全文获取类型
收费全文 | 1068篇 |
免费 | 32篇 |
国内免费 | 1篇 |
专业分类
化学 | 852篇 |
晶体学 | 10篇 |
力学 | 16篇 |
数学 | 26篇 |
物理学 | 197篇 |
出版年
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 22篇 |
2013年 | 46篇 |
2012年 | 48篇 |
2011年 | 48篇 |
2010年 | 26篇 |
2009年 | 24篇 |
2008年 | 47篇 |
2007年 | 46篇 |
2006年 | 43篇 |
2005年 | 65篇 |
2004年 | 51篇 |
2003年 | 42篇 |
2002年 | 38篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 24篇 |
1998年 | 11篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 8篇 |
1982年 | 23篇 |
1981年 | 22篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 14篇 |
1973年 | 10篇 |
1968年 | 8篇 |
排序方式: 共有1101条查询结果,搜索用时 15 毫秒
61.
Reaction of ketene silyl acetals with allylic carbonates in the presence of palladium-phosphine catalyst in dioxane gives α-allyl esters in high yields. When the reaction is carried out with phosphine-free palladium catalyst in nitriles, α,β-unsaturated esters are obtained in good yields. 相似文献
62.
Takuo Kosuge Kuniro Tsuji Koichi Hirai Kentaro Yamaguchi Toshihiko Okamoto Yoichi Iitaka 《Tetrahedron letters》1981,22(35):3417-3420
A new toxin, named neosurugatoxin, was isolated from the toxic Japanese Ivory Shell and its structure was determined by X-ray crystallographic analysis. 相似文献
63.
Kozo Tsuji 《Journal of polymer science. Part A, Polymer chemistry》1973,11(2):467-484
ESR studies were carried out on radical conversions by thermal and photochemical mechanisms in low-density polyethylene irradiated mainly with electron beams at ?196°C both in vacuum and in the presence of CO. According to the spectral change, the following radical conversions were elucidated for the samples irradiated in vacuo [eqs. (1) and (1′)] and in the presence of CO [eqs. (2) and (2′)]. From the resemblance of the ESR spectrum observed after direct photolysis of polyethylene to that observed after photo-induced radical conversions of the allylic radicals, it is concluded that an eight-line ESR spectrum observed immediately after photolysis of polyethylene at ?196°C could be attributed more reasonably to the alkyl radicals ? CH2CHCH3 than to ? CH2CH2 and ? CH2CHCH2? . 相似文献
64.
Hajime Kabashima Hideto Tsuji Hideshi Hattori 《Reaction Kinetics and Catalysis Letters》1996,58(2):255-259
All the alkaline earth oxides exhibit activities for double, bond isomerization of 5-vinylbicyclo[2.2.1]hept-2-ene (VBH) to 5-ethylidenebicyclo[2.2.1]hept-2-ene (EBH) at a reaction temperature of 273 K. The order of the activity on the basis of unit weight of catalyst was CaO>MgO>SrO>BaO when compared under optimum pretreatment conditions. The E/Z ratio in the products is determined by the reaction temperature regardless of the type of catalyst; the ratios were 82/18 and 88/12 for the reaction temperatures of 323 and 273 K, respectively. 相似文献
65.
66.
67.
Shuichi Hirata Kouichi Tanaka Katsuya Matsui Fernando Arteaga Arteaga Yasushi Yoshida Shinobu Takizawa Hiroaki Sasai 《Tetrahedron: Asymmetry》2013,24(19):1189-1192
The introduction of a 1,3-propanediamine unit at the 3-position of (S)-BINOL using a methylene spacer led to the formation of a chiral bifunctional organocatalyst for the aza-Morita–Baylis–Hillman (aza-MBH) reaction. The organocatalyst 1k mediated aza-MBH transformations with high chemical yields and with up to 82% ee. 相似文献
68.
Rational Design for Rotaxane Synthesis through Intramolecular Slippage: Control of Activation Energy by Rigid Axle Length 下载免费PDF全文
Hiroshi Masai Dr. Jun Terao Dr. Tetsuaki Fujihara Dr. Yasushi Tsuji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6624-6630
We describe a new concept for rotaxane synthesis through intramolecular slippage using π‐conjugated molecules as rigid axles linked with organic soluble and flexible permethylated α‐cyclodextrins (PM α‐CDs) as macrocycles. Through hydrophilic–hydrophobic interactions and flipping of PM α‐CDs, successful quantitative conversion into rotaxanes was achieved without covalent bond formation. The rotaxanes had high activation barrier for their de‐threading, so that they were kinetically isolated and derivatized even under conditions unfavorable for maintaining the rotaxane structures. 1H NMR spectroscopy experiments clearly revealed that the restricted motion of the linked macrocycle with the rigid axle made it possible to control the kinetic stability by adjusting the length of the rigid axle in the precursor structure rather than the steric bulkiness of the stopper unit. 相似文献
69.
Hiroya Takada Yoshiaki Nishibayashi Sanjay Kumar Srivastava Kouichi Ohe Sakae Uemura 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):629-632
Asymmetric intramolecular selenocyclisation of alkenoic acids, alkenols and alkenyl urethanes using chiral ferrocenylselenenyl cations proceeds smoothly to give the corresponding lactones, cyclic ethers and N-heterocyclic compounds, respectively, in moderate yields with very high diastereoselectivities. 相似文献
70.
Hiroya Takada Yoshiaki Nishibayashi Kouichi Ohe Sakae Uemura 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):363-364
Prochiral sulfides reacted with Phl=NTs in the presence of a catalytic amount of Cu(I) salt together with a chiral 4,4′-disubstituted bis(oxazoline) ligand to afford the corresponding chiral sulfimides. 相似文献