全文获取类型
收费全文 | 63157篇 |
免费 | 7272篇 |
国内免费 | 6411篇 |
专业分类
化学 | 29346篇 |
晶体学 | 563篇 |
力学 | 2205篇 |
综合类 | 380篇 |
数学 | 4839篇 |
物理学 | 14506篇 |
综合类 | 25001篇 |
出版年
2024年 | 246篇 |
2023年 | 916篇 |
2022年 | 1638篇 |
2021年 | 1809篇 |
2020年 | 1842篇 |
2019年 | 1714篇 |
2018年 | 1584篇 |
2017年 | 1561篇 |
2016年 | 2190篇 |
2015年 | 2504篇 |
2014年 | 3149篇 |
2013年 | 3962篇 |
2012年 | 4630篇 |
2011年 | 4969篇 |
2010年 | 3946篇 |
2009年 | 3934篇 |
2008年 | 4263篇 |
2007年 | 3996篇 |
2006年 | 3505篇 |
2005年 | 3048篇 |
2004年 | 2377篇 |
2003年 | 1805篇 |
2002年 | 1924篇 |
2001年 | 1667篇 |
2000年 | 1418篇 |
1999年 | 1493篇 |
1998年 | 1220篇 |
1997年 | 1157篇 |
1996年 | 1127篇 |
1995年 | 1016篇 |
1994年 | 926篇 |
1993年 | 776篇 |
1992年 | 726篇 |
1991年 | 658篇 |
1990年 | 590篇 |
1989年 | 492篇 |
1988年 | 439篇 |
1987年 | 313篇 |
1986年 | 238篇 |
1985年 | 225篇 |
1984年 | 130篇 |
1983年 | 89篇 |
1982年 | 85篇 |
1981年 | 64篇 |
1980年 | 56篇 |
1979年 | 61篇 |
1978年 | 43篇 |
1976年 | 39篇 |
1974年 | 45篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
The crystal structure, magnetic and magnetotransport properties of the variation of B′-site transition metal in Sr2FeMO6 (M=Mo, W) with double perovskites structure have been investigated systematically. Measurements of magnetization vs. temperature at H=5 T show that Sr2FeMoO6 is a ferromagnet and Sr2FeWO6 is an antiferromagnet with TN∼35 K. Additionally, the large magnetoresistance ratio (MR) of ∼22% (H=3 T) at room temperature (RT) was observed in the Sr2FeWO6 compound. However, the Sr2FeMoO6 compound did not show any significant MR even at high fields and RT (MR∼1%; H=3 T and 300 K). The implications of these findings are supported by band structure calculations to explain the interaction between the 4d(Mo) and 5d(W) orbitals of transition metal ions and oxygen ions. 相似文献
85.
Yang Mujie Zhao Jian Li Aibing Shen Zhiquan Zhang Mingjian Lin Senhao 《Journal of polymer science. Part A, Polymer chemistry》1989,27(11):3829-3835
This paper reports that 60Co γ-ray irradiation can convert cis-polyphenylacetylene (cis-PPA) films prepared with rare-earth coordination catalysts to highly photosensitive materials. The dependence of the photosensitivity on irradiation dose, preparation methods, and microstructure of the PPA films has been investigated by means of a potential discharge technique. The photosensitivity was enhanced with increasing irradiation dose. The critical dose to produce a light response was 5 × 103 Gy. The maximum surface potential discharge rate was 618 V/s, and the dark decay was approximately 2 V/s for cis-PPA films irradiated with 60Co γ-ray (dose: 2 × 105 Gy). The cis-transoidal-PPA and an electrophotographic photoreceptor device incorporating cis-PPA showed a higher irradiation effect. The structure and properties of 60Co γ-ray irradiated rare-earth PPA films are similar to the unirradiated films. 相似文献
86.
TANG Chen ZHANG Fang YAN Hai-Qing CHEN Zhan-Qing LUO Tao 《理论物理通讯》2005,44(3):435-439
We develop the three-step explicit and implicit schemes of exponential fitting methods. We use the three- step explicit exponential fitting scheme to predict an approximation, then use the three-step implicit exponential fitting scheme to correct this prediction. This combination is called the three-step predictor-corrector of exponential fitting method. The three-step predictor-corrector of exponential fitting method is applied to numerically compute the coupled nonlinear Schroedinger equation and the nonlinear Schroedinger equation with varying coefficients. The numerical results show that the scheme is highly accurate. 相似文献
87.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献
88.
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
89.
利用DA算法实现大规模FIR滤波器 总被引:3,自引:0,他引:3
分布式算法是一种广泛地应用在可编程逻辑序列(FPCA)和ASIC设计中计算乘积和的算法。DA算法的处理速度仅与输入的位宽有关,对于大规模乘积和的运算,其计算速度有着明显的优势。当输入位宽过大时,可以将DA算法改进成并串结构以获得更快的处理速度。该文对在FPCA中利用DA算法实现大规模FIR滤波器,提出了具体的实现方案。 相似文献
90.