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101.
Vaisagh Viswanathan Chong Eu Lee Michael Harold Lees Siew Ann Cheong Peter M. A. Sloot 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(2):1-11
Crowd simulation is rapidly becoming a standard tool for evacuation planning and evaluation. However, the many crowd models in the literature are structurally different, and few have been rigorously calibrated against real-world egress data, especially in emergency situations. In this paper we describe a procedure to quantitatively compare different crowd models or between models and real-world data. We simulated three models: (1) the lattice gas model, (2) the social force model, and (3) the RVO2 model, and obtained the distributions of six observables: (1) evacuation time, (2) zoned evacuation time, (3) passage density, (4) total distance traveled, (5) inconvenience, and (6) flow rate. We then used the DISTATIS procedure to compute the compromise matrix of statistical distances between the three models. Projecting the three models onto the first two principal components of the compromise matrix, we find the lattice gas and RVO2 models are similar in terms of the evacuation time, passage density, and flow rates, whereas the social force and RVO2 models are similar in terms of the total distance traveled. Most importantly, we find that the zoned evacuation times of the three models to be very different from each other. Thus we propose to use this variable, if it can be measured, as the key test between different models, and also between models and the real world. Finally, we compared the model flow rates against the flow rate of an emergency evacuation during the May 2008 Sichuan earthquake, and found the social force model agrees best with this real data. 相似文献
102.
Pierce MD Johnston RC Mahapatra S Yang H Carter RG Ha-Yeon Cheong P 《Journal of the American Chemical Society》2012,134(33):13624-13631
Computational study of the mechanisms and stereoselectivities of a dual amino-catalyzed synthesis of cyclohexenones containing all-carbon γ-quaternary and ?-tertiary stereocenters is reported. Extensive conformational search with density functional theory optimizations, the high-accuracy SCS-MP2/cc-pV∞Z energies, and PCM solvation corrections were used to characterize all intermediates and transition states. Six mechanisms were considered, all consistent with available experiments. The reaction proceeds via sequential Michael and Mannich conjugate additions whereby the primary amine activates the aldehyde and the catalyst activates the pentenone. We have discovered a rare duumvirate stereocontrol: the Michael reaction sets the enantioselectivity, but both the Michael and the Mannich reactions control the diastereoselectivity. 相似文献
103.
Yang JJ Choi YJ Oh YS Hogan A Horibe Y Kim K Min BI Cheong SW 《Physical review letters》2012,108(11):116402
Using transmission electron microscopy, the anomalies in resistivity and magnetic susceptibility at ~262 K in IrTe2 are found to accompany the superlattice peaks with q[over q=(1/5,0,-1/5). The wave vector is consistent with our theoretical calculation for the Fermi surface nesting vector, indicating that the ~262 K transition is of the charge-orbital density wave (DW) type. We also discovered that both Pd intercalation and substitution induce bulk superconductivity with T(c) up to ~3 K, which competes with DW in a quantum critical pointlike manner. 相似文献
104.
Choi SK Coldea R Kolmogorov AN Lancaster T Mazin II Blundell SJ Radaelli PG Singh Y Gegenwart P Choi KR Cheong SW Baker PJ Stock C Taylor J 《Physical review letters》2012,108(12):127204
We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zigzag magnetic order. The onset of long-range magnetic order below T(N)=15.3 K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90° Ir-O-Ir bonds required for dominant Kitaev exchange. 相似文献
105.
We propose an approach for the exact dynamic inversion of singularly perturbed second-order linear systems through asymptotic expansion in a singular parameter. We show that the inversion solution, corresponding to the invariant slow manifold, can be expressed as a converging infinite series under desired output constraints composed of exponential support functions in the complex domain. We provide systematic mathematical procedures to obtain the closed-form invariant slow manifold, along with required admissible boundary conditions. Numerical examples are given to validate the proposed approach. 相似文献
106.
Siddiquee S Cheong BE Taslima K Kausar H Hasan MM 《Journal of chromatographic science》2012,50(4):358-367
A simple, fast, repeatable and less laborious sample preparation protocol was developed and applied for the analysis of biocontrol fungus Trichoderma harzianum strain FA1132 by using gas chromatography-mass spectrometry. The match factors for sample spectra with respect to the mass spectra library of fungal volatile compounds were determined and used to study the complex hydrocarbons and other volatile compounds, which were separated by using different capillary columns with nonpolar, medium polar and high polar stationary phases. To date, more than 278 volatile compounds (with spectral match factor at least 90%) such as normal saturated hydrocarbons (C7-C30), cyclohexane, cyclopentane, fatty acids, alcohols, esters, sulfur-containing compounds, simple pyrane and benzene derivatives have been identified. Most of these compounds have not previously been reported. The method described in this paper is a more convenient research tool for the detection of volatile compounds from the cultures of T. harzianum. 相似文献
107.
Klauss H.-H. Baabe D. Mienert D. Birke M. Luetkens H. Litterst F. J. Hücker M. Büchner B. Cheong S. W. 《Hyperfine Interactions》2001,136(3-8):711-715
We report zero field μSR experiments on the lanthanum nickelate La2−x
Sr
x
NiO4+δ system with strontium doping level x between 0 and 0.6. In a single crystal with x=0.33 the internal field distribution shows two separated signals reflecting the antiferromagnetic domains and the non magnetic
antiphase domain walls in the spin and charge ordered state below 190 K. Below 70 K a broadening of the low field line is
observed. A similar behavior is observed in polycrystalline samples with 0.2≤x≤0.5.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
108.
109.
Shengjie Wei Yu Wang Wenxing Chen Zhi Li Weng-Chon Cheong Qinghua Zhang Yue Gong Lin Gu Chen Chen Dingsheng Wang Qing Peng Yadong Li 《Chemical science》2020,11(3):786
Non-noble metal isolated single atom site (ISAS) catalysts have attracted much attention due to their low cost, ultimate atom efficiency and outstanding catalytic performance. Herein, atomically dispersed Fe atoms are prepared by a covalent organic framework (COF)-absorption–pyrolysis strategy. The obtained Fe ISASs anchored on COF-derived N-doped carbon nanospheres (Fe-ISAS/CN) served as a multi-functional catalyst in electro-catalysis and organic catalysis, exhibiting better catalytic performance than commercial Pt/C for the ORR with good stability and methanol tolerance. Besides electro-catalysis, the Fe-ISAS/CN also showed outstanding catalytic performance in organic reactions, such as the selective oxidation of ethylbenzene to acetophenone and dehydrogenation of 1,2,3,4-tetrahydroquinoline with excellent reactivity, selectivity, stability and recyclability. Co and Ni ISAS materials can also be prepared by this method, suggesting that it is a general strategy to obtain metal ISAS catalysts. This work will provide new insight into the design of COF-derived metal ISAS multi-functional catalysts for electro-catalysis and organic reactions using rationally designed synthetic routes and the optimized structure of substrates.Fe isolated single-atom sites anchored on COF-derived N-doped carbon nanospheres as efficient multi-functional catalysts. 相似文献
110.