全文获取类型
收费全文 | 14810篇 |
免费 | 2714篇 |
国内免费 | 2620篇 |
专业分类
化学 | 11906篇 |
晶体学 | 194篇 |
力学 | 651篇 |
综合类 | 256篇 |
数学 | 1574篇 |
物理学 | 5563篇 |
出版年
2024年 | 45篇 |
2023年 | 276篇 |
2022年 | 481篇 |
2021年 | 483篇 |
2020年 | 604篇 |
2019年 | 632篇 |
2018年 | 529篇 |
2017年 | 507篇 |
2016年 | 792篇 |
2015年 | 835篇 |
2014年 | 895篇 |
2013年 | 1184篇 |
2012年 | 1317篇 |
2011年 | 1393篇 |
2010年 | 997篇 |
2009年 | 1008篇 |
2008年 | 1080篇 |
2007年 | 961篇 |
2006年 | 940篇 |
2005年 | 848篇 |
2004年 | 666篇 |
2003年 | 584篇 |
2002年 | 620篇 |
2001年 | 456篇 |
2000年 | 412篇 |
1999年 | 322篇 |
1998年 | 209篇 |
1997年 | 183篇 |
1996年 | 177篇 |
1995年 | 137篇 |
1994年 | 119篇 |
1993年 | 101篇 |
1992年 | 70篇 |
1991年 | 52篇 |
1990年 | 44篇 |
1989年 | 36篇 |
1988年 | 23篇 |
1987年 | 26篇 |
1986年 | 23篇 |
1985年 | 19篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1957年 | 5篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
采用热处理方法提高MEH-PPV单层聚合物有机发光二极管发光性能的研究 总被引:2,自引:1,他引:1
对以MEH-PPV为发光层的单层聚合物有机发光二极管(OLED)器件在最佳条件下进行真空热处理,并用金相显微镜观察施加电压后器件的阴极表面形貌。发现处理后的器件阴极表面的气泡及黑斑明显减少。器件的发光性能显著提高。与未经处理的器件相比,最大相对发光强度提高了一个数量级、启亮电压降低了2.0V,半寿命提高了12.7倍。初步分析表明热处理方法提高器件发光性能的主要原因在于有效地减少了器件在工作过程中由于焦耳热产生的某些气体,从而减少阴极表面气泡及黑斑的出现,另一方面,热处理方法也增强了有机发光层与阴极接触界面的结合力,提高电子注入水平。 相似文献
53.
分形维数与城市规模分布评析 总被引:3,自引:1,他引:2
本在分形概念的基础上,指出城市规模分布是基于统计意义上的一种分形分布,并计算了安徽省1978~1998年城市规模分布的分维值,评析了安徽省城市规模分布变化的特征。 相似文献
54.
55.
Yi Liu David D. Díaz Adrian A. Accurso K. Barry Sharpless Valery V. Fokin M. G. Finn 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5182-5189
1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007 相似文献
56.
介绍了虚拟技术在实验教学改革中的作用与意义,探讨了电子信息系统实验教学改革的新思路与实现措施,并总结了实验教学改革的初步成果. 相似文献
57.
2-Cyanoethyl anilines were controllably cleaved by 1 equiv of potassium t-butoxide in dry THF with a reaction that can be used in situ with the Wittig reaction to synthesize conjugated primary and secondary anilines. 相似文献
58.
DING Xuantong YANG Qingwei YAN Long wen LIU Yi HUANG Yuan LIU Zetian HONG Wenyu SHI Peilan 《核工业西南物理研究院年报(英文版)》2004,(1):1-4
The main mission the HL-2A tokamak is of the experiments on to explore the divertor physics and to investigate the plasma confinement, transport and instabilities with high power auxiliary heating and advanced fuelling, it is necessary to develop more new diagnostics and increase the spatial and temporal resolutions of the measurements for exist system. Up to now, about 30 diagnostic systems have been moved from HL-1M to HL-2A tokamak. Other 10 diagnostic systems are being designed and installed on the device. In developed in last 2 years, will be presented. 相似文献
59.
Yi Qin Thomas Trautmann 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(1):105-114
As a computationally effective tool, the first-order term of the radiative perturbation theory has been computed successfully, and has been applied in a number of areas. In this article, we develop the computational expressions for the higher-order terms of the perturbation expansion in a plane parallel atmosphere. These expressions are then implemented, and numerical results for some typical cases are presented. These results indicate that the computation is successful and that the higher-order terms are essential in cases where the first-order term alone cannot predict the perturbation with sufficient accuracy. 相似文献
60.
Chien Lun Hung Yi Sheng Yeh 《International Journal of Infrared and Millimeter Waves》2003,24(12):2025-2041
Coaxial cavities are used in high power gyrotrons as the beam-wave interaction structure. Much research has been devoted to their mode selective properties. A coaxial cavity lacks a sharp boundary at its open end, so it has some physical features that can only be observed using a spectral model, such as frequency-dependent field profiles and mode overlapping effects. These properties are important since cold tests are usually conducted in the frequency domain. This study applies the incident/reflected wave boundary condition to the wave equation of a weakly irregular coaxial waveguide. The resistivity of the wall is considered in the analysis. Calculations reveal that the fixed-position spectrum yields an uncertain resonant frequency and quality factor. Although the maximum-field spectrum can uniquely determine the properties of the coaxial cavity, the resonant frequency obtained using the maximum-field spectral model is inconsistent with that obtained using the temporal model. The field-energy spectrum explains the low Q nature of the coaxial cavity. Moreover, resonant frequencies evaluated using the field-energy spectrum agree precisely with those evaluated using the temporal model. 相似文献