全文获取类型
收费全文 | 843篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
化学 | 396篇 |
晶体学 | 25篇 |
力学 | 29篇 |
数学 | 96篇 |
物理学 | 317篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 10篇 |
2017年 | 15篇 |
2016年 | 25篇 |
2015年 | 14篇 |
2014年 | 28篇 |
2013年 | 42篇 |
2012年 | 62篇 |
2011年 | 60篇 |
2010年 | 42篇 |
2009年 | 29篇 |
2008年 | 33篇 |
2007年 | 33篇 |
2006年 | 28篇 |
2005年 | 33篇 |
2004年 | 40篇 |
2003年 | 35篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有863条查询结果,搜索用时 15 毫秒
1.
The dependence of the beam propagation factor (M
2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively
studied. Our investigations show that the M
2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due
to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration
associated with the thermal lens induced by the pump beam. Such dependency of M
2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points. 相似文献
2.
Electron mobility has been calculated in a number of binary II–VI compound semiconductors using a displaced Maxwellian distribution function and taking the various scattering mechanisms into consideration at different lattice temperatures and for various amounts of ionized impurity concentrations. It is observed that the low field mobility values can be expressed by a cubic power relationship with lattice temperature and with ionized impurity concentration using a least mean square fit technique with an accuracy better than 5 per cent. Similarly, the field dependence of mobility can also be expressed as a power series of the applied electric field. It is suggested that these equations can be profitably used for a quick estimation of mobility values as a check on experiments and also as sufficiently accurate formulae for simulation and modelling purposes. 相似文献
3.
Santwana Mukhopadhyay 《Mechanics Research Communications》2004,31(1):81-89
The present work is concerned with the thermally induced vibration in a homogeneous and isotropic unbounded body with a spherical cavity. The Green and Nagdhi model of thermoelasticity without energy dissipation is employed. The closed form solutions for distributions of displacement, temperature and stresses are obtained. The solutions valid in the case of small frequency are deduced and the results are compared with the corresponding results obtained in other generalized thermoelasticity theories. Numerical results applicable to a copper-like material are also presented graphically and the nature of variations of the physical quantities with radial coordinate and with frequency of vibration is analyzed. 相似文献
4.
5.
An efficient and practical one-pot method for the synthesis of novel diversified sugar derived dihydro-quinazolino[4,3-b]quinazolin-8-ones has been reported. Various protected sugar hemiacetals were used to synthesize the hybrid tetracyclic ring system. The one-step reductive transformation of 2-(2-nitrophenyl)-3H-quinazolin-4-one with different sugar hemiacetals furnished the desired tetracyclic product in good yields and with high purity. 相似文献
6.
Shefali Pal Sailendra Nath Poddar Gurucharan Mukherjee 《Transition Metal Chemistry》1994,19(4):449-452
Summary Nickel(II) and palladium(II) complexes of the 1,3-di(o-aminophenylthio) propane (H2L1) and 1,2-di(o-aminophenylthio)xylene (H2L2) ligands have been prepared and characterized. The hydrobromide salt of H2L1 gave a 12 ligand-metal complex of PdII, whereas free H2L1 formed the usual 1:1 species. The reaction of Na2PdCl4 with H2L2 resulted in S,S-dealkylation of the ligand and formation of a mononuclear complex of the corresponding thiol, i.e. 2-aminobenzenethiol. NiCl2, NiBr2 and Ni(ClO4)2 did not react directly with H2L2. NiII is a fairly hard ion and therefore does not coordinate to the soft thioether moiety in H2L2 in the absence of soft anions which symbiotically motivate NiII to act as a soft acceptor. It thus does not react with H2L2 in the presence of hard ions such as Cl–, Br- and ClO
4
–
, but, the in situ reaction of the constituents produced the tetrahedral NiII complex, contrary to earlier reports of similar types of octahedral species. 相似文献
7.
An estimate of error in an approximate wave function for a stationary state is put forward that does not require any information about the exact state. The measure is sensitive and direct. Parameters embedded in a trial wave function can be varied to minimize this error as well, leading to a variational principle. Such a scheme works nicely for bound states and the more so for Siegert states, for which the standard energy minimization principle does not apply. Pilot calculations on the anharmonic oscillator system and the radial Stark effect in the hydrogen atom reveal the worth of the endeavor. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
8.
Kinetics of Bz2O2-initiated polymerization of VAC in pyridine at 60° were investigated. The polymerization was significantly retarded by pyridine. The monomer exponent decreased from 2.5 at a relatively low [Bz2O2] (1.0 × 10?2 M) to 2.0 at [Bz2O2] ? 4.0 × 10?2 M. The observed kinetic features were explained on the basis of degradative chain transfer and copolymerization with pyridine. 相似文献
9.
Gurucharan Mukherjee Sailendra Nath Poddar Kingshuk Choudhury Kamalendu Dey 《Transition Metal Chemistry》1988,13(1):58-63
Summary Iron(III) complexes of a quadridentate N2S2 donor ligand, 1,2-di(o-aminophenylthio)ethane (DAPTE) and its Schiff Base with salicylaldehyde, a hexadentate N2S2O2 donor ligand,viz. 1,2-di(o-salicylaldiminophenylthio)ethane (H2DSALPTE) have been synthesised and characterised.The Schiff base ligand (1 mol) gave a dark green tri-iron(III) [Fe3(DSALPTE)(HDSALPTE)Cl3]Cl2 complex when reacted with anhydrous iron(III) chloride (1 mol). The Mössbauer data of this complex suggest the presence of three iron sites, one of which is octahedral and the other two tetrahedral. On the other hand, Fe(ClO4)3 reacted smoothly with H2DSALPTE in ethanol to give a mononuclear pseudo-octahedral complex in which the ligand functions in a dibasic hexadentate fashion. Mössbauer data suggest the presence of a low-spin-high-spin equilibrium in the solid state. The manganese(III) and cobalt(III) complexes of the Schiff base, H2DSALPTE, are also studied for the sake of comparison with the corresponding iron(III) complex. The N2S2 ligand, however, formed a low-spin pseudo-octahedral iron(III) complex. The complexes have been characterised by elemental analysis, molar conductance values, cryomagnetic data and i.r., electronic and Mössbauer spectral data. 相似文献
10.