全文获取类型
收费全文 | 22257篇 |
免费 | 4064篇 |
国内免费 | 2936篇 |
专业分类
化学 | 17353篇 |
晶体学 | 227篇 |
力学 | 1222篇 |
综合类 | 209篇 |
数学 | 2651篇 |
物理学 | 7595篇 |
出版年
2024年 | 20篇 |
2023年 | 496篇 |
2022年 | 537篇 |
2021年 | 750篇 |
2020年 | 1094篇 |
2019年 | 1087篇 |
2018年 | 850篇 |
2017年 | 699篇 |
2016年 | 1149篇 |
2015年 | 1168篇 |
2014年 | 1346篇 |
2013年 | 1658篇 |
2012年 | 2028篇 |
2011年 | 2082篇 |
2010年 | 1450篇 |
2009年 | 1330篇 |
2008年 | 1430篇 |
2007年 | 1299篇 |
2006年 | 1189篇 |
2005年 | 1021篇 |
2004年 | 845篇 |
2003年 | 786篇 |
2002年 | 953篇 |
2001年 | 770篇 |
2000年 | 538篇 |
1999年 | 503篇 |
1998年 | 318篇 |
1997年 | 293篇 |
1996年 | 268篇 |
1995年 | 232篇 |
1994年 | 177篇 |
1993年 | 134篇 |
1992年 | 149篇 |
1991年 | 139篇 |
1990年 | 114篇 |
1989年 | 83篇 |
1988年 | 70篇 |
1987年 | 38篇 |
1986年 | 51篇 |
1985年 | 44篇 |
1984年 | 30篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1957年 | 3篇 |
1936年 | 3篇 |
1930年 | 3篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
FengSHI HongYangLI XiaoJunPENG RongZHANG XiaoQiangCHEN JiangLiFAN LiChengSUN 《中国化学快报》2004,15(12):1407-1410
As photosensitizer for solar cell, a new ruthenium (Ⅱ) complex with four ester groups had been synthesized, in which a phenol substituted by {[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)amino]methyl} is covalently linked to ruthenium (Ⅱ) tris-bipyridine. The structures of the new compounds were confirmed by NMR and ESI-MS spectra. The electrochemical and photochemical properties were also studied. 相似文献
82.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
83.
The distributions of limit cycles of cubic vector fields (P2, Q3) are considered in this paper, where P2 and Q3 are polynomials of x and y of order two and three, respectively. It is possibly seven different distributions of limit cycles given in [1]. We now prove that in which three kinds of distributions are impossible and other four kinds all can be realized by concrete vector fields of (P2,Q3). Some related results are also given. 相似文献
84.
非负矩阵与有向图的谱半径 总被引:2,自引:0,他引:2
本文给出非负矩阵的谱半径的上界、下界,由此给出有向图的谱半径的界. 相似文献
85.
Gang Tian 《Inventiones Mathematicae》1997,130(1):1-37
In this paper, we prove that the existence of K?hler-Einstein metrics implies the stability of the underlying K?hler manifold
in a suitable sense. In particular, this disproves a long-standing conjecture that a compact K?hler manifold admits K?hler-Einstein
metrics if it has positive first Chern class and no nontrivial holomorphic vector fields. We will also establish an analytic
criterion for the existence of K?hler-Einstein metrics. Our arguments also yield that the analytic criterion is satisfied
on stable K?hler manifolds, provided that the partial C
0-estimate posed in [T6] is true.
Oblatum 12-IV-1996 & 8-XI-1996 相似文献
86.
87.
88.
The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques. The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100–200 degrees centigrade through doping with N. The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400°C, and the interface pattern still exists even if they were annealed at 700°C. The Raman spectra analyses give the evidence that the formation of the sp3 bonding in the CN sublayers can be suppressed effectively by doping N with atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding betweenC andN atoms, and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc-Co and hcp-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420°C, leading to the suppression of the grain growth. 相似文献
89.
张(1884—1950),植物学家和生物学教育家.中国近代植物学的先驱、现代实验性植物生理学和植物生态学的奠基人.最先自编我国第一套植物学、植物形态学、植物解剖学、种子植物分类学、植物生态学和植物生理学教科书.长期从事植物学科的教学和研究工作,为我国的生物科学和教育事业的建立和发展,贡献了自己的一切知识和力量. 相似文献