全文获取类型
收费全文 | 186篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
化学 | 76篇 |
力学 | 10篇 |
数学 | 42篇 |
物理学 | 60篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 9篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 11篇 |
2013年 | 12篇 |
2012年 | 17篇 |
2011年 | 13篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有188条查询结果,搜索用时 15 毫秒
131.
This paper proposes new conditions which are sufficient for robust control of a class of chaotic and hyperchaotic driven systems. The drive–driven systems are characterized by non-identical uncertain complex dynamics where complexities are mainly introduced by the switching nature of their vector fields. The controller design is achieved using linear matrix inequalities (LMIs) and the so-called S-procedure and then validated using two numerical examples. To illustrate the robustness of the proposed approach, a comparative study is also established with regard to a related approach. 相似文献
132.
Muhammed Majeed Kalyanam Nagabhushanam Shaheen Majeed Anurag Pande 《液相色谱法及相关技术杂志》2017,40(14):732-740
Introduction: Identification of Oroxylum indicum and Scutellaria baicalensis provides an interesting challenge in selection of biomarker compound to be used in routine analysis. Both plants have similar phytochemical profile and are rich sources of flavones and flavone glycosides. The objective of this study was to prepare the chemical fingerprinting of O. indicum bark and S. baicalensis roots using the liquid chromatography and mass spectroscopy in single chromatographic method. Materials and methods: Extracts prepared using various solvent systems (methanol, aqueous methanol, chloroform, hexane, and water) of both plants were analyzed using C18 reverse phase column with solvent system containing acetonitrile and 0.1% formic acid. Major flavonoids were identified based on mass spectra, fragmentation pattern, and UV spectra. Results: In this article, well-resolved high-performance liquid chromatographic (HPLC) separation in both plant extracts was obtained and chemical fingerprints for both plant extracts were established and flavonoids present (baicalin, oroxylin A-7-O-glucuronide, chrysin-7-O-glucuronide, baicalein, chrysin, oroxylin-A, wogonin, skullcap flavone II) were identified as possible biomarkers. Conclusion: Mass spectrometry coupled with HPLC can be a tool for fingerprinting of various natural products used in dietary supplement industry. The fingerprint developed in the article can be used for quality evaluation as well as identifying possible adulteration of extracts of both the plants. 相似文献
133.
Triflic acid is a functional group of perflourosulfonated polymer electrolyte membranes where the sulfonate group is responsible for proton conduction. However, even at extremely low hydration, triflic acid exists as a triflate ion. In this work, we have developed a force-field for triflic acid and triflate ion by deriving force-field parameters using ab initio calculations and incorporated these parameters with the Optimized Potentials for Liquid Simulations - All Atom (OPLS-AA) force-field. We have employed classical molecular dynamics (MD) simulations with the developed force field to characterize structural and dynamical properties of triflic acid (270-450 K) and triflate ion/water mixtures (300 K). The radial distribution functions (RDFs) show the hydrophobic nature of CF(3) group and presence of strong hydrogen bonding in triflic acid and temperature has an insignificant effect. Results from our MD simulations show that the diffusion of triflic acid increases with temperature. The RDFs from triflate ion/water mixtures shows that increasing hydration causes water molecules to orient around the SO(3)(-) group of triflate ions, solvate the hydronium ions, and other water molecules. The diffusion of triflate ions, hydronium ion, and water molecules shows an increase with hydration. At λ = 1, the diffusion of triflate ion is 30 times lower than the diffusion of triflic acid due to the formation of stable triflate ion-hydronium ion complex. With increasing hydration, water molecules break the stability of triflate ion-hydronium ion complex leading to enhanced diffusion. The RDFs and diffusion coefficients of triflate ions, hydronium ions and water molecules resemble qualitatively the previous findings using per-fluorosulfonated membranes. 相似文献
134.
Vajpayee V Kim H Mishra A Mukherjee PS Stang PJ Lee MH Kim HK Chi KW 《Dalton transactions (Cambridge, England : 2003)》2011,40(13):3112-3115
Self-assemblies between a linear Pt-based donor and ferrocene- chelated metallic acceptors produced novel heterometallic squares 4 and 5, which show fluorescence quenching upon the addition of nitro-aromatics. 相似文献
135.
Kaushik Dey Shebeeb Kunjattu H. Anurag M. Chahande Prof. Dr. Rahul Banerjee 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(3):1177-1181
Covalent organic frameworks (COFs) have attracted attention due to their ordered pores leading to important industrial applications like storage and separation. Combined with their modular synthesis and pore engineering, COFs could become ideal candidates for nanoseparations. However, the fabrication of these microcrystalline powders as continuous, crack-free, robust films remains a challenge. Herein, we report a simple, slow annealing strategy to construct centimeter-scale COF films ( Tp-Azo and Tp-TTA ) with micrometer thickness. The as-synthesized films are porous (SABET=2033 m2 g−1 for Tp-Azo ) and chemically stable. These COFs have distinct size cut-offs (ca. 2.7 and ca. 1.6 nm for Tp-Azo and Tp-TTA , respectively), which allow the size-selective separation of gold nanoparticles. Unlike, other conventional membranes, the durable structure of the COF films allow for excellent recyclability (up to 4 consecutive cycles) and easy recovery of the gold nanoparticles from the solution. 相似文献
136.
Hitoshi Sato Anurag Tyagi Hong Zhong Natalie Fellows Roy B. Chung Makoto Saito Kenji Fujito James S. Speck Steven P. DenBaars Shuji Nakamura 《固体物理学:研究快报》2007,1(4):162-164
We demonstrate a high power green InGaN/GaN multiple‐quantum‐well (MQW) light emitting diode (LED) with a peak emission wavelength of 516 nm grown on low extended defect density semipolar (11 2) bulk GaN substrate by metal organic chemical vapor deposition. The output power and external quantum efficiency (EQE) at drive currents of 20 and 100 mA under direct current (DC) operation were 5.0 mW, 10.5% and 15.6 mW, 6.3%, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
137.
We present an analytical model for the mode of index-guided microstructured fibers. This model exhibits essential symmetry
features of the field unlike the commonly used equivalent step-index (ESI) model. The model is shown to be more accurate than
the equivalent step-index (ESI) model in predicting the effective-indices of the mode. Results for the modal effective index,
near and far fields and dispersion have been included. 相似文献
138.
A method based on symmetrized splitting of the propagation operator in the finite difference scheme for non-paraxial beam propagation is presented. The formulation allows the solution of the second order scalar wave equation without having to make the slowly varying envelope and one-way propagation approximations. The method is highly accurate and numerically efficient. Unlike most Padé approximant based methods, it is non-iterative in nature and requires less computation. The method can be used for bi-directional propagation as well. 相似文献
139.
Low-loss splicing of index-guiding microstructured optical fibers (MOFs) and conventional single-mode fibers (SMFs) can be achieved by enlarging the mode field diameter of MOFs, which leads to an optimum mode field match at the joint interface. We study analytically the low-loss fusion splicing between an MOF and an SMF by expanding the modal field of MOF, using the controlled air-hole collapse method. Our method is simple and offers analytical solution for light coupling between MOFs and SMFs. Comparisons with available experimental and simulation results have also been included. 相似文献
140.
Ram N. Patel Manoj K. Kesharwani Anurag Singh Dheerendra K. Patel Mukesh Choudhary 《Transition Metal Chemistry》2008,33(6):733-738
Three new polyamine Ni(II) complexes, namely [Ni(trien)(phen)](BF4)2
1, [Ni(trien)(bipy)](ClO4)2
2 and [Ni(trien)(en)](ClO4)2
3 [trine = triethylenetetramine, phen = 1,10-phenanthroline, bipy = 2,2′-bipyridyl, en = ethylenediamine] have been synthesized
and characterized by physico-chemical and spectroscopic methods. Complexes 1 and 2 crystallize in monoclinic space group P21/c, and possess a distorted octahedral geometry. Significant hydrogen bonding interactions are found in both complexes. 相似文献