全文获取类型
收费全文 | 867篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 502篇 |
晶体学 | 4篇 |
力学 | 34篇 |
综合类 | 1篇 |
数学 | 114篇 |
物理学 | 227篇 |
出版年
2023年 | 10篇 |
2022年 | 11篇 |
2021年 | 22篇 |
2020年 | 21篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 23篇 |
2014年 | 35篇 |
2013年 | 57篇 |
2012年 | 58篇 |
2011年 | 61篇 |
2010年 | 34篇 |
2009年 | 34篇 |
2008年 | 52篇 |
2007年 | 43篇 |
2006年 | 45篇 |
2005年 | 41篇 |
2004年 | 37篇 |
2003年 | 24篇 |
2002年 | 22篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 15篇 |
1998年 | 2篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1970年 | 4篇 |
1906年 | 3篇 |
1905年 | 3篇 |
排序方式: 共有882条查询结果,搜索用时 270 毫秒
41.
Orlando Lopes 《Journal of Mathematical Analysis and Applications》1976,55(3):686-698
In this paper we derive a differential-difference equation for a circuit involving a lossless transmission line and we give conditions for global asymptotic stability of an equilibrium point, existence and stability of forced oscillations. Some of such problems have been investigated for an equation obtained by R. K. Brayton [Quart. J. Appl. Math.24 (1967), 289–301; O. Lopes, SIAM J. Appl. Math., to appear; M. Slemrod, J. Math. Anal. Appl.36 (1971), 22–40] but, for ours (which governs the same physical problem), better results can be proved. By using suitable Liapunov functionals, we reduce the problem of stability and uniform ultimate boundedness to a scalar ordinary differential inequality. 相似文献
42.
Diego Lomonaco Francisco Jonas Nogueira Maia Selma Elaine Mazzetto 《Journal of Thermal Analysis and Calorimetry》2013,111(1):619-626
In this study, the thermal-oxidative stability of poly(methyl methacrylate), PMMA, 1 % additivated with replenishable phenolic lipids is evaluated by thermogravimetric (TG/DTG) analyses and differential scanning calorimetry (DSC) analyses. Since technical cashew nutshell liquid (CNSL), a byproduct from the cashew industry, is composed basically of two phenolic lipids, cardanol and cardol, the utilization of this industrial waste and its main components as a new source of bioadditives for use as antioxidants is evaluated. The TG analyses revealed that addition of the phenolic constituent of CNSL increased the thermal stability of PMMA films considerably. The results obtained were also confirmed by DSC analyses. 相似文献
43.
44.
Xavier Fernandes Joana Rebelo João Gouveia Rodrigo Maia Nuno Bustorff Silva 《4OR: A Quarterly Journal of Operations Research》2017,15(2):163-181
In this paper, we study the problem of establishing a dynamic charging schedule of electric vehicles (EVs) at a charging station, assuming that limited power implies that only a limited number of EVs can charge simultaneously. The only control we assume to be available to the charging station is the ability to (at any given time) turn on or off the power supply to any EV, with this tool we want to develop a charging schedule that will satisfy the energy demands of the EVs in their intended deadlines. We propose two distinct approaches to this problem: a discretized time version, based on a greedy-like algorithm, and a continuous time version, based on linear programming. We compare these two approaches and numerically study the improvement they yield in the efficiency of the charging procedure, when applied to simulated data based on real parking data. Finally, we illustrate the flexibility of the models by sketching several possible extensions. 相似文献
45.
46.
de Oliveira Elcio Cruz de Santana Maia Lúcio Abdala da Costa Lívio Garcia Lourenço Túlio Campos 《Accreditation and quality assurance》2018,23(6):365-369
Accreditation and Quality Assurance - In any commercial transaction, the presence of tolerances from specification limits is essential to ensure that the true value of the property of interest is... 相似文献
47.
Ana G. Silva Nenad BundaleskiAugusto M.C. Moutinho Orlando M.N.D. Teodoro 《Applied Surface Science》2012,258(6):2006-2009
Water adsorption dynamics on two TiO2 (1 1 0) rutile surfaces at room temperature has been investigated using the work function (WF) change as a function of time. The first surface was prepared in a standard way using sputtering/annealing cycles, whereas the second one was long term annealed at 620 K in moderate vacuum conditions (the residual gas pressure of about 1 × 10−7 mbar) and cleaned afterwards. The WF change show striking difference as compared to those obtained for highly reduced TiO2 (1 1 0) rutile or the (2 × 1) reconstructed surfaces. For the first kind of surface we show that the observed adsorption dynamics can be qualitatively explained by the present understanding of the water adsorption on non-reconstructed TiO2 (1 1 0) rutile surface according to which the bridging oxygen vacancies and Ti rows are the main adsorption sites. Although generally similar to the former results, water adsorption dynamics on the second kind of the surface has an additional feature that can be only explained by a new adsorption site, which we suggest to be due to (2 × 1) reconstructed regions coexisting with the non-reconstructed TiO2 (1 1 0) surface. 相似文献
48.
Thais R. Cruz Eliada A. Silva Douglas P. Oliveira Daniele M. Martins Patrik D.S. Gois Antonio E.H. Machado Pedro Ivo S. Maia Beatriz E. Goi Benedito S. Lima-Neto Valdemiro P. Carvalho-Jr 《应用有机金属化学》2020,34(5):e5602
Arene ruthenium(II) complexes bearing the cyclic amines RuCl2(η6-p-cymene)(pyrrolidine)] ( 1 ), [RuCl2(η6-p-cymene)(piperidine)] ( 2 ), and [RuCl2(η6-p-cymene)(peridroazepine)] ( 3 ) were successfully synthesized. Complexes 1 – 3 were fully characterized by means of Fourier transform infrared, UV–visible, and NMR spectroscopy, elemental analysis, cyclic voltammetry, computational methods, and one of the complexes was further studied by single crystal X-ray crystallography. These compounds were evaluated as catalytic precursors for ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and atom-transfer radical polymerization (ATRP) of methyl methacrylate (MMA). NBE polymerization via ROMP was evaluated using complexes 1 – 3 as precatalysts in the presence of ethyl diazoacetate (EDA) under different [NBE]/[EDA]/[Ru] ratios, temperatures (25 and 50°C), and reaction times (5–60 min). The highest yields of polyNBE were obtained with [NBE]/[EDA]/[Ru] = 5000/28/1 for 60 min at 50°C. MMA polymerization via ATRP was conducted using 1 – 3 as catalysts in the presence of ethyl-α-bromoisobutyrate (EBiB) as initiator. The catalytic tests were evaluated as a function of the reaction time using the initial molar ratio of [MMA]/[EBiB]/[Ru] = 1000/2/1 at 95°C. The increase in molecular weight as function of time indicates that complexes 1–3 were able to mediate the MMA polymerization with an acceptable rate and some level of control. Differences in the rate of polymerization were observed in the order 3 > 2 > 1 for the ROMP and ATRP. 相似文献
49.
Abstract The ability of macrocyclic polyethers to activate enolates has been studied in the alkylation of de-oxybenzoin (1) with butyl derivatives nBuY (Y = Br, I, OMes) catalyzed by crown ether PHDB18C6 (7) or cryptand [2.2.2,C10] (8) under phase-transfer catalysis (PTC) and homogeneous (chlorobenzene) conditions. The enolate reactivity is mainly determined by the ligand (cryptand > crown ether) and solvent (increasing with the polarity, in the order: toluene < chlorobenzene < 1,2dichlorobenzene). Regioselectivity of the reaction is also remarkably affected by ligand and alkylating agent. 相似文献
50.