全文获取类型
收费全文 | 288篇 |
免费 | 45篇 |
国内免费 | 31篇 |
专业分类
化学 | 226篇 |
晶体学 | 2篇 |
力学 | 11篇 |
综合类 | 2篇 |
数学 | 31篇 |
物理学 | 92篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 17篇 |
2020年 | 25篇 |
2019年 | 19篇 |
2018年 | 18篇 |
2017年 | 8篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 25篇 |
2013年 | 17篇 |
2012年 | 34篇 |
2011年 | 29篇 |
2010年 | 14篇 |
2009年 | 20篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
排序方式: 共有364条查询结果,搜索用时 31 毫秒
41.
一种投影式激光方向测量方法 总被引:7,自引:0,他引:7
为了在激光告警中实现全方位角度探测,且达到一定的探测精度,提出了一种投影式激光方向测量方法.通过计算激光照射在参量给定的遮光板上形成的投影量.求解在探测器上由不同探测象限产生的不同的探测电流的比值.再根据投影面积的比值与角度一一对应的关系可事先编码的原理.由对应程序判断激光入射方向.在软件Matlab仿真中计箅得到产生最小分辨率的四个极限角度分别为(0°,90°)、(33°,21°)、(33°,69°)、(45°,90°),并由实验得到最小分辨电压为0.05 V.通过仿真计算与实验数据证明该设计可达到最小识别角度1°的探测要求. 相似文献
42.
Zhichao Zhang 《Mathematical Methods in the Applied Sciences》2020,43(11):6663-6676
Motivated by the well-established phase derivative embedded technique, this study devotes to sharper uncertainty principles related to the Lp-norm type of uncertainty product, giving rise to two kinds of uncertainty inequalities that improve the classical result through providing tighter lower bounds. The conditions that truly reach these better estimates are obtained. Examples and simulations are carried out to verify the correctness of the derived results, and finally, possible applications in time-frequency analysis are also given. 相似文献
43.
In this paper, the electrochemical performance of a new low-temperature electrolyte, 0.9 mol L?1 lithium oxalyldifluoroborate (LiODFB)/LiBF4 (5.365:1, by mass) mixed salts in the ethylene carbonate (EC)/dimethyl sulfite (DMS)/ethyl methyl carbonate (EMC) mixed solvent (1:1:3, by volume, the same below), is studied to seek the promising candidate for advanced low-temperature lithium-ion batteries (LIBs). The results show that LIBs using this new electrolyte can be operable well at temperature below ?20 °C. This is useful to expand the application range of LIBs, especially at specific low-temperature environments, such as military and aerospace applications. 相似文献
44.
A new family of energetic caged compounds was designed by introducing -NH- into the CL-20 skeleton and their energetic properties and impact sensitivity were investigated by using density functional theory. The results indicate that favorable substitution positions of the amine groups in the skeleton is helpful for increasing the heats of formation. Most of the seven compounds have high crystal densities above 1.9 g/cm3. Five compounds have the predominant detonation properties over CL-20. The derivatives with one NH2 group have lower impact sensitivity than those with two NH2 groups. Taking the detonation performance and impact sensitivity into consideration, four compounds may be selected as the potential candidates of high energy density compounds. 相似文献
45.
Zhichao Cheng Dr. Huifang Shi Dr. Huili Ma Lifang Bian Qi Wu Long Gu Suzhi Cai Xuan Wang Prof. Wei‐wei Xiong Prof. Zhongfu An Prof. Wei Huang 《Angewandte Chemie (International ed. in English)》2018,57(3):678-682
A new type of materials, organic salts in the crystal state, have ultralong organic phosphorescence (UOP) under ambient conditions. The change of cations (NH4+, Na+, or K+) in these phosphors gives access to tunable UOP colors ranging from sky blue to yellow green, along with ultralong emission lifetimes of over 504 ms. Single‐crystal analysis reveals that unique ionic bonding can promote an ordered arrangement of organic salts in crystal state, which then can facilitate molecular aggregation for UOP generation. Additionally, reversible ultralong phosphorescence can be realized through the alternative employment of fuming gases (ammonia and hydrogen chloride), demonstrating its potential as a candidate for visual ammonic or hydrogen chloride gas sensing. The results provide an environmental responsible and practicable synthetic approach to expanding the scope of ultralong organic phosphorescent materials as well as their applications. 相似文献
46.
We have developed a convenient method for the efficient monofluorination via the electrophilic fluorocyclization reaction of 2,3-allenoic acids with Selectfluor in MeCN in the presence of 10 equiv of H2O or even in pure water to afford beta-fluorobutenolides in moderate to high yields. 相似文献
47.
Haggenmueller R Rahatekar SS Fagan JA Chun J Becker ML Naik RR Krauss T Carlson L Kadla JF Trulove PC Fox DF Delong HC Fang Z Kelley SO Gilman JW 《Langmuir : the ACS journal of surfaces and colloids》2008,24(9):5070-5078
The use of single wall carbon nanotubes (SWCNTs) in current and future applications depends on the ability to process SWCNTs in a solvent to yield high-quality dispersions characterized by individual SWCNTs and possessing a minimum of SWCNT bundles. Many approaches for the dispersion of SWCNTs have been reported. However, there is no general assessment which compares the relative quality and dispersion efficiency of the respective methods. Herein we report a quantitative comparison of the relative ability of "wrapping polymers" including oligonucleotides, peptides, lignin, chitosan, and cellulose and surfactants such as cholates, ionic liquids, and organosulfates to disperse SWCNTs in water. Optical absorption and fluorescence spectroscopy provide quantitative characterization (amount of SWCNTs that can be suspended by a given surfactant and its ability to debundle SWCNTs) of these suspensions. Sodium deoxy cholate (SDOCO), oligonucleotides (GT)(15), (GT)(10), (AC)(15), (AC)(10), C(10-30), and carboxymethylcellulose (CBMC-250K) exhibited the highest quality suspensions of the various systems studied in this work. The information presented here provides a good framework for further study of SWCNT purification and applications. 相似文献
48.
49.
50.
Fluorescence enhancements of benzene-cored luminophors by restricted intramolecular rotations: AIE and AIEE effects 总被引:3,自引:0,他引:3
Zeng Q Li Z Dong Y Di C Qin A Hong Y Ji L Zhu Z Jim CK Yu G Li Q Li Z Liu Y Qin J Tang BZ 《Chemical communications (Cambridge, England)》2007,(1):70-72
Photoluminescence of simple arylbenzenes with ready synthetic accessibility is enhanced by two orders of magnitude through aggregate formation; viscosity and temperature effects indicate that the emission enhancement is due to the restriction of their intramolecular rotations in the solid state. 相似文献