全文获取类型
收费全文 | 1675篇 |
免费 | 39篇 |
国内免费 | 4篇 |
专业分类
化学 | 1150篇 |
晶体学 | 19篇 |
力学 | 32篇 |
数学 | 54篇 |
物理学 | 463篇 |
出版年
2023年 | 9篇 |
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 28篇 |
2014年 | 21篇 |
2013年 | 51篇 |
2012年 | 63篇 |
2011年 | 85篇 |
2010年 | 49篇 |
2009年 | 55篇 |
2008年 | 93篇 |
2007年 | 76篇 |
2006年 | 71篇 |
2005年 | 73篇 |
2004年 | 82篇 |
2003年 | 71篇 |
2002年 | 65篇 |
2001年 | 52篇 |
2000年 | 54篇 |
1999年 | 17篇 |
1998年 | 25篇 |
1997年 | 19篇 |
1996年 | 27篇 |
1995年 | 21篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 21篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 20篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 24篇 |
1975年 | 21篇 |
1974年 | 12篇 |
1968年 | 7篇 |
排序方式: 共有1718条查询结果,搜索用时 31 毫秒
111.
Laser-diode pumped heavy-doped Yb:YAG ceramic lasers 总被引:1,自引:0,他引:1
Laser performance of heavy-doped Yb:YAG ceramics was investigated using a two-pass pumping miniature laser configuration. Slope efficiency of 52% and optical-to-optical efficiency of 48% have been achieved for 1-mm-thick YAG ceramic doped with 20 at.% ytterbium ions. Laser spectra of Yb:YAG ceramic and single-crystal lasers were addressed under different intracavity laser intensities. Heavy-doped Yb:YAG ceramic is more suitable for a thin disk laser than a single-crystal with the same Yb(3+)-ion lasants. 相似文献
112.
Converging-axicon-based radially polarized ytterbium fiber laser and evidence on the mode profile inside the gain fiber 总被引:3,自引:0,他引:3
The radially polarized mode is achieved from an active Yb fiber by utilizing of an intracavity converging axicon, where the axicon acts as a TM(01) mode selector based on not only its Brewster convex surface but also the distance between its vertex and plane output coupler. The polarization state of the annular laser beam is checked by using a home-made eight-hole aperture. Furthermore, an uncoated plane glass plate is inserted into the cavity, and the reflected beam points to the existence of an annular lasing mode inside the gain fiber. The issues for developing high-power radially polarized fiber lasers also are considered. 相似文献
113.
114.
Raku Watanabe Dr. Nobuki Kato Kengo Hayashi Sho Tozawa Dr. Yusuke Ogura Prof. Shigefumi Kuwahara Prof. Minoru Ueda 《ChemistryOpen》2020,9(10):1008-1017
An efficient and stereoselective syntheses of all the possible stereoisomers of coronafacic acid (CFA) has been developed. The stereochemistries of C3a and C7a were controlled in a diastereoselective Diels-Alder type cycloaddition using a chiral auxiliary. CFA and 6-epi-CFA were synthesized by hydrogenation of a common intermediate. During the synthesis of 6-epi-CFA, we established that its cis-fused configuration is important for the introduction of C4-C5 double bond by dehydration. This report is the first practical synthesis of both 6-epi-CFA, and its enantiomer. 相似文献
115.
Kunihiro Ichimura Masatoshi Kidowaki Haruhisa Akiyama Kazuaki Kudo Veronika Strehmel Bernd Strehmel 《Macromolecular rapid communications》1996,17(8):545-551
The surface-assisted alignment of a nematic liquid crystal yields a persistent ordered structure upon cationic photopolymerization of liquid-crystalline epoxides. Linearly polarized light irradiation of a photocrosslinkable polymer containing azobenzene moieties played a crucial role in this procedure since the photoinduced alignment is not deteriorated by heating for polymerization. 相似文献
116.
117.
118.
119.
Prof. Dr. Masahiro Sadakane Sachie Moroi Yoshifumi Iimuro Dr. Natalya Izarova Prof. Dr. Ulrich Kortz Prof. Dr. Shinjiro Hayakawa Kazuo Kato Dr. Shuhei Ogo Dr. Yusuke Ide Prof. Dr. Wataru Ueda Prof. Dr. Tsuneji Sano 《化学:亚洲杂志》2012,7(6):1331-1339
Ruthenium(III)‐substituted α‐Keggin‐type silicotungstates with pyridine‐based ligands, [SiW11O39RuIII(Py)]5?, (Py: pyridine ( 1 ), 4‐pyridine‐carboxylic acid ( 2 ), 4,4′‐bipyridine ( 3 ), 4‐pyridine‐acetamide ( 4 ), and 4‐pyridine‐methanol ( 5 )) were prepared by reacting [SiW11O39RuIII(H2O)]5? with the pyridine derivatives in water at 80 °C and then isolated as their hydrated cesium salts. These compounds were characterized using cyclic voltammetry (CV), UV/Vis, IR, and 1H NMR spectroscopy, elemental analysis, titration, and X‐ray absorption near‐edge structure (XANES) analysis (Ru K‐edge and L3‐edge). Single‐crystal X‐ray analysis of compounds 2 , 3 , and 4 revealed that RuIII was incorporated in the α‐Keggin framework and was coordinated by pyridine derivatives through a Ru? N bond. In the solid state, compounds 2 and 3 formed a dimer through π? π interaction of the pyridine moieties, whereas they existed as monomers in solution. CV indicated that the incorporated RuIII–Py was reversibly oxidized into the RuIV–Py derivative and reduced into the RuII–Py derivative. 相似文献
120.
K. Kondo H. Kawabata S. Ueda H. Hasegawa J. Inaba O. Mitamura Y. Seike Y. Ohmomo 《Journal of Radioanalytical and Nuclear Chemistry》2003,257(2):305-312
We investigated the distribution of aquatic plants and the absorption of radionuclides by them in the brackish Lake Obuchi, Japan, which is bordered by nuclear fuel cycle facilities. We studied 5 species of submerged plants: Zannichellia palustris, Ruppia maritima, Potamogeton pectinatus, Zostera japonica, and Z. marina. The plants contained many elements, including radionuclides. The concentrations of 238U, 137Cs, and 90Sr in Z. marina were 11.3-12.4, 0.000-0.144, and 0.151-0.202 Bq.kg-1 dw, respectively. Those in Z. japonica were 5.2-8.8, 0.000-0.267, and 0.081-0.175 Bq.kg-1 dw, respectively. The concentrations of these radionuclides in the plants tended to be higher in higher-salinity regions than in lower-salinity regions of the lake. We found a close relationship between photosynthetic activity and the absorption of stable Sr by plants in the laboratory. Salinity, illumination, and water temperature influenced the photosynthetic activity of the plants and the consequent absorption of elements. 相似文献