首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2519篇
  免费   135篇
  国内免费   35篇
化学   1687篇
晶体学   31篇
力学   167篇
数学   429篇
物理学   375篇
  2024年   5篇
  2023年   12篇
  2022年   49篇
  2021年   89篇
  2020年   102篇
  2019年   96篇
  2018年   123篇
  2017年   107篇
  2016年   176篇
  2015年   125篇
  2014年   166篇
  2013年   297篇
  2012年   190篇
  2011年   183篇
  2010年   154篇
  2009年   132篇
  2008年   134篇
  2007年   95篇
  2006年   73篇
  2005年   53篇
  2004年   54篇
  2003年   33篇
  2002年   39篇
  2001年   15篇
  2000年   6篇
  1999年   12篇
  1998年   8篇
  1997年   13篇
  1996年   12篇
  1995年   9篇
  1994年   6篇
  1993年   13篇
  1992年   11篇
  1991年   3篇
  1990年   4篇
  1989年   5篇
  1988年   3篇
  1986年   5篇
  1985年   7篇
  1984年   8篇
  1983年   5篇
  1982年   6篇
  1981年   5篇
  1980年   7篇
  1979年   8篇
  1976年   7篇
  1975年   6篇
  1974年   3篇
  1966年   2篇
  1964年   2篇
排序方式: 共有2689条查询结果,搜索用时 15 毫秒
1.
Molecular Diversity - The preparation, characterization and application of hydroxyapatite silica propyl bis aminoethoxy ethane cuprous complex (HASPBAEECC) as a novel hybrid nano-catalyst for...  相似文献   
2.

In the present research, magnesium aluminate spinel was prepared as catalyst support using a novel, facile, and efficient mechanochemical method. The Co-promoted catalysts with 20 wt.% of Ni were fabricated using an impregnation route and the samples were analyzed by the X-ray diffraction (XRD), N2 adsorption/desorption (BET), temperature-programmed reduction and desorption (H2-TPR and O2-TPD), and field emission scanning electron microscopy (FESEM) tests. The results confirmed that all samples have a mesoporous structure with a high specific surface area and the presence of cobalt caused complete CH4 oxidation at low temperatures, and no side reactions were observed. The results indicated that the 3%Co-20%Ni/MgAl2O4 catalyst was the optimal sample among the prepared catalysts, owing to the improvement of reduction features and oxygen mobility. The 50 and 90% of methane conversion was obtained at 530 and 600 °C, respectively. Also, the influence of calcination temperature, GHSV, and feed ratio was determined on the catalytic activity. The obtained outcomes revealed that the calcination temperature has a significant effect on the textural properties and catalytic efficiency. The sample calcined at 700 °C showed the weakest performance, which was related to the sintering of particles at high temperatures. The catalytic stability showed that the 3%Co-20%Ni/MgAl2O4 has acceptable stability during 600 min time of reaction.

Graphical abstract
  相似文献   
3.
4.
Journal of Thermal Analysis and Calorimetry - Effect of different chain extenders, silica nanoparticle loading, and using sol–gel method on the thermal properties of polyurethane (PU) hybrid...  相似文献   
5.
Journal of Thermal Analysis and Calorimetry - In this research, a biorefinery plant is proposed to generate biofuel through fast pyrolysis and gasification. The proposed biorefinery comprises...  相似文献   
6.
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined.  相似文献   
7.
Developement of numerical methods for obtaining approximate solutions to the three dimensional diffusion equation with an integral condition will be carried out. The numerical techniques discussed are based on the fully explicit (1,7) finite difference technique and the fully implicit (7,1) finite difference method and the (7,7) Crank‐Nicolson type finite difference formula. The new developed methods are tested on a problem. Truncation error analysis and numerical examples are used to illustrate the accuracy of the new algorithms. The results of numerical testing show that the numerical methods based on the finite difference techniques discussed in the present article produce good results. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 193–202, 2002; DOI 10.1002/num.1040  相似文献   
8.
The odd excited negative binomial states are introduced using the photon creation operator by repeated application on negative binomialstates. These states interpolate between the odd displaced Fock states and the odd excited pure thermal states. In this paper both squeezing phenomena (normal squeezing and amplitude squared squeezing) are discussed. Besides discussion of the Glauber second-order correlation function, investigations are carried out for the quasi-probability distribution functions (Wigner function and Q-function). Finally the Pegg-Barnett phase probability distribution is computed for these states.  相似文献   
9.
10.
Possible collapsed forms of poly(N-isopropylacrylamide) molecules are reviewed on the basis of first principle calculations. Various configurations and associated conformations are detailed. The calculated optimized structures exhibit different possibilities of creating networks of intra-molecular bonds of the hydrogen type. We show that the most remarkable one is able to form a local, self-saturated and well ordered helix. We also indicate in which direction the synthesis of the molecule should be oriented to improve its global behavior in term of hydrophobic/hydrophilic behavior.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号