全文获取类型
收费全文 | 11295篇 |
免费 | 1326篇 |
国内免费 | 538篇 |
专业分类
化学 | 6935篇 |
晶体学 | 568篇 |
力学 | 141篇 |
综合类 | 38篇 |
数学 | 69篇 |
物理学 | 5408篇 |
出版年
2024年 | 7篇 |
2023年 | 75篇 |
2022年 | 160篇 |
2021年 | 177篇 |
2020年 | 229篇 |
2019年 | 241篇 |
2018年 | 209篇 |
2017年 | 211篇 |
2016年 | 398篇 |
2015年 | 399篇 |
2014年 | 472篇 |
2013年 | 907篇 |
2012年 | 565篇 |
2011年 | 792篇 |
2010年 | 670篇 |
2009年 | 787篇 |
2008年 | 734篇 |
2007年 | 940篇 |
2006年 | 890篇 |
2005年 | 601篇 |
2004年 | 628篇 |
2003年 | 557篇 |
2002年 | 396篇 |
2001年 | 338篇 |
2000年 | 293篇 |
1999年 | 245篇 |
1998年 | 228篇 |
1997年 | 169篇 |
1996年 | 143篇 |
1995年 | 133篇 |
1994年 | 124篇 |
1993年 | 84篇 |
1992年 | 76篇 |
1991年 | 51篇 |
1990年 | 46篇 |
1989年 | 34篇 |
1988年 | 35篇 |
1987年 | 17篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
Konstantin Karaghiosoff Prof. Dr. Thomas M. Klapötke Prof. Dr. Carles Miró Sabaté Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(5):1164-1176
Methylation of 5-amino-1H-tetrazole ( 1 ) gives 1-methyl-5-amino-1H-tetrazole ( 2 ) and 2-methyl-5-amino-1H-tetrazole ( 3 ). A new family of energetic silver complexes based on ligands 1 , 2 and 3 with perchlorate and nitrate anions ( 10 – 15 ) were synthesized and characterized by using IR, Raman, and NMR (1H, 13C, 14N, and 35Cl NMR) spectroscopy, elemental analysis, and mass spectrometry. The crystal structures of the compounds were determined where possible and reveal interesting structural details that are discussed herein. Additionally, differential scanning calorimetry was used to assess the thermal stability of the new salts, which showed excellent thermal stabilities at temperatures up to and above 225 °C. Standard tests were also used to assess the sensitivity of the materials towards impact and friction. All the silver complexes showed increased sensitivity values in comparison with analogous protonated 5-amino-1H-tetrazolium perchlorate and nitrate salts. Some of these materials have sensitivity values that are comparable to commonly used primary explosives and all of them either deflagrate ( 12 – 14 ) or detonate loudly ( 10 and 11 ) on contact with an open flame. Lastly, nitrate salt 11 is easily initiated by thermal shock. It shows reasonably low sensitivity in comparison with other silver salts (e.g., silver azide or silver fulminate), which makes handling it much less hazardous. Compound 11 also has good thermal stability, decomposing at ≈300 °C, and shows interesting properties as a more environmentally benign alternative to lead(II) diazide in initiation devices for civil and military applications. 相似文献
952.
Intermolecular interactions in a synthesized C-acid, 4-nitrophenyl[bis(ethylsulfonyl)]methane have been analysed and its structure determined by X-ray diffraction. The molecular packing in the crystal is governed by CH…O. The dimensions of the hydrogen bonds and the shortest non-bonded distances are also determined. The possible implications in the formation of the hydrogen bonded complexes with the strong organic bases are also discussed. 相似文献
953.
954.
I. Bartoš 《Surface science》2009,603(2):369-1009
Photoemission multiple scattering theory is used to describe the electron transport in the surface region of a crystal. Intensities of photoemission from core levels of atoms situated in subsurface atomic layers are calculated as a function of the emitter distance from the surface. The electron angle resolved attenuation length (ARAL) is extracted from the exponential fitting of the intensity decays of photoemission into different directions. Substantial anisotropy of the electron ARAL is found for the Cu(1 1 1) surface in Mg Kα photoexcitation of Cu 2p3/2 levels and correlated with the orientation of highly packed atomic rows. Enhanced photoemission contributions from specific subsurface layers, caused by electron forward focusing effects, are reported. 相似文献
955.
Well-ordered clean InAs(1 1 1) A and B surfaces have been prepared using HCl-isopropanol solutions and characterized using low-energy electron diffraction and photoemission spectroscopy. The as-treated surfaces are covered by a layer containing arsenic and small amounts of InClx. Annealing induces desorption of the overlayer and reveals (2 × 2) and (1 × 1) structures on the A and B surfaces, respectively. For both surfaces, the surface components of the In 4d and As 3d reveal a charge transfer from the electropositive surface indium to the electronegative surface arsenic. The major advantage of this preparation method over conventional thermal cleaning is a significant reduction in the annealing temperature (≈250 °C) thereby avoiding anion evaporation. 相似文献
956.
957.
ZHAO Xi LI Bin XU Shan-sheng SONG Hai-bin WANG Bai-quan State Key Laboratory of Elemento-Organic Chemistry College of Chemistry Nankai University Tianjin P. R. China 《高等学校化学研究》2009,(5)
η5-Pentamethylcyclopentadienyl-(η5-exo-tricyclo[5.2.1.02,6]deca-2,5,8-trien-6-yl) iron(3) was synthesized and characterized by 1H NMR, 13C NMR, MS, elemental analysis, IR, UV and X-ray diffraction analysis. Compound 3 was polymerized with ring-opening metathesis polymerization(ROMP) initiator (PCy3)2Cl2Ru=CHPh. 1H NMR and IR spectra revealed the presence of CH=CH units in the polymer and supported the ROMP mechanism. GPC analysis of the polymer showed that the weight-average molecular weights(Mw) was 5967, ... 相似文献
958.
X-ray diffraction experiments onp-dichlorobenzene at high pressures show a transition at ~ 0.3 GPa, to a new phase, the diffraction pattern of which cannot be indexed on the anticipated low temperature monoclinic crystal structure. We have instead found an orthorhombic cell, very closely related to the low temperature monoclinic cell, for this new phase. This structure, which also occurs inp-diiodobenzene at ambient conditions, has cell constantsa =14.02,b = 6.06,c = 7.41Å andZ = 4. The space group is Pbca. This new phase has a non-β herring-bone structure, in contrast with the initialα phase which has aβ-structure with ribbon-like arrangement of molecules, with Cl-Cl contacts of ~ 4A between adjacent molecules. This implies that with pressure the halogen-halogen interaction in this compound plays a less dominant role in crystal engineering. 相似文献
959.
Jorge Antonio Guerrero‐Álvarez Wendy Paloma Mas‐Ku Cesar Garcías‐Morales Armando Ariza‐Castolo 《Magnetic resonance in chemistry : MRC》2010,48(5):356-361
The relative acidities of the cis and trans isomers of a series of 1,5‐oxazaspiro[5.5]undecane derivatives were determined by measuring ΔpK in acid‐base titrations followed by 1 H NMR. Relative structural stabilities were determined by measuring substituent chemical shift and γ‐gauche effects in 13C, 15N, and 17O NMR. Crystallographic characterization of a model spiro[5.5]undecane is presented to support the basicity in solid state. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
960.
Any solid state X-ray photoelectron spectrum (XPS) contains contributions due to multiple inelastic scattering in the bulk, surface excitations, energy losses originating from the screening of the final state hole (intrinsic losses), and, for non-monochromatized incident radiation, ghost lines originating from the X-ray satellites. In the present paper it is shown how all these contributions can be consecutively removed from an experimental spectrum employing a single general deconvolution procedure. Application of this method is possible whenever the contributions mentioned above are uncorrelated. It is shown that this is usually true in XPS to a good approximation. The method is illustrated on experimental non-monochromatized MgK spectra of Au acquired at different detection angles but for the same angle of incidence of the X-rays. 相似文献