全文获取类型
收费全文 | 176篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 116篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 44篇 |
物理学 | 18篇 |
出版年
2024年 | 1篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 8篇 |
2011年 | 18篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 9篇 |
2007年 | 10篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 3篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有182条查询结果,搜索用时 15 毫秒
121.
Betancourt A Yezza A Halasz A Van Tra H Hawari J 《Journal of chromatography. A》2007,1154(1-2):473-476
In the present study, we used microwave energy instead of conventional heating to transform poly-3-hydroxybutyrate (PHB) into methyl 3-hydroxybutyrate (Me-3HB) in acidified methanol (H2SO4, 10%, v/v) mixture in less than 4 min at 10% microwave power. The microwave assisted method was then applied to analyze PHB produced by Alcaligenes latus. The PHB content in the biomass determined using microwave heating was comparable to the amount found by conventional heating. Moreover, the new esterification method was at least 50 times faster than the conventional method, affording a significant saving of time and energy. 相似文献
122.
Anna Rita Bacinello Pietro Millossovich Annamaria Olivieri Ermanno Pitacco 《Insurance: Mathematics and Economics》2011,49(3):285-297
Life annuities and pension products usually involve a number of guarantees, such as minimum accumulation rates, minimum annual payments or a minimum total payout. Packaging different types of guarantees is the feature of so-called variable annuities. Basically, these products are unit-linked investment policies providing a post-retirement income. The guarantees, commonly referred to as GMxBs (namely, Guaranteed Minimum Benefits of type ‘x’), include minimum benefits both in the case of death and survival. In this paper we propose a unifying framework for the valuation of variable annuities under quite general model assumptions. We compute and compare contract values and fair fee rates under ‘static’ and ‘mixed’ valuation approaches, via ordinary and least squares Monte Carlo methods, respectively. 相似文献
123.
Annamaria Mazzia Massimiliano Ferronato Giorgio Pini Giuseppe Gambolati 《Numerical Algorithms》2007,45(1-4):61-74
The meshless local Petrov–Galerkin (MLPG) method is a mesh-free procedure for solving partial differential equations. However,
the benefit in avoiding the mesh construction and refinement is counterbalanced by the use of complicated non polynomial shape
functions with subsequent difficulties, and a potentially large cost, when implementing numerical integration schemes. In
this paper we describe and compare some numerical quadrature rules with the aim at preserving the MLPG solution accuracy and
at the same time reducing its computational cost. 相似文献
124.
Annamaria Barbagallo Patrizia Daniele Sofia Giuffrè Antonino Maugeri 《European Journal of Operational Research》2014
Without using a technical language, but using the universal language of mathematics, we provide simple but significant laws, as Deficit Formula, Balance Law and Liability Formula, for the management of the world economy. Decisions, under these laws, for the recovery of the economy and for the good governance clearly appear. Further a simple but useful economical indicator E(t) is provided and the results are illustrated with a significant example. 相似文献
125.
This work focused on the way several electrolyte components could affect the electroosmotic flow and the capillary electrophoretic migration of aliphatic or aromatic (hydroxy)carboxylic acids. The effects exerted by the electroosmotic flow modifier, hexadecyltrimethylammonium bromide, the addition of metal salt to the electrolyte and the absorbance provider (chromophore) used for indirect detection were investigated. A retention of the organic acids was demonstrated. Its magnitude was shown to depend on the amount of cationic surfactant adsorbed onto the capillary walls. The addition of sodium nitrate led to a remobilization of all the acids except glycolic acid. Moreover, the presence of the chromophore was shown to influence mainly the migration of the glycolic acid. 相似文献
126.
[reaction: see text] Vilsmeier reagents give (Z)-1-aryl-1-haloalkenes from aryl ketones bearing an electron-donating substituent at the ortho- or para-position. These haloalkenes are intermediates in the Vilsmeier haloformylation of the aryl ketones. Another reaction mechanistic pathway is thus available in certain Vilsmeier haloformylations, in competition with the commonly accepted route by way of an enaminoketone. 相似文献
127.
Antonio Del Pra Giuseppe Zanotti Annamaria Piazzesi Umberto Belluco Renzo Ros 《Transition Metal Chemistry》1979,4(6):381-384
Summary The structure of PtCl(CF3)(cis-Ph2PCH=CHPPh2), has been determined from three-dimensional x-ray data. The complex crystallizes in the monoclinic system, space group C
2h
5
-P21/n witha=19.781(6),b=15.024(5),c=8.547(3) Å,=93.2(1)° andZ=4. Least-squares refinement has led to a value of the conventional R index (on F) of 0.055 for the 3199 independent reflections having I2.5 (I). The complex is a typical square-planar PtII complex with structural parameters: Pt-P, 2.275(4) (a)trans to CF3 and 2.236(4) (b)trans to Cl, Pt-Cl, 2.346(4), Pt-C(F), 2.188(8), C(A) = C(B), 1.38(2) Å; Cl-Pt-P(1), 91.1(1), P(1)-Pt-P(2), 86.2(1)°. 相似文献
128.
Nannini D Tittarelli M Ricci L Conte A Di Emidio B Giovannini A Caporale V 《Journal of AOAC International》2004,87(4):965-971
A model interlaboratory testing scheme was developed by the Italian National Reference Laboratory for Brucellosis. This scheme was planned for both qualitative (Rose Bengal Plate Test; RBPT) and quantitative (Complement Fixation Test; CFT) serological tests and involved a total of 42 laboratories. In the preparation of this scheme, reference was made to general protocols and guidelines and to methods reported in the literature, which were applicable to analytical chemistry laboratories. Six field sera from naturally infected animals, one positive serum at a titer below the European Union (EU) positivity threshold, and 5 sera positive at titers between 20 and 851 International Units of Complement Fixation Test (IUCFT)/mL plus one negative serum were used to produce a panel of test sera. To evaluate laboratory performances in the quantitative test for each tested sample examined, z-scores based on robust summary statistics (the median and normalized interquartile range) were used. To evaluate overall laboratory performance, 2 types of combined z-scores were used: Rescaled Sum of Scores and Sum of Squared Scores. In the case of the qualitative test (RBPT), results were analyzed by a Bayesian approach. A Beta distribution, based on the result of each laboratory, was calculated and used to estimate the probability of each laboratory giving a correct result and its uncertainty. 相似文献
129.
Pellegrin Y Quaranta A Dorlet P Charlot MF Leibl W Aukauloo A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(12):3698-3710
The synthesis and characterisation of the heteroditopic ligand N,N'-bis(3,5-di-tert-butylsalicylidene)-5,6-(1,10-phenanthroline)diamine (DPSalH(2)) bearing a phenanthroline and a bis(salicylidene)diimine cavity are reported. This versatile ligand combines two of the most widely used ligands in coordination chemistry. Sequential metallation of the phenanthroline end with Ru(II) and the salophenic cavity with Cu(II) is described. Electrochemical behaviour of the supramolecular complexes [Ru(bpy)(2)(DPSalH(2))](2+) and [Ru(bpy)(2)(DPSalCu)](2+) are analysed in connection with UV/Vis and EPR spectroscopy. The data for the one-electron-reduced species and the singly oxidised species of the binuclear Ru(II)-Cu(II) complex confirmed the formation of metalloradical complexes. Density functional calculations on the free ligand and the copper-only complex indicate in both cases that the HOMOs and LUMOs are developed on the Schiff base cavity with minor contributions on the bipyridine end. These findings support a bichromophoric character for our ruthenium complexes in the ground state, a necessary condition in the design of supramolecular systems for the study of electron transfer. Photophysical studies indicate fast quenching of the triplet excited state in both complexes, which suggests strong intercomponent excited-state interactions. Evidence is presented that this quenching is due to intramolecular electron transfer, at least in the case of [Ru(bpy)(2)(DPSalH(2))](2+), for which a charge-separated state with a remarkable lifetime of about 30 mus was observed. 相似文献
130.
Nicola Angelini Annamaria Quaranta Giovanni Checcucci Pill-Soon Song Francesco Lenci 《Photochemistry and photobiology》1998,68(6):864-868
Abstract— The hypericin analogs blepharismin (BP), oxyblepharismin (OxyBP) and stentorin (ST), the photosensing chromophores responsible for photomotile reactions in the ciliates Blepharisma japonicum (red and blue cells) and Stentor coeruleus, represent a new class of photoreceptor pigments whose chemical structures have recently been determined. In the case of ST it has been shown that the first excited singlet state can be deactivated by donation of an electron to an appropriate acceptor molecule (e.g. a quinone molecule). This charge transfer can be considered a possible mechanism for the primary photoprocess for the photomotile responses in S. coeruleus. To determine whether an electron transfer process also occurs in the deactivation of excited blepharismin, we studied the fluorescence quenching of OxyBP in dimethyl-sulfoxide (DMSO) and in ethanol using electron acceptors with different reduction potentials. Under our experimental conditions ground state and excited state complexes (like fluorescent exciplexes) are not formed between the fluorophore and the quenchers. In DMSO the bimolecular quenching constant values (kq) calculated on the basis of the best fitting procedures clearly show that the quenching efficiency decreases with the quencher negative reduction potential, E0. The kq (M-1 s-1) and E0 (V) values are, respectively, 7.8 times 109 and -0.134 for 1,4-benzoquinone, 8.9 times 109 and -0.309 for 1,4-naphthoquinone, 2.4 times 109 and -0.8 for nitrobenzene, 0.009 times 109 and -1.022 for azobenzene and 0 and -1.448 for benzophenone. These findings point to the conclusion that upon formation of the encounter complex between OxyBP and the quencher, an electron is released from excited OxyBP to the quencher, similar to what happens in ST. It is suggested that in the pigment granules such a light-induced charge transfer from excited blepharismin to a suitable electron acceptor triggers sensory transduction processes in B. japonicum. 相似文献