全文获取类型
收费全文 | 432篇 |
免费 | 21篇 |
专业分类
化学 | 181篇 |
力学 | 22篇 |
数学 | 33篇 |
物理学 | 115篇 |
无线电 | 102篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 16篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 22篇 |
2005年 | 14篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 21篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1971年 | 4篇 |
1933年 | 5篇 |
1886年 | 2篇 |
1883年 | 2篇 |
排序方式: 共有453条查询结果,搜索用时 11 毫秒
111.
Kennedy JH Bowers JL Dodge JA Lugar CW Shepherd TA Sharp VS 《Journal of chromatography. A》2000,872(1-2):75-84
Chromatographic separations of new growth hormone secretagogue compounds were developed to support structure-activity relationship (SAR) studies in conjunction with lead optimization. These new compounds differed from Merck's MK-677 by having two chiral centers and thus diastereomeric mixtures were generated. Separation of initial compounds in the SAR was achieved on a Kromasil C18 column using an ammonium acetate buffer and acetonitrile. However, additional candidates were not separable on C18 columns and a chiral Kromasil CHI-DMB column was used to resolve the diastereomeric compounds. The Kromasil CHI-DMB packing was also used in a preparative chromatographic system to resolve multigram quantities of secretagogue candidates for testing. Chiral separations of different intermediates were also developed in support of evolution of an asymmetric synthetic route. This report summarizes development of the preparative chromatographic system used to purify diastereomeric mixtures and chiral separations of intermediates in the synthesis. 相似文献
112.
113.
Energy spectra for decaying 2D turbulence in a bounded domain 总被引:1,自引:0,他引:1
We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase. 相似文献
114.
115.
R. Manasseh R. F. LaFontaine J. Davy I. Shepherd Y.-G. Zhu 《Experiments in fluids》2001,30(6):672-682
Passive acoustic bubble sizing was investigated in both controlled tests and in a stirred, sparged tank typical of the biotechnology
or minerals processing industries. Acoustic techniques have promise for industrial systems where other bubble analysis methods
are impractical. Acoustic signals were studied for bubbles precisely formed at higher airflow rates. Acoustic pulses varied
with bubble production rate as well as with bubble size. A technique of windowing pulses is proposed. Two alternative versions
of this windowing technique were applied to a stirred, sparged tank, giving good agreement. It was shown that, in some cases,
it may also be possible to acoustically estimate the spatial distribution of void fraction.
Received: 13 June 2000/Accepted: 19 October 2000 相似文献
116.
Kienle F Teh PS Alam SU Gawith CB Hanna DC Richardson DJ Shepherd DP 《Optics letters》2010,35(21):3580-3582
We report a high-energy optical parametric oscillator (OPO) synchronously pumped by a 7.19 MHz, Yb:fiber-amplified, picosecond, gain-switched laser diode. The 42-m-long ring cavity maintains a compact design through the use of an intracavity optical fiber. The periodically poled MgO-doped LiNbO(3) OPO provides output pulse energies as high as 0.49 μJ at 1.5 μm (signal) and 0.19 μJ at 3.6 μm (idler). Tunability from 1.5 to 1.7 μm and from 2.9 to 3.6 μm is demonstrated, and typical M(2) values of 1.5 × 1.3 and 2.8 × 1.9 are measured for the signal and idler, respectively, at high power. 相似文献
117.
Novel integrated paired emitter-detector diode (PEDD) as a miniaturized photometric detector in HPLC
O'Toole M Lau KT Shazmann B Shepherd R Nesterenko PN Paull B Diamond D 《The Analyst》2006,131(8):938-943
A novel low power, low cost, highly sensitive, miniaturized light emitting diode (LED) based flow detector has been used as optical detector for the detection of sample components in high performance liquid chromatography (HPLC). This colorimetric detector employs two LEDs, one operating in normal mode as a light source and the other is reverse biased to work as a light detector. Instead of measuring the photocurrent directly, a simple timer circuit is used to measure the time taken for the photocurrent generated by the emitter LED (lambda(max) 500 nm) to discharge the detector LED (lambda(max) 621 nm) from 5 V (logic 1) to 1.7 V (logic 0) to give digital output directly without using an A/D converter. Employing a post-column reagent method, a Nucleosil 100-7 column (functionalized with iminodiacetic acid (IDA) groups) was used to separate a mixture of transition metal complexes, manganese(II) and cobalt(II) in 4-(2-pyridylazo)-resorcinol (PAR). All optical measurements were taken by using both the in-built HPLC variable wavelength detector and the proposed paired-emitter-detector-diode (PEDD) optical detector configured in-line for data comparison. The concentration range investigated using the PEDD was found to give a linear response to the Mn(II) and Co(II) PAR complexes. The effects of flow rate and emitter LED light source intensity were investigated. Under optimised conditions the PEDD detector offered a linear range of 0.9-100 microM and LOD of 0.09 microM for Mn-PAR complex. A linear range of 0.2-100 microM and LOD of 0.09 microM for Co-PAR complex was achieved. 相似文献
118.
119.
Engineering the embedded software radio 总被引:1,自引:0,他引:1
Software-defined radios allow flexible implementation of different basebands in digital signal processors. For communications transceivers this introduces an engineering problem: how to manage the different protocol stacks that may be required to work above the baseband software. To solve this, we propose a consistent software architectural framework for the dynamic implementation of these different protocols within an embedded environment. We discuss its requirements and present one possible approach based on STREAMS 相似文献
120.
The extremely low efficiency of the intramolecular energy transfer process in europium acetylacetonate compared with the corresponding terbium acetylacetonate is attributed to the presence of a charge-transfer excited state lying below the ligand singlet states. This is supported by the anomalous absorption spectrum of the Eu3+ complex and the effects of added anions in other ligand systems. 相似文献