全文获取类型
收费全文 | 1135篇 |
免费 | 107篇 |
国内免费 | 151篇 |
专业分类
化学 | 659篇 |
晶体学 | 16篇 |
力学 | 257篇 |
综合类 | 16篇 |
数学 | 122篇 |
物理学 | 323篇 |
出版年
2023年 | 13篇 |
2022年 | 33篇 |
2021年 | 38篇 |
2020年 | 29篇 |
2019年 | 26篇 |
2018年 | 35篇 |
2017年 | 48篇 |
2016年 | 42篇 |
2015年 | 36篇 |
2014年 | 53篇 |
2013年 | 82篇 |
2012年 | 72篇 |
2011年 | 68篇 |
2010年 | 52篇 |
2009年 | 57篇 |
2008年 | 57篇 |
2007年 | 88篇 |
2006年 | 75篇 |
2005年 | 74篇 |
2004年 | 65篇 |
2003年 | 58篇 |
2002年 | 36篇 |
2001年 | 32篇 |
2000年 | 28篇 |
1999年 | 27篇 |
1998年 | 28篇 |
1997年 | 24篇 |
1996年 | 11篇 |
1995年 | 18篇 |
1994年 | 23篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1393条查询结果,搜索用时 15 毫秒
51.
计算了球形均匀D-3He先进燃料靶惯性约束聚变(ICF)的燃耗和增益。讨论了这种堆系统的能量平
衡。设计了一种新型的由毛细管阵列组成具有抗辐射损伤、可自动更新的液态金属锂自由表面多孔湿壁,用它取
出聚变能。同时与D-T热核燃料靶系统的燃耗和增益及它们不同的堆工程特性作了比较。 相似文献
52.
量子点器件技术广泛应用于量子计算和光电器件上.成核位置的均匀性、有序性和尺寸一致性,可以有效提高光电器件性能.为了实现阵列量子点的可控性,本文采用湿法刻蚀制备图形化衬底,理论上解释了铟原子在图形化衬底上成核现象,产生有序的量子点分布特征,发现图形衬底的缺陷诱导在平台边缘和沟壑边缘成核,形成较大的量子点.在Stranski-Krastanow模式下图形衬底制备多周期量子点,发现多周期生长可以弱化台阶结构对量子点分布的限制作用. 相似文献
53.
利用基于线性黏聚接触模型的离散元法对不同颗粒系统的堆积过程进行了数值模拟研究,分析了颗粒形状和湿颗粒间液桥力对颗粒堆积形态的影响机理,获得了球形和块状湿颗粒堆基底表面所受的法向力以及堆中颗粒间的法向力和切向力"中心凹陷"式的分布规律,讨论了颗粒形状和黏聚能量密度对基底表面作用力和颗粒间作用力的影响.研究结果表明,颗粒形状和液桥力对颗粒堆的堆积形态具有显著的影响.堆积角随着黏聚能量密度的增加而增大,并且相同条件下的块状颗粒堆积角大于球形颗粒.颗粒形状和黏聚能量密度对基底表面所受作用力和堆中颗粒间的作用力变化及最大幅值均有影响作用.当黏聚能量密度值逐渐增大时,颗粒堆的作用力最大幅值均逐渐增大,并且块状颗粒堆的作用力最大幅值大于球形颗粒堆.当黏聚能量密度值过大时,颗粒堆力学特性更加复杂,液桥力对颗粒堆积特性的影响作用大于颗粒形状的影响. 相似文献
54.
Non-axisymmetrical vibration of elastic circular plate on layered transversely isotropic saturated ground 总被引:1,自引:0,他引:1
黄小岗 《应用数学和力学(英文版)》2007,28(10):1383-1396
The non-axisymmetrical vibration of elastic circular plate resting on a layered transversely isotropic saturated ground was studied.First,the 3-d dynamic equations in cylindrical coordinate for transversely isotropic saturated soils were transformed into a group of governing differential equations with 1-order by the technique of Fourier ex- panding with respect to azimuth,and the state equation is established by Hankel integral transform method,furthermore the transfer matrixes within layered media are derived based on the solutions of the state equation.Secondly,by the transfer matrixes,the general solutions of dynamic response for layered transversely isotropic saturated ground excited by an arbitrary harmonic force were established under the boundary conditions, drainage conditions on the surface of.ground as well as the contact conditions.Thirdly, the problem was led to a pair of dual integral equations describing the mixed boundary- value problem which can be reduced to the Fredholm integral equations of the second kind solved by numerical procedure easily.At the end of this paper,a numerical result concerning vertical and radical displacements both the surface of saturated ground and plate is evaluated. 相似文献
55.
Cu/ZrO2催化剂上乙醇水蒸气重整反应的研究Ⅱ反应条件的影响 总被引:2,自引:1,他引:2
采用沉淀法或醇凝胶法、浸渍法制备Cu/ZrO2催化剂,在常压微型固定床石英管反应器上进行乙醇水蒸气重整反应,采用程序升温还原(TPR)技术表征催化剂的还原特性。考察了催化剂还原温度、反应温度、水醇比、空速等对反应的影响以及催化剂的稳定性。结果表明,在300℃~500℃,随反应温度升高,乙醇转化率增大,H2选择性下降。不同还原温度对转化率的影响不是很大,对于H2选择性,300℃、400℃还原的催化剂优于500℃还原的催化剂。高水醇比有利于提高转化率和H2选择性。随空速增大,转化率和H2选择性呈现下降的趋势。8%Cu/ZrO2催化剂在400℃或450℃反应22h显示出良好的稳定性。 相似文献
56.
在303,514和543K下用0.8%H2O-99.2%H2对Ni2P/SiO2催化剂进行了水蒸气处理,利用N2吸附-脱附、X射线衍射、电感耦合等离子体发射光谱、H2程序升温脱附及原位漫反射红外光谱等技术对水蒸气处理前后Ni2P/SiO2催化剂的结构进行了表征,并在常压固定床反应器上评价了其催化氯苯加氢脱氯活性.结果表明,经水蒸气处理后,Ni2P/SiO2催化剂的物相及元素组成、Ni2P晶粒大小、比表面积及孔结构没有明显改变.与未处理和303K处理的Ni2P/SiO2催化剂不同,513和543K处理的催化剂表面暴露的Ni中心数量减少,表面P-OH基团数量增多.在513K,氯苯空速3.75ml/ 相似文献
57.
Dr. Haoxuan Li Haifei Wen Dr. Zhijun Zhang Dr. Nan Song Prof. Ryan T. K. Kwok Prof. Jacky W. Y. Lam Prof. Lei Wang Prof. Dong Wang Prof. Ben Zhong Tang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20551-20555
Using reverse thinking of the aggregation-induced emission (AIE) principle, we demonstrate an ingenious and universal protocol for amplifying molecular motions to boost photothermal efficiency of fibers. Core–shell nanofibers having the olive oil solution of AIE-active molecules as the core surrounded by PVDF-HFP shell were constructed by coaxial electrospinning. The molecularly dissolved state of AIE-active molecules allows them to freely rotate and/or vibrate in nanofibers upon photoexcitation and thus significantly elevates the proportion of non-radiative energy dissipation, affording impressive heat-generating efficiency. Photothermal evaluation shows that the core–shell nanofibers with excellent durability can reach up to 22.36 % of photothermal conversion efficiency, which is 26-fold as the non-core–shell counterpart. Such a core–shell fiber can be used for photothermal textiles and solar steam generation induced by natural sunlight with green and carbon-zero emission. 相似文献
58.
In order to investigate the influence of steam ingestion on the aerodynamic stability of a two-stage low-speed axial-flow compressor, multiphase flow numerical simulation and experiment were carried out. The total pressure ratio and stall margin of the compressor was decreased under steam ingestion. When the compressor worked at 40% and 53% of the nominal speed, the stall margin decreased, respectively, by 1.5% and 6.3%. The ingested steam reduced the inlet Mach number and increased the thickness of the boundary layer on the suction surface of the blade. The low-speed region around the trailing edge of the blade was increased, and the flow separation region of the boundary layer on the suction surface of the blade was expanded; thus, the compressor was more likely to enter the stall state. The higher the rotational speed, the more significant the negative influence of steam ingestion on the compressor stall margin. The entropy and temperature of air were increased by steam. The heat transfer between steam and air was continuous in compressor passages. The entropy of the air in the later stage was higher than that in the first stage; consequently, the flow loss in the second stage was more serious. Under the combined action of steam ingestion and counter-rotating bulk swirl distortion, the compressor stability margin loss was more obvious. When the rotor speed was 40% and 53% of the nominal speed, the stall margin decreased by 6.3% and 12.64%, respectively. 相似文献
59.
We deal with periodic groups saturated with dihedral groups. In particular, it is proved that periodic groups of bounded period, and also periodic Shunkov groups, saturated with dihedral groups, are locally finite.Supported by RFBR grant No. 03-01-00356 and by the Krasnoyarsk Science Foundation, project 11F0202C.Translated from Algebra i Logika, Vol. 44, No. 1, pp. 114–125, January–February, 2005. 相似文献
60.
N. B. Morozova P. P. Semyannikov S. V. Sysoev V. M. Grankin I. K. Igumenov 《Journal of Thermal Analysis and Calorimetry》2000,60(2):489-495
The temperature dependency of the saturated vapor pressure of Ir(acac)3 has been measured by the method of calibrated volume (MCV), the Knudsen method, the flow transpiration method, and the membrane
method. The thermodynamic parameters of phase transition of a crystal to gas were calculated using each of these methods,
and the following values of ΔH
T
0 (kJ mol−1) and ΔS
T
0 (J mol−1K−1), respectively, were obtained: MCV: 101.59, 156.70; Knudsen: 130.54, 224.40; Flow transpiration: 129.34, 212.23; Membrane:
95.45, 149.44
Coprocessing of obtaining data (MCV, flow transportation method and Knudsen method) at temperature ranges 110−200°C as also
conducted:ΔH
T
0 =127.9±2.1 (kJ mol−1 ); ΔS
T
0 =215.2±5.0 (J mol−1 K−1 ).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献