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排序方式: 共有3137条查询结果,搜索用时 15 毫秒
61.
Laurent Pirolli 《Surface science》2006,600(16):3313-3320
The chemistry of a common copper deposition precursor, (hexafluoroacetylacetonate)Cu(vinyltrimethylsilane), (hfac)Cu(VTMS), on a single crystal Si(1 0 0)-2 × 1 surface is described at the molecular level using a combination of experimental surface analytical techniques under ultra-high vacuum conditions with computational analysis. At a cryogenic temperature of 100 K, (hfac)Cu(VTMS) adsorbs on this surface molecularly, without noticeable decomposition. Upon surface annealing, VTMS is easily released into the gas phase below the room temperature, while the hfac ligand is bound to the surface through the copper atom. When (hfac)Cu(VTMS) is adsorbed at room temperature, VTMS is released into the gas phase immediately, leaving surface adsorbate analogous in structure to the one formed by adsorption at cryogenic temperature and a brief annealing to room temperature. Upon surface annealing, the hfac ligand decomposes and constitutes the main source of impurities in copper deposition process. 相似文献
62.
Laurent Galbrun 《Applied Acoustics》2011,(4):205-209
This paper examines space averaging methods applied to structural level differences measured in lightweight building structures (two beam junction and single plate and beam junction). The methods studied include the averaging assuming a constant input force, the averaging based on a constant vibration level across the source element, and the arithmetic averaging of level differences. Tests indicate that a fairly steady input force can be easily produced when using an impulsive source such as a hammer; the constant input force method is then appropriate and can be used to space average level differences (the two beam structure showing a standard deviation of 0.1 dB from the averaging based on levels normalised to the force). On the other hand, acceleration levels can exhibit significant variations with position due to the low mode count and modal overlap of some lightweight elements such as timber beams. Variations in the vibration level across the source element can then be responsible for large inaccuracies in the level difference calculated from the constant level assumption, the two beams’ results showing errors greater than 5 dB at several 1/3 octave band frequencies. The latter averaging method is then inappropriate and should not be used. 相似文献
63.
Delevoye L Trébosc J Gan Z Montagne L Amoureux JP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(1):94-99
A new decoupling composite pulse sequence is proposed to remove the broadening on spin S=1/2 magic-angle spinning (MAS) spectra arising from the scalar coupling with a quadrupolar nucleus I. It is illustrated on the (31)P spectrum of an aluminophosphate, AlPO(4)-14, which is broadened by the presence of (27)Al/(31)P scalar couplings. The multiple-pulse (MP) sequence has the advantage over the continuous wave (CW) irradiation to efficiently annul the scalar dephasing without reintroducing the dipolar interaction. The MP decoupling sequence is first described in a rotor-synchronised version (RS-MP) where one parameter only needs to be adjusted. It clearly avoids the dipolar recoupling in order to achieve a better resolution than using the CW sequence. In a second improved version, the MP sequence is experimentally studied in the vicinity of the perfect rotor-synchronised conditions. The linewidth at half maximum (FWHM) of 65 Hz using (27)Al CW decoupling decreases to 48 Hz with RS-MP decoupling and to 30 Hz with rotor-asynchronised MP (RA-MP) decoupling. The main phenomena are explained using both experimental results and numerical simulations. 相似文献
64.
Tracking susceptibility effects is a convenient way to detect small inclusions in a bulk tissue matrix by MRI. We propose a quantitative assessment of these susceptibility effects by simultaneously mapping T(2)* and magnetic field from the time course of magnitude and phase using a multiple GE sequence at 4.7 T. A high-pass scheme is also introduced to highlight the mesoscopic magnetic field variations due to local susceptibility differences specifically in the magnetic field map. Applying this method to muscle tissue, we demonstrate that connective tissue generates detectable susceptibility effects through concomitant local magnetic field variation and T(2)* shortening. 相似文献
65.
Laurent Denis 《Monatshefte für Mathematik》1997,123(1):43-51
Lete and be the Carlitz-module analogues of their usual counterparts. We have proved in [4]-that these elements of
are algebraically independent over
whenq3. We study here the remaining caseq=2 and prove among other things that 1,e, are linearly independent over
. 相似文献
66.
67.
Laurent De Moerloose Liesbeth Taelman Patrick Segers Jan Vierendeels Joris Degroote 《国际流体数值方法杂志》2019,89(6):181-195
Fluid-structure interaction (FSI) simulations are used extensively to calculate the vibration of structures subjected to an internal or external flow. In the case of partitioned FSI simulations, separate flow and structure solvers are used, which requires some kind of coupling between both. The time step in both solvers is typically taken the same, but this unnecessarily leads to long calculation times when the time step is small due to stability reasons in one of the two solvers. Subcycling, the procedure where the time step of one solver is chosen smaller than the time step used in the other solver, may reduce the computational cost of the FSI simulation. The subcycling procedure can be either explicit or implicit, the latter implying the use of coupling iterations in each time step. Contrary to explicit subcycling, no stability analyses of implicit subcycling schemes are found in the literature. In this paper, the temporal stability of the implicit subcycling procedure is investigated. The one-dimensional flow in an elastic cylindrical tube is studied analytically. The results of this analysis are subsequently compared to a partitioned two-dimensional axisymmetric FSI calculation with implicit coupling between the flow and structure solvers. 相似文献
68.
69.
We propose here a well-balanced numerical scheme for the one-dimensional Goldstein–Taylor system which is endowed with all the stability properties inherent to the continuous problem and works in both rarefied and diffusive regimes. To cite this article: L. Gosse, G. Toscani, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 337–342. 相似文献
70.