全文获取类型
收费全文 | 313230篇 |
免费 | 2891篇 |
国内免费 | 804篇 |
专业分类
化学 | 148634篇 |
晶体学 | 4752篇 |
力学 | 11086篇 |
综合类 | 12篇 |
数学 | 27545篇 |
物理学 | 84444篇 |
无线电 | 40452篇 |
出版年
2021年 | 2513篇 |
2020年 | 2965篇 |
2019年 | 3218篇 |
2018年 | 4049篇 |
2017年 | 4168篇 |
2016年 | 5954篇 |
2015年 | 3372篇 |
2014年 | 5638篇 |
2013年 | 13102篇 |
2012年 | 9792篇 |
2011年 | 11736篇 |
2010年 | 8844篇 |
2009年 | 9225篇 |
2008年 | 11383篇 |
2007年 | 11486篇 |
2006年 | 11018篇 |
2005年 | 10052篇 |
2004年 | 9291篇 |
2003年 | 8682篇 |
2002年 | 8372篇 |
2001年 | 9686篇 |
2000年 | 7564篇 |
1999年 | 6033篇 |
1998年 | 5100篇 |
1997年 | 4999篇 |
1996年 | 4682篇 |
1995年 | 4346篇 |
1994年 | 4248篇 |
1993年 | 4073篇 |
1992年 | 4768篇 |
1991年 | 4710篇 |
1990年 | 4546篇 |
1989年 | 4411篇 |
1988年 | 4264篇 |
1987年 | 3874篇 |
1986年 | 3674篇 |
1985年 | 4527篇 |
1984年 | 4623篇 |
1983年 | 3711篇 |
1982年 | 3817篇 |
1981年 | 3733篇 |
1980年 | 3471篇 |
1979年 | 3774篇 |
1978年 | 3865篇 |
1977年 | 3951篇 |
1976年 | 3702篇 |
1975年 | 3363篇 |
1974年 | 3343篇 |
1973年 | 3277篇 |
1972年 | 2325篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
Assaderaghi F. Chen J. Solomon R. Chian T.-Y. Ko P.K. Hu C. 《Electron Device Letters, IEEE》1991,12(10):518-520
It has been found that the subthreshold currents of fully depleted silicon-on-insulator (SOI) MOSFETs show a transient behavior under certain front-gate and back-gate voltage conditions. The cause of this anomaly is explained, and applications for the phenomenon are pointed out. Particularly, a simple way to measure the silicon film thickness is suggested 相似文献
222.
Bera L.K. Ray S.K. Mukhopadhyay M. Nayak D.K. Usami N. Shiraki Y. Maiti C.K. 《Electron Device Letters, IEEE》1998,19(8):273-275
Growth of ultrathin (<100 Å) oxynitride on strained-Si using microwave N2O and NH3 plasma is reported. X-ray photoelectron spectroscopy (XPS) results indicate a nitrogen-rich layer at the strained-Si/SiO2 interface. The electrical properties of oxynitrides have been characterized using a metal-insulator-semiconductor (MIS) structure. A moderately low value of insulator charge density (6.1×1010 cm-2) has been obtained for NH3 plasma treated N2O oxide sample. Nitrided oxide shows a larger breakdown voltage and an improved charge trapping properties under Fowler-Nordheim (F-N) constant current stress 相似文献
223.
Fundamental and dual variational principles of magnetostatics of superconductors are formulated. It is shown how test fields can be expressed in terms of vector and scalar potentials. General consequences of the variational magnetostatic formulation are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 97–102, September, 1991. 相似文献
224.
225.
226.
O. B. Lykova 《Ukrainian Mathematical Journal》1992,44(1):28-40
A survey is presented of some results relating to the development of the Bogolyubov-Mitropol'skii method of integral manifolds.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 1, pp. 33–46, January, 1992. 相似文献
227.
The discussion by R. Schanzer (see ibid., vol.44, p.620-1, 1995) tries to correct the algorithms of P.K. Varshney, et al. (see ibid., vol.43, p.378-82, 1994) and K.K Aggarwal (see ibid., vol.37, p.65-9, 1988). But Schanzer doesn't explain why those algorithms have difficulty in calculating the maximum flow. This paper explains the problem and gives a correction of the algorithm so that the basic problem can be solved 相似文献
228.
InGaAs/GaAs(100) multiple-quantum-well-based inverted cavity asymmetric Fabry-Perot modulators are vertically integrated with GaAs/AlGaAs heterojunction phototransistors to yield all-optical photonic switches. The photonic switches using `normally on' modulator pixels exhibit an output on-off ratio of 12:1 with internal optical gain of 4 dB. The photonic switches using `normally off' modulator pixels yield similar contrast and gain, but exhibit intrinsic bistable behavior. The inverted cavity modulators employed permit utilizing the transparency of the GaAs substrate at the operating wavelength and offer advantages for fabricating large arrays for optical signal processing 相似文献
229.
Theoretical studies point to significant improvements in the performance of semiconductor laser amplifiers by injecting carriers with pulsed electric currents of sub-nanosecond duration. A pulsed Fabry-Perot amplifier (FPA) is most sensitive to input lightwave at the instant the carrier density is crossing the critical region, and gives a sharply pulsed sampling effect on the input lightwave signal. Compared with a FPA operating at subcritical electron density, the pulsed amplifier gives much higher gain, peak power, and bandwidth. In fact, pulsed operation of a FPA is also expected to give significantly higher gain and about the same peak output power as a traveling wave amplifier. Pulsed operation also improves the performance of a traveling wave amplifier by attenuating its internally reflected waves 相似文献
230.
1-(3-Alkyl-2,3-dideoxy-alpha,beta-D-erythro-pentofuranosyl)uracils and 1-(3-alkyl-2,3-dideoxy-alpha,beta-D-threo-pentofuranosyl)uracils have been prepared from (E)-4,5-di-O-acetyl-2,3-dideoxy-aldehydo-D-glycero-pent-2-enose by a Michael addition reaction of the appropriate organocopper reagent followed in subsequent order by glycosidation of the resulting 3-alkyl-4,5-diacetoxypentanal with methanolic hydrogen chloride, protection with p-methoxybenzoyl chloride, and trimethylsilyl triflate catalyzed coupling with 2,4-di-O-(trimethylsilyl)uracil. The nucleosides were deprotected by treatment with 33% methylamine in absolute ethanol and separated by reversed-phase HPLC. 相似文献