全文获取类型
收费全文 | 373201篇 |
免费 | 1663篇 |
国内免费 | 700篇 |
专业分类
化学 | 159638篇 |
晶体学 | 5407篇 |
力学 | 23462篇 |
综合类 | 3篇 |
数学 | 73308篇 |
物理学 | 113746篇 |
出版年
2021年 | 3095篇 |
2020年 | 3412篇 |
2019年 | 4190篇 |
2018年 | 16396篇 |
2017年 | 16345篇 |
2016年 | 13804篇 |
2015年 | 4322篇 |
2014年 | 7142篇 |
2013年 | 12380篇 |
2012年 | 13718篇 |
2011年 | 21877篇 |
2010年 | 15410篇 |
2009年 | 15981篇 |
2008年 | 17781篇 |
2007年 | 19627篇 |
2006年 | 10143篇 |
2005年 | 9820篇 |
2004年 | 9801篇 |
2003年 | 9664篇 |
2002年 | 9012篇 |
2001年 | 7888篇 |
2000年 | 6328篇 |
1999年 | 4629篇 |
1998年 | 4433篇 |
1997年 | 4259篇 |
1996年 | 3917篇 |
1995年 | 3409篇 |
1994年 | 3431篇 |
1993年 | 3464篇 |
1992年 | 3431篇 |
1991年 | 3846篇 |
1990年 | 3837篇 |
1989年 | 3852篇 |
1988年 | 3602篇 |
1987年 | 3683篇 |
1986年 | 3377篇 |
1985年 | 3895篇 |
1984年 | 4124篇 |
1983年 | 3523篇 |
1982年 | 3727篇 |
1981年 | 3409篇 |
1980年 | 3177篇 |
1979年 | 3664篇 |
1978年 | 3720篇 |
1977年 | 3873篇 |
1976年 | 3944篇 |
1975年 | 3688篇 |
1974年 | 3536篇 |
1973年 | 3712篇 |
1972年 | 3194篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
It is shown that using position-sensitive detectors in μSR experiments to determine the muon stopping site in a target permits
one to study correlation effects in μSR time histograms produced by the decay of muons stopping in the same domain, i.e. to
obtain time correlators of μSR histograms of decays from a small region. These correlators contain information on the spatial
correlation of magnetic fields in the sample under study. The proposed method (μSR2-technique) allows measuring correlation radii (r
c
) down to 10−5 cm in a bulk sample. Among interesting physical phenomena occuring overr
c≥3×10−6 cm are, for instance, long wavelength fluctuations of the order parameter near the phase transition point in ferromagnets
and antiferromagnets and magnetic field correlations in magnet domains and spin glasses. One may use this method also on heavy-current
accelerators producing pulsed muon beams to investigate the variation in time of spatial correlations in magnets, spin glasses
and superconductors. 相似文献
952.
A method of identifying low-energy nuclei from the readings of an ionizational mass spectrometer is considered. The identification principles for particles recorded by a multilayer detector are discussed, together with the fundamentals of a probabilistic approach to the solution of this problem. The method permits correct analysis of the experimental data obtained. The determination of the charge and isotopic composition of radiation consisting of a mixture of different nuclei is considered. The results of calculations by the given method which permit the determination of the optimal detector parameters for the solution of the specific physical problem are outlined. This approach is also applicable for the analysis of data from other types of measuring apparatus.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 84–88, July, 1991. 相似文献
953.
S K Deshpande S M Chaudhari Ashok Pimpale A S Nigavekar S B Ogale V G Bhide 《Pramana》1991,37(4):373-385
An automated linear laboratory EXAFS spectrometer of the Johansson type has been indigenously developed. Only two translational
motions are required to achieve the necessary Rowland circle configuration for the (fixed) X-ray source, the dispersing and
focusing bent crystal and the receiving slit. With the available crystals the spectral region from 5 to 25 keV can be scanned.
The linear motions of the crystal and receiving slit including the detector assembly are achieved by employing software-controlled
DC motors and utilizing optical encoders for position sensing. The appropriate rotation of the crystal is achieved by the
geometry of the instrument. There is a facility to place the sample alternately in the path of the X-ray beam and out of the
path to record both the incident X-ray intensityI
0 and the transmitted intensityI employing the scintillation detector. An arrangement with a two-window proportional detector before the sample to measureI
0 and the scintillation detector to recordI is also developed; in this case it is not necessary to oscillate the sample. Fast electronic circuits are employed to minimize
counting errors. The instrument is user-friendly and it is operated through a menu-driven IBM compatible PC. EXAFS spectra
of high resolution have been recorded using the spectrometer and employing the Si(111) reflecting planes; the X-ray source
being a Rigaku 12 kW rotating anode with Cu target. We describe the spectrometer and discuss its performance with a few representative
spectra. 相似文献
954.
Fundamental and dual variational principles of magnetostatics of superconductors are formulated. It is shown how test fields can be expressed in terms of vector and scalar potentials. General consequences of the variational magnetostatic formulation are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 97–102, September, 1991. 相似文献
955.
The equilibrium statistical volume distribution in foams, which has been previously demonstrated to be the so-called log-normal, is accounted on probability grounds by a scaling law on the bubble's volume time-evolution. This law states that the conditional probability for a given bubble to have the volume v(t + Δt), he assumption that it was v(t), to depend solely on the relationship v(t + Δt)/v(t), and in particular, to be independent of the time t. The theoretical results, however, allow to go further. Indeed, since the time dependece of its parameters (expectation and variance) are given functions of time, only two parameters are necessary to describe completely the foam. 相似文献
956.
O. P. Gorelik G. A. Dyuzhev D. V. Novikov V. M. Oichenko A. A. Sitnikova 《Technical Physics》2002,47(10):1337-1340
Electron microscopy is used in a study of nanoclusters of the carbon soot deposited on a probe in different areas of arc discharge during graphite vaporization under conditions favorable for fullerene synthesis. It is found that the spatial network of soot nanoclusters consists of alternating regions of higher density or associates of carbon particles. Two types of nanoclusters have been identified with the correlation radii of the associates equal to 0.6–0.8 and 1.6–2.2 nm, respectively. Type I nanoclusters are dominant in the soot microparticles, and their structure shows practically no variations with increasing separation r of the soot collector from the discharge axis over the range of distances studied, r=1–9 cm. The effective radius R 0 of the “elementary” particles making up the associates in the soot nanoclusters of Type I calculated with the use of scaling relationships is 0.15–0.17 nm and is close to the gas-kinetic radius of carbon atoms. Type II nanoclusters have been identified in soot collected at r>3 cm. Values of R 0 calculated in this case are 0.6–0.9 nm and decrease with increasing r, which indicates the presence of fullerene molecules in these nanocluster associates. 相似文献
957.
The system of linearized Einstein and Maxwell equations and a kinetic equation with model collision integral for the cosmological plasma are used to calculate the magnetic field generated by solenoidal perturbations in the radiation-dominated stage of expansion of the universe. The magnetic field is generated by two effects — the Harrison effect and a new effect due to kinetic processes. The second effect contributes to the magnetic field if solenoidal gravitational perturbations exist from the very beginning of the radiation-dominated stage.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 122–126, January, 1992. 相似文献
958.
The energy levels and oscillator strengths for dipole transitions between the levels of low-lying configurations are calculated for ions of the KI isoelectronic sequence. The calculations are based on the energy approach to the effective potential method with the most important polarization effects taken into account, including core polarization by the outer electron. The results, some of which are obtained here for the first time for potassium-like ions, can be useful in a number of related fields, such as laser physics, plasmas, and so on.Odessa Hydrometeorological Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–9, November, 1992. 相似文献
959.
A. V. Levichev 《Siberian Mathematical Journal》1992,33(1):169-171
Novosibirsk. Translated from Sibirskii Matematicheskii Zhurnal, Vol. 33, No. 1, pp. 205–207, January–February, 1992. 相似文献
960.