全文获取类型
收费全文 | 4118篇 |
免费 | 534篇 |
国内免费 | 378篇 |
专业分类
化学 | 981篇 |
晶体学 | 31篇 |
力学 | 132篇 |
综合类 | 127篇 |
数学 | 2519篇 |
物理学 | 1240篇 |
出版年
2024年 | 6篇 |
2023年 | 33篇 |
2022年 | 82篇 |
2021年 | 109篇 |
2020年 | 120篇 |
2019年 | 116篇 |
2018年 | 108篇 |
2017年 | 131篇 |
2016年 | 152篇 |
2015年 | 102篇 |
2014年 | 224篇 |
2013年 | 436篇 |
2012年 | 208篇 |
2011年 | 266篇 |
2010年 | 230篇 |
2009年 | 262篇 |
2008年 | 276篇 |
2007年 | 256篇 |
2006年 | 234篇 |
2005年 | 194篇 |
2004年 | 200篇 |
2003年 | 191篇 |
2002年 | 176篇 |
2001年 | 131篇 |
2000年 | 101篇 |
1999年 | 118篇 |
1998年 | 100篇 |
1997年 | 90篇 |
1996年 | 65篇 |
1995年 | 43篇 |
1994年 | 47篇 |
1993年 | 24篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 27篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有5030条查询结果,搜索用时 15 毫秒
901.
Transport properties and anomalous fatigue effect of Ag/Bi0.9La0.lFeO3/La0.7Sr0.3MnO3 heterostructures 下载免费PDF全文
The transport properties and fatigue effect of Ag/Bi0.9La0.lFeO3/La0.7Sr0.3MnO3 heterostructures are described. By examining the I-V curves, an anomalous fatigue effect was found and its influences on resistive states were studied. I-V curves combined with C-f spectra were used to directly analyze the transport properties and fatigue effect. Compared to the first I-V cycle state, this structure shows more than one order increase of resistance after 100 cycles of "I-V curve training". The redistribution of oxygen vacancies in the depletion layer of Ag/Bi0.9La0.lFeO3 is believed to be responsible for the different resistance mechanisms and tenfold magnitude drop in resistance. The resistive switching is understood to be caused by electric field-induced carrier trapping and detrapping, which changes the depletion layer thickness at the Ag/Bi0.9La0.lFeO3 interface. 相似文献
902.
Exploring new synaptic electronic devices that combine computing and memory is a promising strategy that fundamentally approaches intelligent machines. In this study, the multilevel resistive switching and synaptic behaviors of a MnO-based device is studied. The device is composed of Al/MnO/Ni sandwich structure, has stable resistance switching characteristics, has continuous nonvolatile memory state, can be used as electrically programmable and erasable analog memory. The gradual conductance modulation is realized by changing the compliance current and the maximum scanning voltage. The Al/MnO/Ni devices successfully mimic the basic functions of synapses, including the paired-pulse facilitation, spike-rate-dependent plasticity, excitatory postsynaptic current, short-term plasticity, long-term plasticity, and sike-timing-dependent plasticity. 相似文献
903.
A three-dimensional(3D)silicon-carbide(SiC)trench metal-oxide-semiconductor field-effect transistor(MOSFET)with a heterojunction diode(HJD-TMOS)is proposed and studied in this work.The SiC MOSFET is characterized by an HJD which is partially embedded on one side of the gate.When the device is in the turn-on state,the body parasitic diode can be effectively controlled by the embedded HJD,the switching loss thus decreases for the device.Moreover,a highly-doped P+layer is encircled the gate oxide on the same side as the HJD and under the gate oxide,which is used to lighten the electric field concentration and improve the reliability of gate oxide layer.Physical mechanism for the HJD-TMOS is analyzed.Comparing with the conventional device with the same level of on-resistance,the breakdown voltage of the HJD-TMOS is improved by 23.4%,and the miller charge and the switching loss decrease by 43.2%and 48.6%,respectively. 相似文献
904.
Current-induced multilevel magnetization switching in ferrimagnetic spintronic devices is highly pursued for the application in neuromorphic computing. In this work, we demonstrate the switching plasticity in Co/Gd ferrimagnetic multilayers where the binary states magnetization switching induced by spin-orbit toque can be tuned into a multistate one as decreasing the domain nucleation barrier. Therefore, the switching plasticity can be tuned by the perpendicular magnetic anisotropy of the multilayers and the in-plane magnetic field. Moreover, we used the switching plasticity of Co/Gd multilayers for demonstrating spike timing-dependent plasticity and sigmoid-like activation behavior. This work gives useful guidance to design multilevel spintronic devices which could be applied in high-performance neuromorphic computing. 相似文献
905.
In view of the distinctive characteristics of satellite communication, the physical random access signals used in the terrestrial mobile communication system have to be modified or redesigned for the satellite communication system. In this paper, we boost the random access signal energy by repeating the short Zadoff–Chu (ZC) sequence based preamble signal used in the terrestrial system. Different long ZC sequences are used to scramble this cascaded sequence to distinguish different random access signals for multiple random access user equipments. For correlation performance optimization, properties of the roots for both the short and long ZC sequences are mathematically analyzed and derived. Finally, we illustrate how to construct a root set for these different long ZC sequences based on the obtained propositions in a practical way. This analytical framework provides a useful insight into ZC sequence-based random access signal design and performance analysis in mobile satellite communication systems. 相似文献
906.
Shanwu Ke Li Jiang Yifan Zhao Yongyue Xiao Bei Jiang Gong Cheng Facai Wu Guangsen Cao Zehui Peng Min Zhu Cong Ye 《Frontiers of Physics》2022,17(5):53508
Artificial synapse is one of the potential electronics for constructing neural network hardware. In this work, Pt/LiSiOx/TiN analog artificial synapse memristor is designed and investigated. With the increase of compliance current (C. C.) under 0.6 mA, 1 mA, and 3 mA, the current in the high resistance state (HRS) presents an increasing variation, which indicates lithium ions participates in the operation process for Pt/LiSiOx/TiN memristor. Moreover, depending on the movement of lithium ions in the functional layer, the memristor illustrates excellent conduction modulation property, so the long-term potentiation (LTP) or depression (LTD) and paired-pulse facilitation (PPF) synaptic functions are successfully achieved. The neural network simulation for pattern recognition is proposed with the recognition accuracy of 91.4%. These findings suggest the potential application of the LiSiOx memristor in the neuromorphic computing. 相似文献
907.
908.
Yoon J Bian P Kim J McCarthy TJ Hayward RC 《Angewandte Chemie (International ed. in English)》2012,51(29):7146-7149
Visible light induces switching of surface chemical patterns based on hybrid gels of thermally responsive poly(N-isopropyl acrylamide) copolymer networks containing iron oxide nanoparticles. The swelling of these hybrid gels is reduced upon illumination (see picture), allowing controlled unfolding of creased features formed owing to an elastic surface instability. 相似文献
909.
建立了大体积进样后的在线中和富集及在线标准加入离子色谱法,实现了对大气碱性吸收液中痕量氯离子、亚硝酸根、硝酸根、硫酸根的直接测定。比较了不同阀切换时间窗及在线中和柱的选择,确定了最佳的实验条件。利用戴安公司“谱睿”在线中和技术,通过Inguard H在线中和柱和CRD 200在线二氧化碳去除装置的共同作用,有效地去除了碱性吸收液中的OH~和CO2~3,使测定干扰降低到最小;通过大体积进样和在线富集,改进了样品的检出限,Cl~, NO~2, NO~3和SO2~4的检出限分别为17.5、171、34.7和42.4 ng/L;在线标准加入解决了痕量阴离子标准溶液的配制难题及NO~2低回收率对检测结果的影响。本方法实现了自动化分析,结果准确,重复性好,检测效率高,可用于常规离子色谱条件下无法测定的强碱性基体样品中痕量阴离子的准确测定。 相似文献
910.
van Werven JR Marsman HA Nederveen AJ ten Kate FJ van Gulik TM Stoker J 《Magnetic resonance imaging》2012,30(1):112-121