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201.
We determine the phase diagram of several amphiphilic molecules as a function of the amphiphilic parameter alpha defined as the ratio of the volume of hydrophilic to hydrophobic segments using the Gibbs ensemble Monte Carlo method supplemented by configurational bias scheme. Specifically, we study amphiphilic molecules h(1)t(7), h(2)t(6), and h(3)t(5), for which alpha=0.14, 0.33, and 0.60 respectively, and demonstrate that the former two exhibit phase separation while h(3)t(5) forms micelles, supporting the contention that alpha=0.5 is the border line for phase separation and micellization, as observed in previous lattice Monte Carlo studies [Panagiotopoulos et al., Langmuir 18, 2940 (2002)]. Further, we study the phase separation in amphiphilic molecules as a function of the packing parameter by varying the size of the hydrophilic head for each molecule. We find that a larger hydrophilic head lowers the critical temperature T(c), and raises the critical density rho(c). 相似文献
202.
Three symmetrical positional isomers of bis-2-(n-pyridyl)-1H-benzimidazoles (n=2, 3, 4) were synthesized and DNA binding studies were performed with these isomeric derivatives. Like bisbenzimidazole compound Hoechst 33258, these molecules also demonstrate AT-specific DNA binding. The binding affinities of 3-pyridine (m-pyben) and 4-pyridine (p-pyben) derivatized bisbenzimidazoles to double-stranded DNA were significantly higher compared to 2-pyridine derivatized benzimidazole o-pyben. This has been established by combined experimental results of isothermal fluorescence titration, circular dichroism, and thermal denaturation of DNA. To rationalize the origin of their differential binding characteristics with double-stranded DNA, computational structural analyses of the uncomplexed ligands were performed using ab initio/Density Functional Theory. The molecular conformations of the symmetric head-to-head bisbenzimidazoles have been computed. The existence of intramolecular hydrogen bonding was established in o-pyben, which confers a conformational rigidity to the molecule about the bond connecting the pyridine and benzimidazole units. This might cause reduction in its binding affinity to double-stranded DNA compared to its para and meta counterparts. Additionally, the predicted stable conformations for p-, m-, and o-pyben at the B3LYP/6-31G* and RHF/6-31G* levels were further supported by experimental pKa determination. The results provide important information on the molecular recognition process of such symmetric head to head bisbenzimidazoles toward duplex DNA. 相似文献
203.
Bera Pulakesh Saha Nityananda Kumar Sanjay Banerjee D. Bhattacharya R. 《Transition Metal Chemistry》1999,24(4):425-430
New iron(III) complexes of 5-methyl-3-formylpyrazole thiosemicarbazone (HMPzTS) and 5-methyl-3-formylpyrazole-4-phenylthiosemicarbazone (HMPzPTS), namely [Fe(MPzTS)2]X and [Fe(MPzPTS)2]X respectively, where X=Cl, NO3, SCN and ClO4, have been synthesised and physico-chemically characterised by magnetic measurements (polycrystalline state), electronic, i.r., e.s.r. and Mössbauer spectra. All are cationic complexes containing two monoprotonic tridentate ligands with NNS donor sites and an anionic counterpart; they behave as 1:1 electrolytes in MeOH/DMF. Coordination to central iron(III) via the pyrazolyl nitrogen (2N), the azomethine nitrogen and the thiolato sulphur atom is confirmed in the complexes from i.r. data. E.s.r. data (RT & LNT) reveal the presence of a spin-paired iron(III) cation with d2
xyd2
yzd1
xy configuration. The 57Fe Mössbauer spectral data (RT) are commensurate with the presence of two iron(III) spin states, the percentage of each being dependent upon the counterion of the species. 相似文献
204.
Polycaprolactone (PCL) was grafted onto starch through introduction of urethane linkages. The grafting reaction was carried out in two steps. The first step was the reaction of hydroxyl-terminated PCL with 2,4-tolylene diisocyanate. The isocyanate terminated PCL was then reacted with starch to obtain starch-graft-polycaprolactone (starch-g-PCL). The grafting reaction was confirmed by FT-IR spectroscopy. The compatibility of the starch/PCL blend was enhanced with a compatibilizer, starch-g-PCL, whose amount was 3 wt.-% of the blend. The tensile strength and morphology of the compatibilized blend were determined. It was found that the compatibilized starch/PCL blend has finer phase domains and an improved interfacial adhesion. Mechanical properties of the compatibilized blend were found to be significantly higher than those of the corresponding uncompatibilized starch/PCL blend. 相似文献
205.
Xiao-Tao Chen Bishan Zhou Samit K. Bhattacharya Clare E. Gutteridge Thomas R. R. Pettus Samuel J. Danishefsky 《Angewandte Chemie (International ed. in English)》1998,37(6):789-792
An “sp 2 –sp 3 Stille coupling” of the vinyl triflate 1 and the stannyl compound 2 is a key step toward the completion of the total synthesis of eleutherobin, a natural product exhibiting taxol-like cytotoxic activity. 相似文献
206.
R. Mani M. Bhattacharya J. Tang 《Journal of polymer science. Part A, Polymer chemistry》1999,37(11):1693-1702
Maleic anhydride (MAn) was grafted onto aliphatic and aromatic/aliphatic copolyesters by reactive extrusion in the presence of a free radical initiator using a twin‐screw extruder. The grafting reaction was confirmed by spectroscopic analyses. The presence of succinic anhydride groups was shown by FT‐IR spectroscopy, and NMR spectra indicate that the grafts consist of single succinic anhydride units. The 2D 1H‐NMR spectra (COSY) indicate that grafting reactions take place at aliphatic dicarboxylic acid units of copolyesters. The graft content was determined by a nonaqueous titration method. The effects of concentration of initiator and monomer and reaction temperature on the graft content and intrinsic viscosity were studied. The low percentage grafting in poly(lactic acid) was observed due to the presence of limited free radical sites in the polymer backbone. Temperature and monomer and initiator concentrations affect the graft content, and the desired graft content with minimal degradation can be obtained by controlling these factors. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1693–1702, 1999 相似文献
207.
The requirement of getting continuous electricity at low cost is essential but challenging. Especially in the undeveloped countries there is no sufficient electricity for the people to do their daily regular works. In order to overcome this problem different renewable energy sources are sought and being explored. One of the approaches is to have a cooking system that is energized from the solar power, not directly using a solar cooker but by storing the energy in the form of heat that can be utilized as per requirement. This paper reports the design and fabrication of an alternative system to generate heat using solar radiation. This chulha is helpful in effective heating with the help of solar radiations at lower costs. A cooking technology is presented consisting of a solar panel directly connected to an electric heater inside of a well-insulated chamber. An insulated container with fixed amount of oil is heated up. The heat is found to be retained in the chamber even after sun set which is sufficient for heating water for making tea. The possible causes of temperature drop and possible remedy has been pointed out and discussed in this paper. 相似文献
208.
209.
CdS and Si semiconductor nanopraticles were embedded in a polymer matrix and characterized using various techniques. The surface properties and size distribution of the nanoparticles were monitored by POM and SEM and found to be uniform but around the crystalline frameworks of the polymer. XRD and FTIR analysis have been used to ensure the composite nature and particle size of the semiconductor loaded films. The electrical conductivity of these films were evaluated and found to increase with semiconductor dispersion and attains a percolation threshold at optimum composition. This composition and the distribution of the clusters is shown to vary with the type of the semiconductor, i.e., CdS or Si. 相似文献
210.
K.P. Ghatak S. Bhattacharya S. Pahari D. De R. Benedictus 《Superlattices and Microstructures》2009,46(3):387-414
We investigate the Einstein relation for the diffusivity-mobility ratio (DMR) for n-i-p-i and the microstructures of nonlinear optical compounds on the basis of a newly formulated electron dispersion law. The corresponding results for III-V, ternary and quaternary materials form a special case of our generalized analysis. The respective DMRs for II-VI, IV-VI and stressed materials have been studied. It has been found that taking CdGeAs2, Cd3As2, InAs, InSb, Hg1−xCdxTe, In1−xGaxAsyP1−y lattices matched to InP, CdS, PbTe, PbSnTe and Pb1−xSnxSe and stressed InSb as examples that the DMR increases with increasing electron concentration in various manners with different numerical magnitudes which reflect the different signatures of the n-i-p-i systems and the corresponding microstructures. We have suggested an experimental method of determining the DMR in this case and the present simplified analysis is in agreement with the suggested relationship. In addition, our results find three applications in the field of quantum effect devices. 相似文献