全文获取类型
收费全文 | 9475篇 |
免费 | 301篇 |
国内免费 | 57篇 |
学科分类
数理化 | 9833篇 |
出版年
2023年 | 69篇 |
2022年 | 116篇 |
2021年 | 226篇 |
2020年 | 194篇 |
2019年 | 179篇 |
2018年 | 157篇 |
2017年 | 158篇 |
2016年 | 343篇 |
2015年 | 276篇 |
2014年 | 280篇 |
2013年 | 533篇 |
2012年 | 523篇 |
2011年 | 573篇 |
2010年 | 379篇 |
2009年 | 317篇 |
2008年 | 544篇 |
2007年 | 531篇 |
2006年 | 464篇 |
2005年 | 455篇 |
2004年 | 404篇 |
2003年 | 352篇 |
2002年 | 299篇 |
2001年 | 143篇 |
2000年 | 127篇 |
1999年 | 124篇 |
1998年 | 90篇 |
1997年 | 96篇 |
1996年 | 126篇 |
1995年 | 108篇 |
1994年 | 105篇 |
1993年 | 91篇 |
1992年 | 82篇 |
1991年 | 72篇 |
1990年 | 65篇 |
1989年 | 63篇 |
1988年 | 73篇 |
1987年 | 74篇 |
1986年 | 54篇 |
1985年 | 100篇 |
1984年 | 88篇 |
1983年 | 59篇 |
1982年 | 65篇 |
1981年 | 61篇 |
1980年 | 63篇 |
1979年 | 57篇 |
1978年 | 41篇 |
1977年 | 51篇 |
1976年 | 39篇 |
1975年 | 39篇 |
1974年 | 39篇 |
排序方式: 共有9833条查询结果,搜索用时 15 毫秒
61.
Francesco Michelangeli 《Journal of fluorescence》1991,1(3):203-206
A simple fluorimetric method is presented for measuring calcium uptake and inositol 1,4,5-trisphosphate (InsP3)-induced calcium release in microsomes using Fluo-3. This method is used to investigate the amplitude of calcium release (quantal release) induced by InsP3 from rat cerebellum microsomes. 相似文献
62.
Giancarlo Marconi Sandra Monti Francesco Manoli Stefano Ottani 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):279-282
The Induced Circular Dichroism of the complex formed by inclusion of Licochalcone-A (a powerful antimalarian of natural origin)
and β-cyclodextrin was measured and calculated. The association constant was determined by titration experiments of ICD and
fluorescence. The lowest energy conformations of the complex were obtained through docking procedures and their Circular Dichroism
was evaluated within the Tinoco framework. The geometry of the complex was found to be consistent with the main experimental
features. 相似文献
63.
A. Saxena D. Fabris G. Prete D. V. Shetty G. Viesti B. K. Nayak D. C. Biswas R. K. Choudhury S. S. Kapoor M. Lunardon S. Moretto G. Nebbia S. Pesente V. Rizzi A. M. Samant M. Barbui E. Fioretto M. Cinausero A. Brondi G. La Rana R. Moro E. Vardaci N. Gelli F. Lucarelli 《Nuclear Physics A》2004,730(3-4):299-315
Pre-scission and post-scission multiplicities of neutrons and alpha particles have been simultaneously measured for the fission-like reactions of 340 MeV 28Si on 232Th. Dynamical model calculations using HICOL code predict that about 90% of the observed events are of quasi-fission type while the remaining 10% are from compound nucleus fission decay. Moving source fits were carried out to the observed neutron and alpha particle spectra, measured at different angles with respect to the fragment directions. The pre-scission and post-scission neutron multiplicities are deduced to be 8.7±2.0 and 9.4±2.0, respectively. The corresponding multiplicity values for alpha particles are found to be 0.22±0.08 and 0.1±0.03. From the measured post-scission neutron multiplicity, it is inferred that about 65±20 MeV of the initial excitation energy remains at scission. This may be compared to the value of 85±30 MeV estimated from PACE2 statistical model calculations, adjusted to reproduce the measured pre-scission neutron multiplicity. From a comparison of the Statistical Model predictions with the measured pre-scission neutron multiplicity, the fission delay is estimated to be of 5+7−3×10−20 s which overlaps with the average duration of fission-like process from the contact to the scission point (2×10−20 s) as determined from HICOL-based dynamical calculations. For the delay time deduced as above, the pre-scission alpha particle multiplicity calculated by the PACE2 code is about a factor two larger than the experimental one, demonstrating the difficulties in modelling the alpha particle emission from highly elongated shapes that characterize the fissioning system from the contact point to scission. 相似文献
64.
Prof. Guido Barone Prof. Aldo La Ginestra 《Journal of Thermal Analysis and Calorimetry》1992,38(12):2563-2563
65.
66.
A novel approach to H-phosphonates from hypophosphorous acid using a transfer hydrogenation process was developed. This method is atom-economical, environmentally friendly, catalytic, and efficient, leading easily to H-phosphonate monoesters or ammonium salt in moderate to good yields. 相似文献
67.
68.
Francesco de Giovanni 《Milan Journal of Mathematics》1991,61(1):257-265
69.
Andrea Lodi Monica Caselli Alessandro Casnati Fabio Momicchioli Francesco Sansone Davide Vanossi Glauco Ponterini 《Journal of Molecular Structure》2007,846(1-3):49-54
The sulfonated calixarene I8C12 acts as a host for homologous merocyanines Mc1 and Mc2 in organic solvents, exhibiting neither selectivity towards the guest dyes nor solvent dependence of the complexation equilibria. In water, on the contrary, only the lower homologue, Mc1, is solubilized in the presence of the calixarene. A combination of UV–visible and fluorescence spectroscopic and photophysical analysis and MD structural simulation of the calixarene-dye complexes was employed to account for the observations, and suggests that a radical change in the complexation mode occurs upon moving from an organic to an aqueous environment. 相似文献
70.
An efficient technique for drag reduction uses dilute solutions of a few p.p.m. of polymers. A possible reduction in drag of up to 80% is achieved. Several experimental observations have been made which tend to indicate that the polymers modify the turbulence structures within the buffer layer. Flow visualisations have shown that the changes consist of a weakening of the strength of the streamwise vortices. Existing literature reveals no attempts of numerical simulation of this phenomenon. In this paper an approach is pursued by using a constitutive equation which relates the elongation viscosity to the local properties of the flow. According to this model this viscosity is large in zones where the amount of strain rate is greater than the amount of vorticity, and is zero when the vorticity exceeds the strain rate. Simulations have been performed in a “minimal channel” to give good resolution with a limited number of grid points. The accuracy of the method is tested by comparison with the results of other techniques. For simulations with polymers, quantitative comparisons cannot be made, but the results reproduce the qualitative outputs of the experiments. The mean streamwise velocity is modified in the buffer layer; the peak of the streamwise turbulent intensity, in wall units, increases and its maximum moves far from the wall; and the vertical turbulent intensity is largely reduced in the wall region. An interesting outcome from both the simulation and the experiments is that the strength of the longitudinal vortices is reduced when the polymers are present. 相似文献