全文获取类型
收费全文 | 306篇 |
免费 | 15篇 |
国内免费 | 7篇 |
专业分类
化学 | 221篇 |
力学 | 10篇 |
数学 | 35篇 |
物理学 | 62篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 7篇 |
2014年 | 25篇 |
2013年 | 50篇 |
2012年 | 28篇 |
2011年 | 18篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 17篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有328条查询结果,搜索用时 15 毫秒
81.
Warda Rahim Jonathan M. Skelton Christopher N. Savory Ivana R. Evans John S. O. Evans Aron Walsh David O. Scanlon 《Chemical science》2020,11(30):7904
Accurately modelling polymorphism in crystalline solids remains a key challenge in computational chemistry. In this work, we apply a theoretically-rigorous phonon mode-mapping approach to understand the polymorphism in the ternary metal oxide Bi2Sn2O7. Starting from the high-temperature cubic pyrochlore aristotype, we systematically explore the structural potential-energy surface and recover the two known low-temperature phases alongside three new metastable phases, together with the transition pathways connecting them. This first-principles lattice-dynamics method is completely general and provides a practical means to identify and characterise the stable polymorphs and phase transitions in materials with complex crystal structures.Using a phonon mode-mapping approach, we recover the known experimental phases of the ternary oxide Bi2Sn2O7 and identify three new metastable phases, highlighting the utility of the method for polymorph prediction on many other complex materials. 相似文献
82.
Reactive Violet 5 and its hydrolysis product, which is produced as a side product in the dyeing process, can be determined in an admixture at sub-ppb levels by cathodic stripping voltammetry because the potentials of their azo reduction peaks are separated sufficiently. For both dyes, at intermediate pH values the azo peak is preceded by a complexed -copper reduction peak at a less negative potential, which aids the identification of the dyes. The use of pH 6 EDTA buffer removes the complexed-copper peak, as does the use of an acidic buffer (pH < 3). This unusual use of EDTA as a pH buffer facilitates the determination of mixtures of the dye and its hydrolysis product. 相似文献
83.
Nur Hidayah Zulaikha Othman Zailani Normawati M. Yunus Asyraf Hanim Ab Rahim Mohamad Azmi Bustam 《Molecules (Basel, Switzerland)》2022,27(3)
Ionic liquids, which are extensively known as low-melting-point salts, have received significant attention as the promising solvent for CO2 capture. This work presents the synthesis, thermophysical properties and the CO2 absorption of a series of ammonium cations coupled with carboxylate anions producing ammonium-based protic ionic liquids (PILs), namely 2-ethylhexylammonium pentanoate ([EHA][C5]), 2-ethylhexylammonium hexanoate ([EHA][C6]), 2-ethylhexylammonium heptanoate ([EHA][C7]), bis-(2-ethylhexyl)ammonium pentanoate ([BEHA][C5]), bis-(2-ethylhexyl)ammonium hexanoate ([BEHA][C6]) and bis-(2-ethylhexyl)ammonium heptanoate ([BEHA][C7]). The chemical structures of the PILs were confirmed by using Nuclear Magnetic Resonance (NMR) spectroscopy while the density (ρ) and the dynamic viscosity (η) of the PILs were determined and analyzed in a range from 293.15K up to 363.15K. The refractive index (nD) was also measured at T = (293.15 to 333.15) K. Thermal analyses conducted via a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC) indicated that all PILs have the thermal decomposition temperature, Td of greater than 416K and the presence of glass transition, Tg was detected in each PIL. The CO2 absorption of the PILs was studied up to 29 bar at 298.15 K and the experimental results showed that [BEHA][C7] had the highest CO2 absorption with 0.78 mol at 29 bar. The CO2 absorption values increase in the order of [C5] < [C6] < [C7] anion regardless of the nature of the cation. 相似文献
84.
Acta Mechanica Sinica - A pore network model (PNM) is developed for gas diffusion layer (GDL) in the cathode side of polymer electrolyte membrane fuel cells (PEMFCs). The model is coupled to... 相似文献
85.
A dynamic computable general equilibrium model with overlapping generations is used to appraise the consequences in France of three social security policies: a 20% cut in the replacement rate (‘TM20’), an increase in retirement age from 60 to 65 (‘RET65’), and the creation of a transitory fund (‘FUND’). These policies are described in three scenarios built up around a baseline scenario, in which the current French public pension system, financed on a pay-as-you-go basis, is maintained. Whatever the scenario, the demographic transition is assumed to be close to that described in official projections, in which the most likely fertility rate between years 1995 and 2050 is supposed to be equal to 1.8 children per woman. The main results are the following: maintaining the current system remains a reasonable option since slump should not occur during the transition period. Nevertheless, this option may seem undesirable because of the demographic risk—the realization of a scenario less favourable than the official one cannot be ruled out—and the lack of equity of the current pensions system. If equity is appraised with respect to a simple actuarial criterion (i.e. the ratio of the present value of pensions received by a generation over the present value of its social contributions), the ‘FUND’ option appears to be the most equitable. The ‘RET65’ option is the least fair since people presently working are worse off. When macroeconomic outcomes (e.g. per capita production or consumption) or social welfare are considered, the scenario in which the legal retirement age is increased seems to dominate all other options, owing to its huge effects. Nevertheless, these results hold under restrictive assumptions, among which the most crucial is full employment being restored quickly. The ‘FUND’ option is the less desirable, owing to ambiguous and small macroeconomic and social welfare effects. Finally, a 20% cut in the replacement rate would have intermediate effects: less additional production or welfare than in the ‘RET65’ scenario, but more than in ‘FUND’; less efficient in struggling against the lack of equity than the latter scenario, but more than the former. 相似文献
86.
87.
Majid M. Heravi Sodeh Sadjadi Rahim Hekmatshoar Hossein A. Oskooie Fatemeh F. Bamoharram 《Monatshefte für Chemie / Chemical Monthly》2008,139(2):107-110
Summary. Some N-aminotriazines and -triazoles were treated with Preyssler’s anion as catalyst in acetic acid to afford the corresponding deaminated triazines and triazoles. The reaction is suggested
to proceed via formation of N-nitrosamines with subsequent N–NO bond cleavage. 相似文献
88.
89.
In this paper we use symmetry of Single Walled Carbon Nanotubes (SWCNTs) to generate some types of virtual sub-bands that
are lower in number than the real sub-bands obtained through conventional-TB. It is shown that the virtual sub-bands maintain
the value of band gap. In obtaining the sub bands, the interactions of the nearest and the second and third-nearest neighbors
are taken into account. As the consequence of lower number of sub-bands, a significant reduction in computational effort has
occurred and made the approach useful.
相似文献
90.
For a finite morphism f : X Y of smooth varieties such that f maps X birationally onto X=f(X), the local equations of f are obtained at the double points which are not triple. If C is the conductor of X over X, and
are the subschemes defined by C, then D and are shown to be complete intersections at these points, provided that C has the expected codimension. This leads one to determine the depth of local rings of X at these double points. On the other hand, when C is reduced in X, it is proved that X is weakly normal at these points, and some global results are given. For the case of affine spaces, the local equations of X at these points are computed. 相似文献