全文获取类型
收费全文 | 308篇 |
免费 | 14篇 |
国内免费 | 10篇 |
专业分类
化学 | 227篇 |
晶体学 | 2篇 |
力学 | 13篇 |
数学 | 38篇 |
物理学 | 52篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 15篇 |
2017年 | 8篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 18篇 |
2013年 | 38篇 |
2012年 | 26篇 |
2011年 | 29篇 |
2010年 | 32篇 |
2009年 | 19篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 5篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1986年 | 3篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有332条查询结果,搜索用时 15 毫秒
71.
Silica-bonded S-sulfonic acid (SBSSA) is employed as a recyclable catalyst for the synthesis of α-amino nitriles. These syntheses were performed via a one-pot three-component condensation of aldehydes, amines, and trimethylsilyl cyanide under mild reaction conditions at room temperature. 相似文献
72.
73.
Dyachenko Alla Ischenko Olena Diyuk Vitaliy Goncharuk Olena Borysenko Mykola Mischanchuk Oleksandr Zakharova Tetiana Pryhunova Olha Sternik Dariush Lisnyak Vladyslav 《Research on Chemical Intermediates》2022,48(6):2607-2625
Research on Chemical Intermediates - Oxide Ni(80)Fe(20)/SiO2, Co(93)Fe(7)/SiO2, and Ni(19)Co(77)Fe(4)/SiO2 nanocomposites (NCs) were prepared using highly dispersed silica. It was modified by... 相似文献
74.
In this review article, we describe how methods of electron paramagnetic resonance (EPR) spectroscopy were used to investigate polyion–counterion interactions in polyelectrolyte solutions. This subject is usually treated experimentally by light, X-ray, or neutron scattering techniques. It is shown that a large arsenal of EPR spectroscopic methods–from various sophisticated methods of line shape analysis of continuous-wave EPR, via electron spin echo envelope modulation, nanoscale distance measurements through double electron–electron resonance to high-field pulse EPR–can be used to characterize the intrinsically complicated structures formed in polyelectrolyte solutions. We show that even polymer physical models such as scaling relations can be tested in this way. The distinguishing feature with respect to the numerous scattering studies in this area is that EPR techniques are local methods, and by employing spin-carrying (i.e., EPR-active) probe ions, it is possible to examine polyelectrolytes from the counterions’ point of view. 相似文献
75.
Isotherms of adsorption of Cu(II) and Ni(II) onto solid Azraq humic acid (AZHA) were studied at different pH (2.0-3.7) values and 0.1 M NaClO4 ionic strength. The Langmuir monolayer adsorption capacity was found to range from 0.1 to 1.0 mmol metal ion/g AZHA, where Cu(II) has higher adsorptivity than Ni(II). The previously reported NICA-Donnan parameters for sorption of Cu(II) on HA fit the amount of Cu(bound) determined in the present study at pH 3.7 but underestimates those at pH values of 3.0, 2.4, and 2.0. The contribution of low affinity sites to binding of metal ions increases with decreasing pH and increasing metal ion loading. The aggregation of HA, which is facilitated by decreasing pH and increasing metal loading, may increase the ability of low-affinity sites to encapsulate metal ions. The binding of Ni(II) to HA exhibits less heterogeneity and less multidentism than that of Cu(II). AZHA loaded with Cu(II) and Ni(II) was found to be insoluble in water with no measurable amount of desorbed metal ions. 相似文献
76.
A cylindrical capsule containing a coiled alkane incorporates spacers. The alkane lengthens and gauche strain is relieved. The spacer can be removed to reset the system to the original state. The system represents a spring-loaded device that operates reversibly in response to acids and bases. 相似文献
77.
An even factor of a graph is a spanning subgraph in which each vertex has a positive even degree. Let G be a bridgeless simple graph with minimum degree at least 3. Jackson and Yoshimoto (2007) showed that G has an even factor containing two arbitrary prescribed edges. They also proved that G has an even factor in which each component has order at least four. Moreover, Xiong, Lu and Han (2009) showed that for each pair of edges e1 and e2 of G, there is an even factor containing e1 and e2 in which each component containing neither e1 nor e2 has order at least four. In this paper we improve this result and prove that G has an even factor containing e1 and e2 such that each component has order at least four. 相似文献
78.
M. Khalili A.S. Camanho M.C.A.S. Portela M.R. Alirezaee 《European Journal of Operational Research》2010
The most popular weight restrictions are assurance regions (ARs), which impose ratios between weights to be within certain ranges. ARs can be categorized into two types: ARs type I (ARI) and ARs type II (ARII). ARI specify bounds on ratios between input weights or between output weights, whilst ARII specify bounds on ratios that link input to output weights. DEA models with ARI successfully maximize relative efficiency, but in the presence of ARII the DEA models may under-estimate relative efficiency or may become infeasible. In this paper we discuss the problems that can occur in the presence of ARII and propose a new nonlinear model that overcomes the limitations discussed. Also, the dual model is described, which enables the assessment of relative efficiency when trade-offs between inputs and outputs are specified. The application of the model developed is illustrated in the efficiency assessment of Portuguese secondary schools. 相似文献
79.
Edyta Małolepsza Birgit Strodel Mey Khalili Semen Trygubenko Szilard N. Fejer David J. Wales 《Journal of computational chemistry》2010,31(7):1402-1409
The AMBER and CHARMM force fields are analyzed from the viewpoint of the permutational symmetry of the potential for feasible exchanges of identical atoms and chemical groups in amino and nucleic acids. In each case, we propose schemes for symmetrizing the potentials, which greatly facilitate the bookkeeping associated with constructing kinetic transition networks via geometry optimization. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
80.