全文获取类型
收费全文 | 1575篇 |
免费 | 232篇 |
国内免费 | 296篇 |
专业分类
化学 | 991篇 |
晶体学 | 57篇 |
力学 | 502篇 |
综合类 | 36篇 |
数学 | 276篇 |
物理学 | 241篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 39篇 |
2021年 | 55篇 |
2020年 | 89篇 |
2019年 | 51篇 |
2018年 | 57篇 |
2017年 | 58篇 |
2016年 | 79篇 |
2015年 | 85篇 |
2014年 | 84篇 |
2013年 | 124篇 |
2012年 | 90篇 |
2011年 | 91篇 |
2010年 | 62篇 |
2009年 | 76篇 |
2008年 | 100篇 |
2007年 | 104篇 |
2006年 | 95篇 |
2005年 | 102篇 |
2004年 | 75篇 |
2003年 | 104篇 |
2002年 | 70篇 |
2001年 | 51篇 |
2000年 | 41篇 |
1999年 | 47篇 |
1998年 | 47篇 |
1997年 | 45篇 |
1996年 | 23篇 |
1995年 | 20篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 27篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1971年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有2103条查询结果,搜索用时 15 毫秒
31.
Z. Mikulová P. Čuba J. Balabánová T. Rojka F. Kovanda K. Jirátová 《Chemical Papers》2007,61(2):103-109
The effect of hydrothermal treatment on properties (crystallinity, porous structure, reducibility, acidity, basicity, and
catalytic activity and selectivity in toluene and ethanol total oxidation) of Ni—Al layered double hydroxide precursors and
related mixed oxides was examined. The hydrothermal treatment increased considerably both the content of crystalline phase
and LDH crystallite size. On the other hand, only a slight effect of the precursor hydrothermal treatment on crystallinity
of the related Ni—Al mixed oxides obtained by calcination at 450°C was observed. The reducibility of NiO particles appeared
to be hindered considerably compared to the reducibility of pure NiO. Catalytic activity of the Ni—Al mixed oxides prepared
from the precursors hydrothermally treated for a short time (4 h) was the highest. The highest amount of acetaldehyde formed
during the total oxidation of ethanol, i.e. the worst selectivity was found for the calcined Ni—Al LDH without hydrothermal treatment.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
32.
Anorgano modifiedMgAl layereddoublehydroxide (OMgAl LDH )wassuccessfullyexfoliatedinthexylenesolutionofpolyethylene grafted maleicanhydride (PE g MA )underre fluxingcondition .APE g MA/MgAl LDHexfoliationnano compositewasformedaftertheprecipitationofPE g MAfromthedispersionsystem .ThestructureandthermalpropertyofthePE g MA/MgAl LDHexfoliationnanocompositewerechar acterizedbyX raydiffraction (XRD ) ,transmissionelectronmicroscopy (TEM ) ,andthermogravimetryanalysis (TGA ) .The… 相似文献
33.
以Mn2O3和氢氧化锂为原料,通过焙烧合成出o-LiMnO2。用X射线衍射和扫描电镜对不同温度下合成的粉末样品进行了表征,并研究了材料的电化学性能。通过对不同温度条件下烧结样品的晶胞参数、布拉格(110)晶面峰半高宽及电化学性能研究发现:600 ℃下合成样品的半高宽最大,堆垛层错率高,同时电化学性能也最好,首次放电容量达到156 mAh·g-1,20次循环后仍保持在140 mAh·g-1以上。中高温固相合成的o-LiMnO2材料,在晶粒范围大小相近时,材料电化学性能与材料堆垛层错率相关。 相似文献
34.
M. Wei X. Y. Xu J. He G. Y. Rao H. L. Yang 《Journal of Thermal Analysis and Calorimetry》2006,85(3):795-800
Supramolecular 2,3- and 2,5-pyridinedicarboxylate (PDC) intercalated
ZnAl-layered double hydroxides (2,3- and 2,5-PDC–ZnAl–LDHs) have
been prepared by ion exchange method. The structure and composition of the
intercalated materials have been studied by X-ray diffraction (XRD) and inductively
coupled plasma emission spectroscopy (ICP). The study indicates that the 2,3-PDC
and 2,5-PDC anions are accommodated as interdigitated bilayer and monolayer
arrangement respectively between the sheets of LDHs. Furthermore, their thermal
decomposition processes were studied by the use of in situ high temperature
X-ray diffraction (HT-XRD), and the combined technique of thermogravimetry-differential
thermal analysis-mass spectrometry (TG-DTA-MS) under N2 atmosphere. Based
on the comparison study on the temperatures of both decarboxylation and complete
decomposition of interlayer PDC, it can be concluded that 2,5-PDC–ZnAl–LDHs
has higher thermal stability than that of 2,3-PDC–ZnAl–LDHs. 相似文献
35.
O. N. Litvinenko A. N. Kuznetsov A. V. Olenev B. A. Popovkin 《Russian Chemical Bulletin》2007,56(10):1945-1947
Three new mixed tellurides of nickel and group 13–14 metals Ni3−δMTe2 (M = Sn, In, Ga) were prepared by high-temperature ampoule synthesis and studied by powder X-ray diffraction analysis. The
compound Ni3−δSnTe2 was also studied by single crystal X-ray diffraction analysis. The structural model of this phase and two analogs was described
as consisting of layers with nickel-main group metal bonds confined from the above by tellurium atoms. The van der Waals gap
formed through contacts between the tellurium atoms of neighboring layers is partially occupied by nickel atoms.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1879–1881, October, 2007. 相似文献
36.
W. Schwieger U. Brenn P. Grabner H. Utschick 《Journal of Thermal Analysis and Calorimetry》1998,52(1):21-32
Aluminium-free layered silicates of the metal silicate hydrate type (M-SH) comprise an interesting supplement to the well-known zeolite-like porous materials. Their specific properties allow these materials to be used as catalysts, adsorbents and ion-exchangers. Comparative X-ray diffraction and thermoanalytical investigations (TG and DSC) have shown that the thermoanalytical methods are useful to follow the process of structure formation of ilerite. The interlayer cations influence the properties of the different ilerites. In particular, the hydration behaviour of ilerite is affected. Thus, H+- and DTMA+-ilerite are stable up to temperatures of about 800°C, while the as-synthesized Na-form loses water irreversibly at about 150°C, is dehydroxylated, and is then desomposed structurally at about 400°C. The course of the dehydration exhibits significant differences for the various cation forms.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
37.
A new layered aluminophosphate, denoted AlPO-CJ12, has been synthesized in the system Al(OPri)3-H3PO4-tetramethylethylenediamine-triethyleneglycol and its structure solved by single-crystal X-ray diffraction analysis. It is further characterized by X-ray powder diffraction, ICP, TG, DTA, and elemental analyses. The compound has an empirical formula of [Al3P4O16][(CH3)2NHCH2CH2NH(CH3)2][H3O], and crystallizes in the triclinic space group P-1 (No. 2) with a=8.9907(6) Å b=9.8359(6) Å, c=14.5566(8) Å, α=75.872(3)°, β=88.616(3)°, γ=63.404(3)°, Z=2, R1=0.0451, and wR2=0.1094. The alternation of tetrahedral AlO4 and PO3 (=O) units forms a sheet structure with a 4×6×8 network. The inorganic layers stacked in an AAAA sequence are held together by the protonated organic amine and water molecules. The co-templating role of the water molecules is studied by the calculation of the nonbonding host-guest interaction energies through a computational simulation. 相似文献
38.
An inorganic-organic hybrid thioantimonate(Ⅲ) [CH3(CH2)3NH3]2Sb4S7 1 with layered structure was synthesized by solvothermal method.1 crystallizes in the triclinic system, space group P with a = 7.0124(11), b = 11.919(2), c = 14.879(3) (A), α = 108.791(3), β = 102.441(3), γ = 92.846(2)o, V = 1140.1(3) (A)3, Mr = 859.71, Z = 2, Dc = 2.504 g/cm3, μ= 5.324 mm-1, F(000) = 804, S = 1.013, the final R = 0.0297 and wR = 0.0618 for 3534 observed reflections with I>2σ(I). 1 consists of [C4H9NH3] cations and two-dimensional [Sb4S7]n2n-anion which is composed of three SbS3 trigonal pyramids and one SbS4 unit joined by sharing common corners. The anionic layers are stacked perpendicularly to the c axis of the unit cell forming two-dimensional channels between the layers. The [C4H9NH3] cations interdigitate in a bilayer and reside in the 2D channels leading to a sandwich-like arrangement of the anion and cations. 相似文献
39.
Kjell Ove Kongshaug 《Journal of solid state chemistry》2004,177(6):1852-1857
The two organically pillared layered zinc hydroxides [Zn2(OH)2(ndc)], CPO-6, and [Zn3(OH)4(bpdc)], CPO-7, were obtained in hydrothermal reactions between 2,6-naphthalenedicarboxylic acid (ndc) and zinc nitrate (CPO-6) and 4,4′biphenyldicarboxylate (bpdc) and zinc nitrate (CPO-7), respectively. In CPO-6, the tetrahedral zinc atoms are connected by two μ2-OH groups and two carboxylate oxygen atoms, forming infinite layers extending parallel to the bc-plane. These layers are pillared by ndc to form a three-dimensional structure. In CPO-7, the zinc hydroxide layers are containing four-, five- and six coordinated zinc atoms, and the layers are built like stairways running along the [001] direction. Each step is composed of three infinite chains running in the [010] direction. Both crystal structures were solved from conventional single crystal data. Crystal data for CPO-6: Monoclinic space group P21/c (No. 14), a=11.9703(7), b=7.8154(5), c=6.2428(4) Å, β=90.816(2)°, V=583.97(6) Å3 and Z=4. Crystal data for CPO-7: Monoclinic space group C2/c (No. 15), a=35.220(4), b=6.2658(8), c=14.8888(17) Å, β=112.580(4)°, V=3033.8(6) Å3 and Z=8. The compounds were further characterized by thermogravimetric- and chemical analysis. 相似文献
40.
Yasuhiro Ono Ryuji IshikawaYuzuru Miyazaki Yoshinobu IshiiYukio Morii Tsuyoshi Kajitani 《Journal of solid state chemistry》2002,166(1):177-181
The layered oxide thermoelectric material β-Na0.67CoO2 has been studied by powder neutron diffraction, electric and magnetic measurements. This compound includes an edge-sharing CoO6 slab and a highly vacant Na+ sheet in a unit cell (space group symmetry C2/m, a=4.9023(4) Å, b=2.8280(2) Å, c=5.7198(6) Å and β=105.964(6)° at 300 K). The evaluated formal valence of cobalt ion, +3.33(1), is ascribed to the coexistence of Co3+ and Co4+ in the ratio 2:1. Polycrystalline β-Na0.67CoO2, a p-type thermoelectric material, exhibits metallic behavior of the electric resistivity below 300 K. The Curie-Weiss-type magnetic susceptibility indicates antiferromagnetic interactions between magnetic cobalt ions in the edge-sharing CoO6 slab. 相似文献