全文获取类型
收费全文 | 625篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
化学 | 403篇 |
晶体学 | 8篇 |
力学 | 9篇 |
数学 | 23篇 |
物理学 | 196篇 |
出版年
2022年 | 10篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 14篇 |
2014年 | 29篇 |
2013年 | 58篇 |
2012年 | 45篇 |
2011年 | 55篇 |
2010年 | 35篇 |
2009年 | 25篇 |
2008年 | 37篇 |
2007年 | 39篇 |
2006年 | 25篇 |
2005年 | 28篇 |
2004年 | 22篇 |
2003年 | 11篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 4篇 |
1967年 | 2篇 |
1962年 | 2篇 |
1961年 | 2篇 |
1947年 | 2篇 |
1939年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有639条查询结果,搜索用时 31 毫秒
551.
H. J. Arnikar A. H. Kapadi D. G. Naik J. G. Chandwadkar 《Journal of Radioanalytical and Nuclear Chemistry》1994,185(2):227-230
The products of -radiolysis of solutions of thiourea are reported to be ammonia, sulfur, cyanamide, dicyanamide, and possibly guanidine sulfate. Ammonium thiocyanate, the product of isomerization, has not been observed although it is found to be one of the products in the themal decomposition of aqueous solutions of thiourea over the temperature range of 100–180°C. Hence, the observation of a close to 1% yield of the isomerization product in a 6.25% (0.82M) solution of thiourea, at neutral pH on exposure to -radiation from a60Co suurce at room temperature, would appear to be a result of interest in radiation chemistry. This paper present results on the variation of the yield of the isomerization product with the -dose. The experiments consisted in irradiating 2 ml of 0.82M aqueous solution of thiourea at neutral pH and under normal atmospheric conditions, i.e., at room temperature and with dissolved air present. The source of radiation was a 2.5 kCi (nominal)60Co source. The method used to detect and measure the isomerization product, ammonium thiocyanate was based on the well-known color reaction between CNS– and Fe+3 monitored spectrophotometrically at 450 nm, after obtaining the calibration curve of absorbance and concentration of NH4CNS. The yield of NH4CNS, expressed as
was 0.083 molecules of NH4CNS for 100 eV absorbed. A suitable mechanism for the process of isomerization is suggested involving the hydrated electrone
aq, the major primary product of water radiolysis. The mechanism is consistent with the observed effect of the addition of acetone, a well-known electron scavenger. This suppressed the yield NH4CNS by about 25%. 相似文献
552.
Phase field method based on Cahn–Hilliard free energy formulation is adopted for predicting the behavior of double emulsion droplet suspended in a continuous phase under the influence of a uniform electric field. The role played by the inner droplet on the electric-field-driven fluid flow, and also on deformation of the outer droplet is predicted by present numerical simulation. Three different kind of deformation type of outer and inner droplet (prolate–oblate, prolate–prolate and oblate–prolate) has been observed. With increase in the volume fraction of inner drop, transition in the deformation of outer drop from prolate to oblate occurs at lower value of fluid permittivity ratio. 相似文献
553.
554.
Rate constants for reactions of 2-pyridinol with one electron reductants, such ase
aq
−
and H atoms and one-electron oxidants, viz. OH, N3, Br
2
−
, C1
2
−
and O− have been determined at different pH values using the pulse radiolysis technique. From the corrected absorption spectra of
the product transient species, the extinction coefficients of these species at their respective absorption maxima have been
determined. The kinetics of decay of these transients have been investigated. ThepK
a values of transients formed bye
aq
−
and OH radical reactions have been estimated to be 7.6 and 3.5 respectively. Rate constants for electron transfer from semireduced
2-pyridinol to different electron acceptors have been determined. 相似文献
555.
Reactions of e−aq, OH radicals and H atoms were studied with n-allylthiourea (NATU) using pulse radiolysis. Hydrated electrons reacted with
NATU (k = 2.8×109 dm3 mol−1 s−1) giving a transient species which did not have any significant absorption above 300 nm. It was found to transfer electrons
to methyl viologen. At pH 6.8, the reduction potential of NATU has been determined to be −0.527 V versus NHE. At pH 6.8, OH radicals were found to react with NATU, giving a transient species having absorption maxima at 400–410
nm and continuously increasing absorption below 290 nm. Absorption at 400–410 nm was found to increase with parent concentration,
from which the equilibrium constant for dimer radical cation formation has been estimated to be 4.9×103 dm3 mol−1. H atoms were found to react with NATU with a rate constant of 5 × 109 dm3 mol−1 s−1, giving a transient species having an absorption maximum at 310 nm, which has been assigned to H-atom addition to the double
bond in the allyl group. Acetoneketyl radicals reacted with NATU at acidic pH values and the species formed underwent reaction
with parent NATU molecule. Reaction of Cl.−2 radicals (k = 4.6 × 109 dm3 mol−1 s−1) at pH 1 was found to give a transient species with λmax at 400 nm. At the same pH, reaction of OH radicals also gave transient species, having a similar spectrum, but the yield
was lower. This showed that OH radicals react with NATU by two mechanisms, viz., one-electron oxidation, as well as addition to the allylic double bond. From the absorbance values at 410 nm, it has been
estimated that around 38% of the OH radicals abstract H atoms and the remaining 62% of the OH radicals add to the allylic
double bond. 相似文献
556.
Low-temperature electroluminescence (EL) is observed in n-type modulation-doped AlGaAs/InGaAs/GaAs quantum well samples by applying a positive voltage between the semitransparent Au gate and alloyed Au-Ge Ohmic contacts made on the top surface of the samples. We attribute impact ionization in the InGaAs QW to the observed EL from the samples. A redshift in the EL spectra is observed with increasing gate bias. The observed redshift in the EL spectra is attributed to the band gap renormalization due to many-body effects and quantum-confined Stark effect. 相似文献
557.
R.A. Ganeev A.I. Ryasnyanskiy U. Chakravarty P.A. Naik H. Srivastava M.K. Tiwari P.D. Gupta 《Applied physics. B, Lasers and optics》2007,86(2):337-341
A study of indium nanoparticles prepared by two laser ablation techniques is reported. The suspensions of indium nanoparticles
were prepared using the laser ablation of bulk indium in liquids. The prepared suspensions of indium nanoparticles were analyzed
by the X-ray fluorescence spectroscopy and absorption spectroscopy. The position of the surface plasmon resonance of In-containing
suspensions (350 nm) was consistent with the estimations taking into account the average size of In nanoparticles (43 nm)
measured using the X-ray fluorescence spectroscopy. The nonlinear optical parameters of indium nanoparticles-containing liquids
were studied by the z-scan technique using a picosecond Nd:YAG laser. We compare the laser ablation in liquids with the laser
ablation of indium in vacuum at the tight and weak focusing conditions of a Ti:sapphire laser and analyze the 60 nm indium
nanoparticles synthesized in the latter case.
PACS 42.65.An; 42.65.Hw; 42.65.Jx; 61.46.Df; 78.67.Bf 相似文献
558.
Mukund K GurjarSiddhartha R Chaudhuri Shreerang V JoshiLalji K Gediya Prasad V RanadeSuresh M Kadam Sanjay J Naik 《Tetrahedron letters》2003,44(26):4853-4855
Syntheses of trans-hydroxyglimepiride 2b, a human metabolite of the blood glucose lowering agent glimepiride 1 and its corresponding cis-stereoisomer 2a, are described. 相似文献
559.
C.D. Beling C.C. Ling C.K. Cheung P.S. Naik J.D. Zhang S. Fung 《Applied Surface Science》2006,252(9):3172-3182
Vacancy-sensing positron deep level transient spectroscopy (PDLTS) is a positron beam-based technique that seeks to provide information on the electronic ionization levels of vacancy defects probed by the positron through the monitoring of thermal transients. The experimental discoveries leading to the concept of vacancy-sensing PDLTS are first reviewed. The major problem associated with this technique is discussed, namely the strong electric fields establish in the near surface region of the sample during the thermal transient which tend to sweep positrons into the contact with negligible defect trapping. New simulations are presented which suggest that under certain conditions a sufficient fraction of positrons may be trapped into ionizing defects rendering PDLTS technique workable. Some suggestions are made for techniques that might avoid the problematic electric field problem, such as optical-PDLTS where deep levels are populated using light and the use of high forward bias currents for trap filling. 相似文献
560.
Anil D. Naik Satish M. Annigeri Umesh B. Gangadharmath Vidyanand K. Revankar Vinayak B. Mahale 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(3-4):291-297
New dinuclear complexes of macrocycles/macroacycles/oximeshaving a reactive peripheral thioketo functional group were synthesized using2,6-diformyl-p-cresol as parent compound and thiocarbohydrazide/variousdiamines as side arms. Thioenolization and subsequent coordination to metal ionof the thio-keto sulfur is observed in asymmetric macrocycles and oxime complexes,while it is kept away from the coordination sphere in symmetric macrocycles. Magnetic susceptibility measurements over the range 7–300 K confirm that the copper(II) centersof the symmetric and asymmetric macrocycles are antiferromagnetically coupled, withvalues for the exchange coupling constant J through the phenolate oxygens of -610 to-580 cm-1, respectively. The ligands and their complexes are found to be excellent fungistatic agents. 相似文献