全文获取类型
收费全文 | 40106篇 |
免费 | 2496篇 |
国内免费 | 1944篇 |
专业分类
化学 | 22539篇 |
晶体学 | 237篇 |
力学 | 3932篇 |
综合类 | 543篇 |
数学 | 8156篇 |
物理学 | 9139篇 |
出版年
2024年 | 58篇 |
2023年 | 348篇 |
2022年 | 1040篇 |
2021年 | 1052篇 |
2020年 | 1024篇 |
2019年 | 973篇 |
2018年 | 868篇 |
2017年 | 1098篇 |
2016年 | 1503篇 |
2015年 | 1117篇 |
2014年 | 1600篇 |
2013年 | 2830篇 |
2012年 | 2282篇 |
2011年 | 2060篇 |
2010年 | 1777篇 |
2009年 | 2280篇 |
2008年 | 2247篇 |
2007年 | 2546篇 |
2006年 | 2119篇 |
2005年 | 1912篇 |
2004年 | 1857篇 |
2003年 | 1555篇 |
2002年 | 1204篇 |
2001年 | 988篇 |
2000年 | 953篇 |
1999年 | 862篇 |
1998年 | 805篇 |
1997年 | 720篇 |
1996年 | 658篇 |
1995年 | 638篇 |
1994年 | 565篇 |
1993年 | 461篇 |
1992年 | 428篇 |
1991年 | 370篇 |
1990年 | 331篇 |
1989年 | 220篇 |
1988年 | 221篇 |
1987年 | 138篇 |
1986年 | 117篇 |
1985年 | 146篇 |
1984年 | 117篇 |
1983年 | 59篇 |
1982年 | 95篇 |
1981年 | 54篇 |
1980年 | 49篇 |
1979年 | 76篇 |
1978年 | 35篇 |
1977年 | 15篇 |
1976年 | 23篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
221.
Scaling analysis of the magnitude series (volatile series) has been proposed recently to identify possible non-linear/multifractal signatures in the given data [Y. Ashkenazy, et al. Phys. Rev. Lett. 86 (2001) 1900; Y. Ashkenazy, et al. Physica A 323 (2003) 19; T. Kalisky, Y. Ashkenazy, S. Havlin. Phys. Rev. E 72 (2005) 011913]. In this article, correlations of volatile series generated from stationary first-order linear feedback process with Gaussian and non-Gaussian innovations are investigated. While volatile correlations corresponding to Gaussian innovations exhibited uncorrelated behavior across all time scales, those of non-Gaussian innovations showed significant deviation from uncorrelated behavior even at large time scales. The results presented raise the intriguing question whether non-Gaussian innovations can be sufficient to realize long-range volatile correlations. 相似文献
222.
In this note we study constant mean curvature surfaces in asymptotically flat 3-manifolds. We prove that, outside a given compact subset in an asymptotically flat 3-manifold with positive mass, stable spheres of given constant mean curvature are unique. Therefore we are able to conclude that the foliation of stable spheres of constant mean curvature in an asymptotically flat 3-manifold with positive mass outside a given compact subset is unique.
223.
Yangyang Jiang Chen Guo Huizhou Liu 《中国颗粒学报》2007,5(1):130-133
A magnetically rotational reactor (MRR) has been developed and used in absorbing benzene emissions. The MRR has a permanent magnet core and uses magnetic ionic liquid [bmim]FeCl4 as absorbent. Benzene emissions were carried by N2 into the MRR and were absorbed by the magnetic ionic liquid. The rotation of the permanent magnet core provided impetus for the agitation of the magnetic ionic liquid, enhancing mass transfer and making benzene better dispersed in the absorbent. 0.68 g benzene emissions could be absorbed by a gram of [bmim]FeCl4, 0.27 and 0.40 g/g higher than that by [bmim]PF6 and [bmim]BF4, respectively. The absorption rate increased with increasing rotation rate of the permanent magnet. 相似文献
224.
225.
HL-2Aƫ�����ṹ���켰�ȸ��ɷ��� 总被引:1,自引:1,他引:0
根据HL-2A装置改造的初步方案,选择优化的偏滤器位形所决定的参数,设计出可采取的偏滤器结构及水冷方式。外靶板和拱顶板上采用双剪切连接件和环向水路具有极向水流的冷却方式。通过ANSYS编码对靶板的热负荷进行分析,结果表明这样的冷却方式在降低流速要求的条件下可以提高靶板表面承载能力。 相似文献
226.
本文研究了一维模型分子离子(初态为基态和一个激发束缚态叠加的相干态)在超强超短激光脉冲作用下的谐波发射谱.我们发现在高次谐波谱平台区域出现了周期性的结构变化.我们利用小波变换对谐波谱进行了暂态时间频率分析,结果表明该谐波结构产生的原因是由电离电子返回母离子时与不同束缚态复合而产生的谐波光脉冲之间相干叠加.同时采用半经典计算,对所得到的计算结果进行了分析,验证了我们的结论. 相似文献
227.
Dimensional analysis is presented as a powerful tool in the study of the paste boriding process. In particular, a dimensional method is used to study the growth kinetics of the boride layers FeB and Fe2B. Experiments were performed in AISI 1045 steel and AISI M2 steel, to test the suggested model. Samples of 1045 steel were prepared and treated using boron paste thickness of 3-5 mm, at temperatures of 1193, 1223 and 1273 K, with 2, 4 and 6 h of treatment time. The M2 specimens had boron paste thickness of 3 and 4 mm and temperatures of 1223, 1253 and 1273 K for 2 and 6 h. Results indicate that the growth of boron layers obeys power laws of the form y = αxβ, where α and β constants are a function of the material and the interface of interest. Validation of the model was carried out using experimental data with an average error percentage of 7.6% for Fe2B in 1045 steel, 15.8% for FeB and 3.4% for Fe2B in M2 steel. 相似文献
228.
229.
Effects of Nb2O5 on thermal stability and optical properties of Er3+-doped tellurite glasses
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Er3+-doped tellurite glasses with molar compositions of
xNb2O5-(14.7-x)Na2O--10ZnO--5K2O--10GeO2--
60TeO2--0.3Er2O3
(x=0, 3, 5, 7 and 9) have been investigated for developing 1.5~μm
fibre and planar amplifiers. The effects of Nb2O5 on the thermal stability
and optical properties of Er3+-doped tellurite glasses have been discussed.
It is noted that the incorporation of Nb2O5 (x=5) increases the thermal
stability of tellurite glasses significantly. Er3+-doped niobium tellurite
glasses exhibit a large stimulated emission cross-section (7.2\times 10-21-
10.7×10-21~cm2 and the gain bandwidth, FWHM×\sigmae^{\rm peak} (274\times 10-28 - 480×10-28~cm3), which are
significantly higher than that of silicate and phosphate glasses. In addition, the
intensity of upconversion luminescence of the Er3+-doped niobium tellurite
glasses decreases rapidly with increasing Nb2O5 content. As a result,
Er3+-doped niobium tellurite glasses might be a potential candidate for
developing laser or optical amplifier devices. 相似文献
230.