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81.
Andersen C Sharma PK Christensen MS Steffansen SI Madsen CM Nielsen P 《Organic & biomolecular chemistry》2008,6(21):3983-3988
Oligodeoxynucleotides containing the double-headed nucleoside 5'(S)-C-(2-(thymin-1-yl)ethyl)thymidine were prepared by standard solid phase synthesis. The synthetic building block for incorporating the double-headed moiety was prepared from thymidine, which was stereoselectively converted to a protected 5'(S)-C-hydroxyethyl derivative and used to alkylate the additional thymine by a Mitsunobu reaction. The oligodeoxynucleotides were studied in different nucleic acid secondary structures: duplexes, bulged duplexes, three-way junctions and artificial DNA zipper motifs. The thermal stability of these complexes was studied, demonstrating an almost uniform thermal penalty of incorporating one double-headed nucleoside moiety into a duplex or a bulged duplex, comparable to the effects of the previously reported double-headed nucleoside 5'(S)-C-(thymin-1-yl)methylthymidine. The additional base showed only very small effects when incorporated into DNA or RNA three-way junctions. The various DNA zipper arrangements indicated that extending the linker from methylene to ethylene almost completely removed the selective minor groove base-base stacking interactions observed for the methylene linker in a (-3)-zipper, whereas interactions, although somewhat smaller, were observed for the ethylene linker in a (-4)-zipper motif. 相似文献
82.
Jeppe?FockEmail author Lara?Katrina?Bogart Oliver?Posth Mikkel?Fougt?Hansen Quentin?A.?Pankhurst Cathrine?Frandsen 《Hyperfine Interactions》2016,237(1):23
The magnetite/maghemite content within iron oxide nanoparticles can be determined using the mean isomer shift (\(\overline {\delta }\)). However, accurate characterisation of the composition is limited by the uncertainty associated with \(\overline {\delta }\). We have identified four independent sources of uncertainty and developed a quantitative expression for the uncertainty budget. Sources of uncertainty are categorised as follows: that from the fitting of the Mössbauer spectrum (σ fit), that of the calibration of the α-Fe reference spectrum (σ cal), thermal corrections to the spectrum due to second order Doppler shift (SODS) (σ Δδ ) and other experimental errors (σ err). Each contribution is discussed in detail using 57Fe Mössbauer spectra obtained from an iron oxide nanoparticle system at temperatures between 16 K and 295 K on different spectrometers in two different laboratories. 相似文献
83.
Jensen MH Morris EJ Simonsen AC 《Langmuir : the ACS journal of surfaces and colloids》2007,23(15):8135-8141
A number of morphological and statistical aspects of domain formation in singly and doubly supported ternary membranes have been investigated. Such ternary membranes produce macroscopic phase separation in two fluid phases and are widely used as raft models. We find that membrane interactions with the support surface can have a critical influence on the domain shapes if measures are not taken to screen these interactions. Combined AFM and fluorescence microscopy demonstrate small (500 nm) irregular domains and incomplete formation of much larger (5 microm) round domains. These kinetically trapped structures are the result of interactions between the membrane and the support surface, and they can be effectively removed by employing doubly supported membranes under physiological salt concentrations. These decoupled supported membranes display macroscopic round domains that are easily perturbed by fluid shear flow. The system allows a quantitative characterization of domain coarsening upon being cooled into the coexistence region. We determine the domain growth exponent alpha = 0.31, which is in close agreement with the theoretical value of 1/3. Analysis of the spatial domain pattern in terms of Voronoi polygons demonstrates a close similarity to equilibrated cellular structures with a maximized configurational entropy. 相似文献
84.
C. Thomsen S. Reich H. Jantoljak I. Loa K. Syassen M. Burghard G.S. Duesberg S. Roth 《Applied Physics A: Materials Science & Processing》1999,69(3):309-312
The pressure dependence of the high-energy Raman modes in single- and multi-walled carbon nanotubes was measured in the range
0–10 GPa. We found the pressure coefficient to be linear in both materials but 25% smaller in MWNT. Given that the curvature
effects on vibrational properties of the rolled-up graphene sheets are small, we can explain this difference simply with elasticity
theory.
Received: 17 May 1999 / Accepted 18 May 1999 / Published online: 4 August 1999 相似文献
85.
86.
Lee KK Benedetti LR Jeanloz R Celliers PM Eggert JH Hicks DG Moon SJ Mackinnon A Da Silva LB Bradley DK Unites W Collins GW Henry E Koenig M Benuzzi-Mounaix A Pasley J Neely D 《The Journal of chemical physics》2006,125(1):014701
Laser-driven shock compression of samples precompressed to 1 GPa produces high-pressure-temperature conditions inducing two significant changes in the optical properties of water: the onset of opacity followed by enhanced reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semiconductor<-->electronic conductor transition in water, and is found at pressures above approximately 130 GPa for single-shocked samples precompressed to 1 GPa. Our results indicate that conductivity in the deep interior of "icy" giant planets is greater than realized previously because of an additional contribution from electrons. 相似文献
87.
A general approach to N-arylation and N-alkenylation of all five DNA/RNA nucleobases at the nitrogen atom normally attached to the sugar moiety in DNA or RNA has been developed. Various protected or masked nucleobases engaged readily in the copper-mediated Chan-Lam-Evans-modified Ullmann condensation with a range of different boronic acids at room temperature and were subsequently converted to the corresponding deprotected or unmasked adducts. Different N(3)-protecting groups were examined in the case of thymine, where the benzoyl group afforded the highest yields. A 4-alkylthio-substituted pyrimidin-2(1H)-one served as both a cytosine and a uracil precursor and was N-arylated and N-alkenylated in high yields. Adenine was efficiently and selectively N-arylated and N-alkenylated at the N(9) position by employing a bis-Boc-protected adenine derivative, while a bis-Boc-protected 2-amino-6-chloropurine served as guanine precursor and could also be selectively N(9)-arylated and N(9)-alkenylated. 相似文献
88.
This paper presents an effective methodology to characterize all the constitutive (elastic) parameters of an orthotropic polymeric foam material (Divinycell H100) in one single test using Digital Image Correlation (DIC) in combination with the Virtual Fields Method (VFM). A modified Arcan fixture is used to induce various loading conditions ranging from pure shear or axial loading in tension or compression to bidirectional loading. A numerical optimization study was performed with different loading angles of the Arcan test fixture and off-axis angles of the principal material axes. The objective is to identify the configuration that gives the minimum sensitivity to noise and missing data on the specimen edges, which are the two major issues when identifying the stiffness components from actual DIC measurements. Two optimized Arcan test configurations were chosen. The experimental results obtained for these two optimized test configurations show a significant improvement of the measurement accuracy compared with a pure shear load configuration. The larger sensitivity of the pure shear test to missing data as opposed to the tensile test is also evident from the experimental data and confirms the analysis from the optimization study. The recovery of missing data along the specimen edges is a promising way to further improve the identification results. 相似文献
89.
Peter E. R. Blanchard Emily Reynolds Brendan J. Kennedy Chris D. Ling Zhaoming Zhang Gordon Thorogood Bruce C. C. Cowie Lars Thomsen 《Journal of synchrotron radiation》2014,21(6):1275-1281
Tc L3‐edge XANES spectra have been collected on powder samples of SrTcO3 (octahedral Tc4+) and NH4TcO4 (tetrahedral Tc7+) immobilized in an epoxy resin. Features in the Tc L3‐edge XANES spectra are compared with the pre‐edge feature of the Tc K‐edge as well as other 4d transition metal L3‐edges. Evidence of crystal field splitting is obvious in the Tc L3‐edge, which is sensitive to the coordination number and oxidation state of the Tc cation. The Tc L3 absorption edge energy difference between SrTcO3 (Tc4+) and NH4TcO4 (Tc7+) shows that the energy shift at the Tc L3‐edge is an effective tool for studying changes in the oxidation states of technetium compounds. The Tc L3‐edge spectra are compared with those obtained from Mo and Ru oxide standards with various oxidation states and coordination environments. Most importantly, fitting the Tc L3‐edge to component peaks can provide direct evidence of crystal field splitting that cannot be obtained from the Tc K‐edge. 相似文献
90.
DL Thomsen T Kurtén S Jørgensen TJ Wallington SB Baggesen C Aalling HG Kjaergaard 《Physical chemistry chemical physics : PCCP》2012,14(37):12992-12999
The gas phase hydrogen abstraction reaction between OH and CY(2)XH, where X = H, F, OH, or NH(2) and Y = H, CH(3) or F, in the absence and presence of a single water molecule is investigated using both density function theory, B3LYP, and explicitly correlated coupled cluster theory, CCSD(T)-F12. We find that a single water molecule could have a catalytic effect at low temperatures possible in laboratory experiments, but does not seem to catalyze these reactions at 298 K, and will not play a role under relevant atmospheric conditions. 相似文献