全文获取类型
收费全文 | 2994篇 |
免费 | 87篇 |
国内免费 | 15篇 |
专业分类
化学 | 2084篇 |
晶体学 | 26篇 |
力学 | 44篇 |
数学 | 196篇 |
物理学 | 746篇 |
出版年
2021年 | 23篇 |
2020年 | 40篇 |
2019年 | 33篇 |
2018年 | 28篇 |
2017年 | 29篇 |
2016年 | 62篇 |
2015年 | 42篇 |
2014年 | 67篇 |
2013年 | 128篇 |
2012年 | 149篇 |
2011年 | 166篇 |
2010年 | 81篇 |
2009年 | 88篇 |
2008年 | 167篇 |
2007年 | 174篇 |
2006年 | 175篇 |
2005年 | 158篇 |
2004年 | 121篇 |
2003年 | 114篇 |
2002年 | 95篇 |
2001年 | 74篇 |
2000年 | 65篇 |
1999年 | 46篇 |
1998年 | 31篇 |
1997年 | 30篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 28篇 |
1993年 | 36篇 |
1992年 | 55篇 |
1991年 | 51篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 46篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 58篇 |
1984年 | 44篇 |
1983年 | 34篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 22篇 |
1969年 | 14篇 |
排序方式: 共有3096条查询结果,搜索用时 31 毫秒
21.
Noriki Kutsumura Kota Shibuya Hitoshi Yamaguchi Takao Saito 《Tetrahedron letters》2017,58(43):4099-4102
Regioselective elimination of a vicinal bis-triflate having an adjacent ether oxygen functional group has been developed. Considered in the context of our studies of the regioselective elimination of vicinal dibromide, the key to the mechanism involves the electron-withdrawing inductive effect of the neighboring oxygen functional group. Aliphatic vinyl triflate was shown to be effective in Suzuki–Miyaura cross coupling compared with corresponding aliphatic vinyl bromide. 相似文献
22.
Yohei Saito Atsushi Mizokami Kouji Izumi Renato Naito Masuo Goto Kyoko Nakagawa-Goto 《Molecules (Basel, Switzerland)》2021,26(9)
α-Trifluoromethyl chalcones were prepared and evaluated for their antiproliferative activities against androgen-independent prostate cancer cell lines as well as five additional types of human tumor cell lines. The most potent chalcone 5 showed superior antitumor activity in vivo with both oral and intraperitoneal administration at 3 mg/kg. Cell-based mechanism of action studies demonstrated that 5 induced cell accumulation at sub-G1 and G2/M phases without interfering with microtubule polymerization. Furthermore, several cancer cell growth-related proteins were identified by using chalcone 5 as a bait for the affinity purification of binding proteins. 相似文献
23.
Gustavo Pereira Saito Ana Carolina Lanfredi Matsumoto Renata Pires Assis Iguatemy Loureno Brunetti Marco Aurlio Cebim Marian Rosaly Davolos 《Molecules (Basel, Switzerland)》2021,26(8)
Excessive UV solar radiation exposure causes human health risks; therefore, the study of multifunctional filters is important to skin UV protective ability and also to other beneficial activities to the human organism, such as reduction of reactive oxygen species (ROS) responsible for cellular damages. Potential multifunctional filters were obtained by intercalating of ferulate anions into layered simple metal hydroxides (LSH) through anion exchange and precipitation at constant pH methods. Ultrasound treatment was used in order to investigate the structural changes in LSH-ferulate materials. Structural and spectroscopic analyses show the formation of layered materials composed by a mixture of LSH intercalated with ferulate anions, where carboxylate groups of ferulate species interact with LSH layers. UV-VIS absorption spectra and in vitro SPF measurements indicate that LSH-ferulate systems have UV shielding capacity, mainly UVB protection. The results of reactive species assays show the ability of layered compounds in capture DPPH•, ABTS•+, ROO•, and HOCl/OCl− reactive species. LSH-ferulate materials exhibit antioxidant activity and singular optical properties that enable their use as multifunctional filters. 相似文献
24.
Dr. Manuela Leticia Kim Dr. Deicy Barrera Dr. Mutsumi Kimura Prof. Dr. Juan P. Hinestroza Prof. Dr. Karim Sapag Dr. Eugenio Hernán Otal 《化学:亚洲杂志》2021,16(9):1086-1091
We report on a detailed textural analysis of mechanochemically synthesized MOF-199 including N2 adsorption-desorption and CO2 adsorption isotherms data at 77 K and 273 K (up to atmospheric pressure), respectively, and CH4 adsorption data at 298 K (up to 35 bar). We used the isotherm adsorption data to determine the micropore volume of the MOF-199 structures, to establish their methane uptake capacity and to understand how these properties depended on the Ethanol/BTC ratio used during the synthesis. The maximum methane uptake capacity for our specimens was recorded at 130 v/v at 35 bars. These results open an avenue for a better understanding of alternative manufacturing processes of MOF structures for gas storage applications. 相似文献
25.
The transient heat transfer behavior in the case of heat removal from a cylindrical heat storage vessel packed with spherical particles was investigated experimentally for various factors (flow rate, diameter of spherical particles packed, temperature difference between flowing cold air and spherical particles accumulating heat, and physical properties of spherical particles). The experiments were covered in ranges of Reynolds number based on the mean diameter of spherical particles packed Red = 10.3–2200, porosity?=0.310 to 0.475, ratio of spherical particle diameter to cylinder diameterd/D = 0.0075–0.177 and ratio of length of the cylinder to cylinder diameterL/D=2.5–10. It was found that especially the flow rate and the dimension of spherical particles played an important role in estimating the transient local heat transfer characteristics near the wall of the cylindrical vessel in the present heat storage system. As flow rate and diameter of spherical particles were increased under a given diameter of the cylinder heat storage vessel, the mean heat transfer coefficient between the flow cold air and the hot spherical particles increased and the time period to finish removing heat from the vessel reduced. In addition, the useful experimental correlation equations of mean heat transfer coefficient between both phases and the time period to finish removing heat from the vessel were derived with the functional relationship of Nusselt numberNu d=f [modified Prandtl numberPr * (d/D), Red) and Fourier numberFo = f(d/D, L/D, Pr*, Red). 相似文献
26.
Summary The vibrations of a circular cylindrical shell reinforced with viscoelastic rings are theoretically treated. The frequency equation is derived using the transfer matrix together with the stiffness matrix. The numerical example surveys the damping effect of viscoelastic rings upon the dynamic behavior of the system.
Übersicht Die Schwingungen einer durch viskoelastische Kreisringe versteiften dünnwandigen Kreiszylinderschale werden theoretisch behandelt. Die Frequenzgleichung wird durch eine Kombination der Übertragungsmatrix mit der Steifigkeitsmatrix abgeleitet. An numerischen Beispielen wird ein Überblick über die dämpfende Wirkung der viskoelastischen Kreisringe auf das dynamische Verhalten des Systems gewonnen.相似文献
27.
The electrical conductivity of hexaisothiocyanocyclotriphos-phazene NsPs(NCS)6 and linear diisothiocyanophosphazene polymer (NP(NCS)2)n was determined. It was found that hexaisothiocyanocyclotriphosphazene is ionic and linear diiso-thiocyanocyclotriphosphazene polymer has predominantly electron conductivity. 相似文献
28.
29.
30.
Yutaka Maniwa Yoshinori Kumazawa Yumi Saito Hideki Tou Hiromichi Kataura Hiroyoshi Ishii 《Molecular Crystals and Liquid Crystals》2013,570(1):671-676
Abstract X-ray diffraction (XRD) and electrical resistance measurement on single-walled carbon nan-otube (SWNT) samples prepared by the arc-discharge method are reported. The XRD profile of heat-treated sample indicated that air (oxygen, and/or nitrogen and/or water) can be condensed inside the SWNTs. We also found that the electrical resistance of SWNT soot is significantly affected by exposing to the oxygen gas and humid air. 相似文献