全文获取类型
收费全文 | 284716篇 |
免费 | 4316篇 |
国内免费 | 883篇 |
专业分类
化学 | 154528篇 |
晶体学 | 3860篇 |
力学 | 10826篇 |
综合类 | 3篇 |
数学 | 34425篇 |
物理学 | 86273篇 |
出版年
2020年 | 2335篇 |
2019年 | 2425篇 |
2018年 | 3001篇 |
2017年 | 2915篇 |
2016年 | 4985篇 |
2015年 | 3576篇 |
2014年 | 4986篇 |
2013年 | 13448篇 |
2012年 | 9955篇 |
2011年 | 12216篇 |
2010年 | 7716篇 |
2009年 | 7443篇 |
2008年 | 11058篇 |
2007年 | 11163篇 |
2006年 | 10169篇 |
2005年 | 9463篇 |
2004年 | 8274篇 |
2003年 | 7284篇 |
2002年 | 7124篇 |
2001年 | 7972篇 |
2000年 | 6056篇 |
1999年 | 4729篇 |
1998年 | 3998篇 |
1997年 | 3990篇 |
1996年 | 3846篇 |
1995年 | 3620篇 |
1994年 | 3482篇 |
1993年 | 3629篇 |
1992年 | 3830篇 |
1991年 | 3720篇 |
1990年 | 3542篇 |
1989年 | 3463篇 |
1988年 | 3518篇 |
1987年 | 3386篇 |
1986年 | 3274篇 |
1985年 | 4492篇 |
1984年 | 4665篇 |
1983年 | 3854篇 |
1982年 | 4205篇 |
1981年 | 4124篇 |
1980年 | 3969篇 |
1979年 | 3973篇 |
1978年 | 4227篇 |
1977年 | 4030篇 |
1976年 | 4190篇 |
1975年 | 3751篇 |
1974年 | 3866篇 |
1973年 | 4164篇 |
1972年 | 2485篇 |
1971年 | 1946篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
To Professor Guillermo Torres on the occasion of his 70th birthday. 相似文献
992.
C. S. Creaser M. R. S. McCoustra K. E. O'Neill 《Journal of mass spectrometry : JMS》1991,26(4):335-338
Two fibre-optic interfaces were constructed for laser photodissociation/tandem mass spectrometry using an ion trap spectrometer. These interfaces allow sample introduction from a liquid reservoir, solids probe and gas chromatograph. The laser/ion trap configuration was applied to the analysis of a mixture of alkylbenenes separated by gas chromatography using 573 nm photons. 相似文献
993.
R. M. Trigub 《Ukrainian Mathematical Journal》1991,43(12):1572-1578
New statements are proved regarding multipliers of trigonometric Fourier series in the space C of continuous periodic functions.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 12, pp. 1686–1693, December, 1991. 相似文献
994.
In this paper, the development of decision support tools for dynamic ambulance relocation and automatic ambulance dispatching is described. The ambulance dispatch problem is to choose which ambulance to send to a patient. The dynamic ambulance relocation problem occurs in the operational control of ambulances. The objective is to find new locations for some of the ambulances, to increase the preparedness in the area of responsibility. Preparedness is a way of evaluating the ability to serve potential patients with ambulances now and in the future. Computational tests using a simulation model show that the tools are beneficial in reducing the waiting periods for the patients. 相似文献
995.
In this paper we prove the existence of a solution of a coupled system involving a two phase incompressible flow in the ground and the mechanical deformation of the porous medium where the porosity is a function of the global pressure. The model is strongly coupled and involves a nonlinear degenerate parabolic equation. In order to show the existence of a weak solution, we consider a sequence of related uniformly parabolic problems and apply the Schauder fixed point theorem to show that they possess a classical solution. We then prove the relative compactness of sequences of solutions by means of the Fréchet-Kolmogorov theorem; this yields the convergence of a subsequence to a weak solution of the parabolic system. 相似文献
996.
P.A. Postigo A.R. Alija L.J. Martínez M.L. Dotor D. Golmayo J. Snchez-Dehesa C. Seassal P. Viktorovitch M. Galli A. Politi M. Patrini L.C. Andreani 《Photonics and Nanostructures》2007,5(2-3):79-85
Two-dimensional photonic crystal lasers have been fabricated on III–V semiconductor slabs. Tuning of the spontaneous emission in micro and nanocavities has been achieved by accurate control of the slab thickness. Different structures, some of them of new application to photonic crystal lasers, have been fabricated like the Suzuki-phase or the coupled-cavity ring-like resonators. Laser emission has been obtained by pulsed optical pumping. Optical characterization of the lasing modes have been performed showing one or more laser peaks centred around 1.55 μm. Far field characterization of the emission pattern has been realized showing different patterns depending on the geometrical shape of the structures. These kinds of devices may be used as efficient nanolaser sources for optical communications or optical sensors. 相似文献
997.
Background
Repeated execution of a tactile task enhances task performance. In the present study we sought to improve tactile performance with unattended activation-based learning processes (i.e., focused stimulation of dermal receptors evoking neural coactivation (CA)). Previous studies show that the application of CA to a single finger reduced the stationary two-point discrimination threshold and significantly increased tactile acuity. These changes were accompanied by an expansion of the cortical finger representation in primary somatosensory cortex (SI). Here we investigated the effect of different types of multifinger CA on the tactile performance of each finger of the right hand. 相似文献998.
999.
Al2O3 incorporated HfO2 films grown by atomic layer deposition (ALD) were investigated by high-resolution X-ray photoelectron spectroscopy (HRXPS). The core level energy state of a 15 Å thick film showed a shift to higher binding energy, as the result of a silicate formation and Al2O3 incorporation. The incorporation of Al2O3 into the HfO2 film had no effect on silicate formation at the interface between the film and Si, while the ionic bonding characteristics and hybridization effects were enhanced compared to a pure HfO2 film. The dissociation of the film in an ultrahigh vacuum (UHV) is effectively suppressed compared to a pure HfO2 film, indicating an enhanced thermal stability of Hf-Al-O. Any dissociated Al2O3 on the film surface was completely removed into the vacuum by vacuum annealing treatment over 850 °C, while HfO2 contributed to Hf silicide formation on the film surface. 相似文献
1000.
R W Milne R L Nation G D Reynolds A A Somogyi J T Van Crugten 《Journal of chromatography. A》1991,565(1-2):457-464
Improvements to previously reported methods for the determination of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in human plasma are described. The improved methods involve the use of a solid-phase extraction cartridge and a chromatographic system which uses paired-ion reversed-phase high-performance liquid chromatography with a radially compressed column. Only one cartridge is used to prepare each sample for chromatography and each cartridge may be used for at least fourteen 1-ml plasma samples. The recovery is greater than 85%. The improvements to the method of sample pretreatment and in the chromatographic conditions have allowed determination of morphine, M3G and M6G in human plasma down to 13.3 nmol/l (coefficient of variation = 9.3%), 108 nmol/l (6.6%) and 41 nmol/l (6.7%), respectively, using ultraviolet detection alone. It was shown that all three compounds were stable in plasma for up to 101 weeks when stored at -20 degrees C. 相似文献