全文获取类型
收费全文 | 12705篇 |
免费 | 1980篇 |
国内免费 | 874篇 |
专业分类
化学 | 2411篇 |
晶体学 | 84篇 |
力学 | 1125篇 |
综合类 | 205篇 |
数学 | 7124篇 |
物理学 | 4610篇 |
出版年
2024年 | 11篇 |
2023年 | 117篇 |
2022年 | 168篇 |
2021年 | 328篇 |
2020年 | 351篇 |
2019年 | 387篇 |
2018年 | 366篇 |
2017年 | 469篇 |
2016年 | 524篇 |
2015年 | 389篇 |
2014年 | 609篇 |
2013年 | 1157篇 |
2012年 | 701篇 |
2011年 | 779篇 |
2010年 | 700篇 |
2009年 | 779篇 |
2008年 | 860篇 |
2007年 | 825篇 |
2006年 | 718篇 |
2005年 | 619篇 |
2004年 | 514篇 |
2003年 | 572篇 |
2002年 | 511篇 |
2001年 | 415篇 |
2000年 | 377篇 |
1999年 | 345篇 |
1998年 | 290篇 |
1997年 | 291篇 |
1996年 | 204篇 |
1995年 | 175篇 |
1994年 | 127篇 |
1993年 | 103篇 |
1992年 | 91篇 |
1991年 | 72篇 |
1990年 | 70篇 |
1989年 | 62篇 |
1988年 | 57篇 |
1987年 | 53篇 |
1986年 | 47篇 |
1985年 | 69篇 |
1984年 | 41篇 |
1983年 | 26篇 |
1982年 | 37篇 |
1981年 | 31篇 |
1980年 | 14篇 |
1979年 | 24篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
91.
Hirofumi Tsumura. 《Mathematics of Computation》2004,73(245):251-258
In this paper, we give some evaluation formulas for Tornheim's type of alternating series by an elementary and combinatorial calculation of the uniformly convergent series. Indeed, we list several formulas for them by means of Riemann's zeta values at positive integers.
92.
In this paper, we exhibit a unified treatment of the mixed initial boundary value problem for second order (in time) parabolic linear differential equations in Banach spaces, whose boundary conditions are of a dynamical nature. Results regarding existence, uniqueness, continuous dependence (on initial data) and regularity of classical and strict solutions are established. Moreover, several examples are given as samples for possible applications.
93.
The asymptotic behaviour of partial sums of generalized hypergeometric series of unit argument is investigated.
94.
Carl M. Bender 《Czechoslovak Journal of Physics》2004,54(1):13-28
The Hamiltonian H specifies the energy levels and the time evolution of a quantum theory. It is an axiom of quantum mechanics that H be Hermitian. The Hermiticity of H guarantees that the energy spectrum is real and that the time evolution is unitary (probability preserving). In this talk we investigate an alternative formulation of quantum mechanics in which the mathematical requirement of Hermiticity is replaced by the more physically transparent condition of space-time reflection (PT) symmetry. We show that if the PT symmetry of a Hamiltonian H is not broken, then the spectrum of H is real. Examples of PT-symmetric non-Hermitian Hamiltonians are H=p
2+ix
3 and H=p
2-x
4. The crucial question is whether PT-symmetric Hamiltonians specify physically acceptable quantum theories in which the norms of states are positive and the time evolution is unitary. The answer is that a Hamiltonian that has an unbroken PT symmetry also possesses a physical symmetry that we call C. Using C, we show how to construct an inner product whose associated norm is positive definite. The result is a new class of fully consistent complex quantum theories. Observables exhibit CPT symmetry, probabilities are positive, and the dynamics is governed by unitary time evolution. 相似文献
95.
96.
In this paper, we investigate the exact distribution of the waiting time for ther-th ℓ-overlapping occurrence of success-runs of a specified length in a sequence of two state Markov dependent trials. The
probability generating functions are derived explicitly, and as asymptotic results, relationships of a negative binomial distribution
of orderk and an extended Poisson distribution of orderk are discussed. We provide further insights into the run-related problems from the viewpoint of the ℓ-overlapping enumeration
scheme. We also study the exact distribution of the number of ℓ-overlapping occurrences of success-runs in a fixed number
of trials and derive the probability generating functions. The present work extends several properties of distributions of
orderk and leads us a new type of geneses of the discrete distributions. 相似文献
97.
Frequency dependence of ac conductivity from 1 to 105 Hz and time series of the conductivity at 2 kHz were measured along c-axis of thulium nitrate crystal, Tm(NO3)36H2O at temperatures from 203.15 to 293.15 K. The meta-stability was observed. The frequency spectra of the conductivity were similar to those in disorder system. Aging effect was observed. Non-periodic instability (burst) was found. Non-linear dynamical property was characterized by 1/f noise spectrum, limit cycle in return map and dependence of correlation exponent on embedding dimension. 相似文献
98.
微孔激光器作为应用于近场光信息存储系统中的一种新型光源,它的出射光斑的近场特性对于近场光存储是十分重要的。针对纳米孔径运用角谱进行Fox-Li数值迭代,得到不同孔径微孔激光器的基模光强分布,然后运用二维非线性时域有限差分法分析微孔激光器出射端即微孔金属膜的近场光学性质,模拟计算了不同孔径和厚度的微孔金属膜的光强近场分布,从应用于近场光存储的角度,给出反映其近场光学特性的相关数据。发现由于TM模式下金属存在局域表面等离子增强效应,使得其出射强度比TE模式高一个数量级,从而更适于作为实际中近场光存储系统和原理试验的光学头。 相似文献
99.
This work is devoted to near-optimal controls of large-scale discrete-time nonlinear dynamic systems driven by Markov chains; the underlying problem is to minimize an expected cost function. Our main goal is to reduce the complexity of the underlying systems. To achieve this goal, discrete-time control models under singularly-perturbed Markov chains are introduced. Using a relaxed control representation, our effort is devoted to finding near-optimal controls. Lumping the states in each irreducible class into a single state gives rise to a limit system. Applying near-optimal controls of the limit system to the original system, near-optimal controls of the original system are derived. 相似文献
100.
Nongelatin dichromated holographic film(NGD) is a new holographic recordingmaterial.Holograms recorded on this material have better environmental stability, higherdiffraction efficiency and stronger real time effect, etc..An experimental study to ascertainthe influence of two electron donors, namely,N,N-dimethylformamide(DMF) and dimethyl-sulfoxide(DMSO),on the real time diffraction efficiency(RTDE) of NGD holograms is car-ried out.The pressence of electron donors not only improves the sensitivity,but also enhancesthe real time effect greatly.RTDE of above 60% at±1 orders of NGD plane transimissiongrating is achieved by introducing electron donors. 相似文献