全文获取类型
收费全文 | 119670篇 |
免费 | 19053篇 |
国内免费 | 13611篇 |
专业分类
化学 | 83191篇 |
晶体学 | 1331篇 |
力学 | 6947篇 |
综合类 | 838篇 |
数学 | 14512篇 |
物理学 | 45515篇 |
出版年
2024年 | 392篇 |
2023年 | 2356篇 |
2022年 | 4100篇 |
2021年 | 4383篇 |
2020年 | 4701篇 |
2019年 | 4473篇 |
2018年 | 4176篇 |
2017年 | 3792篇 |
2016年 | 5696篇 |
2015年 | 5605篇 |
2014年 | 6829篇 |
2013年 | 8870篇 |
2012年 | 10636篇 |
2011年 | 10885篇 |
2010年 | 7600篇 |
2009年 | 7176篇 |
2008年 | 7692篇 |
2007年 | 6972篇 |
2006年 | 6455篇 |
2005年 | 5466篇 |
2004年 | 4217篇 |
2003年 | 3432篇 |
2002年 | 3128篇 |
2001年 | 2574篇 |
2000年 | 2292篇 |
1999年 | 2444篇 |
1998年 | 2036篇 |
1997年 | 1868篇 |
1996年 | 1824篇 |
1995年 | 1624篇 |
1994年 | 1505篇 |
1993年 | 1227篇 |
1992年 | 1071篇 |
1991年 | 956篇 |
1990年 | 797篇 |
1989年 | 608篇 |
1988年 | 453篇 |
1987年 | 407篇 |
1986年 | 382篇 |
1985年 | 296篇 |
1984年 | 222篇 |
1983年 | 174篇 |
1982年 | 146篇 |
1981年 | 95篇 |
1980年 | 72篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1976年 | 22篇 |
1975年 | 24篇 |
1957年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Wang Qing-Lun Zhao Bin Liao Dai-Zheng Yan Shi-Ping Cheng Peng Jiang Zong-Hui 《Transition Metal Chemistry》2003,28(3):326-330
The copper(II) complex Na2[Cu(pba)] · 6H2O has been synthesized and its structure determined. It consists of a novel two-dimensional network of [Cu(pba)]2– anions connected to each other through the sodium ion as a bridge. Spectroscopic and magnetic properties have been measured and a spin distribution calculation has been carried out with the GAUSSIAN-94. Theoretical calculations indicate the rather larger spin density on nitrogen atoms should be responsible for the satellite lines appearing beside the main hyperfine coupling signs of copper(II). The antiferromagnetic interaction may be due to the intermolecular interaction and/or different copper(II) ions through the Na+ bridge in the same layer. 相似文献
33.
Jihua Zhang Xi WangWeidong Yu Tao FengFumin Zhang Zhihong ZhengQiong Li Xianghuai Liu 《Solid State Communications》2003,127(4):289-293
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips. 相似文献
34.
A new family of photonucleases, naphthalimide-thiazoles was synthesized and evaluated. These compounds intercalated into DNA efficiently and damaged DNA photochemically at concentrations as low as 5 μM. Mechanistic experiment suggests that a novel naphthalimide-thiazole radical produced via an excited triple state might be involved in the DNA photodamage. Different activity may arise from the impact of substituents at 2-phenyl ring of thiazole on the electron population of excited triple state according to AM1 semi-empirical calculation. 相似文献
35.
Briand et al. (Electron. Comm. Probab. 5 (2000) 101–117) gave a counterexample and proposition to show that given g,g-expectations usually do not satisfy Jensen's inequality for most of convex functions. This yields a natural question, under which conditions on g, do g-expectations satisfy Jensen's inequality for convex functions? In this paper, we shall deal with this question in the case that g is convex and give a necessary and sufficient condition on g under which Jensen's inequality holds for convex functions. To cite this article: Z. Chen et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
36.
37.
Li Yingle Huang Jiying Gong Shuohong 《International Journal of Infrared and Millimeter Waves》2003,24(6):953-961
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references. 相似文献
38.
学生学习知识,一般来说,是从生动的具体的直观开始的,生动的直观能使学生获得关于事物生动而具体的感性认识。但是,感性认识并没有揭露事物的本质,人们对事物本质的认识要通过一系列的抽象来完成。 相似文献
39.
40.
Liuman Ou Guilie Luo Yiping Li 《Journal of Mathematical Analysis and Applications》2003,283(2):534-548
In this paper, we consider an autonomous predator-prey Lotka-Volterra system in which individuals in the population may belong to one of two classes: the immatures and the matures, the age to maturity is represented by a time delay. By using eigenvalue analysis, principal term analyze method, reduction to absurdity, and iterative method, we obtain some simple conditions for global asymptotic stability of the unique positive equilibrium point. Moreover, a condition that the prey population in the system get extinction and the predator population in the system get permanence will be obtained. Meanwhile the theorems extend the corresponding conclusions in which there have no two stage structures. 相似文献