全文获取类型
收费全文 | 7636篇 |
免费 | 292篇 |
国内免费 | 271篇 |
专业分类
化学 | 4018篇 |
晶体学 | 119篇 |
力学 | 165篇 |
综合类 | 31篇 |
数学 | 2476篇 |
物理学 | 1390篇 |
出版年
2023年 | 23篇 |
2022年 | 37篇 |
2021年 | 51篇 |
2020年 | 113篇 |
2019年 | 146篇 |
2018年 | 132篇 |
2017年 | 142篇 |
2016年 | 139篇 |
2015年 | 117篇 |
2014年 | 166篇 |
2013年 | 249篇 |
2012年 | 175篇 |
2011年 | 350篇 |
2010年 | 271篇 |
2009年 | 466篇 |
2008年 | 357篇 |
2007年 | 401篇 |
2006年 | 351篇 |
2005年 | 380篇 |
2004年 | 512篇 |
2003年 | 434篇 |
2002年 | 391篇 |
2001年 | 306篇 |
2000年 | 265篇 |
1999年 | 195篇 |
1998年 | 161篇 |
1997年 | 170篇 |
1996年 | 197篇 |
1995年 | 157篇 |
1994年 | 197篇 |
1993年 | 152篇 |
1992年 | 132篇 |
1991年 | 77篇 |
1990年 | 60篇 |
1989年 | 60篇 |
1988年 | 53篇 |
1987年 | 70篇 |
1986年 | 56篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 13篇 |
1982年 | 38篇 |
1981年 | 41篇 |
1980年 | 48篇 |
1979年 | 67篇 |
1978年 | 52篇 |
1977年 | 52篇 |
1976年 | 37篇 |
1974年 | 13篇 |
1973年 | 17篇 |
排序方式: 共有8199条查询结果,搜索用时 15 毫秒
91.
The main product of the reaction of 1-methylcyclobutanol with Pb(OAc)4 in benzene is 1-phenyl-4-pentanone; the use of Mn(OAc)3 in acetic acid gives a mixture of 2,9-decanedione and methyl propyl ketone; 1-(chloro-, bromo-, thiocyano-, or cyano)-4-pentanone is formed in the presence of the systems Pb(OAc)4-metal halide or Mn(OAc)3-metal halide.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2760013;2763, December, 1992. 相似文献
92.
H. Viernstein S. Reiter P. Wolschann 《Monatshefte für Chemie / Chemical Monthly》1994,125(6-7):681-689
Summary The solubility enhancement of triflumizole, a systemic fungicide, by 0u8/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin inclusion complexation was investigated by electron absorption spectroscopy. The respective association constant determined by different methods was estimated to 470±20M
013;1 in aqueous solution. A model for the host-guest complexation was deduced by molecular calculations.
Löslichkeitsverbesserung von Triflumizole durchHost-Guest-Complexierung mit 0u8/xhuge946.gif" alt="beta" align="MIDDLE" BORDER="0">-Cyclodextrin
Zusammenfassung Die Löslichkeitsverbesserung des systemischen Fungizids Triflumizole durch Komplexierung mit 0u8/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-Cyclodextrin wurde mittels Elektronenabsorptionsspektroskopie untersucht. Die entsprechende Stabilitätskonstante wurde durch verschiedene Methoden erfaßt und betrug im wäßrigen Medium 470±20M 013;1. Ein Model für denHost-Guest-Complex wurde durch Molekülrechnungen erstellt.相似文献
93.
A systematic extension of Ruedenberg's expansion formula is applied to evaluate two-electron integrals occurring in calculations on molecular structure. Minimum STO basis sets are used for all SCF-calculations within the framework of the MEDO-method (Multipole Expansion of Diatomic Overlap). The errors due to this approximation scheme are almost negligible compared to those introduced by the truncated basis set: LiH, Li2 and N2 are chosen as examples. 相似文献
94.
95.
Colin Thomson 《Theoretical chemistry accounts》1973,32(2):93-100
Non-empirical LCAO-MO-SCF calculations on SiF2 using two Gaussian basis sets are reported. The larger basis set gives a calculated geometry in good agreement with experiment. The effect on the energy and population analysis of optimization of the Si 3d exponent was investigated. 3d orbitals are found to be much less important in the bonding than in the isoelectronic molecule SO2. 相似文献
96.
Hidetake Sakuraba Yoshio Tananaka Fujio Toda 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(2):195-204
The asymmetric Michael addition of aromatic thiols to 2-cyclohexenone and maleic acid esters has been carried out by utilizing their crystalline cyclodextrin complexes suspended in water. The best chiral induction, 30% enantiomeric excess (ee), was achieved in combinations of 2-cyclohexenone and octyl maleate with the crystalline 0">-cyclodextrin complex of benzenethiol (method A) to afford (S)-3-phenylthiocyclohexanone and (S)-octyl-2-phenylthiosuccinate, respectively, whereas the reaction of benzenethiol with 2-cyclohexenone included in 0">-cyclodextrin (method B) inversely induced the chiral recognition to give the (R)-adduct with 4013;9% ee. 相似文献
97.
Krishna Gopal Dongol M. Cristina Melo e Silva Kouki Matsubara Taisuke Matsumoto Shuntaro Mataka Thies Thiemann 《无机化学与普通化学杂志》2003,629(6):945-947
The preparation of two η6‐estra‐1, 3, 5(10), 6‐tetraene tricarbonylchromium complexes 4 and 6 are described. In both cases only one stereoisomer can be isolated, in contrast to other estrane‐tricarbonylchromium complexes, where complexations are non‐stereoselective. X‐ray crystal structural analysis of 4 discloses that only the more sterically hindered β‐facial isomer is formed. It is assumed that the 6, 7‐olefinic moiety exerts a directive influence on the complexation. 相似文献
98.
The Wittig014;Horner reaction of CbzNHCH(CO2Me)P(O)(OMe)2 (1) with ArCHO (2) in the presence of Et3N as a base affords methyl (Z)-3-aryl-2-(carbobenzoxyamino)acrylates (3) with high degrees of diastereoselectivity (Z)/(E) > 100">0">1. One recrystallization of the crude product is sufficient to obtain isomerically and chemically pure (Z)-3.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2218-2220, November, 1995.The authors are grateful to the Dupont company (USA) for financing this study 相似文献
99.
It is shown that 2,2-difluoro-3-hydroxymethylbenzo-1,4-oxathianes are formed together with 3-trifluoromethylbenzo-1,4-oxathianes whenortho-(04/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-trifluoromethyl-04/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-chloroethylthio)phenols are boiled with excess aqueous alkali. The mechanism of the reaction is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1457013;1459, August, 1994. 相似文献
100.
M. G. Ezernitskaya B. V. Lokshin T. Yu. Orlova V. N. Setkina V. I. Shilnikov S. Nunziante Cesaro 《Russian Chemical Bulletin》1994,43(11):1841-1845
FTIR spectra have been studied for 046635x17490136/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">staircase046635x17490136/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> cyclopentadienyl complexes containing two or three metal carbonyl fragments bound by the metal-carbon bond Cp(CO)2Fe-CpmMn(CO)3 (1), Cp(CO)2Fe-CpmFe(CO)2CH2Ph (2), Cp(CO)2Fe-Cpm(CO)2Fe-CpmMn(CO)3 (3), Cp(CO)2Mo-Cpm(CO)2Fe-CpmMn(CO)3 (4), Cp(CO)3W-Cpm(CO)2Fe-CpmMn(CO)3 (5), Cp(CO)2Fe-Cpm(CO)2Fe-BmCr(CO)3 (6), Cr(CO)3Bm-CpmFe(CO)2CH2Ph (7), where Cp = 046635x17490136/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0">5-C5H5, Cpm = 046635x17490136/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0">1046635x17490136/xxlarge8758.gif" alt="ratio" align="BASELINE" BORDER="0">046635x17490136/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0">5-C5H4, Bm = 046635x17490136/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0">1046635x17490136/xxlarge8758.gif" alt="ratio" align="BASELINE" BORDER="0">046635x17490136/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0">6-C6H5. Temperature-dependent FTIR spectra were measured inn-pentane solutions over a wide temperature range and in the low-temperature solid matrices of argon and nitrogen. Rotamers, formed due to rotation about the metal-carbon 046635x17490136/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">-bond, were found in solutions and matrices. A molecular mechanics calculation of1 proved the possibility of such rotation.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1952013;1956, November, 1994.The authors are grateful to the Russian Foundation for Basic Research (project code No 93-03-18592) and to the International Science Foundation (project code No MEQ000). 相似文献