全文获取类型
收费全文 | 404篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
化学 | 196篇 |
晶体学 | 1篇 |
力学 | 15篇 |
数学 | 71篇 |
物理学 | 127篇 |
出版年
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 28篇 |
2012年 | 16篇 |
2011年 | 22篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 8篇 |
2002年 | 19篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 9篇 |
1973年 | 7篇 |
1972年 | 9篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1969年 | 5篇 |
1968年 | 3篇 |
排序方式: 共有410条查询结果,搜索用时 31 毫秒
401.
An efficient conversion of artemisinin 1 into three new amino- and hydroxy-functionalized 11-aza prototypes 9, 11, and 12 has been achieved on a multigram scale by reaction with hydrazine, hydroxylamine, and 2-amino ethanol, respectively. Of these, 9 has been further diversified into a wide range of derivatives including imines, amines, amides, and linker based dimers. Prototypes 11 and 12 have been converted into the corresponding ethers in high yields. Some of these compounds have shown a high order of activity against multidrug-resistant malaria in mice by oral route. 相似文献
402.
In this paper we study the phenomenon of nonlinear supratransmission in a semi-infinite discrete chain of coupled oscillators described by modified sine-Gordon equations with constant external and internal damping, and subject to harmonic external driving at the end. We develop a consistent and conditionally stable finite-difference scheme in order to analyze the effect of damping in the amount of energy injected in the chain of oscillators; numerical bifurcation analyses to determine the dependence of the amplitude at which supratransmission first occurs with respect to the frequency of the driving oscillator are carried out in order to show the consequences of damping on harmonic phonon quenching and the delay of appearance of critical amplitude. 相似文献
403.
We present a simulation method for direct computation of chemical potentials in multicomponent systems. The method involves application of a field to generate spatial gradients in the species number densities at equilibrium, from which the chemical potential of each species is theoretically estimated. A single simulation yields results over a range of thermodynamic states, as in high throughput experiments, and the method remains computationally efficient even at high number densities since it does not involve particle insertion at high densities. We illustrate the method by Monte Carlo simulations of binary hard sphere mixtures of particles with different sizes in a gravitational field. The results of the gradient Monte Carlo method are found to be in good agreement with chemical potentials computed using the classical Widom particle insertion method for spatially uniform systems. 相似文献
404.
405.
Different techniques have been used (physical adsorption, physically entrapped sandwich and microencapsulation) for the immobilization of urease enzyme in tetramethylorthosilicate (TMOS) derived sol-gel matrix on the sensing surface of glass-pH-electrode. No significant leaching of enzyme occurs from the microencapsulated and physically entrapped enzyme sandwich films. Potentiometric techniques have been used for the estimation of urea concentration in each instance. Various parameters of biosensor performance have been studied which indicates that microencapsulation technique is a better method of enzyme immobilization in sol-gel films derived from TMOS. The advantage of microencapsulated biosensor over others include higher sensitivity (dpH/dp(C) = 2.4), lower detection limit of 52 μg mL−1, larger linear range (0.01-30 mM) of urea determination and reasonably long-term stability of about 25 days with 80% response signal. 相似文献
406.
Amichai Yavlovich Alok Singh Sergey Tarasov Jacek Capala Robert Blumenthal Anu Puri 《Journal of Thermal Analysis and Calorimetry》2009,98(1):97-104
We describe a novel class of light-triggerable liposomes prepared from a photo-polymerizable phospholipid DC8,9PC (1,2-bis (tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine) and DPPC (1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine). Exposure to UV (254 nm) radiation for 0–45 min at 25 °C resulted in photo-polymerization of DC8,9PC in these liposomes and the release of an encapsulated fluorescent dye (calcein). Kinetics and extents of calcein release
correlated with mol% of DC8,9PC in the liposomes. Photopolymerization and calcein release occurred only from DPPC/DC8,9PC but not from Egg PC/DC8,9PC liposomes. Our data indicate that phase separation and packing of polymerizable lipids in the liposome bilayer are major
determinants of photo-activation and triggered contents release. 相似文献
407.
A simple, rapid, selective, sensitive and economical method has been developed for the simultaneous determination of trace
amounts of palladium and nickel in aqueous methanolic medium using 2-(2-thiazolylazo)-5-dimethylam inobenzoic acid as an analytical
reagent by first derivative spectrophotometr y. Palladium is determined by measuring base to peak distance at λ=695.0 nm while
nickel is estimated by zero crossing method in the mixture. The linearity is maintained between 0.12–1.75 μg mL−1 for palladium and 0.07–1.60 μg mL−1 for nickel in the pH range 2.8–7.2 and 3.4–8.8 respectively. Seven replicate determinations of 1.0 μ g mL−1 of palladium and 0.8 μg mL−1 of nickel in a mixture give a mean signal height of 0.391 for Pd and 0.541 for Ni with relative standard deviations of 0.9%
and 1.2%, respectively. The sensitivity of the proposed method is 0.391 (dA/dλ)/(μg mL−1) for palladium and 0.685 (dA/dλ)/(μg mL−1) for nickel. Various parameters have been optimised for the simultaneous determination of palladium and nickel in various
complex samples.
Received March 30, 1999. Revision November 25, 1999. 相似文献
408.
P. Puri 《Applied Scientific Research》1973,28(1):111-133
Approximate solutions of the Navier-Stokes equations are derived through the Laplace transform for two dimensional, incompressible,
elastico-viscous flow past a flat porous plate. The flow is assumed to be independent of the distance parallel to the plate.
General formulae for the velocity distribution, skin friction and displacement thickness as functions of the given free stream
velocity and suction velocity are obtained.
The response of skin friction to the impulsive perturbations in the stream and suction velocities is studied. It is found
that the order of singularity in the skin friction at t=0 increases due to the elastic property of the fluid in the impulsive case. When the stream is accelerated the skin friction
still anticipates the velocity but the time of anticipation is reduced from 1/4 to (1/4) (1—k), where k is the elastic parameter of the fluid. It is found that in general the resistance of the elastico-viscous fluids to an impulsive
increase in the stream velocity is greater than the viscous fluids, the elasticoviscous fluids also reach the steady state
earlier than the viscous fluids. 相似文献
409.
410.