全文获取类型
收费全文 | 4042篇 |
免费 | 135篇 |
国内免费 | 25篇 |
专业分类
化学 | 3107篇 |
晶体学 | 37篇 |
力学 | 51篇 |
数学 | 251篇 |
物理学 | 756篇 |
出版年
2022年 | 24篇 |
2021年 | 37篇 |
2020年 | 39篇 |
2019年 | 75篇 |
2018年 | 49篇 |
2017年 | 24篇 |
2016年 | 66篇 |
2015年 | 71篇 |
2014年 | 80篇 |
2013年 | 207篇 |
2012年 | 206篇 |
2011年 | 247篇 |
2010年 | 127篇 |
2009年 | 139篇 |
2008年 | 235篇 |
2007年 | 243篇 |
2006年 | 249篇 |
2005年 | 228篇 |
2004年 | 195篇 |
2003年 | 146篇 |
2002年 | 144篇 |
2001年 | 79篇 |
2000年 | 72篇 |
1999年 | 58篇 |
1998年 | 39篇 |
1997年 | 44篇 |
1996年 | 65篇 |
1995年 | 40篇 |
1994年 | 29篇 |
1993年 | 44篇 |
1992年 | 53篇 |
1991年 | 37篇 |
1990年 | 43篇 |
1989年 | 43篇 |
1988年 | 46篇 |
1987年 | 37篇 |
1986年 | 33篇 |
1985年 | 80篇 |
1984年 | 47篇 |
1983年 | 35篇 |
1982年 | 44篇 |
1981年 | 40篇 |
1980年 | 38篇 |
1979年 | 43篇 |
1978年 | 39篇 |
1977年 | 37篇 |
1976年 | 27篇 |
1975年 | 29篇 |
1974年 | 28篇 |
1973年 | 34篇 |
排序方式: 共有4202条查询结果,搜索用时 328 毫秒
111.
Enantioselective Michael addition reactions of tertiary nucleophile precursors, such as substituted malononitriles and cyclic 1,3-diketones, can be successfully activated by the metal complexes derived from R,R-DBFOX/Ph chiral ligand and cationic metal salts. With this method, the enantioselective tertiary/quaternary and quaternary/quaternary carbon–carbon bond formations can be achieved. Use of alcohol solvents is essential for the success, and ,β-unsaturated amides of 3,5-dimethylpyrazole are much better acceptors than those of 2-oxazolidinone. 相似文献
112.
Electron-phonon interactions in the monoanions of polyacetylenes such as C2H4 (2tpa), C4H6 (4tpa), C6H8 (6tpa), and C8H10 (8tpa) are studied and compared with those in the monoanions of polyacenes. The C-C stretching A(g) modes around 1500 cm(-1) the most strongly couple to the lowest unoccupied molecular orbitals (LUMO) in polyacetylenes. The estimated total electron-phonon coupling constants for the monoanions (l(LUMO)) are 0.579, 0.555, 0.463, and 0.401 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. The l(LUMO) values for polyacetylenes are much larger than those for polyacenes. Furthermore, the l(LUMO) value for polyacetylene with C(2h) geometry is estimated to be 0.254 eV, and is larger than that (0.024 eV) for polyacene with D(2h) geometry. The phase patterns difference between the LUMO of polyacenes localized on the edge part of carbon atoms, and the delocalized LUMO of polyacetylenes is the main reason for the calculated results. The single charge transfer through the molecule in polyacetylenes are also discussed. The reorganization energies between the neutral molecule and the corresponding monoanion are estimated to be 0.164, 0.144, 0.125, and 0.113 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. Such reorganization energy decreases with an increase in molecular size. The conditions under which the attractive electron-electron interactions are realized in the monoanions of polyacetylenes and polyacenes are discussed. In terms of the electron-phonon interactions and the reorganization energies, the relationships between the normal and possible superconducting states are briefly discussed. We find that the monoanions with smaller molecular size cannot easily become good conductors, however, the conditions under which the interactions between two electrons are attractive are more easily realized in the monoanions with smaller molecular size than in the monoanions with larger molecular size. 相似文献
113.
Takahiro Makino Kimihiko Kato Hiroyuki Lyozumi Hiroe Honzawa Yoshiaki Tachiiri Mitsuo Hiramatsu † 《Photochemistry and photobiology》1996,64(6):953-956
Abstract— Ultraweak luminescence generated by sweet potato and nonpathogenic Fusarium oxysporum interactions associated with a defense response was detected by a photoncounting method using ultrahigh-sensitive photodetectors. The time-dependent intensity variation, the spectrum and the two-dimensional imaging of the ultraweak luminescence are indicative of the defense response of the sweet potato to F. oxysporum. The production of ipomeamarone as a phytoalexin means that F. oxysporum induced the defense response in the sweet potato. 相似文献
114.
115.
116.
117.
Qi ZM Matsuda N Santos J Yoshida T Takatsu A Kato K 《Journal of colloid and interface science》2004,271(1):249-253
Broadband, time-resolved optical waveguide (OWG) spectroscopy has been used for in situ, real-time investigation into the self-assembly of metal nanoparticle monolayers. The OWG spectroscopy makes it possible to use the transverse electric (TE) and transverse magnetic (TM) modes to measure surface plasmon absorption of immobilized metal nanoparticles in two directions, parallel and normal to the waveguide surface. Therefore, this technique can provide direction-dependent information on the metal nanoparticles at the interface. In this paper, a 50-microm-thick glass plate was used as a slab waveguide and the kinetics of Au nanoparticle adsorption on a hemoglobin-functionalized glass substrate was examined in the early stage of self-assembly. The findings show that with the TE mode the surface plasmon resonance (SPR) behavior for immobilized Au nanoparticles is different from that with the TM mode. 相似文献
118.
Koga T Taguchi K Kinoshita T Higuchi M 《Chemical communications (Cambridge, England)》2002,(3):242-243
A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology. 相似文献
119.
120.
Tetsuo Suami Hiroaki Sasai Kazuhiro Matsuno Nobuo Suzuki Yoshimasa Fukuda Osamu Sakanaka 《Tetrahedron letters》1984,25(40):4533-4536
Tunicamycins and their eight analogs have been synthesized by condensation of a N-acetyl-D-glucosamine derivative and an anomeric chloride of tunicaminyl uracil, followed by deprotections and N-acylation. 相似文献