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排序方式: 共有343条查询结果,搜索用时 171 毫秒
31.
研究了类Be氩离子内壳层电子光电离的激发能级,寿命和辐射速率,谱线波长和振子强度,并给出了位于“水窗”波段的谱线波长和谱线强度。 相似文献
32.
The B-spline density-functional method has been applied to the conformers of the (1R, 2R)-1,2-dibromo-1,2-dichloro-1,2-difluoroethane molecule. The cross section, asymmetry, and dichroic parameters relative to core and valence orbitals, which do not change their nature along the conformational curve, have been systematically studied. While the cross section and the asymmetry parameter are weakly affected, the dichroic parameter appears to be rather sensitive to the particular conformer of the molecule, suggesting that this dynamical property could be a useful tool for conformational analysis. The computational method has also been applied to methyl rotation in methyloxirane. Unexpected and dramatic sensitivity of the dichroic-parameter profile to the methyl rotation, both in the core and valence states, has been found. Boltzmann averaging over the conformers reproduces quite closely the profiles previously obtained for the minimum-energy conformation, which is in good agreement with the experimental results. 相似文献
33.
H.C. Mastwijk M. van Rijnbach J.W. Thomsen P. van der Straten A. Niehaus 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(2):131-137
This paper presents an experimental investigation of cold collisions between metastable helium atoms in an optical trap at
1 mK. Penning (PI) and associative (AI) ionization reactions are distinguished using a mass spectrometer and studied under
influence of near resonant laser light. Dramatic enhancement, by more than a factor 15, of the ion rate is observed when the
laser is tuned close to resonance. Experimental findings are well-described, on an absolute scale, by model predictions.
Received: 9 February 1998 / Revised: 4 May 1998 / Accepted: 14 May 1998 相似文献
34.
采用光电离探测方法,对钐原子奇宇称束缚激发态进行了系统研究.通过设计三条不同的激发路径, 采用共振激发方式,先将钐原子分三步从基态激发到不同的束缚激发态,然后采用光电离手段对其进行探测. 通过对第三步激发光的波长进行大范围的扫描,在同一能域内获得了三组不同的光谱. 通过比对三条路径所得到的三组光谱,不仅精确确定了大量奇宇称束缚激发态的能级位置, 而且还获得了相应跃迁的相对强度的信息.最后,通过运用三条不同的激发路径的选择定则, 还确定了上述能级的总角动量.
关键词:
钐原子
束缚激发态
奇宇称
光电离探测 相似文献
35.
The 3s–np photoionization processes of the ground state 2P1/2 and the metastable state 2P3/2 of Ar5+ are investigated using our recently developed relativistic R-matrix code, where the interactions between the bound states and the continuum states are included. Both resonance positions and the oscillator strengths are in much better agreement with the absolute experimental measurements by Wang et al.[Wang J C, Lu M, Esteves D, Habibi M, Alna’washi G and Phaneuf R A 2007 Phys. Rev. A 75 062712] with a resolution of 80 meV than their theoretical results. The contributions of the two experimental unresolved transitions are distinguished in our calculations, which show that the transitions from the ground state also make significant contributions to some resonances. Our theoretical results are also in good agreement with the measurements for the first resonance with a higher resolution of 20 meV. 相似文献
36.
Wen Li Edita Mjekiqi Wessel Douma Xin Wang Dr. Oksana Kavatsyuk Prof. Dr. Ronnie Hoekstra Dr. Jean-Christophe Poully Dr. Thomas Schlathölter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(70):16114-16119
Vacuum ultraviolet photoionization of a gas-phase oligonucleotide anion leads to the formation of a valence hole. This hole migrates towards an energetically favorable site where it can weaken bonds and ultimately lead to bond cleavage. We have studied Vacuum UV photoionization of deprotonated oligonucleotides containing the human telomere sequence dTTAGGG and G-quadruplex structures consisting of four dTGGGGT single strands, stabilized by NH4+ counter ions. The oligonucleotide and G-quadruplex anions were confined in a radiofrequency ion trap, interfaced with a synchrotron beamline and the photofragmentation was studied using time-of-flight mass spectrometry. Oligonucleotide 12-mers containing the 5'-TTAGGG sequence were found to predominantly break in the GGG region, whereas no selective bond cleavage region was observed for the reversed 5'-GGGATT sequence. For G-quadruplex structures, fragmentation was quenched and mostly non-dissociative single and double electron removal was observed. 相似文献
37.
M. Papanastasiou A.W. McMahon N.S. Allen B.W. Johnson K. Keck-Antoine L. Santos M.G. Neumann 《International journal of mass spectrometry》2008,275(1-3):45-54
The hydrolysis reaction mechanism of phosphite antioxidants is investigated by liquid chromatography-mass spectrometry (LC/MS). The phosphites were chosen because they differed in chemical structure and phosphorus content. Dopant assisted-atmospheric pressure photoionization (DA-APPI) is chosen as the ion source for the ionization of the compounds. In our previous work, DA-APPI was shown to offer an attractive alternative to atmospheric pressure chemical ionization (APCI) since it provided background-ion free mass spectra and higher sensitivity [M. Papanastasiou, et al., Polymer Degradation and Stability 91 (11) (2006) 2675–2682]. In positive ion mode, the molecules are generally detected in their protonated form. In negative ion mode, the phosphites are unstable and only fragment ions are observed; these however, are characteristic of each phosphite and may be used for the identification of the analytes in complex mixtures.The analytes under investigation are exposed to accelerated humid ageing conditions and their hydrolytic pathway and stability is investigated. Different substituents around the phosphorus atom are shown to have a significant effect on the stability of the phosphites, with phenol substituents producing very hydrolytically stable structures. Alkanox P24 and PEP-36 follow a similar hydrolytic pathway via the scission of the first and then the second POphenol bonds, eventually leading to the formation of phenol, phosphorous acid and pentaerythritol as end products. HP-10 exhibits a rather different structure and the products detected suggest scission of either the POhydrocarbon or one of the POphenol bonds. A phenomenon similar to that of autocatalysis is observed for all phosphites and is attributed to the formation of dialkyl phosphites as intermediate products. 相似文献
38.
Photoionization mass spectrometry (PIMS) with vacuum ultraviolet (VUV) light source provides an efficient and fragmentation-free
method for the soft ionization of gaseous compounds, in order to facilitate an understanding of thermal decomposition behavior
and chemical composition of polymeric materials. The PIMS was applied to the evolved gas analysis (EGA) system equipped with
a skimmer interface which is constituted based upon a jet separator principle between a vacuum MS chamber and an atmospheric
sample chamber in a furnace. A photoionization source with a deuterium (D2) lamp was closely installed to the vacuum ionization chamber of a mass spectrometer to improve the ionization efficiency.
The thermal decomposition of typical polymers in inert gas atmosphere was investigated by the EGA-PIMS and the resulting PI
mass spectrum was characterized satisfactorily by only the parent ions with no contribution as a result of fragmentation during
the ionization. The results suggested that the EGA-PIMS was an especially powerful and desirable in situ thermal analysis
method for polymeric materials which evolve organic gases simultaneously and concurrently. The combination of EGA equipped
with skimmer interface with no change of evolved gaseous species and PIMS with fragmentation-free during the ionization is
described briefly, and the effective results are presented by comparing with EGA using conventional electron impact ionization
mass spectrometry. 相似文献
39.
Within the framework of the complex basis function method, the photoionization cross sections of H(2)(+) and H(2) were calculated based on the variational principle for the frequency-dependent polarizabilities. In these calculations, complex orbital exponents of Gaussian-type basis functions for the final state continuum wavefunctions were fully optimized for each photon energy with the numerical Newton-Raphson method. In most cases, the use of only one or two complex Gaussian-type basis functions was enough to obtain excellent agreement with previous high precision calculations and available experimental results. However, there were a few cases, in which the use of complex basis functions having various angular momentum quantum numbers was crucial to obtain the accurate results. The behavior of the complex orbital exponents as a function of photon energy was discussed in relation to the scaling relation and the effective charge for photoelectron. The success of this method implies the effectiveness of the optimization of orbital exponents to reduce the number of basis functions and shows the possibility to calculate photoionization cross sections of general molecules using only Gaussian-type basis functions. 相似文献
40.
Ming-Qiang Huang Huan-Huan Wang Xiao-Bin Shan Liu-Si Sheng Chang-Jin Hu Xue-Jun Gu Wei-Jun Zhang 《中国化学会会志》2023,70(4):938-948
Secondary organic aerosol (SOA) produced by ozonolysis of styrene and other alkene compounds is a major part of fine particles in urban atmospheres. The atmospheric ozonolysis process of styrene is simulated in a smog chamber, and the formed SOA particles are detected on-line by a synchronous radiation vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) in this study. Through molecular ion peaks in the photonionization mass spectra of SOA and the corresponding photoionization efficiency curve, combined with off-line measurement verification of ultraviolet visible and infrared absorption spectra, it is determined that formaldehyde, formic acid, benzene, phenol, benzaldehyde, and benzoic acid are the main constituents of styrene SOA. These provide new information for studying the atmospheric ozonolysis oxidation mechanism of styrene. VUV-PIMS can get over complicated sample preparation procedures, secondary pollution, and other shortcomings of the off-line method and is a useful instrument to measure constituents and unveil the formation process of SOA particles. 相似文献