全文获取类型
收费全文 | 405篇 |
免费 | 16篇 |
国内免费 | 6篇 |
专业分类
化学 | 230篇 |
晶体学 | 3篇 |
力学 | 20篇 |
数学 | 70篇 |
物理学 | 104篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 11篇 |
2015年 | 22篇 |
2014年 | 22篇 |
2013年 | 37篇 |
2012年 | 31篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 35篇 |
2008年 | 26篇 |
2007年 | 20篇 |
2006年 | 19篇 |
2005年 | 11篇 |
2004年 | 21篇 |
2003年 | 9篇 |
2002年 | 1篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1972年 | 1篇 |
1967年 | 2篇 |
1939年 | 1篇 |
1935年 | 1篇 |
1934年 | 2篇 |
1933年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有427条查询结果,搜索用时 31 毫秒
241.
We consider a manufacturer producing original products using virgin materials and remanufactured products using returns from the market where the amount of returns depend on the incentive offered by the manufacturer. We determine the optimal value of this incentive and the optimal production quantities in a stochastic demand setting with partial substitution. We analyze 3 different models in centralized and decentralized settings where the collection process of the returns is managed by a collection agency in the decentralized setting. We also analyze contracts to coordinate the decentralized systems and determine the optimal contract parameters. Finally, we present our computational study to observe the effect of different parameters on the system performance. 相似文献
242.
A continuous contact problem of functionally graded layer resting on an elastic semi-infinite plane, which is loaded with through two different blocks is addressed in this study. The elasticity theory and integral transformation techniques are used in solution of the problem. The problem is reduced to a system of singular integral equations, and solved numerically by the aid of appropriate Gauss–Chebyshev integration formula. It is assumed that the elastic semi-infinite homogeneous plane is isotropic and all surfaces are frictionless and continuous. The shear modulus and the mass density of the FG layer vary exponentially along the thickness direction. 相似文献
243.
Savaş Kaya 《Molecular physics》2018,116(13):1677-1681
A new theoretical route employing the concept of chemical hardness has been developed to predict the surface tension γ and the changes of the standard enthalpies (CSEs) of sublimation ΔsH0 of alkali halides. The values of these quantities have been calculated by means of the ratios ηM/V1/3m where ηM and Vm are the molecular hardness and molecular volume, respectively. The obtained results have been compared with those of previous theoretical models as well as with experimental data. 相似文献
244.
U.?B?yük N.?Mara?l? H.?Kaya E.??ad?rl? K.?Ke?lio?lu 《Applied Physics A: Materials Science & Processing》2009,95(3):923-932
Al–Cu–Ag alloy was prepared in a graphite crucible under a vacuum atmosphere. The samples were directionally solidified upwards
under an argon atmosphere with different temperature gradients (G=3.99–8.79 K/mm), at a constant growth rate (V=8.30 μm/s), and with different growth rates (V=1.83–498.25 μm/s), at a constant gradient (G=8.79 K/mm) by using the Bridgman type directional solidification apparatus. The microstructure of Al-12.80-at.%–Cu-18.10-at.%–Ag
alloy seems to be two fibrous and one lamellar structure.
The interlamellar spacings (λ) were measured from transverse sections of the samples. The dependence of interlamellar spacings (λ) on the temperature gradient (G) and the growth rate (V) were determined by using linear regression analysis. According to these results it has been found that the value of λ decreases with the increase of values of G and V. The values of λ
2
V were also determined by using the measured values of λ and V. The experimental results were compared with two-phase growth from binary and ternary eutectic liquid. 相似文献
245.
Engin?Arslan Mustafa?K.?Ozturk ?zgür?Duygulu Ali?Arslan?Kaya Suleyman?Ozcelik Ekmel?Ozbay 《Applied Physics A: Materials Science & Processing》2009,94(1):73-82
In the present paper, the effect of in-situ substrate nitridation time on crystalline quality of GaN films grown on Si (111)
substrates by metal organic chemical vapor deposition (MOCVD) were investigated. A thin buffer layer of silicon nitride (SiN
x
) with various thicknesses was achieved through the nitridation of substrate at different nitiridation times ranging from
0 to 660 s. The structural characteristics, such as dislocation densities, correlation lengths of columnar crystallites, the
tilt and twist of the mosaic structure, and the angles of rotational disorder, were all studied in detail by using a planar
and cross-sectional view of high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (HRXRD) performed
at different scattering geometries. It was found that the dislocation densities, lateral coherence lengths, vertical coherence
lengths, and the tilt and twist of mosaic blocks in GaN films monotonically varies with the nitridation time. The experimental
findings showed that the nitridation times had more influence on edge dislocation densities than the screw type. 相似文献
246.
Kushnirenko A Alkhazov G Atamantchouk AG Balatz MY Bondar NF Cooper PS Dauwe LJ Davidenko GV Dersch U Dolgolenko AG Dzyubenko GB Edelstein R Emediato L Endler AM Engelfried J Eschrich I Escobar CO Evdokimov AV Filimonov IS Garcia FG Gaspero M Giller I Golovtsov VL Gouffon P Gülmez E Kangling H Iori M Jun SY Kaya M Kilmer J Kim VT Kochenda LM Konorov I Kozhevnikov AP Krivshich AG Krüger H Kubantsev MA Kubarovsky VP Kulyavtsev AI Kuropatkin NP Kurshetsov VF Kwan S Lach J Lamberto A Landsberg LG 《Physical review letters》2001,86(23):5243-5246
We report new precision measurements of the lifetimes of the Lambda(+)(c) and D0 from SELEX, the charm hadroproduction experiment at Fermilab. Based upon 1630 Lambda(+)(c) and 10 210 D0 decays we observe lifetimes of tau[Lambda(+)(c)] = 198.1+/-7.0+/-5.6 fs and tau[D0] = 407.9+/-6.0+/-4.3 fs. 相似文献
247.
The resonance Raman profile of the Jahn-Teller coupled vibrations has been investigated in croconate ion, both experimentally and theoretically. A good qualitative agreement between theory and experiment is found for two non-totally symmetric vibrations which are taken into account in the theoretical calculation. 相似文献
248.
Recent observations (Eur. Phys. J. E 9, 135 (2002)) showed that the vitrification process, which sets in during the linear bulk methyl methacrylate (MMA) polymerization carried out below glass transition temperatures, can be modelled by static percolation picture. To generalize this observation for different kind of bulk linear or crosslinked polymers not enough data are present in the literature. To cover partly this deficit we studied the glass transition of MMA and styrene (Sty) crosslinking copolymerization in varying ratios of MMA and Sty. Both the fluorescence intensity I and the lifetime
of pyrene (Py) used as a nanosecond in situ fluoroprobe were monitored during the gelation time. Both I and
increase dramatically as a result of the reduced mobility of the probes trapped in the glassy regions, appearing near the glass transition point. The average size of the glassy regions just below, and the strength of the infinite network formed upon the connection of the glassy regions above the glass transition point
obey power law relations. The data around
were interpreted on the basis of the percolation theory and we observed that the corresponding exponents
and
give static percolation values independent of the polymer composition.Received: 9 July 2004, Published online: 1 October 2004PACS:
64.60.Ak Renormalization-group, fractal, and percolation studies of phase transitions - 64.70.Pf Glass transitions - 82.35.Jk Copolymers, phase transitions, structure 相似文献
249.
A three-dimensional finite-element numerical model is presented for simulation of the steady-state performance characteristics
of heat pipes. The mass, momentum and energy conservation equations are solved for the liquid and vapor flow in the entire
heat pipe domain. The calculated outer wall temperature profiles are in good agreement with the experimental data. The estimations
of the liquid and vapor pressure distributions and velocity profiles are also presented and discussed. It is shown that the
vapor flow field remains nearly symmetrical about the heat pipe centerline, even under a non-uniform heat load. The analytical
method used to predict the heat pipe capillary limit is found to be conservative. 相似文献
250.
Selda Dogan F. Nazlı Dinçer Kaya Orhan Atakol 《International journal of environmental analytical chemistry》2015,95(8):698-712
The behaviour of some Schiff bases in the presence of metal ions is very selective in complex formation. In this study, new, selective and easily prepared adsorbent materials have been developed. Multiwalled carbon nanotubes (MWCNTs) are quite suitable as supporting material for preparation of new solid phase adsorbents modified with Schiff bases due to their selective nature. Different Schiff bases were designed and synthesised as adsorbent agents for Ni(II) and Cu(II) ions, according to the literature, and MWCNTs were modified with these Schiff bases. The modification of CNTs was performed by adsorption from the alcoholic solution of Schiff base. The measurements of Ni(II) and Cu(II) ions were carried out using ICP-MS. Different parameters such as pH, model and eluent solution flow rates, eluent type, amount of ligand, sample volume and effect of foreign ions, which have an effect upon recovery of analytes, were investigated. The obtained results indicated that enrichment can be done with six modified adsorbent materials for Cu(II) at pH 9 and two modified adsorbent materials for Ni(II) at pH 8. It was concluded that four adsorbent materials were selective only for the enrichment of Cu(II). Merely one modified adsorbent material was noneligible for the enrichment of Cu(II) and Ni(II). The solid phase adsorbents prepared by modification with two of the Schiff bases used in this study showed an enrichment factor of 80 for both metal ions, whereas the solid phase adsorbents prepared by modification with four of the Schiff bases showed an enrichment factor of 40 for Cu(II) ions. The confirmation of the developed method was tested with certified reference materials with satisfactory results. 相似文献