全文获取类型
收费全文 | 556篇 |
免费 | 18篇 |
国内免费 | 3篇 |
专业分类
化学 | 388篇 |
晶体学 | 1篇 |
力学 | 25篇 |
数学 | 108篇 |
物理学 | 55篇 |
出版年
2023年 | 11篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 17篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 34篇 |
2012年 | 33篇 |
2011年 | 35篇 |
2010年 | 21篇 |
2009年 | 17篇 |
2008年 | 32篇 |
2007年 | 34篇 |
2006年 | 35篇 |
2005年 | 36篇 |
2004年 | 23篇 |
2003年 | 24篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1973年 | 4篇 |
1968年 | 2篇 |
1914年 | 1篇 |
排序方式: 共有577条查询结果,搜索用时 205 毫秒
1.
Multiphase flows are critical components of many physical systems; however, numerical models of multiphase flows with large parameter gradients can be challenging. Here, two different numerical methods, volume of fluid (VOF) and smoothed particle hydrodynamics (SPH), are used to model the buoyant rise of isolated gas bubbles through quiescent fluids for a range of Bond and Reynolds numbers. The VOF is an Eulerian grid–based method, whereas the SPH is Lagrangian and mesh free. Each method has unique strengths and weaknesses, and a comparison of the two approaches as applied to multiphase phenomena has not previously been performed. The VOF and SPH simulations are compared, verified, and validated. Results using two-dimensional VOF and SPH simulations are similar to each other and are able to reproduce numerical benchmarks and experimental results for sufficiently large Morton and Reynolds numbers. It is also shown that at low Reynolds numbers, the two methods, SPH and VOF, diverge in the transient regime of the bubble rise. Regimes that require simulations capable of representing three-dimensional drag are identified as well as regimes in which results from VOF and SPH diverge. 相似文献
2.
Dr. Samuel C. Scott Dr. Jamie A. Cadge Grace K. Boden Prof. John F. Bower Dr. Christopher A. Russell 《Angewandte Chemie (International ed. in English)》2023,62(23):e202301526
We describe a AuI complex of a hemi-labile (C^N) N-heterocyclic carbene ligand that is able to mediate oxidative addition of aryl iodides. Detailed computational and experimental investigations have been undertaken to verify and rationalize the oxidative addition process. Application of this initiation mode has resulted in the first examples of “exogenous oxidant-free” AuI/AuIII catalyzed 1,2-oxyarylations of ethylene and propylene. These demanding yet powerful processes establish these commodity chemicals as nucleophilic-electrophilic building blocks in catalytic reaction design. 相似文献
3.
Grace C. Thaggard Dr. Gabrielle A. Leith Daniil Sosnin Dr. Corey R. Martin Kyoung Chul Park Margaret K. McBride Dr. Jaewoong Lim Brandon J. Yarbrough Buddhima K. P. Maldeni Kankanamalage Gina R. Wilson Austin R. Hill Dr. Mark D. Smith Prof. Dr. Sophya Garashchuk Prof. Dr. Andrew B. Greytak Prof. Dr. Ivan Aprahamian Prof. Dr. Natalia B. Shustova 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(2):e202211776
Confinement-imposed photophysics was probed for novel stimuli-responsive hydrazone-based compounds demonstrating a conceptual difference in their behavior within 2D versus 3D porous matrices for the first time. The challenges associated with photoswitch isomerization arising from host interactions with photochromic compounds in 2D scaffolds could be overcome in 3D materials. Solution-like photoisomerization rate constants were realized for sterically demanding hydrazone derivatives in the solid state through their coordinative immobilization in 3D scaffolds. According to steady-state and time-resolved photophysical measurements and theoretical modeling, this approach provides access to hydrazone-based materials with fast photoisomerization kinetics in the solid state. Fast isomerization of integrated hydrazone derivatives allows for probing and tailoring resonance energy transfer (ET) processes as a function of excitation wavelength, providing a novel pathway for ET modulation. 相似文献
4.
Arockiajawahar Anancia Grace Sukumar Thillaiarasi Venkataraman Dharuman 《Electroanalysis》2021,33(4):993-1006
Tungsten oxide (W) decorated titanium oxide (T) adsorbed onto a graphene (Gr) and modified the glassy carbon electrode for the electrochemical quantification of riboflavin (RF) in edible food and pharmaceuticals. For comparison, nanocomposites are formed using graphene oxide (GO), reduced graphene oxide (rGO) and pure graphite (G) sheets to study the electrochemical activities towards riboflavin. The ternary WTGr modified GCE shows the highest electrocatalytic activity due to synergetic interactions between the metal oxide and graphene. The electrochemical observations are supported by the SEM, HRTEM, XRD, UV-Vis, Zeta potential (ζ) and size data. The sensor shows a wide linear range 20 nM–2.5 μM with a detection limit 25.24 nM and sensitivity (4.249×10−8 A/nM). The fabricated sensor is validated in real samples. 相似文献
5.
Emily Grace Armitage Joanna Godzien Vanesa Alonso‐Herranz Ángeles López‐Gonzálvez Coral Barbas 《Electrophoresis》2015,36(24):3050-3060
The origin of missing values can be caused by different reasons and depending on these origins missing values should be considered differently and dealt with in different ways. In this research, four methods of imputation have been compared with respect to revealing their effects on the normality and variance of data, on statistical significance and on the approximation of a suitable threshold to accept missing data as truly missing. Additionally, the effects of different strategies for controlling familywise error rate or false discovery and how they work with the different strategies for missing value imputation have been evaluated. Missing values were found to affect normality and variance of data and k‐means nearest neighbour imputation was the best method tested for restoring this. Bonferroni correction was the best method for maximizing true positives and minimizing false positives and it was observed that as low as 40% missing data could be truly missing. The range between 40 and 70% missing values was defined as a “gray area” and therefore a strategy has been proposed that provides a balance between the optimal imputation strategy that was k‐means nearest neighbor and the best approximation of positioning real zeros. 相似文献
6.
Headspace quantification of pure and aqueous solutions of binary mixtures of key volatile organic compounds in Swiss cheeses using selected ion flow tube mass spectrometry 下载免费PDF全文
7.
Said R. Grace Shurong Sun Yizhuo Wang 《Journal of Applied Mathematics and Computing》2014,44(1-2):119-132
We establish some new criteria for the oscillation of fourth order nonlinear dynamic equations on a time scale. We investigate the case of strongly superlinear and the case of strongly sublinear equations subject to various conditions. Some examples are given here to illustrate our main results. 相似文献
8.
9.
A new nonlinear optical organic crystal l-tryptophan p-nitrophenol (LTPNP) of dimension 19 mm × 2 mm × 1.5 mm has been grown from an aqueous solution for the first time by slow evaporation technique at ambient temperature. The crystal structure of LTPNP was confirmed by single crystal X-ray diffraction. LTPNP crystallizes in non-centrosymmetric monoclinic system with space group P21. The recorded FTIR spectrum confirms the presence of various functional groups in the grown crystal and confirms the formation of LTPNP. Thermal stability and melting temperature of the LTPNP crystal were identified from TG/DTA analysis. The optical absorption study confirms the suitability of the crystal for device applications. LTPNP exhibits SHG efficiency over 1.7 orders of magnitude higher than that of urea and 4 orders of magnitude higher than that of KDP. 相似文献
10.
Marzena Z. Kastyak-Ibrahim Domenico L. Di Curzio Richard Buist Sheryl L. Herrera Benedict C. Albensi Marc R. Del Bigio Melanie Martin 《Magnetic resonance imaging》2013
Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is the most common cause of dementia in aging populations. Although senile plaques and neurofibrillary tangles are well-established hallmarks of AD, changes in cerebral white matter correlate with cognitive decline and may increase the risk of the development of dementia. We used the triple transgenic (3xTg)-AD mouse model of AD, previously used to show that white matter changes precede plaque formation, to test the hypothesis that MRI detectable changes occur in the corpus callosum, external capsule and the fornix. T2-weighted and diffusion tensor magnetic resonance imaging and histological stains were employed to assess white matter in older (11–17 months) 3xTg-AD mice and controls. We found no statistically significant changes in white matter between 3xTg-AD mice and controls, despite well-developed neurofibrillary tangles and beta amyloid immunoreactive plaques. Myelin staining was normal in affected mice. These data suggest that the 3xTg-AD mouse model does not develop MRI detectable white matter changes at the ages we examined. 相似文献