全文获取类型
收费全文 | 266860篇 |
免费 | 3002篇 |
国内免费 | 817篇 |
专业分类
化学 | 136234篇 |
晶体学 | 4163篇 |
力学 | 11505篇 |
综合类 | 2篇 |
数学 | 31555篇 |
物理学 | 87220篇 |
出版年
2020年 | 2237篇 |
2019年 | 2360篇 |
2018年 | 3126篇 |
2017年 | 3049篇 |
2016年 | 4820篇 |
2015年 | 3155篇 |
2014年 | 4855篇 |
2013年 | 11943篇 |
2012年 | 9017篇 |
2011年 | 11164篇 |
2010年 | 7621篇 |
2009年 | 7411篇 |
2008年 | 10389篇 |
2007年 | 10323篇 |
2006年 | 9690篇 |
2005年 | 8778篇 |
2004年 | 7930篇 |
2003年 | 6938篇 |
2002年 | 6831篇 |
2001年 | 7668篇 |
2000年 | 5904篇 |
1999年 | 4624篇 |
1998年 | 3902篇 |
1997年 | 3803篇 |
1996年 | 3750篇 |
1995年 | 3407篇 |
1994年 | 3379篇 |
1993年 | 3544篇 |
1992年 | 3557篇 |
1991年 | 3631篇 |
1990年 | 3403篇 |
1989年 | 3303篇 |
1988年 | 3362篇 |
1987年 | 3234篇 |
1986年 | 3053篇 |
1985年 | 4234篇 |
1984年 | 4404篇 |
1983年 | 3560篇 |
1982年 | 3759篇 |
1981年 | 3702篇 |
1980年 | 3594篇 |
1979年 | 3649篇 |
1978年 | 3768篇 |
1977年 | 3680篇 |
1976年 | 3728篇 |
1975年 | 3413篇 |
1974年 | 3424篇 |
1973年 | 3460篇 |
1972年 | 2362篇 |
1971年 | 1986篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
951.
Liquid crystal televisions have been employed as spatial light modulators in a variety of optical image processing applications. We have used such devices to develop techniques in speckle metrology for the electronic addition of speckle patterns and the display of speckle correlation, and also for the real-time display of object motion. Factors which affect the performance in terms of the useful working range and the accuracy of displacement measurement are discussed. Some modifications to the LCTV which should increase the potential of these devices as spatial light modulators, when used in both amplitude and phase modulation, are considered briefly. 相似文献
952.
953.
In the framework of the extended Hubbard model (copper-oxygen and oxygen-oxygen hopping) the energy and effective mass of a mobile hole is expressed in terms of hopping parameters and the correlators between spins of the background SnSn+1. Due to interaction of the mobile hole with localized holes, its effective mass increases about four times. 相似文献
954.
H. Zöschinger 《Periodica Mathematica Hungarica》1992,25(1):1-11
955.
P. J. Skevington M. A. G. Halliwell M. H. Lyons S. J. Amin M. A. Z. Rejman-Greene G. J. Davies 《Journal of Crystal Growth》1992,120(1-4):328-332
InP/InGaAs multiple quantum well structures with up to 200 periods have been grown by CBE. These structures exhibit exceptional lateral uniformity, measured as ±1 Å in period, ±13 ppm in lattice mismatch and ±0.5 nm in wavelength across a 2 inch wafer. Good surface morphology, sharp interfaces and excellent growth control have all been demonstrated. 相似文献
956.
G. K. Hubler C. N. Waddell E. P. Donovan J. M. Zavada 《Optical and Quantum Electronics》1991,23(7):S883-S893
Precision reflection measurements were performed on GaAs/AlAs superlattices of the same composition but different layer spacings. Nonlinear-least-squares fits to the data were performed to a single layer. Measurements were extracted for the superlattice thickness, thickness of a disturbed interface layer between the superlattice and substrate, the uniformity in composition and/or spacing and the composition. It was demonstrated that these nondestructive measurements in the infrared region (3000 to 12 000 cm–1) in conjunction with a simple single layer model are capable of accurately yielding the above quantities with high precision. 相似文献
957.
Plasmatic accumulation of uraemic toxins in the middle molecular mass range has been reported to be associated with several pathologies observed in uraemic patients. The very low concentration of these toxins in uraemic body fluids makes classical chromatography techniques inadequate in isolating sufficient amounts of these endogenous substances, thus precluding their identification. A scaling up of gel permeation and ion-exchange chromatographies was therefore developed. This considerably increased the amount of uraemic toxins isolated, thus allowing the study of their chemical nature and facilitating understanding of their biological activities. 相似文献
958.
Summary We report on the development of an adaptive optimum filter for processing the data of a resonant bar gravitational-wave detector.
This filter, based on the matched-filter theory, is adaptive in the sense that the function it realizes is derived from the
actual noise spectrum of the data being analysed (instead from an idealized model of the noise). Its implementation is mostly
based on frequency domain techniques. We also report on the application of the new filter to the data of the cryogenic antenna
Explorer of the Rome group, with particular reference to the comparison between its performance and that of an otpimum filter
with fixed values of the parameters. 相似文献
959.
Techniques of uniformization are used to prove that it is not consistent that the Whitehead groups of cardinality ℵ1 are exactly the strongly ℵ1-free groups. Some consequences of the assumption that every strongly ℵ1-free group of cardinality ℵ1 is Whitehead are derived. Other results about uniformization are also proved.
Research partially supported by NSERC grant #9848.
Research partially supported by the BSF. The authors thank Rutgers University for its support. Publication #441. 相似文献
960.