全文获取类型
收费全文 | 445篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
化学 | 258篇 |
力学 | 18篇 |
数学 | 70篇 |
物理学 | 111篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 30篇 |
2021年 | 22篇 |
2020年 | 16篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 34篇 |
2012年 | 29篇 |
2011年 | 37篇 |
2010年 | 24篇 |
2009年 | 14篇 |
2008年 | 24篇 |
2007年 | 10篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 14篇 |
2002年 | 8篇 |
2001年 | 11篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有457条查询结果,搜索用时 15 毫秒
81.
2‐Formylthiophene‐N‐acetylhydrazone (Hait) and 2‐thiophenecarboxaldehyde‐2‐thienylhydrazone (Htit) in the cis and trans conformations were investigated in the gas‐phase by density functional method using B3LYP as the functional set and 6‐311++G(d,p) as the basis set. The cis and trans structures were fully optimized in the C1 and Cs symmetries. Transition states were also modeled for the cis–trans isomerization of the title compounds and the barriers to internal rotation were calculated. This work reports the structural, energetics, and spectroscopic parameters of all the optimized geometries. Some of the structural parameters are in good agreement with experimental literature data. The computed parameters for these compounds are also in good agreement with a related molecule, namely, acetohydrazide. For both Hait and Htit, the trans conformers are more stable than the cis conformers and the energy barriers are larger compared with the energy differences between the cis and trans conformers. This accounts for Hait and Htit existing mostly in the trans conformation. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:144–150, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20526 相似文献
82.
Ahmed Y. Abdallah 《Acta Appl Math》2009,106(1):47-59
Many researchers examined the existence of global attractors for various types of first and second order lattice dynamical
systems. Here we prove the existence of a global attractor for a new type of second order lattice dynamical systems in the
Hilbert space l
2×l
2. For specific choices of the linear operators this system can be regraded as a spatial discretization of a continuous damped
nonlinear Boussinesq equation on ℝ
m
,m≥1.
相似文献
83.
S.A. Pikuz A.Ya. Faenov J. Colgan R.J. Dance J. Abdallah E. Wagenaars N. Booth O. Culfa R.G. Evans R.J. Gray T. Kaempfer K.L. Lancaster P. McKenna A.L. Rossall I.Yu. Skobelev K.S. Schulze I. Uschmann A.G. Zhidkov N.C. Woolsey 《High Energy Density Physics》2013,9(3):560-567
K-shell spectra of solid Al excited by petawatt picosecond laser pulses have been investigated at the Vulcan PW facility. Laser pulses of ultrahigh contrast with an energy of 160 J on the target allow studies of interactions between the laser field and solid state matter at 1020 W/cm2. Intense X-ray emission of KK hollow atoms (atoms without n = 1 electrons) from thin aluminum foils is observed from optical laser plasma for the first time. Specifically for 1.5 μm thin foil targets the hollow atom yield dominates the resonance line emission. It is suggested that the hollow atoms are predominantly excited by the impact of X-ray photons generated by radiation friction to fast electron currents in solid-density plasma due to Thomson scattering and bremsstrahlung in the transverse plasma fields. Numerical simulations of Al hollow atom spectra using the ATOMIC code confirm that the impact of keV photons dominates the atom ionization. Our estimates demonstrate that solid-density plasma generated by relativistic optical laser pulses provide the source of a polychromatic keV range X-ray field of 1018 W/cm2 intensity, and allows the study of excited matter in the radiation-dominated regime. High-resolution X-ray spectroscopy of hollow atom radiation is found to be a powerful tool to study the properties of high-energy density plasma created by intense X-ray radiation. 相似文献
84.
Mohsen Doust Mohammadi Renjith Bhaskaran Hewa Y. Abdullah Hassan H. Abdallah George Biskos Somnath Bhowmick 《International journal of quantum chemistry》2024,124(1):e27288
We have investigated the potential energy curves (PECs) of the LiN heteronuclear diatomic molecule, including its ionic species LiN+ and LiN−, using explicitly correlated multi-reference configuration interaction (MRCI-F12) calculations in conjunction with the correlation consistent quintuple-𝜁 basis set. The effect of core–valence correlation, scalar relativistic effects, and the size of the basis sets has been investigated. A comprehensive set of spectroscopic constants determined based on the above-mentioned calculations are also reported for the lowest electronic states and all systems, including dissociation energies, harmonic and anharmonic vibrational frequencies, and rotational constants. Additional parameters, such as the dipole moments, equilibrium spin-orbit constants, excitation energies, and rovibrational energy levels, are also documented. We found that the three triplet states of LiN, namely, X 3∑−, A 3Π, and 2 3∑−, exhibit substantial potential wells in the PEC diagrams, while the quintet states are repulsive in nature. The ground state of the anion also shows a deep potential well in the vicinity of its equilibrium geometry. In contrast, the ground and excited states of the cation are very loosely bound. Charge transfer properties of each of these states are also analyzed to obtain an in-depth understanding of the interatomic interactions. We found that the core–valence correlation has a substantial effect on the calculated spectroscopic constants. 相似文献
85.
G. Aad B. Abbott J. Abdallah A.A. Abdelalim A. Abdesselam O. Abdinov B. Abi M. Abolins H. Abramowicz H. Abreu E. Acerbi B.S. Acharya D.L. Adams T.N. Addy J. Adelman M. Aderholz S. Adomeit L. Zwalinski 《Physics letters. [Part B]》2012,707(5):459-477
A measurement of the production cross section of top quark pairs () in proton–proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of , a production cross section is measured for an assumed top quark mass of . A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions. 相似文献
86.
T. Abdallah T.A. El‐Brolosy M. B. Mohamed K. Easawi S. Negm H. Talaat 《Journal of Raman spectroscopy : JRS》2012,43(12):1924-1930
Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of different shapes, namely nanospheres (NSs), nanorods (NRs), and nanoprisms (NPs) as well as the three NPs arrays of different interstice prepared by NS lithography, are studied with incident wavenumbers in the near‐dipole and near‐quadrpole regions of the nanoparticles. In the colloidal gold nanoparticles, the SERS enhancement is the largest for the sharp tip followed by the truncated tip NPs, then the NRs and least enhancement for the NSs. This decreasing order of enhancement occurs although the incident wavenumber was near the dipole resonance of NSs and the quadrupole resonance for the NPs. These varied enhancements are explained in part as due to the binding energies of the nanocrystal facets, but the larger contribution results from the plasmon electromagnetic fields. A parallel finite difference time domain (FDTD) calculations were carried out, which corporate the experimental results and show agreement with ratios of the SERS enhancement for the different shapes. The normalized SERS intensity for NPs of different interstice distances show a sharp rise with the decrease of the interstice distances because of interparticle dipolar and quadrupolar coupling as evidenced also by FDTD calculations. Furthermore, these calculations show that the enhancement is polarization independent for an incident wavelength near quadrupole resonance but polarization dependent for an incident wavelength near the plasmon dipole transition. In the last case, the enhancement is larger by an order of magnitude for a polarization parallel to the NPs bisector than for polarization normal to the bisector with no hot spots for the relatively large interstice dimensions used. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
87.
88.
Aad G Abbott B Abdallah J Abdel Khalek S Abdelalim AA Abdesselam A Abdinov O Abi B Abolins M Abouzeid OS Abramowicz H Abreu H Acerbi E Acharya BS Adamczyk L Adams DL Addy TN Adelman J Aderholz M Adomeit S Adragna P Adye T Aefsky S Aguilar-Saavedra JA Aharrouche M Ahlen SP Ahles F Ahmad A Ahsan M Aielli G Akdogan T Akesson TP Akimoto G Akimov AV Akiyama A Alam MS Alam MA Albert J Albrand S Aleksa M Aleksandrov IN Alessandria F Alexa C Alexander G Alexandre G Alexopoulos T Alhroob M Aliev M 《Physical review letters》2012,108(11):111803
A search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9 fb(-1) collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of √s=7 TeV. In the diphoton mass range 110-150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110-150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113-115 GeV and 134.5-136 GeV. 相似文献
89.
Aad G Abbott B Abdallah J Abdelalim AA Abdesselam A Abdinov O Abi B Abolins M AbouZeid OS Abramowicz H Abreu H Acerbi E Acharya BS Adamczyk L Adams DL Addy TN Adelman J Aderholz M Adomeit S Adragna P Adye T Aefsky S Aguilar-Saavedra JA Aharrouche M Ahlen SP Ahles F Ahmad A Ahsan M Aielli G Akdogan T Åkesson TP Akimoto G Akimov AV Akiyama A Alam MS Alam MA Albert J Albrand S Aleksa M Aleksandrov IN Alessandria F Alexa C Alexander G Alexandre G Alexopoulos T Alhroob M Aliev M Alimonti G Alison J 《Physical review letters》2012,108(18):181802
The results of a search for pair production of the scalar partners of bottom quarks in 2.05 fb(-1) of pp collisions at sqrt[s]=7 TeV using the ATLAS experiment are reported. Scalar bottom quarks are searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a bottom quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom quark decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the b(1) - χ(1)(0) mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded. 相似文献
90.
On the basis of fundamental parameter approaches, the validity of standardless wavelength dispersive X‐ray fluorescence (WDXRF) and X‐ray powder diffraction algorithms was confirmed for analyzing Egyptian iron ore samples collected from two different locations, Aswan and Baharyia. The studied Egyptian iron ores represent different depositional environments and consequently exhibit variable mineralogical and chemical compositions. In the case of WDXRF analysis, the ground powders of iron ore samples were mixed and pressed with low contamination binder in a mass ratio of wax: sample = 4: 0.9 g at 120 kN cm?2. A standardless method for quantitative WDXRF was employed, which requires accurate determination of the amount of organic material in the sample. On the basis of differential thermal analysis, a new method is introduced for the determination of loss of ignition. With the application of the proposed method and standardless quantitative analysis, results for 12 elements in iron ores were obtained: Fe, Mn, Mg, Si, Al, Ca, Na, K, S, Ba, Zn, and Cl. The reliability and precision of the adopted procedure were tested against a standard reference material ‘Iron ore concentrate (SRM 690, NIST, USA)’. The quantitative analysis results of the certified reference material were found acceptable. Depending on the WDXRF results, the powder samples were directly introduced to X‐ray powder diffraction goniometry, and the phase compositions were quantitatively determined by using a standardless analysis program based on Rietveld method. The main phases of all iron ore samples are the hematite and goethite, whereas other phases are found with varying ratios, namely quartz, nordstrandite, rhodochrosite, kaolinite, todorokit, bassanit, andydrite, and hydroxyapatite. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献