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971.
Dr. Gaël Rouillé Mathias Steglich Dr. Cornelia Jäger Prof. Dr. Friedrich Huisken Prof. Dr. Thomas Henning Gabriele Theumer Dr. Ingmar Bauer Prof. Dr. Hans‐Joachim Knölker 《Chemphyschem》2011,12(11):2131-2137
We report on the characterization of dibenzo[cde,opq]rubicene (C30H14). The molecule was studied in solution at room temperature with absorption spectroscopy in the visible (vis) and ultraviolet (UV) wavelength ranges, and with emission spectroscopy. The infrared (IR), visible, ultraviolet, and vacuum ultraviolet (VUV) absorption spectra of a thin film were measured also at room temperature. In addition, the UV/vis absorption spectrum was measured at cryogenic temperatures using the matrix isolation spectroscopy technique. The interpretation of spectra was supported by theoretical calculations based on semiempirical and ab initio models, as well as on density functional theory. Finally, the results of the laboratory study were compared with interstellar spectra. 相似文献
972.
Pawlowska Z Lietard A Aloïse S Sliwa M Idrissi A Poizat O Buntinx G Delbaere S Perrier A Maurel F Jacques P Abe J 《Physical chemistry chemical physics : PCCP》2011,13(29):13185-13195
This work reports on the solvatochromic properties of a simple heterocyclic betaine pyridinium, 2-(1-pyridinio)benzimidazolate (SBPa), having promising potentialities in non-linear optics. From advanced PCM-TDDFT calculations, the solvatochromism of SBPa was found to be unusual, involving two different electronic states for absorption (S(0)→ S(2)) and emission (S(1)→S'(0)). To account for this behavior, we developed an innovative physical treatment which consists in a non-linear fit of the solvatochromic data using the Bilot-Kawski theoretical model and visualizing the least-square coefficient χ(2) on a 2D map as a function of the solute polarizability and gas phase absorption energy. In parallel, Kamlet-Taft correlations were undertaken to select a propitious set of electrostatic solvents usable in this treatment. Protic solvents that lead to specific interactions and nonpolar solvents that favor dimerization processes were excluded. From a choice of aprotic solvents with sufficiently high polarity, 4 dipole moments μ(g)(S(0)) = +9.1 D, μ(e)(S(2)) = -1.5 D, μ(e)(S(1)) = 0 D and μ(g)(S'(0)) = +3.31 D were determined, the 3 former values being in close agreement with TDDFT values, although the solute polarizability values seem underestimated. Anyhow, disregarding this discrepancy, we evaluated the static hyperpolarizability to β(0) = -64 × 10(-30) esu from the solvatochromic data in close agreement with DFT calculations. 相似文献
973.
974.
Bauer M Többens DM Mayer E Loerting T 《Physical chemistry chemical physics : PCCP》2011,13(6):2167-2171
A range of techniques has so far been employed for producing amorphous aqueous solutions. In case of aqueous tetrahydrofuran (THF) this comprises hyperquenching of liquid droplets, vapour co-deposition and pressure-induced amorphization of the crystalline cubic structure II clathrate. All of these samples are thermally labile and crystallize at temperatures above 110 K. We here outline a variant of the pressure-amorphization protocol developed by Suzuki [Phys. Rev. B, 2004, 70, 172108], which results in a highly crystallization resistant amorphous THF hydrate. The hydrate produced according to our protocol (annealing to 180 K at 1.8 GPa rather than to 150 K at 1.5 GPa) does not transform to the cubic structure II THF clathrate even at 150 K. We track the reason for this higher stability to the presence of crystalline remnants when following the Suzuki protocol, which are removed when using our protocol involving higher pressures and an annealing step. These crystalline remnants later serve as crystallization seeds lowering the thermal stability of the amorphous sample. Our protocol thus makes a purely amorphous THF hydrate available to the research community. We use powder X-ray diffraction to study the process of nucleation and slow crystal growth in the temperature range 160-200 K and find that the local cage structure and periodicity of the fully crystalline hydrate develops even at the earliest stages of crystallization, when the "clathrate crystal" has a size of about two unit cells. 相似文献
975.
Borcsa B Csupor D Forgo P Widowitz U Bauer R Hohmann J 《Natural product communications》2011,6(4):527-536
The term lipo-alkaloid is used for C19 aconitane alkaloids containing one or two long-chain fatty acid residues. Lipo-alkaloids are transesterified derivatives of the most toxic and highly effective diester-type diterpene alkaloids, such as aconitine, hypaconitine, mesaconitine. Lipo-alkaloids are native minor compounds of aconite drugs, but their amount significantly increases after traditional processing, which is a general method in the Far Eastern traditional medicinal systems. Analytical works demonstrated that cautious processing (usually boiling) of crude aconite roots decreases the amount of normal diterpene alkaloids and increases the concentration of lipo-alkaloids resulting in the reduction of toxicity of the drugs. Many papers reported that lipo-alkaloids occur as a complex mixture in the drugs, and the isolation of the individual components is extremely difficult. These compounds have been identified using highly sensitive analytical methods (HPLC-MS, NMR), and semisynthetic approaches have been developed to ensure lipo-alkaloids in pure form for pharmacological studies. This review summarizes the structure, chemistry, semisynthesis, analytics and bioactivities of lipo-alkaloids. On the basis of 32 references this is the first comprehensive study on this topic, covering the data of 173 compounds. 相似文献
976.
A dynamic terramechanic model for small lightweight vehicles with rigid wheels and grousers operating in sandy soil 总被引:1,自引:0,他引:1
This paper presents a validated dynamic terramechanic model for rigid wheels with grousers that may be used for planetary and terrestrial mobile robots operating in loose sandy soil. The proposed model is based on established analytical terramechanic theories and incorporates two new dimensionless empirical coefficients. The additional terms in the model are based on existing soil mechanic theories that vary as a function of soil properties, slip conditions, and vehicle loading. The proposed model was able to capture and predict the dynamic oscillations observed in experimental data from a single-wheel testbed for the sinkage, drawbar pull and normal load. For the operating conditions tested in this research the simulation results using the proposed model show an improvement over traditional terramechanic models for capturing the dynamic effects of grousers. 相似文献
977.
Euler’s celebrated buckling formula gives the critical load N for the buckling of a slender cylindrical column with radius B and length L as
N/(p3B2)=(E/4)(B/L)2,N/(\pi^3B^2)=(E/4)(B/L)^2, 相似文献
978.
The accuracy of tomographic particle image velocimetry for measurements of a turbulent boundary layer 总被引:1,自引:0,他引:1
Callum Atkinson Sebastien Coudert Jean-Marc Foucaut Michel Stanislas Julio Soria 《Experiments in fluids》2011,50(4):1031-1056
To investigate the accuracy of tomographic particle image velocimetry (Tomo-PIV) for turbulent boundary layer measurements,
a series of synthetic image-based simulations and practical experiments are performed on a high Reynolds number turbulent
boundary layer at Reθ = 7,800. Two different approaches to Tomo-PIV are examined using a full-volume slab measurement and a thin-volume “fat” light
sheet approach. Tomographic reconstruction is performed using both the standard MART technique and the more efficient MLOS-SMART
approach, showing a 10-time increase in processing speed. Random and bias errors are quantified under the influence of the
near-wall velocity gradient, reconstruction method, ghost particles, seeding density and volume thickness, using synthetic
images. Experimental Tomo-PIV results are compared with hot-wire measurements and errors are examined in terms of the measured
mean and fluctuating profiles, probability density functions of the fluctuations, distributions of fluctuating divergence
through the volume and velocity power spectra. Velocity gradients have a large effect on errors near the wall and also increase
the errors associated with ghost particles, which convect at mean velocities through the volume thickness. Tomo-PIV provides
accurate experimental measurements at low wave numbers; however, reconstruction introduces high noise levels that reduces
the effective spatial resolution. A thinner volume is shown to provide a higher measurement accuracy at the expense of the
measurement domain, albeit still at a lower effective spatial resolution than planar and Stereo-PIV. 相似文献
979.
Adrian Renfer Manish K. Tiwari Thomas Brunschwiler Bruno Michel Dimos Poulikakos 《Experiments in fluids》2011,51(3):731-741
Hydrodynamics in microcavities with cylindrical micropin fin arrays simulating a single layer of a water-cooled electronic
chip stack is investigated experimentally. Both inline and staggered pin arrangements are investigated using pressure drop
and microparticle image velocimetry (μPIV) measurements. The pressure drop across the cavity shows a flow transition at pin
diameter–based Reynolds numbers (Re
d
) ~200. Instantaneous μPIV, performed using a pH-controlled high seeding density of tracer microspheres, helps visualize vortex
structure unreported till date in microscale geometries. The post-transition flow field shows vortex shedding and flow impingement
onto the pins explaining the pressure drop increase. The flow fluctuations start at the chip outlet and shift upstream with
increasing Re
d
. No fluctuations are observed for a cavity with pin height-to-diameter ratio h/d = 1 up to Re
d
~330; however, its pressure drop was higher than for a cavity with h/d = 2 due to pronounced influence of cavity walls. 相似文献
980.
Michel Raous 《Comptes Rendus Mecanique》2011,339(7-8):491-501
Interface models coupling friction and adhesion, where adhesion is regarded as interface damage, are briefly reviewed. The most widely used cohesive zone models are presented and discussed. A general framework for these laws, recently developed by Del Piero and Raous in the form of a unified model, is outlined. As an example, it is here established that the RCCM (Raous–Cangémi–Cocou–Monerie) model is a specific case in this general framework. The variational formulation and some associated solvers are briefly recalled in the context of non-smooth mechanics in the cases of both quasi-static and dynamic problems. A few examples in various fields of application are given. Lastly, some open problems and ongoing researches in this field are presented and discussed. 相似文献
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