全文获取类型
收费全文 | 254530篇 |
免费 | 2859篇 |
国内免费 | 871篇 |
专业分类
化学 | 137071篇 |
晶体学 | 3719篇 |
力学 | 10121篇 |
综合类 | 2篇 |
数学 | 28769篇 |
物理学 | 78578篇 |
出版年
2020年 | 1917篇 |
2019年 | 2137篇 |
2018年 | 2607篇 |
2017年 | 2546篇 |
2016年 | 4139篇 |
2015年 | 2898篇 |
2014年 | 4183篇 |
2013年 | 11689篇 |
2012年 | 8599篇 |
2011年 | 10655篇 |
2010年 | 6854篇 |
2009年 | 6716篇 |
2008年 | 9558篇 |
2007年 | 9698篇 |
2006年 | 8898篇 |
2005年 | 8284篇 |
2004年 | 7325篇 |
2003年 | 6520篇 |
2002年 | 6434篇 |
2001年 | 7438篇 |
2000年 | 5558篇 |
1999年 | 4380篇 |
1998年 | 3682篇 |
1997年 | 3708篇 |
1996年 | 3449篇 |
1995年 | 3278篇 |
1994年 | 3089篇 |
1993年 | 3164篇 |
1992年 | 3470篇 |
1991年 | 3448篇 |
1990年 | 3250篇 |
1989年 | 3195篇 |
1988年 | 3248篇 |
1987年 | 3129篇 |
1986年 | 3034篇 |
1985年 | 4103篇 |
1984年 | 4294篇 |
1983年 | 3528篇 |
1982年 | 3883篇 |
1981年 | 3778篇 |
1980年 | 3634篇 |
1979年 | 3680篇 |
1978年 | 3909篇 |
1977年 | 3727篇 |
1976年 | 3927篇 |
1975年 | 3487篇 |
1974年 | 3612篇 |
1973年 | 3904篇 |
1972年 | 2356篇 |
1971年 | 1818篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
The effect of 57Fe hyperfine interaction radiofrequency (rf) modulation by external rotating magnetic field was studied in thin Permalloy foil by means of Mössbauer spectroscopy. The rf effect was investigated as a function of intensity for several rf field frequencies. The experiments show that the external rotating rf field causes considerable changes in the hyperfine pattern. The obtained spectra are in disagreement with those obtained by Perlow [Phys. Rev. 172 (1968) 319]. They also are inconsistent with magnetostriction hypothesis. Proceeding from the Mössbauer spectrum analysis one may conclude that the magnetization of investigated foil changes its direction in a complex manner. However, the undertaken experiments show that the essential number of Mössbauer nuclei experience the rotating magnetic field influence. 相似文献
122.
R. Grac M. Pugnet J.H. Collet B. Lambert C. De Matos H. L'Haridon A. Le Corre J.O. White 《Superlattices and Microstructures》1997,22(4):505-509
We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm−2, and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation. 相似文献
123.
The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare
earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys
has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals
ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of
Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated
for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline
multilayers has been discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
124.
T. Engel M. Würtz S. Borneis St. Becker I. Klaft A. Kohl T. Kühl F. Laeri D. Marx K. Meier R. Neumann F. Schmitt P. Seelig L. Völker 《Hyperfine Interactions》1997,108(1-3):251-258
Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening
is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser
systems specialized on the specific needs of laser spectroscopy at storage rings is reported.
Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different
Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast
qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator.
It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a
frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz.
This laser can be advantageous for laser cooling of ion beams.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
125.
It has been shown by Yu. M. Golubev, M. I. Kolobov, and I. V. Sokolov, Zh. éksp. Teor. Fiz. 111, 1579 (1997) [JETP 84, 864 (1997)], that when an optical cavity is excited by external radiation from a sub-Poisson laser the cavity mode may be
in either a sub-Poisson or a Poisson stationary state. This is not important for a resonant medium which is excited into the
upper laser level while interacting with this mode inside the cavity. The degree of regularity of the excitation will be identical
to that of the initial light flux incident on the cavity, and this ultimately ensures the same sub-Poisson lasing as for strictly
regular pumping of the resonant medium.
Zh. éksp. Teor. Fiz. 113, 1223–1234 (April 1998) 相似文献
126.
127.
G. Hinze R. Böhmer G. Diezemann H. Sillescu 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,131(2):218-223
Four-time stimulated echo experiments have been used to monitor the temporal evolution of the reorientation rates of deuterated molecules or colloidal suspensions. We present extended phase cycles for this seven-pulse experiment. In order to test its performance three vastly different materials are chosen. These include a crystal in which the molecules carry out well-defined 180° flips and a supercooled liquid characterized by a distribution of jump angles centered around 10°. As an example for rotational diffusion, data on a concentrated suspension of polystyrene spheres in a viscous medium are presented. 相似文献
128.
G. Garcia-Belmonte J. Bisquert L. M. Navarro J. R. Jurado F. M. B. Marques 《Ionics》1995,1(5-6):377-383
In ionic conductors, long range-migrating charges are a main cause of polarization processes. This has complicated, up to
date, the study of ionic thermocurrents (ITC) in solid electrolytes. However, the method is appealing, as it probes directly
charge-formation phenomena that are important both from a scientific point of view and for applications.
This work reports on the observation of ITC in solid electrolytes. Under appropriate experimental conditions, the ITC response
of a zirconia sample electroded with platinum is a reproducible one, thus opening the way to a new characterization method
that may complement other well established methods, such as Impedance Spectroscopy and a number of electrochemical techniques.
The general trends of the response, which is composed of two well resolved ITC peaks, is discussed. One of them, taking place
at higher temperatures, conforms to the standard shape of a first order kinetics depolarization process.
Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995 相似文献
129.
The results of Monte Carlo simulations of the beta dose rate to enamel are presented. The dose rates are the most comprehensive to date, incorporating the beta spectrum from 21 different radionuclides, all internal conversion and Auger electrons, the majority of the bremsstrahlung radiation, effects due to radon loss in the uranium series, and variations in the moisture content of the sediment. Applications to a new dating technique in archaeology using electron spin resonance and beta-gradient isochrons are discussed. 相似文献
130.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献