全文获取类型
收费全文 | 59493篇 |
免费 | 1286篇 |
国内免费 | 316篇 |
专业分类
化学 | 34514篇 |
晶体学 | 645篇 |
力学 | 1830篇 |
综合类 | 11篇 |
数学 | 9636篇 |
物理学 | 14459篇 |
出版年
2023年 | 208篇 |
2022年 | 421篇 |
2021年 | 819篇 |
2020年 | 922篇 |
2019年 | 1073篇 |
2018年 | 1470篇 |
2017年 | 1548篇 |
2016年 | 2249篇 |
2015年 | 1357篇 |
2014年 | 2009篇 |
2013年 | 3633篇 |
2012年 | 3623篇 |
2011年 | 4165篇 |
2010年 | 3063篇 |
2009年 | 2857篇 |
2008年 | 3878篇 |
2007年 | 3844篇 |
2006年 | 3570篇 |
2005年 | 2913篇 |
2004年 | 2334篇 |
2003年 | 1810篇 |
2002年 | 1693篇 |
2001年 | 735篇 |
2000年 | 1019篇 |
1999年 | 721篇 |
1998年 | 796篇 |
1997年 | 799篇 |
1996年 | 620篇 |
1995年 | 392篇 |
1994年 | 340篇 |
1993年 | 289篇 |
1992年 | 292篇 |
1991年 | 256篇 |
1990年 | 230篇 |
1989年 | 222篇 |
1988年 | 246篇 |
1987年 | 215篇 |
1985年 | 364篇 |
1984年 | 357篇 |
1983年 | 259篇 |
1982年 | 329篇 |
1981年 | 337篇 |
1980年 | 312篇 |
1979年 | 289篇 |
1978年 | 271篇 |
1977年 | 235篇 |
1976年 | 215篇 |
1975年 | 216篇 |
1974年 | 222篇 |
1973年 | 220篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
Marie-Noelle Avettand-Fènoël N. David G. Reumont J. -M. Fiorani M. Vilasi P. Perrot 《Journal of Thermal Analysis and Calorimetry》2007,90(2):329-332
The Fe-Sn-Zn system is of interest because Sn is one element added to the Zn galvanizing bath to overcome the drawbacks due
to the presence of Si in semi-killed steels. This work has been undertaken with the aim to understand the tin effect on the
microstructure and the layers growth in batch galvanized coatings on low alloyed steels.
Various experimental techniques such as metallography, scanning electron microscopy (SEM) coupled with X-ray energy dispersive
spectroscopy (EDX) are used in order to characterize the microstructure and the properties of such coatings elaborated in
a zinc bath enriched with tin.
Solidification phenomena and layers growth mechanisms during galvanization are explained by means of the ternary phase diagram
Fe-Sn-Zn at 450°C. The Calphad method allows to obtain this phase diagram from the three optimized binary phase diagrams Fe-Sn,
Fe-Zn and Sn-Zn and some experimental data inside the ternary Fe-Sn-Zn system. 相似文献
952.
L. A. Kochergina V. P. Vasil’ev D. V. Krutov O. N. Krutova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(2):182-186
The heat effects of interaction of a solution of citric acid with HNO3 and KOH were measured calorimetrically at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 (KNO3). The heat effects of acid dissociation were calculated using the universal HEAT program. The standard thermodynamic characteristics of step dissociation of citric acid were determined. 相似文献
953.
[reaction: see text] Phenyl 4,6-di-O-benzyl-2,3-O-carbonyl-beta-D-glucothiopyranoside and the regiosiomeric phenyl 2,6-di-O-benzyl-3,4-O-carbonyl-beta-D-glucothiopyranoside were prepared and studied as glucosyl donors at -60 degrees C in dichloromethane with preactivation by 1-benzenesulfinyl piperidine before addition of the acceptor alcohol. The 2,3-O-carbonate protected donor showed moderate to excellent beta-selectivity under these conditions depending on the acceptor employed, thereby providing a means for 1,2-trans-equatorial glycosidic bonds without recourse to neighboring group participation and its associated problem of ortho ester formation. In contrast, the 3,4-O-carbonate protected donor showed moderate to no beta-selectivity under the conditions employed. The results obtained in this study with carbonate protected glucopyranosyl donors are contrasted with those obtained previously in the manno- and rhamnopyranosyl series when the 2,3-O-carbonate protected is alpha-selective and the 3,4-O-carbonate is beta-selective. 相似文献
954.
Ohsuna T Slater B Gao F Yu J Sakamoto Y Zhu G Terasaki O Vaughan DE Qiu S Catlow CR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):5031-5040
High-resolution electron microscopy (HREM) has been used to image the surface structure of nano- and micrometer-sized synthetic crystals of zeolite-Linde-L (LTL). Columnar holes and rotational, nano-sized, wheel-like defects were observed within the crystals, where the hole has a minimum size equal to that of the rotational defect. Predictions of surface structure from atomistic computer simulation concur with the observations from HREM and provide insight into the crystal growth mechanism of perfect and defective LTL. Analysis of the energetics of the formation of rotational defect structures reveals that the driving force for defect creation is thermodynamic and furthermore, the rotational defects could be created in high concentrations. Formation of a columnar hole is found to be slightly energetically unfavourable and therefore we speculate that the incidence of both rotational and nano-sized vacancy defects is strongly dependent on kinetic factors and reaction conditions. The morphology of nano- and microcrystalline LTL is contradistinct and we use insights from simulation to propose an explanation of the disparity in crystal shape. 相似文献
955.
Mulligan A Lane I Rousseau GB Hecht L Johnston SM Lennon D Kadodwala M 《Chemical communications (Cambridge, England)》2004,(21):2492-2493
Using a novel non-linear optical technique enantiomeric excess within a translationally disordered overlayer on a metal surface has been monitored for the first time. 相似文献
956.
957.
Philippe Gerbier Daniel Ruiz-Molina Neus Domingo David B. Amabilino José Vidal-Gancedo Javier Tejada David N. Hendrickson Jaume Veciana 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):265-276
Summary. A new modified approach for the synthesis of Mn12 clusters, based on the use of complex [Mn12O12(O2C
t
Bu)16(H2O)4] (2) as starting material to promote the acidic ligand replacement, is presented here. This new synthetic approach allowed us
to obtain complex [Mn12O12(O2CC6H4N(O•)
t
Bu)16(H2O)4] (3), whose preparation remained elusive by direct replacement of the acetate groups of Mn12Ac (1). Complex 3 bearing open-shell radical units, was prepared to increase the total spin number of its ground state, and consequently, to
increase T
B
, with the expectation that the radical ligands may couple ferromagnetically with the Mn12 core. Unfortunately, magnetic measurements of complex 3 revealed that the sixteen radical carboxylate ligands interact antiferromagnetically with the Mn12 core to yield a S = 2 magnetic ground state.
Corresponding author. E-mail: vecianaj@icmab.es
Received March 27, 2002; accepted May 2, 2002 相似文献
958.
Young PM Price R Lewis D Edge S Traini D 《Journal of colloid and interface science》2003,262(1):298-302
Drug particulate interactions in pressurized metered dose inhalers (pMDI) may lead to a decrease in aerosolization efficiency and subsequent efficacy in patient treatment. The interactions between salbutamol sulfate (commonly used in Ventolin pMDIs) and a series of pMDI canister materials were investigated using the atomic force microscope (AFM) colloid probe technique. Approximately 4000 individual force-distance curves were determined for a drug probe and three surfaces (10 x 10 mum areas) in situ, in a model propellant. The area under each force-distance curve was integrated to obtain separation energy values. Median separation energy values followed the rank order borosilicate glass > aluminum > PTFE, suggesting PTFE to be the most suitable canister coating. 相似文献
959.
Condensation of allylborane reagents 9 and 12 with aldehydes gave anti-3-[(diphenylmethylene)amino]-1-alken-4-ols 10 and 13 with high relative and absolute stereocontrol. Subsequent deprotection gave the corresponding free anti-3-amino-1-alken-4-ols 11 and 14. Alternatively, reaction of imines 13a, 13f, and 13g with trifluoromethanesulfonic anhydride and acidic methanol gave, via rearrangement, double inversion, and hydrolysis, the isomeric anti-4-amino-1-alken-3-ols 22, 38a, and 38b in good yield. The stereochemistry of the rearrangement products has been established by a single crystal X-ray study of compound 37 and by chemical correlation. 相似文献
960.
N. A. El’tekova Yu. A. El’tekov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(2):243-248
The isotherms of adsorption of benzene, anisole, benzyl alcohol, and benzaldehyde on the surface of microspherical mesoporous crosslinked cellulose were calculated from the chromatographic peaks of these compounds with consideration given to the longitudinal smearing of the analyte zone under the action of adsorption forces. The solvents were n-heptane-isopropanol mixtures containing various amounts of isopropanol (up to 2 vol %). The adsorption isotherms were described using equations of the displacement adsorption theory. The mechanism of the sorption of aromatic compounds and the physical meaning of the constants entering into the adsorption isotherm equation were discussed. 相似文献