全文获取类型
收费全文 | 1831篇 |
免费 | 78篇 |
国内免费 | 6篇 |
专业分类
化学 | 1376篇 |
晶体学 | 21篇 |
力学 | 39篇 |
数学 | 280篇 |
物理学 | 199篇 |
出版年
2023年 | 20篇 |
2022年 | 36篇 |
2021年 | 46篇 |
2020年 | 55篇 |
2019年 | 41篇 |
2018年 | 26篇 |
2017年 | 32篇 |
2016年 | 59篇 |
2015年 | 45篇 |
2014年 | 55篇 |
2013年 | 118篇 |
2012年 | 105篇 |
2011年 | 121篇 |
2010年 | 67篇 |
2009年 | 69篇 |
2008年 | 108篇 |
2007年 | 77篇 |
2006年 | 77篇 |
2005年 | 84篇 |
2004年 | 63篇 |
2003年 | 58篇 |
2002年 | 50篇 |
2001年 | 28篇 |
2000年 | 22篇 |
1999年 | 17篇 |
1998年 | 23篇 |
1997年 | 26篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 26篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 15篇 |
1975年 | 16篇 |
1974年 | 15篇 |
1973年 | 14篇 |
1968年 | 6篇 |
排序方式: 共有1915条查询结果,搜索用时 31 毫秒
151.
152.
153.
In this paper we present a mathematical analysis of the photoelectric effect for one-electron atoms in the framework of non-relativistic
QED. We treat photo-ionization as a scattering process where in the remote past an atom in its ground state is targeted by
one or several photons, while in the distant future the atom is ionized and the electron escapes to spacial infinity. Our
main result shows that the ionization probability, to leading order in the fine-structure constant, α, is correctly given by formal time-dependent perturbation theory, and, moreover, that the dipole approximation produces an
error of only sub-leading order in α. In this sense, the dipole approximation is rigorously justified. 相似文献
154.
155.
156.
157.
An Invitation to C-semigroups 总被引:1,自引:0,他引:1
158.
159.
Grasping the historical volatility of stock market indices and accurately estimating are two of the major focuses of those involved in the financial securities industry and derivative instruments pricing. This paper presents the results of employing the intrinsic entropy model as a substitute for estimating the volatility of stock market indices. Diverging from the widely used volatility models that take into account only the elements related to the traded prices, namely the open, high, low, and close prices of a trading day (OHLC), the intrinsic entropy model takes into account the traded volumes during the considered time frame as well. We adjust the intraday intrinsic entropy model that we introduced earlier for exchange-traded securities in order to connect daily OHLC prices with the ratio of the corresponding daily volume to the overall volume traded in the considered period. The intrinsic entropy model conceptualizes this ratio as entropic probability or market credence assigned to the corresponding price level. The intrinsic entropy is computed using historical daily data for traded market indices (S&P 500, Dow 30, NYSE Composite, NASDAQ Composite, Nikkei 225, and Hang Seng Index). We compare the results produced by the intrinsic entropy model with the volatility estimates obtained for the same data sets using widely employed industry volatility estimators. The intrinsic entropy model proves to consistently deliver reliable estimates for various time frames while showing peculiarly high values for the coefficient of variation, with the estimates falling in a significantly lower interval range compared with those provided by the other advanced volatility estimators. 相似文献
160.
Paulo Debiagi Coskun Yildiz Marcel Richter Jochen Ströhle Bernd Epple Tiziano Faravelli Christian Hasse 《Proceedings of the Combustion Institute》2021,38(3):4053-4061
Coal combustion releases elevated amounts of pollutants to the atmosphere including SOX. During the pyrolysis step, sulfur present in the coal is released to the gas phase as many different chemical species such as H2S, COS, SO2, CS2, thiols and larger tars, also called SOX precursors, as they form SOX during combustion. Understanding the sulfur release process is crucial to the development of reliable kinetic models, which support the design of improved reactors for cleaner coal conversion processes. Sulfur release from two bituminous coals, Colombian hard coal (K1) and American high sulfur coal (U2), were studied in the present work. Low heating rate (LHR) experiments were performed in a thermogravimetric analyzer coupled with mass spectrometry (TG-MS), allowing to track the mass loss and the evolution of many volatile species (CO, CO2, CH4, SO2, H2S, COS, HCl and H2O). High heating rate (HHR) experiments were performed in an entrained flow reactor (drop-tube reactor – DTR), coupled with MS and nondispersive infrared sensor (NDIR). HHR experiments were complemented with CFD simulation of the multidimentional reacting flow field. A kinetic model of coal pyrolysis is employed to reproduce the experiments allowing a comprehensive assessment of the process. The suitability of this model is confirmed for LHR. The combination of HHR experiments with CFD simulations and kinetic modeling revealed the complexity of sulfur chemistry in coal combustion and allowed to better understand of the individual phenomena resulting in the formation of the different SOX precursors. LHR and HHR operating conditions lead to different distribution of sulfur species released, highly-dependent on the gas-phase temperature and residence time. Higher retention of total sulfur in char is observed at LHR (63%) when compared to HHR (37–44%), at 1273 K. These data support the development of reliable models with improved predictability. 相似文献