全文获取类型
收费全文 | 22644篇 |
免费 | 2695篇 |
国内免费 | 4386篇 |
专业分类
化学 | 18995篇 |
晶体学 | 2626篇 |
力学 | 548篇 |
综合类 | 91篇 |
数学 | 282篇 |
物理学 | 7183篇 |
出版年
2024年 | 46篇 |
2023年 | 174篇 |
2022年 | 501篇 |
2021年 | 529篇 |
2020年 | 672篇 |
2019年 | 659篇 |
2018年 | 651篇 |
2017年 | 791篇 |
2016年 | 1008篇 |
2015年 | 807篇 |
2014年 | 1194篇 |
2013年 | 2317篇 |
2012年 | 1298篇 |
2011年 | 1290篇 |
2010年 | 1202篇 |
2009年 | 1323篇 |
2008年 | 1428篇 |
2007年 | 1529篇 |
2006年 | 1589篇 |
2005年 | 1450篇 |
2004年 | 1471篇 |
2003年 | 1131篇 |
2002年 | 929篇 |
2001年 | 654篇 |
2000年 | 658篇 |
1999年 | 664篇 |
1998年 | 554篇 |
1997年 | 482篇 |
1996年 | 535篇 |
1995年 | 447篇 |
1994年 | 415篇 |
1993年 | 338篇 |
1992年 | 308篇 |
1991年 | 194篇 |
1990年 | 93篇 |
1989年 | 75篇 |
1988年 | 69篇 |
1987年 | 52篇 |
1986年 | 30篇 |
1985年 | 47篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Using infrared reflection absorption spectroscopy (IRRAS), quartz crystal microbalance (QMB) measurements, and X-ray photoelectron spectroscopy (XPS) in combination with chemical derivatization techniques the VUV photolysis of polyethylene (PE), polypropylene (PP), and polystyrene (PS) was investigated. A mass balance obtained from the quantification of the data was used to suggest reaction path ways. Although PE and PP behave similar, the mass loss is about 8 times higher in the case of PP. These differences originate from the higher disproportionation to recombination ratio for the branched polymer. Both polymers form double bonds and at extended treatment times they tend to crosslink. PS is rather stable due to the possibility of the energy dissipation by fluorescence. 相似文献
42.
Evert J. Ditzel Xavier L. R. Fontaine Norman N. Greenwood John D. Kennedy Mark Thornton-Pett 《无机化学与普通化学杂志》1992,616(10):79-85
The action of SMe2 on the ten-vertex nido-ruthenaborane [6-(η6-C6Me6)RuB9Hl3] ( 1 ) provides a high-yield route to the unsubstituted isocloso-ruthenaborane [1-(η6-C6Me6)RuB9H9] (2). The benzene analogue [1-(η6-C6Me6)RuB9H9] is prepared similarly. By contrast, reaction of (1) with PhNH2 gives a variety of B-phenylamino isocloso derivatives, including orange crystals of [1-(η6-C6Me6)-2-(PhNH)-isocloso-1-RuB 9 H8] ( 3 ), red-orange [1-(η6-C6Me6)-2,3-(PhNH)2-isocloso-1-RuB9H7] ( 4 ) and dark-red [1-(η6-C6Me6)-5,6,7-(PhNH)3-isocloso-1-RuB9H6] ( 5 ). Detailed 1H and 11B nmr properties of these various compounds are described. The structure of ( 3 ) has been established by a single-crystal X-ray diffraction study of the solvate [1-(η6-C6Me6)-2-(PhNH)-isocloso-1-RuB9H8] · 1/2 CH2Cl2; the crystals were monoclinic, space group C2/c, with a = 1895.1(3), b = 1556.6(3), c = 1716.4(3) pm, β = 104.37(1)° and z = 8. 相似文献
43.
The reaction of alkali metal hexacyanoferrate(II/III) with (CH2)6N4 (hexamethylenetetramine, abbreviated HMT) in an acidic medium yielded crystalline compounds of stoichiometries HK2[Fe111(CN)6]·2HMT·4H2O, H2K2[Fe11(CN)6]·2HMT·4H2O, and HNa2[Fe111(CN)6]· 2HMT·5H2O. Their crystal structures are based on a packing of three molecular components: neutral and/orprotonated HMT, hexacyanoferrate, and an alkali metal ion-water cluster. The resulting three-dimensional supramolecular framework is constructed from the coordination of the alkali metal ion by aqua ligands as well as [Fe(CN)6]{n–} and HMT units, and further stabilization is achieved by hydrogen bonding between water molecules and the noncoordinated nitrogen atoms of HMT and hexacyanoferrate. 相似文献
44.
I. V. Korol’kov A. I. Gubanov K. V. Yusenko I. A. Baidina S. A. Gromilov 《Journal of Structural Chemistry》2007,48(3):486-493
Several non-equilibrium solid solutions belonging to the platinum-osmium systems Os0.9Pt0.1, Os0.8Pt0.2, Os0.5Pt0.5, Os0.7Pt0.3, Os0.75Pt0.25 are prepared and studied. The thermal decomposition of [Pt(NH3)4][OsCl6] in the hydrogen and helium atmosphere is investigated. It is found that the Pt0.5Os0.5 solid solution develops through the formation of (NH4)2[OsCl6] and a metallic phase based on Pt. The crystal structure of a double complex salt [Pt(NH3)4][OsCl6] is studied (X8-APEX Bruker, 1508 independent reflections, R = 2.04%). Crystal data for PtOsN4Cl6H12 are: a = 11.6216(5) Å, b = 11.0016(5) Å, c = 10.3819(5) Å, V = 1327.4(1) Å3, space group Cmca, Z = 4, d x = 3.333 g/cm3. The coordination polyhedron around Os is octahedral: 〈Os-Cl〉 2.357 Å, ∠Cl-Os-Cl 89.5–90.5°, while around Pt it is square-planar: Pt-N 2.046 Å, ∠ N-Pt-N 89.59° and 90.41°. 相似文献
45.
O. LeynaudA. Lafond Y. MoëloP. Palvadeau A. Meerschaut 《Journal of solid state chemistry》2002,168(1):41-51
Crystal structures of two new misfit compounds, [SrGd0.5S1.5]1.16NbS2 and [Sr(Fe,Nb)0.5S1.5]1.13NbS2, were determined through the composite approach, i.e., by refining each subpart (Q, H-parts, and the common part) of these composite materials, separately. The Q-part is a three-atom-thick layer, with the NaCl-type structure, where external SrS planes enclose the inner GdS or (Fe,Nb)S plane; the structural difference between these two compounds lies in the central layer within the Q-part: Gd and S atoms are in special positions (octahedral coordination), while Fe and S atoms are statistically distributed on split (×4) positions (tetrahedral coordination) around a central unique site (=special position occupied by Nb). The H-part is a sandwich of sulfur planes enclosing the inner Nb plane as observed for the structure of the binary compound NbS2 itself. The Sr-Gd derivative shows a paramagnetic behavior in the whole studied temperature range (2-300 K). On the other hand, antiferromagnetic interactions occur in the Sr-Fe derivative; the complex magnetic behavior of this compound is related to the statistical distribution of Fe atoms which leads to frustration of the magnetic interactions. At room temperature, experimental values obtained from Mössbauer spectrum correspond to Fe3+ in tetrahedral sulfur environment: isomer shift δ=0.32 mm s−1, and quadrupole splitting ΔE=0.48 mm s−1. 相似文献
46.
A. M. Astakhov A. D. Vasiliev M. S. Molokeev L. A. Kruglyakova A. M. Sirotinin R. S. Stepanov 《Journal of Structural Chemistry》2004,45(3):537-540
The structure of 5-nitraminotetrazole sodium salt sesquihydrate was determined by X-ray diffraction. The crystals are monoclinic, space group P21/c;a = 3.551(1) Å, b = 21.834(4) Å, c = 9.075(2) Å; = 110.68(3)°; V = 658.3(2) Å3; Z = 4; calc = 1.807 g/cm3. The anion is planar and has an intramolecular hydrogen bond. The negative charge of the anion is localized on one of the oxygens of the nitro group. The sodium cation (c.n.6) is coordinated by three oxygen atoms of different anions and three oxygens of crystallization water. One of the crystallization water molecules is disordered in the unit cell. The anions are hydrogen-bonded with each other and with crystallization water molecules.Original Russian Text Copyright © 2004 by A. M. Astakhov, A. D. Vasiliev, M. S. Molokeev, L. A. Kruglyakova, A. M. Sirotinin, and R. S. StepanovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 562–565, May–June 2004. 相似文献
47.
D. M. Roitershtein K. A. Lyssenko P. A. Belyakov M. Yu. Antipin E. S. Petrov 《Russian Chemical Bulletin》1997,46(9):1590-1594
The reaction of the cyclopentadienyllutetium anthracenide, C5H5Lu(C14H10)2−(THF)2 (1), with azobenzene yielded the [C5H5(THF)Lu(μ−η2:η2−PhN—NPh)]2(THF)2 (2) binuclear complex. The structure of the reaction product was established by X-ray structural analysis. The dynamic behavior
of complex2 in a THF-d8 solution was studied by1H NMR spectroscopy in the temperature range of 265–330 K.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1667–1671, September, 1997. 相似文献
48.
D. Levy F. Del Monte X. Quintana J.M. Otón 《Journal of Sol-Gel Science and Technology》1997,8(1-3):1063-1066
Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass
dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals;
no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative
study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid
crystal microdroplets is presented. 相似文献
49.
Qian-Feng Zhang Yu-Jie Liu Richard D. Adams Alexander Rothenberger Dieter Fenske Wa-Hung Leung 《Journal of Cluster Science》2006,17(3):445-455
Treatment of tetracopper(I)-phosphonitocavitand [1·Cu4(μ-Cl)4(μ4-Cl)] (2) (1 = tetraphosphonitocavitand [rccc-2,8,14,20-tetrakis-(iso-butyl)-phosphonitocavitand (C44H48O8P4Ph4)]) with PhSeSiMe3 in THF at low temperature afforded a novel polyanionic cluster [pyH]6[(CuCl)9(μ3-SePh)5(μ4-SePh)] (4) as a major product along with a new tetracopper(I)-phosphonitocavitand (3) with a centered μ3-Cl. Molecular structure of anionic cluster in 4 consists of six PhSe− bridging ligands containing five μ3-SePh and one exceptional μ4-SePh bridging nine copper atoms, of which eight copper atoms have trigonal coordination geometry and the other has distorted
tetrahedral geometry.
Dedicated to Professor Han-Qin Liu on the occasion of his 70th birthday. 相似文献
50.
Structures with AIB2? and BaAl4?type Units. I The Compounds Sr4Pd5P5 and Sr2Pd3P3 Sr4Pd5P5 (Cmcm, a = 4.177(1) Å, b = 31.377(5) Å, c = 8.581(2) Å, Z = 4) und Sr2 Pd3P3(Pmmm, a = 4.199(1) Å, b = 4.212(1) Å, c = 34.227(4) Å, Z = 4) have been prepared by heating the elements. Both structures contain exclusively units characteristic for the AIB2? and BaAl4?type. The ratio between isolated P-atoms and P2?pairs is interpreted with an ionic splitting of the formulas. 相似文献