全文获取类型
收费全文 | 105991篇 |
免费 | 9334篇 |
国内免费 | 6492篇 |
专业分类
化学 | 25562篇 |
晶体学 | 1823篇 |
力学 | 6560篇 |
综合类 | 644篇 |
数学 | 36272篇 |
物理学 | 50956篇 |
出版年
2023年 | 419篇 |
2022年 | 409篇 |
2021年 | 727篇 |
2020年 | 1365篇 |
2019年 | 1703篇 |
2018年 | 1620篇 |
2017年 | 1280篇 |
2016年 | 1209篇 |
2015年 | 1046篇 |
2014年 | 2240篇 |
2013年 | 4020篇 |
2012年 | 2378篇 |
2011年 | 3302篇 |
2010年 | 3851篇 |
2009年 | 8508篇 |
2008年 | 9663篇 |
2007年 | 8057篇 |
2006年 | 7268篇 |
2005年 | 5396篇 |
2004年 | 4972篇 |
2003年 | 5150篇 |
2002年 | 6213篇 |
2001年 | 4487篇 |
2000年 | 4238篇 |
1999年 | 4009篇 |
1998年 | 3351篇 |
1997年 | 2434篇 |
1996年 | 2105篇 |
1995年 | 2504篇 |
1994年 | 2385篇 |
1993年 | 1783篇 |
1992年 | 1288篇 |
1991年 | 1019篇 |
1990年 | 843篇 |
1989年 | 687篇 |
1988年 | 659篇 |
1987年 | 487篇 |
1985年 | 1039篇 |
1984年 | 709篇 |
1983年 | 538篇 |
1982年 | 728篇 |
1981年 | 870篇 |
1980年 | 775篇 |
1979年 | 617篇 |
1978年 | 616篇 |
1977年 | 569篇 |
1976年 | 563篇 |
1975年 | 323篇 |
1974年 | 366篇 |
1973年 | 478篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
961.
962.
ErWeiLI KunGAO ZhongJianJIA 《中国化学快报》2004,15(4):425-427
Two new acetylxylosides,ent-manool-13-O-β-D-2′-acetylxylopyranoside(1)and entmanool-13-O-β-D-2′,4′-diacetylxylopyranoside(2)were isolated from Aster veitchianus.Their structures were elucidated by spectroscopic methods. 相似文献
963.
L.E. Payne 《Journal of Mathematical Analysis and Applications》2003,284(1):283-293
We consider some initial-boundary value problems for the linear and nonlinear heat equation where the gradient of the solution is prescribed on the boundary. Assuming that a solution exists, we obtain bounds for the solution and its gradient by maximum principle arguments or by means of differential and integral inequalities. 相似文献
964.
本文利用拟线性常微分方程解的非存在性定理得到了一类拟线性反应扩散方程(非牛顿渗流方程)爆破界的估计,从而推广了半线性反应扩散方程(牛顿渗流方程)相应结果. 相似文献
965.
A finite volume solver for the 2D depth‐integrated harmonic hyperbolic formulation of the mild‐slope equation for wave propagation is presented and discussed. The solver is implemented on unstructured triangular meshes and the solution methodology is based upon a Godunov‐type second‐order finite volume scheme, whereby the numerical fluxes are computed using Roe's flux function. The eigensystem of the mild‐slope equations is derived and used for the construction of Roe's matrix. A formulation that updates the unknown variables in time implicitly is presented, which produces a more accurate and reliable scheme than hitherto available. Boundary conditions for different types of boundaries are also derived. The agreement of the computed results with analytical results for a range of wave propagation/transformation problems is very good, and the model is found to be virtually paraxiality‐free. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
966.
Zhongyi Huang 《计算数学(英文版)》2003,(1)
In this paper, a new high accuracy numerical method for the thin-film problems of micron and submicron size ferromagnetic elements is proposed. For the computation of stray field, we use the finite element method(FEM) by introducing a semi-discrete artificial boundary condition [1, 2]. In our numerical experiments about the domain patterns and their movement, we can see that the results are accordant to that of experiments and other numerical methods. Our method are very convenient to deal with arbitrary shape of thin films such as a polygon with high accuracy. 相似文献
967.
A. I. Golovashkin G. N. Izmaïlov G. V. Kuleshova T. Q. Khánh A. M. Tskhovrebov L. N. Zherikhina 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):243-249
A scheme of magnetic calorimeter for registration of rare events
characterized by small energy release (cosmic rays, WIMPs, solitary X-ray
quanta) is proposed. The calorimeter is brought to operation by adiabatic
demagnetization, and its magnetic response is measured by a quantum
interferometer (SQUID, A. Barone and G. Paterno, Physics and applications of Josephson Effect). Special consideration is given to the specific
features of calorimeter operation in the ferromagnetic transition region.
The trigger registration of ultrasmall energy release by a ferromagnetic
system in the metastable state is described. 相似文献
968.
Yu. S. Dedkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):15-19
The spin-resolved electronic structure of thin Cr overlayers on top of the Fe(110) surface was investigated by means of spin-
and angle-resolved photoelectron spectroscopy. The initial fast drop of photoelectron spin-polarization at the Fermi level,
followed by weak oscillatory behavior with the period of about 2 ML, can give an evidence for the first time spectroscopic
observation of the short period oscillations in (110)-oriented thin Cr films. 相似文献
969.
The Raman spectroscopic studies of two rare earth trihydrides: Y H3, HoH3, have been performed in the pressure range from ambient up to 16 GPa and 25 GPa respectively. For the first time samples of REH3 in the form of powder have been studied by Raman spectroscopy using the Diamond Anvil Cell (DAC) technique. A rapid decrease of Raman activity has been observed for the hydrides under pressure values in the vicinity of structural phase transition. Metallization as a possible reason for the observed dramatic change of the REH3 Raman activity has been discussed. 相似文献
970.
从非线性自回归模型Xt+1=-αXtλ+1+βXt+γ出发,通过变量替换Xt=aYt,推出三参数混沌动力学系统模型Yt+1=kYt(1-Ytλ)+c;采用线性回归与非线性回归相结合的改进的混合法,对模型参数作了估计;实际研究表明,该模型可以用于对国内生产总值GDP增长的研究. 相似文献