全文获取类型
收费全文 | 184955篇 |
免费 | 2671篇 |
国内免费 | 848篇 |
专业分类
化学 | 101551篇 |
晶体学 | 2570篇 |
力学 | 8062篇 |
综合类 | 7篇 |
数学 | 20041篇 |
物理学 | 56243篇 |
出版年
2021年 | 1121篇 |
2020年 | 1303篇 |
2019年 | 1294篇 |
2018年 | 1313篇 |
2017年 | 1302篇 |
2016年 | 2609篇 |
2015年 | 2144篇 |
2014年 | 2765篇 |
2013年 | 8387篇 |
2012年 | 6901篇 |
2011年 | 8807篇 |
2010年 | 5302篇 |
2009年 | 5416篇 |
2008年 | 8020篇 |
2007年 | 8038篇 |
2006年 | 7792篇 |
2005年 | 7279篇 |
2004年 | 6547篇 |
2003年 | 5659篇 |
2002年 | 5549篇 |
2001年 | 6207篇 |
2000年 | 4735篇 |
1999年 | 3615篇 |
1998年 | 2779篇 |
1997年 | 2793篇 |
1996年 | 2772篇 |
1995年 | 2427篇 |
1994年 | 2315篇 |
1993年 | 2150篇 |
1992年 | 2471篇 |
1991年 | 2441篇 |
1990年 | 2140篇 |
1989年 | 2095篇 |
1988年 | 2155篇 |
1987年 | 2080篇 |
1986年 | 1959篇 |
1985年 | 2950篇 |
1984年 | 2952篇 |
1983年 | 2351篇 |
1982年 | 2604篇 |
1981年 | 2472篇 |
1980年 | 2426篇 |
1979年 | 2360篇 |
1978年 | 2422篇 |
1977年 | 2365篇 |
1976年 | 2293篇 |
1975年 | 2253篇 |
1974年 | 2169篇 |
1973年 | 2247篇 |
1972年 | 1263篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Kvon Z. D. Tkachenko V. A. Plotnikov A. E. Sablikov V. A. Renard V. Portal J. C. 《JETP Letters》2004,79(1):36-39
JETP Letters - An experimental study of the two-, three-, and four-terminal resistance of a ballistic wire is carried out. The wire is fabricated on the basis of high-mobility 2D electron gas in an... 相似文献
912.
Microscopic petrified grains were collected from a mafic–ultramafic pipe, NE of Dreikeesh, NW Syria. The grains were identified as anthers/gynoecia in herb/grass flowers. Three of the grains showed evidence of magnetism, two slowly dissolved in concentrated HCl, and three microprobed grains showed a montmorillonitic composition. Iron originating from pyroxene was oxidized to magnetite. Released silica formed the mineral suite agate–chalcedony–opal. Warm/cold paleoclimatic fluctuations, occurring during late Pliocene–Holocene, depended on water vapor, CO2 production, and cinders in the atmosphere. Most of these were associated with changing volcanic/tectonic events. Fluctuations were controlled by heat reflected from the Earth's surface being absorbed by water vapor and CO2, which both re-reflected the heat back to the surface, thus, raising the temperature. This cycle was repeated several times during late Pliocene–Holocene. 相似文献
913.
The oxidations of diethyl sulfide by potassium dichromate, pyridinium dichromate, quinolinium dichromate, imidazolium dichromate, nicotinium dichromate, isonicotinium dichromate, pyridinium fluorochromate, quinolinium fluorochromate, imidazolium fluorochromate, pyridinium chlorochromate, quinolinium chlorochromate, and pyridinium bromochromate follow identical kinetic orders—first‐order each with respect to the chromium(VI) reagents, sulfide and hydrogen ion, and moderately inhibited by manganese(II) ion. The energy of activation varies linearly with the logarithm of frequency factor and so does the enthalpy of activation with the entropy of activation. Also, the activation free energies do not differ significantly. The dichromates and halochromates of heterocyclic bases oxidize diethyl sulfide via a common mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 1–8, 2003 相似文献
914.
915.
916.
P. Pellegrino B. Garrido C. García R. Ferr J. A. Moreno J. R. Morante 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):424
The ability of surface passivation to enhance the photoluminescence (PL) emission of Si nanocrystals in SiO2 has been investigated. Silicon precipitation in implanted samples takes place in a time scale of few minutes at 1100°C. For longer annealing at the same temperature, the PL intensity of the Si nanocrystals increases and eventually reaches saturation, while it correlates inversely with the amount of Si dangling bonds at the Si–SiO2 interface (Pb centers), as measured by electron spin resonance. This combined behavior is independent on the silica matrix properties, implantation profiles and annealing atmosphere and duration. The observation that the light emission enhancement is directly related to the annealing of Pb centers is confirmed by treatment in forming gas. This mild hydrogenation at much lower temperature (450°C) leads to a complete passivation of the Pb defects, increasing at the same time the PL yield and the lifetime. 相似文献
917.
S. Y. Wang S. C. Chen S. D. Lin C. J. Lin C. P. Lee 《Infrared Physics & Technology》2003,44(5-6):527-532
InAs/GaAs quantum dot infrared photodetectors were fabricated with quantum dots grown at three different temperatures. Large detection wavelength shift (5–14.5 μm) was demonstrated by changing 40 degrees of the epitaxy temperature. The smaller quantum dots grown at lower temperature generate 14.5 μm responses. The detectivity of the normal incident 15 μm QDIP at 77 K is 3 × 108 cm Hz1/2/W. A three-color detector was also demonstrated with quantum dots grown at medium temperature. The three-color detection comes from two groups of different sizes of dots within one QD layer. This new type of multicolor detector shows unique temperature tuning behavior that was never reported before. 相似文献
918.
Role of the microstructure on the transport properties of Y-doped zirconia and Gd-doped ceria 总被引:1,自引:1,他引:0
Transmission electron microscopy characterizations and XPS analyses have allowed us to show the influence of the microstructure
and nanochemistry on the transport properties of Y2O3-(9 mol%)-stabilized zirconia (YSZ) and Gd2O3 (10 mol%)-doped ceria (GDC). The grain boundary electrical conductivity (σgb) and oxygen diffusion coefficient (Do) of conventional YSZ ceramics increase with the grain size, while an opposite behavior was found for GDC samples. This difference
was attributed to glassy precipitates present at YSZ grain boundaries. Furthermore, it was shown that kinetic demixing processes
take place during cooling, at the end of sintering. This causes important changes in the cationic species distribution at
interfaces and plays an important role on the transport properties of these two materials.
Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002. 相似文献
919.
W. Shi Y.J. Ding C. Fang Q. Pan Q. Gu 《Applied Physics A: Materials Science & Processing》2003,77(3-4):567-570
The optimal corona-poling temperature of polymer films was accurately determined by measuring the temperature dependence of the in situ second-harmonic (SH) intensity profile under the applied poling electric field. The in situ SH intensity profile was first measured by probing both the surface voltages and the poling currents induced by surface/space charges for the corona-poled polymer films. Moreover, charge effects on the stability of the chromophore orientation were first studied by using the thermally stimulated discharge-current technique. PACS 72.20.Jv; 42.65.Ky; 73.61.Ph; 81.40.Tv 相似文献
920.
A Tandem Queue with Coupled Processors: Computational Issues 总被引:2,自引:0,他引:2
In Resing and Örmeci [16] it is shown that the two-stage tandem queue with coupled processors can be solved using the theory of boundary value problems. In this paper we consider the issues that arise when calculating performance measures like the mean queue length and the fraction of time a station is empty. It is assumed that jobs arrive at the first station according to a Poisson process and require service at both stations before leaving the system. The amount of work that a job requires at each of the stations is an independent, exponentially distributed random variable. When both stations are nonempty, the total service capacity is shared among the stations according to fixed proportions. When one of the stations becomes empty, the total service capacity is given to the nonempty station. We study the two-dimensional Markov process representing the numbers of jobs at the two stations. The problem of finding the generating function of the stationary distribution can be reduced to two different Riemann-Hilbert boundary value problems, where both problems yield a complete analytical solution. We discuss the similarities and differences between the two problems, and relate them to the computational aspects of obtaining performance measures. 相似文献