全文获取类型
收费全文 | 15804篇 |
免费 | 2158篇 |
国内免费 | 2216篇 |
专业分类
化学 | 11961篇 |
晶体学 | 285篇 |
力学 | 573篇 |
综合类 | 139篇 |
数学 | 636篇 |
物理学 | 6584篇 |
出版年
2024年 | 32篇 |
2023年 | 166篇 |
2022年 | 494篇 |
2021年 | 673篇 |
2020年 | 588篇 |
2019年 | 498篇 |
2018年 | 459篇 |
2017年 | 619篇 |
2016年 | 704篇 |
2015年 | 688篇 |
2014年 | 906篇 |
2013年 | 1410篇 |
2012年 | 1178篇 |
2011年 | 1074篇 |
2010年 | 795篇 |
2009年 | 1036篇 |
2008年 | 1040篇 |
2007年 | 1112篇 |
2006年 | 868篇 |
2005年 | 809篇 |
2004年 | 746篇 |
2003年 | 604篇 |
2002年 | 503篇 |
2001年 | 382篇 |
2000年 | 345篇 |
1999年 | 361篇 |
1998年 | 295篇 |
1997年 | 302篇 |
1996年 | 226篇 |
1995年 | 185篇 |
1994年 | 180篇 |
1993年 | 177篇 |
1992年 | 147篇 |
1991年 | 130篇 |
1990年 | 75篇 |
1989年 | 80篇 |
1988年 | 58篇 |
1987年 | 34篇 |
1986年 | 32篇 |
1985年 | 30篇 |
1984年 | 29篇 |
1983年 | 14篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1973年 | 6篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
提出了一种工作在C波段的新型平面结构异向介质,它除了带宽宽和损耗小外,还具有体积小、结构简单的优点,而且能够实现工作频段的平移,频率平移范围为4—20 GHz.基于电磁波由自由空间入射半无限大异向介质平板的传输和反射数据,计算出了电波在其中传播时的相速随频率的变化曲线,结果表明所讨论的异向介质确实在预想的频段上表现出后向波特性;同时利用相位观察法进一步验证了上述的后向波特性,从而肯定了异向介质的存在.
关键词:
异向介质
宽频带
小单元
后向波特性 相似文献
92.
利用多靶磁控溅射技术制备了Au/SiO2纳米颗粒分散氧化物多层复合薄膜.研究了在保持Au单层颗粒膜沉积时间一定时薄膜厚度一定、变化SiO2的沉积时间及SiO2的沉积时间一定而改变薄膜厚度时,多层薄膜在薄膜厚度方向的微观结构对吸收光谱的影响.研究结果表明:具有纳米层状结构的Au/SiO2多层薄膜在560 nm波长附近有明显的表面等离子共振吸收峰,吸收峰的强度随Au颗粒的浓度增加而增强,在Au颗粒浓度相同的情况下,复合薄膜
关键词:
2纳米复合薄膜')" href="#">Au/SiO2纳米复合薄膜
多靶磁控溅射
吸收光谱
有效介质理论 相似文献
93.
Very weak water vapor absorption lines have been investigated by intracavity laser absorption spectroscopy (ICLAS) in the 11 335-11 947 and 12 336-12 843 cm−1 spectral regions dominated by the ν1 + 3ν2 + ν3 and ν2 + 3ν3 bands, respectively. A detectivity on the order of αmin ∼ 10−9 cm−1 was achieved with an ICLAS spectrometer based on a Ti: Sapphire laser. It allowed detecting transitions with an intensity down to 5 × 10−28 cm/molecule which is about 10 times lower than the weakest line intensities previously detected in the considered region. A line list corresponding to 1281 transitions with intensity lower than 5 × 10−26 cm/molecule has been generated. A detailed comparison with the line lists provided by the HITRAN database and by recent investigations by Fourier transform spectroscopy associated with very long multi pass cell is presented. The rovibrational assignment performed on the basis of the ab initio calculations of Schwenke and Partridge, has allowed for determining 176 new energy levels belonging to a total of 16 vibrational states. 相似文献
94.
Jun Hua YU Xue Song WANG Bao Wen ZHANG* Yi CAO Technical Institute of Physics Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2002,13(10)
Porphyrin derivatives attract much more interest in photodynamic therapy (PDT). Their importance as therapeutic drugs and targeting agents has been widely recognized1, and many of the efforts have been put towards crafting new porphyrin-based molecular entities to achieve enhanced tumor localization, better tissue penetration and increased singlet oxygen quantum yield2. The states of porphyrins in tissue models such as micelles, lipid bilayers are extensively investigated focusing more or l… 相似文献
95.
根据热力学第一定律和理想气体状态方程推导了理想气体的热容量公式,并对理想气体在p-V图上的直线过程和循环过程的温度变化及吸热和放热进行了讨论. 相似文献
96.
97.
Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, while the high-frequency one was independent of it. The cell shape effect was simulated by an ellipsoidal cell model but the comparison between theory and experiment was far from being satisfactory. Prompted by the discrepancy, we proposed the use of spectral representation to analyze more realistic cell models. We adopted a shell-spheroidal model to analyze the effects of the cell membrane. It is found that the dielectric property of the cell membrane has only a minor effect on the dispersion magnitude ratio and the characteristic frequency ratio. We further included the effect of rotation of dipole induced by an external electric field, and solved the dipole-rotation spheroidal model in the spectral representation.Good agreement between theory and experiment has been obtained. 相似文献
98.
Jaime Pfretzschner Pedro Cobo Francisco Simón María Cuesta Alejandro Fernández 《Applied Acoustics》2006,67(1):62-73
Microperforated panels (MPPs) coupled to a rigid wall have been proposed recently as an alternative to porous absorbers in situations having concerns with bacterial contamination and small particles discharge, like food, pharmaceutical and microelectronic industries. There exists also an increasing interest for MPP absorbers in the transportation industry and civil engineering. In general, an optimally designed MPP with good broadband absorption requires many submillimetric holes distributed over a panel of also submillimetric thickness. Such thin plates or foils become so fragile that they need to be protected from mechanical damage. In this paper, an alternative strategy is investigated which allows the design of MPPs with panels of millimetric thickness while maintaining their acoustic performance. These absorbers, named microperforated insertion units (MIUs), avoid the structural problems of the classical MPPs. An assessment of the sound absorption properties of these structures is presented. Comparisons between calculations and measurements are also made under two experimental conditions: plane waves at normal incidence (impedance tube) and free field (anechoic room). 相似文献
99.
脑细胞激活素药物的化学成分分析 总被引:1,自引:0,他引:1
采用日本岛津LC-60A型高压液相色谱仪和美国P-E3030型原子吸收分光光度计,对该药进行了氨基酸、维生素和化学元素的含量测定。结果表明,该药含有18种氨基酸,不少于3种维生素和20几种化学元素,为进一步改进该药物的合理配制方法和临床应用提供了参考数据。 相似文献
100.