全文获取类型
收费全文 | 673篇 |
免费 | 204篇 |
国内免费 | 43篇 |
专业分类
化学 | 85篇 |
晶体学 | 55篇 |
力学 | 1篇 |
综合类 | 2篇 |
数学 | 3篇 |
物理学 | 774篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 17篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 33篇 |
2013年 | 47篇 |
2012年 | 35篇 |
2011年 | 58篇 |
2010年 | 46篇 |
2009年 | 47篇 |
2008年 | 46篇 |
2007年 | 50篇 |
2006年 | 71篇 |
2005年 | 47篇 |
2004年 | 49篇 |
2003年 | 29篇 |
2002年 | 49篇 |
2001年 | 18篇 |
2000年 | 46篇 |
1999年 | 17篇 |
1998年 | 17篇 |
1997年 | 21篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有920条查询结果,搜索用时 15 毫秒
121.
对p型掺杂13 μm InAs/GaAs量子点激光器的最大模式增益进行了实验和理论分析.实验上,测量了不同腔长激光器阈值电流密度与总损耗的对应关系,拟合出的最大模式增益为175 cm-1,与相同结构非掺杂量子点激光器的最大模式增益一致.同时理论分析表明,p型掺杂对InAs/GaAs量子点激光器的最大模式增益并无影响,并且最大模式增益的计算结果与实验值相符.具有较小高度或高宽比的量子点能达到更高的最大模式增益,而较高的最大模式增益对p型掺杂13 μm InAs/GaAs自组织量子点激光器在光通信系统中的应用具有重要意义.
关键词:
最大模式增益
p型掺杂
InAs/GaAs量子点激光器 相似文献
122.
Plastic deformation in two‐inch diameter GaAs wafers resulted from standard thermal treatments which accompanied epitaxial growth in molecular beam epitaxy (MBE) machines of three different makes. Synchrotron based X‐ray transmission topography was used to distinguish between thermal treatment induced dislocation bundles and misfit dislocations. Eradication of the wafer slip related dislocation bundles has been achieved by modifications to the sample holder of a user built MBE machine. These modifications are discussed, the extent of the problem is briefly outlined, and an extrapolation of the susceptibility of GaAs wafers of higher diameters to this type of plastic deformation is given. 相似文献
123.
M. Udhayasankar J. Kumar P. Ramasamy D.K. Avasthi D. Kabiraj 《Crystal Research and Technology》2000,35(10):1173-1182
Hydrogen detection and analysis was carried out on the undoped semi‐insulating (S.I.) gallium arsenide (GaAs) single crystal using conventional elastic recoil detection analysis (ERDA) technique with high energy, heavy ion beam. Presence of hydrogen (nearly 3 x 1020 atoms/cc) has been observed on the as‐grown samples and further high concentration of atomic hydrogen (total concentration of 7 x 1020 atoms/cc) was found at the surface and was found to be decreasing with depth after 100 nm. Further the low energy hydrogen and oxygen ions implanted separately in GaAs at room temperature were also analysed by ERDA technique. From the analysis, the projected range (Rp) of 100 keV hydrogen and oxygen ions in GaAs was determined to be 891 nm (with Δ Rp equal to 320 nm), 170 nm (with Δ Rp equal to 120 nm) respectively. The experimentally determined values of both Rp and Δ Rp are more as compared with the values obtained using the TRIM theoretical program. Low temperature (4K) photoluminescence (PL) measurements of un‐implanted and H+ implanted samples show the passivation of intrinsic deep level defect EL2 and shallow acceptor impurity carbon by the low energy implanted hydrogen ions. The low energy hydrogen implantation may be used as a method of hydrogenation for passivation. 相似文献
124.
125.
S.B. Lisesivdin H. Altuntas A. Yildiz M. Kasap E. Ozbay S. Ozcelik 《Superlattices and Microstructures》2009,45(6):604-611
Experimental Hall data that were carried out as a function of temperature (60–350 K) and magnetic field (0–1.4 T) were presented for Si-doped low Al content (x=0.14) n–AlxGa1−xAs/GaAs heterostructures that were grown by molecular beam epitaxy (MBE). A 2-dimensional electron gas (2DEG) conduction channel and a bulk conduction channel were founded after implementing quantitative mobility spectrum analysis (QMSA) on the magnetic field dependent Hall data. An important decrease in 2DEG carrier density was observed with increasing temperature. The relationship between the bulk carriers and 2DEG carriers was investigated with 1D self consistent Schrödinger–Poisson simulations. The decrement in the 2DEG carrier density was related to the DX-center carrier trapping. With the simulation data that are not included in the effects of DX-centers, 17 meV of effective barrier height between AlGaAs/GaAs layers was found for high temperatures (T>300 K). With the QMSA extracted values that are influenced by DX-centers, 166 meV of the DX-center activation energy value were founded at the same temperatures. 相似文献
126.
First-principles study of palladium atom adsorption on the boron- or nitrogen-doped carbon nanotubes
Guo-Xiang Chen Jian-Min Zhang Dou-Dou Wang Ke-Wei Xu 《Physica B: Condensed Matter》2009,404(21):4173-4177
We have performed first-principles calculation to investigate the adsorption of a single palladium atom on the surface of the pristine and boron- or nitrogen-doped carbon nanotubes (CNTs). The results show that for the adsorption of a single palladium atom on the pristine CNT surface, the most stable site is Bridge1 site above the axial carbon–carbon bond. Either boron- or nitrogen-doped CNTs can assist palladium surface adsorption, but the detailed mechanisms are different. The enhanced palladium adsorption on boron-doped CNT is attributed to the palladium d orbital strongly hybridized with both boron p orbital and carbon p orbital. The enhancement in palladium adsorption on nitrogen-doped CNT results from activating the nitrogen-neighboring carbon atoms due to the large electron affinity of nitrogen. Furthermore, the axial bond is preferred over the zigzag bond for a palladium atom adsorbed on the surface of all three types of CNTs. The most energetically favorable site for a palladium atom adsorbed on three types of CNTs is above the axial boron–carbon bond in boron-doped CNT. The enhancement in palladium adsorption is more significant for the boron-doped CNT than it is for nitrogen-doped CNT with a similar configuration. So we conclude that accordingly, the preferred adsorption site is determined by the competition between the electron affinity of doped and adsorbed atoms and preferred degree of the axial bond over the zigzag bond. 相似文献
127.
用高温熔融法制备了不同Ho3+离子掺杂浓度65GeO2-12B2O-10BaO-10Na2O-3Al2O3-χHo2O3(χ=0.25,0.75,1.25mol%)锗酸盐玻璃。从吸收特性出发,应用McCumber理论计算了Ho3+离子能级5I8→5I7(~2.0μm)跃迁的吸收截面和5I7→5I8的受激发射截面。根据掺杂离子的浓度以及获得的吸收截面和受激发射截面得到Ho3+离子在此玻璃中的增益截面函数,从该函数可反映出材料的粒子数反转特性。获得的基本光学参数与其它掺杂的玻璃进行了比较,其吸收截面、发射截面和增益截面的最大值具有一定的优势。认为该玻璃在~2.0μm波段的中红外激光器中将有潜在的较大应用前景。 相似文献
128.
锁模脉冲波长连续可调谐光纤激光器 总被引:2,自引:1,他引:1
利用在腔内加入可调谐光纤光栅滤波器使“8”字形腔掺Yb3+光纤激光器在锁模状态下实现波长连续可调谐.实验中,在保证锁模状态稳定的情况下,通过调节可调谐光纤光栅滤波器,使激光器输出锁模脉冲的中心波长在1 047 nm~1 055 nm范围内连续调谐,重复频率稳定维持在4.9 MHz.在中心波长1 053 nm处,测得锁模脉冲输出平均功率为8.02 mW,光谱带宽1 nm,脉冲宽度为259.3 ps.这种“8”字形腔被动锁模光纤激光器在锁模状态下对波长连续可调谐,并可长时间稳定工作. 相似文献
129.
V. A. Morozova O. G. Koshelev E. P. Veretenkin V. N. Gavrin Yu. P. Kozlova 《Moscow University Physics Bulletin》2009,64(2):177-181
Photo-emf in the range hv = 0.76 ? 1.35 eV was found in p-i-n structures produced from undoped GaAs crystals with known parameters; the current sensitivities in the impurity and intrinsic (hv > 1.35 eV) regions were comparable. It was proven that the impurity photovoltaic effect results from EL2 and EL3 structural defects creating deep donor levels in the forbidden zone. Calculations were performed that justified the possibility of observing this effect on the investigated structures. 相似文献
130.
Transparent glass-ceramics have been fabricated by heat treatment with 1.0 mol% Tb2O3-doped 45SiO2-20Al2O3-10CaO-25CaF2 aluminosilicate glass. The precipitated crystalline phase in the glass-ceramics is CaF2 nanocrystals with a size of 15-27 nm and dispersed in the amorphous phase. Both photo- and radioluminescence measurements show that the increase of Tb3+ 545 nm line intensity by a factor of 4 and 3.5 is obtained in glass-ceramics with respect to the as-made glass, respectively. 相似文献