全文获取类型
收费全文 | 135篇 |
免费 | 1篇 |
专业分类
化学 | 3篇 |
物理学 | 133篇 |
出版年
2017年 | 1篇 |
2016年 | 2篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 7篇 |
2011年 | 3篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 10篇 |
2005年 | 5篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 15 毫秒
91.
The generation of continuously tunable UV radiation in the wavelength range 2300–3000 Å by frequency doubling the output of a nitrogen pumped dye laser is described. A lithium formate monohydride crystal 10 mm long yields a conversion efficiency of typically 2% at fundamental powers in excess of 50 kW and allows the generation of harmonic radiation at wavelengths 150 Å below those attainable using a refrigerated ammonium dihydrogen phosphate crystal. 相似文献
92.
K. Eggert K.L. Giboni W. Thomé B. Betev P. Darriulat P. Dittmann M. Holder K.T. McDonald H.G. Pugh G. Vesztergombi T. Modis K. Tittel V. Eckardt H.J. Gebauer R. Meinke O.R. Sander P. Seyboth 《Nuclear Physics B》1975,98(1):49-72
We present a study of the transverse momentum spectrum of π0's produced at c.m. angles θ = 90° and 53° in pp collisions at √s = 23.6, 30.8, 45.1, 53.2, and 62.9 GeV. The experiment was performed with a lead-glass detector. The data can be described with the usual parametrization , with n = 7.2 ± 0.2. Comparison between the 90° and 53° data further indicates no appreciable dependence on θ, at least for xT < 0.3. Two-particle inclusive cross sections for π0's produced alongside are also presented. They are observed to have a dependence upon the transverse momentum of the dipion similar to that of single-particle cross sections and with the same value of n. Two-photon decays of η mesons are observed between 3 and 4 GeV/c transverse momentum with a production cross section half of that of π0. 相似文献
93.
A sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) was evaluated for the detection of trace levels of ethylene
at atmospheric pressure using a fiber coupled DFB diode laser emitting in the 1.62 μm spectral range. A noise-equivalent QEPAS signal of ∼4 ppm C2H4 was achieved for a 0.7 s data acquisition time using wavelength-modulation with a second-harmonic detection scheme on the
strongest C2H4 absorption peak at 6177.14 cm−1 with an average optical power of ∼15 mW. Improved detection sensitivity of 0.5 and 0.3 ppm C2H4 (1σ) was demonstrated using longer averaging time of 70 and 700 s, respectively. Important characteristics for the QEPAS based
sensor operation in real-world conditions are presented, particularly the influence of external temperature variations. Furthermore,
the response time of the ethylene sensor was measured in different configurations and it is shown that the QEPAS technique
can provide a response time in a few seconds range even without active gas flow. 相似文献
94.
Kosterev AA Curl RF Tittel FK Rochat M Beck M Hofstetter D Faist J 《Applied physics. B, Lasers and optics》2002,75(2-3):351-357
Pulsed thermoelectrically cooled QC-DFB lasers operating at 15.6 μm were characterized for spectroscopic gas sensing applications.
A new method for wavelength scanning based on repetition rate modulation was developed. A non-wavelength-selective pyroelectric
detector was incorporated in the sensor configuration giving the advantage of room-temperature operation and low cost. Absorption
lines of CO2 and H2O were observed in ambient air, providing information about the concentration of these species.
Received: 29 April 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-713/348-5686, E-mail: akoster@rice.edu 相似文献
95.
A portable modular gas sensor for measuring the 13C/12C isotopic ratio in CO2 with a precision of 0.8‰(±1σ) was developed for volcanic gas emission studies. This sensor employed a difference frequency generation (DFG)-based spectroscopic
source operating at 4.35 μm (∼2300 cm-1) in combination with a dual-chamber gas absorption cell. Direct absorption spectroscopy using this specially designed cell
permitted rapid comparisons of isotopic ratios of a gas sample and a reference standard for appropriately selected CO2 absorption lines. Special attention was given to minimizing undesirable precision degrading effects, in particular temperature
and pressure fluctuations.
Received: 16 April 2002 / Revised version: 28 May 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-713/5245237, E-mail: fkt@rice.edu 相似文献
96.
K. Eggert H. Frenzel K.L. Giboni W. Thomé B. Betev P. Darriulat P. Dittmann M. Holder K.T. McDonald H.G. Pugh T. Modis K. Tittel V. Eckardt H.J. Gebauer R. Meinke O.R. Sander P. Seyboth 《Nuclear Physics B》1975,98(1):93-99
We present a measurement of the total cross section σt in proton-proton collisions at the CERN ISR. The method involves determination of the total interaction rate and machine luminosity. A two-arm scintillation hodoscope observes ~ 90% of the total interaction rate, while a streamer chamber is employed for event topologies missed by the main trigger. An increase of about 10% in σt is observed in the energy range √s = 23.6 to √s = 62.8 GeV/c in agreement with previous experiments. 相似文献
97.
Larrabee DC Khodaparast GA Tittel FK Kono J Scalari G Ajili L Faist J Beere H Davies G Linfield E Ritchie D Nakajima Y Nakai M Sasa S Inoue M Chung S Santos MB 《Optics letters》2004,29(1):122-124
Quantum-cascade lasers operating at 4.7, 3.5, and 2.3 THz have been used to achieve cyclotron resonance in InAs and InSb quantum wells from liquid-helium temperatures to room temperature. This represents one of the first spectroscopic applications of terahertz quantum-cascade lasers. Results show that these compact lasers are convenient and reliable sources with adequate power and stability for this type of far-infrared magneto-optical study of solids. Their compactness promises interesting future applications in solid-state spectroscopy. 相似文献
98.
D.?WeidmannEmail author F.K.?Tittel T.?Aellen M.?Beck D.?Hofstetter J.?Faist S.?Blaser 《Applied physics. B, Lasers and optics》2004,79(7):907-913
A recently developed distributed feedback quantum cascade laser (QCL) capable of thermoelectric-cooled (TEC) continuous-wave (cw) operation and emitting at 9 m is used to perform laser chemical sensing by tunable infrared spectroscopy. A quasi-continuous-wave mode of operation relying on long current pulses (5 Hz, 50% duty cycle) is utilized rather than pure cw operation in order to extend the continuous frequency tuning range of the quantum cascade laser. Sulfur dioxide and ammonia were selected as convenient target molecules to evaluate the performance of the cw TEC QCL based sensor. Direct absorption spectroscopy and wavelength-modulation spectroscopy were performed to demonstrate chemical sensing applications with this novel type of quantum cascade laser. For ammonia detection, a 18-ppm noise-equivalent sensitivity (1 ) was achieved for a 1-m absorption path length and a 25-ms data-acquisition time using direct absorption spectroscopy. The use of second-harmonic-detection wavelength-modulation spectroscopy instead of direct absorption increased the sensitivity by a factor of three, achieving a normalized noise-equivalent sensitivity of 82 ppbHz-1/2 for a 1-m absorption path length, which corresponds to 2×10-7 cm-1Hz-1/2. PACS 42.55.Px; 42.62.Fi; 07.88.+y 相似文献
99.
A.K.Y. Ngai S.T. Persijn I.D. Lindsay A.A. Kosterev P. Gro? C.J. Lee S.M. Cristescu F.K. Tittel K.-J. Boller F.J.M. Harren 《Applied physics. B, Lasers and optics》2007,89(1):123-128
A continuous wave optical parametric oscillator, generating up to 300 mW idler output in the 3–4 μm wavelength region, and
pumped by a fiber-amplified DBR diode laser is used for trace gas detection by means of quartz-enhanced photoacoustic spectroscopy
(QEPAS). Mode-hop-free tuning of the OPO output over 5.2 cm-1 and continuous spectral coverage exceeding 16.5 cm-1 were achieved via electronic pump source tuning alone. Online monitoring of the idler wavelength, with feedback to the DBR
diode laser, provided an automated closed-loop control allowing arbitrary idler wavelength selection within the pump tuning
range and locking of the idler wavelength with a stability of 1.7×10-3 cm-1 over at least 30 min.
Using this approach, we locked the idler wavelength at an ethane absorption peak and obtained QEPAS data to verify the linear
response of the QEPAS signal at different ethane concentrations (100 ppbv-20 ppmv) and different power levels. The detection
limit for ethane was determined to be 13 ppbv (20 s averaging), corresponding to a normalized noise equivalent absorption
coefficient of 4.4×10-7 cm-1 W/Hz1/2.
PACS 42.55.Wd; 42.65.Yj; 42.62.Fi 相似文献
100.
We present a setup for quantum cryptography based on photon pairs in energy-time Bell states and show its feasibility in a laboratory experiment. Our scheme combines the advantages of using photon pairs instead of faint laser pulses and the possibility to preserve energy-time entanglement over long distances. Moreover, using four-dimensional energy-time states, no fast random change of bases is required in our setup: Nature itself decides whether to measure in the energy or in the time base, thus rendering eavesdropper attacks based on "photon number splitting" less efficient. 相似文献