全文获取类型
收费全文 | 265篇 |
免费 | 2篇 |
专业分类
化学 | 154篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 32篇 |
物理学 | 69篇 |
出版年
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2016年 | 4篇 |
2014年 | 8篇 |
2013年 | 15篇 |
2012年 | 16篇 |
2011年 | 13篇 |
2010年 | 11篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 9篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 1篇 |
1968年 | 2篇 |
1963年 | 1篇 |
1958年 | 3篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有267条查询结果,搜索用时 828 毫秒
111.
Tina Chakrabarty Amaranadh Jasti N.K. Goel Vinod K. Shahi Sunil Sabharwal 《Radiation Physics and Chemistry》2011,80(7):803-809
Radiation-induced and thermal cross-linked sulfonated poly(ether sulfone) (SPS)–sulfonated poly(ether ether ketone) (SPK) composite ion-exchange membranes (SPS/SPK(γ) and SPS/SPK(T), respectively) were prepared. Their performances for water electrolysis were comparatively assessed. Thermal cross-linked membrane (SPS/SPK(T)) showed cross-linking of part functional groups (–SO3H) and thus deterioration in membrane conductivity. While, radiation-induced cross-linked membrane (SPS/SPK(γ)) avoided any cross-linking between functional groups and thus conductivity. Electrolysis performances of these membranes were evaluated in comparison with Nafion117 membrane. Relatively low current efficiency (CE) for SPS/SPK and SPS/SPK(T) membranes was due to their high mass transfer (water) via electro-osmotic drag, which was negligible for SPS/SPK(γ) membrane. SPS/SPK(γ) membrane exhibited comparable stabilities and water splitting performance with Nafion117 membrane, which revealed its suitability as substitute for electrochemical applications. 相似文献
112.
In this paper we carry out the performance analysis of traffic groomed multilayer optical networks. It is seen that the number of wavelength channels required decreases as the wavelength grooming factor increases. We have evaluated blocking probability for different load and grooming factor. The performance of the network has been evaluated for different conditions; first for fixed number of links with grooming factor set to 3 and subsequently with increase in grooming factor up to 18 in steps. The load on each link is selected as 2, 5, 9, 12, 15 and 20 Erlangs and the blocking probability as function of number of optical channels has been evaluated. In this work the effect of number of wavelength channels, traffic load and grooming factor on network blocking probability has been studied. The investigation reveals that the blocking probability decreases with increase in wavelength channels. Similarly we found that the blocking probability increases with increase in traffic load which is quite evident. Further it is shown that when the grooming factor is increased to significant value (16), the number of wavelengths requirement (8) becomes relatively stable. 相似文献
113.
Reduction of dinitrogen to ammonia under ambient conditions is a long-standing challenge. The few metal-based catalysts proposed have conspicuous disadvantages such as high cost, high energy consumption, and being hazardous to the environment. Single-atom catalysis has emerged as a new frontier in heterogeneous catalysis and metal atoms atomically dispersed on supports receive more and more attention owing to rapid advances in synthetic methodologies and computational modeling. Herein, we propose metal atoms embedded in divacant graphene as a catalyst for N2 fixation based on density functional calculations. We systematically investigate the potential of using transition metal like Cr, Mn, Fe, Mo and Ru as catalysts and our study reveals that Cr embedded in graphene exhibit good catalytic activity for N2 fixation. The synergy between the metal atoms and graphene surface provides a stable support to the metal center that has a high spin density to promote adsorption of N2 and activation of its N≡N triple bond. Our study deciphers the mechanism of conversion of N2 to ammonia following two possible reaction pathways, distal and enzymatic routes, via sequential protonation and reduction of activated N2. The study provides a rational framework for conversion of dinitrogen to ammonia using single atom catalyst. 相似文献
114.
115.
Recently, simulated annealing methods have proven to be a valuable tool for global optimization. We propose a new stochastic method for locating the global optimum of a function. The proposed method begins with the subjective specification of a probing distribution. The objective function is evaluated at a few points sampled from this distribution, which is then updated using the collected information. The updating mechanism is based on the entropy of a move selecting distribution and is loosely connected to some notions in statistical thermodynamics. Examples of the use of the proposed method are presented. These indicate its superior performance as compared with simulated annealing. Preliminary considerations in applying the method to discrete problems are discussed. 相似文献
116.
Y-Ba-Cu-O films are grown on strontium titanate substrates by RF sputtering from a single composite target. A barium-deficient annular ring with diameter equal to that of the target dimension is repeatedly observed. Films inside this ring are deposited exclusively at the close target-substrate distance. At larger distances the films grow more in exterior regions rather than in the interior region of the ring. Stoichiometry, structural morphology and superconducting transition temperatures are studied for various regions of the film. The films are superconducting when sintered in flowing oxygen at 950°C with onset at 100 K and a broad transition width. 相似文献
117.
Mn0.2ZnxNi0.8−xFe2O4 (x=0.2, 0.3, 0.4, 0.5, 0.6) are synthesized by the citrate precursor method. Effects of zinc substitution on DC resistivity, dielectric relaxation intensity, initial permeability, saturation magnetization and Curie temperature have been investigated. It is observed that resistivity increases with increase in zinc concentration up to x=0.5 and then decreases. The observed behaviour is explained in terms of hopping and site preference of ions in the lattice. The main contribution to dielectric relaxation intensity is observed to be due to space charge polarization. Initial permeability is observed to increase with increase in zinc concentration. Saturation magnetization increases up to x=0.4 and then starts decreasing. Canting effect is observed for higher zinc concentrations. 相似文献
118.
A new molybdenum(VI) oxalato complex, Ba[MoO3(C2O4)]·3H2O (BMO), was prepared and characterized by chemical analysis and infrared spectral studies. Thermal decomposition studies were made using thermogravimetry and differential thermal analysis. Dehydration reactions take place up to 280°C in three stages with loss of one half, one and a half and one mole of water per mole of BMO, respectively. Decomposition of oxalate takes place between 280 and 435°C in a single step to give BaMoO4 as the end product, which was characterized by chemical analysis, infrared and X-ray studies. The X-ray diffraction pattern of BMO shows that it is an amorphous compound. A chain structure containing MoO6 octahedra linked through oxygen is proposed on the basis of the infrared absorption spectrum. 相似文献
119.
2-(Tributylstannoxy)-, 2(triphenylstannoxy)- and 2-(trimethylsiloxy)-3- hydro-4-alkyl- or -4-phenyl-1,3,5,2-oxadiazaboroles have been synthesized, and their properties examined. 相似文献
120.
Platinum(II) hydridotin complexes containing bulky phosphine ligands, trans-Pt(H)L2(SnR3) have been prepared from: (i) the equimolar reaction between corresponding platinum(II) dihydride complexes and HSnR3 (Cy = cyclohexyl), P-i-Pr3, P-t-BuPh2, P-t-Bu2Me; R = Ph), (ii) the oxidative addition of the corresponding zerovalent complexes, Pt0L2, with HSnR3 (L = P-i-Pr3, P-t-BuPh2; R = Ph), (iii) the reaction of the corresponding platinum(II) dihydride complexes with ClSnR3 in the presence of pyridine in benzene (L = P-i-Pr3, P-t-BuPh2; R = CH3, n-Bu), (iv) the sodium borohydride reduction of the corresponding hydridochloride complexes Pt(H)Cl(PR3)2 with ClSnR3 in THF (L = PCy3; R = Ph), these compounds have been characterized by their elemental analysis, infrared, 1H and 31P NMR spectral data. 相似文献