全文获取类型
收费全文 | 149554篇 |
免费 | 36408篇 |
国内免费 | 42608篇 |
专业分类
化学 | 96431篇 |
晶体学 | 4605篇 |
力学 | 10676篇 |
综合类 | 3441篇 |
数学 | 23139篇 |
物理学 | 90278篇 |
出版年
2024年 | 639篇 |
2023年 | 1359篇 |
2022年 | 3483篇 |
2021年 | 3345篇 |
2020年 | 3446篇 |
2019年 | 3696篇 |
2018年 | 3653篇 |
2017年 | 5563篇 |
2016年 | 4310篇 |
2015年 | 5851篇 |
2014年 | 6617篇 |
2013年 | 9083篇 |
2012年 | 9990篇 |
2011年 | 12193篇 |
2010年 | 15920篇 |
2009年 | 16524篇 |
2008年 | 11297篇 |
2007年 | 9913篇 |
2006年 | 9578篇 |
2005年 | 8763篇 |
2004年 | 8194篇 |
2003年 | 6081篇 |
2002年 | 6042篇 |
2001年 | 6360篇 |
2000年 | 5929篇 |
1999年 | 4416篇 |
1998年 | 3050篇 |
1997年 | 2621篇 |
1996年 | 2890篇 |
1995年 | 3345篇 |
1994年 | 3325篇 |
1993年 | 3393篇 |
1992年 | 2944篇 |
1991年 | 2466篇 |
1990年 | 2097篇 |
1989年 | 2220篇 |
1988年 | 2177篇 |
1987年 | 1415篇 |
1986年 | 1426篇 |
1985年 | 983篇 |
1984年 | 1129篇 |
1983年 | 514篇 |
1982年 | 994篇 |
1981年 | 825篇 |
1980年 | 852篇 |
1979年 | 640篇 |
1978年 | 550篇 |
1977年 | 644篇 |
1976年 | 1046篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
给出了Banach空间的一个增算子不动点定理,将这一定理应用到Banach空间的积分-微分方程,给出了一类积分-微分方程的连续可微最大解和连续可微最小解的存在性定理. 相似文献
143.
Songxin Tan Ram M. Narayanan Sunil K. Shetty 《International Journal of Infrared and Millimeter Waves》2005,26(8):1175-1194
There is growing interest in the use of lidar for remote sensing of vegetation owing to the emergence of reliable and rugged lasers and highly sensitive detectors. Lidar remote sensing has a distinct advantage over conventional techniques in vegetation remote sensing due to its capability for three-dimensional characterization of vegetative targets. The Multiwavelength Airborne Polarimetric Lidar (MAPL) system was developed primarily for vegetation remote sensing applications from an airborne platform of up to 1,000 -m altitude. The lidar system has full waveform capture and polarimetric measurement capability at two wavelengths in the near-infrared (1064 nm) and the green (532 nm) spectral regions. This study presents preliminary ground-based lidar reflectance measurements on a variety of deciduous and coniferous trees under fully foliated conditions with a view towards tree species discrimination. Variations in the reflectance characteristics of selected deciduous trees under unfoliated and fully foliated conditions were also investigated. Our study reveals distinct differences in the reflectance characteristics of various trees. 相似文献
144.
145.
146.
Ultrasonic longitudinal velocity and adsorption have been measured in ceramic superconductors YBa2Cu3Oy with various porosity and also in BiSrCaCu2Oy. A velocity drop of about 400 ppm was found at Tc only in the measurements on cooling. The magnitude of the velocity drop is anomalously large compared with the value expected from the thermodynamics. A hysteresis of velocity with respect to temperature was observed in all the samples studied. It is suggested that some structural change at pore size level is responsible for this phenomenon. 相似文献
147.
This paper proposes and analyzes a GaAs traveling-wave optical modulator which uses a modulated coplanar strip electrode with periodic cross-tie overlay. This slow-wave structure can be designed to satisfy phase velocity and impedance matching conditions simultaneously. The dominant conductor loss in the slow-wave structure is reduced using the modulated coplanar strip electrode. The calculated 3-dB modulation bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of conventional electrode structures that are limited by phase velocity mismatch.This work was supported by the U.S. Army Research Office under contract DAAL-03-88-K-0005 and the Texas Advanced Technology Program. 相似文献
148.
Hiroshi Maruyama Tadao Ishii Naruhiko Bamba Hironobu Maeda Akihisa Koizumi Yuzo Yoshikawa Hitoshi Yamazaki 《Physica C: Superconductivity and its Applications》1989,160(5-6):524-532
The temperature dependence of the extended X-ray absorption fine structure (EXAFS) is studied in the high Tc superconductors, YBa2Cu3O7−δ. The measurements were done at the Cu K-edge for samples of two orthorhombic phases (Tc≈90 K and ≈58 K, respectively) and a nonsuperconducting tetragonal phase. Interatomic distances and mean square relative displacements σ2 for Cu-O bonds are determined by the least squares refinement. The results indicate that values of σ2 increase near Tc for both the orthorhombic samples. It is concluded that this anomalous behavior related to Tc is caused by an anomalous vibration of oxygen atoms in the Ba-O layer. Changes in the Cu-O distances from 300 to 20 K are not found. 相似文献
149.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as
far as the calibration of a satellite altimeter is concerned. 相似文献
150.