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91.
Xiao Y Fisher K Smith MC Newton WE Case DA George SJ Wang H Sturhahn W Alp EE Zhao J Yoda Y Cramer SP 《Journal of the American Chemical Society》2006,128(23):7608-7612
Nitrogenase catalyzes a reaction critical for life, the reduction of N(2) to 2NH(3), yet we still know relatively little about its catalytic mechanism. We have used the synchrotron technique of (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the dynamics of the Fe-S clusters in this enzyme. The catalytic site FeMo-cofactor exhibits a strong signal near 190 cm(-)(1), where conventional Fe-S clusters have weak NRVS. This intensity is ascribed to cluster breathing modes whose frequency is raised by an interstitial atom. A variety of Fe-S stretching modes are also observed between 250 and 400 cm(-)(1). This work is the first spectroscopic information about the vibrational modes of the intact nitrogenase FeMo-cofactor and P-cluster. 相似文献
92.
Seyyed Javad Sabounchei Parisa Shahriary Zabiholla Bolboli Nojini Hamid Reza Khavasi Cengiz Arici Hakan Dal 《Heteroatom Chemistry》2010,21(7):475-485
Stable phosphoranes, Ar3P = CHCOR (R = C6H5, C6H4NO2, C6H4OCH3, CH3, OCH2C6H5; Ar = p‐tolyl or phenyl), have been C‐acylated by acetic anhydride to obtain new types of phosphorus ylides. Synthesis and characterization of six phosphorus ylides of the type Ar3PC(COCH3)(COR) are reported. The reaction of {(p‐tolyl)3PCHCOC6H5} ( I ), {(p‐ tolyl)3PCHCOC6H4NO2} ( II ), {Ph3PCHCOC6H4NO2} ( III ), {Ph3PCHCOC6H4OCH3} ( IV ), {(p‐tolyl)3PCHCOCH3} ( V ), and {Ph3PCHCOOCH2C6H5} ( VI ) with acetic anhydride in dry chloroform as solvent gives (p‐tolyl)3PC(COMe)(COC6H5), α‐acetyl‐α‐benzoylmethy‐lenetriphenylphosphorane ( 1 ), {(p‐tolyl)3PC(COMe) (COC6H4NO2)} ( 2 ), {Ph3PC(COMe)(COC6H4NO2)} ( 3 ), {Ph3PC(COMe)(COC6H4OCH3)} ( 4 ), {(p‐tolyl)3 PC(COCH3)2} ( 5 ), and {Ph3PC(COMe)(COOCH2 C6H5)} ( 6 ). Single crystal X‐ray analyses for ylides 2 , 5 , and 6 reveal the monoclinic ( 2, 5 ) and triclinic ( 6 ) crystal systems. Characterization of the obtained compounds was also performed by elemental analysis, IR, 1H, 31P, and 13C NMR. The geometries of these compounds have been investigated using density functional theory (DFT). In addition, electronic parameters of these compounds such as HOMO and LUMO energy, Mulliken partial charge, and dipole moment were obtained. In this paper, the reactivity of these ylides is discussed in regard to the aforementioned data. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:475–485, 2010; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20633 相似文献
93.
Shafqat Hussain Hakan F. Öztop Khalid Mehmood Nidal Abu-Hamdeh 《Chinese Journal of Physics (Taipei)》2018,56(2):484-501
A computational analysis has been performed on mixed convection in a double sided lid-driven cavity in the presence of volumetric heat generation or absorption. Effects of inclined magnetic field are also studied. The governing parameters are solved via Galerkin weighted residual finite element method in space and the Crank–Nicolson in time. Governing parameters are nanoparticle volume fraction (0.0?≤???≤?0.04), Richardson number (0.01?≤?Ri?≤?10), internal heat generation or absorption parameter inclination angle of magnetic field (0°?≤?γ?≤?90°) and Hartmann number (0?≤?Ha?≤?100). It is observed that the highest heat transfer is obtained in case of the maximum value of heat absorption. As a further finding, heat transfer decreases with increasing of Hartmann number and increases with increasing of nanoparticle volume fraction. 相似文献
94.
The crystal structure of 2-((5-amino-1,3,4-thiadiazol-2-yl)thio)-1-phenylethanone was determined by X-ray diffraction method. The compound crystallizes in orthorhombic crystal system, sp. gr. Pbca. The atoms that constitute thiadiazole and phenyl rings do not form any significant deviation from the ring planes. Compound has two intermolecular N–H···N hydrogen bonds and one C–H···π interaction. Using DFT/B3LYP method with 6-31G(d), 6-311G(d), 6-311G(d, p), and 6-311++G(d, p) basis sets, the molecular geometry of the compound was optimised. Bond lenghts, bond angles, torsion angles, dihedral angles, and HOMO–LUMO were calculated from the optimised geometry of the compound. The results obtained by X-ray diffraction method were compared with the results obtained through four different basis sets. Total energy of the molecule was calculated for four different basis sets. 相似文献
95.
Gülşen Akin Evingür Hakan Kaygusuz F. Bedia Erim Önder Pekcan 《Journal of Macromolecular Science: Physics》2014,53(7):1157-1167
Spherical alginate beads were prepared by ionotropic gelation of sodium alginate through the use of calcium ions. Pyranine (Py) was added to the alginate solution as a small molecule probe for fluorescence studies. Desorption of Py in water from the alginate beads cross-linked with calcium ions was studied by using the steady state fluorescence technique. The fluorescence emission intensity (I) from Py was monitored during the desorption process at 512 nm using the time drive mode of the spectrofluorometer. The increase in I was attributed to Py release from the beads. The Fickian diffusion model was used to calculate the desorption coefficients, D, which were found to be increased up to 3% (w/v) CaCl2 concentration in the beads, and then decreased with a further increase of CaCl2 content. On the other hand, the encapsulation efficiency of Py in the calcium alginate beads presented the reverse behavior compared to D. It was observed that, when the content of CaCl2 was increased, the incubation time, t0, for the start of desorption increased. 相似文献
96.
We have theoretically investigated how the low-energy conformers of the neutral and the zwitterionic forms of glycine as well as methylcarbamic acid are stabilized by the presence water. The MP2/6-311++G(d,p) method was utilized to conduct calculations on glycine and methylcarbamic acid in both isolated clusters and in clusters embedded in the conductor-like polarizable continuum model (C-PCM), where the clusters explicitly contain between one and ten water molecules. The neutral forms of glycine and methylcarbamic acid were found to have similar hydration energies, whereas the neutral methylcarbamic acid was determined to be approximately 32 kJ mol(-1) more stable than the neutral glycine in the isolated clusters and 30 kJ mol(-1) more stable in the C-PCM embedded clusters. Both the number and strength of the hydrogen bonding interactions between water and the zwitterions drive the stability. This lowers the relative energy of the glycine zwitterion from 50 kJ mol(-1) above neutral glycine, when there are two water molecules in the clusters to 11 kJ mol(-1) below for the clusters containing ten water molecules. For the methylcarbamic acid clusters with two water molecules, the zwitterion is 51 kJ mol(-1) higher in energy than the neutral form, but it remains 13 kJ mol(-1) above the neutral methylcarbamic acid in the clusters containing ten water molecules. When the bulk water environment is simulated by the C-PCM calculations, we find both the methylcarbamic acid and glycine zwitterionic forms have similar energies at 20 kJ mol(-1) above the neutral methylcarbamic acid energy and 10 kJ mol(-1) lower than the neutral glycine energy. Although neither methylcarbamic acid nor glycine have been detected in the interstellar medium yet, our findings indicate that methylcarbamic acid is the more stable product from methylamine and carbon dioxide reactions in a water ice. This suggests that methylcarbamic acid likely plays a role in the intermediate steps if glycine is formed in the interstellar medium. 相似文献
97.
This paper aims to investigate the direct relationship between inflation and inflation uncertainty by employing a dynamic method for the monthly country–region–place United States data for the time period 1976–2007. While the bulk of previous studies has employed GARCH models in investigating the link between inflation and inflation uncertainty, in this study Stochastic Volatility in Mean models are used to capture the shocks to inflation uncertainty within a dynamic framework. These models allow researchers to assess the dynamic effects of innovations in inflation as well as inflation volatility on inflation and inflation volatility over time, by incorporating the unobserved volatility as an explanatory variable in the mean (inflation) equation. Empirical findings suggest that innovations in inflation volatility increases inflation. This evidence is robust across various definitions of inflation and different sub-periods. 相似文献
98.
Pelegrina-Bonilla G Hausmann K Liu K Sayinc H Morgner U Neumann J Kracht D 《Optics letters》2012,37(11):1844-1846
We developed a fused fiber coupler (FFC) capable of multiplexing wavelengths in the range of 795 nm and 2 μm. A simple 2D simulation model to calculate the pretaper length for matching the propagation constants in the coupling region was established. Based on the numerical data, we fabricated an asymmetric FFC consisting of two different fibers with single-mode guidance for the respective wavelength, achieving a transmission of 90% in the signal fiber for both wavelengths. In order to demonstrate the application, we integrated the FFC into a core pumped thulium-doped fiber amplifier. 相似文献
99.
Nguyen HN Cee VJ Deak HL Du B Faber KP Gunaydin H Hodous BL Hollis SL Krolikowski PH Olivieri PR Patel VF Romero K Schenkel LB Geuns-Meyer SD 《The Journal of organic chemistry》2012,77(8):3887-3906
Herein we describe a general three-step synthesis of 4-substituted chlorophthalazines in good overall yields. In the key step, N,N-dimethylaminophthalimide (8a) directs the selective monoaddition of alkyl, aryl, and heteroaryl organometallic reagents to afford 3-substituted 3-hydroxyisoindolinones 9b, 9i-9am. Many of these hydroxyisoindolinones are converted to chlorophthalazines 1b-1v via reaction with hydrazine, followed by chlorination with POCl(3). We have also discovered two novel transformations of 3-vinyl- and 3-alkynyl-3-hydroxyisoindolinones. Addition of vinyl organometallic reagents to N,N-dimethylaminophthalimide (8a) provided dihydrobenzoazepinediones 15a-15c via the proposed ring expansion of 3-vinyl-3-hydroxyisoindolinone intermediates. 3-Alkynyl-3-hydroxyisoindolinones react with hydrazine and substituted hydrazines to afford 2-pyrazolyl benzoic acids 16a-16d and 2-pyrazolyl benzohydrazides 17a-17g rather than the expected alkynyl phthalazinones. 相似文献
100.
Hu C Barabanschikov A Ellison MK Zhao J Alp EE Sturhahn W Zgierski MZ Sage JT Scheidt WR 《Inorganic chemistry》2012,51(3):1359-1370
Nuclear resonance vibrational spectra have been obtained for six five-coordinate imidazole-ligated iron(II) porphyrinates, [Fe(Por)(L)] (Por = tetraphenylporphyrinate, octaethylporphyrinate, tetratolylporphyrinate, or protoporphyrinate IX and L = 2-methylimidazole or 1,2-dimethylimidazole). Measurements have been made on both powder and oriented crystal samples. The spectra are dominated by strong signals around 200-300 cm(-1). Although the in-plane and out-of-plane vibrations are seriously overlapped, oriented crystal spectra allow their deconvolution. Thus, oriented crystal experimental data, along with density functional theory (DFT) calculations, enable the assignment of key vibrations in the spectra. Molecular dynamics are also discussed. The nature of the Fe-N(Im) vibrations has been elaborated further than was possible from resonance Raman studies. Our study suggests that the Fe motions are coupled with the porphyrin core and peripheral groups motions. Both peripheral groups and their conformations have significant influence on the vibrational spectra (position and shape). 相似文献