全文获取类型
收费全文 | 711篇 |
免费 | 30篇 |
国内免费 | 1篇 |
学科分类
数理化 | 742篇 |
出版年
2023年 | 7篇 |
2021年 | 8篇 |
2020年 | 21篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 33篇 |
2012年 | 42篇 |
2011年 | 48篇 |
2010年 | 36篇 |
2009年 | 33篇 |
2008年 | 46篇 |
2007年 | 50篇 |
2006年 | 60篇 |
2005年 | 50篇 |
2004年 | 40篇 |
2003年 | 41篇 |
2002年 | 35篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有742条查询结果,搜索用时 639 毫秒
81.
An enzyme immunoelectrode for the amperometric determination of serum insulin is described. The device consists of an immunoreactive membrane combined with a hydrogen peroxide electrode. The surface of a microporous hydrophobic polypropylene membrane is modified by water vapour plasma treatment to make it partially hydrophilic. Subsequent treatment with octamethylenediamine and glutaraldehyde enables the surface of this membrane to interact with various proteins. Anchoring of the antibody to Protein A immobilized on the membrane was effective for immunoreactivity. 相似文献
82.
In this paper, we obtain the Varadhan type small time asymptotics for diffusion processes on path groups. 相似文献
83.
84.
Shigeki Yonezawa Yuji Muraoka Yutaka Ueda Zenji Hiroi 《Solid State Communications》2004,129(4):245-248
Effects of epitaxial stress on the metal-insulator transition of V2O3 have been studied for in the form of epitaxial thin films grown on α-Al2O3 (0001) and LiTaO3 (0001) substrates. A metallic phase is stabilized down to 2 K in the V2O3 thin film on α-Al2O3 (0001), where the a-axis is compressed by 4% owing to large epitaxial stress. On the other hand, the transition temperature TMI is raised by 20 K from the value of 170 K in bulk samples in the film on LiTaO3 (0001), where the a-axis is expanded. These results suggest an intimate relationship between the a-axis length and TMI in V2O3. The conductivity of the metallic ultrathin films shows logarithmic temperature dependence below 20 K, probably due to the Anderson localization in two-dimensional systems. 相似文献
85.
A new chemical vapor deposition (CVD) method, called ionization CVD, was developed, to produce non-agglomerated nanoparticles in which reactant gases are charged. A sonic-jet corona discharger was used as an ionizer in the developed nanoparticle generator. For a tetraethylorthosilicate (TEOS)/O2 chemical system, SiO2 nanoparticles were prepared. All particles formed by the ionization CVD were charged unipolarly. SEM micrographs of particles showed that the repulsive Coulombic force between charged particles reduces their coagulation rate and produces non-agglomerated nanoparticles that have a relatively high number concentration and small size. An external field was used to collect the charged particles onto Si wafers. These collected samples indicated that the deposition of charged particles could be controlled by the external electric field. Particle concentration measurement with a condensation nucleus counter at various TEOS concentrations suggested the particle formation mechanism in the ionization CVD was an ion-induced nucleation. 相似文献
86.
Shigeki Habaue Ryo Muraoka Akiko Aikawa Soichiro Murakami Hideyuki Higashimura 《Journal of polymer science. Part A, Polymer chemistry》2005,43(8):1635-1640
The oxidative coupling polymerization of 2,3‐dihydroxynaphthalene with the novel dinuclear‐type copper(II) catalysts successfully produced poly(2,3‐dihydroxy‐1,4‐naphthylene). For example, the MeOH‐insoluble polymer with a number average molecular weight of 4.4 × 103 from the polymerization using the complex of CuCl2 and N,N′‐bis(2‐morpholinoethyl)‐p‐xylylenediamine ( p ‐ 1 ) at room temperature under an O2 atmosphere followed by acetylation of the hydroxyl groups was obtained in 63% yield. The structures of the tetraamine ligands and the counter anion of the copper(II) salts significantly influenced the catalyst activity. The polymerization of 2,2′‐dimethoxy‐1,1′‐binaphthalene‐3,3′‐diol with the 2CuCl2‐ p ‐ 1 catalyst, however, resulted in a lower yield. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1635–1640, 2005 相似文献
87.
88.
Novel chiral phosphonoacetates bearing a stereogenic phosphorus atom were successfully synthesized by enzyme-catalyzed kinetic resolution of racemic phosphonoacetates. 相似文献
89.
Takahashi T Kuroiwa S Ogura T Yoshikawa S 《Journal of the American Chemical Society》2005,127(28):9970-9971
The process of dioxygen reduction catalyzed by cytochrome c oxidase was investigated by examining intact porcine mitochondrial preparations using a novel time-resolved resonance Raman measurement system at experimental accuracy levels equivalent to those of the reaction system of the solubilized and purified enzyme. The resonance Raman bands assignable to the initial three intermediates were detected at frequencies identical to those observed with purified enzyme preparations. However, the lifetime of the initial intermediate (the oxygenated species) in the mitochondrial preparation was found to be significantly longer than that observed in purified preparations, suggesting that control of the stability of the oxygenated species is imposed by the mitochondrial membrane system. 相似文献
90.
Yamagiwa N Qin H Matsunaga S Shibasaki M 《Journal of the American Chemical Society》2005,127(38):13419-13427
The full details of a catalytic asymmetric aza-Michael reaction of methoxylamine promoted by rare earth-alkali metal heterobimetallic complexes are described, demonstrating the effectiveness of Lewis acid-Lewis acid cooperative catalysis. First, enones were used as substrates, and the 1,4-adducts were obtained in good yield (57-98%) and high ee (81-96%). Catalyst loading was successfully reduced to 0.3-3 mol % with enones. To broaden the substrate scope of the reaction to carboxylic acid derivatives, alpha,beta-unsaturated N-acylpyrroles were used as monodentate, carboxylic acid derivatives. With beta-alkyl-substituted N-acylpyrroles, the reaction proceeded smoothly and the products were obtained in high yield and good ee. Transformation of the 1,4-adducts from enones and alpha,beta-unsaturated N-acylpyrroles afforded corresponding chiral aziridines and beta-amino acids. Detailed mechanistic studies, including kinetics, NMR analysis, nonlinear effects, and rare earth metal effects, are also described. The Lewis acid-Lewis acid cooperative mechanism, including the substrate coordination mode, is discussed in detail. 相似文献