全文获取类型
收费全文 | 635篇 |
免费 | 20篇 |
国内免费 | 2篇 |
专业分类
化学 | 359篇 |
晶体学 | 3篇 |
力学 | 20篇 |
数学 | 69篇 |
物理学 | 206篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 27篇 |
2018年 | 24篇 |
2017年 | 18篇 |
2016年 | 33篇 |
2015年 | 20篇 |
2014年 | 26篇 |
2013年 | 62篇 |
2012年 | 47篇 |
2011年 | 58篇 |
2010年 | 35篇 |
2009年 | 31篇 |
2008年 | 39篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 14篇 |
2002年 | 3篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 2篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1968年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有657条查询结果,搜索用时 468 毫秒
191.
192.
A. S. Singha Ashish Guleria Raj K. Rana Ashvinder K. Rana 《International Journal of Polymer Analysis and Characterization》2013,18(5):377-389
A novel redox system, ascorbic acid-hydrogen peroxide, was employed to initiate graft copolymerization of ethyl acrylate and methyl methacrylate binary monomer mixtures onto Abelmoschus esculentus fibers at a temperature of 45°C for 90 min in an aqueous medium. Factors affecting grafting such as feed molarity and comonomer composition were investigated. Contrary to the lower affinity of methyl methacrylate for grafting on Abelmoschus fibers, a synergistic effect of ethyl acrylate on methyl methacrylate was observed when graft copolymers were prepared using different feed compositions (fMMA). The percentage of grafting increased from 40.2% to 89.74% at 0.4 mole fraction of fMMA. The graft copolymers were characterized by FT-IR, TGA, and SEM techniques. 相似文献
193.
Brijesh Pandey Veda P. Pandey A. K. Shasany U. N. Dwivedi 《Applied biochemistry and biotechnology》2014,172(7):3414-3423
A cinnamyl alcohol dehydrogenase (CAD) from the secondary xylem of Leucaena leucocephala has been purified to homogeneity through successive steps of ammonium sulfate fractionation, DEAE cellulose, Sephadex G-75, and Blue Sepharose CL-6B affinity column chromatographies. CAD was purified to 514.2 folds with overall recovery of 13 % and specific activity of 812. 5 nkat/mg. Native and subunit molecular masses of the purified enzyme were found to be ~76 and ~38 kDa, respectively, suggesting it to be a homodimer. The enzyme exhibited highest catalytic efficiency (Kcat/Km 3.75 μM?1 s?1) with cinnamyl aldehyde among all the substrates investigated. The pH and temperature optima of the purified CAD were pH 8.8 and 40 °C, respectively. The enzyme activity was enhanced in the presence of 2.0 mM Mg2+, while Zn2+ at the same concentration exerted an inhibitory effect. The inclusion of 2.0 mM EDTA in the assay system activated the enzyme. The enzyme was inhibited with caffeic acid and ferulic acid in a concentration-dependent manner, while no inhibition was observed with salicylic acid. Peptide mass analysis of the purified CAD by MALDI-TOF showed a significant homology to alcohol dehydrogenases of MDR superfamily. 相似文献
194.
Garima Singhal Riju Bhavesh Kunal Kasariya Ashish Ranjan Sharma Rajendra Pal Singh 《Journal of nanoparticle research》2011,13(7):2981-2988
Development of green nanotechnology is generating interest of researchers toward ecofriendly biosynthesis of nanoparticles.
In this study, biosynthesis of stable silver nanoparticles was done using Tulsi (Ocimum sanctum) leaf extract. These biosynthesized nanoparticles were characterized with the help of UV–vis spectrophotometer, Atomic Absorption
Spectroscopy (AAS), Dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR),
and Transmission electron microscopy (TEM). Stability of bioreduced silver nanoparticles was analyzed using UV–vis absorption
spectra, and their antimicrobial activity was screened against both gram-negative and gram-positive microorganisms. It was
observed that O. sanctum leaf extract can reduce silver ions into silver nanoparticles within 8 min of reaction time. Thus, this method can be used
for rapid and ecofriendly biosynthesis of stable silver nanoparticles of size range 4–30 nm possessing antimicrobial activity
suggesting their possible application in medical industry. 相似文献
195.
The complex of o-phenylenediamine (o-PDA) and benzoin (BN) was synthesized adopting solid state reaction by mixing of their melt together followed by chilling.
The phase diagram study shows the formation of a complex in 1:1 molar ratio with congruent melting point and two eutectics
lying on either side of complex. The formation of complex was confirmed using the FTIR, NMR, mass spectroscopy, powder XRD
and DSC studies. The optical properties of the parent component, their complex and few other compositions nearby the complex
were studied using absorption and laser luminescence techniques. The significantly higher green/yellow emission was noted
with newly synthesized complex as compared to that of their parents as well as other compositions of o- PDA and BN. 相似文献
196.
Ram Prakash Dwivedi 《Optics Communications》2011,284(5):1418-1423
We report, for the first time, on the design of a plasmonic modulator working on the principle of the elasto-optic effects in a directional coupling structure, utilizing three parallel metal-dielectric-metal waveguides. We propose to achieve the active switching of the power propagation using the elasto-optic effect and optimize the extinction ratio of the optical modulation. The device is characterized and numerically analyzed using the finite-element-method at the wavelengths of 1.55 μm. For the modulator length of 2.33 μm, the extinction ratio of the modulation is nearly 14 dB, and the calculated attenuation loss is 4.5 dB. The calculated driving voltage is 4.8 V for the given modulator. The effect of the applied voltage on the modulation is also analyzed. 相似文献
197.
Enhanced luminescence and degradation resistance in Tb modified Yttrium Borate core-nano silica shell phosphor under UV and VUV excitation 总被引:1,自引:0,他引:1
Santa Chawla RavishankerA.F. Khan Ashish YadavH. Chander V. Shanker 《Applied Surface Science》2011,257(16):7167-7171
Composition variation in optimized solid state reaction conditions has been done to achieve intense green emission in YTbxBO3 phosphor under UV and VUV (147 nm resonant Xe*, 172 nm Xe2* excimer band) excitation. Inert interface layer created by fabricating a shell of silica nanoparticles over individual phosphor grain protected the phosphor surface from deterioration and oxidation of luminescent ion (Tb3+) thus completely arresting phosphor degradation. At optimum Tb content of 20 mol%, integrated photoluminescence intensity of developed YTbxBO3 phosphor is four times higher than commercial green YBT. With short decay time of 4 ms, YTbxBO3 core-nano silica shell green emitting phosphor has great application potential in PDP panel and phosphor coated Xe lamps. 相似文献
198.
Neeraj Dwivedi Sushil Kumar H.K. MalikGovind C.M.S. RauthanO.S. Panwar 《Applied Surface Science》2011,257(15):6804-6810
In the present work the correlation of electrical, optical and nano-mechanical properties of argon-diluted diamond-like carbon (Ar-DLC) thin films with sp3 and sp2 fractions of carbon have been explored. These Ar-DLC thin films have been deposited, under varying C2H2 gas pressures from 25 to 75 mTorr, by radio frequency-plasma enhanced chemical vapor deposition technique. X-ray photoelectron spectroscopy studies are performed to estimate the sp3 and sp2 fractions of carbon by deconvoluting C 1s core level spectra. Various electrical, optical and nano-mechanical parameters such as conductivity, I-V characteristics, optical band gap, stress, hardness, elastic modulus, plastic resistance parameter, elastic recovery and plastic deformation energy have been estimated and then correlated with calculated sp3 and sp2 fractions of carbon and sp3/sp2 ratios. Observed tremendous electrical, optical and nano-mechanical properties in Ar-DLC films deposited under high base pressure conditions made it a cost effective material for not only hard and protective coating applications but also for electronic and optoelectronic applications. 相似文献
199.
Ashish Jain R. Pankajavalli R. Babu S. Anthonysamy 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1279-1287
The standard Gibbs energies of formation of Nd2TeO6 and M6TeO12 (where M = Nd, Sm) were determined from vapour pressure measurements. The vapour pressure of TeO2(g) was measured by employing thermogravimetry-based transpiration technique. The temperature dependence of the vapour pressure of TeO2(g) over the mixtures Nd2TeO6+Nd6TeO12, generated by the incongruent vapourisation reaction, 3Nd2TeO6(s) → Nd6TeO12(s)+2TeO2(g)+O2(g), was measured in the temperature range 1,408–1,495 K. Similarly, the vapour pressure of TeO2(g) over the mixtures M6TeO12+M2O3 (where M = Nd, Sm), generated by the incongruent vapourisation reaction, M6TeO12(s) → 3M2O3(s)+TeO2(g)+½O2(g), was measured in the temperature range 1,703–1,773 and 1,633–1,753 K for Nd6TeO12(s) and Sm6TeO12(s), respectively. Enthalpy increments of M2TeO6(s) (where M = Nd, Sm) were determined by inverse drop calorimetric method in the temperature range 573–1,273 K. The thermodynamic functions, viz., heat capacity, entropy and free energy functions, were derived from the measured values of enthalpy increments. A mean value of ?2,426.2 ± 0.6 and ?2,417.9 ± 1.1 kJ mol?1 was obtained for $ \Updelta_{\text{f} } H_{298}^{\text{o}} $ (Nd2TeO6, s) and $ \Updelta_{\text{f}} H_{298}^{\text{o}} $ (Sm2TeO6, s), respectively, by combining the value of $ \Updelta_{\text{f}} G^{\text{o}} $ (Nd2TeO6, s) and $ \Updelta_{\text{f}} G^{\text{o}} $ (Sm2TeO6, s) derived from vapour pressure data and the free energy functions derived from the drop calorimetric data. 相似文献
200.
Kamlesh Pandey Mrigank Mauli Dwivedi Markandey Singh Nidhi Asthana S. L. Agrawal 《Russian Journal of Electrochemistry》2014,50(2):170-175
In the present work, improvement in ion transport property of polyvinyl formal (PVF)-based nanocomposite polymer electrolytes has been studied upon dispersal of multiwall carbon nanotube (MWCNT) filler. Nanocomposite polymer electrolyte (NCPE) films of xPVF: (1 ? x)CH3COONH4 (ammonium acetate) were prepared by solution cast technique. The formation of nanocomposite has been ascertained by X-ray diffraction (XRD) pattern, which also shows that doping of salt increases amorphousness through polymer salt complexation. Changes in surface morphology have been observed in optical microscopy and Scanning Electron Microscopic (SEM) images. Variation of dielectric constant, dielectric loss, tangent loss and modulus spectra with the change in frequency and temperature were studied with the aid of impedance spectroscopy. 相似文献