全文获取类型
收费全文 | 301篇 |
免费 | 2篇 |
国内免费 | 4篇 |
专业分类
化学 | 143篇 |
晶体学 | 3篇 |
力学 | 8篇 |
数学 | 76篇 |
物理学 | 77篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 15篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 11篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有307条查询结果,搜索用时 17 毫秒
71.
Leung MK Viswanath MB Chou PT Pu SC Lin HC Jin BY 《The Journal of organic chemistry》2005,70(9):3560-3568
[structure: see text] Anti-[2.2](1,4)biphenylenophane (4) was synthesized from de Meijere's tetrabromo[2.2]paracyclophane (5) through a four-step reaction sequence. Although an average separation of 3.09 A between the inner ring of the biphenylene units is normal for [2.2]paracyclophanes, a bond distance of 1.54 Afor the ethano C-C bridge at room temperature is shorter than usual. In addition, trimethylsilyl-substituted anti-[2.2](1,4)biphenylenophane 8 sublimes at 220 degrees C under a pressure lower than 1 x10(-5) Torr without decomposition or thermal isomerization. The high thermal stability of 8 suggested that the ethano bridges of the biphenylenophanes are less strained than those of [2.2]paracyclophane. Bathochromic shifts are observed in their UV-vis absorption spectra. The phane state interactions of 4 and 8 were evidenced by the weak structureless fluorescent emission maximized at 537 and 550 nm in CH(2)Cl(2) along with longer relaxation lifetimes of 229 and 292 ps, respectively. 相似文献
72.
James P. Annaraj Kanagasabai M. Ponvel Periakaruppan Athappan Sankaran Srinivasan 《Transition Metal Chemistry》2004,29(7):722-727
Several new CuII complexes, having positive reduction potentials in an in situmanner, were synthesized by reaction of the Knoevenagel condensate, 4-salicylidene-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (from curcumin) with 4-X-anilines and CuCl2. The solution electronic spectra of these complexes show intense absorption around 530 nm with unusual high extinction values (, 1600--3600 m-1 cm-1) due to the low symmetry L--d (Cu) LMCT transition. The e.s.r. spectral features with g
|| > g
|| > 2.0 having four g
|| values and a broadening of the g
||component with moderately low A
|| (110 × 10-4 cm-1) also suggest a lower symmetry around CuII. The cyclic voltammetric studies of the CuII complexes in MeCN show a positive reduction potential (E
pc=502--138 mV) with high peak-to-peak separation (E
p=87--335 mV). The higher and low A
||values together with positive reduction potentials for these CuII complexes suggest that they can mimic the functional properties of blue copper proteins, but have poor redox stability. 相似文献
73.
V. Sankaran Shiow-Ching Lin C. S. Marvel 《Journal of polymer science. Part A, Polymer chemistry》1980,18(2):495-503
New Processable Polyaromatic amides were prepared from 2,2′-diiododiphenyl-4,4′-dicarbonyl dichloride (I) and several aromatic diamines. Phenylethynyl groups were introduced in these polymides by replacing the iodine groups with copper phenyl acetylide. On thermal curing, 2,2′-di(phenylethynyl)biphenyl group undergoes intramolecular cyclization to form 9-phenyl dibenzanthracene derivative. The cured polymers showed increased heat and chemical stabilities. No melting points were observed for all the polymers below 500°C. The viscosity of the polymers was decreased on substitution of the iodine by phenylethynyl groups. 相似文献
74.
Jingqiao Zhang Viswanath Avasarala Raj Subbu 《European Journal of Operational Research》2010,200(2):557-567
Statistical transition probability matrices (TPMs), which indicate the likelihood of obligor credit state migration over a certain time horizon, have been used in various credit decision-making applications. A standard approach of calculating TPMs is to form a one-year empirical TPM and then project it into the future based on Markovian and time-homogeneity assumptions. However, the one-year empirical TPM calculated from historical data generally does not satisfy desired properties. We propose an alternative methodology by formulating the problem as a constrained optimization problem requiring satisfaction of all the desired properties and minimization of the discrepancy between predicted multi-year TPMs and empirical evidence. The problem is high-dimensional, non-convex, and non-separable, and is not effectively solved by nonlinear programming methods. To address the difficulty, we investigated evolutionary algorithms (EAs) and problem representation schemas. A self-adaptive differential evolution algorithm JADE, together with a new representation schema that automates constraint satisfaction, is shown to be the most effective technique. 相似文献
75.
Kunpeng Li Appa Iyer Sivakumar Viswanath Kumar Ganesan 《European Journal of Operational Research》2008
In this paper, we study the problem of synchronized scheduling of assembly and air transportation to achieve accurate delivery with minimized cost in consumer electronics supply chain. This problem was motivated by a major PC manufacturer in consumer electronics industry. The overall problem is decomposed into two sub-problems, which consist of an air transportation allocation problem and an assembly scheduling problem. The air transportation allocation problem is formulated as an integer linear programming problem with the objective of minimizing transportation cost and delivery earliness tardiness penalties. The assembly scheduling problem seeks to determine a schedule ensuring that the orders are completed on time and catch the flights such that the waiting penalties between assembly and transportation is minimized. The problem is formulated as a parallel machine scheduling problem with earliness penalties. The computational complexities of the two sub-problems are investigated. The air transportation allocation problem with split delivery is shown to be solvable. The parallel machine assembly scheduling problem is shown to be NP-complete. Simulated annealing based heuristic algorithms are presented to solve the parallel machine problem. 相似文献
76.
Summary Cumene is prepared selectively through an eco-friendly route using naturally available montmorillonite clay as the green catalyst.
Pillaring of montmorillonite is done to improve the structural stability for long-term use. Alumina pillaring and the influence
of mixed pillaring with zirconia and chromia on the structural as well as textural properties are characterized. Montmorillonite
shows very high conversion, selectivity and regenerability upon pillaring towards isopropylation of benzene. 相似文献
77.
Mixing of binary mixtures of nanopowders afforded by rapid expansion of high pressure and supercritical suspensions (REHPS)
is investigated to examine the roles of two previously reported deagglomeration mechanisms. The quality of mixing was characterized
through intensity and scale of segregation using concentration data obtained through energy dispersive X-ray spectroscopy;
the corresponding deagglomeration was quantified using differential mobility and image analyses in conjunction with electron
microscopy. Increasing the pressure from which expansion was carried out, and decreasing the nozzle diameter led to improved
deagglomeration. However, increased pressure alone did not influence the mixture quality, which was found to also depend on
the scale of mixedness of the constituents before transport through the nozzle, establishing that the REHPS mixing is significantly
improved by improving the quality of the premix. The scale of segregation correlated with the size of the most energetic eddies
present during flow through the nozzle, both of which increased with nozzle diameter, corroborating the importance of previously
reported shear-induced deagglomeration mechanism. Finally, REHPS was also shown to be capable of deagglomerating carbon nanotube
bundles and mix them well with alumina, silica, and titania at submicron scale. 相似文献
78.
We report a simple, compact electronic speckle-pattern interferometer (ESPI) incorporating holographic optical elements (HOEs) for the study of out-of-plane vibration. Reflection and transmission HOEs provide reference and object beams in the interferometer. The alignment difficulties with conventional ESPI systems are minimized using HOEs. The time-average ESPI subtraction method is used to generate the fringe pattern and remove background speckle noise by introducing a phase shift between consecutive images. The amplitude and phase maps are obtained using path-difference modulation. 相似文献
79.
Nishizawa S Sankaran NB Seino T Cui YY Dai Q Xu CY Yoshimoto K Teramae N 《Analytica chimica acta》2006,556(1):133-139
In combination with abasic site (AP site)-containing DNAs, potential use of a biotic fluorescence compound, Vitamin B2 (riboflavin), is demonstrated for the fluorescence detection of the thymine (T)-related single-nucleotide polymorphisms. Our method is based on construction of the AP site in DNA duplexes, which allows small ligands to bind to target nucleotides accompanied by fluorescence signaling: an AP site-containing probe DNA is hybridized with a target DNA so as to place the AP site toward a target nucleobase, by which hydrophobic microenvironments are provided for ligands to recognize target nucleotides through stacking and hydrogen-bonding interactions. In 10 mM sodium cacodylate buffer solutions (pH 7.0) containing 100 mM NaCl and 1.0 mM EDTA, Vitamin B2 is found to selectively bind to T (K11 = 1.8 × 106 M−1 at 5 °C) over other nucleobases, and this is accompanied by significant quenching of its fluorescence. While the sensing functions depend on the flanking sequences to the AP site, Vitamin B2 is applicable to the detection of T/C (cytosine), T/G (guanine) and T/A (adenine) mutation sequences of the CYP2A6 gene, where the flanking nucleobases are guanines in both positions (-GXG-, X = AP site). 相似文献
80.
Parameswaran Sankaran 《Proceedings of the American Mathematical Society》2006,134(7):1875-1880
We show that the group of piecewise-linear homeomorphisms of having bounded slopes surjects onto the group of all quasi-isometries of . We prove that the following groups can be imbedded in : the group of compactly supported piecewise-linear homeomorphisms of , the Richard Thompson group , and the free group of continuous rank.