全文获取类型
收费全文 | 28240篇 |
免费 | 5067篇 |
国内免费 | 3619篇 |
专业分类
化学 | 16866篇 |
晶体学 | 521篇 |
力学 | 3088篇 |
综合类 | 264篇 |
数学 | 1331篇 |
物理学 | 14856篇 |
出版年
2024年 | 52篇 |
2023年 | 277篇 |
2022年 | 919篇 |
2021年 | 967篇 |
2020年 | 1129篇 |
2019年 | 971篇 |
2018年 | 869篇 |
2017年 | 1041篇 |
2016年 | 1319篇 |
2015年 | 1166篇 |
2014年 | 1426篇 |
2013年 | 2837篇 |
2012年 | 1682篇 |
2011年 | 1871篇 |
2010年 | 1506篇 |
2009年 | 1654篇 |
2008年 | 1720篇 |
2007年 | 1737篇 |
2006年 | 1717篇 |
2005年 | 1430篇 |
2004年 | 1377篇 |
2003年 | 1154篇 |
2002年 | 1006篇 |
2001年 | 904篇 |
2000年 | 796篇 |
1999年 | 628篇 |
1998年 | 678篇 |
1997年 | 574篇 |
1996年 | 525篇 |
1995年 | 443篇 |
1994年 | 409篇 |
1993年 | 363篇 |
1992年 | 337篇 |
1991年 | 225篇 |
1990年 | 196篇 |
1989年 | 168篇 |
1988年 | 178篇 |
1987年 | 129篇 |
1986年 | 98篇 |
1985年 | 81篇 |
1984年 | 75篇 |
1983年 | 27篇 |
1982年 | 51篇 |
1981年 | 45篇 |
1980年 | 25篇 |
1979年 | 34篇 |
1978年 | 26篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
31.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
32.
Elena Kardash-Strochkova Yakov I. Tur’yan I. Kuselman Naphtali Brodsky 《Accreditation and quality assurance》2002,7(6):250-254
The results of two interlaboratory comparisons of acid number determinations in used motor oils are discussed. It is shown
that the comparability of the measurement results is not as good as that required by known standards for petroleum products.
The problem is motor oil contaminants which accumulated during use, and which are the source of a matrix effect in the acid
number determination. The standard methods’ drawbacks are analyzed and some improvements are proposed. Repeatability and accuracy
of the improved methods are evaluated.
Received: 11 December 2001 Accepted: 15 February 2002 相似文献
33.
34.
35.
Srinivasan G. 《物理学报》2006,55(5):2548-2552
讨论了Ni0.8Zn0.2Fe2O4 (NZFO)与锆钛酸铅(PZT)的双层膜结构样品的磁电(ME)效应.NZFO粉料由溶胶-凝胶法制成,再经900℃热压,并高温烧结.在该双层膜中测量到了很强的磁电相互作用.发现横向的磁电效应比纵向效应大一个数量级,并且随NZFO烧结温度的提高而增加.当烧结温度从950℃上升到1380℃时,横向ME电压系数(αE)的最大值变化范围为25.6 mV Am-2≤αE≤199.6 mV Am-2.理论分析显示NZFO-PZT双层膜样品中ME效应源于NZFO与PZT之间相对良好的磁电耦合.
关键词:
镍铁氧体
PZT
热压法
ME效应 相似文献
36.
S. Meenakshi B.K. Godwal I. Orgzall S. Tkachev 《Journal of Physics and Chemistry of Solids》2006,67(8):1660-1667
We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes. 相似文献
37.
The molding processes of polymer melts involve geometrically complex dies. Such dies are usually tapered or streamlined to achieve a maximum output rate under conditions of laminar flow. The model of a generalized second-grade fluid of power-law type is used and the results obtained are illustrated by examples of convergent flows in conical and wedge-shaped dies. 相似文献
38.
39.
40.