全文获取类型
收费全文 | 25794篇 |
免费 | 3953篇 |
国内免费 | 2392篇 |
专业分类
化学 | 17934篇 |
晶体学 | 309篇 |
力学 | 1535篇 |
综合类 | 109篇 |
数学 | 2912篇 |
物理学 | 9340篇 |
出版年
2024年 | 70篇 |
2023年 | 523篇 |
2022年 | 947篇 |
2021年 | 965篇 |
2020年 | 1006篇 |
2019年 | 991篇 |
2018年 | 826篇 |
2017年 | 727篇 |
2016年 | 1201篇 |
2015年 | 1153篇 |
2014年 | 1345篇 |
2013年 | 1790篇 |
2012年 | 2403篇 |
2011年 | 2412篇 |
2010年 | 1579篇 |
2009年 | 1500篇 |
2008年 | 1643篇 |
2007年 | 1510篇 |
2006年 | 1357篇 |
2005年 | 1155篇 |
2004年 | 839篇 |
2003年 | 642篇 |
2002年 | 608篇 |
2001年 | 442篇 |
2000年 | 438篇 |
1999年 | 513篇 |
1998年 | 426篇 |
1997年 | 437篇 |
1996年 | 455篇 |
1995年 | 358篇 |
1994年 | 306篇 |
1993年 | 234篇 |
1992年 | 234篇 |
1991年 | 198篇 |
1990年 | 169篇 |
1989年 | 144篇 |
1988年 | 97篇 |
1987年 | 109篇 |
1986年 | 87篇 |
1985年 | 83篇 |
1984年 | 47篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
针对多台阶器件结构深层表面光刻工艺中存在的问题,对不同台阶高度分别测量了台阶表面及台阶底部沉积的光刻胶厚度,并对台阶高度与光刻胶厚度的关系进行数值描述与分析.基于Beer定律对薄光刻胶光吸收系数的描述,分析了通过实验得到的不同曝光时间下光刻胶的光强透过率曲线,解释了随着曝光时间的增加光刻胶光强透过率发生变化的原因,同时认为光刻胶光吸收系数与光刻胶厚度密切相关.在此基础上,确定了台阶底部堆积光刻胶完全曝光所需时间.优化平面光刻工艺,在不同台阶高度的深台阶表面及底部同时制作出窄线条的高质量图形. 相似文献
992.
A temperature independent 80-Gb/s 100-km transmission system is demonstrated with the use of spectral phase modulation-based tunable dispersion compensator (TDC). The principle of dispersion compensation based on spectral phase modulation as well as the relationship between spectral phase modulation function and group velocity dispersion (GVD) are theoretically studied. TDC based on spectral phase modulation is implemented. The performance of 80-Gb/s transmission system is experimentally evaluated. The nonlinear relationship between temperature and temperature-induced dispersion fluctuations is demonstrated through the asymmetric temperature-induced power penalty without dispersion compensation. With respect to the low temperature area, the temperature-induced dispersion fluctuations are smaller than those in the high temperature area. By using the proposed TDC, temperature independent 80-Gb/s transmission is successfully demonstrated under a temperature range of -20 - 60 ?C with a power penalty of less than 0.8 dB. 相似文献
993.
25倍中红外连续变焦光学系统设计 总被引:6,自引:2,他引:6
针对制冷型320pixel×240pixel凝视焦平面阵列探测器,设计了一个25倍中红外连续变焦光学系统。该系统由变焦系统和二次成像系统构成。变焦系统由两个子变焦系统串联而成,可以实现高变焦比;二次成像系统的作用是压缩物镜口径和实现冷光阑效率的要求。该中波红外连续变焦系统光学系统的工作波段位于3.7~4.8μm,可以实现12~300mm连续变焦,F数达到2.5,满足100%冷光阑效率的要求。该系统具有变焦比大、相对孔径大、变焦行程短和变焦轨迹平滑等优点。 相似文献
994.
We report the preparation of Pt–CeO2 nanoparticles on the multi-walled carbon nanotubes (MWNTs) by a reverse micellar method. Transmission electron microscopy
(TEM) analysis indicated that well-dispersed small Pt–CeO2 nanoparticles were formed on the MWCNTs. X-ray diffraction (XRD) analysis confirmed the formation of the Pt–CeO2 nanoparticles on the MWNTs. Cyclic voltammetry (CV) results demonstrated that the Pt–CeO2/MWNT exhibited a higher methanol oxidation than did the Pt/MWNT catalyst. The CO stripping test showed that CeO2 can make CO stripped at a lower potential, which is helpful for CO and methanol electro-oxidation. 相似文献
995.
This paper characterizes holographic scattering and demonstrates its application in determining the kinetic parameters in
materials with high transmittance and strong holographic scattering like phenanthrenequinone doped poly (methyl methacrylate)
(PQ-PMMA). We define a polymerization rate parameter which can be determined by the temporal evolution of the scattering losses.
Two basic kinetic parameters, quantum yield and molar-absorption coefficient, are obtained by nonlinear fitting the curve
of the polymerization rate parameter as a function of the thickness, which are 1.9×10−6 mol/einstein and 2.1×104 cm2/mol for a wavelength of 532 nm respectively. These results improve the understanding of photochemical behaviors and allow
us to describe the grating formation in the photopolymer reasonably. 相似文献
996.
997.
The transmissions of oxygen ions through Al2O3 nanocapillaries each 50 nm in diameter and 10 μm in length at a series of different tilt angles are measured,where the ions with energies ranging from 10 to 60 keV and charge states from 1 up to 6 are involved.The angular distribution and the transmission yields of transported ions are investigated.Our results indicate both the existence of a guiding effect when ions pass through the capillary and a significant dependence of the ion transmission on the energy and the charge state of the ions.The guiding effects are observed to be enhanced at lower projectile energies and higher charge states.Meanwhile,the results also exhibit that the transmission yields increase as the tilt angle decreases at a given energy and charge state. 相似文献
998.
Phase transition,dielectric and piezoelectric properties of NaNbO3–Bi0.5Li0.5TiO3 lead-free ceramics
Lingling Fu Dunmin Lin Qiaoji Zheng Xiaochun Wu Lang Wu Hailing Sun Yang Wan Ximing Fan Chenggang Xu 《Current Applied Physics》2012,12(6):1523-1528
Lead-free ceramics (1?x)NaNbO3–xBi0.5Li0.5TiO3 have been fabricated by an ordinary sintering technique, and their electric properties and temperature characteristics have been studied. All the ceramics possess a perovskite structure with orthorhombic symmetry, indicating that (Bi0.5Li0.5)TiO3 diffuses into NaNbO3 lattices to form a new solid solution. A low (Bi0.5Li0.5)TiO3 doping level transforms the NaNbO3 ceramics from antiferroelectric to ferroelectric. The ceramics with x ≤ 0.075 are normal ferroelectric, and the ferroelectric-paraelectric phase become diffusives with the doping level of Bi0.5Li0.5TiO3 increasing. As x increases, the Curie temperature of the ceramics decreases linearly, while the relative permittivity εr increases. 0.925NaNbO3–0.075(Bi0.5Li0.5)TiO3 ceramic exhibits the relatively large piezoelectric constant (d33 = 58 pC/N), high Curie temperature (TC = 228 °C) and good temperature stability, suggesting that the ceramics are one of new possible candidates for lead-free piezoelectric materials. 相似文献
999.
A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) as the electron source. The sensor consists of the anode sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) cathode in the micro-vacuum chamber. MWNTs on the silicon substrate were grown by thermal CVD. The prototype pressure sensor has a measured sensitivity of about 0.17-0.77 nA/Pa (101-550 KPa). The work shows the potential use of CNTs-based field-emitter in microsensors, such as accelerometers and tactile sensors. 相似文献
1000.
T. Rajagopalan J.A. Lubguban S. Gangopadhyay J. Sun S.L. Simon R. Butler 《Applied Surface Science》2006,252(18):6323-6331
Hexamethyldisilazane (HMDS) vapor treatment of plasma-damaged nanoporous organosilicate thin films has been studied as a function of treatment temperature in this work. Although, the HMDS vapor treatment facilitated incorporation of methyl (CH3) groups subsequent to the removal of free hydroxyl (OH) groups in the damaged films at treatment temperature as low as 55 °C, the bonded OH groups were not removed. More significantly, detailed analysis of the results reveals that HMDS vapor modified only the surface of the plasma-damaged samples and not the entire film as expected. This is attributed to the formation of a thin solid layer on the surface, which effectively prevents penetration of HMDS vapors into the bulk. The Fourier transform-infrared (FT-IR) absorption and dielectric constant measurements confirm that the vapor treatment assists only partial curing of the plasma-damaged films. Alternative processes of curing the films with HMDS dissolved in supercritical carbon dioxide (SCCO2) as a medium of reaction in static and pulsed modes were also attempted and the results are presented in this paper. 相似文献