首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7139篇
  免费   191篇
  国内免费   459篇
化学   4967篇
晶体学   76篇
力学   105篇
综合类   5篇
数学   78篇
物理学   1204篇
无线电   1354篇
  2024年   6篇
  2023年   157篇
  2022年   70篇
  2021年   82篇
  2020年   121篇
  2019年   102篇
  2018年   153篇
  2017年   177篇
  2016年   152篇
  2015年   142篇
  2014年   332篇
  2013年   287篇
  2012年   770篇
  2011年   422篇
  2010年   382篇
  2009年   384篇
  2008年   395篇
  2007年   476篇
  2006年   374篇
  2005年   337篇
  2004年   313篇
  2003年   272篇
  2002年   193篇
  2001年   182篇
  2000年   186篇
  1999年   179篇
  1998年   184篇
  1997年   149篇
  1996年   150篇
  1995年   114篇
  1994年   91篇
  1993年   96篇
  1992年   102篇
  1991年   76篇
  1990年   60篇
  1989年   43篇
  1988年   17篇
  1987年   12篇
  1986年   8篇
  1985年   11篇
  1984年   9篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1980年   4篇
  1979年   4篇
  1975年   2篇
  1974年   1篇
  1969年   1篇
  1966年   1篇
排序方式: 共有7789条查询结果,搜索用时 203 毫秒
61.
首先建立缺陷空间分布和粒径分布的模型,并讨论了缺陷通过版图产生电路错误的过程,给出了IC功能成品率模拟器XD-YES的实现。用XD-YES对微电子测试图和实际IC的功能成品率模拟和分析表明,其结果与实际符合很好,从而表明XD-YES的可行性和实用性。  相似文献   
62.
刘建源  陆宗鹏 《分析化学》1993,21(9):1022-1027
本文研究了鸟瞟呤(Gua)和次黄嘌呤(Hxa)铜络合物在悬汞电极(HMDE)上的吸附作用和电极反应机理,溶液中形成的1:1络合物有强烈吸附性,通过分子结构的比较,推断出Cu~(2+)与Gua和Hxa的咪唑环N(7)和外环氧O(6)原子结合形成封闭的五元环。嘌呤环的π-电子有使分子呈平面吸附的趋势,但是Gua络合物分子优先取“倾斜”定向;随着表面吸附浓度增加,Hxa络合物分子存在从“平面”向“垂直”的再定向作用。本文测定了单层吸附浓度、包含的电量和每个分子占据的面积。络合物吸附得到S形等温线,它与Frumkin吸附等温线接近。本文还列出有关吸附参数B、a、△G_A~O和θ~*的计算结果。  相似文献   
63.
The adsorption behavior and thermal activation of carbon dioxide on the Cu(1 1 1), Cu(1 0 0), and Cu(1 1 0) surfaces have been investigated by means of density functional theory calculations and cluster models and periodic slabs. According to the cluster models, the optimized results indicate that the basis set of C and O atoms has a distinct effect on the adsorption energy, but an indistinct one on the equilibrium geometry. For the CO2/Cu(hkl) adsorption systems studied here, the final structure of adsorbed CO2 is near linear and the preferred modes for the adsorption of CO2 onto the Cu(1 1 1), Cu(1 0 0), and Cu(1 1 0) surfaces are the side-on adsorption at the cross bridge site with an adsorption energy of 13.06 kJ/mol, the side-on adsorption at the short bridge site (13.54 kJ/mol), and the end-on adsorption on the on-top site with C–O bonds located along the short bridge site (26.01 kJ/mol), respectively. However, the calculated adsorption energies from periodic slabs are lower as compared to the experimental data as well as the cluster model data, indicating that the periodic slab approach of generalized gradient approximation in the density function theory may be not suitable to obtain quantitative information on the interaction of CO2 with Cu(hkl) surfaces.  相似文献   
64.
The adsorption of CN on Cu(1 1 1), Ni(1 1 1) and Ni(1 0 0) has been investigated using density functional theory (DFT). While experimental studies of CN on Cu(1 1 1) show the molecular axis to be essentially parallel to the surface, the normally-preferred DFT approach using the generalised gradient approximation (GGA) yields a lowest energy configuration with the C-N axis perpendicular to the surface, although calculations using the local density approximation (LDA) do indicate that the experimental geometry is energetically favoured. The same conclusions are found for CN on Ni(1 1 1); on both surfaces bonding through the N atom is always unfavourable, in contrast to some earlier published results of ab initio calculations for Ni(1 1 1)/CN and Ni(1 0 0)/CN. The different predictions of the GGA and LDA approaches may lie in subtly different relative energies of the CN 5σ and 1π orbitals, a situation somewhat similar to that for CO adsorbed on Pt(1 1 1) which has proved challenging for DFT calculations. On Ni(1 0 0) GGA calculations favour a lying-down species in a hollow site in a geometry rather similar to that found experimentally and in GGA calculations for CN on Ni(1 1 0).  相似文献   
65.
The purpose of this work was to investigate the effect of several factors (anion type in the copper salt, pH and concentration of the salt solution) on the structure and thermo-oxidative degradation of the polyacrylamidoxime-copper chelates, by using elemental analysis, IR spectroscopy and dynamic thermogravimetry. The chelates containing copper ions as sulphate exhibit a better initial thermal stability than the polyacrylamidoxime fibre presumably due to the crosslinking generated by the intermolecular complexation of the ions; the removal of the sulphate anions takes place concomitantly with the second step of polymeric chain decomposition. The initial thermal decomposition of the chelates formed by copper ions as nitrate begins at lower temperatures as compared to the polyacrylamidoxime fibre, probably by the nitrate anion release, which partly overlaps the initial decomposition of the copper ion-crosslinked polymeric chains. Copper ions as either sulphate or nitrate catalyse the reactions involved in the main step of polyacrylamidoxime fibre decomposition; the higher the copper amount, the stronger the catalytic effect.  相似文献   
66.
Nanocrystalline thin films of copper selenide have been grown on glass and tin doped-indium oxide substrates using chemical method. At ambient temperature, golden films have been synthesized and annealed at 200 °C for 1 h and were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy and UV-vis spectrophotometry techniques, respectively. Cu2−xSe phase was confirmed by XRD pattern and spherical grains of 30 ± 4 - 40 ± 4 nm in size aggregated over about 130 ± 10 nm islands were seen by SEM images. Effect of annealing on crystallinity improvement, band edge shift and photoelectrochemical performance (under 80 mW/cm2 light intensity and in lithium iodide electrolyte) has been studied and reported. Observed p-type electrical conductivity in copper selenide thin films make it a suitable candidate for heterojunction solar cells.  相似文献   
67.
Ternary Ti-Si-N refractory barrier films of 15 nm thick was prepared by low frequency, high density, inductively coupled plasma implantation of N into TixSiy substrate. This leads to the formation of Ti-N and Si-N compounds in the ternary film. Diffusion of copper in the barrier layer after annealing treatment at various temperatures was investigated using time-of-flight secondary ion mass spectrometer (ToF-SIMS) depth profiling, X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and sheet resistance measurement. The current study found that barrier failure did not occur until 650 °C annealing for 30 min. The failure occurs by the diffusion of copper into the Ti-Si-N film to form Cu-Ti and Cu-N compounds. FESEM surface morphology and EDX show that copper compounds were formed on the ridge areas of the Ti-Si-N film. The sheet resistance verifies the diffusion of Cu into the Ti-Si-N film; there is a sudden drop in the resistance with Cu compound formation. This finding provides a simple and effective method of monitoring Cu diffusion in TiN-based diffusion barriers.  相似文献   
68.
应用X光光电子能谱法测定了几种彩色胶片表面层中氟的1s能级的结合能;分别比较了水处理前后、溅蚀前后胶片护膜层氟的变化,表明氟化物分布在护膜最表层,是一种易溶于水的氟化物;测定了彩色片护膜层所含硅2p能级的结合能,与自制彩色片护膜层测定结果比较,优质片含一种较多负电性,用与自制片的无机硅不同的硅化物作毛面剂;对溅蚀前后优质片和自产彩色片中的硅铝比变化进行比较,提出优质彩色片F-400的护膜层可能是双  相似文献   
69.
本文介绍了一个可对含连接线的电路进行瞬态分析的电路模拟器,该模拟器是在SPICE基础上经修改扩充而成的,连接线的处理采用了文献[1]的方法.文中介绍了方法的基本原理,讨论了数值Laplace反变换时参数的选择与误差的控制.实际VHSIC电路的试算结果表明,该模拟器是相当有效的.  相似文献   
70.
用于VLSI的SiO_xN_y薄膜的界面陷阱   总被引:3,自引:1,他引:2  
采用雪崩热电子注入技术研究了用于VLSI的快速热氮化的SiO_xN_y薄膜界面陷阱。给出这种薄介质膜禁带中央界面陷阱密度随氮化时间的变化关系,观察到这种薄膜存在着不同类型的密度悬殊很大的电子陷阱。指出雪崩热电子注入过程中在Si/SiO_xN_y界面上产生两类性质不同的快界面态陷阱,并给出这两种陷阱在禁带中能级位置及密度大小关系;同时还给出禁带中央界面陷阱密度随雪崩注入剂量呈现弱“N”形变化关系,并对实验结果进行了讨论。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号