全文获取类型
收费全文 | 7198篇 |
免费 | 574篇 |
国内免费 | 466篇 |
专业分类
化学 | 2477篇 |
晶体学 | 48篇 |
力学 | 1745篇 |
综合类 | 55篇 |
数学 | 1663篇 |
物理学 | 2250篇 |
出版年
2024年 | 9篇 |
2023年 | 129篇 |
2022年 | 199篇 |
2021年 | 192篇 |
2020年 | 260篇 |
2019年 | 178篇 |
2018年 | 173篇 |
2017年 | 239篇 |
2016年 | 300篇 |
2015年 | 209篇 |
2014年 | 395篇 |
2013年 | 536篇 |
2012年 | 377篇 |
2011年 | 462篇 |
2010年 | 359篇 |
2009年 | 502篇 |
2008年 | 452篇 |
2007年 | 434篇 |
2006年 | 364篇 |
2005年 | 319篇 |
2004年 | 274篇 |
2003年 | 255篇 |
2002年 | 203篇 |
2001年 | 153篇 |
2000年 | 175篇 |
1999年 | 138篇 |
1998年 | 121篇 |
1997年 | 124篇 |
1996年 | 83篇 |
1995年 | 91篇 |
1994年 | 89篇 |
1993年 | 72篇 |
1992年 | 69篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 34篇 |
1988年 | 35篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1971年 | 4篇 |
1957年 | 6篇 |
排序方式: 共有8238条查询结果,搜索用时 31 毫秒
121.
J.B Goodenough J.-S Zhou F Rivadulla E Winkler 《Journal of solid state chemistry》2003,175(1):116-123
Bond-length fluctuations in transition-metal oxoperovskites may give rise to two-phase fluctuations in what appears to be a single phase to a diffraction experiment. Orbital disorder at Jahn-Teller ions results in bond-length fluctuations that give 3D-ferromagnetic, vibronic Mn(III)-O-Mn(III) superexchange interactions and allow disproportionation into Mn(IV) and Mn(II) in LaMnO3; where orbitally ordered and disordered phases coexist, an external magnetic field stabilizes the orbitally disordered, ferromagnetic phase relative to the orbitally ordered, antiferromagnetic phase. Spin-lattice interactions in the paramagnetic phase of charge-transfer compounds give bond-length fluctuations arising from the semicovalent component of the superexchange interactions. At the crossover from localized to itinerant electronic behavior, the coexistence of two-phase fluctuations has been demonstrated in both the single-valent RNiO3 family (R=rare-earth, A=alkaline-earth) and the mixed-valent R0.5A0.5MnO3 perovskites. “Bad-metal” behavior is found to be associated with bond-length fluctuations. 相似文献
122.
123.
Shao Hua SHI Li Jian LIU 《中国化学快报》2006,17(3):361-364
Poly(N-isopropylacrylamide) (PNIPAM) hydrogel, which is insoluble but shrinkable or swellable in aqueous media when temperature rises or drops across 33oC1,2, has been extensively studied due to its potential applications in the fields of controlled drug … 相似文献
124.
The effect of the micelles on the dynamic surface tension of micellar surfactant solutions is studied experimentally by means of the maximum bubble pressure method. Different frequencies of bubbling ranging approximately between 1 and 30 s–1 are applied. The time dependence of the surface tension is calculated using a dead time correction. Water solutions of two types of surfactants with different concentrations are investigated: sodium dodecyl sulfate and nonylphenol polyglycol ether. The surface tension relaxes more quickly in the presence of micelles. The characteristic times of relaxation of the surface tension seem to be in the millisecond range. The time constants observed experimentally are explained in terms of the theory of surfactant diffusion affected by micellization kinetics. 相似文献
125.
A novel extraction method, namely dynamic ultrasound-assisted extraction, is investigated. This technique is efficient with respect to both time and solvent consumption because it utilizes ultrasonic energy in dynamic mode during extraction. Polyphenols (chlorogenic acid, esculetin, rutin, scopoletin, and quercitrin) are extracted from a tobacco (Nicotina tobaccum L.) sample for 10 min with 6 mL of solvent. Fresh solvent is continuously pumped through the sample, with which the analytes can be rapidly extracted, and the possibility of degradation efficiently avoided. Methanol involving 0.5% w/v ascorbic acid was used as extraction solvent; optimal flow rate and extraction time were investigated. The extract was cleaned up by C18 disposable cartridge. The spiked and nonspiked tobacco samples were used for the evaluation of the proposed method. Recoveries obtained were varied from 96 to 108% and RSDs from 2.0 to 4.6%. This extraction technique was revealed to recover larger amounts of polyphenols from tobacco, compared to the static ultrasound-assisted extraction method. 相似文献
126.
Elisângela Corradini Luís C. de Morais Nicole R. Demarquette José A. M. Agnelli Luiz H. C. Mattoso 《先进技术聚合物》2007,18(10):861-867
This work involved a study of the effect of processing variables (temperature, water content, rotor speed, and time) on the mechanical properties of starch:gluten:glycerol mixtures in the weight ratio of 40:40:20. The properties of the materials were affected by the processing variables. The torque decreased with water content, indicating that water facilitates the plasticization of mixtures, whereas the increase in temperature accelerated the evaporation of water, thus increasing the torque. Ultimate tensile strength was achieved at the lowest temperature (110°C) and the highest water content (20%), whereas maximum elongation was achieved for the material processed at the highest temperature, 150°C, and the fastest rotor speed, 70 rpm. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
127.
指出了当前流行的差示扫描量热法DSC单峰法测样品纯度所基于的假定有一些不确切的地方,并用计算机动态摸拟了DSC实验过程,结果证实了本文的论断。 相似文献
128.
Marie-Hélène Paclet Cécile F. Rousseau Campion Yannick Françoise Morel Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):353-357
The effects of para-Sulphonato-calix[4]arene, para-Sulphonato-calix[6]arene and para-Sulphonato-calix[8]arene on the activation of NADPH oxidase in neutrophils has been studied. All three molecules do not induce NADPH oxidase activation, and hence do not stimulate neutrophils. Measurement of cell viability demonstrates that these three water-soluble calix[n]arene derivatives are not cytotoxic. 相似文献
129.
The potential response of the platinum indicator electrode in the uncatalyzed bromate oscillator (UBO) with three different
substrates, namely gallic acid (GA), pyrogallol (PG) and veratraldehyde (VA) has been analyzed. The large amplitude oscillations
obtained with a Pt electrode are due to the sequential response of the indicator electrode to the varying concentration ratios
of the redox couples present in the reaction mixture. 相似文献
130.
Production of micron-sized monodispersed composite polymer particles by seeded polymerization utilizing the dynamic swelling method 总被引:1,自引:0,他引:1
In order to develop the seeded polymerization technique utilizing the dynamic swelling method (DSM) proposed by authors for
the production of micron-sized mono-dispersed “composite” polymer particles consisting of two kinds of polymers, the seeded
polymerization for the dispersion of ethyl methacry-late (EMA)-swollen PS particles prepared utilizing DSM was carried out.
Monodispersed PS/poly(ethyl methacrylate) (PEMA) composite particles having 7 μm in diameter were produced by the addition
of NaCl to lower the solubility of EMA in medium and by the addition of CuCl2 as a water-soluble inhibitor to depress the by-production of submicron-sized PEMA particles.
Received: 16 July 1996 Accepted: 10 October 1996 相似文献