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71.
Klodian Xhanari Kristin Syverud Gary Chinga-Carrasco Kristofer Paso Per Stenius 《Cellulose (London, England)》2011,18(2):257-270
Adsorption isotherms of single and double chain cationic surfactants with different chain length (cetyltrimethyl-, didodecyl-
and dihexadecyl ammonium bromide) onto cellulose nanofibrils were determined. Nanofibrillated cellulose, also known as microfibrillated
cellulose (MFC), with varying contents of carboxyl groups (different surface charge) was prepared by TEMPO-mediated oxidation
followed by mechanical fibrillation. The fibril charge was characterized by potentiometric and conductometric titration. Surfactant
adsorption was verified by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). Wetting
and adhesion of water onto fibril films was determined by contact angle measurements. Small aggregates (admicelles) of surfactant
were shown to form on the nanofibril surfaces, well below critical micelle concentrations. The results demonstrate the possibility
of using cationic surfactants to systematically control the degree of water wettability of cellulose nanofibrils. 相似文献
72.
A valveless microdevice has been developed for the integration of solid phase extraction (SPE) and polymerase chain reaction (PCR) on a single chip for the short tandem repeat (STR) analysis of DNA from a biological sample. The device consists of two domains--a SPE domain filled with silica beads as a solid phase and a PCR domain with an ~500 nL reaction chamber. DNA from buccal swabs was purified and amplified using the integrated device and a full STR profile (16 loci) resulted. The 16 loci Identifiler? multiplex amplification was performed using a non-contact infrared (IR)-mediated PCR system built in-house, after syringe-driven SPE, providing an ~80-fold and 2.2-fold reduction in sample and reagent volumes consumed, respectively, as well as an ~5-fold reduction in the overall analysis time in comparison to conventional analysis. Results indicate that the SPE-PCR system can be used for many applications requiring genetic analysis, and the future addition of microchip electrophoresis (ME) to the system would allow for the complete processing of biological samples for forensic STR analysis on a single microdevice. 相似文献
73.
Xhanari K Syverud K Chinga-Carrasco G Paso K Stenius P 《Journal of colloid and interface science》2011,356(1):58-62
The nature of layers formed by cellulose nanofibrils that had been surface modified (hydrophobized) at the oil/water (o/w) interface was investigated. The aim of the study was to clarify the mechanism underlying the excellent ability of these nanoparticles to stabilize emulsions. Layers of hydrophobized nanofibrillated cellulose spread at the o/w interface were deposited on glass slides by the Langmuir-Blodgett deposition technique. Overall evaluation of layer structures was performed by image analysis based on a Quadtree decomposition of images obtained from a flatbed scanner. A more detailed characterization of the layer structures was performed by Atomic Force Microscopy (AFM), and Field-Emission Scanning Electron Microscopy (FE-SEM). The results show that nanofibrils that were able to stabilize emulsions occur as single, dispersed fibrils or form large, network-like aggregates at the o/w interface. Fibrils that were insufficiently hydrophobized and therefore did not stabilize emulsions were only partially deposited and formed small, compact aggregates. We conclude that it is likely that the network formation is the main mechanism by which the fibrils prevent coalescence of emulsion droplets. 相似文献
74.
We show that the value function of a singular stochastic
control problem is equal to the integral of the value function
of an associated optimal stopping problem. The connection is
proved for a general class of diffusions using the
method of viscosity solutions. 相似文献
75.
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77.
D. von der Linde O. F. Schirmer H. Kurz 《Applied Physics A: Materials Science & Processing》1978,15(2):153-156
The photorefractive effect of undoped LiNbO3 crystals of high purity is studied by means of two-photon excitation of picosecond light pulses. We show that two-photon
photorefractive recording is accompanied by characteristic changes of the optical absorption and electron spin resonance spectra
due to the formation of color centers. The role of these centers for the photorefractive process in discussed. 相似文献
78.
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80.
Banita D. White Kristin A. Arnold Frank R. Fronczek Richard D. Gandour George E. Gokel 《Tetrahedron letters》1985,26(34):4035-4038
Structural and cation binding data for the title compound demonstrate that the large value of Ks results from complete K+ cation encapsulation by one nitrogen and six oxygen atoms despite the presence of a twelve-membered macroring. 相似文献