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671.
n-Hexane and dichloromethane extracts obtained from Laurencia dentroidea (Rhodophyta) and Canistrocarpus cervicornis (Phaeophyta) were investigated for their acaricidal and repellent properties against Tetranychus urticae under laboratory conditions. The two extracts displayed moderate toxicity and good repellent proprieties, and were significantly more toxic (36-fold) than the positive control (eugenol), whereas eugenol was tenfold more repellent than either seaweed extract. The sesquiterpenoid elatol (1) was isolated from L. dentroidea and the diterpenoid seco-dolastane (4R,9S,14S)-4alpha-acetoxy-9beta, 14alpha-dihydroxydolast-1(15),7-diene (2) from C. cervicornis, the chemical structures of which were characterized by NMR spectroscopic data (1H and 13C) and by comparison with literature data. These compounds exhibited moderate toxicity, but a high degree of repellent activity against T. urticae. The findings suggest that marine natural products, specifically terpenes, can be employed for the development of new pesticides and become prototype agrochemical agents. 相似文献
672.
Kämmer E Dörfer T Csáki A Schumacher W Da Costa Filho PA Tarcea N Fritzsche W Rösch P Schmitt M Popp J 《The journal of physical chemistry. C, Nanomaterials and interfaces》2012,116(10):6083-6091
UV-SERS measurements offer a great potential for environmental or food (detection of food contaminats) analytics. Here, the UV-SERS enhancement potential of various kinds of metal colloids, such as Pd, Pt, Au, Ag, Au-Ag core-shell, and Ag-Au core-shell with different shapes and sizes, were studied using melamine as a test molecule. The influence of different activation (KF, KCl, KBr, K(2)SO(4)) agents onto the SERS activity of the nanomaterials was investigated, showing that the combination of a particular nanoparticle with a special activation agent is extremely crucial for the observed SERS enhancement. In particular, the size dependence of spherical nanoparticles of one particular metal on the activator has been exploited. By doing so, it could be shown that the SERS enhancement increases or decreases for increasing or decreasing size of a nanoparticle, respectively. Overall, the presented results demonstrate the necessity to adjust the nanoparticle size and the activation agent for different experiments in order to achieve the best possible UV-SERS results. 相似文献
673.
Augusto Rivera Dency José PachecoJaime Ríos-Motta Karla FejfarováMichal Dušek 《Tetrahedron letters》2012,53(45):6132-6135
The cyclic aminal 4,9-dimethyl-1,3,6,8-tetraazatricyclo[4.4.1.13,8]dodecane 4c was synthesized by the reaction of commercial rac-1,2-propanediamine with paraformaldehyde in an aqueous solution. 1H NMR analysis clearly revealed that the compound is chiral and racemic with an axis of chirality. To our knowledge, this is the first example of an azaadamantane derivative having axial chirality. This aminal was used in a Mannich type reaction with p-chlorophenol yielding 2,2′-[(4-methylimidazolidine-1,3-diyl)dimethanediyl]bis(4-chlorophenol) 7 as a racemic mixture. The crystal structure of 7 was determined by single X-ray diffraction analysis. 相似文献
674.
The lithium salts of the conjugated bases of 4-methoxy- and 4-acetylamino-2(1H)-pyrimidinones 1-3 undergo highly chemoselective N1-methylation or ethylation when treated with methyl- or ethylsulfate (hard electrophiles) in dry dioxane, while the use of DMF as solvent results in competitive O2-alkylation. Potassium salts of the same bases in DMF undergo prevalent O2-attack. Under the same conditions, a similar but less chemoselective behaviour is observed in alkylation of thymine and uracil, where some N3-attack occurs. This can be rationalised in terms of the HSAB principle. 相似文献
675.
de Oliveira CA Hamelberg D McCammon JA 《The journal of physical chemistry. B》2006,110(45):22695-22701
Our group recently proposed a robust bias potential function that can be used in an efficient all-atom accelerated molecular dynamics (MD) approach to simulate the transition of high energy barriers without any advance knowledge of the potential-energy landscape. The main idea is to modify the potential-energy surface by adding a bias, or boost, potential in regions close to the local minima, such that all transitions rates are increased. By applying the accelerated MD simulation method to liquid water, we observed that this new simulation technique accelerates the molecular motion without losing its microscopic structure and equilibrium properties. Our results showed that the application of a small boost energy on the potential-energy surface significantly reduces the statistical inefficiency of the simulation while keeping all the other calculated properties unchanged. On the other hand, although aggressive acceleration of the dynamics simulation increases the self-diffusion coefficient of water molecules greatly and dramatically reduces the correlation time of the simulation, configurations representative of the true structure of liquid water are poorly sampled. Our results also showed the strength and robustness of this simulation technique, which confirm this approach as a very useful and promising tool to extend the time scale of the all-atom simulations of biological system with explicit solvent models. However, we should keep in mind that there is a compromise between the strength of the boost applied in the simulation and the reproduction of the ensemble average properties. 相似文献
676.
Augusto Visintin 《Annali di Matematica Pura ed Applicata》2006,185(4):487-519
This work deals with an initial- and boundary-value problem for a quasilinear parabolic equation that includes a possibly
discontinuous hysteresis operator,
:
In particular the case of
equal to a so-called relay operator is studied. Well-posedness is proved, as well as regularity of the solution and its robustness w.r.t. perturbations of
. The large-time behaviour is studied; asymptotic stability and compactness are shown. For a time-periodic f, existence of a periodic solution is also established.
Mathematics Subject Classification (2000) 35K60, 35R35, 47J40 相似文献
677.
José Alberto Fracassi da Silva Nathan Vitorazzi de Castro Dosil Pereira de Jesus Adriana F. Faria Marcus V. N. De Souza Marcone Augusto Leal de Oliveira 《Electrophoresis》2010,31(3):570-574
A method for the determination of ethambutol (EMB), a first‐line drug against tuberculosis, based on CE with capacitively coupled contactless conductivity detection is proposed. The separation of EMB and its main product of degradation were achieved in less than 3 min with a resolution of 2.0 using a BGE composed of 50 mmol/L histidine and 30 mmol/L MES, pH 6.30. By raising the pH to 8.03, the analysis time was reduced to 1.0 min, but with a significant loss of resolution (0.7). Using the best separation conditions, linearity of 0.9976 (R2, five data points), sensitivity of 1.26×10?4 V min μmol?1 L, and LOD and quantification of 23.5 and 78.3 μmol/L, respectively, were obtained. Recoveries at four levels of concentration ranged from 95 to 102% and the concentration range studied ranged from 100 to 500 μmol/L. The results obtained for the determination of EMB in pharmaceutical formulations were compared with those obtained by using CE with photometric detection. 相似文献
678.
S. Ferrara M. Porrati A. Sagnotti R. Stora A. Yeranyan 《Fortschritte der Physik》2015,63(3-4):189-197
We investigate supersymmetric Born–Infeld Lagrangians with a second non–linearly realized supersymmetry. The resulting non–linear structure is more complex than the square root present in the standard Born–Infeld action, and nonetheless the quadratic constraints determining these models can be solved exactly in all cases containing three vector multiplets. The corresponding models are classified by cubic holomorphic prepotentials. Their symmetry structures are associated to projective cubic varieties. 相似文献
679.
Fabiana Inoue Rmulo Augusto Ando Paola Corio 《Journal of Raman spectroscopy : JRS》2011,42(6):1379-1383
Nanocomposites of carbon nanotubes and titanium dioxide (TiO2) have attracted much attention due to their photocatalytic properties. Although many examples in the literature have visualized these nanocomposites by electron microscopic images, spectroscopic characterization is still lacking with regard to the interaction between the carbon nanotube and TiO2. In this work, we show evidence of the attachment of nanostructured TiO2 to multiwalled carbon nanotubes (MWNTs) by Raman spectroscopy. The nanostructured TiO2 was characterized by both full‐width at half‐maximum (FWHM) and the Raman shift of the TiO2 band at ca 144 cm−1, whereas the average diameter of the crystallite was estimated as approximately 7 nm. Comparison of the Raman spectra of the MWNTs and MWNTs/TiO2 shows a clear inversion of the relative intensities of the G and D bands, suggesting a substantial chemical modification of the outermost tubes due to the attachment of nanostructured TiO2. To complement the nanocomposite characterization, scanning electronic microscopy and X‐ray diffraction were performed. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
680.
A bisphenol-A diglycidyl ether resin, cured with isophorone-diamine at 60°C, was modified by means of preformed core-shell acrylic rubber particles. Blends with rubber contents up to 30 phr by wt were tested. The fracture toughness depended linearly on the amount of rubber and significant improvement was found. No deterioration of temperature resistance was also observed. The viscosity of resin/modifier mixtures was controlled by means of antifoaming agents. A comparison with liquid acrylonitrile-butadiene copolymers showed that core-shell particles are efficacious tougheners. The effect of a bimodal particle size distribution was considered. In the size range investigated (0.2+5μm) no synergic effect was observed. 相似文献