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排序方式: 共有162条查询结果,搜索用时 31 毫秒
91.
Shigeki Matsuo Haruki Sumi Satoshi Kiyama Takuro Tomita Shuichi Hashimoto 《Applied Surface Science》2009,255(24):9758-9760
A femtosecond laser-assisted etching technique was applied to Pyrex glass, a kind of borosilicate glass, to perform removal processing with three-dimensional arbitrarity in design and micrometer-order spatial resolution. An aqueous solution of potassium hydroxide (KOH) was adopted as a highly selective etchant. The rate and selectivity of etching were evaluated from in situ images, and fabrication of three-dimensional microchannels was demonstrated. 相似文献
92.
By phase manipulation of a short laser pulse, it is possible to selectively generate ultracold excitons in a two-photon process while quenching the multiphoton excitation of hot electrons and holes. We show how this technique allows us to suppress the heating of n=1 orthoexcitons in Cu(2)O at high density. Using a laser pulse having an energy of a few microJ and duration of 100 fs, we are thus able to produce a cold exciton gas up to a density of 10(15) cm(-3). 相似文献
93.
Takuro Mochizuki 《Journal of Pure and Applied Algebra》2003,179(3):287-330
We calculate some quandle cohomology groups; the rational cohomology groups of any finite Alexander quandles, the second cohomology groups with a finite field coefficient of any finite Alexander quandles over a finite fields, and the third cohomology groups of the finite Alexander quandles of the form . 相似文献
94.
Infrared spectroscopy of Cu+(H2O)(n) and Ag+(H2O)(n): coordination and solvation of noble-metal ions
Iino T Ohashi K Inoue K Judai K Nishi N Sekiya H 《The Journal of chemical physics》2007,126(19):194302
M(+)(H(2)O)(n) and M(+)(H(2)O)(n)Ar ions (M=Cu and Ag) are studied for exploring coordination and solvation structures of noble-metal ions. These species are produced in a laser-vaporization cluster source and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region using a triple quadrupole mass spectrometer. Density functional theory calculations are also carried out for analyzing the experimental IR spectra. Partially resolved rotational structure observed in the spectrum of Ag(+)(H(2)O)(1) x Ar indicates that the complex is quasilinear in an Ar-Ag(+)-O configuration with the H atoms symmetrically displaced off axis. The spectra of the Ar-tagged M(+)(H(2)O)(2) are consistent with twofold coordination with a linear O-M(+)-O arrangement for these ions, which is stabilized by the s-d hybridization in M(+). Hydrogen bonding between H(2)O molecules is absent in Ag(+)(H(2)O)(3) x Ar but detected in Cu(+)(H(2)O)(3) x Ar through characteristic changes in the position and intensity of the OH-stretch transitions. The third H(2)O attaches directly to Ag(+) in a tricoordinated form, while it occupies a hydrogen-bonding site in the second shell of the dicoordinated Cu(+). The preference of the tricoordination is attributable to the inefficient 5s-4d hybridization in Ag(+), in contrast to the extensive 4s-3d hybridization in Cu(+) which retains the dicoordination. This is most likely because the s-d energy gap of Ag(+) is much larger than that of Cu(+). The fourth H(2)O occupies the second shells of the tricoordinated Ag(+) and the dicoordinated Cu(+), as extensive hydrogen bonding is observed in M(+)(H(2)O)(4) x Ar. Interestingly, the Ag(+)(H(2)O)(4) x Ar ions adopt not only the tricoordinated form but also the dicoordinated forms, which are absent in Ag(+)(H(2)O)(3) x Ar but revived at n=4. Size dependent variations in the spectra of Cu(+)(H(2)O)(n) for n=5-7 provide evidence for the completion of the second shell at n=6, where the dicoordinated Cu(+)(H(2)O)(2) subunit is surrounded by four H(2)O molecules. The gas-phase coordination number of Cu(+) is 2 and the resulting linearly coordinated structure acts as the core of further solvation processes. 相似文献
95.
Sakakura A Kawajiri K Ohkubo T Kosugi Y Ishihara K 《Journal of the American Chemical Society》2007,129(47):14775-14779
With regard to atom economy and E-factor, catalytic condensation of carboxylic acids with equimolar amounts of alcohols is the most desirable. Although several highly active dehydration catalysts have been reported, more efficient alternatives are still strongly needed because the dehydrative esterification of tertiary alcohols, phenols, acid-sensitive alcohols, amino acids, and hardly soluble alcohols has never proceeded satisfactorily. Here we report new insights into the classical DMAP-catalyzed acylation of alcohols: surprisingly, only a 0.05-2 mol % of DMAP can efficiently promote acylation of alcohols with acid anhydrides under auxiliary base- and solvent-free conditions to give the corresponding esters in high yields. Furthermore, we achieved the recovery and reuse of commercially available polystyrene-supported DMAP without using any solvents. These serendipitous findings provide widely useful and environmentally benign esterification methods, which might be more practical and reliable than catalytic dehydrative condensation methods, in particular, for the less reactive alcohols which hardly condense with carboxylic acid directly. 相似文献
96.
Sakurai K Fukumoto T Noguchi K Sato N Asaka H Moriyama N Yohda M 《Organic letters》2010,12(24):5732-5735
The 3D structures of an antitumor glycosylsterol OSW-1 and its closely related congener were investigated by NMR studies and an X-ray crystallographic analysis. The disaccharide moiety was found as a structural scaffold for the formation of a hydrophobic cluster by the biologically required functionalities. 相似文献
97.
An all-optical stabilization method of laser pulse energy is proposed using the optical Kerr effect (OKE). The method uses the OKE induced by a portion of the laser pulse as a power controller. The decrease (increase) in the throughput of the optical setup for OKE compensates for the increase (decrease) in pulse energy, thereby stabilizing the pulse-to-pulse fluctuation in pulse energy. The validity of this principle was proven by experiments with a femtosecond laser. 相似文献
98.
Takuro Tomita Ryota Kumai Hidenori Nomura Shigeki Matsuo Shuichi Hashimoto Ken Morita Toshiro Isu 《Applied Physics A: Materials Science & Processing》2011,105(1):89-94
Spontaneous nanostructure formations on roughened and smooth silicon surface by the femtosecond laser irradiation with the
repetition rate of 100 kHz were systematically studied. In addition to the widely accepted so-called coarse ripple, which
has the period analogous to the wavelength of the laser beam and aligns perpendicularly to the electric field of the incident
laser beam, the ripple which has the period similar to the wavelength of the incident laser beam but aligns parallel to the
electric field of the laser beam was observed on the roughened surface for the lower fluence and the higher number of pulse
irradiation. Furthermore, the ensemble of dots formed by the enhancement of the local electric field was found on the roughened
surface. This structure is preferentially formed around the scratches aligned perpendicularly to the electric field of the
laser beam. These novel nanostructures are considered to be peculiar to the femtosecond laser irradiation and open the possibilities
for precise control of the spontaneous nanostructure formation by femtosecond laser irradiation. 相似文献
99.
Taguchi S Matsumoto T Ichikawa T Kato T Ohno H 《Chemical communications (Cambridge, England)》2011,47(40):11342-11344
1-Ethyl-3-methylimidazolium leucine, a typical amino acid ionic liquid, turns into a thermotropic and ion conductive gel while retaining its ion pair upon adding a phosphonium-type zwitterion. 相似文献
100.
A cyclic order in the vertex set of a digraph is said to be coherent if any arc is contained in a directed cycle whose winding
number is one. This notion plays a key role in the proof by Bessy and Thomassé (2004) of a conjecture of Gallai (1964) on
covering the vertex set by directed cycles. This paper presents an efficient algorithm for finding a coherent cyclic order
in a strongly connected digraph, based on a theorem of Knuth (1974). With the aid of ear decomposition, the algorithm runs
in O(nm) time, where n is the number of vertices and m is the number of arcs. This is as fast as testing if a given cyclic order is coherent. 相似文献