全文获取类型
收费全文 | 7005篇 |
免费 | 2433篇 |
国内免费 | 3017篇 |
专业分类
化学 | 4122篇 |
晶体学 | 322篇 |
力学 | 1538篇 |
综合类 | 213篇 |
数学 | 1079篇 |
物理学 | 5181篇 |
出版年
2024年 | 79篇 |
2023年 | 248篇 |
2022年 | 349篇 |
2021年 | 329篇 |
2020年 | 274篇 |
2019年 | 302篇 |
2018年 | 233篇 |
2017年 | 304篇 |
2016年 | 340篇 |
2015年 | 371篇 |
2014年 | 657篇 |
2013年 | 586篇 |
2012年 | 521篇 |
2011年 | 566篇 |
2010年 | 548篇 |
2009年 | 642篇 |
2008年 | 639篇 |
2007年 | 538篇 |
2006年 | 565篇 |
2005年 | 550篇 |
2004年 | 513篇 |
2003年 | 460篇 |
2002年 | 374篇 |
2001年 | 354篇 |
2000年 | 273篇 |
1999年 | 238篇 |
1998年 | 225篇 |
1997年 | 219篇 |
1996年 | 209篇 |
1995年 | 187篇 |
1994年 | 146篇 |
1993年 | 109篇 |
1992年 | 121篇 |
1991年 | 112篇 |
1990年 | 104篇 |
1989年 | 91篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
V. A. KHATSKEVICH V.A. SENDEROV 《数学学报(英文版)》2006,22(6):1687-1694
The operator sets, which are the subject of this paper, have been studied in many papers where, under different restrictions on the generating operators, convexity, compactness in the weak operator topology, and nonemptiness were proved for sets of different classes under study. Then the results obtained were used in these papers to solve several applied problems. Namely, they played the key role in establishing the dichotomy of nonautonomous dynamical systems, with either continuous or discrete time. In the present paper, we generalize and sharpen the already known criteria and obtain several new criteria for convexity, compactness, and nonemptiness of several special operator sets. Then, using the assertions obtained, we construct examples of sets of the form under study which are nonconvex, noncompact in the weak operator topology, as well as empty, and are generated by "smooth" operators of a special class. The existence problem for such sets remained open until the authors of this paper announced some of its results. 相似文献
72.
用落球法测粘滞系数的二级近似公式,有些教材是以过时的戈尔茨坦(Goldstein)公式为依据得出来的,而雷诺(Reynolds)数R~2项的系数却与原公式不一致。本文提出一些商榷意见,并讨论一下落球法的使用范围。一、正确的二级近似公式直径为d的小球,在粘滞系数为η、 相似文献
75.
76.
双包层椭圆光波导解析解 总被引:3,自引:0,他引:3
解析求解了双包层椭圆光纤中的波动方程,得到了模式精确解有模式特征方程。对基模的特征方程进行了数值计算,给出了不同椭圆比下的归一化双折射和模间色散随归一化频率的变化关系曲线,并与高斯近似解的结果进行了比较。 相似文献
77.
Effects of Processing Parameters on Microstructure and Properties of Nanoscale ZrC/ZrB2 Multilayered Coatings
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
ZrC/ZrB2 multilayered coatings with bilayer periods of 3.5-40nm are synthesized by rf magnetron sputtering. Analyses of x-ray diffraction, scanning electron microscopy and nanoindentation indicate that multilayered coatings possess much higher hardness and greater fracture resistance than monolithic ZrC and ZrB2 coatings. A maximum hardness (41.TCPa) and a critical fracture load (73.7mN) are observed in the multilayer with A = 32 nm deposited at the substrate bias -40 V. Higher residual stress built in the ZrC layer can be released by periodic insertion of ZrB2 into the ZrC layer. A clear multilayered structure with mixed ZrB2(001), ZrB2 (002) and ZrC (111) orientations should be responsible for the enhanced mechanical properties. 相似文献
78.
采用热处理方法提高MEH-PPV单层聚合物有机发光二极管发光性能的研究 总被引:2,自引:1,他引:1
对以MEH-PPV为发光层的单层聚合物有机发光二极管(OLED)器件在最佳条件下进行真空热处理,并用金相显微镜观察施加电压后器件的阴极表面形貌。发现处理后的器件阴极表面的气泡及黑斑明显减少。器件的发光性能显著提高。与未经处理的器件相比,最大相对发光强度提高了一个数量级、启亮电压降低了2.0V,半寿命提高了12.7倍。初步分析表明热处理方法提高器件发光性能的主要原因在于有效地减少了器件在工作过程中由于焦耳热产生的某些气体,从而减少阴极表面气泡及黑斑的出现,另一方面,热处理方法也增强了有机发光层与阴极接触界面的结合力,提高电子注入水平。 相似文献
79.
80.
Experimental Study of Capillary Effect in Porous Silicon Using Micro-Raman Spectroscopy and X-Ray Diffraction
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
LEIZhen-Kun KANGYi-Lan QIUYu HUMing CENHao 《中国物理快报》2004,21(7):1377-1380
We investigate the capillary effect and the residual stress evolution in the wetting, drying and rewetting stages of porous silicon using x-ray diffraction and micro-Raman spectroscopy. A reversible capillary effect and an irreversible oxidation effect are the driving forces for the residual stress evolution. The lattice expansion of the porous-silicon layer is observed to decrease slightly by x-ray diffraction and the tensile residual stress increases rapidly by micro-Raman spectroscopy, with the change of about 82 MPa for the oxidation effect and the change of 2.78 GPa (enough for cracking) for the capillary effect. Therefore, the capillary effect plays a major role in the residual stress evolution in the stages. A simple microscopic liquid-bridge model is introduced to explain the capillary effect and its reversibility. The capillary emergence has a close relation with a great deal of the micro-pore structure of porous silicon. 相似文献