全文获取类型
收费全文 | 920篇 |
免费 | 44篇 |
国内免费 | 3篇 |
专业分类
化学 | 689篇 |
晶体学 | 9篇 |
力学 | 5篇 |
数学 | 59篇 |
物理学 | 205篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 20篇 |
2015年 | 19篇 |
2014年 | 21篇 |
2013年 | 30篇 |
2012年 | 42篇 |
2011年 | 61篇 |
2010年 | 33篇 |
2009年 | 41篇 |
2008年 | 59篇 |
2007年 | 50篇 |
2006年 | 45篇 |
2005年 | 46篇 |
2004年 | 43篇 |
2003年 | 63篇 |
2002年 | 31篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 19篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 14篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有967条查询结果,搜索用时 31 毫秒
891.
Junichiro Mizusaki Masafumi Yoshihiro Shigeru Yamauchi Kazuo Fueki 《Journal of solid state chemistry》1985,58(2):257-266
In order to elucidate the defect structure of the perovskite-type oxide solid solution La1?xSrxFeO3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, PO2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of PO2 ≥ 0.13 atm, δ in La1?xSrxFeO3?δ was found to be close to 0. With decreasing log PO2, δ increased and asymptotically reached . The value corresponding to was about ?10 at 1000°C. With further decrease in log PO2, δ slightly increased. For LaFeO3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log PO2 is interpreted on the basis of the defect equilibrium among Sr′La (or V?La for the case of LaFeO3?δ), V··O, Fe′Fe, and Fe·Fe. Calculations were made for the equilibrium constants Kox of the reaction and Ki for the reaction Using these constants, the defect concentrations were calculated as functions of PO2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements. 相似文献
892.
Superhydrophobic and lipophobic properties of self-organized honeycomb and pincushion structures 总被引:5,自引:0,他引:5
Yabu H Takebayashi M Tanaka M Shimomura M 《Langmuir : the ACS journal of surfaces and colloids》2005,21(8):3235-3237
This report describes the simple preparation of superhydrophobic and lipophobic surfaces by self-organization. Microporous polymer films of a fluorinated polymer with hexagonally arranged pores were prepared by casting from solution under humid conditions. Hexagonally packed water microdroplets were formed by evaporative cooling on the surface of the casting solution. After solvent evaporation, a honeycomb-patterned polymer film was formed with the water droplet array acting as a template; the water droplets themselves evaporated soon after the solvent. Two porous polymer layers were stacked vertically, separated by pillars at the hexagon vertexes. After peeling off the top layer using adhesive tape, a pincushion-like structure was obtained. Here, we show that superhydrophobic behavior was achieved, with the maximum contact angle, 170 degrees, observed using these pincushion structures. Theoretical calculations fit the experimental results well. The lipophobic properties of the films are also discussed. 相似文献
893.
Hirota K Tajima K Hashimoto K 《Langmuir : the ACS journal of surfaces and colloids》2005,21(25):11592-11595
Taking advantage of both the self-organizing characteristics and the amphiphilic property of poly(styrene-block-ethyleneoxide) (P(S-b-EO)), we have realized one-step fabrication of nanoelectrode ensembles (NEEs). By choosing the electrolyte solution elaborately, only the poly(ethylene oxide) (PEO) segment in the P(S-b-EO) film was swollen to serve as nanoscale tunnels for solvated ions, whereas the polystyrene segment remained robust to be the electrode mask. An electrochemical analysis indicated that a transition between linear diffusion and nonlinear diffusion could be observed due to the small diffusion coefficient of ferrocene in PEO nanodomains. 相似文献
894.
Kenji Sasaki Yuhki Sekiya Hideko Fujiwara Hiromi Ohtomo Taiji Nakayama Takashi Hirota 《Journal of heterocyclic chemistry》1993,30(4):993-995
The synthesis of 4-substituted 5,6-dihydrobenzo[h]quinazolines and 6,7-dihydro-5H-benzo[6,7]cyclohepta-[1,2-d]pyrimidines with substituents which are an electron-attracting group such as a nitrite, an amide, a thione, or a carboxyl group is described. Their inhibitory activity against collagen-induced platelet aggregation was also investigated. 相似文献
895.
Single crystal EPR and phosphorescence studies of indene, indole, benzofuran and coumarin were made using DBB host. It was shown unambiguously that D < 3 |E| for these systems. (Z axis is perpendicular to the molecular plane.) The directions of the magnetic axes were also determined. Spin densities at the 6 and 5 positions in indole were estimated and compared with those of other substituted benzenes. It is concluded that large spin density is located at the CC group. 相似文献
896.
Four new 3,4-dihydroxystyrene dimers (3, 4, 5, and 9) have been isolated from a marine sponge Jaspis sp. along with the known narains (1 and 2), of which 3–5 induced metamorphosis of ascidian Halocynthia roretzi larvae. Structures of these metabolites were elucidated on the basis of spectral data. Biogenesis of these compounds is also discussed. 相似文献
897.
Noboru Morita Mitsuhiro Kurita Koichi Saito Maki Kinjo Shunji Ito Toyonobu Asao Masako Ueno Toshio Sato Akio Tajiri Masafumi Yasunami 《Journal of organometallic chemistry》1998,570(2):3223
The reactivities of tricarbonyl(2,4-cycloheptadiene-1,6-dione)iron toward several kinds of nucleophiles and electrophiles were investigated. As a result, it was found that tricarbonyl(2,4-cycloheptadiene-1,6-dione)iron has several reaction sites and undergoes several types of reactions. A new synthetic route to hinokitiol and tricarbonyl-(7,8-diphenylheptariafulvalene-1,6-quinone)iron from (2,4-cycloheptadiene-1,6-dione)iron was explored. 相似文献
898.
Ken Hirota 《Journal of solid state chemistry》2003,174(1):80-86
The presence of SmCrO4 is experimentally established. In Mg2+-substituted SmCrO3, single-phase perovskite Sm(Cr1−xMgx)O3, where x=0-0.23, are formed at ∼830°C by decomposition of Sm(Cr1−xMgx)O4 which crystallizes at 530-570°C from amorphous materials prepared by the hydrazine method. Sm(Cr1−xMgx)O3 solid solution powders consisting of submicrometer-size particles are sinterable; dense materials can be fabricated by sintering for 2 h at 1700°C in air. The relative densities, grain sizes, and electrical conductivities increase with increased Mg2+ content. Sm(Cr0.77Mg0.23)O3 materials exhibit an excellent direct current electrical conductivity of 2.2×103 S m−1 at 1000°C. 相似文献
899.
Kawasaki H Uota M Yoshimura T Fujikawa D Sakai G Annaka M Kijima T 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):11468-11473
Single-crystalline platinum nanosheets have been prepared via a new methodology based on the chemical reduction of a platinum salt (H2PtCl6) with hydrazine at a graphite/solution interface, using polyoxyethylene (20) sorbitan monostearate (Tween 60) based self-assembly (hemicylindrical micelle) templates. The platinum nanosheets with a uniform thickness of as thin as 3.5 +/- 1 nm are surface-smooth and continuous over relatively large length scales of micrometer sizes. In striking contrast to the Tween 60 based system, no Pt nanosheets are obtained with nonaethylene glycol monododecyl ether (C12EO9) and polyoxyethylene (23) dodecyl ether (C12EO23). No Pt nanosheets are also obtainable with a laterally homogeneous layer of Tween 60 formed at the silica/solution interface. These results indicate that surfactant Tween 60 molecules with a triple polyoxyethylene structure, as well as their hemicylindrical micelle templates, play an essential role for the formation of the Pt nanosheets. It is also suggested that the interfacially directed growth of Pt metals within the aqueous shells of the Tween 60 hemicylindrical micelles induces the thin Pt crystals as thick as the aqueous shells. The present approach could be extended to prepare a wide range of novel nanostructures of noble metals, using various micelle-like self-assemblies at interfaces. 相似文献
900.
Hua DH Tamura M Huang X Stephany HA Helfrich BA Perchellet EM Sperfslage BJ Perchellet JP Jiang S Kyle DE Chiang PK 《The Journal of organic chemistry》2002,67(9):2907-2912
A number of substituted 9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrones have been synthesized and their anticancer and antimalarial activities evaluated. A one-pot synthesis of 2,5,8-trimethoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4-dione (4) was achieved by heating a mixture of 1,4-dimethoxyanthracene, methoxyhydroquinone, silver oxide, and zinc iodide in toluene. Regioselective bromination of 4 and 2-methoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrone (7) with N-bromosuccinimide provided 2-bromo-3,5,8-trimethoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4-dione and 2-bromo-3-methoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrone (1), respectively. The reactions of 1 with aliphatic primary amines and secondary amines, respectively, produced different products, a result most likely attributed to the different basicities (or nucleophilicities) and steric effects of the two kinds of amines. The structure of the displacement product, 2-bromo-3-[2-(tert-butoxycarbonyl)ethylamino]-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4,5,8-tetrone, from the reaction of 1 with tert-butyl 3-aminopropanoate was unequivocally determined by a single-crystal X-ray analysis. IC(50) values of triptycene bisquinones for the inhibition of L1210 leukemia cell viability are in the 0.11-0.27 microM range and for the inhibition of Plasmodium falciparum 3D7 are in the 4.7-8.0 microM range. 相似文献