全文获取类型
收费全文 | 16421篇 |
免费 | 2846篇 |
国内免费 | 1903篇 |
专业分类
化学 | 11696篇 |
晶体学 | 175篇 |
力学 | 1218篇 |
综合类 | 81篇 |
数学 | 1820篇 |
物理学 | 6180篇 |
出版年
2024年 | 39篇 |
2023年 | 368篇 |
2022年 | 505篇 |
2021年 | 574篇 |
2020年 | 679篇 |
2019年 | 620篇 |
2018年 | 552篇 |
2017年 | 503篇 |
2016年 | 870篇 |
2015年 | 754篇 |
2014年 | 947篇 |
2013年 | 1183篇 |
2012年 | 1516篇 |
2011年 | 1491篇 |
2010年 | 1022篇 |
2009年 | 962篇 |
2008年 | 1108篇 |
2007年 | 973篇 |
2006年 | 884篇 |
2005年 | 792篇 |
2004年 | 551篇 |
2003年 | 454篇 |
2002年 | 457篇 |
2001年 | 365篇 |
2000年 | 312篇 |
1999年 | 338篇 |
1998年 | 275篇 |
1997年 | 250篇 |
1996年 | 278篇 |
1995年 | 278篇 |
1994年 | 195篇 |
1993年 | 160篇 |
1992年 | 165篇 |
1991年 | 156篇 |
1990年 | 132篇 |
1989年 | 105篇 |
1988年 | 89篇 |
1987年 | 68篇 |
1986年 | 53篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
三维射频加速腔程序包MAFIA的开发和应用 总被引:2,自引:1,他引:1
介绍了三维射频加速器计算机辅助设计(CAD)程序包MAFIA的特点、功能及其应用。用CAD的方法实现了射频加速器特别是非轴对称带耦合腔的加速器的三维腔形设计。同时介绍了节省内存、节约机时的模型方法,使得在中小型机器上运行大程序(八万条)成为可能。文章主要对L波段的加速腔进行了数值模拟,并和实验进行了比较,结果符合较好;通过三维数值模拟及图形模拟的方法比较了各种形状谐振腔的性能;计算分析了输入耦合腔及高阶模耦合器对加速腔电磁场分布等参量的影响;提出了加耦合器后谐振频率改变的补偿方法。 相似文献
74.
一要明确实验目的、原理和步骤;不要目的不明,原理不清,做一步想一步。 二要会从多种器材中选用精度要求和量程符合的器材;不要随意选用精度和量程不符合实际要求的仪器。 相似文献
75.
76.
平衡规划问题的熵函数方法及其在混合交通流中的应用 总被引:1,自引:0,他引:1
将参变极值问题的极大熵函数方法应用到求解平衡规划问题中,通过先验分布信息和Kullback熵概念,给出了平衡规划问题基于Kullback熵表示的熵函数求解方法,并将平衡规划的极大熵函数方法应用于求解混合交通平衡分配问题. 相似文献
77.
We establish upper and lower bounds for the metric entropy and bracketing entropy of the class of d-dimensional bounded monotonic functions under Lp norms. It is interesting to see that both the metric entropy and bracketing entropy have different behaviors for p<d/(d-1) and p>d/(d-1). We apply the new bounds for bracketing entropy to establish a global rate of convergence of the MLE of a d-dimensional monotone density. 相似文献
78.
In this paper, we discuss the controllability of a nonlinear degenerate parabolic system with bilinear control. Based on the shrinking property of the solutions, we prove that the system is not globally approximately controllable. Furthermore, we give an approximate null controllability result. We also prove that the system is not globally exactly null controllable by a comparison principle. 相似文献
79.
Guosong Wu Xiaoqin Zeng Wenbin Ding Xingwu Guo Shoushan Yao 《Applied Surface Science》2006,252(20):7422-7429
Ceramic thin films have been widely used to protect the metal substrate as coatings in the past years. In order to improve the poor corrosion resistance of AZ31 magnesium alloy, the study in this paper used the electron beam evaporation method to prepare ceramic PVD films on its surface with TiO2 and Al2O3 as donors, respectively. Atomic force microscopy (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the surface morphology, composition and microstructure of the thin films. Both films deposited on AZ31 took on compact top surface morphologies and grew as amorphous structures on substrate. AES test not only showed that films compositions deviated the standard stoichiometric ratios, but also found that element Mg diffused into films and existed as magnesium oxide in the TiOx film as well as the AlOx film. In the electrochemical corrosion test, the AlOx coating on AZ31 exhibited the largest electrochemical impedance in a 3.5% NaCl solution. But it did not show better corrosion resistance than others for the poorer adhesion. Even if its thickness was small, the TiOx coating on AZ31 exhibited the best corrosion resistance in this study. According to the observation and analysis, the damage of these films on AZ31 in aggressive solutions was mainly due to the existence of pores, microcracks, vacancies and poor adhesion between coating and substrate. 相似文献
80.
Thin films of oxide materials are playing a growing role as critical elements in optoelectronic devices and nanoscale devices. In this work, thin films of some typical oxides such as WO3, Ga2O3 and SrTiO3 were investigated. We present measurements of those films, using various optical techniques like photoconductivity transients over a wide time range and photo-Hall measurements. Analysis of the photo-Hall and photoconductivity data permits the determination of the contribution to the photoconductivity made by the carrier mobility and concentration. A model for dispersive carrier transport was proposed to explain the relaxation of the photoconductivity in oxide thin films. In addition, photoluminescence characterization was used to study microstructures and energy band in oxide thin films. The broad emission from oxide host, consisting of several band peaks, was likely due to a recombination process with several possible paths. The dependence of the luminescent intensity on the annealing atmosphere was associated with the presence of oxygen vacancies. It is suggested that our optical analysis efforts have improved the understanding of oxide thin films, and this should lead to the necessary advancements in a variety of devices. 相似文献