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   14999篇
  免费   1396篇
  国内免费   3623篇
化学   14454篇
晶体学   444篇
力学   541篇
综合类   173篇
数学   1727篇
物理学   2679篇
  2025年   11篇
  2024年   149篇
  2023年   151篇
  2022年   343篇
  2021年   366篇
  2020年   436篇
  2019年   371篇
  2018年   371篇
  2017年   420篇
  2016年   488篇
  2015年   435篇
  2014年   684篇
  2013年   1151篇
  2012年   1469篇
  2011年   799篇
  2010年   681篇
  2009年   882篇
  2008年   999篇
  2007年   1049篇
  2006年   969篇
  2005年   961篇
  2004年   866篇
  2003年   720篇
  2002年   626篇
  2001年   501篇
  2000年   502篇
  1999年   479篇
  1998年   423篇
  1997年   361篇
  1996年   351篇
  1995年   340篇
  1994年   302篇
  1993年   222篇
  1992年   272篇
  1991年   203篇
  1990年   161篇
  1989年   117篇
  1988年   91篇
  1987年   66篇
  1986年   67篇
  1985年   48篇
  1984年   34篇
  1983年   18篇
  1982年   23篇
  1981年   10篇
  1980年   7篇
  1979年   3篇
  1978年   4篇
  1977年   5篇
  1936年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Two octacyanometallate-based NiII–MIV [M?=?Mo(1), W(2)] bimetallic assemblies chelated with tetradentate macrocyclic ligands have been synthesized by slow diffusion and characterized structurally. In both complexes, M and Ni centers acting as linker and connector, respectively, are connected by M–CN–Ni–NC–M linkages to form a 3-D diamond-type topological network. Magnetic behaviors of both complexes show a very weak antiferromagnetic interaction between NiII ions mediated by the diamagnetic [M(CN)8]4? bridges.  相似文献   
22.
Two new discrete Btz-bridged pentanuclear metal complexes, [HDMF][NaHg4(Btz)6I4] (1) and [Zn5(Btz)6(L)3(Ac)]?·?0.5MeOH?·?0.5H2O (2) (Btz?=?deprotonated benzotriazole, L?=?p-aminobenzoate, HDMF?=?protonated DMF, and Ac?=?acetate), were synthesized using three-layered diffusion and natural evaporation methods, respectively. In 1, the pentanuclear anion [NaHg4(Btz)6I4]? is composed of a tetrahedral arrangement of four four-coordinate Hg(II) ions centered on the six-coordinate Na(I), and thereby forming a rare Btz-bridged hetero-metal complex. Compound 2 is a neutral pentanuclear homo-metal complex, consisting of a tetrahedral arrangement of four five-coordinate Zn(II) ions centered on the fifth six-coordinate Zn(II). The thermal stabilities and solid-state photoluminescence of the two complexes have been investigated.  相似文献   
23.
The crystal structure of the title complex was determined by single-crystal X-ray diffraction methods. The unit cell contains two independent molecules, A and B. B is a mononuclear Cu(II) complex with square-planar coordination geometry formed by two benzimidazole molecules and two hydroxylbenzoate anions. A is a dimer of B, formed by bridging hydroxybenzoate, and copper assumes square-pyramidal geometry. Aromatic π–π stacking is observed between parallel benzimidazole rings of neighboring A molecules. IR spectra of the compound are assigned in line with the crystal structure.  相似文献   
24.
The title complex has been synthesized and characterized by elemental and thermal analysis, IR and electronic spectroscopy, conductivity studies and X-ray crystallography. In the crystal, the complex has two-fold symmetry and the copper atom adopts square pyramidal coordination. Bond valences for Cu were computed. Cu–O(propionate) bonds are slightly stronger than the Cu–N bonds, and the Cu–O(water) bond is distinctly weaker. Molecules are linked by O–H···O hydrogen bonds to form infinite hydrogen-bonded chains along the y axis.  相似文献   
25.
A path-integral Monte Carlo algorithm for the simulation of electrons solvated in polar liquids is briefly outlined, and results are presented for the electron solvated in liquid water.  相似文献   
26.
A new model is proposed to explain coiling of myelins composed of fluid bilayers. This model allows the constituent bilayer cylinders of a myelin to be non-coaxial and the bilayer lateral tension to vary from bilayer to bilayer. The calculations show that a myelin would bend or coil to lower its free energy when the bilayer lateral tension is sufficiently large. From a mechanical point of view, the proposed coiling mechanism is analogous to the classical Euler buckling of a thin elastic rod under axial compression. The analysis of a simple two-bilayer case suggests that a bilayer lateral tension of about 1 dyne/cm can easily induce coiling of myelins of typical lipid bilayers. This model signifies the importance of bilayer lateral tension in determining the morphology of myelinic structures.  相似文献   
27.
A method for measuring complex permittivity based on an electric-field cross-correlation Fourier transform spectrometer was proposed. Its principle can be extended over the whole microwave region. Two typical solid media, teflon and plexigrass, and a kind of sand were measured in 8mm-wave region by the method. The results show that this method has potentialities to perform accurate permittivity measurements.Supported by Foundation of Specialities Opened to Doctorate Study  相似文献   
28.
The spin-crossover behaviors of mixed-valence iron compounds [FeIIH3L][FeIIIL](NO3)2 (1) and [FeIIH3LMe][FeIIILMe](NO3)2 (2) have been investigated by 57Fe Mössbauer spectroscopy, where H3L is a hexadentate N6 tripod ligand containing three imidazole groups and H3LMe is its 2-methylimidazole derivative. Deconvolution analyses of the Mössbauer spectra revealed that a two-step SCO (LS FeII–LS FeIII→HS FeII–LS FeIII→HS FeII–HS FeIII) proceeds in each compound on elevating the temperature. Compound 2 exhibited lower spin-transition temperatures than 1. “Frozen-in effect” was observed below 120 and 50 K for 1 and 2, respectively.  相似文献   
29.
The electronic structures and transport properties of (10,0)(10,0) single-walled carbon nanotube ((10,0)(10,0) (SWNT)) with oxygen-containing defect complex are investigated using density functional theory in combination with nonequilibrium Green?s function method. The complex delocalizes the local states of (10,0)(10,0) SWNT induced by mono- and di-vacancy but strengthens the localization of the states induced by the Stone–Wales defect. As a result, the complex partially restores the transport properties of (10,0)(10,0) SWNT with vacancies, but reduces the transmission of (10,0)(10,0) SWNT with Stone–Wales defect. However, the oxygen-containing defect complex only slightly influences the transmission gap and threshold voltage of the system.  相似文献   
30.
This study aims at figuring out the crucial topological ingredients which affect the outcomes of the ultimatum game located on different networks,encompassing the regular network,the random network,the small world network,and the scale-free network.With the aid of random interchanging algorithm,we investigate the relations between the outcomes of the ultimatum game and some topological ingredients,including the average range,the clustering coefficient and the heterogeneity,and so forth.It is found that for the regular,random and small-work networks,the average range and the clustering coefficient have evident impacts on the ultimatum game,while for the scale-free network the original degree heterogeneity and the underlying rich-club characterizations are the mainly important topologica ingredients that influence the outcomes of ultimatum game substantially.  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