全文获取类型
收费全文 | 480篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
化学 | 327篇 |
晶体学 | 7篇 |
力学 | 23篇 |
数学 | 22篇 |
物理学 | 124篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 21篇 |
2014年 | 12篇 |
2013年 | 27篇 |
2012年 | 22篇 |
2011年 | 33篇 |
2010年 | 18篇 |
2009年 | 16篇 |
2008年 | 39篇 |
2007年 | 28篇 |
2006年 | 24篇 |
2005年 | 17篇 |
2004年 | 18篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1913年 | 1篇 |
排序方式: 共有503条查询结果,搜索用时 31 毫秒
161.
162.
J. Dweck R. S. Leonardo M. L. M. Valle 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1317-1325
Efficiencies of four commercial antioxidants used during the storage of two biodiesel, BS-ethyl and BS-methyl, respectively obtained from soybean oil by ethylic and methylic routes, were evaluated by measuring their oxidative stability using a low pressurized DSC (low P-DSC) method developed by the authors and by Rancimat method, which is specified by the American ASTM D6751 and European EN 14214 standard methods. The operating temperature of the low P-DSC method was the same as that used in the Rancimat procedure (110 °C). The antioxidants, used in 500 mg kg?1 content, have the following active components: phenol, biphenol, phenol + amine mixture, and a hydroquinone + organic acid mixture. Samples of each biodiesel–antioxidant mixture were evaluated simultaneously by the two methods, right after their preparation and 30, 60, 90, and 120 days of storage at 23 ± 1 °C. A non-dimensional oxidative induction time parameter, defined as the ratio between the oxidation induction time (OIT) or induction time (IT) values at a storage time t and at t = 0, was used to evaluate the antioxidant activity. For the same mixture, changes of this non-dimensional parameter calculated from OIT or IT show a similar trend with storage time, indicating that it can be determined either from low P-DSC or Rancimat method data. As the efficiency of the studied antioxidants depends on their composition, their interaction with each biodiesel, and on the storage time, this parameter can be used to indicate the best storage time for each antioxidant–biodiesel mixture. 相似文献
163.
A. Rodríguez-López A. Reyes-Del Valle J. M. Juárez-García M. Monroy-Mendoza M. J. Ávila-Salas J. L. Ortíz-Aparicio R. Antaño-López 《Accreditation and quality assurance》2013,18(5):383-389
Linear voltammetry and electrochemical impedance spectroscopy experiments were performed in order to obtain basic information about the electrochemical behavior of the primary cell of electrolytic conductivity at Centro Nacional de Metrología. Linear voltammetry shows that the amplitude of the sinusoidal perturbation must be smaller than 300 mV. Electrochemical impedance results indicate that optimal frequency interval extends from 5 to 0.6 kHz. Regarding sinusoidal signal amplitude, a lower bias with respect to electrolytic conductivity of an independent reference solution is obtained at 10 mV than at larger amplitudes; in addition, electrode integrity is improved. 相似文献
164.
A comparison of four protocols for the immobilization of an aptamer on graphite composite electrodes
We have performed a comparative study on four protocols for the immobilization of the thrombin aptamer on a graphite-epoxy composite electrode with the aim to identify the most practical method for designing the corresponding impedimetric aptasensor. The protocols included (a) physical adsorption, (b) avidin-biotin affinity interaction, (c) electrochemical activation and covalent bonding via amide groups, and (d) electrochemical grafting using 4-carboxybenzenediazonium coupling. The properties of the sensing surface were probed by electrochemical impedance measurements in the presence of the (ferri/ferro)hexacyanide redox couple. An increase in the interfacial charge transfer resistance (Rct) was noted in all cases after the aptamer-thrombin interaction had occurred. The selectivity of the aptasensor over common serum proteins was also systematically investigated. Physical adsorption resulted in the lowest detection limit of the probe (4.5 pM), while avidin-biotin interaction resulted in highest selectivity and reproducibility exhibiting a 4.9 % relative standard deviation at pM thrombin concentration levels. Figure
The study and comparison of four protocols for the immobilization of a DNA aptamer is reported to detect thrombin onto a graphite-epoxy composite electrode and with use of Electrochemical Impedance spectroscopy as the detection technique. 相似文献
165.
Adare A Afanasiev S Aidala C Ajitanand NN Akiba Y Al-Bataineh H Alexander J Angerami A Aoki K Apadula N Aramaki Y Atomssa ET Averbeck R Awes TC Azmoun B Babintsev V Bai M Baksay G Baksay L Barish KN Bassalleck B Basye AT Bathe S Baublis V Baumann C Bazilevsky A Belikov S Belmont R Bennett R Berdnikov A Berdnikov Y Bhom JH Blau DS Bok JS Boyle K Brooks ML Buesching H Bumazhnov V Bunce G Butsyk S Campbell S Caringi A Chen CH Chi CY Chiu M Choi IJ Choi JB Choudhury RK Christiansen P Chujo T 《Physical review letters》2011,107(17):172301
Back-to-back hadron pair yields in d+Au and p+p collisions at √s(NN)=200 GeV were measured with the PHENIX detector at the Relativistic Heavy Ion Collider. Rapidity separated hadron pairs were detected with the trigger hadron at pseudorapidity |η|<0.35 and the associated hadron at forward rapidity (deuteron direction, 3.0<η<3.8). Pairs were also detected with both hadrons measured at forward rapidity; in this case, the yield of back-to-back hadron pairs in d+Au collisions with small impact parameters is observed to be suppressed by a factor of 10 relative to p+p collisions. The kinematics of these pairs is expected to probe partons in the Au nucleus with a low fraction x of the nucleon momenta, where the gluon densities rise sharply. The observed suppression as a function of nuclear thickness, p(T), and η points to cold nuclear matter effects arising at high parton densities. 相似文献
166.
Giovanni Valle Valerio Peruzzo Giuseppe Tagliavini Paolo Ganis 《Journal of organometallic chemistry》1984,276(3):325-329
The crystal structure analysis of {[(CH3)2SnO2CCH2Cl]2O}2 is reported. The compound consists of dimeric units located on symmetry centers; the dimers are weakly bonded to form rows oriented in the a direction. The two tin atoms of the structural unit have different environments; but the coordination numbers cannot be assigned. 相似文献
167.
168.
J.W.F. Valle 《Physics letters. [Part B]》1985,159(1):49-56
I show how to accomodate the 17 keV state recently reported by Simpson as one of the neutrinos of the standard model. Experimental constraints can only be satisfied if the μ and τ neutrino combine to a very good approximation to form a Dirac neutrino of 17 keV leaving a light νe. Neutrino oscillations will provide the most stringent test of the model. The cosmological bounds are also satisfied in a natural way in models with Goldstone bosons. Explicit examples are given in the framework of majoron-type models. Constraints on the lepton symmetry breaking scale which follow from astrophysics, cosmology and laboratory experiments are discussed. 相似文献
169.
170.
J. W. F. Valle 《International Journal of Theoretical Physics》1979,18(12):923-934
A heuristic construction of Hilbert superspaces using Grassmann numbers is suggested. Simple applications are given which include a coherent-state formalism for Fermi oscillator systems. 相似文献