全文获取类型
收费全文 | 514篇 |
免费 | 72篇 |
国内免费 | 65篇 |
专业分类
化学 | 269篇 |
晶体学 | 4篇 |
力学 | 11篇 |
综合类 | 3篇 |
数学 | 53篇 |
物理学 | 151篇 |
无线电 | 160篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 16篇 |
2021年 | 17篇 |
2020年 | 18篇 |
2019年 | 27篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 19篇 |
2014年 | 32篇 |
2013年 | 26篇 |
2012年 | 43篇 |
2011年 | 40篇 |
2010年 | 28篇 |
2009年 | 30篇 |
2008年 | 34篇 |
2007年 | 22篇 |
2006年 | 29篇 |
2005年 | 38篇 |
2004年 | 17篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 16篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 4篇 |
1985年 | 1篇 |
排序方式: 共有651条查询结果,搜索用时 15 毫秒
141.
给出相对于外磁场不同取向的五氧硼酸钾(KB5)单晶的1HNMR室温谱.发现当外磁场在晶体的bc平面里,1HNMR谱最多有6个峰.而在ah或ac平面里,最多仅有5个峰.用计算机拟合NMR谱表明:在五氧硼酸钾中,氢原子是以羟基和水分子集团的形式存在.在羟基集团中,O—H的距离为0.1005±0.001nm和0.1054±0.001nm;而在水分子中,O—H的距离为0.0983±0.001nm和0.0968±0.001nm,并且H—O—H夹角为108°±1°.这些显示本文的数据与中子衍射结果相近,而X射线衍射所得到的质子位置的数据则与我们的结果相距甚远. 相似文献
142.
本文阐述的是,铜及其合金精密零件氢气保护扩散钎接焊工艺问题。这是一种界于TLP扩散焊和钎焊工艺之间的一种新型先进工艺,兼有两者之长。文中对扩散元素,共晶相系的选取、筛选和扩散——共晶反应过程机理分析作了重点论述,并对其接头组织,性能和焊接质量及本工艺的应用情况作了简要介绍。 相似文献
143.
硒对慢性活动性肝炎的影响 总被引:2,自引:0,他引:2
50例慢性活动性肝炎(慢活肝)随机分为治疗组和对照组。25例治疗组接受12周补硒治疗,结果显示,治疗组与对照组比较,血清ALT显著下降,谷胱甘肽过氧化物酶活力明显升高,提示补硒能防治自由基引起的肝损伤,防止慢性肝病的发展。 相似文献
144.
Zhe Jiang Shengbao Diao Ren Li Wei Zhou Jinfeng Sun Yi Zhou 《Natural product research》2018,32(9):1017-1021
A new 1,4-napthoquinone derivative, namely (S)-(-)-3-(8-hydroxy-1,4-dioxo-1,4-dihydro-naphthalen-2-yl)-3-(4-hydroxy-3-methoxyphenyl)-propionic acid methyl ester (1), was isolated from the roots of Juglans mandshurica Maxim. The structure was identified based on HR-ESI-MS, 1D and 2D NMR spectroscopic methods. 相似文献
145.
Chao-Ying Fan Dan Xie Xiao-Hua Zhang Wan-Yue Diao Ru Jiang Xing-Long Wu 《Advanced functional materials》2021,31(32):2102158
3D carbon hosts can enable low-stress Li metal anodes (LMAs) with improved structural and interfacial stability. However, the uneven Li+ flux and large concentration polarization, resulting from intrinsically poor Li affinity and limited porosity of carbon scaffolds, make the precise control of Li plating/stripping still one the key challenges facing advanced LMAs. Here it is demonstrated that a lightweight carbon scaffold, featuring parallel-aligned porous fibers, can work well for homogeneous Li+ flux distribution and reduced concentration gradient to form a stable solid electrolyte interphase, and then synergistically guide smooth Li nucleation/growth even at low temperatures. As a result, the obtained LMAs delivers a high areal capacity up to 15 mAh cm−2, ultralong lifespan (4800 cycles at 4 mA cm−2) with very low voltage hysteresis of ≈21 mV, a high practically available specific capacity of 863.9 mAh g−1 after 1000 cycles, and a long-term stable behavior at low-temperature operation. As coupling with the commercial LiNi1/3Co1/3Mn1/3O2 cathodes and common carbonate-based electrolyte, the corresponding practical cells also possess an ultralong lifespan and outstanding low-temperature functionality. This study not only presents an advanced carbon host candidate but also sheds new light on crucial design principles of carbon scaffolds for practically feasible rechargeable metal batteries. 相似文献
146.
Yingjie Tang Hao Zhou Xiupeng Sun Ninghua Diao Jianbo Wang Baosen Zhang Cheng Qin Erjun Liang Yanchao Mao 《Advanced functional materials》2020,30(5)
An intelligent human–machine interface (HMI) is a crucial medium for exchanging information between people and electronics. As one of the most important HMI devices, touch screen sensors are widely applied in personal electronics in daily life. However, as the most commonly used touch screen sensor, capacitive sensors can only detect limited kinds of gestures such as touching and sliding. Here, a triboelectric touch‐free screen sensor (TSS) is reported for recognizing diverse gestures in a noncontact operating mode by utilizing the charges naturally carried on the human body. Compared with conventional capacitive sensors, the TSS is capable of detecting various gestures such as the drop and lift of finger with different speeds, making a fist, opening palm, and flipping palm with different directions. Based on the TSS, an intelligent noncontact screen control system is further developed, which is used to unlock the smartphone interface by the noncontact operating mode. This research for the first time proposes the concept that taking the human body itself to participate in triboelectric self‐powered noncontact sensing and provides a touch‐free design concept to develop the next generation of screen sensors. It can alter the usual way that people operating their personal electronics. 相似文献
147.
Ziqian Wang Xuefei Bai Shengxi Diao Fujiang Lin 《Analog Integrated Circuits and Signal Processing》2017,91(2):277-292
Physical layer security has emerged as a promising approach to strengthen security of wireless communications. Particularly, extracting secret keys from channel randomness has attracted an increasing interest from both academic and industrial research groups. In this paper, we present a complete implantation of a secret key generation (SKG) protocol which is compliant with existing widespread Radio Access Technologies. This protocol performs the quantization of the channel state information, then information reconciliation and privacy amplification. We also propose an innovative algorithm to reduce the correlation between quantized channel coefficients that significantly improves the reliability and the resilience of the complete SKG scheme. Finally we assess the performance of our protocol by evaluating the quality of secret keys generated in various propagation environments from real single sense LTE signals, and real single and dual sense WiFi signals. 相似文献
148.
Metallic nanoparticles bridge the length scale between atoms and crystals, exhibiting mesoscopic properties unique to their size. Thus, they have generated much interest for their potential applications as chemical or biological sensors and particularly as waveguides for light in nanoscale structures. [Y. W. C. Cao, R. C. Jin, and C. A. Mirkin, Science 297, 1536 (2002); H. J. Lezec et al., Science 297, 820 (2002); S. A. Maier, P. G. Kik, and H. A. Atwater, Appl. Phys. Lett. 81, 1714 (2002); J. M. Oliva and S. K. Gray, Chem. Phys. Lett. 379, 325 (2003)]. One important direction of research into the properties of individual metal nanoparticles involves the controlled variation of their geometry, which can yield new and tunable optical properties that simple spherical configurations do not possess. [T. S. Ahmadi, Z. L. Wang, T. C. Green, A. Henglein, and M. A. Ei-Sayed, Science 272, 1924 (1996)]. A prime example of this is the core-shell nanostructure that has a central material surrounded by differing cladding layer. 相似文献
149.
150.
Well-aligned ZnO nanorod arrays were prepared on substrates by hydrothermal growth under different conditions. The effect of preparing conditions on the deposition of ZnO nanorods was systematically studied by scanning electron microscopy, X-ray diffraction and photoluminescence spectroscopy. It is demonstrated that the growth conditions such as pre-treatment of the substrates, growth temperature, deposition time and the concentration of the precursors have great influence on the morphology and the alignment ordering of ZnO nanorod arrays. Pre-treatment of substrates, including dispersion of ZnO nanoparticles and subsequent annealing, not only plays a main role in governing the rod diameter, but also greatly improves the rod orientation. Although the rod diameter and its distribution are mainly determined by pre-coated ZnO nanoparticles, they can also be monitored to some extent by changing the concentration of the precursors. The growth temperature has a little influence on the orientation of nanorods but it has great impact on their aspect ratio and the photoluminescent property. Kinetic studies show that the growth of ZnO nanorods contains two distinct step: a fast steps within the first hour, in which the nanorods tend to be short and wide, and a slow step, in which long rods with high aspect ratio are obtained. 相似文献