全文获取类型
收费全文 | 598篇 |
免费 | 22篇 |
专业分类
化学 | 388篇 |
晶体学 | 16篇 |
力学 | 16篇 |
数学 | 50篇 |
物理学 | 150篇 |
出版年
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 22篇 |
2013年 | 31篇 |
2012年 | 44篇 |
2011年 | 43篇 |
2010年 | 28篇 |
2009年 | 22篇 |
2008年 | 26篇 |
2007年 | 33篇 |
2006年 | 21篇 |
2005年 | 22篇 |
2004年 | 33篇 |
2003年 | 17篇 |
2002年 | 27篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有620条查询结果,搜索用时 15 毫秒
81.
82.
Oba Y Watanabe N Kouchi A Hama T Pirronello V 《Physical chemistry chemical physics : PCCP》2011,13(35):15792-15797
We investigated the OH-related formation routes of two astrophysically important molecules, H(2)O and CO(2), under relatively warm astrophysical conditions. OH radicals, together with other neutral species such as H, O, H(2), and O(2), were produced in H(2)O microwave-discharge plasma and cooled to 100 K before being deposited on an Al substrate at 40-60 K. H(2)O formed at 40 and 50 K, but not at 60 K. Taking the experimental conditions into account, a possible route of H(2)O formation is via reactions involving OH + OH, which yield H(2)O(2) as the main reaction product. The present study is the first to show experimentally that surface reactions of two OH radicals can yield H(2)O at low temperatures. The products' branching ratio was 0.2 and 0.8 for H(2)O and H(2)O(2), respectively. When CO was co-deposited with neutral species that formed in the H(2)O plasma, CO(2) was formed at 40-60 K. H(2)CO(3) formed at 40 and 50 K. The present results may suggest that chemical reactions related to OH radicals are effective at yielding various molecules in relatively warm astrophysical environments, such as protostars. 相似文献
83.
Accolla M Congiu E Dulieu F Manicò G Chaabouni H Matar E Mokrane H Lemaire JL Pirronello V 《Physical chemistry chemical physics : PCCP》2011,13(17):8037-8045
The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H(2) formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H(2) is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the thickness of the ice and has a value of ?(0) = 2 × 10(16) D-atoms cm(-2) per layer of H(2)O. We also use a model which confirms that the binding sites on the porous ice are destroyed regardless of their energy depth, and that the reduction of the porosity corresponds in fact to a reduction of the effective area. This reduction appears to be compatible with the fraction of D(2) formation energy transferred to the porous ice network. Under interstellar conditions, this effect is likely to be efficient and, together with other compaction processes, provides a good argument to believe that interstellar ice is amorphous and non-porous. 相似文献
84.
Valerio Magnasco Massimo Ottonelli Giuseppe Figari Marina Rui Camilla Costa 《Journal of Molecular Structure》1998,430(1-3):231-239
The real spherical tensor theory of long-range intermolecular coefficients developed in previous papers is applied to derive explicit formulae for the first three dispersion coefficients for like centrosymmetric linear molecules. The expansion of angle-dependent coefficients in associated Legendre polynomials allows one to identify the isotropic and anisotropic components of the dispersion interaction in terms of London dispersion constants, the treatment of higher coefficients being simplified by the coupling of the elementary (l, l′)-polarizations to resultant angular momenta LA and LB onto each molecule. The contributions from all coupling schemes are given explicitly for C6, C8, C10, and numerical results are presented for H2-H2 using two-term reduced spectra values from the Kaiserlautern group. 相似文献
85.
Mycelia of Aspergillus oryzae display high enantioselectivity towards (R)-flurbiprofen and can be efficiently used in pure organic solvent for the resolution of (R,S)-flurbiprofen through esterification. The use of the lyophilized mycelia facilitates the separation process so that in one step the two enantiomers of flurbiprofen, which are both valuable for pharmaceutical applications, can be easily separated. The biotransformation can be carried out in different apolar solvents using different primary alcohols as nucleophiles under very mild conditions. 相似文献
86.
C. Brescianini A. Mazzucotelli F. Valerio R. Frache G. Scarponi 《Fresenius' Journal of Analytical Chemistry》1988,332(1):34-36
Summary The interferences due to the presence of large amounts of atoms such as iron, sodium, cadmium, magnesium and potassium on the ETA-AAS determination of trace amounts of chromium(VI) in welding fumes are discussed. An ion-exchange liquid extraction separation procedure is proposed to overcome these interactions. Results obtained on international standards of welding fumes, distributed in two round robin experiments, are also presented.
Bestimmung von Chrom(VI) in Schweißereidämpfen nach Abtrennung mit Hilfe eines flüssigen IonenaustauschersUntersuchung der Störungen相似文献
87.
We prove a series of inequalities among the parameters of a strongly resolvable design. By means of examples it is shown that these inequalities are best possible. 相似文献
88.
89.
Weissker HC Serrano J Huotari S Bruneval F Sottile F Monaco G Krisch M Olevano V Reining L 《Physical review letters》2006,97(23):237602
We present an investigation of the dynamic structure factor and of the dielectric function epsilonM(Q,omega) of the prototypical semiconductor silicon for finite momentum transfer, combining inelastic x-ray scattering experiments and ab initio calculations. In contrast with optical spectra, for finite momentum transfer time-dependent density-functional theory in the adiabatic local-density approximation together with lifetime broadening describes the physics of valence excitations correctly. Major structures in the spectra, governed by short-range crystal and exchange-correlation local-field effects, are strongly influenced by a mixing of transitions of positive and negative energies, in striking difference to spectra for vanishing momentum transfer. This mixing gives rise to a pronounced Fano asymmetry. 相似文献
90.
Marcotullio MC Pagiotti R Campagna V Maltese F Fardella G Altinier G Tubaro A 《Natural product research》2006,20(10):917-921
In this work the mushroom Sarcodon glaucopus was studied. A new cyathane, glaucopine C (1), was isolated from the hexane extract and identified by 1H and 13C NMR spectra analysis. Glaucopine C showed anti-inflammatory acitvity. 相似文献