全文获取类型
收费全文 | 298453篇 |
免费 | 2698篇 |
国内免费 | 683篇 |
专业分类
化学 | 141980篇 |
晶体学 | 4162篇 |
力学 | 11922篇 |
综合类 | 9篇 |
数学 | 29481篇 |
物理学 | 82832篇 |
无线电 | 31448篇 |
出版年
2019年 | 2504篇 |
2018年 | 3384篇 |
2017年 | 3341篇 |
2016年 | 4809篇 |
2015年 | 2799篇 |
2014年 | 4645篇 |
2013年 | 11269篇 |
2012年 | 8468篇 |
2011年 | 10389篇 |
2010年 | 7607篇 |
2009年 | 7777篇 |
2008年 | 10482篇 |
2007年 | 10982篇 |
2006年 | 10227篇 |
2005年 | 9426篇 |
2004年 | 8730篇 |
2003年 | 7936篇 |
2002年 | 7869篇 |
2001年 | 8479篇 |
2000年 | 6845篇 |
1999年 | 5413篇 |
1998年 | 4938篇 |
1997年 | 4903篇 |
1996年 | 4519篇 |
1995年 | 4245篇 |
1994年 | 4343篇 |
1993年 | 4024篇 |
1992年 | 4445篇 |
1991年 | 4513篇 |
1990年 | 4378篇 |
1989年 | 4158篇 |
1988年 | 4181篇 |
1987年 | 3818篇 |
1986年 | 3613篇 |
1985年 | 4688篇 |
1984年 | 4970篇 |
1983年 | 4166篇 |
1982年 | 4258篇 |
1981年 | 4191篇 |
1980年 | 4133篇 |
1979年 | 4075篇 |
1978年 | 4392篇 |
1977年 | 4307篇 |
1976年 | 4369篇 |
1975年 | 4014篇 |
1974年 | 4091篇 |
1973年 | 4242篇 |
1972年 | 3010篇 |
1971年 | 2499篇 |
1970年 | 2307篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Thermal Characterization of 1.3 μm InAsP/InGaAsP Ridge Waveguide MQW Lasers Based on Spectroscopy Method 总被引:1,自引:1,他引:0
An experimental way to analyze the thermal characterization of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed. By using this way the thermal characteristics of strain compensated 1.3 μm InAsP/InGaAsP ridge waveguide MQW laser diodes have been investigated. Results show that by measuring and analyzing the lasing spectra under appropriate driving parameters and temperature ranges, the thermal resistance of the laser diodes could be deduced easily. A higher thermal resistance of 640 K/W has been measured on a narrow ridge laser chip without soldering. Other thermal and spectral properties of the lasers have also been measured and discussed. 相似文献
994.
A scheme is proposed for increasing the sampling rate of analogue-to-digital conversion by more than an order of magnitude by combining state-of-the-art A/D converters with photonic technology. Ultra-high speed sampling is performed optically by a multiwavelength pulse train. Wavelength demultiplexers convert the high repetition rate data stream of samples into parallel data streams that can be handled by available electronic A/D converters 相似文献
995.
D. Kast A. Jungclaus K.P. Lieb M. Górska G. de Angelis P.G. Bizzeti A. Dewald C. Fahlander H. Grawe R. Peusquens M. De Poli H. Tiesler 《The European Physical Journal A - Hadrons and Nuclei》1998,3(2):115-128
In the neutron deficient isotopes 104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler
shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the
problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model
calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and
still fair agreement for most measured B(M1) and B(E2) values.
Received: 30 June 1998 相似文献
996.
Polyethyleneimine (PEIM) samples crosslinked by a commercial epoxy resin (Epon 828) were prepared, and their adsorption capacity for acidic gases was studied. The swelling and deswelling characteristics of the crosslinked samples were also examined as part of this program. Reactivation of these adsorbents could be carried out by heat, or by a combination of heat and treatment in dilute alkalies. 相似文献
997.
998.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. E. Stronach M. Davis S. Uchida H. Takagi Y. Tokura Y. Hidaka T. Murakami E. A. Early J. T. Markert M. B. Maple C. L. Seaman 《Hyperfine Interactions》1991,63(1-4):311-317
We report muon spin relaxation/rotation measurements on sintered powder samples of Nd2−x
Ce
x
CuO4−y
and a large single crystal of Nd2CuO4−y
. We find an electronic phase diagram which is quite similar to that of hole-doped superconductors such as La2−x
Sr
x
CuO4−y
, although the doping of electrons into the system is less efficient in destroying the static moments on the copper spins.
Static magnetic order in Nd2CuO4−y
appears below about 250 K, and two spin reorientations are seen atT=75 K andT=35 K. Measurements of the magnetic field penetration depth have been unsuccessful due to the rare-earth paramagnetism of
these materials. 相似文献
999.
W. Loveland K. Aleklett J. O. Liljenzin G. T. Seaborg 《Journal of Radioanalytical and Nuclear Chemistry》1992,160(1):181-189
The use of radioanalytical techniques to study heavy ion induced nuclear reactions offers some distinct advantages over conventional physical techniques. Among these are (a) unit Z and A resultion in detecting the reaction products (b) high sensitivity for low probability events (c) lack of low energy thresholds or cutoffs in measuring reactcion product energy spectcra (d) economical use of accelerator time and (e) simple, portable experimental apparatus allowing broad survey measurements of reaction mechanisms at a variety of nuclear particle accelerators. We describe examples of these advantages from our research in nuclear chemistry. 相似文献
1000.
G. Principi A. Maddalena Ajay Gupta R. Dal Maschio S. Diré 《Hyperfine Interactions》1992,69(1-4):619-622
Conversion electron Mössbauer spectroscopy (CEMS) has been used to study tin oxide films prepared by sol-gel dipping and sputtering. The spectra of films prepared by sol-gel route result close to that of crystalline SnO2 after heat treatment at a temperature as low as 150°C. The Mössbauer parameters of as sputter deposited films indicate that the structure of the deposited stannic oxide has an amorphous character more pronounced for thinner samples. The structure becomes predominantly that of crystalline SnO2 by heating at 550°C for 30 min provided the film thickness is higher than 10 nm. 相似文献