全文获取类型
收费全文 | 473篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
化学 | 256篇 |
晶体学 | 7篇 |
力学 | 8篇 |
数学 | 93篇 |
物理学 | 116篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 12篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 22篇 |
2012年 | 34篇 |
2011年 | 36篇 |
2010年 | 19篇 |
2009年 | 18篇 |
2008年 | 24篇 |
2007年 | 46篇 |
2006年 | 31篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 21篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有480条查询结果,搜索用时 15 毫秒
101.
The paper shows the ability of the fluorochrome tris(2,2'-bipyridine) ruthenium (II) (Rubipy) to detect heparan sulfate, heparin, and heparinase activity of M3 murine mammary adenocarcinoma cells as well as bacterial heparinases I, II, and III in native polyacrylamide gel electrophoresis (PAGE). The technique is based on the electrophoretic mobility of high molecular weight heparins and subsequent staining with Rubipy (50 micrograms/mL). The minimum content of heparin detected by fluorescence in a UV transilluminator was 25-50 ng. The number of Rubipy molecules bound to heparin, determined in relationship to the number of disaccharide units (DU), showed that two to six heparin disaccharide units are bound by each fluorochrome molecule. Scatchard plot analysis showed one Rubipy-binding site (Kd = (8.56 +/- 2.97) x 10(-5) M). Heparinase activity was determined by densitometric analysis of the fluorescence intensity of the heparin-containing band of the gel. While heparinase I (EC 4.2.2.7.) degraded heparin and, to a lower degree, partially N-desulfated N-acetylated heparin (N-des N-Ac), heparinase II (no EC number) could efficiently degrade heparan sulfate (HS) and partially N-des N-Ac heparin. Finally, heparinase III (EC 4.2.2.8.) degraded HS almost exclusively. Only heparin and N-des N-Ac heparin were substrates for M3 tumor cell heparinases. We describe a qualitative, sensitive and simple method to detect heparinase activity and determine its substrate specificity using Rubipy fluorescence with heparin and heparan sulfate in multiple biological samples tested in parallel. 相似文献
102.
Angel Alberola Luis Calvo Teresa Rodríguez Rodríguez Carmen Saudo 《Journal of heterocyclic chemistry》1992,29(2):445-450
The reactivity of 3-methyl-5-phenylisoxazole against electrophilic compounds in the presence of different bases is studied. With n-BuLi, alkylated products at C-4 position and C-3 methyl group, and, in a few cases, dialkylated isoxazoles are obtained. When the reactions are carried out with LICA, the nature of the alkylated products depends on the alkyl halide used. By using LICA-TMEDA, as deprotonating system, regio-selective reaction at the C-3 methyl group is found. 相似文献
103.
Solving the capacitated location-routing problem by a GRASP complemented by a learning process and a path relinking 总被引:1,自引:0,他引:1
Christian Prins Caroline Prodhon Roberto Wolfler Calvo 《4OR: A Quarterly Journal of Operations Research》2006,4(3):221-238
As shown in recent researches, the costs in distribution systems may be excessive if routes are ignored when locating depots. The location routing problem (LRP) overcomes this drawback by simultaneously tackling location and routing decisions. This paper presents a new metaheuristic to solve the LRP with capacitated routes and depots. A first phase executes a GRASP, based on an extended and randomized version of Clarke and Wright algorithm. This phase is implemented with a learning process on the choice of depots. In a second phase, new solutions are generated by a post-optimization using a path relinking. The method is evaluated on sets of randomly generated instances, and compared to other heuristics and a lower bound. Solutions are obtained in a reasonable amount of time for such a strategic problem. Furthermore, the algorithm is competitive with a metaheuristic published for the case of uncapacitated depots. 相似文献
104.
Photoluminescence (PL) properties of Er-doped silicon rich oxide thin films deposited on Si substrate by co-evaporation of silicon monoxide and Er under different atmospheres are investigated. The samples exhibit luminescence peak at 1.54 μm which could be assigned to the recombination in intra-4f Er3+ transition. PL shows that this transition is highest when ammonia atmosphere is used during deposition followed by an annealing temperature at 850 °C in 95% N2+5% H2 gas (forming gas). In fact, we believe that the presence of the N atoms around Er ions increases the intensity of the 1.54 μm luminescence. 相似文献
105.
We are concerned with Runge-Kutta-Nyström methods for the integration of second order systems of the special formd
2
y/dt
2=f(y). If the functionf is the gradient of a scalar field, then the system is Hamiltonian and it may be advantageous to integrate it by a so-called canonical Runge-Kutta-Nyström formula. We show that the equations that must be imposed on the coefficients of the method to ensure canonicity are simplifying assumptions that lower the number of independent order conditions. We count the number of order conditions, both for general and for canonical Runge-Kutta-Nyström formulae.This research has been supported by Junta de Castilla y León under project 1031-89 and by Dirección General de Investigación Científica y Técnica under project PB89-0351. 相似文献
106.
A precise definition of a fractalF
p
r
1 derived from Pascal's triangle modulop
r
(p prime) is given. The number of nonzero terms in the firstp
s
lines of Pascal's triangle modulop
r
is computed. From this result the Hausdorff dimension and Hausdorff measure ofF
p
r
1 are deduced. The nonself-similarty ofF
p
r
1,r2, is also discussed. 相似文献
107.
Agnello M Belli G Bendiscioli G Bertin A Botta E Bressani T Bruschi M Bussa MP Busso L Calvo D Cereda B Cerello PG Cicalò C Corradini M Costa S De Castro S Donzella A Feliciello A Ferrero L Filippi A Filippini V Fontana A Galli D Garfagnini R Giacobbe B Gianotti P Grasso A Guaraldo C Iazzi F Lanaro A Lodi Rizzini E Lucherini V Marcello S Marconi U Masoni A Minetti B Montagna P Morando M Nichitiu F Panzieri D Pauli G Piccinini M Puddu G Rossetto E Rotondi A Rozhdestvensky AM Saino A Salvini P 《Physical review letters》1995,74(3):371-374
108.
Daniel Calvo 《Microchemical Journal》2007,87(1):27-34
A fast novel complexometric titration procedure is proposed, in which equivalence concentrations were determined using a potentiometric electronic tongue. The titration consists in a reduced number of fixed additions of titrant and the recording of the potentials of an array of ion-selective electrodes with cross-selectivity response. The generated data (number of sensors × number of additions) were used as input data to an artificial neural network response model previously trained with standards. The application of this procedure is demonstrated with automated EDTA titrations of Ca2+, Mg2+ and Sr2+ mixtures, up to 3.3 mM total ion concentration. In the studied case, good results predicting the three concentrations were obtained using five 1 mL fixed volume additions plus the readings of eight sensors. The unique additional step required was the pH buffering of the sample to pH 9.5. Good comparisons were observed between obtained and expected concentrations for the three cations with the external validation samples (n = 17, with RMSE values of 0.18, 0.28 and 0.32 mM for Ca2+, Mg2+ and Sr2+, respectively). The proposed procedure was applied to mineral waters and compared with reference methods. 相似文献
109.
In this paper the effect of changing step size on the local discretization error of BDF and Adams type methods is considered. According to Shampine and Bogacki the usual assumption for variable step size multistep methods of orderp, that the local discretization error changes by
p+1 as the step size changes by a factor of , is incorrect and may lead to unreliability in step size selection algorithms. Here, by using the true expression of the local discretization error for variable step size BDF-, Adams- and FLC methods, new algorithms for step size control are proposed. It is shown that the new algorithms are more accurate and reliable than those employed in usual codes. to confirm the advantages of the new algorithms some numerical experiments based on a modified version of EPISODE are presented. 相似文献
110.