全文获取类型
收费全文 | 489篇 |
免费 | 14篇 |
国内免费 | 6篇 |
专业分类
化学 | 308篇 |
晶体学 | 8篇 |
力学 | 22篇 |
数学 | 63篇 |
物理学 | 108篇 |
出版年
2021年 | 8篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 39篇 |
2012年 | 19篇 |
2011年 | 22篇 |
2010年 | 19篇 |
2009年 | 11篇 |
2008年 | 20篇 |
2007年 | 17篇 |
2006年 | 24篇 |
2005年 | 24篇 |
2004年 | 15篇 |
2003年 | 18篇 |
2002年 | 24篇 |
2001年 | 7篇 |
2000年 | 19篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 8篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1964年 | 3篇 |
1955年 | 2篇 |
1927年 | 2篇 |
1925年 | 2篇 |
排序方式: 共有509条查询结果,搜索用时 15 毫秒
101.
G.F. Diaz Lankenau K. Skonieczny W.L. Whittaker D.S. Wettergreen 《Journal of Terramechanics》2012,49(6):341-348
Bucket-wheels enable planetary rovers to perform lightweight digging operations in support of sustained space exploration. Using an excavation tool whose performance scales well for robots of varying sizes builds confidence in a wide range of future digging missions, much as scaled versions of the rocker-bogie suspension have enabled mobility for Mars rovers of vastly different sizes. Bucket-wheel excavation force increases approximately with the cube of excavation dimensions. The excavation forces were measured for bucket-wheels of different scales at proportionate depths and advance speeds, and these results were compared to predictions by excavation models. Analytical and empirical investigated models exhibit force scaling tendency similar to experiment despite their independent backgrounds. Soil particle motion imaging shows that a curved shear interface is prevalent for the conditions tested. This agrees with literature and allows the application of analytical models. 相似文献
102.
In this study, methanol extracts (MEs) and essential oil (EO) of Angelica purpurascens (Avé-Lall.) Gill obtained from different parts (root, stem, leaf, and seed) were evaluated in terms of antioxidant activity, total phenolics, compositions of phenolic compound, and essential oil with the methods of 2,2-azino-bis(3ethylbenzo-thiazoline-6-sulfonic acid (ABTS•+), 2,2-diphenyl-1-picrylhydrazil (DPPH•) radical scavenging activities, and ferric reducing/antioxidant power (FRAP), the Folin–Ciocalteu, liquid chromatography−tandem mass spectrometry (LC−MS/MS), and gas chromatography-mass spectrometry (GC−MS), respectively. The root extract of A. purpurascens exhibited the highest ABTS•+, DPPH•, and FRAP activities (IC50: 0.05 ± 0.0001 mg/mL, IC50: 0.06 ± 0.002 mg/mL, 821.04 ± 15.96 µM TEAC (Trolox equivalent antioxidant capacity), respectively). Moreover, EO of A. purpurascens root displayed DPPH• scavenging activity (IC50: 2.95 ± 0.084 mg/mL). The root extract had the highest total phenolic content (438.75 ± 16.39 GAE (gallic acid equivalent), µg/mL)). Twenty compounds were identified by LC−MS/MS. The most abundant phenolics were ferulic acid (244.39 ± 15.64 μg/g extract), benzoic acid (138.18 ± 8.84 μg/g extract), oleuropein (78.04 ± 4.99 μg/g extract), and rutin (31.21 ± 2.00 μg/g extract) in seed, stem, root, and leaf extracts, respectively. According to the GC−MS analysis, the major components were determined as α-bisabolol (22.93%), cubebol (14.39%), α-pinene (11.63%), and α-limonene (9.41%) among 29 compounds. Consequently, the MEs and EO of A. purpurascens can be used as a natural antioxidant source. 相似文献
103.
First experimental results on broad‐band, time‐resolved Near Infrared (NIR;here loosely defined as covering from 750 to 1650 nm) passive spectroscopy using a high sensitivity InGaAs detector are reported for the TJ‐II Stellarator. Experimental set‐up is described together with its main characteristics, the most remarkable ones being its enhanced NIR response, broadband spectrum acquisition in a single shot, and time‐resolved measurements with up to 1.8 kHz spectral rate. Prospects for future work and more extended physics studies in this newly open spectral region in TJ‐II are discussed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
104.
L. N. Coelho B. Diaz R. Magalhães-Paniago A. Malachias 《The European physical journal. Special topics》2012,208(1):217-229
In this work we depict schematically the use of resonant (anomalous) X-ray diffraction as a tool to directly probe strain
and composition of self-assembled semiconductor islands. By employing a direct analysis at the Eu L3 edge its composition gradient is quantified for EuTe:SnTe capped islands. Projection maps are proposed to visualize the results,
providing an alternative capability to infer quantum dot properties. A more complex methodology is applied to the study of
InP:GaAs islands, in which complementary anomalous measurements are performed. For this system the number of samples analyzed
allows us to extract the activation energy for Ga adatoms diffusion from the substrate to the islands. 相似文献
105.
Gerardo Diaz 《Heat and Mass Transfer》2010,46(11-12):1335-1344
Liquid desiccant systems have received significant attention as a way to reduce latent loads. Tests of liquid desiccant systems in humid climates have shown significant reductions in energy consumption. As moisture in the air is absorbed at the dehumidifier, the temperature of the liquid desiccant increases due to the addition of heat from the enthalpy of condensation of the water vapor. Thus, the coupled effects of heat and mass transfer are relevant for these applications. A two-dimensional mathematical model of the transient heat and mass transfer for an absorber where a thin film of liquid desiccant flows down its walls and dehumidifies the air in parallel-flow configuration is developed and the dynamics of the modeled system are analyzed. 相似文献
106.
T. Galeano Diaz A. Guiberteau J. M. Ortiz M. D. López F. Salinas 《Chromatographia》2001,53(1-2):40-46
Summary We have used an artificial neural network to optimize the composition of the mobile phase for an isocratic HPLC method for
the analysis of nitrophenol pesticides and related compounds, on the basic of different response functions, and have compared
the results with those obtained by application of response-surface methodology. These studies resulted in the selection the
mobile phase 10:30:15:45 methanol-acetonitrile-tetrahydrofuran-buffer solution (0.1m acetic acid and 0.1m sodium perchlorate); the flow-rate was 1 mL min−1. Under these conditions a chromatogram showing twelve well-resolved peaks was obtained in 14 min. Although the peaks corresponding
to ethylparathion and medinoterb acetate overlapped severely, it was possible, by use, of a diode-array spectrophotometer
for detection, and by combining the absorbance measured at different wavelengths as the signal, to separate the peaks corresponding
to one or other of the compounds. Calibration plots were constructed for the concentration range 2–10 ppm. Detection limits,
calculated by the method of Clayton et al., were approximately 0.32–0.69 ppm. The method has been applied to the analysis
of these compounds in fortified river water samples, after previous preliminary preconcentration by solid-liquid extraction
on a C18 cartridge. 相似文献
107.
Francisco Diaz Camacho Salvador Lopez Morales Ronan Le Lagadec Larissa Alexandrova 《Macromolecular Symposia》2006,242(1):25-33
Polymerizations of n-butyl acrylate (BA), methyl methacrylate (MMA) and styrene (St) were promoted by the Ru(II) cyclometalated complex with labile MeCN ligand in the presence of Al(OiPr)3. The polymerization proceeds via radical mechanism and requires the loss of MeCN ligand. The poor control over the polymerizations can be explained in terms of the traditional ATRP scheme. However, the controllability may be significantly improved by addition of reducing SnCl2. Mechanism of the process is proposed. 相似文献
108.
We investigate the dynamics and control of a nonlinear oscillator that is described mathematically by a Variable Order Differential Equation (VODE). The dynamic problem in question arises from the dynamical analysis of a variable viscoelasticity oscillator. The dynamics of the model and the behavior of the variable order differintegrals are shown in variable phase space for different parameters. Two different controllers are developed for the VODEs under study in order to track an arbitrary reference function. A generalization of the van der Pol equation using the VODE formulation is analyzed under the light of the methods introduced in this work. 相似文献
109.
Franco Cristiani Francesco A. Devillanova Angelo Diaz Francesco Isaia Gaetano Verani 《Heteroatom Chemistry》1990,1(5):363-367
Using a series of N-methylated thiohydantoins as substrates, the donor properties of the sulfur atom are measured by determining the stability constants (K) of their adducts with molecular iodine. The K's have been determined by recording the UV-visible spectra of several CH2Cl2 solutions with different amounts of the reagents. The experimental data fit the 1:1 adduct model for all the compounds. The K values, compared with those previously found for the unsubstituted hydantoins and with those obtained for 5-methyl-2-thiohydantoin, show that the hydrogen-bonding interaction between the NH hydrogen and the S-bonded iodine plays an important role in determining the stability of the adduct. The K values obtained for several pentaatomic rings, all containing the thioureido group HN C() NH , are discussed on the basis of the influence of the substituents at C-4 and C-5 on the donor properties of the sulfur atom. 相似文献
110.
Pei Su Hang Hu Daisy Unsihuay Di Zhang Dr. Tiziano Dainese Dr. Rosa E. Diaz Jongsu Lee Dr. Don K. Gunaratne Prof. Haiyan Wang Prof. Flavio Maran Prof. Jianguo Mei Prof. Julia Laskin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(20):7785-7790
The design of functional interfaces is central to both fundamental and applied research in materials science and energy technology. We introduce a new, broadly applicable technique for the precisely controlled high-throughput preparation of well-defined interfaces containing polyatomic species ranging from small ions to nanocrystals and large protein complexes. The mass-dispersive deposition of ions onto surfaces is achieved using a rotating-wall mass analyzer, a compact device which enables the separation of ions using low voltages and has a theoretically unlimited mass range. We demonstrate an efficient deposition of singly charged Au144(SC4H9)60 ions (33.7 kDa), which opens up exciting opportunities for the structural characterization of nanocrystals and their assemblies using transmission electron microscopy. Our approach also enables the high-throughput deposition of mass-selected ions from multicomponent mixtures, which is of interest to the controlled preparation of surface gradients and rapid screening of molecules in mixtures for a specific property. 相似文献