全文获取类型
收费全文 | 266374篇 |
免费 | 4697篇 |
国内免费 | 2708篇 |
专业分类
化学 | 127519篇 |
晶体学 | 4083篇 |
力学 | 14264篇 |
综合类 | 189篇 |
数学 | 40114篇 |
物理学 | 87610篇 |
出版年
2022年 | 1439篇 |
2021年 | 1801篇 |
2020年 | 2002篇 |
2019年 | 2040篇 |
2018年 | 11114篇 |
2017年 | 11934篇 |
2016年 | 7554篇 |
2015年 | 3387篇 |
2014年 | 3589篇 |
2013年 | 7623篇 |
2012年 | 10995篇 |
2011年 | 20313篇 |
2010年 | 12616篇 |
2009年 | 12552篇 |
2008年 | 17502篇 |
2007年 | 20933篇 |
2006年 | 6700篇 |
2005年 | 12732篇 |
2004年 | 8653篇 |
2003年 | 8180篇 |
2002年 | 6023篇 |
2001年 | 6150篇 |
2000年 | 4716篇 |
1999年 | 3618篇 |
1998年 | 2530篇 |
1997年 | 2605篇 |
1996年 | 2577篇 |
1995年 | 2333篇 |
1994年 | 2321篇 |
1993年 | 2067篇 |
1992年 | 2492篇 |
1991年 | 2578篇 |
1990年 | 2400篇 |
1989年 | 2302篇 |
1988年 | 2271篇 |
1987年 | 2276篇 |
1986年 | 2072篇 |
1985年 | 2515篇 |
1984年 | 2557篇 |
1983年 | 2033篇 |
1982年 | 2031篇 |
1981年 | 1874篇 |
1980年 | 1852篇 |
1979年 | 2141篇 |
1978年 | 2231篇 |
1977年 | 2086篇 |
1976年 | 2050篇 |
1975年 | 1920篇 |
1974年 | 1907篇 |
1973年 | 1978篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
H.L. Xu A. Persson S. Svanberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):233-236
New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity
levels belonging to the 4f5d26p and 4f
25d
2 configurations of Ce I and 6 even-parity levels belonging to the 5d26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II
levels range in energy from 26 545 to 29 102 cm-1, and 42 573 to 48 152 cm-1, respectively.
Received 25 September 2002 Published online 4 March 2003 相似文献
103.
R. Pizzoferrato L. Lagonigro T. Ziller A. Di Carlo R. Paolesse F. Mandoj A. Ricci C. Lo Sterzo 《Chemical physics》2004,300(1-3):217-225
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials. 相似文献
104.
M. V. Zyubin I. A. Rudnev V. A. Kashurnikov 《Journal of Experimental and Theoretical Physics》2003,96(6):1065-1077
A system of Abrikosov vortices in a quasi-two-dimensional HTSC plate is considered for various periodic lattices of pinning centers. The magnetization and equilibrium configurations of the vortex density for various values of external magnetic field and temperature are calculated using the Monte Carlo method. It is found that the interaction of the vortex system with the periodic lattice of pinning centers leads to the formation of various ordered vortex states through which the vortex system passes upon an increase or a decrease in the magnetic field. It is shown that ordered vortex states, as well as magnetic field screening processes, are responsible for the emergence of clearly manifested peaks on the magnetization curves. Extended pinning centers and the effect of multiple trapping of vortices on the behavior of magnetization are considered. Melting and crystallization of the vortex system under the periodic pinning conditions are investigated. It is found that the vortex system can crystallize upon heating in the case of periodic pinning. 相似文献
105.
For ϕ a δ-subharmonic function, sharp results are obtained that connectA(r, ϕ), B(r, ϕ) andT(r, ϕ), whereA(r, ϕ)=inf|z|=r
ϕ(z),B(r, ϕ)=sup|z|=r
ϕ(z), andT(r, ϕ) is the Nevanlinna characteristics. 相似文献
106.
In his recent series of lectures, Prof. B. I. Plotkin discussed geometrical properties of the variety of associativeK-algebras. In particular, he studied geometrically noetherian and logically noetherian algebras and, in this connection, he
asked whether there exist uncountably many simpleK-algebras with a fixed finite number of generators. We answer this question in the affirmative using both crossed product
constructions and HNN extensions of division rings. Specifically, we show that there exist uncountably many nonisomorphic
4-generator simple Ore domains, and also uncountably many nonisomorphic division algebras having 2 generators as a division
algebra.
The first author is grateful to Professor B. I. Plotkin for communicating this problem to him and for stimulating conversations. 相似文献
107.
A brief account of applications of polarized inelastic neutron scattering in condensed matter research is given. We show that
full polarization analysis is the only tool allowing to discriminate unambiguously between different magnetic modes in various
magnetic materials. We show by means of recent results in the Heisenberg ferromagnet EuS that the effects of dipolar interactions
can be studied on a microscopic scale. Moreover, we have found for the first time indications for the divergence of the longitudinal
fluctuations belowT
c. In the itinerant antiferromagnet chromium we demonstrate that the dynamics of the longitudinal and transverse excitations
are very different, resolving a long standing puzzle concerning the slope of their dispersion. Finally, we show that a measurement
of the polarization-dependent part of the cross section of non-centrosymmetric MnSi proves directly that the chirality of
the magnetic fluctuations is left-handed. 相似文献
108.
Porous silicon (PS) exhibits several photoluminescence (PL) bands, whose spectral position and intensity depend strongly on the actual conditions of preparation of PS, its treatment, and subsequent use. The PS PL band peaking at about 1.8 eV and usually assigned to the intrinsic emission of silicon nanocrystals was studied. It was shown that the temperature-induced variation of the PL kinetics in the 80 to 300-K interval follows a complex pattern and depends noticeably on the actual point on the band profile. The temperature behavior of PL decay in the 1.8-eV band is determined by the electron-hole recombination rate within a nanocrystal and the cascade carrier transitions from small to large nanocrystals, with an attendant decrease in energy. 相似文献
109.
Vinod Kumar Pragya Das R.P. Singh S. Muralithar R.K. Bhowmik 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):153-157
The fusion evaporation reaction 122Sn(14N, 4n)132La was used to populate the high-spin states of 132La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2- and the isomeric state 6-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh
11/2 ⊗ νh
11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies
in the spin assignment of the band head.
Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003 相似文献
110.
The results of a numerical study are described in which the interactions of a primary shock wave with a secondary diaphragm
in expansion tubes are taken into account. The developing wave pattern in the interacting process of the shock with a secondary
diaphragm are visualized by many kinds of figures (e.g., the time-distance diagrams of the wave phenomena on the axis, the
acoustic impedance contours, and the time histories of the pitot pressure on the axis), and the influences of the shape and
rupture process of the diaphragm on the quality of the test gas are explored. 相似文献