全文获取类型
收费全文 | 14291篇 |
免费 | 2254篇 |
国内免费 | 1352篇 |
专业分类
化学 | 7129篇 |
晶体学 | 89篇 |
力学 | 682篇 |
综合类 | 85篇 |
数学 | 1210篇 |
物理学 | 4605篇 |
无线电 | 4097篇 |
出版年
2024年 | 69篇 |
2023年 | 379篇 |
2022年 | 455篇 |
2021年 | 617篇 |
2020年 | 541篇 |
2019年 | 505篇 |
2018年 | 440篇 |
2017年 | 432篇 |
2016年 | 627篇 |
2015年 | 647篇 |
2014年 | 732篇 |
2013年 | 984篇 |
2012年 | 1176篇 |
2011年 | 1247篇 |
2010年 | 813篇 |
2009年 | 859篇 |
2008年 | 861篇 |
2007年 | 764篇 |
2006年 | 755篇 |
2005年 | 628篇 |
2004年 | 473篇 |
2003年 | 430篇 |
2002年 | 395篇 |
2001年 | 311篇 |
2000年 | 330篇 |
1999年 | 301篇 |
1998年 | 281篇 |
1997年 | 264篇 |
1996年 | 217篇 |
1995年 | 254篇 |
1994年 | 228篇 |
1993年 | 188篇 |
1992年 | 138篇 |
1991年 | 111篇 |
1990年 | 110篇 |
1989年 | 81篇 |
1988年 | 55篇 |
1987年 | 42篇 |
1986年 | 39篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 24篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
Yanbin Luo Jianhui Zhang Alexandrov P. Fursin L. Zhao J.H. Burke T. 《Electron Device Letters, IEEE》2003,24(11):695-697
This letter reports the design and fabrication of 4H-SiC bipolar junction transistors with both high voltage (>1kV) and high dc current gain (/spl beta/=32) at a collector current level of I/sub c/=3.83A (J/sub c/=319 A/cm/sup 2/). An Al-free base ohmic contact has been used which, when compared with BJTs fabricated with Al-based base contact, shows clearly improved blocking voltage. A specific on-resistance of 17 m/spl Omega//spl middot/cm/sup 2/ has been achieved for collector current densities up to 289 A/cm/sup 2/. 相似文献
12.
Retractable structures which alter their geometries according to practical requirements are widely used in roof structures of stadiums for their versatility. A retractable structure based on threefold-symmetric Bricard linkages and rotating rings of tetrahedra is proposed and developed in this paper. By replacing each link of a threefold-symmetric Bricard linkage with a tetrahedron, a retractable structure is obtained which can repeatedly open and close by rotating the tetrahedra. The geometric relationship between the retractable structure and the threefold-symmetric Bricard linkage is derived and ranges of main geometric parameters are determined to ensure a continuous and smooth movement in the deployment of the structure. Then the relative displacement of the support and the open rate of the structure, two main parameters concerned in practical applications, are investigated. Preferred ranges of main geometric parameters are proposed and a physical model is manufactured to verify them. A discussion on some possible improvements and modifications of the structure is also presented. 相似文献
13.
14.
Examines the use of magnetic fields to functionally stimulate peripheral nerves. All electric fields are induced via a changing magnetic field whose flux is entirely confined within a closed magnetic circuit. Induced electric fields are simulated using a nonlinear boundary element solver. The induced fields are solved using duality theory. The accuracy of these predictions is verified by saline bath experiments. Next, the theory is applied to the stimulation of nerves using small, partially occluded ferrite and laminated vanadium permendur cores. Experiments demonstrate the successful stimulation of peripheral nerves in the African bullfrog with 11 mA, 153 mV excitations. These results offer a new vista of possibilities in the area of functional nerve stimulation. Unlike functional electric stimulation (FES), FMS does not involve any half cell reactions, and thus would not have the commensurate FES restrictions regarding balanced biphasic stimulation, strength duration balances, and oxidation issues, always exercising care that the electrodes remain in the reversible operating regime 相似文献
15.
Gillespie J.K. Fitch R.C. Sewell J. Dettmer R. Via G.D. Crespo A. Jenkins T.J. Luo B. Mehandru R. Kim J. Ren F. Gila B.P. Onstine A.H. Abernathy C.R. Pearton S.J. 《Electron Device Letters, IEEE》2002,23(9):505-507
The low temperature (100°C) deposition of Sc2O3 or MgO layers is found to significantly increase the output power of AlGaN/GaN HEMTs. At 4 GHz, there was a better than 3 dB increase in output power of 0.5×100 μm2 HEMTs for both types of oxide passivation layers. Both Sc2 O3 and MgO produced larger output power increases at 4 GHz than conventional plasma-enhanced chemical vapor deposited (PECVD) SiNx passivation which typically showed ⩽2 dB increase on the same types of devices. The HEMT gain also in general remained linear over a wider input power range with the Sc2O3 or MgO passivation. These films appear promising for reducing the effects of surface states on the DC and RF performance of AlGaN/GaN HEMTs 相似文献
16.
17.
18.
[reaction: see text]. The riboflavin-catalyzed photooxidation of 2',3',5'-tri-O-acetyl-8-oxo-7,8-dihydroguanosine generates a radical intermediate that is competitively trapped by H(2)O, O2(-)(*), or O(2). The products of H(2)O trapping have been previously described as the spiroiminodihydantoin (pH >or= 7) and iminoallantoin/guanidinohydantoin (pH < 7) nucleosides. Trapping by O2(-)(*) leads to the oxaluric acid (pH or= 8.6) pathways (R' ', R' ' = H or 2,3,5-tri-O-Ac-ribofuranosyl). The pH-dependent role of superoxide was probed using Mn-SOD and compared to guanosine and 8-methoxyguanosine photooxidation. 相似文献
19.
20.
X. Zhou Y. Guo X. Sun X. Lei X. Chen Z. Liu Y. Zhang H. Jin Y. Luo S. X. Wen G. J. Yuan G. S. Li C. X. Yang 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(1):3-4
The high spin states of119Te, populated in110Pd(13C,4n) and110Pd(12C,3n) reactions, have been studied through -ray spectroscopy. The level scheme has been established upto a spin of 55/2. Three-quasiparticle states, based on g2
7/2h11/2 and g7/2d5/2h11/2 configurations, have been identified. The 35/2 and 39/2 states are suggested to be the fully aligned states constituted by five valence h11/2
3, g7/2, d5/2 quasiparticles. 相似文献