全文获取类型
收费全文 | 15498篇 |
免费 | 2512篇 |
国内免费 | 1699篇 |
专业分类
化学 | 11496篇 |
晶体学 | 196篇 |
力学 | 830篇 |
综合类 | 72篇 |
数学 | 1580篇 |
物理学 | 5535篇 |
出版年
2024年 | 39篇 |
2023年 | 314篇 |
2022年 | 420篇 |
2021年 | 516篇 |
2020年 | 632篇 |
2019年 | 630篇 |
2018年 | 563篇 |
2017年 | 496篇 |
2016年 | 721篇 |
2015年 | 749篇 |
2014年 | 945篇 |
2013年 | 1187篇 |
2012年 | 1385篇 |
2011年 | 1493篇 |
2010年 | 1067篇 |
2009年 | 919篇 |
2008年 | 1054篇 |
2007年 | 955篇 |
2006年 | 841篇 |
2005年 | 729篇 |
2004年 | 546篇 |
2003年 | 457篇 |
2002年 | 426篇 |
2001年 | 309篇 |
2000年 | 305篇 |
1999年 | 256篇 |
1998年 | 226篇 |
1997年 | 199篇 |
1996年 | 185篇 |
1995年 | 145篇 |
1994年 | 188篇 |
1993年 | 130篇 |
1992年 | 127篇 |
1991年 | 98篇 |
1990年 | 93篇 |
1989年 | 85篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 35篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 17篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1967年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
使用叠栅层析技术测量超音速风洞中的非对称复杂密度场 总被引:1,自引:1,他引:0
使用叠栅层析技术解决超音速风洞中复杂密度场的测量难题。应用高灵敏度叠栅偏折仪和间隔角度旋转模型的方法获取超音速风洞中流场的多方向叠栅条纹图。层析计算中使用一种新的偏折角修正迭代的叠栅层析算法,该方法可以实现对有限角采样和包含遮挡物的非完全数据重建,迭代过程中结合内边界平滑滤波提高重建精度。实验中获取了马赫数为2.52的超音速风洞中9幅不同采样角的条纹图,经过50次迭代计算后重建出膨胀波区非对称密度场的截面分布,并对测量结果和误差进行了分析和讨论。使用计算流体力学技术对该密度场进行建模和计算,验证了叠栅层析重建结果的正确性,证实了该技术在测量复杂流场领域的重要价值。 相似文献
954.
955.
Can Liao Wei Wang Junling Wang Longfei Han Shuilai Qiu Lei Song Zhou Gui Yongchun Kan Yuan Hu 《Journal of Energy Chemistry》2021,(5):1-10
To date,lithium-ion batteries are becoming increasingly significant in the application of portable devices and electrical vehicles,and revolutionary progress in theoretical research and industrial application has been achieved.However,the commercial polyolefin separators with unsatisfying electrolytes affinity and poor thermal stability have extremely restricted the further application of lithium-ion batteries,especially in the high-temperature fields.In this work,magnetron sputtering deposition technique is employed to modify the commercial polyimide separator by coating silicon nitride on both sides.Magnetron sputtering deposition modified polyimide(MSD-PI)composite separator shows high thermal stability and ionic conductivity.More importantly,compared with the cells using Celgard separator,the cells with MSD-PI separator exhibit superior electrochemical performance,especially long-term cycle performance under high temperature environment,owing to the high thermal conductivity of surface Si3 N4 particles.Hence,lithium-ion batteries with MSD-PI separator are capable of improving thermal safety and capacity retention,which demonstrates that magnetron sputtering deposition technique could be regarded as a promising strategy to develop advanced organic/inorganic composite separators for high-temperature lithium-ion batteries. 相似文献
956.
957.
958.
959.
Wei Song Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1996,34(14):2945-2953
The effect of reaction conditions, including catalyst concentration, temperature, and immobilization on support, have been investigated for syndioselective propylene polymerization by the “bare” zirconocenium ion generated from 1,1-diphenyl-methylidene(1-η5-cyclopentadienyl)(9-η5-fluorenyl)zirconium-dichloride precursor (2). Neither variation of the catalyst concentration nor immobilization of 2 on silica support affect the syndiospecificity of polymerization. The stereoregularity of the syndiotactic polypropylene, as judged from the melting transition temperature and homosteric r-pentad population by 13C-NMR, were found to be proportional to polymer molecular weight. These behaviors are compared with a typical isoselective catalyst ethylenebis(4,5,6,7-tetrahydroindenyl) Zr precursor (4). They are in close resemblance in the case of the S-enantiomeric complex of 4, but the racemic mixture of 4 is markedly inferior. The origins of stereo- and regio-errors are discussed. © 1996 John Wiley & Sons, Inc. 相似文献
960.
Fengfu Li Yingtai Jin Chunlei Song Yonghua Lin Fengkui Pei Fosong Wang Ninghai Hu 《应用有机金属化学》1996,10(10):761-771
Three new lanthanide (Ln)–alkylaluminium (Al) bimetallic complexes with the formula [(μ-CF3CO2)2Ln(μ-CF3CHO2)AlR2 · 2THF]2 (Ln=Nd, Y, R=i-C4H9 (i-Bu); Ln=Eu, R=C2H5(Et); THF=tetrahydrofuran) were synthesized by the reaction of Ln(CF3CO2)3 (Ln=Nd, Y) with HAl (i-Bu)2 and of Eu(CF3CO2)3 with AlEt3, respectively. Their crystal structures were determined by X-ray diffraction at 233 K. [(μ-CF3CO2)2Nd (μ-CF3CHO2)Al(i-Bu)2 · 2THF]2 (Nd–Al) and [(μ-CF3CO2)2Y(μ-CF3CHO2)Al(i- Bu)2 · 2THF]2 (Y–Al) are isomorphous and crystallize in space group P 1 with a =12.441(3) Å [12.347(5) Å for Y–Al], b =12.832(3) Å [12.832(4) Å], c =11.334(3) Å [11.292(8) Å], α=104.93 (2)° [104.45(4)°], β=98.47(2)° [98.81(4)°], γ=64.60(2)° [64.30(3)°], R =0.519 [0.113], R w=0.0532 [0.110], Z =1 and [(μ-CF3CO2)2Eu(CF3 CHO2)AlEt2 · 2THF]2(Eu–Al) in space group P 21/ n with a =11.913(6) Å, b =14.051(9) Å, c =17.920(9) Å, α=101.88(11)°, β=γ=90°, R =0.0509, R w=0.0471 and Z =2. The six CF3CO 相似文献