全文获取类型
收费全文 | 2538篇 |
免费 | 92篇 |
国内免费 | 17篇 |
专业分类
化学 | 1658篇 |
晶体学 | 9篇 |
力学 | 52篇 |
数学 | 486篇 |
物理学 | 442篇 |
出版年
2023年 | 24篇 |
2022年 | 23篇 |
2021年 | 74篇 |
2020年 | 72篇 |
2019年 | 58篇 |
2018年 | 53篇 |
2017年 | 56篇 |
2016年 | 101篇 |
2015年 | 80篇 |
2014年 | 87篇 |
2013年 | 203篇 |
2012年 | 207篇 |
2011年 | 211篇 |
2010年 | 122篇 |
2009年 | 102篇 |
2008年 | 154篇 |
2007年 | 164篇 |
2006年 | 149篇 |
2005年 | 106篇 |
2004年 | 101篇 |
2003年 | 79篇 |
2002年 | 76篇 |
2001年 | 27篇 |
2000年 | 24篇 |
1999年 | 31篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 3篇 |
排序方式: 共有2647条查询结果,搜索用时 15 毫秒
191.
Ricardo Alcántara Pedro Lavela Gregorio Ortiz Inés Rodríguez José L. Tirado 《Hyperfine Interactions》2008,187(1-3):13-17
Cobalt–tin intermetallic compounds with different particle size have been obtained and characterized by using 119Sn Mössbauer spectroscopy as a main tool. The electrochemical behavior of the Co–Sn compounds has been evaluated in lithium test cells. The Lamb–Mössbauer factors for CoSn with different crystallite sizes have been calculated. The results f nano???CoSn(300 K) = 0.19 and f coarse???CoSn(300 K) = 0.55 are obtained. Nano-CoSn exhibits larger capacity to react with lithium than coarse-CoSn. 相似文献
192.
Patricia G. Belelli Ricardo M. Ferullo Norberto J. Castellani 《Surface science》2010,604(3-4):386-395
In this work, the adsorption of several unsaturated hydrocarbon molecules on a stepped Pd(4 2 2) surface was studied. Using a periodic method based on the Density Functional Theory (DFT) formalism, different adsorption geometries for ethylene, three butene isomers (cis/trans-2-butene and 1-butene), acetylene and 2-butyne were investigated. The results were compared with those obtained for a free defect surface as Pd(1 1 1). The 1-butene is more stable on the free defect surface than on Pd(4 2 2). On the stepped surface, the olefins adsorb tilted towards the step and increases, in almost all the cases, the magnitude of the adsorption energy. Conversely, the 3-fold site is the most stable for the alkynes adsorption on the stepped surface, as it was found on Pd(1 1 1). The analysis of the dipole moment change indicate a charge transfer from the double bond of the olefin to the metallic surface, being higher for the Pd(1 1 1) surface. In case of the alkynes, an important back-donation is produced. Except the alkynes and the 1-butene molecule, the results show the preference of ethylene and cis/trans-2-butene to be adsorbed on the stepped surface. These observations are related with experimental catalytic results. 相似文献
193.
194.
de Souza Cabrini F. da Cunha Alessandra L. M. C. Auclio Ricardo Queiroz 《Chromatographia》2009,70(9-10):1461-1466
Micellar electrokinetic capillary chromatography was used for the determination of picoxystrobin and pyraclostrobin. The background electrolyte consisted of borate buffer (40 mmol L−1 pH 8.5), SDS (30 mmol L−1) and acetonitrile (15% in volume). Runs were made at 25 °C with 25 kV applied potential. The developed method was applied to analyte fortified urine samples. On-line analyte concentration, combined with a capillary of a longer optical path length, allowed limits of quantification of 8.6 × 10−8 mol L−1 for picoxystrobin and 1.8 × 10−7 mol L−1 for pyraclostrobin.
相似文献195.
Hypotheses from elasticity theory were used for modeling stress distribution in a semi-infinite-homogeneous medium when a point load was applied on its surface. A Concentration factor coefficient was introduced to adapt the equations to the characteristics of the investigated soil. An expression for continuous load distributions and variations in the geometry of the contact area between soil and tire were obtained by means of the superposition principle. Some simulations for different areas and load distributions are discussed and compared with field measurements. 相似文献
196.
197.
198.
Time and temperature induced phase transformation in L‐isoleucine hydrochloride monohydrated crystal
Ricardo S. Ferreira Júnior Geanso M. Moura Andreia C. Pereira Paulo R. da Silva Ribeiro Luzeli M. da Silva Adenilson O. dos Santos 《Crystal Research and Technology》2016,51(12):738-741
Semi organic crystals have been intensively studied aiming applications in nonlinear optical (NLO). Such applicability requires crystals with both high quality and thermal stability, which make the full characterization of this material a topic issue. In this paper, single crystals of L‐isoleucine hydrochloride monohydrated (L‐Ile.H2O.HCl) was synthesized by slow evaporation technique and characterized by thermal analysis and X‐ray diffraction (XRD) measurements. XRD results at 298 K showed that the sample crystallize with the orthorhombic structure, and the lattice parameters obtained by Rietveld refinement were a = 5.873(3) Å, b = 24.814(4) Å, and c = 6.873(5) Å. Thermal analysis measurements shows four decomposition stages between 328 ‐480 K which were associated with loss of water by desolvation, loss crystallization water and decomposition of L‐Ile.HCl. XRD measurements as a function of temperature up to 428 K show an irreversible phase transformation. This transformation was obtained after 32 hours keeping the L‐Ile.HCl.H2O sample at 413 K. The analysis shows that phase transformation occurs due to water and chlorine losses without destroy the amino acid carbon chain and in the end of transformation only the precursor amino acid remains. L‐Ile.HCl.H2O present low thermal stability and the phase transformation is time and temperature dependent. 相似文献
199.
José Ricardo Cammarata Rocío Rivera Franmerly Fuentes Yomaira Otero Edgar Ocando-Mavárez Alejandro Arce Juan M. Garcia 《Tetrahedron letters》2017,58(43):4078-4081
An air stable copper(I)-phosphole complex, [CuCl{2,5-bis(2-thienyl)-1-phenylphosphole}2] (1), was utilized as a catalyst in single and double A3-coupling reactions for preparing mono- and bi-propargylamines. A variety of aldehydes, amines and terminal alkynes were tested. Most of these reactions led to formation of the expected propargylamines in good yields using low amounts catalyst and obviating both the use of purified reagents as employ of a glovebox. 相似文献
200.
Processes and products have by nature many quality characteristics that must be in some sense optimized simultaneously. With this aim, a method which can be used easily and efficiently by practitioners for optimizing multi‐response problems is proposed. Implementation steps and considerations, in addition to optimization measures to assess method's solutions and guide the analyst in finding an effective compromise solution, are also presented. Three classical examples from the literature are used to assess the performance of several prominent methods in the response surface methodology (RSM) framework and help practitioners make a better‐informed choice among them. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献