全文获取类型
收费全文 | 1783篇 |
免费 | 39篇 |
国内免费 | 13篇 |
专业分类
化学 | 1072篇 |
晶体学 | 8篇 |
力学 | 79篇 |
数学 | 186篇 |
物理学 | 490篇 |
出版年
2021年 | 12篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2016年 | 24篇 |
2015年 | 14篇 |
2014年 | 24篇 |
2013年 | 75篇 |
2012年 | 68篇 |
2011年 | 119篇 |
2010年 | 47篇 |
2009年 | 54篇 |
2008年 | 82篇 |
2007年 | 87篇 |
2006年 | 82篇 |
2005年 | 89篇 |
2004年 | 67篇 |
2003年 | 58篇 |
2002年 | 56篇 |
2001年 | 33篇 |
2000年 | 35篇 |
1999年 | 26篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 24篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 25篇 |
1991年 | 23篇 |
1990年 | 36篇 |
1989年 | 30篇 |
1988年 | 35篇 |
1987年 | 29篇 |
1986年 | 26篇 |
1985年 | 33篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 17篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 23篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 25篇 |
1974年 | 12篇 |
1973年 | 29篇 |
1972年 | 10篇 |
1970年 | 12篇 |
1967年 | 10篇 |
排序方式: 共有1835条查询结果,搜索用时 187 毫秒
41.
Laser projection-patterned etching of GaAs in a HCl and CH3Cl atmosphere performed using a pulsed KrF-excimer laser (=248 nm, =15 ns) and deep-UV projection optics (resolution 2 m) is reported. The etching process carried out in a vacuum system having a base pressure of 10–6 mbar is shown to result from a purely thermochemical reaction. Etching takes place in two steps: (i) between the laser pulses, the etchant gas reacts with the GaAs surface-atomic layer to form chlorination products (mainly As and Ga monochlorides), (ii) local laser surface heating results in the desorption of these products allowing further reaction of the gas with the surface. The influence of the etching parameters (laser energy density, gas pressure and pulse repetition rate) on the etch rate and the morphology of the etched features was studied. Etch rates up to 0.15 nm per pulse, corresponding to the removal of 0.5 GaAs molecular layer, are achieved. The spatial resolution of the etching process is shown to be controlled by the heat spread in the semiconductor and by the nonlinear dependence of the etch rate on the surface temperature. As a result, etched features smaller or larger than the projected features of the photomask are achieved depending on the laser energy density. Etched lines having a width of 1.3 m were obtained at low fluences by the projection of 2 m wide lines onto the GaAs surface. 相似文献
42.
Ahlen S Ambrosio M Antolini R Auriemma G Baker R Baldini A Bam BB Barbarino GC Barish BC Battistoni G Bellotti R Bemporad C Bernandini P Bilokon H Bisi V Bloise C Bower C Bussino S Cafagna F Calicchio M Campana D Campana P Carboni M Cecchini S Cei F Chiarella V Cormack R Corona A Coutu S De Cataldo G Dekhissi H De Marzo C De Vincenzi M Di Credico A Diehl E Erriquez O Favuzzi C Ficenec D Forti C Fusco P Giacomelli G Giannini G Giglietto N Giubellino P Grassi M Green P Grillo A Guarino F 《Physical review letters》1994,72(5):608-612
43.
44.
Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Halling AM Jedicke R Karchin PE Kwan S Leuking LH Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review D: Particles and fields》1994,49(9):R4317-R4320
45.
Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Dagenhart WD Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Karchin PE Kennedy C Kwan S Lueking LH de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review letters》1996,77(12):2388-2391
46.
47.
48.
Alves GA Amato S Anjos JC Appel JA Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Kaplan D Karchin PE Kwan S Leedom I Lueking LH Luste GJ Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Rafatian A dos Reis AC Reucroft S Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wu Z 《Physical review letters》1993,70(6):722-725
49.
[reaction: see text]. The synthesis of a range of 3-pyrrolines has been achieved from primary amine starting materials using a two-step alkylation/alkylidene carbene CH-insertion reaction sequence. We have shown that insertion into a range of CH-bond types is possible, and the formation of nitrogen-bearing quaternary stereocenters is a relatively facile process. The insertion reaction occurs with >95% retention of stereochemistry, but the presence of protecting groups on nitrogen is generally deleterious to the cyclization process. 相似文献
50.
Haque SA Palomares E Cho BM Green AN Hirata N Klug DR Durrant JR 《Journal of the American Chemical Society》2005,127(10):3456-3462
In this paper we focus upon the electron injection dynamics in complete dye-sensitized nanocrystalline metal oxide solar cells (DSSCs). Electron injection dynamics are studied by transient absorption and emission studies of DSSCs and correlated with device photovoltaic performance and charge recombination dynamics. We find that the electron injection dynamics are dependent upon the composition of the redox electrolyte employed in the device. In a device with an electrolyte composition yielding optimum photovoltaic device efficiency, electron injection kinetics exhibit a half time of 150 ps. This half time is 20 times slower than that for control dye-sensitized films covered in inert organic liquids. This retardation is shown to result from the influence of the electrolyte upon the conduction band energetics of the TiO2 electrode. We conclude that optimum DSSC device performance is obtained when the charge separation kinetics are just fast enough to compete successfully with the dye excited-state decay. These conditions allow a high injection yield while minimizing interfacial charge recombination losses, thereby minimizing "kinetic redundancy" in the device. We show furthermore that the nonexponential nature of the injection dynamics can be simulated by a simple inhomogeneous disorder model and discuss the relevance of our findings to the optimization of both dye-sensitized and polymer based photovoltaic devices. 相似文献