全文获取类型
收费全文 | 462篇 |
免费 | 30篇 |
国内免费 | 1篇 |
专业分类
化学 | 314篇 |
力学 | 13篇 |
数学 | 36篇 |
物理学 | 130篇 |
出版年
2024年 | 2篇 |
2023年 | 21篇 |
2022年 | 19篇 |
2021年 | 21篇 |
2020年 | 22篇 |
2019年 | 31篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 22篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 30篇 |
2012年 | 36篇 |
2011年 | 28篇 |
2010年 | 27篇 |
2009年 | 19篇 |
2008年 | 18篇 |
2007年 | 32篇 |
2006年 | 22篇 |
2005年 | 23篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有493条查询结果,搜索用时 15 毫秒
121.
Dr. Sourav Khan Dr. Rayappan Pavul Raj Dr. Laurel George Dr. G. S. Kamali Kannangara Dr. Adriyan Milev Prof. Dr. Upadhyayula V. Varadaraju Prof. Dr. Parasuraman Selvam 《ChemistryOpen》2020,9(1):23-31
The synthesis of morphology-controlled carbon-coated nanostructured LiFePO4 (LFP/Carbon) cathode materials by surfactant-assisted hydrothermal method using block copolymers is reported. The resulting nanocrystalline high surface area materials were coated with carbon and designated as LFP/C123 and LFP/C311. All the materials were systematically characterized by various analytical, spectroscopic and imaging techniques. The reverse structure of the surfactant Pluronic® 31R1 (PPO-PEO-PPO) in comparison to Pluronic® P123 (PEO-PPO-PEO) played a vital role in controlling the particle size and morphology which in turn ameliorate the electrochemical performance in terms of reversible specific capacity (163 mAh g−1 and 140 mAh g−1 at 0.1 C for LFP/C311 and LFP/C123, respectively). In addition, LFP/C311 demonstrated excellent electrochemical performance including lower charge transfer resistance (146.3 Ω) and excellent cycling stability (95 % capacity retention at 1 C after 100 cycles) and high rate capability (163.2 mAh g−1 at 0.1 C; 147.1 mAh g−1 at 1 C). The better performance of the former is attributed to LFP nanoparticles (<50 nm) with a specific spindle-shaped morphology. Further, we have also evaluated the electrode performance with the use of both PVDF and CMC binders employed for the electrode fabrication. 相似文献
122.
We prove that first-passage percolation times across thin cylinders of the form [0, n] × [?h n , h n ] d-1 obey Gaussian central limit theorems as long as h n grows slower than n 1/(d+1). It is an open question as to what is the fastest that h n can grow so that a Gaussian CLT still holds. Under the natural but unproven assumption about existence of fluctuation and transversal exponents, and strict convexity of the limiting shape in the direction of (1, 0, . . . , 0), we prove that in dimensions 2 and 3 the CLT holds all the way up to the height of the unrestricted geodesic. We also provide some numerical evidence in support of the conjecture in dimension 2. 相似文献
123.
Akbar Hossain Milan Skalicky Marian Brestic Sagar Maitra Sukamal Sarkar Zahoor Ahmad Hindu Vemuri Sourav Garai Mousumi Mondal Rajan Bhatt Pardeep Kumar Pradipta Banerjee Saikat Saha Tofazzal Islam Alison M. Laing 《Molecules (Basel, Switzerland)》2021,26(4)
The trace element selenium (Se) is a crucial element for many living organisms, including soil microorganisms, plants and animals, including humans. Generally, in Nature Se is taken up in the living cells of microorganisms, plants, animals and humans in several inorganic forms such as selenate, selenite, elemental Se and selenide. These forms are converted to organic forms by biological process, mostly as the two selenoamino acids selenocysteine (SeCys) and selenomethionine (SeMet). The biological systems of plants, animals and humans can fix these amino acids into Se-containing proteins by a modest replacement of methionine with SeMet. While the form SeCys is usually present in the active site of enzymes, which is essential for catalytic activity. Within human cells, organic forms of Se are significant for the accurate functioning of the immune and reproductive systems, the thyroid and the brain, and to enzyme activity within cells. Humans ingest Se through plant and animal foods rich in the element. The concentration of Se in foodstuffs depends on the presence of available forms of Se in soils and its uptake and accumulation by plants and herbivorous animals. Therefore, improving the availability of Se to plants is, therefore, a potential pathway to overcoming human Se deficiencies. Among these prospective pathways, the Se-biofortification of plants has already been established as a pioneering approach for producing Se-enriched agricultural products. To achieve this desirable aim of Se-biofortification, molecular breeding and genetic engineering in combination with novel agronomic and edaphic management approaches should be combined. This current review summarizes the roles, responses, prospects and mechanisms of Se in human nutrition. It also elaborates how biofortification is a plausible approach to resolving Se-deficiency in humans and other animals. 相似文献
124.
Chandana Rath Sonal Singh P. Mallick D. Pandey N. P. Lalla N. C. Mishra 《Indian Journal of Physics》2009,83(4):415-421
Ferromagentic semiconductors have been actively pursued because of their potential as spin polarized carrier sources and easy
integration into semiconductor technology. One such material, ZnO has been shown to be a potential Diluted Magnetic Semiconductor
(DMS). The appearance of ferromagnetism, however, is found to be sensitive to the processing conditions. We report synthesis
of ZnO nanoparticles of size ∼20 nm by a simple co-precipitation technique using metal nitrates and NaOH as precipitant. The
particles are self-organised and reveal single crystalline behaviour in electron diffraction pattern. Incorporation of Co
in ZnO matrix leads not only to the reduction in crystallite size but also to the modification of the structure. At 5% Co,
the particles are highly textured. The particles also aggregate and the aggregated mass have nearly rectangular shape as seen
through TEM. Increasing Co to 10%, results into further reduction of particle size and the particles self organize in a line,
which looks like nanofibers. This alignment of particles increases by increasing the Co content further. This type of growth
of nanofibers above Co ≥ 10% is well correlated with the anisotropic peak broadening observed in the XRD spectra. In addition,
Co substitute Zn site up to 20% without showing any extra phase in XRD spectra as compared to 7 to 10% in case of bulk. Transport
and magnetic studies indicate that conductivity increases with increasing Co content, but carrier mediated ferromagnetism
is absent down to 10 K.
相似文献
125.
For the 1D fully asymmetric exclusion model with open boundary conditions, we calculate exactly the fluctuations of the current of particles. The method used is an extension of a matrix technique developed recently to describe the equatime steady-state properties for open boundary conditions and the diffusion constant for particles on a ring. We show how the fluctuations of the current are related to non-equal-time correlations. In the thermodynamic limit, our results agree with recent results of Ferrari and Fontes obtained by working directly in the infinite system. We also show that the fluctuations of the current become singular when the system undergoes a phase transition with discontinuities along the first-order transition line. 相似文献
126.
A central limit theorem is proved for the free energy of the random field Ising model with all plus or all minus boundary condition, at any temperature (including zero temperature) and any dimension. This solves a problem posed by Wehr and Aizenman (J Stat Phys 60:287–306, 1990). The proof uses a variant of Stein’s method.
相似文献127.
P. Mallick Chandana Rath J. K. Dash R. Biswal D. C. Agarwal D. Behera D. K. Avasthi D. Kanjilal P. V. Satyam N. C. Mishra 《Indian Journal of Physics》2010,84(10):1399-1404
NiO thin films grown on Si(100) substrates by electron beam evaporation, were sintered at 500 °C and 700 °C. The films were
irradiated with 120 MeV Au9+ ions. Irradiation had different effects depending upon the initial microstructure of the films. Irradiation of the films
at a fluence of 3 × 1011 ions cm−2 leads to grain growth for the films sintered at 500 °C and grain fragmentation for the films sintered at 700 °C. At still
higher fluences of irradiation, grain size in 500 °C sintered film decreased, but the same improved in 700 °C sintered film.
Associated with the grain size, texturing of the films was also shown to undergo significant modifications under irradiation. 相似文献
128.
We describe how the thermal counterpart of a vacuum two-point function may be obtained in the real time formalism in a simple
way by using directly the 2×2 matrices that different elements acquire in this formalism. Using this procedure we calculate
the analytic (single component) thermal amplitude for the pion pole term in the ensemble average of two axial-vector currents
to two loops in chiral perturbation theory. The general expressions obtained for the effective mass and the decay constants
of the pion are evaluated in the chiral and the non-relativistic limits.
PACS 11.10.Wx; 12.38.Mh; 12.39.Fe 相似文献
129.
Tandra?Das Biplab?K.?Bera Subhasis?Mallick Parnajyoti?Karmakar Arup?Mandal Subala?Mondal Gauri?S.?De Alak?K.?Ghosh 《Transition Metal Chemistry》2010,35(7):885-890
The interaction of thiosemicarbazide with the title complex has been studied spectrophotometrically in aqueous medium as a
function of [complex], [thiosemicarbazide], pH and temperature at constant ionic strength. At pH 7.4, the reaction shows two
distinct paths; both of which are [thiosemicarbazide] dependent. A parallel reaction scheme fits well with the experimental
findings. An associative interchange mechanism is proposed for both the paths; the activation parameters calculated from Eyring
plots are ΔH1≠ = 14.2 ± 0.8 kJ mol−1, ΔS1≠ = −241 ± 2 JK−1 mol−1, ΔH2≠ = 30.8 ± 1.4 kJ mol−1 and ΔS2≠ = −236 ± 4 JK−1 mol−1. From the temperature dependence of the outer sphere association complex equilibrium constants, the thermodynamic parameters
calculated are ΔH1° = 34.25 ± 1.9 kJ mol−1, ΔS1° = 146 ± 6 J K−1 mol−1 and ΔH2° = 9.4 ± 1.1 kJ mol−1, ΔS2° = 71 ± 3 JK−1 mol−1, which gives a negative ΔG° at all temperatures studied, supporting the spontaneous formation of an outer sphere association
complex. 相似文献
130.
Mott-Hubbard anti-ferromagnetic insulator, NiO shows p-type semiconducting behaviour due to vacancy at Ni2+ site in its bunsenite structure. We report the modification of structural and magnetic order in NiO on Fe doping. NiO samples
at different Fe concentrations in the range 0 to 5 at.% have been prepared by chemical co-precipitation and post thermal decomposition
method. Both structural and magnetic characterization reveal that with increasing Fe doping concentration, NiO evolves as
a magnetically inhomogeneous state out of the parent homogeneous antiferromagnetic state. In addition, structural inhomogeneity
was also observed with Fe precipitating to γ-Fe2O3 phase, the signature of which could be clearly seen for Fe content beyond 2 at.%. At lower Fe content however, some amount
of Fe occupies lattice and interstitial sites in the NiO matrix and drive the latter to acquire ferromagnetic ordering, which
was evident from a clear hysteresis loop at 300 K.
相似文献