全文获取类型
收费全文 | 10934篇 |
免费 | 1311篇 |
国内免费 | 624篇 |
专业分类
化学 | 7041篇 |
晶体学 | 58篇 |
力学 | 305篇 |
综合类 | 189篇 |
数学 | 814篇 |
物理学 | 4462篇 |
出版年
2024年 | 25篇 |
2023年 | 151篇 |
2022年 | 358篇 |
2021年 | 516篇 |
2020年 | 409篇 |
2019年 | 357篇 |
2018年 | 289篇 |
2017年 | 500篇 |
2016年 | 529篇 |
2015年 | 503篇 |
2014年 | 733篇 |
2013年 | 708篇 |
2012年 | 739篇 |
2011年 | 652篇 |
2010年 | 544篇 |
2009年 | 680篇 |
2008年 | 636篇 |
2007年 | 621篇 |
2006年 | 538篇 |
2005年 | 544篇 |
2004年 | 487篇 |
2003年 | 331篇 |
2002年 | 253篇 |
2001年 | 192篇 |
2000年 | 175篇 |
1999年 | 186篇 |
1998年 | 142篇 |
1997年 | 136篇 |
1996年 | 141篇 |
1995年 | 127篇 |
1994年 | 74篇 |
1993年 | 81篇 |
1992年 | 72篇 |
1991年 | 43篇 |
1990年 | 63篇 |
1989年 | 53篇 |
1988年 | 56篇 |
1987年 | 52篇 |
1986年 | 28篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 30篇 |
1981年 | 17篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
因特网防御DoS攻击技术评述Ⅰ--攻击分类与特征·包过滤·攻击检测与防御 总被引:1,自引:0,他引:1
概述了因特网上DoS攻击的相应分类及基本特征,评述了包过滤、攻击检测及防御技术的最新成果.前一部分介绍了入口过滤、基于路由的过滤网和有效源地址强制协议.后一方面主要讨论了适合于检测攻击包的技术,介绍了新近提出的频谱分析方法和泛滥检测系统.简要评述了已有的防御SYN泛滥攻击的技术措施,介绍了Cisco的TCP拦截技术,提出了改进策略. 相似文献
62.
63.
64.
65.
66.
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
67.
This study demonstrates the separation of active ingredients in acne formulations (salicylic acid, cloramphenicol and resorcinol in presence of azulene) by capillary zone electrophoresis. Factors affecting their separations were the buffer pH and concentration, applied voltage, sample preparation, and presence of additives. Optimun results were obtained with a 50 mM sodium tetraborate-50 mM sodium phosphate, pH 9.0. The carrier electrolyte gave baseline separation with good resolution, short migration times (<6 min), great reproducibility and accuracy. Calibration plots were linear over at least three orders of magnitude of analyte concentrations, the lower limits of detection being within the range 0.39-1.25 μg ml−1. The procedure was fast and reliable and commercial pharmaceuticals could be analysed without prior sample clean-up procedure. 相似文献
68.
In this paper an automatic technique for handling discontinuous IVPs when they are solved by means of adaptive Runge–Kutta codes is proposed. This technique detects, accurately locates and passes the discontinuities in the solution of IVPs by using the information generated by the code along the numerical integration together with a continuous interpolant of the discrete solution. A remarkable feature is that it does not require additional information on the location of the discontinuities. Some numerical experiments are presented to illustrate the reliability and efficiency of the proposed algorithms. 相似文献
69.
采用淋洗液发生器阴离子交换-抑制电导检测法,同时分离和检测阿思巴甜、甜蜜素、安赛蜜和糖精4种常见的甜味剂.由于采用了淋洗液发生器,使背景电导大大降低,可以实现甜味剂的高灵敏度检测和分离.该方法具有良好的重现性、线性关系和较低的检测限.阿思巴甜、甜蜜素、安赛蜜和糖精的检测限分别是:1.27、0.045、0.033、0.063 mg/L;样品测定的回收率分别为99.7%、102.8%、98.6%、103.5%. 相似文献
70.
Frank Rutz Martin Koch Shilpa Khare Martin Moneke Heike Richter Uwe Ewert 《International Journal of Infrared and Millimeter Waves》2006,27(4):547-556
We report on experiments that evaluate the potential of terahertz (THz) time-domain spectroscopy (TDS) for quality control
of polymeric compounds. We investigate specimens out of a polyethylene compound with silver-coated titanium dioxide nanospheres
and a glass-fiber reinforced epoxy composite. We further examine an industrial polymer product produced by injection molding.
Our data demonstrates that THz imaging is a powerful tool for contactless quality control in the polymer industry. 相似文献