全文获取类型
收费全文 | 692篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 313篇 |
晶体学 | 7篇 |
力学 | 23篇 |
数学 | 58篇 |
物理学 | 299篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 36篇 |
2012年 | 38篇 |
2011年 | 44篇 |
2010年 | 32篇 |
2009年 | 28篇 |
2008年 | 36篇 |
2007年 | 47篇 |
2006年 | 31篇 |
2005年 | 32篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 3篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 14篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1969年 | 4篇 |
排序方式: 共有700条查询结果,搜索用时 15 毫秒
1.
Microwave-induced organic reaction enhancement (‘MORE’) chemistry technique (open vessel; controlled microwave energy to stay below the boiling point of the reaction mixture) was used for the N-formylation of aliphatic and aromatic amines and amino heterocycles with aq formic acid (80%) on a multiple gram scale in a few minutes. 相似文献
2.
A theoretical model of Dewangan, in which the total scattering wave function is approximated by a distorted wave containing
two Coulomb wave functions, is discussed and its relation with the Brauner-Briggs-Klar model for ionization is examined. An
important feature of the theory is that it includes a second Born amplitude naturally and in addition, contains, albeit approximately,
both real and imaginary parts of all higher order Born terms. The theory is applied to study the 1s→2s excitation of hydrogen by electrons in the energy range 54.4 to 400eV. The differential and integral cross sections predicted
by the theory are compared with the results of other theories and experimental data at 54.4eV and a good agreement is found. 相似文献
3.
It is shown how the traditional method of neglecting the energy of acoustic phonons and approximating their distribution by the equipartition law leads to significant errors in the phonon growth rate in a many-valley model semiconductor when the lattice temperature is low. 相似文献
4.
The Gelfand-Zetlin basis is adapted toSU(N)
q
forq a root of unit. Extra parameters are incorporated in the matrix elements of the generators to obtain all the invariants corresponding to the augmented center. A crucial identity is derived and proved, which guarantees the periodicity of the action of the generators. Full periodicity is relaxed by stages, some raising and lowering operators remaining injective while others become nilpotent with corresponding changes in the dimension of the representation. In the extreme case of highest weight representations. all the raising and lowering operators are nilpotent. As an alternative approach an auxiliary algebra giving all the periodic representations is presented. An explicit solution of this system forN=3, while fully equivalent to the G.-Z. basis, turns out to be much simpler. 相似文献
5.
Raj Gandhi Kamales Kar S. Uma Sankar Abhijit Bandyopadhyay Rahul Basu Pijushpani Bhattacharjee Biswajoy Brahmachari Debrupa Chakraborti M. Chaudhury J. Chaudhury Sandhya Choubey E. J. Chun Atri Desmukhya Anindya Datta Gautam Dutta Sukanta Dutta Anjan Giri Sourendu Gupta Srubabati Goswami Namit Mahajan H. S. Mani A. Mukherjee Biswarup Mukhopadhyaya S. N. Nayak M. Randhawa Subhendu Rakshit Asim K. Ray Amitava Raychaudhuri D. P. Roy Probir Roy Suryadeep Roy Shiv Sethi G. Sigl Arunansu Sil N. Nimai Singh Mark Vagins Urjit Yagnik 《Pramana》2003,60(2):405-409
This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in
long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed. 相似文献
6.
In this paper we present a new method for the solution of optimization problems with PDE constraints. It is based on simultaneous pseudo-time stepping for evolution equations. The new method can be viewed as a continuous reduced SQP method in the sense that it uses a preconditioner derived from that method. The reduced Hessian in the preconditioner is approximated by a pseudo-differential operator, whose symbol can be investigated analytically. We apply our method to a boundary control model problem. The new optimization method needs 3.2-times the overall computational effort of the solution of simulation problem alone. 相似文献
7.
Schwinger variational principle has been used to calculate triple differential cross-sections for ionization of hydrogen atoms
by positrons at intermediate and high energies for Ehrhardt type asymmetric geometry. The results agree in general with the
calculations of Brauneret al [8] and with the second Born calculation. 相似文献
8.
Summary We present the preliminary results of a time-dependent simulation, with the Smoothed-Particle Hydrodynamics tecnique, of the
accretion of gas onto Schwartzschild black holes. The flow should exibit a stable shock for the parameters chosen. In the
case of 1D axisymmetric simulations, we find that the predicted inner shock position is unstable. For 2D axisymmetric simulations,
in the light of the first runs, we argue that in this case shocks may be a more common result. 相似文献
9.
R. U. Khan P. Chakrabarti B. B. Pal 《Applied Physics A: Materials Science & Processing》1987,42(4):303-309
Large signal characterisation of double heterostructure DDR Impatt diode has been carried out in the millimeter-wave range considering the MITATT mode of operation. The structure of the device is p+-p2-p1-n1-n2-n+ where impact ionisation and tunneling takes place in the p1-n1 region. In this study we have considered two well-known heterostructures, e.g., InP/GaInAs/InP and InP/InGaAsP/InP and one nonconventional structure GaAs/InP/GaAs. The theoretical results of the performances of these devices as regards of output power, efficiency, and negative conductance revealed that the structures are quite promising as the source of power in the millimeter-wave range. The analysis may be used for other mm wave DDR heterostructure Impatts. 相似文献
10.