全文获取类型
收费全文 | 890篇 |
免费 | 36篇 |
国内免费 | 4篇 |
专业分类
化学 | 590篇 |
晶体学 | 6篇 |
力学 | 20篇 |
数学 | 83篇 |
物理学 | 231篇 |
出版年
2023年 | 2篇 |
2022年 | 24篇 |
2021年 | 31篇 |
2020年 | 15篇 |
2019年 | 19篇 |
2018年 | 21篇 |
2017年 | 15篇 |
2016年 | 32篇 |
2015年 | 32篇 |
2014年 | 35篇 |
2013年 | 55篇 |
2012年 | 53篇 |
2011年 | 70篇 |
2010年 | 56篇 |
2009年 | 49篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 33篇 |
2005年 | 32篇 |
2004年 | 27篇 |
2003年 | 11篇 |
2002年 | 26篇 |
2001年 | 22篇 |
2000年 | 20篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1924年 | 2篇 |
排序方式: 共有930条查询结果,搜索用时 0 毫秒
851.
Jo?o Carlos de Andrade Aline R Coscione Ronei J Poppi Cesar Mello 《Analytical sciences》2008,24(9):1147-1150
An artificial neural network (ANN) calibration model was developed to determine aluminum in the presence of iron in soil extracts, using xylenol orange as chromogenic reagent. The spectral data of synthetic mixtures of Al(3+) and Fe(3+) as well as of the soil extracts, were recorded in the range between 410 and 580 nm. Method validation was carried out using 18 soil extracts. The results gave good linear correlations between the ANN model and the ICP OES measurements for both species. 相似文献
852.
Y. Hama R. P. G. Andrade F. Grassi W. -L. Qian T. Osada C. E. Aguiar T. Kodama 《Physics of Atomic Nuclei》2008,71(9):1558-1564
By using the NeXSPheRIO code, we study the elliptic-flow fluctuations in Au + Au collisions at 200 A GeV. It is shown that, by fixing the parameters of the model to correctly reproduce the charged pseudorapidity and the transverse-momentum
distributions, reasonable agreement of 〈v
2〉 with data is obtained, both as function of pseudorapidity as well as of transverse momentum, for charged particles. Our
results on elliptic-flow fluctuations are in good agreement with the recently measured data on experiments.
The text was submitted by the authors in English. 相似文献
853.
854.
Fragment-based and classical quantitative structure–activity relationships for a series of hydrazides as antituberculosis agents 总被引:1,自引:1,他引:0
Andrade CH Salum Lde B Castilho MS Pasqualoto KF Ferreira EI Andricopulo AD 《Molecular diversity》2008,12(1):47-59
Worldwide, tuberculosis (TB) is the leading cause of death among curable infectious diseases. Multidrug-resistant Mycobacterium tuberculosis is an emerging problem of great importance to public health, and there is an urgent need for new anti-TB drugs. In the present work, classical 2D quantitative structure-activity relationships (QSAR) and hologram QSAR (HQSAR) studies were performed on a training set of 91 isoniazid derivatives. Significant statistical models (classical QSAR, q (2) = 0.68 and r (2) = 0.72; HQSAR, q (2) = 0.63 and r (2) = 0.86) were obtained, indicating their consistency for untested compounds. The models were then used to evaluate an external test set containing 24 compounds which were not included in the training set, and the predicted values were in good agreement with the experimental results (HQSAR, [Formula: see text] ; classical QSAR, [Formula: see text]). 相似文献
855.
Andrade LH Lima SM Novatski A Udo PT Astrath NG Medina AN Bento AC Baesso ML Guyot Y Boulon G 《Physical review letters》2008,100(2):027402
This Letter reports the formation of Ti3+ in OH- free aluminosilicate glass melted under vacuum condition, with a very long lifetime (170 micros) and broad emission band shifted towards the visible region. This lifetime value was attributed to the trapping of the excited electrons by the glass defects and detrapping by thermal energy, and it is 2 orders of magnitude higher than those published for Ti3+ doped materials. Our results suggest that this glass is a promising system to overcome the challenge of extending the spectral range of traditional tunable solid state lasers towards the visible region. 相似文献
856.
L. R. Calixto D. M. Lima R. S. Queiroz A. N. S. Rastelli V. S. Bagnato M. F. Andrade 《Laser Physics》2008,18(11):1365-1369
The purpose of this study was to evaluate the polymerization effectiveness of a composite resin (Z-250) utilizing microhardness testing. In total, 80 samples with thicknesses of 2 and 4 mm were made, which were photoactivated by a conventional halogen light-curing unit, and light-curing units based on LED. The samples were stored in water distilled for 24 h at 37°C. The Vickers microhardness was performed by the MMT-3 microhardness tester. The microhardness means obtained were as follows: G1, 72.88; G2, 69.35; G3, 67.66; G4, 69.71; G5, 70.95; G6, 75.19; G7, 72.96; and G8, 71.62. The data were submitted to an analysis of variance (ANOVA’s test), adopting a significance level of 5%. The results showed that, in general, there were no statistical differences between the halogen and LED light-curing units used with the same parameters. 相似文献
857.
Leida M. Pretto Mateus Mittersteiner Valquiria P. Andrade Helio G. Bonacorso Marcos A.P. Martins Nilo Zanatta 《Tetrahedron letters》2019,60(52):151336
The synthetic versatility of ethyl 2-(2-ethoxy-3,4-dihydro-2H-pyran-5-yl)-2-oxoacetate for the synthesis of ethyl 2-oxo-2-(1-alkyl/aryl-6-(amino/ethoxy)-1,4,5,6-tetrahydropyridin-3-yl)acetates, from the reaction with primary amines, is presented. The methodology proposed herein is highly chemoselective, and twenty products were obtained in moderate to good yields (up to 87%). 相似文献
858.
Summary The complex intraparticle structure typical of chromatographic column packings has been analyzed by use of an equivalent network
model which emphasizes pore size distribution and connectivity. Special attention is given as to the way in which diffusion
and adsorption interact and display modified peak spreading characteristics according to the morphology of the pore space.
This study reveals a very significant increase in the column band broadening over that expected from physical adsorption which
can arise from particular distributions of pore sizes. This has implications for designing packings which take advantage of
the separating power due to adsorption but do not compromise the resolution of the chromatographic system. 相似文献
859.
L. C. Garcia de Andrade 《International Journal of Theoretical Physics》1991,30(2):235-238
A Ricci recurrent space-time with covariantly constant stress tensor is an Einstein space-time. We extend this result to Ricci recurrent space-times with torsion. The result is applied to the case of Riemann-Cartan space-times with spin density. 相似文献
860.
Andrade Plácido do Socorro Pereira Maria 《Bulletin of the Brazilian Mathematical Society》1990,21(1):79-89
We show that the cohomology groupH
1 (M, f) is an infinite dimensional vector space, for a dense set of one dimensional foliations on a closed manifold. In particular we compute this cohomology, for some foliations on the torus T2. 相似文献