全文获取类型
收费全文 | 396篇 |
免费 | 17篇 |
专业分类
化学 | 246篇 |
晶体学 | 4篇 |
力学 | 25篇 |
数学 | 55篇 |
物理学 | 83篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 33篇 |
2012年 | 31篇 |
2011年 | 32篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 25篇 |
2007年 | 27篇 |
2006年 | 25篇 |
2005年 | 17篇 |
2004年 | 10篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有413条查询结果,搜索用时 78 毫秒
61.
A non-linear partial differential equation modelling the flow of a fourth-grade fluid is derived. Both analytical and numerical travelling wave solutions admitted by the model equation are obtained. 相似文献
62.
Hub location problems involve locating hub facilities and allocating demand nodes to hubs in order to provide service between origin–destination pairs. In this study, we focus on cargo applications of the hub location problem. Through observations from the Turkish cargo sector, we propose a new mathematical model for the hub location problem that relaxes the complete hub network assumption. Our model minimizes the cost of establishing hubs and hub links, while designing a network that services each origin–destination pair within a time bound. We formulate a single-allocation hub covering model that permits visiting at most three hubs on a route. The model is then applied to the realistic instances of the Turkish network and to the Civil Aeronautics Board data set. 相似文献
63.
Redouane Kara Mourad Ahmane Jean Jacques Loiseau Said Djennoune 《Nonlinear Analysis: Hybrid Systems》2009,3(4):738-748
This paper deals with constrained regulation of continuous Petri nets under the so-called infinite servers semantics. Our aim is to design feedback gains that permit us to reach both desired stationary marking vector and desired asymptotic firing rate vector. The proposed approach takes into account constraints on the control, the marking of the Petri net, and the stability of the closed-loop system. The existence of a solution is first expressed geometrically, in terms of the inclusion of two polyhedral sets. They are reformulated algebraically as linear matrix inequalities, which provides an effective way to calculate feedback gains answering the problem. Finally, an application to an assembly production system is given. 相似文献
64.
The photon transmission method was used to study latex film formation from poly(vinyl acetate) (PVAc) particles induced by two different solvents. Films with the same latex content were prepared from PVAc particles and exposed to vapor of ethanol-water and acetone-water mixtures in various compositions. Transmitted photon intensities, Itr, from these films increased with increasing vapor exposure time. The increase in Itr is attributed to the increase in crossing density at the polymer-polymer junction. The Prager-Tirrell model was employed to obtain the back-and-forth frequency, nu, of the reptating polymer chain during film formation induced by solvent vapor. It was observed that the produced nu values increase as the solvent content is increased for both solvents. Abilities of both solvents to form films were interpreted with the solubility parameters of the solvents and the PVAc. 相似文献
65.
Tekin N Kadinci E Demirbaş O Alkan M Kara A 《Journal of colloid and interface science》2006,296(2):472-479
The adsorption of polyvinylimidazole (PVI) onto kaolinite from aqueous solutions has been investigated systematically as a function of parameters such as calcination temperature of kaolinite, pH, ionic strength, and temperature. According to the experimental results, the adsorption of PVI increases with pH from 8.50 to 11.50, temperature from 25 to 55 degrees C, and ionic strength from 0 to 0.1 mol L(-1). The kaolinite sample calcined at 600 degrees C has a maximum adsorption capacity. Adsorption isotherms of PVI onto kaolinite have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The physical properties of this adsorbent are consistent with the parameters obtained from the isotherm equations. Furthermore, the zeta potentials of kaolinite suspensions have been measured in aqueous solutions of different PVI concentrations and pH. From the experimental results, (i) pH strongly alters the zeta potential of kaolinite; (ii) kaolinite has an isoelectric point at about pH 2.35 in water and about pH 8.75 in 249.9 ppm PVI concentration; (iii) PVI changes the interface charge from negative to positive for kaolinite. The study of temperature effect has been quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy changes. The dimensionless separation factor (RL) has shown that kaolinite can be used for adsorption of PVI from aqueous solutions. 相似文献
66.
Arif Selcuk Ogrenci Onder Pekcan Selim Kara Ayse Humeyra Bilge 《Journal of Macromolecular Science: Physics》2018,57(5):364-376
The thermal phase transition temperatures of high (HMP) and low melting point (LMP) agarose gels were investigated by using UV–vis spectroscopy techniques. Transmitted light intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol–gel) processes. It was observed that the transition temperatures, Tm, defined as the location of the maximum of the first derivative of the sigmoidal transition paths obtained from the UV–vis technique, slightly increased by increasing the agarose concentration in both the HMP and LMP samples. Here, we express the phase transitions of the agar-water system, as a representative of reversible physical gels, in terms of a modified Susceptible-Infected-Susceptible epidemic model whose solutions are the well-known 5-point sigmoidal curves. The gel point is hard to determine experimentally and various computational techniques are used for its characterization. Based on previous work, we locate the gel point, T0, of sol-gel and gel-sol transitions in terms of the horizontal shift in the sigmoidal transition curve. For the gel-sol transition (heating), T0 is greater than Tm, i.e. later in time, and the difference between T0 and Tm is reduced as the agarose content increases. For the sol-gel transition (cooling), T0 is again greater than Tm, but it is earlier in time for all agarose contents and moves forward in time and gets closer to Tm as the agarose content increases. 相似文献
67.
Zhang M Imm S Bähn S Neubert L Neumann H Beller M 《Angewandte Chemie (International ed. in English)》2012,51(16):3905-3909
Amid(e) them all: primary carboxamides and ureas react with aromatic and aliphatic amines in the presence of a copper catalyst to give a wide range of functionalized amides. 相似文献
68.
Neubert L Michalik D Bähn S Imm S Neumann H Atzrodt J Derdau V Holla W Beller M 《Journal of the American Chemical Society》2012,134(29):12239-12244
A novel and convenient protocol for the catalytic hydrogen-deuterium exchange of biologically active tertiary amines utilizing the borrowing hydrogen methodology has been developed. In the presence of the readily available Shvo catalyst, excellent chemoselectivity toward α- and β-protons with respect to the nitrogen atom as well as high degree of deuterium incorporation and functional group tolerance is achieved. This allowed for the deuteration of complex pharmaceutically interesting substrates, including examples for actual marketed drug compounds. Notably, this method constitutes a powerful tool for the generation of valuable internal standard materials for LC-MS/MS analyses highly demanded for various life-science applications. 相似文献
69.
Rasim Dermez S. Abdel Khalek Kemal Kara Bekir Deveci G. N. Günayd?n 《Journal of Russian Laser Research》2012,33(1):42-51
Our aim is to investigate the entanglement dynamics and quantum correlations of a full-trapped ion interacting with two time-independent
laser beams in view of the Lamb–Dicke parameter. For this purpose, the three probability amplitudes in the trapped ion is
taken as ?{1