全文获取类型
收费全文 | 434篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 331篇 |
晶体学 | 9篇 |
力学 | 9篇 |
数学 | 39篇 |
物理学 | 62篇 |
出版年
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 13篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 16篇 |
2016年 | 13篇 |
2015年 | 3篇 |
2014年 | 10篇 |
2013年 | 37篇 |
2012年 | 14篇 |
2011年 | 43篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 26篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1992年 | 8篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有450条查询结果,搜索用时 31 毫秒
261.
Kinetics of Ni,V and Fe Leaching from a Spent Catalyst in Microwave-Assisted Acid Activation Process
Tian Wang Jing Ren Annavarapu V. Ravindra Yan Lv Thiquynhxuan Le 《Molecules (Basel, Switzerland)》2022,27(7)
Ni, V and Fe are the main contaminant metals that lead to the deactivation of the spent fluid catalytic cracking (SFCC) catalyst. In this work, the properties and distribution of Ni, V and Fe in the SFCC catalyst are investigated by employing EPMA-EDX, SEM and XPS techniques. The kinetics of Ni, V, Fe and Al leaching in organic and inorganic acids are studied under microwave heating. The EPMA-EDX results show that Fe and Ni mainly accumulate near the particle surface, while V eventually distributes throughout the catalyst particle. The XPS result suggests that the phase speciations of Ni in the SFCC catalyst are Ni, Ni2SiO4 and NiAl2O4, while Fe is present in a mixture of Fe3O4, Fe2O3 and Fe2SiO4. V is in the forms of V2O5 and VO2. Compared with oxalic acid, sulfuric acid has a better removal effect of contaminant metals, especially for Ni. The leaching kinetics results indicate that using either sulfuric acid or oxalic acid, the apparent activation energy of V is obviously lower than that of Fe and Ni, and the priority of the three contaminant metals in the removal effect is V > Fe > Ni. In addition, the leaching kinetics of contaminant metals in the microwave-assisted acid activation process are controlled by the surface chemical reaction control model. 相似文献
262.
Fredy W. Aquino Ravindra Shinde Bryan M. Wong 《Journal of computational chemistry》2020,41(12):1200-1208
We present a new assessment of the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) approach with an emphasis on its performance for predicting energies as a function of fractional occupation numbers (FONs) for various multielectron systems. Our approach is implemented in the massively parallelized NWChem quantum chemistry software package and has been benchmarked on the prediction of total energies, atomization energies, and ionization potentials of small molecules and relatively large aromatic systems. Within our study, we also derive an alternate expression for the FLO-SIC energy gradient expressed in terms of gradients of the Fermi-orbital eigenvalues and revisit how the FLO-SIC methodology can be seen as a constrained unitary transformation of the canonical Kohn–Sham orbitals. Finally, we conclude with calculations of energies as a function of FONs using various SIC-scaling methods to test the limits of the FLO-SIC formalism on a variety of multielectron systems. We find that these relatively simple scaling methods do improve the prediction of total energies of atomic systems as well as enhance the accuracy of energies as a function of FONs for other multielectron chemical species. 相似文献
263.
264.
Ravindra D. Yeole Vipul P. Rane Vinod K. Ahirrao Rajesh P. Chavan Anasuya M. Patel Prasad K. Deshpande Mahesh V. Patel Kiran R. Patil 《Biomedical chromatography : BMC》2019,33(7)
WCK 771 is an l ‐arginine salt of levonadifloxacin (LND) being developed in intravenous dosage form and has recently completed a phase III trial in India. The pharmacokinetics of WCK 771, a novel anti‐MRSA fluoroquinolone, were examined in mice, rats, rabbits, dogs, monkeys and humans after systemic administration during pre‐clinical and clinical investigations. Urine and serum were evaluated for identification of metabolites. It was observed that LND mainly follows phase II biotransformation pathways. All of the species showed a different array of metabolites. In mice, rabbit and dog, the drug was mainly excreted in the form of O‐glucuronide (M7) and acyl glucuronide (M8) conjugates, whereas in rat and human major metabolite was sulfate conjugate (M6). Monkeys exhibited equal distribution of sulfate (M6) and glucuronide conjugates (M7, M8). In addition to these three major phase II metabolites; five phase I oxidative metabolites (M1, M2, M3, M4 and M5) were identified using liquid chromatography tandem mass spectrometry. Out of these eight metabolites M2, M3, M5, M7 and M8 are reported for the first time. 相似文献
265.
266.
Thin films of pure Pd and composite of Pd and 1% multiwalled carbon nanotube have been obtained on glassy carbon electrodes
by borohydride reduction method and investigated as electrocatalysts for the oxidation of phenol in acid medium at 25 °C,
using cyclic voltammetry (CV), chronopotentiometry, and high-performance liquid chromatography. The CV study showed that both
the electrocatalysts are quite stable and active for the phenol oxidation in acid medium. Further, these electrodes do not
seem to undergo deactivation due to intermediates and products formed during the phenol oxidation. With the increase in phenol
concentration from 2 to 25 mM, the peak current (I
p) increases initially, reaches maximum at about 15 mM, and tends to decrease thereafter. The peak potential (E
p) value was found to be practically unchanged with phenol concentration. The rate for phenol oxidation (I
p) at the surface of both the electrocatalysts increased with the decrease in pH of the reaction mixture. The electrocatalytic
activity of the composite electrode was, however, higher than that of pure Pd under similar experimental conditions. Benzoquinone
and hydroquinone were identified as the major phenol degradation intermediate products. 相似文献
267.
268.
Sinha S Misra A Rathi M Kumar V Pandey RM Luthra K Jagannathan NR 《Magnetic resonance imaging》2009,27(1):94-100
We report the determination of intramyocellular lipids (IMCLs) of the soleus muscle of patients with type 2 diabetes mellitus (T2DM) using proton magnetic resonance spectroscopy. In addition, the various anthropometric and biochemical profiles of these patients were determined, including estimation of C-reactive protein (CRP), an inflammatory marker of coronary heart disease, and insulin resistance [Homeostasis Model Assessment (HOMA-IR)]. The estimated CRP level and the IMCL content in these patients were correlated with body mass index, percentage of body fat, other measures of abdominal obesity, serum lipoproteins, fasting and post-oral glucose load serum insulin levels and other surrogate markers of insulin resistance. The IMCL content (P=.04), CRP (P=.008) and insulin resistance (P=.0007) were significantly higher in T2DM patients compared to healthy controls. However, IMCL content did not correlate with values of fasting insulin, HOMA-IR or CRP in either group. These findings have strong implications of increased cardiovascular risk in Asian Indians with T2DM. The absence of relationship between CRP and IMCL needs to be explored further in a study using a large sample size. 相似文献
269.
H. J. Ravindra K. Chandrashekaran W. T. A. Harrison S. M. Dharmaprakash 《Applied physics. B, Lasers and optics》2009,94(3):503-511
Single crystals of a chalcone co-crystal (C18H19NO4/C17H16NO3Br; 0.972/0.028) have been grown by slow evaporation from solution. The powder second harmonic generation (SHG) efficiency
of this chalcone co-crystal is 7 times that of urea. The dependence of second harmonic (SH) intensity on particle size revealed
the existence of phase matching direction in this crystal. The large SHG efficiency observed is mainly due to the unidirectional
alignment of molecular dipoles, in which the dipole moment of each molecule adds to establish a net polarization. The weak
N–H⋅⋅⋅O hydrogen-bond interactions help to stabilize the noncentrosymmetric crystal packing and also contribute partly to the SHG.
The better thermal stability, transparency and high laser damage resistance (>1.5 GW cm−2 at 532 nm, 8 ns) of this chalcone co-crystal indicate that it is a promising material for frequency doubling of diode lasers
down to 470 nm. This molecule also shows a third-order NLO response and good optical limiting property of 8 ns laser pulses
at 532 nm. The mechanism for optical limiting in this chalcone was attributed to two-photon induced excited state absorption
that leads to reverse saturable absorption. The structure–property relationship in this chalcone and related compounds is
discussed based on the experimental results and semiempherical hyperpolarizability calculations. 相似文献
270.
David Groh Ravindra Pandey Munima B. Sahariah Isabelle Baraille 《Journal of Physics and Chemistry of Solids》2009,70(5):789-795
Optical properties such as the dynamic dielectric function, reflectance, and energy-loss function of beryllium oxide (BeO) in its ambient and high-pressure phases are reported for a wide energy range of 0-50 eV. The calculations of optical properties employ first-principles methods based on all-electron density functional theory together with sum over states and finite-field methods. Our results show subtle differences in the calculated optical properties of the wurtzite, zincblende, rocksalt and CsCl phases of BeO, which may be attributed to the higher symmetry and packing density of these phases. For the wurtzite phase, the calculated band gap of 10.4 eV corresponds well with the experimental value of 10.6 eV and the calculated (average) index of refraction of 1.70 shows excellent agreement with the experimental value of 1.72. 相似文献