全文获取类型
收费全文 | 59060篇 |
免费 | 776篇 |
国内免费 | 302篇 |
专业分类
化学 | 27486篇 |
晶体学 | 1029篇 |
力学 | 3202篇 |
综合类 | 8篇 |
数学 | 4656篇 |
物理学 | 23757篇 |
出版年
2022年 | 537篇 |
2021年 | 479篇 |
2020年 | 447篇 |
2019年 | 426篇 |
2018年 | 574篇 |
2017年 | 497篇 |
2016年 | 895篇 |
2015年 | 635篇 |
2014年 | 990篇 |
2013年 | 2502篇 |
2012年 | 2342篇 |
2011年 | 3021篇 |
2010年 | 2134篇 |
2009年 | 2176篇 |
2008年 | 2761篇 |
2007年 | 2599篇 |
2006年 | 2460篇 |
2005年 | 2185篇 |
2004年 | 1990篇 |
2003年 | 1756篇 |
2002年 | 1656篇 |
2001年 | 3006篇 |
2000年 | 2151篇 |
1999年 | 1556篇 |
1998年 | 1084篇 |
1997年 | 1060篇 |
1996年 | 887篇 |
1995年 | 783篇 |
1994年 | 705篇 |
1993年 | 624篇 |
1992年 | 951篇 |
1991年 | 950篇 |
1990年 | 852篇 |
1989年 | 749篇 |
1988年 | 733篇 |
1987年 | 797篇 |
1986年 | 655篇 |
1985年 | 885篇 |
1984年 | 828篇 |
1983年 | 570篇 |
1982年 | 562篇 |
1981年 | 533篇 |
1980年 | 499篇 |
1979年 | 622篇 |
1978年 | 651篇 |
1977年 | 660篇 |
1976年 | 576篇 |
1975年 | 484篇 |
1974年 | 521篇 |
1973年 | 453篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper shows that the graphW(n, n – 2, k) is chromatically unique for any even integern 6 and any integerk 1. 相似文献
992.
In location-routing problems, the objective is to locate one or many depots within a set of sites (representing customer locations or cities) and to construct delivery routes from the selected depot or depots to the remaining sites at least system cost. The objective function is the sum of depot operating costs, vehicle acquisition costs and routing costs. This paper considers one such problem in which a weight is assigned to each site and where sites are to be visited by vehicles having a given capacity. The solution must be such that the sum of the weights of sites visited on any given route does not exceed the capacity of the visiting vehicle. The formulation of an integer linear program for this problem involves degree constraints, generalized subtour elimination constraints, and chain barring constraints. An exact algorithm, using initial relaxation of most of the problem constraints, is presented which is capable of solving problems with up to twenty sites within a reasonable number of iterations. 相似文献
993.
Manganese oxide (hausmannite) nanowires were prepared by annealing precursor powders at a temperature of 800 °C for 3 h, which
were produced in a novel inverse microemulsion (IμE) system. The microstructures of the as-prepared Mn3O4 nanowires were investigated by means of X-ray diffraction, transmission electron microscopy, and Raman spectra. It has been
found that the Mn3O4 nanowires were relatively straight and their surfaces were smooth with a typical diameter of 75–150 nm. The formation mechanism
of the Mn3O4 nanowires is discussed.
Received: 30 May 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002
RID="*"
ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: wangqun@nju.edu.cn 相似文献
994.
Criteria for strict monotonicity, lower local uniform monotonicity, upper local uniform monotonicity, and uniform monotonicity of Musielak-Orlicz spaces over any σ-finite and complete measure space, endowed with the Amemiya norm are given. The fact that the spaces are considered over arbitrary σ-finite measure space is essential because, as it is shown in Example 3, the Musielak-Orlicz spaces need not be strictly monotone even if their restrictions to the nonatomic part and the purely atomic part are strictly monotone. 相似文献
995.
A relation between a metallic film covering on diamond formed during growth and nanosized inclusions in HPHT as-grown diamond single crystals 总被引:3,自引:0,他引:3
L.-W. Yin M.-S. Li Z.-G. Gong Y.-J. Bai F.-Z. Li Z.-Y. Hao 《Applied Physics A: Materials Science & Processing》2003,76(7):1061-1065
One of the most important characteristics and basic phenomena during diamond growth from liquid metal catalyst solutions saturated
with carbon at high temperature–high pressure (HPHT) is that there exists a thin metallic film covering on the growing diamond,
through which carbon-atom clusters are delivered to the surface of the growing diamond by diffusion. A study of microstructures
of such a metallic film and a relation between the thin metallic film and the inclusions trapped in HPHT as-grown diamond
single crystals may be helpful to obtain high-purity diamond single crystals. It was found that both the metallic film and
the HPHT as-grown diamond single crystals contain some nanostructured regions. Examination by transmission electron microscopy
suggests that the microstructure of the thin metallic film is in accordance with nanosized particles contained in HPHT as-grown
diamond single crystals. The nanosized particles with several to several tens of nanometers in dimension distribute homogeneously
in the metallic film and in the diamond matrix. Generally, the size of the particles in the thin metallic film is relatively
larger than that within the diamond matrix. Selected area electron diffraction patterns suggest that the nanosized particles
in the metallic film and nanometer inclusions within the diamond are mainly composed of f.c.c. (FeNi)23C6, hexagonal graphite and cubic γ-(FeNi). The formation of the nanosized inclusions within the diamond single crystals is thought
not only to relate to the growth process and rapid quenching from high temperature after diamond synthesis, but also to be
associated with large amounts of defects in the diamond, because the free energy in these defect areas is very high. The critical
size of carbide, γ-(FeNi)and graphite particles within the diamond matrix should decrease and not increase according to thermodynamic
theory during quenching from HPHT to room temperature and ambient pressure.
Received: 13 September 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002
RID="*"
ID="*"Corresponding author. Fax: +86-0531/295-5081; E-mail: yinlw@sdu.edu.cn 相似文献
996.
A. M. Tkachuk S. É. Ivanova L. I. Isaenko A. P. Yelisseyev M. -F. Joubert Y. Guyot S. Payne 《Optics and Spectroscopy》2003,95(5):722-740
Optical spectra, intensities of radiative and nonradiative transitions, and luminescence kinetics in erbium-doped potassium-lead double chloride crystals KPb2Cl5:Er3+s(KPC:Er3+) were investigated. The crystals were grown by the Bridgman-Stockbarger method. Their absorption and luminescence spectra were studied experimentally. The crystal-matrix absorption edge was determined at 80 and 300 K. Intensity parameters, radiative transition probabilities, branching ratios, and nonradiative relaxation rates were estimated by the Judd-Ofelt method. The luminescence kinetics from the emitting levels 4 G 11/2, 2 G 9/2, 4 S 3/2, and 4 F 9/2 upon selective excitation was studied. 相似文献
997.
Stereoscopic imaging and reconstruction technique is introduced to reconstruct the flame structures that are subject to acoustic excitation. The laminar diffusion flame under investigation was created in a cylindrical tube and excited by a loudspeaker. Stereo images were taken at a shutter speed of 1/10000th second using a ‘stereo camera’ and the depth cue of the flame structures along the camera viewing direction were then computed using machine vision methodology. By visualizing the computed three-dimensional flame models, as well as judging the corresponding attribute such as surface gradient, the understanding of the flame and acoustic wave interaction could be improved. 相似文献
998.
R.V.S.S.N Ravikumar R Komatsu A.V Chandrasekhar Y.P Reddy 《Journal of Physics and Chemistry of Solids》2003,64(2):261-264
Electron paramagnetic resonance and optical investigations of copper and chromium doped LiRbB4O7 glasses are carried out. From the results and discussions, it is predicted that both the transition metal ions exhibit octahedral environment. In the case of Cr3+, the site symmetry is near octahedral, whereas in the case of Cu2+, it is tetragonally distorted octahedral environment. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. The bonding parameters are suggesting ionic. 相似文献
999.
S. Katsumoto K. Kobayashi H. Aikawa A. Sano Y. Iye 《Superlattices and Microstructures》2003,34(3-6):151
We investigate coherent transport through hybrid systems of quantum dots and Aharonov–Bohm (AB) rings. Strong coherence over the entire system leads to the Fano effect, which originates from the interference and the phase shift caused by the discrete states in the dots. The high controllability of the system parameters reveals that the Fano effect in mesoscopic transport can be a powerful tool for detecting the phase shift of electrons. We apply it to detect electrostatic phase modulation and the phase shift in a quantum wire with a side-coupled dot. Finally, we provide an experimental answer to the problem of “neighboring in-phase Coulomb peaks”. 相似文献
1000.
We investigate coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot. This fully tunable qubit is manipulated with a high-speed voltage pulse that controls the energy and decoherence of the system. Coherent oscillations of the qubit are observed for several combinations of many-body ground and excited states of the quantum dots. Possible decoherence mechanisms in the present device are also discussed. 相似文献