全文获取类型
收费全文 | 312篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 244篇 |
晶体学 | 1篇 |
力学 | 10篇 |
数学 | 14篇 |
物理学 | 58篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 26篇 |
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 19篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 9篇 |
2013年 | 28篇 |
2012年 | 19篇 |
2011年 | 30篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 12篇 |
2006年 | 12篇 |
2005年 | 1篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1968年 | 3篇 |
1937年 | 1篇 |
排序方式: 共有327条查询结果,搜索用时 15 毫秒
71.
M. Al-Amin A. A. Islam M. Tofazzal H. Tarafder M. Chanmiya Sheikh M. Ashraful Alam Ennio Zangrando 《Transition Metal Chemistry》2011,36(5):531-537
The condensation of 4-benzyloxybenzaldehyde with S-methyldithiocarbazate (SMDTC) yielded the Schiff base methyl-3-[(4-benzyloxyphenyl)methylene]
dithiocarbazate (HL) that, upon reaction with different metal ions, afforded bis-chelated complexes, ML2 [where M=Ni(II), Cu(II), Zn(II), Cd(II) or Pd(II)]. The ligand and all the metal complexes were characterized by physico-chemical
and spectroscopic methods. The Schiff base and its bis-chelated Ni(II) complex were characterized also by single crystal X-ray
analyses. The crystallographic results show that the Schiff base exists in thione tautomeric form with the dithiocarbazate
fragment adopting an EE configuration with respect to the C=N bond of the group. In the NiL2 complex, the metal is chelated by two mononegatively charged Schiff bases coordinating via the β-nitrogen and thiolate sulfur anion, generated in situ during the complexation process, and adopts a distorted square planar
geometry. 相似文献
72.
A systematic study of magnetoelectric composite system (x) CoFe2O4+(1−x) Pb(Mg1/3Nb2/3)0.67Ti0.33O3 with x=0, 0.15, 0.30, 0.45 and 1 was carried out. The lattice strain was calculated using Williamson and Hall equation, which depends on the content of constituent phases in composites. The microstructure was studied using scanning electron microscopy. The ferroelectric transition temperature was independent of the content of individual phases, suggesting that the ferroelectric character is maintained in the composite. Observed P–E and M–H loops indicate that the multiferroic nature of magnetoelectric ceramics is dependent on the content of individual phases. The variation of magnetostriction with dc magnetic field was studied. The maximum magnetoelectric voltage coefficient of 7.2 mV/cm Oe is obtained for the synthesized composites. The magnetoelectric measurements are well explained with magnetostrictive behavior of the magnetic phase. 相似文献
73.
Ebrahim Paimozd Ali Ghasemi Abdolhamid Jafari Hassan Sheikh 《Journal of magnetism and magnetic materials》2008
BaFe12O19 powders with nanocrystalline size were prepared by sol–gel techniques. Nitric, hydrochloric, acetic and stearic acid were used to improve the magnetic properties. Amorphous gels were formed with Fe/Ba molar ratio of 10.5. Then powders were obtained by subsequent heat treatment at 800–1000 °C for 1 h. Barium ferrite powder was also synthesized by solid state reaction at 1210 °C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM) experiments were conducted to evaluate structural properties of the samples. The value of the effective magnetic susceptibility was measured. The results show that the magnetoplumbite structure was formed in all of the powders. The TEM observation showed that the minimum particle size (20 nm) was produced with the stearic acid catalyst. The highest value of the effective magnetic susceptibility was achieved also using stearic acid. 相似文献
74.
In the laser cleaving of brittle materials, using controlled fracture technique, thermal stresses are used to induce the crack and the material is separated along the cutting path by extending the crack. One of the problems in laser cutting of glass with this technique is the cut path deviation at the leading and the trailing edges of the glass sheet. Previous work has shown this deviation to be partly due to the high magnitudes of thermal stresses generated near the edges of the sheet. This paper reports on the experimental results of the effects of glass thickness, laser power and the cutting speed on cut path deviation in diode laser cutting of glass. Finite element modelling of the cutting process has also been used to simulate the transient effects of the moving beam and predict thermal fields and stress distributions. These predictions are validated against the experimental data and are used to explain the process mechanisms. It is shown that an increase in the thickness of the glass sheet for the same power and cutting speed or an increase in the cutting speed with constant power and a given sheet thickness results in smaller cut path deviations at the leading and trailing edges of the glass sheet. 相似文献
75.
Lifetime of levels up to 22+, have been measured in 78Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations.
Calculations further show that 78Kr is highly γ-soft nucleus. The experimental Q
t values coupled with theoretical calculations indicate an oblate shape for 78Kr at low spins and triaxial shape at higher spins 相似文献
76.
77.
B. Jaleh P. Parvin N. Sheikh F. Ziaie M. Haghshenas L. Bozorg 《Radiation Physics and Chemistry》2007,76(11-12):1715-1719
In this work, polycarbonate (PC) film samples were irradiated with 10 MeV electrons at different doses ranging from 25 to 250 kGy. Characterization techniques viz. thermogravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction analysis (XRD) and electron paramagnetic resonance (EPR) were exploited to understand the induced changes in the physico-chemical properties of the polymer. An increase in the decomposition temperature with increasing dose was observed, while the crystallinity remained unchanged as a result of the formation of cross-link bond. EPR technique characterized the stability of the free radicals in the irradiated PC. The result showed that cross-linking process occurs at low absorbed doses, whereas polymer degradation happens at higher doses. 相似文献
78.
The triphenylmethyl (trityl) moiety is frequently used for the protection of alcohols but the mass spectra of such trityl ethers have hitherto escaped scrutiny. It has now been found that triphenylmethyl derivatives of primary alcohols yield abundant molecular ions which permit the determination of the isotopic purity of the parent alcohol. Upon electron impact the triphenyl-methyl entity directs the fragmentation of trityl ethers as demonstrated by a detailed study of n-pentyl trityl ether and its deuterated analogs. Ions formed by migration of phenyl groups were observed in the mass spectra of the trityl ethers investigated as well as in the spectrum of triphenyl-methane itself. 相似文献
79.
Mehrazar Mehrdad Hassankalhori Mahdi Toolabi Mahsa Goli Fereshteh Moghimi Setareh Nadri Hamid Bukhari Syed Nasir Abbas Firoozpour Loghman Foroumadi Alireza 《Molecular diversity》2020,24(4):997-1013
Molecular Diversity - A new series of compounds based on benzodiazepine-1,2,3-triazole were synthesized and evaluated as cholinesterase inhibitors by Ellman’s method. The compounds proved to... 相似文献
80.
The 3 + 1 GRMHD equations for Schwarzschild spacetime in Rindler coordinates with isothermal state of plasma are formulated.
We consider the cases of non-rotating and rotating backgrounds with non-magnetized and magnetized plasmas. For these cases,
the perturbed form of these equations are linearized and Fourier analyzed by introducing plane wave type solutions. The determinant
of these equations in each case leads to two dispersion relations which give value of the wave number k. Using the wave number, we obtain information like phase and group velocities etc. which help to discuss the nature of the
waves and their characteristics. These provide interesting information about the black hole magnetosphere near the horizon.
There are cases of normal and anomalous dispersion. We find a case of normal dispersion of waves when the plasma admits the
properties of Veselago medium. Our results agree with those of Mackay et al. according to which rotation of a black hole is
required for negative phase velocity propagation. 相似文献