全文获取类型
收费全文 | 406篇 |
免费 | 25篇 |
专业分类
化学 | 272篇 |
晶体学 | 7篇 |
力学 | 10篇 |
数学 | 23篇 |
物理学 | 119篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 27篇 |
2015年 | 18篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 39篇 |
2011年 | 26篇 |
2010年 | 31篇 |
2009年 | 18篇 |
2008年 | 22篇 |
2007年 | 18篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有431条查询结果,搜索用时 15 毫秒
31.
Expedient Protocols for the Installation of 1,5‐Benzoazepino‐Based Privileged Templates on the 2‐Position of 1,4‐Benzodiazepine Through a Phenoxyl Spacer
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An efficient novel strategy for the hetero‐annulation of 2‐chloro‐1,4‐benzodiazepine ring, substituted on its 5‐position with a carboxamido group ( 5 ), has been developed to allow the incorporation of 1,5‐benzodiazepine, 1,5‐benzothiazepine, and 1,5‐benzoxazepine ( 8 , 9 , 10 , 11 , 12 , 13 ) rings through their dimethylaminomethylene ketone intermediate ( 7 ). 相似文献
32.
Ratnasekhar ChMohit Tyagi Premanand Ramrao PatilK.P. Ravindranathan Kartha 《Tetrahedron letters》2011,52(44):5841-5846
A simple, mild and efficient solvent-free method for the acetylation of carbohydrates, and their partially protected derivatives, as well as non-carbohydrate substances in excellent yields in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) is described with the advantage of tolerance to various functional groups, short reaction time and ease of product isolation. 相似文献
33.
Sayed FN Grover V Dubey KA Sudarsan V Tyagi AK 《Journal of colloid and interface science》2011,353(2):445-453
A series of doped CeF(3): RE(3+) (RE(3+): Tb(3+), Eu(3+) and Dy(3+)) nanoparticles were synthesized, with the aim of obtaining a white light emitting composition, by a simple polyol route at 160°C and characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR) and photoluminescence. Uniformly distributed and highly water-dispersible rectangular nanoparticles (length ~15-20 nm, breadth ~5-10 nm) were obtained. The steady state and time resolved luminescence studies confirmed efficient energy transfer from the host to activator ions. Lifetime studies revealed that optimum luminescence is observed for 2.5 mol% Dy(3+) and 7.5 mol% Tb(3+). The energy transfer efficiencies (Ce(3+) to activators) were found to be 89% for CeF(3): Tb(3+) (7.5 mol%) nanoparticles and 60% for CeF(3): Dy(3+) (2.5 mol%) nanoparticles. Different concentrations of Tb(3+), Eu(3+) and Dy(3+) were doped to achieve a white light emitting phosphor for UV-based LEDs (light emitting diodes). Finally CeF(3), triply doped with 2.0 mol%Tb(3+), 4.5 mol% Eu(3+) and 3.5 mol% Dy(3+), was found to have impressive chromaticity co-ordinates, close to broad day light. The colloidal solutions of doped CeF(3) nanoparticles emitted bright green (Tb(3+)), blue (Dy(3+)) and white (triply doped) luminescence upon host excitation. Composites of poly methyl methacrylate (PMMA) and poly vinyl alcohol (PVA) were made with CeF(3): 5.0 mol%Tb(3+), CeF(3): 5.0 mol% Dy(3+) and triply doped white light emitting composition. The CeF(3)/PMMA (PVA) nanocomposite films, so obtained, are highly transparent (in the visible spectral range) and exhibit strong photoluminescence upon UV excitation. 相似文献
34.
ABSTRACT The mixed metal fluorides containing alkali metals have a range of important applications in optical and electronic devices. Raman spectrums of two such fluorides were examined. Raman spectrum of KCuF3 at 300 K exhibited bands at 261, 295, 363, 468, 519, and 549 cm?1, indicating site symmetry (orthorhombic) lower than the tetragonal symmetry as observed from the powder X-ray diffraction pattern. Cubic KNiF3 showed bands at 410, 468, and 657 cm?1. The first two bands were attributed to the second-order phonon scattering, and the band at 657 cm?1 was assigned to two-magnon peak. 相似文献
35.
36.
Influence of ultrasonication and Fenton oxidation pre-treatment on rheological characteristics of wastewater sludge 总被引:1,自引:0,他引:1
The effect of ultrasonication and Fenton oxidation as physico-chemical pre-treatment processes on the change of rheology of wastewater sludge was investigated in this study. Pre-treated and raw sludges displayed non-Newtonian rheological behaviour with shear thinning as well as thixotropic properties for total solids ranging from 10 g/L to 40 g/L. The rheological models, namely, Bingham plastic, Casson law, NCA/CMA Casson, IPC Paste, and power law were also studied to characterize flow of raw and pre-treated sludges. Among all rheological models, the power law was more prominent in describing the rheology of the sludges. Pre-treatment processes resulted in a decrease in pseudoplasticity of sludge due to the decrease in consistency index K varying from 42.4 to 1188, 25.6 to 620.4 and 52.5 to 317.9; and increase in flow behaviour index n changing from 0.5 to 0.35, 0.62 to 0.55 and 0.63 to 0.58, for RS, UlS and FS, respectively at solids concentration 10–40 g/L. The correlation between improvement of biodegradability and dewaterability, decrease in viscosity, and change in particle size as a function of sludge pre-treatment process was also investigated. Fenton oxidation facilitated sludge filterability resulting in capillary suction time values which were approximately 50% of the raw sludges, whereas ultrasonication with high input energy deteriorated the filterability. Biodegradability was also enhanced by the pre-treatment processes and the maximum value was obtained (64%, 77% and 73% for raw, ultrasonicated and Fenton oxidized sludges, respectively) at total solids concentration of 25 g/L. Hence, pre-treatment of wastewater sludge modified the rheological properties so that: (1) the flowability of sludge was improved for transport through the treatment train (via pipes and pumps); (2) the dewaterability of wastewater sludge was enhanced for eventual disposal and; (3) the assimilation of nutrients by microorganisms for further value-addition was increased. 相似文献
37.
Tyagi B Chudasama CD Jasra RV 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,64(2):273-278
The structural modifications and the Bronsted acid sites generated during the acid treatment of montmorillonite clay with varied concentration of sulphuric acid was determined using FT-IR spectroscopy. Octahedral sheet is affected at low acid concentration resulting into the dissolution of cations; among them Mg2+ cations are prone to dissolve than Fe2+/3+ and Al3+. Tetrahedral sheet is affected at higher acid concentration. The partial substitution of octahedral Al3+ by Mg2+ or Fe2+/3+ cations and the presence of other non-smectite minerals such as kaolinites was also been clearly identified, thus making FT-IR spectroscopy as a rapid technique for monitoring the structural features of montmorillonite clay. 相似文献
38.
Bianchi Type-V Magnetized String Cosmological Model with Variable Magnetic Permeability for Viscous Fluid distribution
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigate the Bianchi type-V magnetized string cosmological model with variable magnetic permeability for viscous fluid distribution. The magnetic field is due to an electric current produced along the x-axis. Thus the magnetic field is in yz-plane and F23 is the only non-vanishing component of electromagnetic field tensor Fij. To obtain the deterministic model in terms of cosmic time t, we assume the condition ξθ const where ξ is the coefficient of bulk viscosity and θ the expansion in the model. 相似文献
39.
Deepika K. S. Rathore N. S. Saxena 《Applied Physics A: Materials Science & Processing》2010,98(2):441-448
Se58Ge42−x
Pb
x
(9≤x≤20) glasses have been prepared using conventional melt quenching technique. Differential Scanning Calorimetric (DSC) measurements
show single glass transition and double crystallization, which indicate the occurrence of phase separation in the samples.
The phases present in the samples were identified using XRD. The kinetics of the glass transition has been studied in terms
of the variation of glass transition temperature with composition and heating rate. In addition to this, activation energy
of the glass transition (E
t
) has also been evaluated and its composition dependence is also investigated. The thermal stability of these glasses has
been investigated using various stability criteria: Deiztal first glass criterion, ΔT, Saad and Poulain weighted thermal stability, H′ and the S-parameter. The values of these parameters were obtained using various characteristic temperatures such as the glass transition
temperature, T
g
, the onset temperature of crystallization, T
c
, and the peak crystallization temperature, T
p
. The values of stability parameters show that the phase corresponding to second crystallization is more stable than the phase
corresponding to first one. The stability in terms of the lead (Pb) content has been determined considering the values of
stability parameters of the phase corresponding to second peak. It was found that the stability increases with the lead content. 相似文献
40.
Existence of nonnegative solutions for a class of semilinear elliptic systems with indefinite weight
J. Tyagi 《Nonlinear Analysis: Theory, Methods & Applications》2010,73(9):2882-2889
We prove the existence of nonnegative solutions to the system