全文获取类型
收费全文 | 28947篇 |
免费 | 4124篇 |
国内免费 | 1619篇 |
专业分类
化学 | 5128篇 |
晶体学 | 93篇 |
力学 | 1178篇 |
综合类 | 231篇 |
数学 | 3341篇 |
物理学 | 7866篇 |
无线电 | 16853篇 |
出版年
2024年 | 105篇 |
2023年 | 291篇 |
2022年 | 511篇 |
2021年 | 562篇 |
2020年 | 676篇 |
2019年 | 571篇 |
2018年 | 603篇 |
2017年 | 870篇 |
2016年 | 982篇 |
2015年 | 1160篇 |
2014年 | 1718篇 |
2013年 | 1877篇 |
2012年 | 1976篇 |
2011年 | 2200篇 |
2010年 | 1718篇 |
2009年 | 1923篇 |
2008年 | 1951篇 |
2007年 | 1908篇 |
2006年 | 1819篇 |
2005年 | 1394篇 |
2004年 | 1210篇 |
2003年 | 1125篇 |
2002年 | 870篇 |
2001年 | 744篇 |
2000年 | 647篇 |
1999年 | 553篇 |
1998年 | 433篇 |
1997年 | 384篇 |
1996年 | 310篇 |
1995年 | 240篇 |
1994年 | 187篇 |
1993年 | 202篇 |
1992年 | 156篇 |
1991年 | 123篇 |
1990年 | 86篇 |
1989年 | 102篇 |
1988年 | 79篇 |
1985年 | 455篇 |
1984年 | 321篇 |
1983年 | 254篇 |
1982年 | 230篇 |
1981年 | 170篇 |
1980年 | 135篇 |
1979年 | 150篇 |
1978年 | 84篇 |
1977年 | 91篇 |
1976年 | 94篇 |
1975年 | 89篇 |
1974年 | 117篇 |
1973年 | 136篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
光纤传感振动检测系统及其实验研究 总被引:3,自引:0,他引:3
实际工程结构中的振动检测是十分重要的,也是十分复杂的,常用的结构振动检测传感器易受工程现场恶劣环境的影响.而光纤传感器具有小巧、抗电磁干扰、灵敏度高、适合长期监测等优点。本文建立了基于马赫—曾德(Mech-Zehnder)干涉原理的光纤传感振动检测系统.研制了运用先进的数字信号处理技术采集和处理数据的专用软件,并在典型结构件——钢制悬臂梁结构上进行了外加信号作用下的强迫振动检测和冲击载荷作用下的自由衰减振动检测,测量了该结构件的频率及振幅,其结果与同时进行的成熟的电测结果相近,说明光纤传感器用于结构件的振动测量是可靠的。本文为光纤传感器应用于实际工程的振动检测提供了新的技术装置,具有工程应用前景。 相似文献
112.
The problem of investigation of the amplitude and phase structure of a time-varying probing optical signal and the structure of time-varying inhomogeneities of a substance tested by this signal is considered. The analysis is concerned, in particular, with determination of the structure of signals and processes with resolution in the pico- and femtosecond range. The scheme used for the analysis is based on registration of four spatially separated spectra of the studied radiation. The spectra are formed in a four-channel scheme with a twin-wave Michelson interferometer and a spectral device. Modulators based on electrooptical crystals (perovskites) are placed in the channels. The sum spectra are formed: without modulators, with the effect of either of the modulators, and with both of them affecting the radiation. The effect of the studied substance implies either modulating the radiation (in this case it is described by multiplication) or redistributing the radiation (then it is described by convolution). 相似文献
113.
Milan V. Patel Samir A. Patel Arabinda Ray Rajni M. Patel 《Journal of polymer science. Part A, Polymer chemistry》2004,42(20):5227-5234
Copolymers of monomers 2,4‐dichlorophenyl methacrylate (2,4‐DMA) and methyl methacrylate (MMA) were synthesized with different monomer feed ratios using toluene as a solvent and 2,2′‐azobisisobutyronitrile (AIBN) as an initiator at 70 °C. The copolymers were characterized by IR‐spectroscopy, and copolymer composition was determined with UV‐spectroscopy. The linearization method of Fineman–Ross was employed to obtain the monomer reactivity ratios. The molecular weights and polydispersity indexes were determined by gel permeation chromatography (GPC). Thermogravimetric analyses of polymers were carried out in nitrogen atmosphere. The homo‐ and copolymers were tested for their antimicrobial properties against selected microorganisms. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5227–5234, 2004 相似文献
114.
115.
Mean value in invexity analysis 总被引:1,自引:0,他引:1
In this paper, a generalization of the mean value theorem is considered in the case of functions defined on an invex set with respect to η (which is not necessarily connected). 相似文献
116.
Gert van der Horn Johan H. Huijsing 《Analog Integrated Circuits and Signal Processing》1997,14(3):207-222
In many applications electronic sensors are used toimprove performance and reliability of measurement systems. Suchsensors should provide a correct transfer from the physical signalto be measured to the electrical output signal. One importantstep to achieve this, is to calibrate each sensor by applyingdifferent reference input signals and adjusting the sensor transferaccordingly. Besides expensive reference equipment the calibrationprocess takes much time and attention per individual sensor,which means a considerable increase in sensor production costs.By including at the sensor or sensor interface chip a programmablecalibration facility the calibration of such smart sensors caneasily be automated and can be executed for a batch of sensorsat a time, thus minimizing the calibration time and costs. Thispaper presents a calibration method and options for integrationin the smart sensor concept, in hardware as well as in software.An advantage of the proposed method is that it does not needa large matrix of calibration data, which needs to be storedin a look-up table or converted into a correction formula, butinstead it uses a step-by-step approach to correct the sensortransfer at each calibration measurement until the error is sufficientlysmall. 相似文献
117.
118.
自动线性跟踪Butterworth有源滤波器研究 总被引:2,自引:0,他引:2
滤波是通信、测试、数据采集和实时控制等领域至关重要的环节。通常的模拟滤波器,由于截止频率固定,在某些宽频率动态范围且有实时性要求的应用场合,往往达不到预期的滤波效果,有时甚至影响整个系统的正常运行。本文从有源滤波器的机理分析入手,提出了一种由单片机参与的滤波系统,它能自动跟踪输入信号频率,线性地选择合适的滤波器截止频率,弥补了原有滤波器的不足。 相似文献
119.
120.
HANXI'AN HUANGXILI 《高校应用数学学报(英文版)》1998,13(4):445-450
For two rational quadratic B-spline curves with same control vertexes, the cross ratio of four eollinear points are represented; which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the twocurves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Beeier curves, the value is generally related with the loeation of the ray, and the necessary and sufficient condition o5 the ratio being independent of the ray‘s loeation is showed. Alsn another cross ratio o5 the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initlal vertex intersects respectivdy with the curve segmentt the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only whh the ray‘s location, butnot with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments. 相似文献