全文获取类型
收费全文 | 2381篇 |
免费 | 195篇 |
国内免费 | 529篇 |
专业分类
化学 | 2627篇 |
晶体学 | 97篇 |
力学 | 26篇 |
综合类 | 7篇 |
数学 | 2篇 |
物理学 | 346篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 47篇 |
2021年 | 57篇 |
2020年 | 74篇 |
2019年 | 79篇 |
2018年 | 56篇 |
2017年 | 74篇 |
2016年 | 103篇 |
2015年 | 99篇 |
2014年 | 126篇 |
2013年 | 263篇 |
2012年 | 161篇 |
2011年 | 148篇 |
2010年 | 112篇 |
2009年 | 136篇 |
2008年 | 148篇 |
2007年 | 142篇 |
2006年 | 147篇 |
2005年 | 136篇 |
2004年 | 146篇 |
2003年 | 129篇 |
2002年 | 104篇 |
2001年 | 64篇 |
2000年 | 63篇 |
1999年 | 75篇 |
1998年 | 50篇 |
1997年 | 46篇 |
1996年 | 53篇 |
1995年 | 58篇 |
1994年 | 37篇 |
1993年 | 18篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有3105条查询结果,搜索用时 109 毫秒
61.
The conversion of amorphous tricalcium phosphate with different hydration ratio into apatite in water at 25 °C has been studied by microcalorimetry and several physical-chemical methods. The hydrolytic transformation was dominated by two strong exothermic events. A fast, relatively weak, wetting process and a very slow but strong heat release assigned to a slow internal rehydration and the crystallization of the amorphous phase into an apatite. The exothermic phenomenon related to the rehydration exceeded the crystalline transformation enthalpy. Rehydration occurred before the conversion of the amorphous phase into apatite and determined the advancement of the hydrolytic reaction. The apatitic phases formed evolved slightly with time after their formation. The crystallinity increased whereas the amount of HPO42− ion decreased. These data allow a better understanding of the behavior of biomaterials involving amorphous phases such as hydroxyapatite plasma-sprayed coatings. 相似文献
62.
Odile Meyer Jean-Franois Hoeffler Catherine Grosdemange-Billiard Michel Rohmer 《Tetrahedron》2004,60(52):12153-12162
An optimised gram scale synthesis allows the production of 1-deoxy-d-xylulose and 1-deoxy-d-xylulose 5-phosphate with possible deuterium labelling at C-5. Such substrates are required for investigations on the mevalonate-independent 2-C-methyl-d-erythritol 4-phosphate pathway for isoprenoid biosynthesis in bacteria and chloroplasts of phototrophic eukaryotes and for the biosynthesis of vitamins B1 (thiamine diphosphate) and B6 (pyridoxol phosphate) in bacteria. 相似文献
63.
Sizov A. I. Zvukova T. M. Belsky V. K. Bulychev B. M. 《Russian Chemical Bulletin》2001,50(11):2200-2202
The heterometallic zirconocene(iii) aluminum hydride complex (Cp2ZrH)2HAlCl2·C4H8O2·C6H6 was synthesized by reduction of Cp2ZrCl2 with lithium aluminum hydride in the presence of Cp2TiBH4 and 1,4-dioxane, and its structure was established by X-ray diffraction analysis. 相似文献
64.
Santiago MB Vélez MM Borrero S Díaz A Casillas CA Hofmann C Guadalupe AR Colón JL 《Electroanalysis》2006,18(6):559-572
We present a carbon paste electrode (CPE) modified using the electron mediator bis(1,10‐phenanthroline‐5,6‐dione)(2,2′‐bipyridine)ruthenium(II) ([Ru(phend)2bpy]2+) exchanged into the inorganic layered material zirconium phosphate (ZrP). X‐Ray powder diffraction showed that the interlayer distance of ZrP increases upon [Ru(phend)2bpy]2+ intercalation from 10.3 Å to 14.2 Å. The UV‐vis and IR spectroscopies results showed the characteristic peaks expected for [Ru(phend)2bpy]2+. The UV‐vis spectrophotometric results indicate that the [Ru(phend)2bpy]2+ concentration inside the ZrP layers increased as a function of the loading level. The exchanged [Ru(phend)2bpy]2+ exhibited luminescence even at low concentration. Modified CPEs were constructed and analyzed using cyclic voltammetry. The intercalated mediator remained electroactive within the layers (E°′=–38.5 mV vs. Ag/AgCl, 3.5 M NaCl) and electrocatalysis of NADH oxidation was observed. The kinetics of the modified CPE shows a Michaelis–Menten behavior. This CPE was used for the oxidation of NADH in the presence of Bakers' yeast alcohol dehydrogenase. A calibration plot for ethanol is presented. 相似文献
65.
醇体系中新型晶体磷酸锆的合成和表征赵玉娥,宋天佑,徐家宁,徐如人(吉林大学化学系,长春,130023)关键词磷酸锆,合成,表征自1964年首次合成磷酸锆晶体[1]以来,人们又合成出多种磷酸锆晶体[2~4]。但在非水体系中合成磷酸锆的工作尚未见报道。本... 相似文献
66.
Veiros LF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2505-2518
The mechanisms of three closely related reactions were studied in detail by means of DFT/B3 LYP calculations with a VDZP basis set. Those reactions correspond to 1) the reductive elimination of methane from [Zr(eta5-Ind)2(CH3)(H)] (Ind=C9H7-, indenyl), 2) the formation of the THF adduct, [Zr(eta5-Ind)(eta6-Ind)(thf)] and 3) the interconversion between the two indenyl ligands in the Zr sandwich complex, [Zr(eta5-Ind)(eta9-Ind)], which forms the link between the two former reactions. An analysis of the electronic structure of this species indicates a saturated 18-electron complex. A full understanding of the indenyl interchange process required the characterisation of several isomers of the Zr-bis(indenyl) species, corresponding to different spin states (S=0 and S=1), different coordination modes of the two indenyl ligands (eta5/eta9, eta5/eta5 and eta6/eta9), and three conformations for each isomer (syn, anti, and gauche). The fluxionality observed was found to occur in a mechanism involving bis(eta5-Ind) intermediates, and the calculated activation energy (11-14 kcal mol(-1)) compares very well with the experimental values. Two alternative mechanisms were explored for the reductive elimination of methane from the methyl/hydride complex. In the more favourable one, the initial complex, [Zr(eta5-Ind)2(CH3)(H)], yields [Zr(eta5-Ind)2] and methane in one crucial step, followed by a smooth transition of the Zr intermediate to the more stable eta5/eta9-species. The overall activation energy calculated (Ea=29 kcal mol(-1)) compares well with experimental values for related species. The formation of the THF adduct follows a one step mechanism from the appropriate conformer of the [Zr(eta5-Ind)(eta9-Ind)] complex, producing easily (Ea=6.5 kcal mol(-1)) the known product, [Zr(eta5-Ind)(eta6-Ind)(thf)], a species previously characterised by X-ray crystallography. This complex was found to be trapped in a potential well that prevents it from evolving to the 3.4 kcal mol(-1) more stable isomer, [Zr(eta5-Ind)2(thf)], with both indenyl ligands in a eta5-coordination mode and a spin-triplet state (S=1). 相似文献
67.
Ludvík Beneš Vítězslav Zima 《Journal of inclusion phenomena and macrocyclic chemistry》1994,20(4):381-391
The course of intercalation of water into 1-VOPO4 has been studied by thermomechanical analysis and X-ray diffraction. Neither formation of vanadyl phosphate monohydrate nor staging were observed during the intercalation. The broadening and the shift of the positions of the lines in the diffractograms have been explained by the random stacking of intercalated and nonintercalated layers in the sample. 相似文献
68.
Yoshitsugu Hasegawa Suguru Kontani Isao Tomita 《Journal of inclusion phenomena and macrocyclic chemistry》1993,16(4):329-337
Intercalation of alkylalcohols into -zirconium phosphate was investigated at 25°C and/or under reflux.n-Alcohols having two to five carbons and 2-propanol were taken up at 25°C. These alcohols, andn-hexanol and heptanol, also intercalated under reflux.n-Alcohols having eight to eighteen carbon atoms intercalated when a stepwise method was employed. 2-Butanol and tertiary amylalcohols intercalated under reflux using a butanol intercalate as a starting material. Ethanol-to-butanol intercalates were unstable at room temperature, losing alcohols and changing to -zirconium phosphate. The particle size of the -zirconium phosphate did not affect the intercalation of alcohols. 相似文献
69.
Feng LIN Shao Yong BAI 《中国化学快报》2005,16(9):1158-1160
1, 3-Dimethyluracil (DMU) in phosphate buffered-saline (PBS, pH=8) was irradiated by a medium pressure mercury lamp (MPML) and produced a novel compound C6H9N2O6P. The composition and structure of the compound has been identified by elemental analysis, EIMS, UV, IR, ^1H and ^31P-NMR. 相似文献
70.
S. V. Baires D. É Vallen K. M. Enikeev A. S. Khramov V. E. Bel'skii A. V. Il'yasov B. E. Ivanov 《Russian Chemical Bulletin》1992,41(10):1801-1804
The interaction of synthetic analogs of active centers of iron-sulfur proteins with phosphates of different structures was studied. It was shown that the process involves ligand exchange and obeys the first-order reaction kinetic equation. The most rapid exchange occurred with the most acidic compound diphenyl phosphate.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences, 420083 Kazan'. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2301–2305, October, 1992. 相似文献