全文获取类型
收费全文 | 48323篇 |
免费 | 9067篇 |
国内免费 | 7072篇 |
专业分类
化学 | 35141篇 |
晶体学 | 692篇 |
力学 | 3186篇 |
综合类 | 480篇 |
数学 | 5577篇 |
物理学 | 19386篇 |
出版年
2024年 | 145篇 |
2023年 | 905篇 |
2022年 | 1721篇 |
2021年 | 1818篇 |
2020年 | 1952篇 |
2019年 | 1957篇 |
2018年 | 1744篇 |
2017年 | 1737篇 |
2016年 | 2305篇 |
2015年 | 2548篇 |
2014年 | 3069篇 |
2013年 | 3880篇 |
2012年 | 4489篇 |
2011年 | 4580篇 |
2010年 | 3352篇 |
2009年 | 3361篇 |
2008年 | 3651篇 |
2007年 | 3112篇 |
2006年 | 2874篇 |
2005年 | 2328篇 |
2004年 | 1743篇 |
2003年 | 1463篇 |
2002年 | 1448篇 |
2001年 | 1198篇 |
2000年 | 968篇 |
1999年 | 888篇 |
1998年 | 701篇 |
1997年 | 583篇 |
1996年 | 562篇 |
1995年 | 496篇 |
1994年 | 471篇 |
1993年 | 379篇 |
1992年 | 303篇 |
1991年 | 285篇 |
1990年 | 279篇 |
1989年 | 194篇 |
1988年 | 169篇 |
1987年 | 138篇 |
1986年 | 128篇 |
1985年 | 108篇 |
1984年 | 52篇 |
1983年 | 61篇 |
1982年 | 39篇 |
1981年 | 34篇 |
1980年 | 21篇 |
1979年 | 29篇 |
1978年 | 15篇 |
1977年 | 21篇 |
1974年 | 11篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Direct synthesis of phenol by hydroxylation of benzene with H2O2 over the vanadium-substituted heteropolymolybdic acid catalyst was investigated at 70 °C. H2O2 was used as an oxidant while 36 wt.% MeCO2H was employed as the solvent. After 100 min the selectivity for phenol was 93% and the yield of PhOH was 10.1%. The catalyst
was characterized by elemental analysis, thermal gravimetric analysis, infrared spectroscopy, u.v.–vis spectroscopy, X-ray
diffraction, and 31P-n.m.r. and 51V-n.m.r. techniques. The experimental conditions such as reaction temperature, the amounts of H2O2 and catalyst were explored. The as-prepared phenol could be separated by column chromatography and was characterized by infrared
and mass spectrometry. 相似文献
992.
This paper is the study of the fluorescence enhancement of Eu3+-1-ethyl-6-fluoro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridin-3-carbonic acid (enoxacin, EFLX) system by surfactants. It was
found that sodium dodecylbenzenesulfonate (SDBS) exhibits great enhancement on the fluorescence of the Eu-EFLX system. The
molar ratio is 1:2:1 for Eu:EFLX: SDBS. Under the optimum conditions, the fluorescence intensity is a linear function of europium
in the range of 1.0 × 10−8 ∼ 5.0 × 10−6 mol/L, the detection limit is 1.0 × 10−9 mol/L. The application of the Eu-EFLX-SDBS system for the determination of trace europium in rare earth samples gave satisfactory
results.
Received October 19, 2000. Revision August 10, 2001. 相似文献
993.
Xin-Rui Wang Hui-Min Cheng Xue-Wei Gao Wei Zhou Shu-Jing Li Xue-Li Cao Dongpeng Yan 《中国化学快报》2019,30(4):919-923
The inhibitor of melanin and the bacteriostatic agent kojic acid was inserted into Zn-Ti layered double hydroxide (LDH) by anion-exchange reaction. The structure, slow release, antibacterial and skin whitening activity were studied. 相似文献
994.
995.
环状碳酸酯低聚物的合成及其开环聚合的研究 总被引:4,自引:0,他引:4
环状碳酸酯低聚物的合成及其开环聚合的研究陈雨萍魏玮李革(中国科学院化学研究所工程塑料国家重点实验室北京100080)关键词环状碳酸酯低聚物,聚碳酸酯,开环聚合环状单体的开环聚合在合成高聚物方面具有突出的优点,即在聚合过程中没有副产物、热效应低、聚合... 相似文献
996.
997.
998.
Guihua Huang Yipeng Huang Wei Xu Qiuhong Yao Xiaofang Liu Caifeng Ding Xi Chen 《中国化学快报》2019,30(5):1021-1023
Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)_3, as a light absorber, we report a highly effective UV and blue light blocking film. The CsPb(Cl/Br)_3 nanocrystals are well dispersed in the ethyl cellulose(EC) matrix to compose a UV and blue light shielding film, and the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The CsPbCl_2 Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the range of 500–800 nm, which makes it excellent for UV and blue light shielding. In addition, the as-prepared EC-CsPb(Cl/Br)_3 film shows excellent photostability under UV irradiation. Results demonstrate that this EC-CsPb(Cl/Br)_3 based materials with sharp absorbance edges, tunable blocking wavelength, and high photostability can be useful for the applications in UV and blue light blocking and optical filters 相似文献
999.
1000.
Catalyzed collapse and enhanced hydrogen storage of BN nanotubes 总被引:1,自引:0,他引:1
Tang C Bando Y Ding X Qi S Golberg D 《Journal of the American Chemical Society》2002,124(49):14550-14551
The novel morphology of BN nanotubes with a collapsed structure has been discovered by a metal-catalyzed treatment. The collapse causes the dramatic enlargement of a specific surface area of BN nanotubes and remarkably enhances the hydrogen storage capacity of BN nanotubes. 相似文献