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991.
992.
An Extension of the Effective Index Method to Analyze Leakage Losses in Rib Type Waveguides 总被引:1,自引:0,他引:1
Ben-Hur V. Borges Murilo A. Romero Amilcar C. Cesar 《International Journal of Infrared and Millimeter Waves》1999,20(10):1783-1793
An extension of the effective index method is proposed as a tool to investigate leakage losses in two-dimensional waveguides. The above method, referred to as the Extended Effective Index Method (EEIM), utilizes the Transfer Matrix Technique (TMT) for the calculation of the complex propagation constants. The results show that the EEIM can be applied to conventional rib leaky waveguides as well as to rib ARROW leaky waveguides. The results for rib ARROW waveguides show excellent agreement when compared to those obtained with Finite Element Method. 相似文献
993.
Y.W. Duan L. Shi M. Feng X. Zhu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(2):191-197
The hyperspherical-coordinate approach is employed to a one-dimensional model of three ions in a Paul trap. It is shown that
the eigen wave functions have well-defined nodal structure indicating a near separability in the hyperspherical coordinates, then two approximate good quantum numbers
are introduced to classify the eigenstates. Three important classical periodic motions, including the breathing motion and
the (distorted-)symmetric or anti-symmetric stretching motion, are found to dominate the wave function distribution.
Received: 10 February 1999 / Received in final form: 25 March 1999 相似文献
994.
《中国物理 B》2021,30(6):64214-064214
A tunable selective emitter with hollow zigzag SiO_2 metamaterials, which are deposited on Si_3 N_4 and Ag film, is proposed and numerically investigated for achieving excellent radiative cooling effects. The average emissivity reaches a high value of 98.7% in the atmospheric window and possesses a high reflectivity of 92.0% in the solar spectrum. To reveal the enhanced absorptivity, the confined electric field distribution is investigated, and it can be well explained by moth eye effects. Moreover, tunable emissivity can also be initiated with different incident angles and it stays above 83% when the incident angle is less than 80°, embodying the excellent cooling performance in the atmospheric transparency window.Its net cooling power achieves 100.6 W·m~(-2), with a temperature drop of 13°, and the cooling behavior can persist in the presence of non-radiative heat exchange conditions. Therefore, high and tunable selective emitters based on our designed structure could provide a new route to realizing high-performance radiative cooling. This work is also of great significance for saving energy and environmental protection. 相似文献
995.
受二次流的影响,气膜冷却端壁表面存在大量难冷区域。紧凑型层板结构可以实现端壁的双侧冷却,从而缩小难冷面积。本文通过改变气膜孔布局,设计了一种可以有效改善局部难冷区域的层板冷却端壁。在主冷流温比1.5下,测量了端壁表面的温降特性和综合冷却效率分布,通过与均匀气膜布局的层板端壁相比较,发现:采用改进后的层板结构,可以显著降低端壁表面温度,缩小难冷区域面积,获得更均匀的冷却效果。且压力侧根部区域与吸力面前缘区域冷却效果增幅尤甚。另外,此层板的改进优势随着质量流量比的增加变得更明显。 相似文献
996.
Thermal management has become a critical issue owing to the increasing need for various devices including heat dissipation and adsorption. Recently, the rapid growth of scientific reports is seen to improve thermal management efficiency by developing materials with high transfer coefficient and surface improvement to enhance heat transfer rate. Inspired by nature, constructing superlyophilic interfaces has been proved to be an effective way for thermal management and applied in industry and daily life. Herein, state-of-the-art developments of superlyophilic interfaces assisted thermal management are reported mainly from four perspectives around boiling, evaporation, radiation, and condensation. In particular, we discussed the unique role of superlyophilic interfaces during the heat transfer process, such as increasing bubble detachment rate, superspreading assisted efficient evaporation, directional liquid transfer in textiles during radiative cooling, and so forth. Finally, challenges of thermal management assisted by superlyophilic interfaces toward future applications are presented. 相似文献
997.
ZhongHui Yuan DongYang Wang ChengHua Bai HaoTian Yang HongFu Wang AiDong Zhu 《中国科学:物理学 力学 天文学(英文版)》2020,(3):25-32
We propose a ground-state cooling scheme for a nanomechanical oscillator(NMO)that interacts with an optical cavity via radiation pressure at one side and with a superconducting microwave cavity via a capacitor at the other side.By driving these two cavities on their respective red sidebands with extra laser and microwave fields,the NMO’s dual cooling channel is created through electro-optomechanical cooperation.Differing from the conventional optomechanical system with a single optical cavity wherein ground-state cooling is limited in the resolved sideband,the proposed scheme allows the optical cavity to function in an unresolved sideband regime under the cooperation of a microwave cavity with a high quality factor,or vice versa.In a weak coupling regime we demonstrate that the NMO can be cooled to near its ground-state from a finite temperature with a cooling rate that is significantly faster than that of the single-cavity optomechanical system.The heating process can be completely suppressed by the cooperation of the dual cooling channel by appropriately selecting the system’s parameters.With a decreasing thermal phonon number,the numerical results of final mechanical occupancy gradually approach the analytical cooling limit. 相似文献
998.
许多工程(如采矿、隧道掘进、地热开采等)都涉及到岩石损伤及破碎问题.传统的岩石损伤破碎技术,如爆破法、水射流法、机械掘进法等均面临着一系列问题,利用岩石的热损伤性质辅助机械破岩有望实现安全、高效破岩的目的.大理岩是一种典型的硬岩,常见许多工程之中,因此本文以大理岩为研究对象,首先将均质性较好的大理岩试样加热至不同温度(20~1000 °C)后放入液氮中进行急速冷处理,然后对其进行了系列的物理力学性质测试.试验结果表明:处理后密度、纵波波速、抗拉强度、单轴抗压强度(UCS)和弹性模量整体上都随温度的上升而下降;当加热温度在100 °C之前,大理岩表现出一定的热硬化现象,即随着温度升高,其UCS、纵波波速以及弹性变形模量均增大;UCS变化的阈值温度为400 °C左右,一旦温度超过400 °C,UCS迅速下降,其速率达到了9 MPa/100 °C,当温度超过500 °C弹性模量迅速下降,其速率达到7.00 GPa/100 °C,表明岩样抵抗变形能力减弱.整体上,热加载降低了大理岩的脆性,使其在单轴作用下的破坏模式由脆性破坏逐渐转化为弹塑性破坏. 相似文献
999.
Origin,characteristics, and suppression of residual nitrogen in MPCVD diamond growth reactor 下载免费PDF全文
Unintentional nitrogen incorporation has been observed in a set of microwave plasma chemical vapor deposition (MPCVD)-grown samples. No abnormality has been detected on the apparatus especially the base pressure and feeding gas purity. By a comprehensive investigation including the analysis of the plasma composition, we found that a minor leakage of the system could be significantly magnified by the thermal effect, resulting in a considerable residual nitrogen in the diamond material. Moreover, the doping mechanism of leaked air is different to pure nitrogen doping. The dosage of several ppm of pure nitrogen can lead to efficient nitrogen incorporation in diamond, while at least thousands ppm of leaked air is required for detecting obvious residual nitrogen. The difference of the dosage has been ascribed to the suppression effect of oxygen that consumes nitrogen. As the unintentional impurity is basically detrimental to the controllable fabrication of diamond for electronic application, we have provided an effective way to suppress the residual nitrogen in a slightly leaked system by modifying the susceptor geometry. This study indicates that even if a normal base pressure can be reached, the nitrogen residing in the chamber can be "activated" by the thermal effect and thus be incorporated in diamond material grown by a MPCVD reactor. 相似文献
1000.
Fangping Zhuo Huimin Qiao Jiaming Zhu Shuize Wang Yang Bai Xinping Mao Hong-Hui Wu 《中国化学快报》2021,32(7):2097-2107
As a close relative of ferroelectricity,antiferroelectricity has received a recent resurgence of interest driven by technological aspirations in energy-efficient applications,such as energy storage capacitors,solid-state cooling devices,explosive energy conversion,and displacement transducers.Though prolonged efforts in this area have led to certain progress and the discovery of more than 100 antiferroelectric materials over the last 70 years,some scientific and technological issues remain unresolved.Herein,we provide perspectives on the development of antiferroelectrics for energy storage and conversion applications,as well as a comprehensive understanding of the structural origin of antiferroelectricity and field-induced phase transitions,followed by design strategies for new lead-free antiferroelectrics.We also envision unprecedented challenges in the development of promising antiferroelectric materials that bridge materials design and real applications.Future research in these directions will open up new possibilities in resolving the mystery of antiferroelectricity,provide opportunities for comprehending structure-property correlation and developing antiferroelectric/ferroelectric theories,and suggest an approach to the manipulation of phase transitions for real-world applications. 相似文献