全文获取类型
收费全文 | 1656篇 |
免费 | 227篇 |
国内免费 | 94篇 |
专业分类
化学 | 604篇 |
晶体学 | 11篇 |
力学 | 68篇 |
综合类 | 6篇 |
数学 | 105篇 |
物理学 | 412篇 |
无线电 | 771篇 |
出版年
2024年 | 7篇 |
2023年 | 49篇 |
2022年 | 37篇 |
2021年 | 63篇 |
2020年 | 56篇 |
2019年 | 48篇 |
2018年 | 39篇 |
2017年 | 50篇 |
2016年 | 55篇 |
2015年 | 65篇 |
2014年 | 69篇 |
2013年 | 121篇 |
2012年 | 120篇 |
2011年 | 125篇 |
2010年 | 85篇 |
2009年 | 85篇 |
2008年 | 93篇 |
2007年 | 100篇 |
2006年 | 99篇 |
2005年 | 65篇 |
2004年 | 62篇 |
2003年 | 52篇 |
2002年 | 49篇 |
2001年 | 51篇 |
2000年 | 38篇 |
1999年 | 33篇 |
1998年 | 25篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 23篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1938年 | 1篇 |
排序方式: 共有1977条查询结果,搜索用时 0 毫秒
1.
Chun-Tsen Lu Kun-Wei Lin Huey-Ing Chen Hung-Ming Chuang Chun-Yuan Chen Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(6):390-392
A new and interesting Pd-oxide-Al/sub 0.3/Ga/sub 0.7/As MOS hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations has been measured at various temperatures. Based on the large Schottky barrier height and presence of oxide layer, the studied device exhibits a high hydrogen detection sensitivity and wide temperature operating regime. The studied device exhibits the low-leakage current and obvious current changes when exposed to hydrogen-contained gas. Even at room temperature, a very high hydrogen detection sensitivity of 155.9 is obtained when a 9090 ppm H/sub 2//air gas is introduced. Furthermore, when exposed to hydrogen-contained gas at 95/spl deg/C, both the forward and reverse currents are substantially increased with increased hydrogen concentration. In other words, the studied device can be used as a hydrogen sensor under the applied bidirectional bias. Under the applied voltage of 0.35 V and 9090 ppm H/sub 2//air hydrogen ambient, a fast adsorption response time about 10 s is found. The transient and steady-state characteristics of hydrogen adsorption are also investigated. 相似文献
2.
Chun-Yuan Chen Shiou-Ying Cheng Wen-Hui Chiou Hung-Ming Chuang Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(3):126-128
A novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) is fabricated and demonstrated. The studied device exhibits a very small collector-emitter offset voltage of 40 mV and an extremely wide operation regime. The operation region is larger than 11 decades in magnitude of collector current (10/sup -12/ to 10/sup -1/A). A current gain of 3 is obtained even if the device is operated at an ultralow collector current of 3.9 /spl times/ 10/sup -12/A (1.56 /spl times/ 10/sup -7/A/cm/sup 2/). Furthermore, the common-emitter breakdown voltage of the studied device is higher than 2 V. Consequently, the studied device shows a promise for low supply voltage, and low-power consumption circuit applications. 相似文献
3.
A theory for the electronic band structure and the free-carrier optical gain of wurtzite-strained quantum-well lasers is presented. We take into account the strain-induced band-edge shifts and the realistic band structures of the GaN wurtzite crystals. The effective-mass Hamiltonian, the basis functions, the valence band structures, the interband momentum matrix elements, and the optical gain are presented with analytical expressions and numerical results for GaN-AlGaN strained quantum-well lasers. This theoretical model provides a foundation for investigating the electronic and optical properties of wurtzite-strained quantum-well lasers. 相似文献
4.
A wireless personal communications system, based on a TDMA architecture, using asynchronous ports (radio base stations) and the TDD (time division duplexing) method is evaluated using computer simulations. It is shown that, without port synchronisation TDD methods cannot achieve the uplink quality obtainable by the FDD (frequency division duplexing) method.<> 相似文献
5.
6.
Eleven human hair samples were taken from the Chinese residents of Hong Kong for the study of hair trace elemental level and
environmental exposures. Absolute neutron activation analysis and Ge(Li) gamma-ray spectrometry were applied in the determination
of the trace elemental level. All results are reported in parts per million except for sulfur and oxygen which are reported
in percent. The trace element content of hair from a drug addict was found to be considerably different from other sampled
people. Comparison of the normal concentrations of the trace elements of the Chinese residents of Hong Kong was made with
those from people of various other national, socio-cultural and environmental backgrounds. It was found that together with
a few other trace elements, Ni, Sr, Zr and Hg content of the Chinese Residents of Hong Kong show a higher level than those
of the other sampled people. 相似文献
7.
8.
9.
Methods for synthesizing bistolane liquid crystal materials with lateral methyl and ethyl substituents are presented. Some of the bistolanes are nematic at room temperature. These highly conjugated mesogens exhibit wide nematic ranges, small enthalpies of fusion, high birefringence and modest viscosity. Their potential applications for flat panel displays employing light scattering or Bragg reflection and for infrared optically phased arrays are foreseeable. 相似文献
10.