全文获取类型
收费全文 | 202777篇 |
免费 | 1474篇 |
国内免费 | 426篇 |
专业分类
化学 | 104675篇 |
晶体学 | 3391篇 |
力学 | 10271篇 |
综合类 | 10篇 |
数学 | 21828篇 |
物理学 | 64502篇 |
出版年
2021年 | 1969篇 |
2020年 | 2008篇 |
2019年 | 2565篇 |
2018年 | 3656篇 |
2017年 | 3668篇 |
2016年 | 4806篇 |
2015年 | 2342篇 |
2014年 | 4295篇 |
2013年 | 8579篇 |
2012年 | 6829篇 |
2011年 | 8039篇 |
2010年 | 6454篇 |
2009年 | 6639篇 |
2008年 | 7629篇 |
2007年 | 7592篇 |
2006年 | 6689篇 |
2005年 | 5915篇 |
2004年 | 5635篇 |
2003年 | 5161篇 |
2002年 | 5151篇 |
2001年 | 5606篇 |
2000年 | 4137篇 |
1999年 | 3132篇 |
1998年 | 2698篇 |
1997年 | 2757篇 |
1996年 | 2540篇 |
1995年 | 2209篇 |
1994年 | 2326篇 |
1993年 | 2225篇 |
1992年 | 2522篇 |
1991年 | 2644篇 |
1990年 | 2552篇 |
1989年 | 2622篇 |
1988年 | 2531篇 |
1987年 | 2551篇 |
1986年 | 2411篇 |
1985年 | 3032篇 |
1984年 | 3101篇 |
1983年 | 2596篇 |
1982年 | 2562篇 |
1981年 | 2527篇 |
1980年 | 2335篇 |
1979年 | 2708篇 |
1978年 | 2671篇 |
1977年 | 2870篇 |
1976年 | 2872篇 |
1975年 | 2664篇 |
1974年 | 2602篇 |
1973年 | 2711篇 |
1972年 | 2085篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
962.
963.
UV–visible upconversion emission from terbium in a Tb–Yb codoped tellurite glass has been observed on 980-nm excitation. The
ultraviolet and violet upconversion emissions involve three photons and the blue, green, yellow, and red emissions arise due
to two incident photons. The mechanism involved in these emissions is discussed. The effects of doping concentration and of
the sample temperature on the upconversion emissions have also been studied.
PACS 74.25.Gz; 42.70.Hj; 73.61.Jc; 76.30.Kg; 42.70.Ce 相似文献
964.
N. S. Bukhman 《Technical Physics》2006,51(12):1608-1617
The waveform of the net signal from a set of closely spaced acoustic or electromagnetic transmitters generating identical (up to phase and amplitude factor) quasi-monochromatic signals is considered. If the partial signals are sufficiently long, the waveform of the envelope of the net signal from the set of transmitters turns out to be close to that of the partial signal envelope up to delay. The delay does not necessarily coincide with the time it takes for an optical (or acoustic) signal to travel the distance from the transmitter to the point of observation. At different sites of the space, the delay time may be real or complex. Its real part may be positive or negative and exceed, or be shorter than, the optical (acoustic) delay time. The delay strongly depends on the position of the point of observation (i.e., on whether it is located near a dark or bright interference fringe) and, in the case of short-wave signals, may vary considerably even at a slight displacement of the point of observation. 相似文献
965.
N. G. Kanev 《Acoustical Physics》2006,52(5):571-575
Effect of errors of different origin on the efficiency of sound absorption by a local active absorber is investigated. Degradation of the efficiency of absorption because of the errors is shown to be minimal in the case when the controller does not detect the field of the secondary radiator. Estimates of admissible errors are presented. Several active absorber configurations in which the radiator does not affect the receiver are considered. 相似文献
966.
E. S. Filatov S. V. Sysoev Ludmila N. Zelenina Tamara P. Chusova V. A. Logvinenko P. P. Semyannikov I. K. Igumenov 《Journal of Thermal Analysis and Calorimetry》2006,86(2):537-539
Thermal behaviour
of a series of lithium β-diketonates: Li(dpm) (dpm=dipivaloylmethanate
(2,2,6,6-tetramethylheptane-3,5- dionate)), Li(pta) (pta=pivaloyltrifluoracetonate
(2,2-dimethyl-6,6,6-trifluoro-3,5-hexanedionate)), Li(tfa) (tfa=trifluoracetylacetonate
(1,1,1-trifluoro-2,4-pentandionate)), Li(hfa) (hfa=hexafluoracetylacetonate
(1,1,1,5,5,5-hexafluoro-2,4-pentandionate)) has been investigated. Gas phase
composition of these complexes has been established. Temperature dependences
of vapor pressure of lithium compounds were obtained by static and dynamic
methods, and thermodynamic parameters were calculated. Dependence of compound
volatility on ligand structure is shown. For Li(dpm) detailed investigation
has been done by differential scanning calorimetry (DSC). 相似文献
967.
Various methods for assessing the performance of levelers in batch dyeing of synthetic fibrous materials were analyzed. Criteria most suitable for technological and scientific applications were chosen. 相似文献
968.
I. P. Dobrovol’skaya M. K. Mokeev Yu. N. Sazanov A. V. Gribanov T. E. Sukhanova 《Russian Journal of Applied Chemistry》2006,79(7):1178-1180
Changes in the supramolecular structure of heat-resistant fibers based on polyimide PM were studied by X-ray diffraction analysis and NMR spectroscopy. 相似文献
969.
970.
The frequency and the amplitude of the driving AC current dependence on the harmonic behavior of the giant magneto-impedance (GMI) voltage of Co-rich amorphous wire have been studied. Single-peak, two-peak and three-peak behavior in the GMI characteristics was studied with the change of amplitude and frequency of the AC current. GMI ratio was calculated from the first harmonic signals which were initially increased and then decreased monotonically with the increase of frequency (f) and the amplitude (IAC) of the driving current. The response of the GMI voltage was found non-linear with the generation of higher harmonics at higher amplitude of the driving current. The second and third harmonic signals were also evaluated and their dependence on the driving current amplitude and frequency were presented in the paper. The experimental results were analyzed using single domain rotational model. The voltage harmonics were calculated through Fourier transform of the time derivative of the estimated circular magnetization of the sample. 相似文献