全文获取类型
收费全文 | 1195篇 |
免费 | 39篇 |
国内免费 | 14篇 |
专业分类
化学 | 858篇 |
晶体学 | 10篇 |
力学 | 28篇 |
数学 | 81篇 |
物理学 | 271篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 14篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 28篇 |
2015年 | 29篇 |
2014年 | 25篇 |
2013年 | 52篇 |
2012年 | 59篇 |
2011年 | 64篇 |
2010年 | 38篇 |
2009年 | 54篇 |
2008年 | 87篇 |
2007年 | 71篇 |
2006年 | 68篇 |
2005年 | 62篇 |
2004年 | 52篇 |
2003年 | 50篇 |
2002年 | 48篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 17篇 |
1998年 | 13篇 |
1997年 | 15篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 20篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 8篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1976年 | 8篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1970年 | 4篇 |
1965年 | 7篇 |
排序方式: 共有1248条查询结果,搜索用时 439 毫秒
141.
-Nitrophenylhydrazones, unsusceptible to autoxidation, are readily oxygenated in the presence of a five-coordinate cobalt(II)-Schiff base complex, Co(II)(MeOSalen) (Py) leading to quantitative formation of novel 1-(-nitrophenylazo)-1-peroxy Co(III) complexes 2, which were isolated as crystals. A plausible mechanism involving hydrogen abstraction by Co(III)(O2?.) from the substrate followed by formation of a substrate anion Co(III) complex intermediate is proposed. 相似文献
142.
Summary The behavior of a spherical bubble near a solid wall is analysed by considering the liquid compressibility. The equation of motion of the bubble with first order correction for the effects of liquid compressibility and solid wall is derived. The equation obtained here coincides with the known result in case of L or C
. Further experimental study is made on the motion of bubbles produced by a spark discharge in water. The theoretical results are in good agreement with the experiments.
Das Verhalten einer kugelförmigen Blase in einer kompressiblen Flüssigkeit in der Nähe einer festen Wand
Übersicht Bei Berücksichtigung der Flüssigkeitskompressibilität wird das Verhalten einer kugelförmigen Blase in der Nähe einer festen Wand analysiert. Die Gleichung der Bewegung der Blase wird mit der Korrektur erster Ordnung für den Einfluß der Flüssigkeitskompressibilität und der festen Wand angegeben. Aus der erhaltenen Gleichung wird für L oder C das bekannte Ergebnis hergeleitet. Darüber hinaus wird eine experimentelle Untersuchung der Blasenbewegung durchgeführt. Die Blase wird mit Hilfe von Funkendurchschlägen zwischen Elektroden in Wasser erzeugt. Die theoretischen Ergebnisse stimmen gut mit den Experimenten überein.相似文献
143.
H. Ikezoe N. Shikazono Y. Tomita K. Ideno Y. Sugiyama E. Takekoshi 《Nuclear Physics A》1985,444(2):349-364
Velocity spectra of fusion-like residues produced in the reactions of 90 MeV and 150 MeV 16O with 27Al were measured. At 90 MeV the velocity spectra were well reproduced by a statistical model calculation. At 150 MeV the observed centroids of the velocity spectra deviate from the statistical model predictions. The centroid shifts as a function of the atomic and mass numbers of evaporation residues were analyzed by two different model calculations based on the assumption that incomplete fusion is (a) a peripheral process, or (b) independent on the angular momentum of the entrance channel, respectively. The later assumption is in better agreement with the presented data. 相似文献
144.
Yasunari Hashimoto Junichi Ushiba Akio Kimura Meigen Liu Yutaka Tomita 《BMC neuroscience》2010,11(1):117
Background
For severely paralyzed people, a brain-computer interface (BCI) provides a way of re-establishing communication. Although subjects with muscular dystrophy (MD) appear to be potential BCI users, the actual long-term effects of BCI use on brain activities in MD subjects have yet to be clarified. To investigate these effects, we followed BCI use by a chronic tetraplegic subject with MD over 5 months. The topographic changes in an electroencephalogram (EEG) after long-term use of the virtual reality (VR)-based BCI were also assessed. Our originally developed BCI system was used to classify an EEG recorded over the sensorimotor cortex in real time and estimate the user's motor intention (MI) in 3 different limb movements: feet, left hand, and right hand. An avatar in the internet-based VR was controlled in accordance with the results of the EEG classification by the BCI. The subject was trained to control his avatar via the BCI by strolling in the VR for 1 hour a day and then continued the same training twice a month at his home. 相似文献145.
[Structure: see text] 12-hydroxydaphnetoxins, members of the structurally fascinating daphnane diterpene family, exhibit a wide range of significant biological activities. A general route to the BC-ring system of 12-hydroxy daphnetoxins is reported based on D-ribose. Depending on the choice of protecting groups and solvent, the oxidopyrylium-alkene [5+2] cycloaddition originating from A provides cycloadduct diastereomer B or C with good to excellent selectivity. 相似文献
146.
Tsukamoto K Ohishi H Hiyama Y Maezaki N Tanaka T Ishida T 《Chemical communications (Cambridge, England)》2006,(34):3606-3608
Potassium salts of p-tert-butylcalix[6]arene p-bromophenylalanine derivative formed sizable octameric cages in the solid state that were revealed by X-ray crystallographic analysis. 相似文献
147.
A new method to evaluate the weights of resonance structures from molecular orbital wave function is proposed, which is based on the second quantization of singlet-coupling. The present method is useful to analyze molecules of which the electronic structures are well localizable. The evaluation is carried out through localization of molecular orbitals followed by algebraic calculation of density matrices. This method is applied to H(2)O, H(3)O(+), and BH(3). The calculated weights of covalent and ionic structures are in excellent agreement with those of the previous works and our chemical intuition. 相似文献
148.
Rietveld IB Kobayashi K Yamada H Matsushige K 《The journal of physical chemistry. B》2006,110(46):23351-23364
Poly(vinylidene fluoride) film formation with electrospray deposition has been studied with support of a droplet evaporation model. The input parameters of the model consist basically of the solvent, the solute concentration, the flow rate, and the solution conductivity. The model provides the droplet size, the solute concentration, the droplet velocity, and the shear stress of the droplet at impact as a function of the distance between the nozzle and the substrate. With some additional experimental information such as the size change of the film with spray distance and the viscosity of the solution, the growth rate of the film and the shear rate of the droplet at impact can be determined. Growth rate is shown to define distinct regimes of film formation. In those regimes, only a single factor or a limited number of factors controls the film morphology. The most important factors include the shear rate and the surface energy. It is found that at a specific range of growth rates only the shear rate determines the morphology of the polymer film. Growth rate, as the defining quantity of film morphology, is not limited to polymer solutions. Therefore, the growth rate, in combination with the control factors mentioned above, functions as a general framework through which understanding and control of film formation with electrospray deposition can be improved. 相似文献
149.
[structure: see text] The feasibility of assembling 3JH,H profiles from NMR data collected on relevant, but not necessarily specific, NMR database compounds representing a given stereocluster was demonstrated. By this approach, the 3JH,H profile was created for the contiguous tetraol peracetate stereocluster. The reliability and applicability of the database thus assembled were demonstrated for known peracetates derived from two heptoses. 相似文献
150.
A new type of mesh generator is developed by using a self-organized pattern in a reaction–diffusion system. The system is the Gray–Scott model, which creates a spot pattern in a specific parameter region. The spots correspond to nodes of a mesh. The mesh generator has several advantages: the algorithm is simple and processes to improve the mesh, such as smoothing, (locally) addition, and removal of nodes, are automatically performed by the system. 相似文献