全文获取类型
收费全文 | 3138篇 |
免费 | 362篇 |
国内免费 | 355篇 |
专业分类
化学 | 193篇 |
晶体学 | 7篇 |
力学 | 135篇 |
综合类 | 70篇 |
数学 | 2879篇 |
物理学 | 571篇 |
出版年
2024年 | 10篇 |
2023年 | 40篇 |
2022年 | 43篇 |
2021年 | 71篇 |
2020年 | 89篇 |
2019年 | 85篇 |
2018年 | 86篇 |
2017年 | 113篇 |
2016年 | 133篇 |
2015年 | 73篇 |
2014年 | 158篇 |
2013年 | 250篇 |
2012年 | 166篇 |
2011年 | 190篇 |
2010年 | 152篇 |
2009年 | 205篇 |
2008年 | 202篇 |
2007年 | 188篇 |
2006年 | 201篇 |
2005年 | 161篇 |
2004年 | 127篇 |
2003年 | 137篇 |
2002年 | 155篇 |
2001年 | 115篇 |
2000年 | 104篇 |
1999年 | 98篇 |
1998年 | 87篇 |
1997年 | 59篇 |
1996年 | 45篇 |
1995年 | 34篇 |
1994年 | 43篇 |
1993年 | 28篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 25篇 |
1984年 | 18篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1936年 | 4篇 |
排序方式: 共有3855条查询结果,搜索用时 31 毫秒
101.
We will focus on the existence of nontrivial solutions to the following Hamiltonian elliptic system where are numbers belonging to the interval [0, 2), V is a continuous potential bounded below on by a positive constant and the functions f and g possess exponential growth range established by Trudinger–Moser inequalities in Lorentz–Sobolev spaces. The proof involves linking theorem and a finite‐dimensional approximation. 相似文献
102.
103.
In this paper, an unstable linear time invariant (LTI) ODE system is stabilized exponentially by the PDE compensato—a wave equation with Kelvin‐Voigt (K‐V) damping. Direct feedback connections between the ODE system and wave equation are established: The velocity of the wave equation enters the ODE through the variable vt(1,t); meanwhile, the output of the ODE is fluxed into the wave equation. It is found that the spectrum of the system operator is composed of two parts: point spectrum and continuous spectrum. The continuous spectrum consists of an isolated point , and there are two branches of asymptotic eigenvalues: the first branch approaches to , and the other branch tends to ?∞. It is shown that there is a sequence of generalized eigenfunctions, which forms a Riesz basis for the Hilbert state space. As a consequence, the spectrum‐determined growth condition and exponential stability of the system are concluded. 相似文献
104.
A mixed hp FEM for the approximation of fourth‐order singularly perturbed problems on smooth domains
P. Constantinou S. Franz L. Ludwig C. Xenophontos 《Numerical Methods for Partial Differential Equations》2019,35(1):114-127
We consider fourth‐order singularly perturbed problems posed on smooth domains and the approximation of their solution by a mixed Finite Element Method on the so‐called Spectral Boundary Layer Mesh. We show that the method converges uniformly, with respect to the singular perturbation parameter, at an exponential rate when the error is measured in the energy norm. Numerical examples illustrate our theoretical findings. 相似文献
105.
《Annals of Differential Equations》2012,(3):283-289
By applying the properties of almost periodic function and exponential dichotomy of linear system as well as Banach fixed point theorem,we establish the conditions for the existence and uniqueness of square-mean almost periodic solution to some stochastic functional differential equations. 相似文献
106.
Based on QCD sum rules we explore the consequences of a scenario for the ρ meson, where the chiral symmetry breaking condensates are set to zero whereas the chirally symmetric condensates remain at their vacuum values. This clean-cut scenario causes a lowering of the ρ spectral moment by about 120 MeV. The complementarity of mass shift and broadening is discussed. A simple parametrization of the ρ spectral function leads to a width of about 280 MeV if no shift of the peak position is assumed. 相似文献
107.
《Acta Crystallographica. Section C, Structural Chemistry》2017,73(11):896-904
Since the discovery of electrochemically active LiFePO4, materials with tunnel and layered structures built up of transition metals and polyanions have become the subject of much research. A new quaternary arsenate, sodium calcium trinickel aluminium triarsenate, NaCa1–x Ni3–2x Al2x (AsO4)3 (x = 0.23), was synthesized using the flux method in air at 1023 K and its crystal structure was determined from single‐crystal X‐ray diffraction (XRD) data. This material was also characterized by qualitative energy‐dispersive X‐ray spectroscopy (EDS) analysis and IR spectroscopy. The crystal structure belongs to the α‐CrPO4 type with the space group Imma . The structure is described as a three‐dimensional framework built up of corner‐edge‐sharing NiO6, (Ni,Al)O6 and AsO4 polyhedra, with channels running along the [100] and [010] directions, in which the sodium and calcium cations are located. The proposed structural model has been validated by bond‐valence‐sum (BVS) and charge‐distribution (CHARDI) tools. The sodium ionic conduction pathways in the anionic framework were investigated by means of the bond‐valence site energy (BVSE) model, which predicted that the studied material will probably be a very poor Na+ ion conductor (bond‐valence activation energy ∼7 eV). 相似文献
108.
研究了一个三阶半线性微分方程的奇摄动非线性混合边值问题.利用边界层函数法构造了该问题的形式渐近解,并采用微分不等式理论证明了解的存在性,给出了渐近解的误差估计,最后得出了边界层函数指数型衰减的结论. 相似文献
109.
A new family of univariate exponential slash distribution is introduced, which is based on elliptical distributions and defined by means of a stochastic representation as the scale mixture of an elliptically distributed random variable with respect to the power of an exponential random variable. The same idea is extended to the multivariate case. General properties of the resulting families, including their moments and kurtosis coefficient, are studied. And inferences based on methods of moment and maximum likelihood are discussed. A real data is presented to show this family is flexible and fits much better than other related families. 相似文献
110.
The main purpose of this paper is using estimates for trigonometric sums and properties of congruence to study the computation of one kind of fourth power mean of a generalized three-term exponential sum, and give an interesting identity for it. 相似文献