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   23397篇
  免费   1373篇
  国内免费   4955篇
化学   23207篇
晶体学   626篇
力学   535篇
综合类   150篇
数学   1822篇
物理学   3385篇
  2024年   29篇
  2023年   285篇
  2022年   462篇
  2021年   465篇
  2020年   599篇
  2019年   575篇
  2018年   606篇
  2017年   717篇
  2016年   730篇
  2015年   574篇
  2014年   957篇
  2013年   1541篇
  2012年   2748篇
  2011年   1281篇
  2010年   1056篇
  2009年   1333篇
  2008年   1524篇
  2007年   1699篇
  2006年   1470篇
  2005年   1406篇
  2004年   1248篇
  2003年   1054篇
  2002年   879篇
  2001年   700篇
  2000年   696篇
  1999年   693篇
  1998年   596篇
  1997年   507篇
  1996年   498篇
  1995年   472篇
  1994年   403篇
  1993年   317篇
  1992年   368篇
  1991年   276篇
  1990年   220篇
  1989年   152篇
  1988年   103篇
  1987年   83篇
  1986年   84篇
  1985年   61篇
  1984年   43篇
  1983年   21篇
  1982年   31篇
  1981年   23篇
  1980年   24篇
  1979年   24篇
  1978年   14篇
  1977年   22篇
  1976年   16篇
  1973年   10篇
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
181.
The infrared and Raman spectra of a platinum complex of the antiinflammatory drug piroxicam (Pir) and dimethylsulfoxide (DMSO) of composition [PtCl2Pir(DMSO)] were recorded and briefly discussed on the basis of its structural characteristics. The metal-to-ligand vibrations are analyzed in detail.  相似文献   
182.
X-Ray diffuse scattering from a series of examples where the reason for the existence of incommensurable features is fairly well understood, is described. They include in particular non stoichiometric compounds such as [DIPS Φ4(l3)0.76] and such as intercalated graphite RbC24. and quasi one dimensional conductors. A particular emphasis is given on various 1 - D conductors and to the relation of the incommensurability to the characteristics of the electron conduction bands.  相似文献   
183.
Y.Z. Chen  X.Y. Lin  X.Z. Wang 《哲学杂志》2013,93(26):2239-2253
A hypersingular integral equation for the curved crack problems of an elastic half-plane is introduced. Formulation of the equation is based on the usage of a modified complex potential. The potential is generally expressed in the form of a Cauchy-type integral. The modified complex potential is composed of the principal part and the complementary part. The principal part of the complex potential is actually equivalent to the original complex potential for the curved crack in an infinite plate. The role of the complementary part is to eliminate the boundary traction along the boundary of the half-plane caused by the principal part. From the assumed boundary traction condition, a hypersingular integral equation is obtained for the curved crack problems of an elastic half-plane. The curve length coordinate method is used to obtain a final solution. Several numerical examples are presented that prove the efficiency of the suggested method.  相似文献   
184.
185.
A powdered sample of Phyllanthus amarus herb of Kadapa district of Andhra Pradesh, India, is used in the present study. ICP-MS analysis indicates that copper is present in higher concentration when compared to other elements. Although the Pb is toxic, it is within the permissible limit. The evaluated soil and herb physico-chemical parameters indicate that the sample is acidic in nature in comparison with the soil. An EPR study on powdered sample confirms the presence of Fe(III), Mn(II) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. MIR results are due to carbonate fundamentals.  相似文献   
186.
We investigate a new generalized projective synchronization between two complex dynamical networks of different sizes. To the best of our knowledge, most of the current studies on projective synchronization have dealt with coupled networks of the same size. By generalized projective synchronization, we mean that the states of the nodes in each network can realize complete synchronization, and the states of a pair of nodes from both networks can achieve projective synchronization. Using the stability theory of the dynamical system, several sufficient conditions for guaranteeing the existence of the generalized projective synchronization under feedback control and adaptive control are obtained. As an example, we use Chua's circuits to demonstrate the effectiveness of our proposed approach.  相似文献   
187.
Uninuclear europium (Eu), as well as binuclear Eu and terbium (Tb), complexes were synthesized using acrylic acid (AA) as the first ligand and 1,10-phenanthroline (Phen) as the second ligand. The relative weight ratio of the europium (III) (Eu3+) to terbium (III) (Tb3+) ions of the binuclear complex was 1:1 as determined via energy dispersive X-ray analysis. The structures of the Eu(AA)3Phen and Eu0.5Tb0.5(AA)3Phen complexes were characterized by Fourier transform infrared spectroscopy. A series of tri-cellulose acetate (TCA)/ the Eu(AA)3Phen and TCA/Eu0.5Tb0.5(AA)3Phen composites were prepared by solution blending, and their luminescent properties were investigated by fluorescence spectrophotometry. The excitation spectra of all composites indicated that the TCA matrix probably affected the energy absorption and transfer of organic ligands. In TCA/Eu0.5Tb0.5(AA)3Phen composites the introduced Tb3+ ions had some influence on energy absorption and transfer of organic ligands; the energy transfer process of the complex is suggested to be as follows: Phen→AA→Tb3+ion→Eu3+ion. The emission spectra indicated that the luminescent intensity of the TCA/Eu0.5Tb0.5(AA)3Phen composites was noticeably stronger than that of the TCA/Eu(AA)3Phen composites, suggesting that the comparatively stable and high-efficiency energy transfer process was only slightly influenced by the TCA matrix. In summary, the TCA/Eu0.5Tb0.5(AA)3Phen (90/10) composite possesses fine luminescent properties for potential usage as red fluorescent materials.  相似文献   
188.
针对六参数实用黏弹性阻尼耗能结构,基于Davenport风速谱系列响应问题进行了系统的研究.首先,利用六参数黏弹性阻尼器的微分型本构关系,建立了耗能结构基于Davenport风速谱激励下的运动方程;然后,运用复模态法将耗能结构的运动方程由二阶微分方程转化为一阶方程,获得了耗能结构系统对风振激励响应的频域解和功率谱密度函数表达式;最后,利用数学恒等式,基于随机振动理论获得了耗能结构系统在Davenport风速谱激励下的响应和阻尼器受力的解析解.该文方法不仅考虑了结构系统在风振激励作用下全振型展开的结果,表达式较现有结果更为简便,效率及精度更高,且适用于非经典阻尼结构.  相似文献   
189.
很多现实的复杂网络都具有无标度特性,其节点度具有幂律分布的规律。主要讨论幂指数γ<2的无标度网络的性质,指出当γ<2时,网络中最小度的节点数以及网络的平均度都与网络大小N有某种数量关系。通过与γ≥2的无标度网络对比,该类特殊网络呈现出不同的性质和行为,网络的边与节点相比呈现快速增长,具有更大的平均度,网络中有更多的边,网络不再稀疏。  相似文献   
190.
本文详细地考查了原子捕集的测定条件及介质的影响,成功地测定了人发中的微量铜。原子捕集法的灵敏度在捕集时间为1min时为常规法的8.7倍,加标回收率94.4%-100.4%。  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