全文获取类型
收费全文 | 72305篇 |
免费 | 23203篇 |
国内免费 | 17009篇 |
专业分类
化学 | 45189篇 |
晶体学 | 938篇 |
力学 | 4963篇 |
综合类 | 20篇 |
数学 | 9444篇 |
物理学 | 51963篇 |
出版年
2024年 | 433篇 |
2023年 | 658篇 |
2022年 | 639篇 |
2021年 | 535篇 |
2020年 | 781篇 |
2019年 | 1313篇 |
2018年 | 1298篇 |
2017年 | 1945篇 |
2016年 | 2037篇 |
2015年 | 2249篇 |
2014年 | 2068篇 |
2013年 | 3798篇 |
2012年 | 4083篇 |
2011年 | 5626篇 |
2010年 | 9076篇 |
2009年 | 9327篇 |
2008年 | 3138篇 |
2007年 | 2655篇 |
2006年 | 2348篇 |
2005年 | 2747篇 |
2004年 | 3665篇 |
2003年 | 2940篇 |
2002年 | 2761篇 |
2001年 | 3037篇 |
2000年 | 2247篇 |
1999年 | 2484篇 |
1998年 | 2104篇 |
1997年 | 1915篇 |
1996年 | 2241篇 |
1995年 | 2695篇 |
1994年 | 2765篇 |
1993年 | 2841篇 |
1992年 | 2416篇 |
1991年 | 2076篇 |
1990年 | 1736篇 |
1989年 | 1839篇 |
1988年 | 1829篇 |
1987年 | 1120篇 |
1986年 | 1176篇 |
1985年 | 840篇 |
1984年 | 963篇 |
1982年 | 884篇 |
1981年 | 729篇 |
1980年 | 768篇 |
1979年 | 525篇 |
1978年 | 530篇 |
1977年 | 633篇 |
1976年 | 1041篇 |
1973年 | 436篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
Accelerated phase transformations and chemical reactions of metastable aluminas and kaolinite, doped with Cu2
+, Mn3
+/Mn2
+ and Fe3
+/Fe2
+ ions, are accompanied with accelerated decrease of surface area and pore volume values. The phenomena in metal ion doped
samples are explained by a catalytic mechanism, in terms of the Jahn-Teller effect.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
172.
枸杞产地的红外指纹图谱与聚类分析法研究 总被引:20,自引:5,他引:15
本文首次采用傅里叶变换红外 (FTIR)光谱法并结合SMICA聚类分析法对不同产地 :宁夏玉西、宁夏中宁及内蒙古托克托旗的枸杞进行了聚类分析。结果表明 ,聚类分析技术对来自不同产地的枸杞可进行鉴别 ,该法快速、准确 ,为客观评价中药材的来源提供了一种新的方法。 相似文献
173.
Pengbo Jiang Tiexin Cheng Yan Liu Xianghao Cui Yingli Bi Kaiji Zhen 《Reaction Kinetics and Catalysis Letters》2004,82(1):49-56
The novel phase transfer catalysts S-8 [4-(dimethyloctylammonium) propansultan] and DB-X [1,4-bis(triethylmethylammonium)benzene dibromide] were synthesized and employed for high conversion synthesis of dichlorocyclopropane from various olefins.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
174.
175.
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
176.
177.
178.
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
179.
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
180.
The effect of oxygen isotope substitution on the transition temperature Tc of a superconducting (Nd1−xCex)2CuO4−δ system was studied, where the special synthetic method was taken to minimize ambiguous factors on the oxygen concentration and to guarantee the complete substitution of 16O by 18O. The isotope exponent in the relationship of Tc∝1/M was estimated to be less than 0.15 by magnetic susceptibility measurements. 相似文献