全文获取类型
收费全文 | 286篇 |
免费 | 8篇 |
国内免费 | 2篇 |
专业分类
化学 | 169篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 34篇 |
物理学 | 87篇 |
出版年
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 7篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 6篇 |
2008年 | 7篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1962年 | 2篇 |
1911年 | 2篇 |
1866年 | 1篇 |
排序方式: 共有296条查询结果,搜索用时 640 毫秒
81.
Intramolecular N-H...O hydrogen bonds in 3-(aminomethylene)pyran-2,4-dione and its simple derivatives (F, Li, and BeH substituents) were analyzed theoretically. The systems were optimized at the B3LYP/6-311++G(d,p) level of approximation. For some fluorine derivatives the corresponding tautomers with O-H...N intramolecular H-bonds were investigated, and for such pairs of tautomers, the calculations on transition states of the N-H...O <--> N...H-O proton-transfer reaction were carried out. The geometrical and energetic parameters for these species were characterized. The topological parameters derived from Bader theory were also analyzed; these are characteristics of H-bond critical points and also of ring critical points. Besides N-H...O and O-H...N intramolecular hydrogen bonds, there are the other intramolecular interactions, mostly ionic such as Be(+delta)...(-delta)O, Li(+delta)...(-delta)O, and Li(+delta)...(-delta)F. The F...O interactions also exist for some of species investigated. They may be classified as energetically stabilizing ones since the corresponding bond paths and critical points exist. The numerous correlations and dependencies between geometrical, topological, and energetic parameters were detected and described. 相似文献
82.
Magdalena Długosz Paweł Grabowski Henryk Bem 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):719-725
The concentration of two important radionuclides: 210Pb and its decay product 210Po in the urban air in the center of the Polish city of Lodz were measured during the winter and spring seasons of 2008–2009. Urban airborne particulate matter was collected using two methods: an Anderson 9-stage impactor, and a high-volume aerosol sampler type ASS500 working in the frames of the aerosol sampling network in Poland, established for radionuclide monitoring. Average concentrations for 10 months sampling period for 210Pb and 210Po were 0.556 and 0.067 mBq/m3, respectively. However remarkable fluctuations due to meteorological condition were observed: from 0.010 to 0.431 mBq/m3 for 210Po and from 0.167 to 1.847 mBq/m3 for 210Pb. The highest concentrations, almost 60% of the total activities, of both radionuclides were found in the first two fine aerosol fractions with particle diameters below 0.36 μm. The aerosol residence times calculated from the 210Po/210Pb ratio ranged from 7 to 120 days. 相似文献
83.
From coupled-cluster theory and many-body perturbation theory we derive the local exchange-correlation potential of density functional theory in an orbital dependent form. We show the relationship between the coupled-cluster approach and density functional theory, and connections and comparisons with our previous second-order correlation potential [OEP-MBPT(2) (OEP-optimized effective potential)] [I. Grabowski, S. Hirata, S. Ivanov, and R. J. Bartlett, J. Chem. Phys. 116, 4415 (2002)]. Starting from a general theoretical framework based on the density condition in Kohn-Sham theory, we define a rigorous exchange-correlation functional, potential and orbitals. Specifying initially to second-order terms, we show that our ab initio correlation potential provides the correct shape compared to those from reference quantum Monte Carlo calculations, and we demonstrate the superiority of using Fock matrix elements or more general infinite-order semicanonical transformations. This enables us to introduce a method that is guaranteed to converge to the right answer in the correlation and basis set limit, just as does ab initio wave function theory. We also demonstrate that the energies obtained from this generalized second-order method [OEP-MBPT2-f] and [OEP-MBPT2-sc] are often of coupled-cluster accuracy and substantially better than ordinary Hartree-Fock based second-order MBPT=MP2. 相似文献
84.
Preparation and Vibrational Spectra of trans-[Pt(acac)2X2] (X ? Cl, Br, I, SCN, SeCN, N3) By electrolytical oxidation of [Pt(acac)2] in presence of chloride or bromide, dissolved in dichlormethane, trans-[Pt(acac)2X2], X ? Cl, Br, are formed. On treatment of trans-[Pt(acac)2I2] with silver pseudohalides trans-[Pt(acac)2X2], X ? SCN, SeCN, N3, are obtained. Beside the nearly persistent bands of coordinated acetylacetonate in the Raman spectra the intensive and sharp symmetric, in the IR spectra the corresponding antisymmetric stretching vibration of the X? Pt? X axis is observed. The observance of the rule of mutual exclusion proves the complexes to belong to point group D2h. From the resonance Raman spectrum of trans-[Pt(acac)2I2] for vs (Pt? I), Ag, the harmonic frequency ω1 = 142.45 cm?1 and the inharmonicity constant x11 = 0.48 cm?1 is calculated. In the Raman spectrum of trans-[Pt(acac)2Cl2] vs (Pt? Cl) is splitted by the isotops 35Cl/37Cl into the triplet 340, 335, 330 cm?1 giving the force constant fPtCl = 2.01 N/cm. 相似文献
85.
MP2/aug-cc-pVTZ calculations were carried out on complexes wherein the proton or the lithium cation is located between π-electron systems, or between π-electron and σ-electron units. The acetylene or its fluorine and lithium derivatives act as the Lewis base π-electron species similarly to molecular hydrogen, which acts as the electron donor via its σ-electrons. These complexes may be classified as linked by π-H∙∙∙π/σ hydrogen bonds and π-Li∙∙∙π/σ lithium bonds. The properties of these interactions are discussed, and particularly the Lewis acid units are analyzed, because multi-center π-H or π-Li covalent bonds may occur in these systems. Various theoretical approaches were applied here to analyze the above-mentioned interactions—the Quantum Theory of Atoms in Molecules (QTAIM), the Symmetry-Adapted Perturbation Theory (SAPT) and the Non-Covalent Interaction (NCI) method. 相似文献
86.
87.
Joachim Armbruster Stefan Grabowski Thomas Ruch Horst Prinzbach 《Angewandte Chemie (International ed. in English)》1998,37(16):2242-2245
Technical olefins and azodicarbonic ester are the starting materials for C2-symmetrical C16 and C12 1,4-diamino-2,3-diol building blocks (see structure), which are of interest for a variable access to potentially bioactive compounds (peptide mimetics, enzyme inhibitors). MOM = methoxymethyl. 相似文献
88.
89.
L. T. Demoranville D. L. Knies K. S. Grabowski A. C. Mignerey 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(1):305-308
The Naval Research Laboratory’s Trace Element AMS system’s use of a Pretzel magnet as a recombinator and mass filter offers
a unique opportunity to study a new type of time-of-flight (TOF) spectrometry. Mass filtering prior to TOF analysis removes
extraneous species, shortening the analysis time for a single beam pulse, thereby improving the duty cycle. Time dilation
results from a longer flight path for a heavier mass in the Pretzel magnet. Computer TOF simulations of these factors and
the resulting impact on mass resolution for high mass atomic and molecular species are discussed. Initial measurements of
carbon and silicon to confirm the validity of the model are presented. 相似文献
90.
Fürstner A Radkowski K Grabowski J Wirtz C Mynott R 《The Journal of organic chemistry》2000,65(25):8758-8762
The first total synthesis of a major component of the microbial biosurfactant sophorolipid has been achieved. This approach to the 26-membered macrolide 1 containing a Z-configured alkene group in its lipidic tether spanning the sophorose backbone is based on a ring-closing metathesis reaction of diyne 21 catalyzed by Mo[N(t-Bu)(Ar)](3) (5; Ar = 3,5-dimethylphenyl) activated in situ by CH(2)Cl(2), followed by Lindlar reduction of the resulting cycloalkyne 22. The two beta-glycosidic linkages of compound 21 were installed by means of the glucal epoxide method and a modified Koenigs-Knorr reaction promoted by AgOTf/lutidine, respectively. 相似文献