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991.
Entropic splitter for particle separation 总被引:1,自引:0,他引:1
We present a particle separation mechanism which induces the motion of particles of different sizes in opposite directions. The mechanism is based on the combined action of a driving force and an entropic rectification of the Brownian fluctuations caused by the asymmetric form of the channel along which particles proceed. The entropic splitting effect shown could be controlled upon variation of the geometrical parameters of the channel and could be implemented in narrow channels and microfluidic devices. 相似文献
992.
In this study, we use an ion funnel (IF) at ambient pressure to enhance the sensitivity of secondary electrospray ionization (SESI). Atenolol, salbutamol and cocaine as test compounds are delivered to the SESI interface in the gas phase and are charged with three nano electrosprays. In our experiments, we show that the compounds can be detected at concentrations in the low pptv range, which is an increase of two orders of magnitude compared with the results without the IF. With a standard SESI interface, the compounds could not be detected at all. With the use of the SESI IF interface for the headspace analysis of bananas and limes, we can detect many more compounds and at higher intensities than with a standard SESI interface. 相似文献
993.
Spiecker E Schmid AK Minor AM Dahmen U Hollensteiner S Jäger W 《Physical review letters》2006,96(8):086401
We study the formation of planar network nanostructures, which develop during metal deposition on initially smooth surfaces of layered compounds. Using in situ low-energy electron microscopy for dynamic observation and high-resolution transmission electron microscopy for structure analysis, we have observed the rapid formation of hexagonal networks of linear "nanofolds" with prismatic cavities on top of layered VSe2 crystals. Their formation results from relaxation of compressive strains which build up during Cu intercalation into a thin surface layer. 相似文献
994.
Helmuth JA Schmid H Stutz R Stemmer A Wolf H 《Journal of the American Chemical Society》2006,128(29):9296-9297
We have demonstrated microcontact printing (muCP) of self-assembled monolayers in the millisecond regime. The contact formation and separation of the stamp and substrate was studied with high-speed video recordings. Using high ink concentrations and contact times as short as 1 ms, we printed monolayers of hexadecanethiol on Au, which served as a selective etch resist. High-speed muCP yields defect-free monolayers that are independent of the dimensions of the printed patterns, have high contrast between printed and unprinted areas, and enable perfect reproducibility of prints. 相似文献
995.
Schmid T 《Analytical and bioanalytical chemistry》2006,384(5):1071-1086
Photoacoustic spectroscopy (PAS) is based on the absorption of electromagnetic radiation by analyte molecules. The absorbed
energy is measured by detecting pressure fluctuations in the form of sound waves or shock pulses. In contrast to conventional
absorption spectroscopy (such as UV/Vis spectroscopy), PAS allows the determination of absorption coefficients over several
orders of magnitude, even in opaque and strongly scattering samples. Small absorption coefficients, such as those encountered
during trace gas monitoring, can be detected with cells with relatively short pathlengths. Furthermore, PA techniques allow
absorption spectra of solid samples (including powders, chips or large objects) to be determined, and they permit depth profiling
of layered systems. These features mean that PAS can be used for on-line monitoring in technical processes without the need
for sample preparation and to perform depth-resolved characterization of industrial products. This article gives an overview
on PA excitation and detection schemes employed in analytical chemistry, and reviews applications of PAS in process analytical
technology and characterization of industrial products. 相似文献
996.
997.
M. Schmid E. Lundgren G. Leonardelli A. Hammerschmid B. Stanka P. Varga 《Applied Physics A: Materials Science & Processing》2001,72(4):405-412
Interlayer diffusion, i.e. mass transport between different terraces, is known to be an essential process for obtaining layer-by-layer
growth, avoiding formation of three-dimensional (3D) islands when growing thin films. We present experimental results for
the growth of cobalt on Pt (111), which demonstrate the importance of kinks and corners for interlayer diffusion. We show
that Co grows two-dimensionally as long as strain caused by the Pt-Co interface keeps the step edges rough, with a high kink
density, and then transforms to 3D growth with straight steps. The results for growth with adsorbed carbon monoxide show that
CO acts as a surfactant, causing two-dimensional growth unless heterogeneous nucleation occurs. Again, this process is related
to roughening of the steps, being a new mechanism for the action of a surfactant. A scanning tunneling microscopy study at
the atomic scale confirms the fact that step descent happens only at kinks and (concave) corners, and in conjunction with
simulations allows us to identify some of the relevant atomic-exchange processes. We finally argue that the dependence of
the growth mode on the step morphology, together with straightening of the steps by step–step interaction, can lead to an
instability of the growth mode.
Received: 27 March 2000 / Accepted: 4 September 2000 / Published online: 7 March 2001 相似文献
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