全文获取类型
收费全文 | 1204篇 |
免费 | 34篇 |
国内免费 | 9篇 |
专业分类
化学 | 795篇 |
晶体学 | 77篇 |
力学 | 16篇 |
数学 | 79篇 |
物理学 | 280篇 |
出版年
2023年 | 13篇 |
2022年 | 25篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 33篇 |
2018年 | 33篇 |
2017年 | 34篇 |
2016年 | 34篇 |
2015年 | 40篇 |
2014年 | 55篇 |
2013年 | 102篇 |
2012年 | 64篇 |
2011年 | 93篇 |
2010年 | 46篇 |
2009年 | 47篇 |
2008年 | 77篇 |
2007年 | 47篇 |
2006年 | 46篇 |
2005年 | 28篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 36篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 6篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1974年 | 6篇 |
排序方式: 共有1247条查询结果,搜索用时 15 毫秒
151.
Babu KR Lingam ChB Tewari SP Vaitheeswaran G 《The journal of physical chemistry. A》2011,115(17):4521-4529
The structural, electronic, optical, and vibrational properties of LiN(3) under high pressure have been studied using plane wave pseudopotentials within the generalized gradient approximation for the exchange and correlation functional. The calculated lattice parameters agree quite well with experiments. The calculated bulk modulus value is found to be 23.23 GPa, which is in good agreement with the experimental value of 20.5 GPa. Our calculations reproduce well the trends in high-pressure behavior of the structural parameters. The present results show that the compressibility of LiN(3) crystal is anisotropic and the crystallographic b-axis is more compressible when compared to a- and c-axes, which is also consistent with experiment. Elastic constants are predicted, which still awaits experimental confirmation. The computed elastic constants clearly show that LiN(3) is a mechanically stable system and the calculated elastic constants follow the order C(33) > C(11) > C(22), implying that the LiN(3) lattice is stiffer along the c-axis and relatively weaker along the b-axis. Under the application of pressure the magnitude of the electronic band gap value decreases, indicating that the system has the tendency to become semiconductor at high pressures. The optical properties such as refractive index, absorption spectra, and photoconductivity along the three crystallographic directions have been calculated at ambient as well as at high pressures. The calculated refractive index shows that the system is optically anisotropic and the anisotropy increases with an increase in pressure. The observed peaks in the absorption and photoconductivity spectra are found to shift toward the higher energy region as pressure increases, which implies that in LiN(3) decomposition is favored under pressure with the action of light. The vibrational frequencies for the internal and lattice modes of LiN(3) at ambient conditions as well as at high pressures are calculated from which we predict that the response of the lattice modes toward pressure is relatively high when compared to the internal modes of the azide ion. 相似文献
152.
Sangeetha K Babu RR Ramamurthi K Prakash J Khan SA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(5):884-888
L-arginine hydrochloride monohydrate and L-arginine hydrobromide monohydrate single crystals are irradiated by 100 MeV Ag8+ swift heavy ions. The residual gases liberated from the irradiated samples are monitored as a function of ion fluence using quadrupole mass analyzer. The C2H3+, C2H2, N2, CO, HCl and CO2 are the dominant gases liberated. Fourier transform infrared spectra of irradiated crystals explain the breaking of bonds in a localized region of the crystals. The crystallinity of irradiated crystals is analyzed by powder X-ray diffractions. 相似文献
153.
Babu SS Saeki A Seki S Möhwald H Nakanishi T 《Physical chemistry chemical physics : PCCP》2011,13(11):4830-4834
The coassembly of C(60) derivatives through arene-perfluoroarene interactions has been used for the first time to develop millimeter-sized flat crystalline sheets. Time-resolved microwave conductivity (TRMC) measurements exhibited anisotropic features with over double the charge carrier mobility in the direction parallel to the plane of the crystal than perpendicular to the plane. This study demonstrates a strategy to obtain large-sized 2-dimensional architectures of C(60) with anisotropic optoelectronic functions. 相似文献
154.
The essential oil of Eucalyptus cinerea is reported to possess a higher 1,8-cineole content than other Eucalyptus species. Variations in the quantitative and qualitative characteristics of E. cinerea oil produced by hydrodistillation (HD) and supercritical carbon dioxide extraction (SCE) techniques and a comparison between glycoside-bound and free volatile constituents produced by HD have been studied. It was found that HD produced higher oil (free volatiles) content (3.1%) as compared with SCE (1.1%), whereas bound volatiles constituted only about 0.4%. Gas chromatographic (GC) analysis of the oil samples revealed significant difference in their chemical composition. The essential oil (free volatiles) produced by HD contained 1,8-cineole (85.1%) as the major constituent, followed by a-terpineol (7.2%) and limonene (4.4%). In the bound volatile fraction produced by HD, 1,8 cineole (20.6%), alpha-terpineol (7.6%), p-cymene (6.3%), and limonene (4.5%) were found as major constituents. The extract produced by SCE was dominated by 1,8-cineole (70.4%), a-terpineol (8.6%), globulol (3.1%), aromadendrene (2%), citronellal (1.7%), viridiflorol (1.3%), phytol (1.1%) and terpinen-4-ol (1%). Although HD produced higher oil yields, SCE produced better extract in terms of the number of components detected. 相似文献
155.
This paper deals with the preparation and optical analysis of Er3+ (0.2 mol%) boro-fluoro-phosphate glasses in the following glass compositions:
-
Series A: 69.8 B2O3–10 P2O5–10(ZnO/CdO/TeO2)–10 AlF3
-
Series B: 69.8 B2O3–10 P2O5–10(ZnO/CdO/TeO2)–10 LiF
156.
157.
This paper pertains to a detailed simulation study conducted on a typical Flexible Manufacturing System (FMS). Initially, the configurations of the FMS under study have been established. Two types of FMSs have been evolved: one is failure free and the other is failure prone. For each of these cases, simulation models have been developed using SLAMSYSTEM. Orders arriving randomly at the FMS are subjected to three levels of scheduling decisions namely, launching of parts into the system, routing of parts through machines and sequencing of parts on AGVs at a central buffer. The simulation results have been used to develop metamodels for the two types of FMSs. These metamodels have been subjected to statistical analysis to ascertain their adequacy to represent the simulation models. These metamodels have been found to be useful for simulating the FMSs under study so as to evaluate various multi-level scheduling decisions in the FMS. 相似文献
158.
159.
We study hereL 1-convergence of a complex trigonometric sum and obtain a new necessary and sufficient condition for theL 1-convergence of Fourier series. 相似文献
160.
The finite temperature effective potential for a scalar field with Φ6 interaction is calculated by extending the CJT formalism for composite operators. It is found that unrenormalized terms appear
in the effective potential due to the presence of an unrenormalized mass term. Nonzero turning points are obtained both for
positive and negativeλ. High temperature expansion is performed and the results are analysed numerically. Graphical analysis indicates symmetry
restoration whenT→0. 相似文献