全文获取类型
收费全文 | 1185篇 |
免费 | 31篇 |
国内免费 | 6篇 |
专业分类
化学 | 886篇 |
晶体学 | 4篇 |
力学 | 19篇 |
数学 | 72篇 |
物理学 | 241篇 |
出版年
2023年 | 7篇 |
2022年 | 8篇 |
2021年 | 19篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 20篇 |
2017年 | 18篇 |
2016年 | 29篇 |
2015年 | 26篇 |
2014年 | 21篇 |
2013年 | 55篇 |
2012年 | 62篇 |
2011年 | 78篇 |
2010年 | 39篇 |
2009年 | 25篇 |
2008年 | 75篇 |
2007年 | 70篇 |
2006年 | 66篇 |
2005年 | 75篇 |
2004年 | 63篇 |
2003年 | 73篇 |
2002年 | 55篇 |
2001年 | 28篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 20篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 9篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有1222条查询结果,搜索用时 9 毫秒
1.
Tomohiro Kyotani Sonoko Kakui Takehito Mizuno Naoto Shimotsuma Soushi Inoue Junji Saito 《Analytical sciences》2006,22(7):1031-1034
A zeolite NaA (LTA) membrane supported by an alumina porous support tube for pervaporation (PV) dehydration of ethanol was characterized by transmission electron microscopy (TEM) using a focused ion beam (FIB) thin-layer specimen preparation technique and by Fourier transform infrared attenuated total reflectance method (FTIR-ATR) using a diamond prism as the waveguide. FIB-TEM clearly presented cross-section images up to about 15 microm depth from the membrane surface. FTIR-ATR monitored the Si-O asymmetric stretching vibration spectrum. The Si-O spectrum was compared with the TEM image and their relationships were discussed. By combining the two methods, we could study the thickness of surface LTA crystals, the grain boundary, the LTA/alumina interface structure and the crystallinity and density of materials inside of the alumina porous support. Consequently, fine structure changes of the LTA membrane corresponding to the hydrothermal synthesis condition could be sensitively detected. 相似文献
2.
Shigeru Katayama Mika Horiike Kazuyuki Hirao Naoto Tsutsumi 《Journal of Polymer Science.Polymer Physics》2002,40(24):2800-2806
We investigated the structures induced by an irradiation of a near‐infrared (NIR) femtosecond laser pulse in dye‐doped polymeric materials {poly(methyl methacrylate) (PMMA), thermoplastic epoxy resin (Epoxy), and a block copolymer of methyl methacrylate and ethyl acrylate‐butyl acrylate [p(MMA/EA‐BA) block copolymer]}. Dyes used were classified into two types—type 1 with absorption at 400 nm and type 2 with no absorption at 400 nm. The 400‐nm wavelength corresponds to the two‐photon absorption region by the irradiated NIR laser pulse at 800 nm. Type 1 dye‐doped PMMA and p(MMA/EA‐BA) block copolymer showed a peculiar dye additive effect for the structures induced by the line irradiation of a NIR femtosecond laser pulse. On the contrary, dye‐doped Epoxy did not exhibit a dye additive effect. The different results among PMMA, p(MMA/EA‐BA) block copolymer, and Epoxy matrix polymers are supposed to be related to the difference of electron‐acceptor properties. The mechanism of this type 1 dye‐additive‐effect phenomenon for PMMA and p(MMA/EA‐BA) block copolymer is discussed on the basis of two‐photon absorption of type 1 dye at 400 nm by the irradiation of a femtosecond laser pulse with 800 nm wavelength and the dissipation of the absorbed energy to the polymer matrix among various transition processes. Dyes with a low‐fluorescence quantum yield favored the formation of thicker grating structures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2800–2806, 2002 相似文献
3.
4.
Yoshito Ikada Yasuko Nishizaki Hiroo Iwata Ichiro Sakurada 《Journal of polymer science. Part A, Polymer chemistry》1977,15(2):451-460
Poly(vinyl alcohol) (PVAI) was oxidized by ceric ion, Ce(IV), in aqueous HNO3 medium at different temperatures and found to be degraded as a result of selective cleavage of the 1,2-glycol unit existing in PVAl. The rate of oxidation increased with increasing temperature. The aldehyde groups formed at the ends of the degraded polymer upon oxidation were relatively stable at 0°C. With rise of temperature, the aldehyde groups reacted either with excess of Ce(IV) to carboxylic acids or with hydroxyl groups of PVAl molecules to give acetal linkage. When the acetalization predominated over the oxidation to carboxyl group, gelation of the reaction mixture was observed. Based on these results, a plausible mechanism of oxidation of PVAl with Ce(IV) and the subsequent reactions is discussed. 相似文献
5.
To examine the antithrombogenicity of cultured endothelial cell-detached surface, a simple hybrid vascular model tube consisting of a glass tube and endothelial cells was constructed. To detach the endothelial cells from the inner surface of the model tube, a steady shear stress of 2 or 8 N m(-2) was imposed onto the surface of endothelial cell monolayer by means of a coaxial double cylinder rotational-type apparatus. Coagulation of blood in contact with the endothelial cell-detached surface was examined using a damped oscillation rheometer. Coagulation of whole blood in the cell-detached tube occurred at about 40 min, which was almost the same as that in the endothelial cell-coated tube. A few platelets without shape change adhered to the endothelial cell-detached surface. These data suggest that the endothelial cell-detached surface may exhibit antithrombogenic and anticoagulant surfaces. Biochemical analyses showed that the glass surface, where endothelial cell was detached, was covered with components such as collagen type IV that is considered to be produced from the endothelial cells on the glass surface. 相似文献
6.
Some results of approximate ab initio calculations of the “correlation” contribution to the true parameters of the pi electron hamiltonian are presented for the ethylene molecule. In particular, by using sum-of-the-pairs type generalized perturbation theory, it is shown that there is a large core “correlation” contribution to singlet-triplet splittings within pi electron theories that results from the difference in the degree of ionicity of the isoconfigurational states. 相似文献
7.
Kaoru Iwata Tsuneo Hagiwara Hiroshi Matsuzawa 《Journal of polymer science. Part A, Polymer chemistry》1986,24(5):1043-1051
The reciprocity effect under intense illumination was studied with photocrosslinkable polyesters of p-phenylenebis(α-cyanobutadiene carboxylic acid) (I), m-phenylenebis(α-cyanobutadiene carboxylic acid) (II), and p-phenylenebis(acrylic acid) (III), with an argon ion laser as a light source. The reciprocal sensitivities of I, II, and III were 5.0, 1800, and > 105 mJ/cm2, respectively. II and III required sensitization to enhance their sensitivities to a level at which reciprocity effects could be measured. I obeyed the reciprocity law over a wide range of exposure times from seconds to microseconds. Both II′, a copolyester of II, and III showed a dramatic decrease of sensitivity in high-intensity/short-time exposure when sensitized by 9,10-phenanthraquinone and pyrylium salts. 相似文献
8.
3,4-Dhydro-6,7-dimethoxy-4-methyl-3-oxo-quinoxaline-2-carbonyl azide is a highly senstive fluorescence derivatization reagent for primary, secondary and tertiary alcohols for high-performance liquid chromatography. Reaction conditions are optimized with benzyl alcohol, n-hexanol, cyclohexanol and 2-methyl-2-butanol. The reagent reacts with the alcohols in benzene to produce the corresponding fluorescent carbamic acid esters, which can be separated on a reversed-phase column YMC Pack C8 with aqueous methanol as eluent. the detection limits for the alchols are 2–5 fmol per 10-μl njection. The reagent also reacts with hydroxysteroids with primary, secondary and/or tertiary alcoholic group(s) to form fluorescent derivatives. Hydroxycarboxylic acids and phenols do not give any chromatographic peaks. 相似文献
9.
10.
Keitaro Tanoi Natsuko I. Kobayashi Takayuki Saito Naoko Iwata Atsushi Hirose Yoshimi Ohmae Ren Iwata Hisashi Suzuki Tomoko M. Nakanishi 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):749-751
The time course of Mg uptake and release using intact rice plants and 28Mg as a tracer is presented. Since there is no conventional Mg tracer available, 28Mg was produced via 27Al(α, 3p)28Mg reaction using a cyclotron. Using the purified 28Mg tracer, it was found that the uptake amount of 28Mg by the rice plants increased linearly during 30 min of application. After 28Mg treatment for 90 min, the roots were sequentially washed with iced solution for 120 min. Within about 10 min, almost all of the 28Mg, that was thought to be weakly bound to the apoplast, was washed away. 相似文献