全文获取类型
收费全文 | 1741篇 |
免费 | 210篇 |
国内免费 | 260篇 |
专业分类
化学 | 595篇 |
晶体学 | 15篇 |
力学 | 31篇 |
综合类 | 4篇 |
数学 | 773篇 |
物理学 | 793篇 |
出版年
2024年 | 5篇 |
2023年 | 44篇 |
2022年 | 62篇 |
2021年 | 79篇 |
2020年 | 57篇 |
2019年 | 59篇 |
2018年 | 59篇 |
2017年 | 89篇 |
2016年 | 87篇 |
2015年 | 93篇 |
2014年 | 86篇 |
2013年 | 124篇 |
2012年 | 138篇 |
2011年 | 132篇 |
2010年 | 120篇 |
2009年 | 145篇 |
2008年 | 108篇 |
2007年 | 142篇 |
2006年 | 134篇 |
2005年 | 97篇 |
2004年 | 69篇 |
2003年 | 51篇 |
2002年 | 58篇 |
2001年 | 35篇 |
2000年 | 23篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 13篇 |
1987年 | 2篇 |
排序方式: 共有2211条查询结果,搜索用时 15 毫秒
91.
王在洪 《数学年刊A辑(中文版)》2003,(1)
本文研究二阶微分方程χ"+aχ+-bχ-+f(χ)g(χ'=p(t)周期解的存在性,这里χ+=max{χ,0},χ-=max{-χ,0},a,6是正常数并且点(a,b)位于某一条Fucik谱曲线上.当g(χ)的极限lim.g(χ)=g(+∞),lim g(χ)=g(-∞)和f(χ)的极限lim,g(χ)=f(+∞),lim f(χ)=f(-∞)都存在且有限时,给出了此方程存在周期解的充分条件. 相似文献
92.
LongGuangHE DeShouZHONG 《数学学报(英文版)》2003,19(4):745-756
In this paper,some properties of reduction for symplectic F-spaces are discussed.The properties of stable subgroups are discussed.We find that the symplectic action of a symplectic groupoid on a symplectic manifold can induce a symplectic map between reduced symplectic manifolds.This symplectic action can be characterized by the action of its induced symplectic groupoid on a symplectic manifold.Lastly,we shall discuss Poisson reduction and give a Poisson reduction theorem. 相似文献
93.
Orthogonal expansions in product Jacobi polynomials with respect to the weight function Wα, β(x)=∏dj=1 (1−xj)αj (1+xj)βj on [−1, 1]d are studied. For αj, βj>−1 and αj+βj−1, the Cesàro (C, δ) means of the product Jacobi expansion converge in the norm of Lp(Wα, β, [−1, 1]d), 1p<∞, and C([−1, 1]d) if
Moreover, for αj, βj−1/2, the (C, δ) means define a positive linear operator if and only if δ∑di=1 (αi+βi)+3d−1. 相似文献
Full-size image
94.
利用柠檬酸法制备出了Mo-Fe-MgO,Mo-Co-MgO和W-Co-MgO催化剂,在小型流化床中,以Ar气为载气,在1123 K下催化裂解CH4来制备单壁碳纳米管(SWCNTs).利用透射电子显微镜和拉曼光谱方法研究了催化剂组分对SWCNTs制备的影响,并对SWCNTs的生长机理进行了探索,研究结果表明,柠檬酸法是一种制备负载型SWCNTs催化剂的有效方法,三种催化剂都能够得到质量较好的SWCNTs,在1123 K左右,SWCNTs在三种催化剂上的生长过程可能类似于“微液相模型”.催化剂的组分对SWCNTs的管径分布影响较小,不同催化剂所得到的SWCNTs在内部结构上存在一定的差异.催化剂中加入第二组分Mo和W能有效提高产物的碳产率.
关键词:
单壁碳纳米管
催化化学气相沉积法
生长机理
拉曼光谱 相似文献
95.
Reduced-temperature ordering of FePt nanoparticle assembled films by Fe30Pt70/Fe3O4 core/shell structure
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this paper, Fe30Pt70/Fe3O4 core/shell nanoparticles were synthesized by chemical routine and the layered polyethylenimine (PEI)-Fe30Pt70/Fe3O4 structure was constructed by molecule-mediated self-assembly technique. The dimension of core/shell structured nanoparticles was that of 4nm core and 2 nm shell. After annealing under a flow of forming gas (50%Ar2+30%H2) for 1 h at or above 400℃, the iron oxide shell was reduced to Fe and diffused to Pt-rieh core, which leaded to the formation of L1. phase FePt at low temperature. The x-ray diffraction results and magnetic properties measurement showed that the chemical ordering temperature of Fe30Pt70/Fe3O4 core/shell nanoparticles assembly can be reduced to as low as 400℃. The sample annealed at 400℃ showed the eoereivity of 4KOe with the applied field of 1.5T. The core/shell structure was suggested to be an effective way to reduce the ordering temperature obviously.[第一段] 相似文献
96.
We consider the permeability estimation problem in two-phase porous media flow. We try to identify the permeability field by utilizing both the production data from wells as well as inverted seismic data. The permeability field is assumed to be piecewise constant, or can be approximated well by a piecewise constant function. A variant of the level set method, called Piecewise Constant Level Set Method is used to represent the interfaces between the regions with different permeability levels. The inverse problem is solved by minimizing a functional, and TV norm regularization is used to deal with the ill-posedness. We also use the operator-splitting technique to decompose the constraint term from the fidelity term. This gives us more flexibility to deal with the constraint and helps to stabilize the algorithm. 相似文献
97.
Xianquan Liao Yuxin Liu Qi Jia Prof. Jing Zhou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(43):11094-11101
Solar-driven photothermal antibacterial devices have attracted a lot of interest due to the fact that solar energy is one of the cleanest sources of energy in the world. However, conventional materials have a narrow absorbance band, resulting in deficient solar harvesting. In addition, lack of knowledge on temperature change in these devices during the photothermal process has also led to a waste of energy. Here, we presented an elegant multi-channel optical device with a multilayer structure to simultaneously address the above-mentioned issues in solar-driven antibacterial devices. In the photothermal channel, semiconductor IrO2-nanoaggregates exhibited higher solar absorbance and photothermal conversion efficiency compared with nanoparticles. In the luminescence channel, thermal-sensitive Er-doped upconversion nanoparticles were utilized to reflect the microscale temperature in real-time. The bacteria were successfully inactivated during the photothermal effect under solar irradiation with temperature monitoring. This study could provide valuable insight for the development of smart photothermal devices for solar-driven photothermal bacterial inactivation in the future. 相似文献
98.
The effect of delay on nonlinear chemical signal in a coupled limit cycle system is investigated. Simulation results reveal that the inherent oscillatory signal can be significantly controlled by the delay in the coupled inter-system communication. Besides, under the influence of noise, the signal-to-noise ratio and signal frequency can also be prominently adjusted by the delay. 相似文献
99.
ZHAO Zhen Gang 《数学研究与评论》2009,29(4)
An important property of the reproducing kernel of D2(Ω, ρ) is obtained and the reproducing kernels for D2(Ω, ρ) are calculated when Ω = Bn × Bn and ρ are some special functions. A reproducing kernel is used to construct a semi-positive definite matrix and a distance function defined on Ω×Ω. An inequality is obtained about the distance function and the pseudodistance induced by the matrix. 相似文献
100.
Weiping Yin 《Journal of Mathematical Analysis and Applications》2008,339(1):295-302
Monge-Ampère equation is a nonlinear equation with high degree, therefore its numerical solution is very important and very difficult. In present paper the numerical method of Dirichlet's problem of Monge-Ampère equation on Cartan-Hartogs domain of the third type is discussed by using the analytic method. Firstly, the Monge-Ampère equation is reduced to the nonlinear ordinary differential equation, then the numerical method of the Dirichlet problem of Monge-Ampère equation becomes the numerical method of two point boundary value problem of the nonlinear ordinary differential equation. Secondly, the solution of the Dirichlet problem is given in explicit formula under the special case, which can be used to check the numerical solution of the Dirichlet problem. 相似文献