首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   285篇
  免费   4篇
化学   192篇
晶体学   3篇
力学   7篇
数学   15篇
物理学   72篇
  2023年   1篇
  2022年   2篇
  2021年   4篇
  2020年   2篇
  2019年   3篇
  2018年   2篇
  2017年   3篇
  2016年   2篇
  2015年   3篇
  2014年   3篇
  2013年   14篇
  2012年   13篇
  2011年   18篇
  2010年   10篇
  2009年   9篇
  2008年   19篇
  2007年   22篇
  2006年   22篇
  2005年   14篇
  2004年   19篇
  2003年   16篇
  2002年   10篇
  2001年   5篇
  2000年   6篇
  1999年   5篇
  1996年   5篇
  1995年   4篇
  1994年   7篇
  1993年   2篇
  1992年   2篇
  1991年   1篇
  1990年   4篇
  1989年   2篇
  1988年   1篇
  1987年   3篇
  1986年   5篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   4篇
  1979年   5篇
  1978年   2篇
  1977年   1篇
  1975年   1篇
排序方式: 共有289条查询结果,搜索用时 15 毫秒
1.
The motion of a moored floating body under the action of wave forces, which is influenced by fluid forces, shape of the floating body and mooring forces, should be analysed as a complex coupled motion system. Especially under severe storm conditions or resonant motion of the floating body it is necessary to consider finite amplitude motions of the waves, the floating body and the mooring lines as well as non-linear interactions of these finite amplitude motions. The problem of a floating body has been studied on the basis of linear wave theory by many researchers. However, the finite amplitude motion under a correlated motion system has rarely been taken into account. This paper presents a numerical method for calculating the finite amplitude motion when a floating body is moored by non-linear mooring lines such as chains and cables under severe storm conditions.  相似文献   
2.
Nanocomposites consisting of conducting polyaniline and clay minerals were successfully synthesized from mechanochemically intercalated anilinium fluoride; the nanocomposites prepared by the mechanochemical intercalation method contained much more polyaniline in the clay layers than those prepared by a conventional solution method.  相似文献   
3.
4.
To the best of our knowledge, we demonstrate for the first time the generation of photon number squeezing by spectral filtering for ultrabroadband light generated by microstructure fibers at 800 nm. A maximum squeezing of 4.6 dB is observed, corresponding to 10.3 dB after correcting for detection losses. We numerically analyzed the quantum dynamics of ultrashort laser pulse propagation through optical fibers by solving a nonlinear quantum Schr?dinger equation that included Raman scattering, especially for the quantum correlation of photon number fluctuation among frequency modes in broadband pulses.  相似文献   
5.
Ground-state properties of C, O, and Ne isotopes are described in the framework of Hartree-Fock-Bogoliubov theory with density-dependent finite-range Gogny interaction D1S. We include all the contributions to the Hartree-Fock and pairing feld arising from Gogny and Coulomb interaction as well as the center of mass correction in the numerical calcu/ations. These ground-state properties of C, O, and Ne isotopes are compared with available experimental results, Hartree-Fock plus BCS, shell model and relativistic Hartree--Bogoliubov calculations. The agreement between experiments and our theoretical results is pretty well. The predicted drip-line is dependent strongly on the model and effective interaction due to their sensitivity to various theoretical details. The calculations predict no evidence for halo structure predicted for C,O, and Ne isotopes in a previous RHB study.  相似文献   
6.
The relative yield of the C-O bond breaking with respect to the C-C bond breaking in ethanol cation C2H5OH+ is maximized in intense laser fields (10(13)-10(15) Wcm2) by open-loop and closed-loop optimization procedures. In the open-loop optimization, a train of intense laser pulses are synthesized so that the temporal separation between the first and last pulses becomes 800 fs, and the number and width of the pulses within a train are systematically varied. When the duration of 800 fs is filled with laser fields by increasing the number of pulses or by stretching all pulses in a triple pulse train, the relative yield of the C-O bond breaking becomes significantly large. In the closed-loop optimization using a self-learning algorithm, the four dispersion coefficients or the phases of 128 frequency components of an intense laser pulse are adopted as optimized parameters. From these optimization experiments it is revealed that the yield ratio of the C-O bond breaking is maximized as far as the total duration of the intense laser field reaches as long as approximately 1 ps and that the intermittent disappearance of the laser field within a pulse does not affect the relative yields of the bond breaking pathways.  相似文献   
7.
This review highlights recent developments and applications of on-line sample preconcentration techniques to enhance the detection sensitivity in microchip electrophoresis (MCE); references are mainly from 2008 and later. Among various developed techniques, we focus on the sample preconcentration based on the changes in the migration velocity of analytes in two or three discontinuous solutions system, since they can provide the sensitivity enhancement with relatively easy experimental procedures and short analysis times. The characteristic features of the on-line sample preconcentration applied to microchip electrophoresis (MCE) are presented, categorized on the basis of "field strength-" or "chemically" induced changes in the migration velocity. The preconcentration techniques utilizing field strength-induced changes in the velocity include field-amplified sample stacking, isotachophoresis and transient-isotachophoresis, whereas those based on chemically induced changes in the velocity are sweeping, transient-trapping and dynamic pH junction.  相似文献   
8.
Glutamate synthesis by reductive amination of 2-oxoglutarate was performed by the combination of NADH regeneration system and glutamate dehydrogenase (GluDH). The conversion of 2-oxoglutamate to glutamate was 98% after 3 h, and the turnover number of NAD+was 17.  相似文献   
9.
Recently, we have developed novel Eu(III) complexes with three beta-diketonates and one asymmetric bis(phosphine) oxide whose light emission intensity is drastically increased. In this paper, one of these complexes is investigated by the density functional theory calculation. Sixteen isomers of this complex have been considered. The ratio of the existence for the most stable isomer (B1_1a) is found to be about 51%, and the sum of the ratio of the existence for the six most stable isomers (B1_1a, B1_3a, B1_8a, B1_2a, B1_1b, and B1_5a) is about 100%, assuming the Boltzmann distribution (T = 300 K). The coordination structures of the six most stable isomers in the ground states are similar, and we can expect asymmetric ligand fields for them, favorable for the efficient light emission. Vertical excitation energies and oscillator strengths for each isomer have been obtained by the time-dependent density functional theory. With the red-shift of the wavelength and the interpolation by Gaussian convolution, both the calculated absorption spectra for the most stable isomer B1_1a and the calculated absorption spectra for the ensemble average of the isomers are found to be similar to the experimental fluorescence excitation spectra. The efficiency of energy transfer from the triplet excited state to the Eu(III) ion is considered by calculating DeltaEET (difference between the adiabatic excitation energy of the complex for the lowest triplet state and the emission energy of the Eu(III) ion for 5D0 to 7F2). The characters for the lowest triplet states for the isomers are investigated by the spin density distributions of the triplet states.  相似文献   
10.
Photoinduced alignment in a polymer liquid crystal prepared from 6-{1-[4-(2-cyano-4-nitrophenylazo)phenyl]piperazino}hexyl acrylate and 4'-[6-(methacryloyloxy)hexyloxy]-4-cyanobiphenyl was investigated for the first time on irradiation with a polarized He-Ne laser beam at 633 nm. The azobenzene moieties as well as the inert cyanobiphenyl mesogenic units were aligned with the molecular long axis perpendicular to the polarization direction of the irradiation light. Alignment induced on short irradiation was reversible, while that induced under prolonged irradiation was irreversible due to the occurrence of crosslinking which might be caused by photoinduced decomposition of the azobenzene moieties during the photoirradiation process.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号