phys J B59:535–543,
2007) minimal and maximal depth models. The advantage of the label models is that they are tractable and at the same time provide
approximations and bounds for the depth models. For the depth of nodes in label models we give the average behavior and exact
distributions involving Stirling’s numbers and derive Gaussian limit laws. 相似文献
207.
In this paper, we investigate the problem of robust global exponential stability analysis for a class of neutral-type neural networks. The interval time-varying delays allow for both slow and fast time-varying delays. The values of the time-varying uncertain parameters are assumed to be bounded within given compact sets. Improved global exponential stability condition is derived by employing new Lyapunov-Krasovskii functional and the integral inequality. The developed nominal and robust stability criteria is delay-dependent and characterized by linear-matrix inequalities (LMIs). The developed results are less conservative than previous published ones in the literature, which are illustrated by representative numerical examples. 相似文献
208.
ABSTRACTNonlinear propagation of dust-ion-acoustic shock waves in an unmagnetized, collisionless four-component quantum plasma containing electrons, positrons, ions and negatively charged dust grains affected by dust charge variations and viscosity of ions is studied using quantum hydrodynamic model. Considering dust charge variation give rise to calculating of charging currents of the plasma particles. These currents have been calculated with orbit limited motion theory and using Fermi-distribution functions or Boltzmann–Maxwell distribution depending on quantum or classical particles, respectively. The basic characteristics of quantum dust-ion-acoustic shock waves are investigated by deriving Korteweg–de Vries–Burgers equation under the reductive perturbation method. Depending on the relative values of the dispersive and dissipative coefficients, oscillatory and monotonic shock waves can propagate in the plasma model. The effect of chemical potential and density of dust particles on the shock wave’s height and thickness is investigated. In addition, the critical value of H (Hc) is calculated and it is shown that for R?>?0 compressive shock waves and for R?<?0 rarefactive ones can exist. The present study is applicable to researchers on quantum nonlinear structures in dense astrophysical objects and ultra-small micro- and nano-electronic devices. 相似文献
209.
This paper considers the pricing of contingent claims using an approach developed and used in insurance pricing. The approach is of interest and significance because of the increased integration of insurance and financial markets and also because insurance-related risks are trading in financial markets as a result of securitization and new contracts on futures exchanges. This approach uses probability distortion functions as the dual of the utility functions used in financial theory. The pricing formula is the same as the Black-Scholes formula for contingent claims when the underlying asset price is log-normal. The paper compares the probability distortion function approach with that based on financial theory. The theory underlying the approaches is set out and limitations on the use of the insurance-based approach are illustrated. The probability distortion approach is extended to the pricing of contingent claims for more general assumptions than those used for Black-Scholes option pricing. 相似文献
210.
1H-NMR spectrum of tiaprofenic acid in CDCI3 was obtained and proton chemical shifts from tetramethylsilane were assigned to each proton and set of equivalent protons of the molecule. The hydroxy proton of the carboxylic acid group was confirmed by deuterium exchange. The natural abundance C-13 nuclear magnetic resonance spectrum of the compound in CDCI3 was recorded using Fourier transorm technique. The chemical shifts of carbon resonances have been assigned on the basis of the chemical shift additivity theory and the signal multiplicity observed in the single frequency off-resonance decoupled (SFORD) spectrum. Also comparison with carbon chemical shifts of model compounds were useful. 相似文献