全文获取类型
收费全文 | 407975篇 |
免费 | 4934篇 |
国内免费 | 3005篇 |
专业分类
化学 | 220803篇 |
晶体学 | 5595篇 |
力学 | 18191篇 |
综合类 | 76篇 |
数学 | 50979篇 |
物理学 | 120270篇 |
出版年
2021年 | 3647篇 |
2020年 | 4023篇 |
2019年 | 4523篇 |
2018年 | 6190篇 |
2017年 | 6224篇 |
2016年 | 8772篇 |
2015年 | 5188篇 |
2014年 | 7877篇 |
2013年 | 17721篇 |
2012年 | 15290篇 |
2011年 | 17881篇 |
2010年 | 12966篇 |
2009年 | 12964篇 |
2008年 | 16486篇 |
2007年 | 16326篇 |
2006年 | 15043篇 |
2005年 | 13699篇 |
2004年 | 12837篇 |
2003年 | 11043篇 |
2002年 | 10919篇 |
2001年 | 11458篇 |
2000年 | 8726篇 |
1999年 | 6537篇 |
1998年 | 5656篇 |
1997年 | 5421篇 |
1996年 | 5336篇 |
1995年 | 4640篇 |
1994年 | 4692篇 |
1993年 | 4611篇 |
1992年 | 4866篇 |
1991年 | 5098篇 |
1990年 | 4815篇 |
1989年 | 4742篇 |
1988年 | 4575篇 |
1987年 | 4526篇 |
1986年 | 4373篇 |
1985年 | 5724篇 |
1984年 | 5769篇 |
1983年 | 4834篇 |
1982年 | 5113篇 |
1981年 | 4817篇 |
1980年 | 4412篇 |
1979年 | 4828篇 |
1978年 | 5139篇 |
1977年 | 5231篇 |
1976年 | 5383篇 |
1975年 | 4972篇 |
1974年 | 4974篇 |
1973年 | 5129篇 |
1972年 | 4034篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V. P. Koshelets S. V. Shitov L. V. Filippenko P. N. Dmitriev A. N. Ermakov A. S. Sobolev M. Yu. Torgashin 《Radiophysics and Quantum Electronics》2003,46(8-9):618-630
We overview recent achievements in the field of cryogenic submillimeter-wave receivers based on superconductor–insulator–superconductor (SIS) tunnel junctions. The main attention is paid to the novel superconducting integrated receivers (SIRs) with an on-chip superconducting local oscillator. The single-chip microcircuit of the receiver, which integrates a quantum mixer based on the nonlinearity of a quasi-particle current in the SIS junction, a planar superconducting receiving antenna, and a cryogenic local oscillator, is described. Being dc-powered only by batteries, such a microcircuit operates as a submillimeter-wave superheterodyne receiver without any additional microwave equipment. Such receivers are very attractive for radioastronomical research, space communication systems, and monitoring of the environment from satellites, balloons, and special aircraft. A breadboard of a superconducting spectrometer with a phase-locked flux-flow oscillator (FFO) has been developed and tested. A frequency resolution better than 10 kHz was reached at a frequency of 365 GHz. We describe a balloon-borne 500-650 GHz integrated spectrometer for oblique atmospheric sounding, developed for the international Terahertz Limb Sounder (TELIS) project. The first flight is scheduled for 2005. 相似文献
992.
In this paper, we propose and analyze an SQP-type method for solving linearly constrained convex minimization problems where the objective functions are too complex to be evaluated exactly. Some basic results for global convergence and local superlinear convergence are obtained according to the properties of the approximation sequence. We illustrate the applicability of our approach by proposing a new method for solving two-stage stochastic programs with fixed recourse. 相似文献
993.
994.
To Professor Guillermo Torres on the occasion of his 70th birthday. 相似文献
995.
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.
We demonstrate a simple passive technique, using phase shifted fibre Bragg gratings, for extraction of optical clock signals from RZ optical data signals . The generation of an optical clock signal at 12.5 GHz from a 12.5 Gbs RZ optical data stream is experimentally demonstrated with simulation of optical clock extraction at 10 GHz fro m 40 Gbs OTDM data streams . 相似文献
998.
P. V. Pavlov I. V. Babushkin N. A. Loiko N. N. Rosanov S. V. Fedorov 《Radiophysics and Quantum Electronics》2004,47(10-11):898-904
We consider spatial dissipative solitons arising in the system of two nonlinear thin films which interact resonantly with light. Symmetric and nonsymmetric solitons and methods of their exciting and switching are studied. 相似文献
999.
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
1000.