全文获取类型
收费全文 | 662篇 |
免费 | 44篇 |
国内免费 | 12篇 |
专业分类
化学 | 541篇 |
晶体学 | 11篇 |
力学 | 17篇 |
数学 | 48篇 |
物理学 | 101篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 40篇 |
2021年 | 28篇 |
2020年 | 21篇 |
2019年 | 27篇 |
2018年 | 25篇 |
2017年 | 17篇 |
2016年 | 43篇 |
2015年 | 26篇 |
2014年 | 22篇 |
2013年 | 77篇 |
2012年 | 42篇 |
2011年 | 52篇 |
2010年 | 34篇 |
2009年 | 22篇 |
2008年 | 24篇 |
2007年 | 24篇 |
2006年 | 19篇 |
2005年 | 15篇 |
2004年 | 13篇 |
2003年 | 16篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1957年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有718条查询结果,搜索用时 31 毫秒
61.
Ion-acoustic waves in plasma of warm ions and isothermal electrons using time-fractional KdV equation
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sayed A. El-Wakil Essam M. Abulwaf Emad K. El-Shewy Abeer A. Mahmoud 《中国物理 B》2011,20(4):40508-040508
The ion-acoustic solitary wave in collisionless unmagnetized plasma consisting of warm ions-fluid and isothermal electrons is studied using the time fractional KdV equation. The reductive perturbation method has been employed to derive the Korteweg-de Vries equation for small but finite amplitude ion-acoustic wave in warm plasma. The Lagrangian of the time fractional KdV equation is used in a similar form to the Lagrangian of the regular KdV equation with fractional derivative for the time differentiation. The variation of the functional of this Lagrangian leads to the Euler-Lagrange equation that gives the time fractional KdV equation. The variational-iteration method is used to solve the derived time fractional KdV equation. The calculations of the solution are carried out for different values of the time fractional order. These calculations show that the time fractional can be used to modulate the electrostatic potential wave instead of adding a higher order dissipation term to the KdV equation. The results of the present investigation may be applicable to some plasma environments,such as the ionosphere plasma. 相似文献
62.
The major objective of this work was the development of a reliable model to describe volumetric properties of ionic liquids
(ILs). In this regard, we have applied the Ihm–Song–Mason equation of state (EOS) to some phosphonium- and imidazolium-based
ILs. Three temperature-dependent parameters in the equation of state have been scaled based on the surface tension and the
liquid density at room temperature. In order to improve the predictive power of the mentioned EOS for ILs, we have proposed
using a simple modification. We have taken 1,228 experimental points to show the reliability of the improved EOS. The comparison
of predicted densities with literature data over a broad range of temperature, 293–472 K, and pressures up to 200 MPa led
to encouraging results. The average absolute deviation of calculated densities from literature values was found to be 0.75%. 相似文献
63.
M. F. El‐Sayed G. M. Moatimid M. H. M. Moussa R. M. El‐Shiekh A. A. El‐Satar 《Mathematical Methods in the Applied Sciences》2014,37(8):1113-1120
Symmetry group analysis and similarity reduction of nonlinear system of coupled Burger equations in the form of nonlinear partial differential equation are analyzed via symmetry method. The symmetry method has led to similarity reductions of this equation to solvable form to third‐order partial differential equation. The infinitesimal, similarity variables, dependent variables, and reduction have been tabulated. The search for solutions of these systems by using the improved tanh method has yielded certain exact solutions expressed by rational functions. Some figures are given to show the properties of the solutions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
64.
Abdelwahed R. Sayed 《Tetrahedron letters》2010,51(34):4490-4493
Efficient syntheses of 1,3,4-thiadiazoles and bis-thiadiazoles by the reaction of hydrazonoyl halides with carbonothioic dihydrazide are reported. In addition, 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole is obtained via oxidative cyclization of bis-(substituted methylene)carbonothioic dihydrazone. 相似文献
65.
We consider a class of quasilinear elliptic boundary problems, including the following Modified Nonlinear Schrödinger Equation as a special case: $$\begin{cases} ∆u+ \frac{1}{2} u∆(u^2)−V(x)u+|u|^{q−2}u=0 \ \ \ in \ Ω, \\u=0 \ \ \ \ \ \ \ ~ ~ ~ on \ ∂Ω, \end{cases}$$ where $Ω$ is the entire space $\mathbb{R}^N$ or $Ω ⊂ \mathbb{R}^N$ is a bounded domain with smooth boundary, $q∈(2,22^∗]$ with $2^∗=2N/(N−2)$ being the critical Sobolev exponent and $22^∗= 4N/(N−2).$ We review the general methods developed in the last twenty years or so for the studies of existence, multiplicity, nodal property of the solutions within this range of nonlinearity up to the new critical exponent $4N/(N−2),$ which is a unique feature for this class of problems. We also discuss some related and more general problems. 相似文献
66.
A novel, cost‐effective, and simple electrocatalyst based on a Pt‐modified glassy carbon electrode (GCE), using cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, is reported. Am‐phiphilic... 相似文献
67.
Triple Emission from p‐Dimethylaminobenzonitrile–Cucurbit[8]uril Triggers the Elusive Excimer Emission
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Mhejabeen Sayed Dr. Frank Biedermann Dr. Vanya D. Uzunova Khaleel I. Assaf Dr. Achikanath C. Bhasikuttan Dr. Haridas Pal Prof. Werner M. Nau Dr. Jyotirmayee Mohanty 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):691-696
The intriguing dual‐emission behavior of p‐ dimethylaminobenzonitrile (DMABN) and the identity of the associated excited states is, arguably, the most extensively investigated and also controversially discussed molecule‐ specific phenomenon of modern photochemistry. We have now found a new, third fluorescence band when DMABN is encapsulated within the water‐soluble molecular container cucurbit[8]uril (CB8). It is centered between the previously observed emissions and assigned to the elusive excimer emission from DMABN through 1:2 CB8:DMABN complex formation. Heating of the CB8 ? (DMABN)2 complex from 0 to 100 °C results in the dissociation of the ternary complex and restoration of the dual‐emission properties of the monomer. Alternatively, monomer emission can be obtained by selecting cucurbit[7]uril (CB7), a host homologue that is too small to accommodate two DMABN molecules, or by introducing ethyl instead of methyl groups at the amino terminus of the aminobenzonitrile guest. 相似文献
68.
Asra S. Razavian Sayed M. Ghoreishi Amir S. Esmaeily Mohsen Behpour Lorena M. A. Monzon J. Michael D. Coey 《Mikrochimica acta》2014,181(15-16):1947-1955
An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO2 nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO2 coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM?1, while for epinephrine these values are ~60 nM and 0.19 μA μM?1. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.
69.
Rukhsana Ilays Kureshy K. Jeya PrathapManish Kumar Prasanta Kumar BeraNoor-ul Hasan Khan Sayed Hasan Razi AbdiHari Chandra Bajaj 《Tetrahedron》2011,67(43):8300-8307
A series of chiral macrocyclic Cr(III) salen complexes 1-8 were synthesized and characterized. These complexes were found to be highly active, regio-, diastereo-, and enantioselective catalysts in aminolytic kinetic resolution (AKR) of racemic trans-epoxides as well as asymmetric ring opening (ARO) of prochiral meso-epoxides with various anilines as nucleophiles at room temperature in 18-24 h. Excellent yields (>99% with respect to the nucleophile) with high enantioselectivity (ee, >99%) of chiral anti-β-amino alcohols was achieved with concomitant recovery of corresponding epoxides in high ee (up to >99%). The complex 1 also catalyzed the ARO of meso-epoxides to provide corresponding syn-β-amino alcohols in high yield (99%) and ee (up to 91%). Due to built-in basic sites in the catalyst, no external base (as an additive) was required to promote AKR and ARO reactions. The catalyst 1 was conveniently recycled several times with retention of its performance. The AKR of trans-stilbene oxide with aniline was successfully demonstrated at relatively higher scale (10 mmol) using the catalyst 1. 相似文献
70.
M. A. Ahmed El Sayed Yousef M. F. Abdel-Messih 《Journal of Sol-Gel Science and Technology》2011,60(1):58-65
Nanocomposite samples containing various molar compositions of tin and titanium oxides were synthesized by a sol–gel method
using octadecylamine as controlling template agent. The structural and the crystalline features of the samples were investigated
with Fourier Transformer Infra-red, X-ray diffraction, Transmission electron microscope (TEM) where the surface area was estimated
by BET analysis. The crystalline parameters and the particle size were estimated by Rietveld quantitative phase analysis.
It is interesting to mention that a reduction in the lattice parameters was detected upon introduction of various molar compositions
of titanium oxide revealing that a part of titania is incorporated into the SnO2 lattice forming Ti1−xSnxO2 solid solution. The quantitative analysis claims that part of titanium oxide is incorporated substitutionally in the crystal
lattice of SnO2, forming a solid solution and other parts are either segregated as separate rutile titania phase or dispersed as amorphous
phase on the grain boundary of SnO2. The results show a remarkable reduction in particle size from 42 to 5 nm and increasing in the specific surface area up
to 176 m2/g upon introduction of various content of titania implying the role of titania particles in preventing SnO2 crystallites from further growing up during the progress of calcination. TEM images show that pure tin oxide particles arranged
in large aggregation in wormhole like structure, while the existence of titanium oxide are successfully creates spherical
nanoparticles system organized in a definite structure. The optical absorbance spectra indicate a red shift and band gap narrowing
upon introduction of titania which increase with increasing in titania contents. 相似文献