全文获取类型
收费全文 | 22914篇 |
免费 | 2168篇 |
国内免费 | 6337篇 |
专业分类
化学 | 28805篇 |
晶体学 | 377篇 |
力学 | 129篇 |
综合类 | 182篇 |
数学 | 101篇 |
物理学 | 1825篇 |
出版年
2024年 | 23篇 |
2023年 | 201篇 |
2022年 | 446篇 |
2021年 | 630篇 |
2020年 | 826篇 |
2019年 | 686篇 |
2018年 | 704篇 |
2017年 | 775篇 |
2016年 | 1094篇 |
2015年 | 1072篇 |
2014年 | 1351篇 |
2013年 | 2289篇 |
2012年 | 1587篇 |
2011年 | 1638篇 |
2010年 | 1377篇 |
2009年 | 1583篇 |
2008年 | 1635篇 |
2007年 | 1714篇 |
2006年 | 1732篇 |
2005年 | 1647篇 |
2004年 | 1583篇 |
2003年 | 1347篇 |
2002年 | 873篇 |
2001年 | 599篇 |
2000年 | 509篇 |
1999年 | 524篇 |
1998年 | 476篇 |
1997年 | 429篇 |
1996年 | 334篇 |
1995年 | 329篇 |
1994年 | 290篇 |
1993年 | 276篇 |
1992年 | 261篇 |
1991年 | 138篇 |
1990年 | 93篇 |
1989年 | 88篇 |
1988年 | 73篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 36篇 |
1984年 | 28篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
A novel hybrid tungstocuprate(Ⅱ) [Cu(2,2'-bpy)3]2H4[CuW12O40]·6H2O(2,2'-bpy=2,2'-bipyridine) was synthesized via hydrothermal method and characterized using elemental analyses, IR, UV, XPS, TG-DSC, EPR, and X-ray single crystal diffraction. The structural analysis shows that the complex consists of an unusual Keggin-type polyoxoanion [CuW12O40]6- and a pair of chiral complex cations [Cu(2,2'-bpy)3] together with four protons and six crystallization water molecules, and the Keggin polyoxoanion is connected with [Cu(2,2'-bpy)3] via multiple C-H…O hydrogen bonds resulting in a dimer. 相似文献
992.
993.
994.
Pascal LangCatherine Gerez Denis TritschMarc Fontecave Jean-François BiellmannAlain Burger 《Tetrahedron》2003,59(37):7315-7322
The synthesis of 5′-di- and 5′-triphosphate of 8-vinyladenosine to be tested on ribonucleotide reductases requires the modification of known methods. The phosphate group was introduced by treatment with an in situ generated chlorophosphite. Protection of the 2′,3′ diol with acetyl groups suppressed depurination during acid removal of the phosphotriester protecting groups. The di- and triphosphate compounds were obtained by treatment of the activated adenylic acid with phosphate or pyrophosphate anions followed by removal of the acetate protecting groups. Preliminary studies were conducted on Escherichia coli ribonucleotide reductase and have shown that the diphosphate compound is efficiently reduced. 相似文献
995.
Luo J Zheng QY Chen CF Huang ZT 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(20):5917-5928
A series of inherently chiral calix[4]arenes with cone and partial cone conformations and with crown ether moieties of variable size have been readily synthesized. By taking advantage of the carboxy appendage on the lower rim, these were condensed with the chiral auxiliary (S)-BINOL to form diastereomers which, in most cases, could be separated by preparative TLC, or more desirably, by column chromatography on silica gel (diastereomeric excess >99 % based on HPLC analysis). Seven enantiopure antipodes of inherently chiral calix[4]crowns were obtained after hydrolysis. It has been found that both the size of the crown moiety and alkylation of the last phenolic hydroxy group (accompanied with or without a change in the conformation) affect the separation of the diastereomers. 相似文献
996.
O. A. Bogdanova E. I. Zhilyaeva R. N. Lyubovskaya N. S. Ovanesyan S. I. Pirumova O. S. Roskchupkina 《Russian Chemical Bulletin》1996,45(9):2210-2212
The synthesis, IR spectra, and the temperatures of the transition into a ferromagnetic state (T
c) of layered ferromagnetics [R3RX[MCr(C2O4)3 (M = Mn, Fe, Co, Cu, and Ni) with the [Ph3BuP]+, [Bu3RN]+ (R = Pr, Et, and Me) cations capable of subsequently changing the distances between metallooxalate layers have been considered. The temperatureT
c has been found to be independent of the size of the organic cation. It is believed that the determining factors in the transition to a ferromagnetic state are exchange interactions inside the metallooxalate layer.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2327–2330, September, 1996. 相似文献
997.
998.
Gerald Giester 《Monatshefte für Chemie / Chemical Monthly》1991,122(4):229-234
Summary The crystal structure of synthetic Cu3SeO4(OH)4 was determined by single crystal X-ray methods:a=8.382 (2) Å,b=6.087 (1) Å,c=12.285 (2) Å,V=626.8 Å3,Z=4, space group Pnma,R=0.026,R
w
=0.021 for 1255 independent reflections (sin / 0.8 Å–1). The crystal structure is isotypic to that of the mineral antlerite, Cu3SO4(OH)4. The copper atoms are Jahn-Teller distorted with Cu[4+2]O6 polyhedra forming triple chains along [010]. These chains are linked via SeO4 tetrahedra and weak hydrogen bonds to a framework structure.
Die Kristallstruktur von synthetischem Cu3SeO4(OH)4
Zusammenfassung Die Kristallstruktur von synthetischem Cu3SeO4(OH)4 wurde mittels Einkristall-Röntgenmethoden ermittelt:a=8.382 (2) Å,b=6.087 (1) Å,c=12.285 (2) Å,V=626.8 Å3,Z=4, Raumgruppe Pnma,R=0.026,R w =0.021 für 1255 unabhängige Reflexe (sin / 0.8 Å–1). Die Kristallstruktur ist isotyp mit der des Minerals Antlerit, Cu3SO4(OH)4. Die Kupferatome sind Jahn-Teller-verzerrt, die Cu[4+2]O6 Polyeder bilden Dreierketten entlang [010]. Diese Ketten sind über SeO4-Tetraeder und schwache Wasserstoffbrücken zu einer Gerüststruktur verbunden.相似文献
999.
Using a mass spectrometric sampling method, we have observed the decomposition of CH4 in an rf plasma usedfor diamond deposition. The gas samples were extracted through an orifice located downstream of the plasma zone and analyzed online. For the experiments a dilute mixture of H2 and CH4 containing 0.1–3% CH4 has been used. CH4 is converted to C2H2 and C2H4 quantitatively. Small amounts of heavier hydrocarbons are formed. A comparison of the experimental results with a recent kinetic model treating a purely thermal environment is made and the differences between our experiment and the model are explained. The role of acetylene as a species formed in an atmosphere rich in atomic hydrogen is proposed. The electron impact dissociation process is suggested as the rare-determining step in the plasma-chemical decomposition of methane. 相似文献
1000.