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排序方式: 共有337条查询结果,搜索用时 15 毫秒
331.
Miranda R Delgado F Velasco L Perez J Salmon M 《Rapid communications in mass spectrometry : RCM》2000,14(3):188-193
Mass spectrometric detection and identification of ortho- and para-benzyltoluenes and oligotoluenes, C(21)-C(49), in several reaction mixtures was performed. Thus, the corresponding electron impact spectra were acquired and analyzed, this in addition to constant B/E linked scans and high-resolution data. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
332.
Velasco E Navascués G Mederos L 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3158-3164
Using a first-order perturbation theory, we have studied the phase diagram of a binary mixture of hard spheres for different values of the size ratio. Recent models for the two-body depletion potential between large spheres are used to take into account the role of the small spheres. The theory predicts a complex phase diagram including a fluid-solid transition at high packing fraction of small spheres, metastability of fluid-fluid demixing, an isostructural solid-solid transition at high packing fraction of the large spheres for sufficiently small values of the size ratio q of the spheres, and the tendency to sticky-sphere behavior in the limit q-->0. The agreement with recent simulation results is quite good. We also show that this phenomenology was already implicit in the pioneering work of Asakura and Oosawa. 相似文献
333.
Mora FD Ríos N Rojas LB Díaz T Velasco J Carmona JA Silva B 《Natural product communications》2011,6(7):1051-1053
In this paper, preliminary studies on the chemical characterization of Phthirusa adunca Meyer essential oil, obtained by hydrodistillation, is presented. The separation of the components was performed by GC-MS. Twenty-three compounds (94.5% of the sample) were identified of which the three major ones (76% of the sample) were beta-phellandrene (38.1%), germacrene D (26.8%) and beta-pinene (11.5%). The essential oil showed a broad spectrum of activity against Salmonella Typhi CDC 57 (100 microg/mL), Staphylococcus aureus ATCC 25923 (200 microg/mL), Enterococcus faecalis ATCC 29212 (250 microg/mL), Escherichia coli ATCC 25922 y Klebsiella pneumoniae ATCC 23357 (500 microg/mL). This is the first report on the composition and activity of the essential oil of this species. 相似文献
334.
C. Lavín A. M. Velasco I. Martín J. V. Pitarch-Ruíz A. M. J. Sánchez de Merás J. Sánchez-Marín 《Theoretical chemistry accounts》2011,129(1):53-61
In this work, the linear response formalism with a triples-corrected CCSD reference wave function, LR-CCSDR(3), is applied
to the calculation of vertical excitation energies of singlet states of the F2CO molecule. A basis set of atomic natural orbitals augmented with a series of Rydberg functions has been used in the calculations.
A large number of electronically excited states were calculated, and the valence, Rydberg, or mixed character of the states
were investigated. In addition, the molecular quantum defect orbital (MQDO) method has been used to determine transition intensities
involving Rydberg states. Excitation energies and transition intensities for Rydberg states with n > 3 are reported for the first time. 相似文献
335.
The synthesis and liquid crystalline properties of a new asymetrically tetrasubstituted porphyrin, namely 2,4-bis[2-(o-didodecyloxyphenoxycarbonyl)ethenyl]-6,7-bis[2-(m -didodecyloxycarbonyl)ethyl]-1,3,5,8-tetramethylporphyrin, 1 (figure 1), obtained from a commercially available porphyrin, hemin 2, are reported here. The synthetic route basically consists of two reactions: on the one hand, one esterification of the two propionic acid groups in positions 6 and 7 in the hemin 2 with the phenol 12, and on the other hand, a Heck-type reaction between the two vinyl groups in positions 2 and 4 of the hemin 2 and the iodo-aryl derivative 9. This is the first example of a porphyrin-based discotic liquid crystal which is neither symmetrically substituted nor prepared via total synthesis from monopyrrole units. It exhibits a well-defined enantiotropic discotic lamellar mesophase (DL) in a range of temperature from -2°C to the clearing point at 70°C. This interval includes room temperature, which makes this molecule suitable for a wide variety of applications. 相似文献
336.
Increasing the isomerisation kinetics of azo dyes by chemical bonding to liquid-crystalline polymers
Garcia-Amorós J Finkelmann H Velasco D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(23):6518-6523
It is well known that the proper substitution of the azobenzene core allows tuning the thermal cis-to-trans isomerisation kinetics of azo dyes. The thermal isomerisation process of nitro-substituted azobenzenes is accelerated up to 13 times with respect to that in the common isotropic solvents when they are doped in nematic low molar mass liquid crystals. This kinetic acceleration is even stronger when these azo dyes are covalently linked to a nematic siloxane polymer. In this environment, the isomerisation process is accelerated more than 10(3) times. This effect is presented herein for the first time. The possible application of the networks obtained as possible photo-actuators has been also considered. 相似文献
337.