全文获取类型
收费全文 | 3089篇 |
免费 | 96篇 |
国内免费 | 15篇 |
专业分类
化学 | 2525篇 |
晶体学 | 44篇 |
力学 | 30篇 |
数学 | 203篇 |
物理学 | 398篇 |
出版年
2023年 | 19篇 |
2022年 | 21篇 |
2021年 | 21篇 |
2020年 | 43篇 |
2019年 | 45篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 58篇 |
2015年 | 53篇 |
2014年 | 89篇 |
2013年 | 186篇 |
2012年 | 146篇 |
2011年 | 181篇 |
2010年 | 123篇 |
2009年 | 109篇 |
2008年 | 186篇 |
2007年 | 172篇 |
2006年 | 191篇 |
2005年 | 192篇 |
2004年 | 176篇 |
2003年 | 137篇 |
2002年 | 145篇 |
2001年 | 51篇 |
2000年 | 53篇 |
1999年 | 29篇 |
1998年 | 48篇 |
1997年 | 37篇 |
1996年 | 27篇 |
1995年 | 26篇 |
1994年 | 33篇 |
1993年 | 24篇 |
1992年 | 30篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 36篇 |
1984年 | 49篇 |
1983年 | 29篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 32篇 |
1979年 | 30篇 |
1978年 | 20篇 |
1977年 | 27篇 |
1976年 | 22篇 |
1975年 | 15篇 |
1974年 | 20篇 |
排序方式: 共有3200条查询结果,搜索用时 15 毫秒
991.
Gaseous formaldehyde is extremely unstable and readily undergoes self-polymerization to a solid paraformaldehyde or disproportionation to methanol and formic acid in the presence of moisture. We disclose a simple method to stably store such a labile formaldehyde as a monomer in a nanoporous faujasite zeolite at 5 degrees C for at least 50 days without self-polymerization or disproportionation. The greater stability of formaldehyde encapsulated in zeolite was confirmed by 13C MAS NMR spectroscopy. Formaldehyde was not only stabilized within the zeolite cages but functioned as a powerful electrophile toward various olefins. Zeolite-encapsulated formaldehyde was proved to be a stable but highly reactive C1 reagent. 相似文献
992.
The asymmetric conjugate addition of arylcopper reagents to chiral 1-[2-(p-tolylsulfinyl)]indolyl and 1-[3-(p-tolylsulfinyl)]indolyl enones was examined. With the 2-sulfinyl-indolyl derivatives, the reaction of the arylcopper reagent gave high diastereoselectivities (81-88% de's) to afford the adducts in excellent yields, although the similar addition reaction of the 3-sulfinyl derivatives afforded poor diastereoselectivities. 相似文献
993.
Kondo M Hayakawa Y Miyazawa M Oyama A Unoura K Kawaguchi H Naito T Maeda K Uchida F 《Inorganic chemistry》2004,43(19):5801-5803
A new two-dimensional coordination polymer with cobalticinium 1,1'-dicarboxylate (ccdc) incorporated in the framework has been prepared, the ccdc functioning as unique monoanionic dicarboxylate ligands. The compound shows a high redox activity based on the ccdc units. 相似文献
994.
Total reflection total conversion electron yield X-ray absorption fine structure is applied to the evaluation of ion exchange occurring at the surface monolayer of two-tailed ammonium ions. X-ray absorption measurements at a Br K-edge allow us to detect ion-exchange equilibria between Br- and Cl- added in a subphase. The ion-exchange selectivity of Br- over Cl- basically increases as the monolayer is compressed, indicating that Cl- is selectively squeezed out by compression because of its larger hydrated ionic radius. 相似文献
995.
[reaction: see text] An aldol reaction of trimethoxysilyl enol ether catalyzed by lithium binaphtholate, in which water serves as an additive and plays a pivotal role in stereoselectivities, was developed. This is the first example of an aldol reaction of trimethoxysilyl enol ether catalyzed by a chiral base. 相似文献
996.
Makoto Katori Norio Konno Aidan Sudbury Hideki Tanemura 《Journal of Theoretical Probability》2004,17(1):131-144
We study the Domany–Kinzel model, which is a class of discrete-time Markov processes in one-dimension with two parameters (p
1,p
2)[0,1]2. When p
1= and p
2=(2–
2) with (,)[0,1]2, the process can be identified with the mixed site-bond oriented percolation model on a square lattice with probabilities of a site being open and of a bond being open. This paper treats dualities for the Domany–Kinzel model
t
A
and the DKdual
t
A
starting from A. We prove that
, as long as one of A,B is finite and p
2p
1. 相似文献
997.
We report atomic-resolution imaging and site-specific quantitative force measurements on a single-walled carbon nanotube by dynamic force microscopy and three-dimensional force field spectroscopy at low temperatures. The topography imaged in the attractive force regime reflects the trigonal arrangement of the hollow sites as maxima. Individual force curves were unambiguously assigned to carbon atoms and hollow sites, respectively. Site-specific quantitative evaluation revealed that the short-range interatomic van der Waals forces are responsible for the atomic-scale contrast. 相似文献
998.
Makoto Shimizu Rumiko OnoShozo Suto Takenari GotoMao-Ching Fang Akira WatanabeMinoru Matsuda 《Journal of luminescence》2002,99(3):197-203
We have measured absorption, photoluminescence, and photoluminescence excitation spectra, and the photoluminescence time response for films of silylene-biphenylene copolymer, ((C6H4)2(Si(CH3)2)m)n with m=1,2,4, and 6. The excitation spectra clearly reveal that the lowest absorption band in each copolymer consists of two bands, i.e., a band at 4.7 eV and a band of which energy depends on m. Since the latter band is absent in the copolymer with m=1, the former band is attributed to the lowest π−π* transition in biphenylene subunits. The latter band is attributed to the lowest σ−σ* transition in the silylene subunits, considering its dependence on m. In contrast to the result for solution, the peak energy of photoluminescence band is independent of m. The band has a Stokes shift of more than 1 eV and a large band width of 0.5 eV. The time responses of photoluminescence intensity consist of more than two decay components and the intensity decays more slowly at smaller energy. The large Stokes shift is explained as due to excimer formation between biphenylene subunits. In order to explain the energy dependence of time responses, energy migration is discussed. 相似文献
999.
Taguchi H Ghoroku K Tadaki M Tsubouchi A Takeda T 《The Journal of organic chemistry》2002,67(24):8450-8456
Successive treatment of the (Z)-gamma-trimethylsilyl allylic alcohols with copper(I) tert-butoxide and allylic halides followed by the tetrabutylammonium fluoride-assisted hydrolysis produced the allylation products, 2,5-alkadien-1-ols, with complete retention of configuration. Similar treatment of the organometallic intermediates with aryl and vinylic halides in the presence of palladium(0) catalyst gave the corresponding cross-coupling products in good yields. The stereoselective preparation of the starting materials is also described. 相似文献
1000.