全文获取类型
收费全文 | 6432篇 |
免费 | 603篇 |
国内免费 | 588篇 |
专业分类
化学 | 4741篇 |
晶体学 | 22篇 |
力学 | 235篇 |
综合类 | 45篇 |
数学 | 70篇 |
物理学 | 2510篇 |
出版年
2024年 | 13篇 |
2023年 | 101篇 |
2022年 | 203篇 |
2021年 | 220篇 |
2020年 | 268篇 |
2019年 | 245篇 |
2018年 | 180篇 |
2017年 | 329篇 |
2016年 | 353篇 |
2015年 | 301篇 |
2014年 | 400篇 |
2013年 | 404篇 |
2012年 | 474篇 |
2011年 | 415篇 |
2010年 | 311篇 |
2009年 | 354篇 |
2008年 | 382篇 |
2007年 | 398篇 |
2006年 | 326篇 |
2005年 | 295篇 |
2004年 | 317篇 |
2003年 | 209篇 |
2002年 | 180篇 |
2001年 | 120篇 |
2000年 | 120篇 |
1999年 | 125篇 |
1998年 | 114篇 |
1997年 | 111篇 |
1996年 | 71篇 |
1995年 | 60篇 |
1994年 | 42篇 |
1993年 | 43篇 |
1992年 | 24篇 |
1991年 | 28篇 |
1990年 | 25篇 |
1989年 | 16篇 |
1988年 | 9篇 |
1987年 | 14篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
排序方式: 共有7623条查询结果,搜索用时 62 毫秒
961.
A light intensity modulation fiber-optic sensor, which can measure curvature directly, has been developed. It is suitable for the measurement of thin, embedded or highly flexible structures. An experimental analysis on the static and dynamic characteristics of sensor has been undertaken. The results show that the output voltage has polarity and a good linear relationship with curvature when the curvature radius is larger than 60 mm. The mathematical model relating the relative output loss, parameters of sensitive zone’s configuration (depth, number, height and half angle of tooth) and bending radius is described analytically based on the geometric optics. Curvature fiber-optic sensors can be used to build a quasi-distributed fiber-optic sensor system, which can measure curvature and torsion angle simultaneously. 相似文献
962.
An angle-resolved laser detector based on a pair of a non-mechanical scanning Fabry-Perot cavities is described. The differential signal from the two cavities is approximately independent from the polarization of the incident laser beam and it is used to determine the angle of incidence of the beam on the Fabry-Perot cavities. The F-P etalon is made of interferometric filter combination. A laser incident angle sensor experimental platform is built up, and the experiment is carried out with a given laser range finder. When the incident angle is less than 5°, the transmission difference measured by the laser angle sensor is significantly lower than theoretical value, and deviation is more than 10%. When the incident angle is greater than 10°, the deviation is much lower than that of the situation of the incident angle is lower than 10°. 相似文献
963.
A novel stable multi-wavelength fiber Bragg grating laser is achieved and its sensing characteristic with the strain is studied. The beat signals generated by the multi-wavelength fiber laser are measured under different strains. Four-wave mixing (FWM) is firstly observed in such a short-cavity fiber laser. 相似文献
964.
This paper proposes a new concept of birefringence-based sensor using the entangled photon timing walk-off compensation. The superposition of nonlinear light known as four-wave mixing is introduced by the Kerr nonlinear effects type within the ring device. The possible two entangled photon pairs are randomly generated using the polarization control unit. Results obtained have shown that the entangled state walk-off of light traveling within the ring device can be compensated. This means the changes in walk-off parameters can be relatively measured to the changes in the applied physical parameters. The potential of using such a proposed system for birefringence-based sensor applications is plausible and discussed. 相似文献
965.
This paper introduces a novel method for designing the transducer of a highly directional ultrasonic range sensor for detecting obstacles in mobile robot applications. The transducer consists of wave generation, amplification, and radiation sections, and a countermass. The operating principle of this design is based on the parametric array method where the frequency difference between two ultrasonic waves is used to generate a highly directional low-frequency wave with a small aperture. The aim of this study was to design an optimal transducer to generate the two simultaneous longitudinal modes efficiently. We first derived an appropriate mathematical model by combining the continuum model of a bar and countermass with the compatibility condition between a piezoelectric actuator and a linear horn. Then we determined the optimal length of the aluminum horn and the piezoelectric actuator using a finite element method. The proposed sensor exhibited a half-power bandwidth of less than ±1.3° at 44.8 kHz, a much higher directivity than existing conventional ultrasonic range sensors. 相似文献
966.
A new active layer for CO2 sensing based on semiconducting CuO-CuxFe3−xO4 (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO2 target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite-spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130-475 °C) and frequencies (0.5-250 kHz). The results showed a high response of 50% (Rair/RCO2=1.9) at 250 °C and 700 Hz for a CO2 concentration of 5000 ppm. 相似文献
967.
968.
969.
970.
基于刚性苯多羧酸H4BPTC(联苯-3,3′,5,5′-四甲酸),构筑了一例孔壁修饰高密度自由羧基氧的三维刚性锌基金属有机骨架:{[Zn2(BPTC)(H2O)(DMF)2]·DMF·H2O}n (SXNU-5-Zn)。SXNU-5-Zn具有好的酸碱稳定性(pH=3~8)和热稳定性。以SXNU-5-Zn构建了基于纯 MOFs材料的电化学传感器(SXNU-5-Zn/GCE),其可高灵敏、选择性的检测对乙酰氨基酚(AC),检测的线性范围宽(0.02~765 μmol·L-1),检测限低至 0.013 8 μmol·L-1(S/N=3)。此外,所制备的 SXNU-5-Zn/GCE 传感器已成功应用于实际样品复方对乙酰氨基酚片中AC含量的检测。 相似文献