全文获取类型
收费全文 | 12033篇 |
免费 | 388篇 |
国内免费 | 19篇 |
专业分类
化学 | 7209篇 |
晶体学 | 191篇 |
力学 | 222篇 |
数学 | 2231篇 |
物理学 | 2587篇 |
出版年
2023年 | 56篇 |
2022年 | 76篇 |
2021年 | 114篇 |
2020年 | 180篇 |
2019年 | 218篇 |
2018年 | 267篇 |
2017年 | 296篇 |
2016年 | 537篇 |
2015年 | 413篇 |
2014年 | 494篇 |
2013年 | 939篇 |
2012年 | 616篇 |
2011年 | 746篇 |
2010年 | 481篇 |
2009年 | 425篇 |
2008年 | 744篇 |
2007年 | 641篇 |
2006年 | 576篇 |
2005年 | 501篇 |
2004年 | 396篇 |
2003年 | 348篇 |
2002年 | 261篇 |
2001年 | 216篇 |
2000年 | 195篇 |
1999年 | 118篇 |
1998年 | 144篇 |
1997年 | 110篇 |
1996年 | 116篇 |
1995年 | 106篇 |
1994年 | 86篇 |
1993年 | 104篇 |
1992年 | 84篇 |
1991年 | 97篇 |
1990年 | 87篇 |
1989年 | 90篇 |
1988年 | 81篇 |
1987年 | 96篇 |
1986年 | 80篇 |
1985年 | 135篇 |
1984年 | 137篇 |
1983年 | 110篇 |
1982年 | 93篇 |
1981年 | 99篇 |
1980年 | 91篇 |
1979年 | 74篇 |
1978年 | 58篇 |
1977年 | 54篇 |
1976年 | 61篇 |
1975年 | 49篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Numerical Algorithms - We present an asymptotic analysis of adaptive methods for Lp approximation of functions f ∈ Cr([a, b]), where $1\le p\le +\infty $ . The methods rely on piecewise... 相似文献
2.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献
3.
4.
Rutkowski Paweł Klimczyk Piotr Jaworska Lucyna Stobierski Ludosław Dubiel Aleksandra 《Journal of Thermal Analysis and Calorimetry》2015,122(1):105-114
Journal of Thermal Analysis and Calorimetry - The work concerns the alumina–graphene materials sintered by two different pressure methods. The different particle sizes of graphene were used.... 相似文献
5.
6.
7.
Dapeng Liu Binod R. Giri Milán Szőri Béla Viskolcz Et-touhami Es-sebbar Aamir Farooq 《Proceedings of the Combustion Institute》2021,38(1):967-976
NOx mitigation is a central focus of combustion technologies with increasingly stringent emission regulations. NOx can also enhance the autoignition of hydrocarbon fuels and can promote soot oxidation. The reaction between allyl radical (C3H5) and NOx plays an important role in the oxidation kinetics of propene. In this work, we measured the absolute rate coefficients for the redox reaction between C3H5 and NOx over the temperature range of 1000–1252 K and pressure range of 1.5–5.0 bar using a shock tube and UV laser absorption technique. We produced C3H5 by shock heating of C3H5I behind reflected shock waves. Using a Ti:Sapphire laser system with frequency quadrupling, we monitored the kinetics of C3H5 at 220 nm. Unlike low-temperature chemistry, the two target reactions, C3H5 + NO → products (R1) and C3H5 + NO2 → products (R2), exhibited a strong positive temperature dependence for this radical-radical type reaction. However, these reactions did not show any pressure dependence over the pressure range of 1.5–5.0 bar, indicating that the measured rate coefficients are close to the high-pressure limit. The measured values of the rate coefficients resulted in the following Arrhenius expressions (in unit of cm3/molecule/s):To our knowledge, these are the first high-temperature measurements of allyl + NOx reactions. The reported data will be highly useful in understanding the interaction of NOx with resonantly stabilized radicals as well as the mutual sensitization effect of NOx on hydrocarbon fuels. 相似文献
8.
It is known that under resonance conditions, a group of strongly interacting bosonic atoms, trapped in a double-well potential, mimics a single particle, performing Rabi oscillations between the wells. By implication, all atoms need to tunnel at roughly the same time, even though the Bose–Hubbard Hamiltonian accounts only for one-atom-at-a-time transfers. The mechanism of this collective behavior is analyzed, the Rabi frequencies in the process are evaluated, and the limitation of this simple picture is discussed. In particular, it is shown that the small rapid oscillations superimposed on the slow Rabi cycle result from splitting the transferred cluster at the sudden onset of tunnelling, and disappear if tunnelling is turned on gradually. 相似文献
9.
Teobald Kupka Małgorzata A. Broda Piotr P. Wieczorek 《Magnetic resonance in chemistry : MRC》2020,58(6):584-593
The biologically active alkaloid muscimol is present in fly agaric mushroom (Amanita muscaria), and its structure and action is related to human neurotransmitter γ-aminobutyric acid (GABA). The current study reports on determination of muscimol form present in water solution using multinuclear 1H and 13C nuclear magnetic resonance (NMR) experiments supported by density functional theory molecular modeling. The structures of three forms of free muscimol molecule both in the gas phase and in the presence of water solvent, modeled by polarized continuous model, and nuclear magnetic isotropic shieldings, the corresponding chemical shifts, and indirect spin–spin coupling constants were calculated. Several J-couplings observed in proton and carbon NMR spectra, not available before, are reported. The obtained experimental spectra, supported by theoretical calculations, favor the zwitterion form of muscimol in water. This structure differs from NH isomer, previously determined in dimethyl sulfoxide (DMSO) solution. In addition, positions of signals C3 and C5 are reversed in both solvents. 相似文献
10.