全文获取类型
收费全文 | 81577篇 |
免费 | 410篇 |
国内免费 | 394篇 |
专业分类
化学 | 26497篇 |
晶体学 | 840篇 |
力学 | 6779篇 |
数学 | 32153篇 |
物理学 | 16112篇 |
出版年
2020年 | 44篇 |
2019年 | 51篇 |
2018年 | 10455篇 |
2017年 | 10287篇 |
2016年 | 6102篇 |
2015年 | 902篇 |
2014年 | 345篇 |
2013年 | 509篇 |
2012年 | 3925篇 |
2011年 | 10672篇 |
2010年 | 5729篇 |
2009年 | 6150篇 |
2008年 | 6768篇 |
2007年 | 8946篇 |
2006年 | 440篇 |
2005年 | 1479篇 |
2004年 | 1641篇 |
2003年 | 2094篇 |
2002年 | 1151篇 |
2001年 | 345篇 |
2000年 | 403篇 |
1999年 | 229篇 |
1998年 | 237篇 |
1997年 | 190篇 |
1996年 | 262篇 |
1995年 | 165篇 |
1994年 | 112篇 |
1993年 | 137篇 |
1992年 | 119篇 |
1991年 | 106篇 |
1990年 | 93篇 |
1989年 | 100篇 |
1988年 | 120篇 |
1987年 | 106篇 |
1986年 | 110篇 |
1985年 | 112篇 |
1984年 | 105篇 |
1983年 | 66篇 |
1982年 | 84篇 |
1981年 | 77篇 |
1980年 | 89篇 |
1979年 | 85篇 |
1978年 | 71篇 |
1977年 | 62篇 |
1975年 | 51篇 |
1974年 | 43篇 |
1973年 | 49篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
991.
In the EURACHEM/CITAC draft ”Quantifying uncertainty in analytical measurement” estimations of measurement uncertainty in
analytical results for linear calibration are given. In this work these estimations are compared, i.e. the uncertainty deduced
from repeated observations of the sample vs. the uncertainty deduced from the standard residual deviation of the regression.
As a result of this study it is shown that an uncertainty estimation based on repeated observations can give more realistic
values if the condition of variance homogeneity is not correctly fulfilled in the calibration range. The complete calculation
of measurement uncertainty including assessment of trueness is represented by an example concerning the determination of zinc
in sediment samples using ICP-atomic emission spectrometry.
Received: 9 February 2002 Accepted: 17 April 2002 相似文献
992.
Aamer Saeed 《Chemistry of Heterocyclic Compounds》2007,43(8):1072-1075
An efficient, rapid, microwave-accelerated one-step synthesis of some 5-aryl-2-(2-hydroxy-phenyl)-1,3,4-oxadiazoles by reaction
of salicylic hydrazide with carboxylic acids in the presence of thionyl chloride under neat conditions is described.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1264–1267, August, 2007. 相似文献
993.
Stéphanie Etienne C. Becker D. Ruch B. Grignard G. Cartigny C. Detrembleur C. Calberg R. Jerome 《Journal of Thermal Analysis and Calorimetry》2007,87(1):101-104
Silica nanoparticles of various sizes have
been incorporated by melt compounding in a poly(methyl methacrylate) (PMMA)
matrix to enhance its thermal and mechanical properties. In order to improve
nanoparticles dispersion, PMMA grafted particles have been prepared by atom
transfer radical polymerization (ATRP) from well-defined silica nanoparticles.
This strategy was expected to ensure compatibility between both components
of the PMMA nanocomposites. TEM analysis have been performed to evaluate the
nanosilica dispersion whereas modified and non-modified silica/PMMA nanocomposites
thermal stability and mechanical properties have been investigated by both
thermogravimetric and dynamical mechanical analysis. 相似文献
994.
Yasuhiro Takahashi Yusuke Ozaki Minoru Takase W. R. Krigbaum 《Journal of Polymer Science.Polymer Physics》1993,31(9):1135-1143
Redetermination of the crystal structure of poly(p-benzamide) was made by using newly collected intensity data. The molecular conformation is TCTC, where the internal rotation angles about the N? C bond of the amide group and about the virtual bond of N-phenyl-C are T (trans) and C (cis) conformations, respectively. Two molecular chains pass through a rectangular unit cell with dimension, a = 7.75 Å, b = 5.30 Å, c (fiber axis) = 12.87 Å, and the space group, P212121-D. The reflection observed at the spacing of 010 may be attributed to the reflection due to another crystal polymorph or the diffuse scattering due to disorder. © 1993 John Wiley & Sons, Inc. 相似文献
995.
Koichi Shiomi Masao Shimono Hiromi Arimoto Seiji Takahashi 《Journal of separation science》1991,14(11):729-737
A slightly modified, commercially available high resolution capillary gas chromatograph and a PC-based data processing system running proprietary software (“PONA”) have been employed in the development of a system for petroleum type analysis which would be equivalent or superior to the FIA (fluorescent indicator adsorption) method in terms of ease of use and the speed, variety, and accuracy of the analytical data produced. The system is capable of performing identification and quantitation of most of the individual components in a complex gasoline sample consisting of more than 230 components and can report weight percentage and/or volume percentage for each component as well as types by carbon number (e.g., isoparaffins, normal paraffins, olefins, naphthenes, aromatic compounds) within a ca. 70 minute analysis cycle. Precolumn sulfonation to trap olefins and aromatic compounds has been used as an complementary technique to the basic mass spectrometric identification of components of interest. The estimation of correction factors for weight percentage (or volume percentage) calculation are also discussed. Comparisons are made between this system and others, and the results indicate that the proposed method supersedes the conventional method employing FIA. 相似文献
996.
The relativistic ground and low-lying excited state potential energy curves of AgH and AuH in the presence of a cylindrical
harmonic confining potential were calculated using the multi-state multi-reference perturbation theory with the spin-free
no-pair Hamiltonian obtained via the third-order Douglas–Kroll transformation, incorporated with the full two-electron Breit–Pauli
spin–orbit operator. The spectroscopic parameters were obtained for both the scalar- and quasi-relativistic potentials. The
spin–orbit coupling constants were calculated for several strengths of the confining potential, and the effects of the applied
potential on the coupling constants were analyzed using configuration interaction.
This paper is dedicated to Serafín Fraga—colleague, mentor, and friend. 相似文献
997.
The boundary effect on the drag on two identical, nonuniformly structured flocs moving along the axis of a cylindrical tube
filled with a Newtonian fluid is investigated at a small to medium larger Reynolds number. A two-layer model is adopted to
simulate various possible structures of a floc, and the flow field inside is described by Darcy–Brinkman model. The results
of numerical simulation reveal that a convective flow is present in the rear region of a floc when Reynolds number is on the
order of 40. The presence of the tube wall and/or the porous structure of a floc has the effect of reducing that convective
flow. For a fixed level of the volume-average permeability of a floc, the influence of the tube wall on the drag depends upon
floc structure; the influence on a nonuniformly structured floc is more significant than that on a uniformly structured floc.
The more nonuniform the floc structure, the more appreciable the deviation of the drag coefficient–Reynolds number curve from
a Stokes’-law-like relation becomes. The smaller the volume-average permeability of a floc and/or the smaller the separation
distance between the two flocs, the greater is the deviation, but the presence of the tube wall has the effect of reducing
that deviation. 相似文献
998.
Antonio Doménech María Teresa Doménech-Carbó María Luisa Vázquez de Agredos Pascual 《Journal of Solid State Electrochemistry》2007,11(9):1335-1346
The preparation of indigo from Indigofera suffruticosa following the procedures attributed to ancient Mayas was electrochemically monitored using the voltammetry-of-microparticles
approach. The mechanism formation of indigotin and indirubin from its precursors, indican and isatan, is discussed. Comparison
of voltammetric profiles for differently prepared and commercial indigos and genuine Maya Blue samples suggests that the preparation
procedure of indigo changed during the Late Classical Maya period.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
999.
M. H. Wang Y. Sawada K. Saito S. Horie T. Uchida M. Ohtsuka S. Seki S. Kobayashi T. Arii A. Kishi T. Takahashi Y. Nishimoto T. Wakimoto K. Monzen I. Kashima T. Nishikiori L. X. Sun R. Ozao 《Journal of Thermal Analysis and Calorimetry》2007,89(2):363-366
The thermal change of the tris(8-hydroxyquinolinato)aluminum (Alq3) is currently investigated by XRD-DSC and TG. The phase transition of Alq3 from α-phase to γ-phase takes place at 643–669 K. A very sharp peak with the peak temperature at approx. 709 K is ascribed
to the melting of the Alq3. The decomposition of the Alq3 was observed accompanied with the melting and evaporation at >703K. The effect of the atmospheres on the mass loss procedure
was studied by TG. It was found that thermal process of Alq3 was strongly influenced by the partial pressure of water vapor in the atmosphere instead of oxygen. 相似文献
1000.