全文获取类型
收费全文 | 453篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
化学 | 267篇 |
晶体学 | 8篇 |
力学 | 7篇 |
数学 | 68篇 |
物理学 | 118篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 28篇 |
2011年 | 37篇 |
2010年 | 15篇 |
2009年 | 21篇 |
2008年 | 39篇 |
2007年 | 28篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 18篇 |
2003年 | 11篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1967年 | 2篇 |
1959年 | 3篇 |
1958年 | 3篇 |
1956年 | 5篇 |
1948年 | 3篇 |
1947年 | 5篇 |
1946年 | 4篇 |
1944年 | 2篇 |
排序方式: 共有468条查询结果,搜索用时 15 毫秒
391.
Allylation of 2-aminophenol-derived aldimines using allyltrichlorosilane under catalyst free conditions has been developed. This reaction afforded the corresponding homoallylic amines in good to excellent yields (68–94%). The salicylaldehyde-derived aldimines as well as benzoylhydrazone also found to react with allyltrichlorosilane smoothly under the same conditions, to furnish the corresponding homoallylic amine derivatives. This study suggests that the phenolic –OH group acts as an anchoring group for the transfer of allyl group from allyl silane reagent. 相似文献
392.
Sruthi Santhanam Vimala Ramani Ramanathan Srinivasan 《Journal of Solid State Electrochemistry》2012,16(3):1019-1032
The effect of solution resistance on the nonlinear electrochemical impedance spectra under quasi-potentiostatic conditions
was investigated by numerical simulations. An electron transfer reaction, a reaction with an adsorbed intermediate and a reaction
exhibiting negative resistance were chosen as the candidates and large amplitude perturbations were employed. The potential
across the interface drifts initially and stabilizes after a certain time, which depends on the solution resistance and the
kinetic parameter values. The fraction of the applied potential drop occurring across the metal–solution interface depends
on the frequency and the amplitude of the perturbation as well as the value of solution resistance. This in turn leads to
the possibility that, for a given conditions, a part of the spectrum may be acquired in the linear regime while the remaining
part may be acquired in the nonlinear regime. The sensitivity of the Kramers Kronig transform (KKT) to identify these cases
is evaluated. The results show that although the spectra are distorted by poorly conducting solution, the sensitivity of KKT
to identify the nonlinear effects is not enhanced by the introduction of significant solution resistance. 相似文献
393.
394.
S. Guruswamy G. Garside C. Ren B. Saha M. Ramanathan 《Progress in Crystal Growth and Characterization of Materials》2011,57(2-3):43-64
Short-range and long-range ordering in α-Fe terminal solid solution phase (A2 phase with bcc structure) influences its physical, mechanical, magnetic and magnetostrictive behavior. Single crystal sample forms are ideal for examining order in these alloys using X-ray and neutron scattering techniques. Limited structural information available suggests that the lattice of A2 phase at room temperature contains a mixture of regions with local atomic environments similar to those expected in the long-range ordered structures in stable/metastable equilibrium with the A2 phase. The nature and extent of these regions are sensitive to alloy composition and the thermal history. The lattice strain modulations result from the nature of solute atom distribution (short-range ordering) in each region and impact the physical, mechanical, corrosion and magnetic behaviors. A need for a fundamental understanding of ordering in Fe and other alloys through structural evaluations of local atomic environments in alloy single crystals is suggested in this review. 相似文献
395.
The paper deals with a thorough investigation on the antimicrobial activity of RF oxygen plasma and Azadirachtin (neem extract) treated cotton fabric. The hydrophilicity of cotton fabric was found to improve when treated with RF oxygen plasma. The process parameters such as electrode gap, time of exposure and oxygen pressure have been varied to study their effect on improving the hydrophilicity of the cotton fabric. The static immersion test has been carried out to assess the hydrophilicity of the oxygen plasma treated samples and the process parameters were optimized based on these test results. The formation of carbonyl group during surface modification in the plasma treated sample was analysed using FTIR studies. The surface morphology has been studied using SEM micrographs.The antimicrobial activity was imparted to the RF oxygen plasma treated samples using methanolic extract of neem leaves containing Azadirachtin. The antimicrobial activity of these samples has been analysed and compared with the activity of the cotton fabric treated with neem extract alone. The investigation reveals that the surface modification due to RF oxygen plasma was found to increase the hydrophilicity and hence the antimicrobial activity of the cotton fabric when treated with Azadirachtin. 相似文献
396.
K. Natarajan Jayakumar 《Tetrahedron》2005,61(3):603-608
Ferrocene-cored unsymmetric and symmetric arylalkyl ether dendrimers based on an AB2 monomer (3,5-dihydroxybenzyl alcohol) were prepared. Their electrochemical properties were compared with the unsymmetric and symmetric ferrocene-cored dendrimers based on a relatively rigid and three-dimensionally disposed AB4 monomer. The thermodynamics and kinetics of heterogeneous electron transfer in these dendrimers show that G2n of AB2 dendrimers behave similar to Gn of AB4 dendrimers. For example, the redox reaction shows significant irreversibility especially at higher scan rates in the case of G4 didendron based on AB2 monomer and G2 didendron based on AB4 monomer. Despite the fact that AB4 building blocks are more rigid, the effective encapsulation in both these dendrimers are similar. This result is attributed to the three dimensional disposition of the branching points in the AB4 monomer. 相似文献
397.
Mathura P. Ramanathan Damodharan Lalithakumari 《Applied biochemistry and biotechnology》1999,80(1):1-12
Organophosphorus insecticides are widely used in agriculture. Despite their biodegradable nature, some are highly toxic and
their residues are found in the environment. Reports on the mineralization of a spectrum of these insecticides by a single
potential strain are scarce. We have isolated a soil isolate, Pseudomonas sp. A3, through enrichment technique, able to degrade methylparathion (MP), malathion, monocrotophos, and Diazinon. The potential
of this strain to mineralize MP as a carbon and/or phosphorus source has been evaluated. On hydrolysis of MP, the aromatic
portion (p-nitrophenol) was used as a carbon and energy source whereas the alkyl moiety (dithiomethylphosphorothioate) was broken down
for the phosphorus source. The results from the experiments involving [U-14C]p-nitrophenol provided the evidence for incorporation of carbon into the cellular constituents and release of CO2 from this insecticide. During the breakdown of MP, nitrite was released as a catabolic by-product. 相似文献
398.
Recent experimental data on single hadron production by two-photon beams inpetra andpep have provided a unique opportunity for testing specific models of confinement through a study of one of their cleanest predictionsviz the γγ →H amplitudes. Motivated by this new facility, aqcd-oriented Bethe-Salpeter model of harmonic confinement, which has already been found to describe rather well several classes
of hadronic data (from mass spectra to electromagnetic and pionic couplings), is now employed for a detailed comparison of
its predictions onP → γγ andT → γγ couplings with the data. The agreement is quite good for all cases except one (η → γγ).
This paper is offered as a “Festschrift” in honour of Dr Raja Ramanna on the occasion of his sixtieth birthday. The subject
is theoretical in content but seeks to exploit an entirely new window opened by the latest experimental technology (on two-photon
physics). As such it is appropriately dedicated to one of the main architects of nuclear science in India. 相似文献
399.
The numbern
1
ofi-edge network cutsets in a graph is an important parameter in reliability analysis. Using a theorem of Lomonosov and Polesskii,
Ball and Provan have shown that the numbern
i
of minimum cardinality network cutsets can be determined in polynomial time. This paper gives a polynomial time algorithm
for determiningn
r+k
for any fixedk, as a special case of counting cuts of specified maximum weight in an edge-weighted graph. The resulting improvement in existing
reliability bounds is shown to be substantial. 相似文献
400.