全文获取类型
收费全文 | 326篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 254篇 |
晶体学 | 4篇 |
力学 | 12篇 |
数学 | 17篇 |
物理学 | 57篇 |
出版年
2024年 | 1篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 19篇 |
2017年 | 8篇 |
2016年 | 23篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 47篇 |
2012年 | 23篇 |
2011年 | 31篇 |
2010年 | 8篇 |
2009年 | 11篇 |
2008年 | 19篇 |
2007年 | 9篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 10篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 46 毫秒
81.
82.
Sudhakar Maddala Anirban Panua Dr. Parthasarathy Venkatakrishnan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(64):16013-16020
While intramolecular Scholl oxidative coupling between two arenes is common, successful C−C heterocoupling between thiophene and arene is scarce. The latter is due to the notorious reactivity of thiophene towards polymerization under oxidative conditions. This report systematically demonstrates how topological variation of electronics and reactivity in thiophene substrates can lead to efficient oxidative heterocoupling. Bis(biaryl)thiophenes having reactive α- and β-positions open are the choice of substrates. The cyclizing arene partners are so electronically tuned for thiophene's reactivity (at α- and β-) as to establish C−C bond oxidatively generating symmetrical as well as unsymmetrical diphenanthrothiophenes which are basic thiananographenes. Depending on the cyclizing-couple's electronics, either arene- or thiophene-centered oxidation initiates C−C heterocoupling. The potential utility of these simple thiananographenes is further unfurled by converting them to functional N−/C-graphene segments that are aza-corannulene precursor and tetrabenzospirobifluorene. Their bright emission and extended electrochemical stability are remarkable that may be potentially important and applicable. 相似文献
83.
Dhamodharan K. Aneesh T. Pius Anitha 《Journal of Radioanalytical and Nuclear Chemistry》2019,319(3):1127-1133
Journal of Radioanalytical and Nuclear Chemistry - In dissolution studies involving plutonium oxide, oxides of cerium are employed as a non radioactive surrogate. A reductive dissolution of cerium... 相似文献
84.
Interpenetrating networks are the most recent development in polymeric blend materials. Due to the crosslinking of both the continuous and dispersed phases, a high degree of molecular mixing is achieved in these materials. Notwith-standing that poly(methyl methacrylate)-polyurethane (PMMA-PUR) interpene-trating and semi-interpenetrating networks have been extensively investigated by Meyer et al., ultrasonic relaxation technique has been applied here for the first time. These materials were found to be highly ultrasound absorbing.It is observed that ultrasonic absorption has a peak at a particular composition of PMMA-PUR interpenetrating network. The absorption coefficient increases with frequencyf. The absorption is of relaxational nature and is not due to the scattering of ultrasonic waves by the domains of the dispersed phase. At every composition of the interpenetrating network, the/f
2 vs.f curve indicates the presence of a relaxation frequency below 2 MHz and that the absorption increases with the temperature at some compositions which indicates the presence of thermal relaxation. An attempt is made to relate the absorption with the relaxation of pendent groups of polyurethane in the continuous phase. 相似文献
85.
Web‐spline‐based finite element approximation of some quasi‐newtonian flows: Existence‐uniqueness and error bound 下载免费PDF全文
Sudhakar Chaudhary V. V. K. Srinivas Kumar 《Numerical Methods for Partial Differential Equations》2015,31(1):54-77
This article deals with the web‐spline‐based finite element approximation of quasi‐Newtonian flows. First, we consider the scalar elliptic p‐Laplace problem. Then, we consider quasi‐Newtonian flows where viscosity obeys power law or Carreau law. We prove well‐posedness at the continuous as well as the discrete level. We give some error bounds for the solution of quasi‐Newtonian flow problem based on the web‐spline method. Finally, we provide the numerical results for the p‐Laplace problem. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq31: 54–77, 2015 相似文献
86.
Hydrides of period 2 and 3 elements are promising candidates for hydrogen storage but typically have heats of reaction that are too high to be of use for fuel cell vehicles. Recent experimental work has focused on destabilizing metal hydrides through alloying with other elements. A very large number of possible destabilized metal hydride reaction schemes exist. The thermodynamic data required to assess the enthalpies of these reactions, however, are not available in many cases. We have used first principles density functional theory calculations to predict the reaction enthalpies for more than 100 destabilization reactions that have not previously been reported. Many of these reactions are predicted not be useful for reversible hydrogen storage, having calculated reaction enthalpies that are either too high or too low. More importantly, our calculations identify five promising reaction schemes that merit experimental study: 3LiNH(2) + 2LiH + Si --> Li(5)N(3)Si + 4H(2), 4LiBH(4) + MgH(2) --> 4LiH + MgB(4) + 7H(2), 7LiBH(4) + MgH(2) --> 7LiH + MgB(7) + 11.5H(2), CaH(2) + 6LiBH(4) --> CaB(6) + 6LiH + 10H(2), and LiNH(2) + MgH(2) --> LiMgN + 2H(2). 相似文献
87.
Effect of Atomic‐Scale Differences on the Self‐Assembly of Thiophene‐based Polycatenars in Liquid Crystalline and Organogel States 下载免费PDF全文
Balaram Pradhan V. M. Vaisakh Dr. Geetha G. Nair Dr. D. S. Shankar Rao Dr. S. Krishna Prasad Dr. Achalkumar Ammathnadu Sudhakar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(49):17843-17856
Two series of polycatenars are reported that contain a central thiophene moiety connected to two substituted oxadiazole or thiadiazole units. The number, position, and length of the peripheral chains connected to these molecules were varied. The oxadiazole‐based polycatenars exhibited columnar phases with rectangular and hexagonal or oblique symmetry, whereas the thiadiazole‐based polycatenars exhibited columnar phases with rectangular and/or hexagonal symmetry. All of the compounds exhibited bright emission in the solution and thin‐film states. Two oxadiazole‐based molecules and one thiadiazole‐based molecule exhibited supergelation ability in hydrocarbon solvents, which is mainly supported by attractive π–π interactions. These gels showed aggregation‐induced enhanced emission, which is of high technological importance for applications in solid‐state emissive displays. X‐ray diffraction studies of the xerogel fibers of oxadiazole‐based polycatenars revealed a columnar rectangular organization, whereas a hexagonal columnar arrangement was observed for thiadiazole‐based polycatenars. Rheological measurements carried out on the samples quantitatively confirmed the formation of gels and showed that these gels are mechanically robust. The impact of an atomic‐scale difference (oxygen to sulfur, <2 % of the molecular weight) on the self‐assembly and the macroscopic properties of those self‐assembled structures are clearly visualized. 相似文献
88.
Sudhakar M Djurovich PI Hogen-Esch TE Thompson ME 《Journal of the American Chemical Society》2003,125(26):7796-7797
Energy transfer between phosphors and conjugated polymers was investigated using a fluorene trimer (F3) as a model conjugated material. The phosphors studied were bis-cyclometalated iridium complexes (FP, PPY, BT, PQ, and BTP), with triplet energies of 2.6, 2.4, 2.2, 2.1, and 2.0 eV, respectively (based on phosphorescence spectra). Stern-Volmer analysis of luminescent quenching shows that energy transfer from either FP or PPY to F3 is an exothermic process with Stern-Volmer quenching constants (kqSV) of near 109 M-1 s-1 while energy transfer from BT, PQ, and BTP is endothermic (kqSV = 107-106 M-1 s-1). On the the basis of above results, the triplet energy of F3 is estimated to be less than 2.3 eV (530 nm). This study suggests that conjugated polymers, which typically have lower T1 energies than F3, should also quench phosphorescent emission in thin films and organic light-emitting diodes (OLEDs) incorporating these and related phosphorescent dopants. 相似文献
89.
Anitha Srinivasan. 《Mathematics of Computation》1998,67(223):1285-1308
In this paper an unconditional probabilistic algorithm to compute the class number of a real quadratic field is presented, which computes the class number in expected time . The algorithm is a random version of Shanks' algorithm. One of the main steps in algorithms to compute the class number is the approximation of . Previous algorithms with the above running time , obtain an approximation for by assuming an appropriate extension of the Riemann Hypothesis. Our algorithm finds an appoximation for without assuming the Riemann Hypothesis, by using a new technique that we call the `Random Summation Technique'. As a result, we are able to compute the regulator deterministically in expected time . However, our estimate of on the running time of our algorithm to compute the class number is not effective.
90.
Some new 3,5‐diphenyl and 1,3,5‐triphenyl‐2‐pyrazolines derivatives were synthesized by reacting 1,3‐diphenyl‐2‐propen‐1‐ones with hydrazine hydrates and phenyl hydrazine in ethanol. The structural elucidation of the compounds was performed by IR, 1H NMR and elemental analysis. All examined compounds showed appreciable antibacterial activity. 相似文献