全文获取类型
收费全文 | 195020篇 |
免费 | 1933篇 |
国内免费 | 615篇 |
专业分类
化学 | 107907篇 |
晶体学 | 3295篇 |
力学 | 7817篇 |
综合类 | 4篇 |
数学 | 18347篇 |
物理学 | 60198篇 |
出版年
2016年 | 2268篇 |
2015年 | 1690篇 |
2014年 | 2404篇 |
2013年 | 7833篇 |
2012年 | 5270篇 |
2011年 | 6612篇 |
2010年 | 4427篇 |
2009年 | 4360篇 |
2008年 | 5992篇 |
2007年 | 6166篇 |
2006年 | 5915篇 |
2005年 | 5419篇 |
2004年 | 4963篇 |
2003年 | 4435篇 |
2002年 | 4317篇 |
2001年 | 5782篇 |
2000年 | 4390篇 |
1999年 | 3512篇 |
1998年 | 2742篇 |
1997年 | 2779篇 |
1996年 | 2726篇 |
1995年 | 2517篇 |
1994年 | 2391篇 |
1993年 | 2284篇 |
1992年 | 2780篇 |
1991年 | 2663篇 |
1990年 | 2612篇 |
1989年 | 2639篇 |
1988年 | 2578篇 |
1987年 | 2584篇 |
1986年 | 2403篇 |
1985年 | 3266篇 |
1984年 | 3282篇 |
1983年 | 2712篇 |
1982年 | 2908篇 |
1981年 | 2845篇 |
1980年 | 2752篇 |
1979年 | 2894篇 |
1978年 | 3138篇 |
1977年 | 2960篇 |
1976年 | 2895篇 |
1975年 | 2755篇 |
1974年 | 2702篇 |
1973年 | 2716篇 |
1972年 | 1760篇 |
1971年 | 1468篇 |
1968年 | 1929篇 |
1967年 | 2129篇 |
1966年 | 1920篇 |
1965年 | 1498篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A kinematically correct treatment of the full transition amplitude for many-body hypernuclear production is presented. By an example of (+, K+) reaction, effects of the spin-flip amplitude and its interference with the spin-non-flip amplitude are demonstrated and specified for
12
C.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.The discussions with many colleagues are appreciated, in particular those with R. Mach, L. Majling and T. Motoba were of much use. 相似文献
992.
Considering a system ofN identical interacting particles, which obey Fermi-Dirac or Bose-Einstein statistics, we derive new formulas for correlation functions of the type
(whereB
j is diagonal in the free-particle states) in the thermodynamic limit. Thereby we apply and extend a superoperator formalism, recently developed for the derivation of long-time tails in semiclassical systems. As an illustrative application, the Boltzmann equation value of the time-integrated correlation functionC(t) is derived in a straightforward manner. Due to exchange effects, the obtained t-matrix and the resulting scattering cross section, which occurs in the Boltzmann collision operator, are now functionals of the Fermi-Dirac or Bose-Einstein distribution. 相似文献
993.
We calculate the moments t
q
, whereq is not necessarily an integer, of the first passage time to trapping for a simple diffusion problem in one dimension. If a characteristic length of the system isL and t
q
~L
(q) asL, then we show that there is a phase transition atq=q
c
such that whenq<q
c
,(g)=0, and forq>q
c
, (q) is a linear function ofq. These analytical results can be used to explain results for large moments for diffusion on a hierarchic structure. We also show how to calculate noninteger moments in terms of characteristic functions. 相似文献
994.
Büttiker and Landauer studied scattering off an oscillating rectangular barrier in order to shed light on the time aspects of tunneling. The expression for the traversal time resulting from this study is controversial. In addition, doubts have recently been expressed on technical aspects of their work. In an attempt to clarify these issues, we investigate a generalization of their model to arbitrary oscillating barriers,V(x, t)=V
0(x)+V
1(x)cos t. In the process, we confirm that Büttiker and Landauer's work is technically sound. However, we show, by several examples, that no direct general relation exists between the characteristic frequency of an oscillating barrier and the duration of the tunneling process. For a wide range of realistic parameters this characteristic frequency does not even exist.This paper is dedicated to E. G. D. Cohen. 相似文献
995.
996.
997.
998.
A. Barhdadi H. Amzil J. C. Muller P. Siffert 《Applied Physics A: Materials Science & Processing》1989,49(3):233-237
We have studied the influence of conventional and rapid thermal treatments at 850°C for 30 min and 10 s, respectively, on the recombination activity of the9,13 (P-type) and25 (N-type) grain boundaries in silicon. The analyses were made by scanning electron microscopy (SEM) working in the electron beam induced current mode (EBIC) and completed by minority carrier diffusion length measurements. The main result obtained from this study shows the importance of the rapid thermal process as a suitable thermal treatment for polycrystalline materials. 相似文献
999.
D. Mauri D. Scholl H. C. Siegmann E. Kay 《Applied Physics A: Materials Science & Processing》1989,49(5):439-447
The spin polarizationP of the low energy cascade electrons excited with a primary unpolarized electron beam is measured with ultrathin films of permalloy (Ni80Fe20) as a function of film thickness, external magnetic field, and temperatureT. Surface adsorbates of small concentrations of less than 10% of a monolayer can change the Curie point and the saturation value ofP
0(T0) by as much as 30%. The Ta-substrate induces a magnetically dead region in permalloy. Conventional spin wave theory cannot account for the observed smallT-dependence of the magnetizationM. Films on a nonmagnetic substrate are compared to similar films coupled to bulk permalloy over an interface of Ta. TheT-dependence ofM with the coupled films can be explained by spin wave theory. At lowT, the films coupled to the bulk exhibit a faster decrease ofM than the uncoupled films. We propose that this thermal stabilization of the magnetization in very thin ferromagnetic films is due to quenching of the long wavelength spin modes. 相似文献
1000.
F. El Akkad H. F. Ragaie M. Abdel Naby 《Applied Physics A: Materials Science & Processing》1989,48(5):493-495
Zn
x
Cd1–x
S thin films (0x0.20) were prepared using rf sputtering in argon atmosphere and characterized using X-ray diffraction, optical transmission, electrical resistivity and photoconductive decay measurements. The films were found to possess hexagonal structure. The crystallite size and degree of preferential orientation were found to decrease with the increase ofx and to improve upon annealing in vacuum at 250 °C. The transmission edge shifted towards shorter wavelengths with the increase ofx in agreement with the expected shift in the energy band gap. The films were found to exhibit room temperature resistivity in the range 100–1000 cm. The obtained values of long wavelength transmission (70–80%) and minority carrier diffusion length (30 m) are high enough for the application of these films in the field of solar cells. 相似文献