全文获取类型
收费全文 | 5816篇 |
免费 | 926篇 |
国内免费 | 436篇 |
专业分类
化学 | 944篇 |
晶体学 | 18篇 |
力学 | 682篇 |
综合类 | 47篇 |
数学 | 257篇 |
物理学 | 5230篇 |
出版年
2024年 | 4篇 |
2023年 | 29篇 |
2022年 | 103篇 |
2021年 | 107篇 |
2020年 | 113篇 |
2019年 | 83篇 |
2018年 | 88篇 |
2017年 | 233篇 |
2016年 | 250篇 |
2015年 | 231篇 |
2014年 | 364篇 |
2013年 | 366篇 |
2012年 | 366篇 |
2011年 | 406篇 |
2010年 | 291篇 |
2009年 | 349篇 |
2008年 | 420篇 |
2007年 | 428篇 |
2006年 | 357篇 |
2005年 | 295篇 |
2004年 | 292篇 |
2003年 | 269篇 |
2002年 | 221篇 |
2001年 | 234篇 |
2000年 | 207篇 |
1999年 | 159篇 |
1998年 | 144篇 |
1997年 | 144篇 |
1996年 | 104篇 |
1995年 | 90篇 |
1994年 | 58篇 |
1993年 | 68篇 |
1992年 | 47篇 |
1991年 | 45篇 |
1990年 | 36篇 |
1989年 | 30篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 12篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有7178条查询结果,搜索用时 796 毫秒
91.
Applications of electronic speckle interferometry (ESI) techniques for spacecraft structural components 总被引:1,自引:0,他引:1
Laser-based electronic speckle interferometry (ESI) techniques, viz., electronic speckle pattern interferometry (ESPI) and electronic speckle shearographic interferometry (ESSI) are used for testing of spacecraft structural components. The combined ESPI and ESSI system developed in house was successfully used for the non-destructive evaluation (NDE) of honeycomb sandwich panels and propellant tanks of Indian Space Research Organization (ISRO). Debonds between face sheet and the honeycomb core were identified using (i) thermal and (ii) dual vacuum stressing methods. On-line NDE of the propellant tanks under internal pressure loading for identification of the minute cracks and thickness reduction areas were successfully implemented by ESI. 相似文献
92.
93.
Soraya A. Khodier 《Optics & Laser Technology》2004,36(1):355-67
A combined interference and diffraction pattern, in the form of equidistant interference fringes, resulting from illuminating a vertical metallic wire by a laser beam is analyzed to measure the diameter of four standard wires. The diameters range from 170 to 450 μm. It is found that the error in the diameter measurements increases for small metallic wires and for small distances between the wire and the screen due to scattering effects. The intensity of the incident laser beam was controlled by a pair of sheet polaroids to minimize the scattered radiation. The used technique is highly sensitive, but requires controlled environmental conditions and absence of vibration effects. The expanded uncertainty for k=2 is calculated and found to decrease from U(D)=±1.45 μm for the wire of nominal diameter 170 μm to ±0.57 μm for the diameter 450 μm. 相似文献
94.
工业污染排放中气──固两相流的光学测量 总被引:1,自引:0,他引:1
烟尘及各种工业性粉尘排放是典型的气-固两相系.迄今为止,国内外尚缺少有效的监测其排放的手段.本文基于光的散时原理,提出了一种非接触的光学方法,能对上述固体颗粒物的污染排放浓度及粒径大小进行实时、在线的监测。计算机模拟和实验研究表明,该方法具有广阔的工业应用前景。 相似文献
95.
G. Carelli A. Di Siena N. Ioli A. Moretti G. Moruzzi F. Strumia 《International Journal of Infrared and Millimeter Waves》1994,15(4):619-633
We have measured the frequencies of four CH3OH far-infrared laser lines that were previously known only by wavelength measurement. Two of these lines turned out to be doublets, bringing the total number of measured lines to six. We can now confirm the assignments of five of them and definitely disprove the assignments proposed for the sixth.In particular we confirm the assignments for the four strong laser lines at 205 and 208 µm pumped by the 9-P(34) CO2 laser line. These lines share a common upper level in the first excited CO-stretch state, and terminate in the upper and lower levels of a hybrid state with J=5. Heterodyne frequency measurements and conventional microwave spectroscopy show that both lines are split into two components approximately 3.5 MHz apart. The origin of this further splitting is interpreted as a perturbed K-splitting.Work supported by Consiglio Nazionale delle Ricerche -Italia 相似文献
96.
Conducting drop tests to investigate impact behavior and identify failure mechanisms of small-size electronic products is
generally expensive and time-consuming. Nevertheless, strict drop/impact performance criteria for hand-held electronic products
such as cellular phones play a decisive role in the design because they must withstand unexpected shocks. The design of product
durability on impact has heavily relied on the designer's intuition and experience. In this study, a reliable drop/impact
simulation for a cellular phone is carried out using the explicit code LS-DYNA. Subsequently globallocal experimental verification
is accomplished by means of high-speed photography and impact response measurement. Using this methodology, we predict potential
damage locations in a cellular phone and compare them with real statistical data. It is envisaged that development of a reliable
methodology of drop/impact simulation will provide us with a powerful and efficient vehicle for improvement of the design
quality and reduction of the product development cycle. 相似文献
97.
田兴 《新疆大学学报(理工版)》1991,8(1):53-55
本文分析计算了荧光光纤温度传感器的温敏元件——GsAlAs/GaAs双异质结半导体材料的荧光辐射效率与激励光波长的关系。讨论了温度测量范围及温敏元件GaAlAs层铝含量对激励光源的限制,在0~200℃测温范围内,若采用LED作激励光源,其峰值波长应在0.70~0.76μm之间选择。 相似文献
98.
99.
100.
一种新型温度自补偿高灵敏度折射率计 总被引:7,自引:0,他引:7
基于高频CO2激光脉冲写入的新型超长周期光纤光栅(ULPFG),提出了一种可实现温度自补偿的新型高灵敏度折射率计。理论与实验表明,新型超长周期光纤光栅不同闪耀阶次谐振峰对外界折射率与温度变化的灵敏度各自不同,特别的是,该光栅存在对外界折变不敏感的谐振峰,测量中除了可以利用该峰实现温度同时测量外,还可以补偿另一个测量折变的谐振峰因温度变化带来的测量误差。该折射率计具有制作简单、成本低、强度好,灵敏度高等优点,当外界折射率在1.43~1.45范围内变化时,其折射率测量灵敏度可达每单位折射率240 nm,在实际工业应用中具有较大的潜在实用价值。 相似文献