全文获取类型
收费全文 | 277篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 185篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 31篇 |
物理学 | 58篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 16篇 |
2013年 | 15篇 |
2012年 | 19篇 |
2011年 | 33篇 |
2010年 | 12篇 |
2009年 | 7篇 |
2008年 | 8篇 |
2007年 | 21篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 10篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1966年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有289条查询结果,搜索用时 15 毫秒
61.
Some novel Y-shaped imidazole derivatives were developed and characterized by NMR and mass spectral techniques. The photophysical
properties of these imidazole derivatives were studied in several solvents. The Kamlet-Taft and Catalan’s solvent scales were
found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The adjusted
coefficient representing the electron releasing ability or basicity of the solvent, C
β
or C
SB has a negative value, suggesting that the absorption and fluorescence bands shift to lower energies with the increasing electron-donating
ability of the solvent. This effect can be interpreted in terms of the stabilization of the resonance structures of the chromophore.
The observed lower fluorescence quantum yield may be due to an increase in the non-radiative deactivation rate constant. This
is attributed to the loss of planarity in the excited state provided by the non co-planarity of the cinnamaldehyde ring attached
to C(2) atom of the imidazole ring. Such a geometrical change in the excited state leads to an important Stokes shift, reducing
the reabsorption and reemission effects in the detected emission in highly concentrated solutions. 相似文献
62.
Jayaraman Jayabharathi Venugopal Thanikachalam Marimuthu Venkatesh Perumal 《Journal of luminescence》2012,132(3):707-712
The interaction between the imidazole derivative 2-(2,4-difluorophenyl)-1-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (dfppip) and bovine serum albumin (BSA) was investigated by fluorescence and UV–vis absorbance spectroscopy. From the experimental results, it was found that the imidazole derivative has strong ability to quench the intrinsic fluorescence of BSA by forming complexes. Electrostatic interactions play an important role to stabilize the complex. The binding constants and the number of binding sites have been determined in detail. The distance (r) between the donor and the acceptor was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence spectroscopy. The effect of metal ions such as Cu2+, Zn2+, Ca2+, Mg2+, Ni2+, Co2+ and Fe2+ on the binding constants between the imidazole derivative and BSA were also studied. 相似文献
63.
M. S. Alam A. A. S. Awwal P. McWhorter R. Venkatesh S. Mathur M. Dugar B. Grewal 《Optics & Laser Technology》2000,32(4)
A new synthetic discriminant-function-based amplitude modulated phase-only filtering technique is proposed for scale invariant pattern recognition. This technique has been found to yield improved correlation output when compared with the alternate techniques. The proposed technique is inherently suitable for optical implementation using the currently available spatial light modulators. Simulation results confirm the effectiveness of the proposed technique. 相似文献
64.
Venkatesh Gopal Sushil Mujumdar Hema Ramachandran A. K. Sood 《Optics Communications》1999,170(4-6):331-345
We study by means of experiments and Monte Carlo simulations, the scattering of light in random media, to determine the distance up to which photons travel along almost undeviated paths within a scattering medium, and are therefore capable of casting a shadow of an opaque inclusion embedded within the medium. Such photons are isolated by polarisation discrimination wherein the plane of linear polarisation of the input light is continuously rotated and the polarisation preserving component of the emerging light is extracted by means of a Fourier transform. This technique is a software implementation of lock-in detection. We find that images may be recovered to a depth far in excess of that predicted by the diffusion theory of photon propagation. To understand our experimental results, we perform Monte Carlo simulations to model the random walk behaviour of the multiply scattered photons. We present a new definition of a diffusing photon in terms of the memory of its initial direction of propagation, which we then quantify in terms of an angular correlation function. This redefinition yields the penetration depth of the polarisation preserving photons. Based on these results, we have formulated a model to understand shadow formation in a turbid medium, the predictions of which are in good agreement with our experimental results. 相似文献
65.
The rates of gas‐phase thermal elimination reaction of esters of 2‐pyridine sulfonic acid and 8‐quinoline sulfonic acid have been measured over at least 50° for each compound. The relative rates of the first‐order unimolecular decomposition at 500 K for the primary:secondary esters suggest that C O bond breaking is kinetically more significant than C H bond breaking, leading to a transition state of carbocationic character. This is consistent with the electron‐donating effect provided by the methoxy substituent in 2‐p‐methoxyphenylethyl of 2‐pyridine and 8‐quinoline sulfonate esters stabilizing the carbocation center. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 771–775, 2000 相似文献
66.
Litov and Anderson after various considerations suggested a four constant potential function for a-Se as well as a-As2S3. Hence we also used a four constant potential function with the sole purpose of applying this potential function to obtain
several acoustic, thermodynamic and other properties. We calculated several acoustic properties of a-Se like second order
elastic constants (SOECs), their pressure derivatives, the longitudinal and transverse Grüneisen constant by two different
methods, phonon frequencies, absorption band position through the use of Nath-Smith-Delaunay’s equation, and the thermodynamic
properties like heat capacity, bulk modulus, thermal Grüneisen constant, the pressure derivative of the bulk modulus (dK
T/dP=C
1), the pressure derivative ofC
1 which is related to Anderson-Grüneisen parameter, pressure derivative of Grüneisen constant namelyγ′
g
which is related to second Grüneisen constant, characteristics of phonon frequencies, potential energy function through the
use of fitted parameters and third order elastic constants. Finally we calculatedK
T at the reduced density ofρ/ρ
0=1.1.K
T is obtained from the potential function with the fitted parameters. In all the above cases the calculated values are found
to be in good agreement with experiment wherever available. In this connection it is important to point out that we eliminated
‘C’ a constant in the potential function using the equilibrium condition as was done by Litovet al in a-Se and Gerlichet al in the case of a-As2S3 as all amorphous substances are isotropic as mentioned by several authors. We contemplate to calculate several other properties
for a-Se and a-As2S3 and present them at a later stage. 相似文献
67.
Ramesh B. Reddy Premansh Dudhe Priyanka Chauhan Sagnik Sengupta Venkatesh Chelvam 《Tetrahedron》2018,74(48):6946-6953
An efficient synthesis of N-Boc-tubuphenylalanine benzyl ester (N-Boc-Tup-OBn, 1a) and N-Boc-epi-tubuphenylalanine benzyl ester (N-Boc-epi-Tup-OBn, 1b) is reported herein. Regioselective aziridine 4 ring opening with carbon nucleophiles followed by hydroboration of 1,1-substituted aminoalkene 3 using 9-BBN and subsequent oxidation in an alkaline medium are used as the key steps to provide N-tosyl 1,4-aminoalcohols. The 1,4-aminoalcohols are successfully transformed into the desired products with an overall yield of 23% for 1a and 11% for 1b over 8 consecutive steps separately. 相似文献
68.
Palani N. S. Kavitha N. S. Venkatesh K. S. Ashok Kumar K. Thirumal V. Pandurangan A. Sekar C. Ilangovan R. 《Journal of Solid State Electrochemistry》2018,22(10):3273-3287
Journal of Solid State Electrochemistry - Graphene sheet/multiwall carbon nanotube (GMC) and its composites with NiO and Ni(OH)2 are synthesized by microwave-assisted technique for the application... 相似文献
69.
Complex formation between cationically modified gold nanoparticles and DNA: an atomic force microscopic study 总被引:1,自引:0,他引:1
Ganguli M Babu JV Maiti S 《Langmuir : the ACS journal of surfaces and colloids》2004,20(13):5165-5170
Atomic force microscopy has been used for direct visualization of the wrapping of DNA around 30-nm-sized functionalized gold nanoparticles for the first time. The morphology of the complexes seems to be dictated by the relative concentration of the nanoparticles and DNA. A higher concentration of the former leads to the formation of a network of nanoparticles assembled on DNA. This assembly pattern seems to be significantly different from the manner in which cationically modified gold nanoparticles of smaller size (< 5 nm) arrange linearly on DNA, as shown in the literature. A DNA-gold nanoparticle can be developed as a model system for in vitro studies on the mechanism of DNA condensation and also for developing novel methods of nanoparticle self-assembly on the DNA template. 相似文献
70.
The cross-coupling reaction of triarylbismuths with acid chlorides using a catalytic amount of PdCl2/PPh3 afforded the corresponding ketones in high yields. The reactions of aromatic and aliphatic acid chlorides occurred with atom efficiency, as 3 equiv of acid chlorides coupled effectively with 1 equiv of triarylbismuths to yield 3 equiv of the corresponding diaryl and alkyl aryl ketones. 相似文献