全文获取类型
收费全文 | 730篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
化学 | 459篇 |
晶体学 | 1篇 |
力学 | 10篇 |
数学 | 46篇 |
物理学 | 231篇 |
出版年
2022年 | 16篇 |
2021年 | 16篇 |
2020年 | 22篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 16篇 |
2015年 | 24篇 |
2014年 | 28篇 |
2013年 | 64篇 |
2012年 | 40篇 |
2011年 | 60篇 |
2010年 | 42篇 |
2009年 | 63篇 |
2008年 | 40篇 |
2007年 | 32篇 |
2006年 | 40篇 |
2005年 | 20篇 |
2004年 | 34篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 2篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有747条查询结果,搜索用时 78 毫秒
81.
H.-D. Pfannes D. S. Vieira Junior R. Paniago J. H. Dias Filho 《Hyperfine Interactions》2005,165(1-4):247-252
The formation of local moments and the effect of charge carrriers in dilute magnetic semiconductors can be well understood using local probe techniques like Mossbauer Spectroscopy. We report here on Mossbauer studies in the systems Fe0.008Ge1 ? x D x (D = As, Bi), Fe0.008Ge1 ? x In x , and Fe0.008Ge1 ? x Sn x . At room temperature magnetic interactions were observed for donor (D) impurities at the Fe site in the Fe0.008Ge system. No such magnetic ordering was observed for acceptor (In) or neutral (Sn) impurities. 相似文献
82.
The first author was supported in part by CNPq 相似文献
83.
A Novel Alkaloid from Aspidosperma pyricollum (Apocynaceae) and Complete 1H and 13C Chemical Shift Assignments
下载免费PDF全文
![点击此处可从《Helvetica chimica acta》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hádria M. do Carmo Raimundo Braz‐Filho Ivo J. Curcino Vieira 《Helvetica chimica acta》2015,98(10):1381-1386
A novel natural product indole, alkaloid, named rel‐pyricolluminol ( 1 ), was isolated from Aspidosperma pyricollum Müll .Arg . together with six known metabolites sitsirikine ( 2 ), aparicin ( 3 ), ulein ( 4 ), stemmadenine ( 5 ), lupeol ( 6 ), and (3β)‐sitoster‐3‐yl β‐D ‐glucopyranoside ( 7 ). These compounds were characterized on the basis of their spectral data, mainly 1D‐ (1H,13C‐DEPTQ) and 2D‐NMR (1H,1H‐COSY, NOESY, HSQC, and HMBC), and mass spectra (EI‐MS and HR‐ES‐MS), involving also comparison with data from the literature. 相似文献
84.
We present a form of the Mean Value Theorem (MVT) for a continuous function f between metric spaces, connecting it with the possibility to choose the relation of f in a homeomorphic way. We also compare our formulation of the MVT with the classic one when the metric spaces are open subsets of Banach spaces. As a consequence, we derive a version of the Mean Value Propriety for measure spaces that also possesses a compatible metric structure. 相似文献
85.
Thayana da C. Alves Mariele R. S. Gonçalves Francyne C. S. Correia Virgínia C. da Silva Paulo T. de Sousa Jr. Mário G. de Carvalho Raimundo Braz‐Filho Evandro L. Dall'Oglio 《Helvetica chimica acta》2014,97(11):1469-1474
From the hexane and MeOH extracts of Annona coriacea Mart . (Annonaceae) seeds, two novel acetogenins, coriapentocins A and B ( 1 and 2 , resp.) were isolated. The known acetogenin bullacin ( 3 ) was also isolated from the hexane extract. The structures of compounds 1 – 3 were elucidated by NMR and MS analysis, and relative configurations were established by comparison with literature data. 相似文献
86.
G.D. Saraiva J.A. Lima Jr.F.F. de Sousa P.T.C. FreireJ. Mendes Filho A.G. Souza Filho 《Vibrational Spectroscopy》2011,55(1):101-106
Temperature dependent Raman study of l-ascorbic acid has been performed from 15 to 418 K. Changes in the wavenumber vs. temperature plots for some internal modes were interpreted as conformational molecular change and the discontinuity in the wavenumber vs. temperature plots along with the appearance of a new vibrational mode in the temperature range 200-270 K suggests that l-ascorbic acid undergoes a structural phase transition. For temperatures higher than 300 K, no relevant modification was observed on the Raman spectra thus indicating a stable structure at high temperatures. Additionally, a correlation between OH stretching wavenumber and the behavior of hydrogen bond is also made. 相似文献
87.
Laura L. G. Fuentes Sarita C. Rabelo Rubens Maciel Filho Aline C. Costa 《Applied biochemistry and biotechnology》2011,163(5):612-625
The objective of this work was to determine the optimum conditions of sugarcane bagasse pretreatment with lime to increase
the enzymatic hydrolysis of the polysaccharide component and to study the delignification kinetics. The first stage was an
evaluation of the influence of temperature, reaction time, and lime concentration in the pretreatment performance measured
as glucose release after hydrolysis using a 23 central composite design and response surface methodology. The maximum glucose yield was 228.45 mg/g raw biomass, corresponding
to 409.9 mg/g raw biomass of total reducing sugars, with the pretreatment performed at 90°C, for 90 h, and with a lime loading
of 0.4 g/g dry biomass. The enzymes loading was 5.0 FPU/dry pretreated biomass of cellulase and 1.0 CBU/dry pretreated biomass
of β-glucosidase. Kinetic data of the pretreatment were evaluated at different temperatures (60°C, 70°C, 80°C, and 90°C),
and a kinetic model for bagasse delignification with lime as a function of temperature was determined. Bagasse composition
(cellulose, hemicellulose, and lignin) was measured, and the study has shown that 50% of the original material was solubilized,
lignin and hemicellulose were selectively removed, but cellulose was not affected by lime pretreatment in mild temperatures
(60–90°C). The delignification was highly dependent on temperature and duration of pretreatment. 相似文献
88.
Izumi E Ueda-Nakamura T Dias Filho BP Veiga Júnior VF Nakamura CV 《Natural product reports》2011,28(4):809-823
Here, we review studies that have investigated the activity of plant-derived compounds against Trypanosoma cruzi, the etiologic agent of Chagas’ disease. In the last decade, more than 300 species belonging to almost 100 families have been evaluated for activity, and here we describe the compounds isolated; 85 references are cited. 相似文献
89.
Milton C. Lopes Filho Evelyne Miot Helena J. Nussenzveig Lopes 《Journal of Nonlinear Science》2011,21(5):685-703
The vortex-wave system is a coupling of the two-dimensional vorticity equation with the point-vortex system. It is a model
for the motion of a finite number of concentrated vortices moving in a distributed vorticity background. In this article,
we prove existence of a weak solution to this system with an initial background vorticity in L
p
, p>2, up to the time of first collision of point vortices. 相似文献
90.
Ccallata HJ Tomaz Filho L Watanabe S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(4):1272-1277
Natural silicate mineral of zoisite, Ca(2)Al(3)(SiO(4))(Si(2)O(7))O(OH), has been investigated concerning γ-radiation, UV-radiation and high temperature annealing effects on thermoluminescence (TL). X-ray diffraction (XRD) measurement confirmed zoisite structure and X-ray fluorescence (XRF) analysis revealed besides Si, Al and Ca that are the main crystal components, other oxides of Fe, Mg, Cr, Na, K, Sr, Ti, Ba and Mn which are present in more than 0.05 wt%. The TL glow curve of natural sample contains (130-150), (340-370) and (435-475)°C peaks. Their shapes indicated a possibility that they are result of composition of two or more peaks strongly superposed, a fact confirmed by deconvolution method. Once pre-annealed at 600°C for 1h, the shape of the glow curves change and the zoisite acquires high sensitivity. Several peaks between 100 and 400°C appear superposed, and the high temperature peak around 435°C cannot be seen. The ultraviolet radiation, on the other hand, produces one TL peak around 130°C and the second one around 200°C and no more. 相似文献