全文获取类型
收费全文 | 114788篇 |
免费 | 18860篇 |
国内免费 | 12336篇 |
专业分类
化学 | 61159篇 |
晶体学 | 923篇 |
力学 | 5711篇 |
综合类 | 524篇 |
数学 | 10192篇 |
物理学 | 35893篇 |
无线电 | 31582篇 |
出版年
2024年 | 297篇 |
2023年 | 3011篇 |
2022年 | 3109篇 |
2021年 | 4426篇 |
2020年 | 4728篇 |
2019年 | 4127篇 |
2018年 | 3662篇 |
2017年 | 3503篇 |
2016年 | 5102篇 |
2015年 | 5268篇 |
2014年 | 6350篇 |
2013年 | 8104篇 |
2012年 | 9831篇 |
2011年 | 10081篇 |
2010年 | 7054篇 |
2009年 | 7070篇 |
2008年 | 7614篇 |
2007年 | 6729篇 |
2006年 | 6472篇 |
2005年 | 5390篇 |
2004年 | 3794篇 |
2003年 | 3149篇 |
2002年 | 2894篇 |
2001年 | 2483篇 |
2000年 | 2339篇 |
1999年 | 2676篇 |
1998年 | 2318篇 |
1997年 | 2143篇 |
1996年 | 2095篇 |
1995年 | 1771篇 |
1994年 | 1568篇 |
1993年 | 1297篇 |
1992年 | 1174篇 |
1991年 | 983篇 |
1990年 | 762篇 |
1989年 | 571篇 |
1988年 | 447篇 |
1987年 | 353篇 |
1986年 | 354篇 |
1985年 | 293篇 |
1984年 | 184篇 |
1983年 | 130篇 |
1982年 | 112篇 |
1981年 | 66篇 |
1980年 | 49篇 |
1979年 | 16篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
191.
192.
In this letter, bandpass filters with one or two tunable transmission zeros are proposed. The reconfigurable transmission zeros are implemented through varactors in combination with tapped quarter-wavelength stubs. Based on mixed mode simulations including EM simulation and circuit simulation, the proposed filters were designed and fabricated on low-cost FR4 board. The measurement results verified the design concepts. 相似文献
193.
This article describes the different methods to design regular low density parity-check (LDPC) codes with large girth. In graph terms, this corresponds to designing bipartite undirected regular graphs with large girth. Large girth speeds the convergence of iterative decoding and improves the performance at least in the high SNR range, by slowing down the onsetting of the error floor. We reviewed several existing constructions from exhaustive search to highly structured designs based on Euclidean and projective finite geometries and combinatorial designs. We describe GB and TS LDPC codes and compared the BER performance with large girth to the BER performance of random codes. These studies confirm that in the high SNR regime these codes with high girth exhibit better BER performance. The regularity of the codes provides additional advantages that we did not explore in this article like the simplicity of their hardware implementation and fast encoding. 相似文献
194.
对铜在酸性CuCl_2溶液中蚀刻反应机理论述,利用氧化-还原电动势原理,详细论述了Ni80Cr20合金在酸性CuCl_2溶液中化学蚀刻反应机理,以及影响蚀刻速度的因素,并对溶液中金属离子的存在形式作了验证。 相似文献
195.
196.
197.
用保角变换法对共面波导金属厚度效应进行了理论分析,编制了相应的计算机程序,给出了数值解,并对此进行了多元曲线拟合,导出了考虑金属厚度后的形状比k、有效介电常数、特征阻抗、损耗的闭定表达式。用此修正表达式求得特征阻抗及损耗的数值解,并与K.C.格普塔的修正值及实验测量值进行了详细比较,结果表明此修正公式与实验值相符较好。 相似文献
198.
Bijian Lan Chunming Liu Xiang Yin Hua Zhang Wei Xu Zhongyi Hua 《Frontiers of Chemistry in China》2006,1(3):296-299
Organic materials of D-π-A type MR-X (MR-1: p-dimethylaminophenylethenetrica-rbonitrile and MR-2: p-diphenylaminophenylethene tricarbonitrile) were designed and synthesized. The device with a sandwich structure shows good
rectificative phenomena. The highest rectification ratio 10000 was achieved in device Cu/MR-1/Ag, and about 100 in other device
M/MR-X/M (M: Cu, Ag). It has been found that rectificative phenomena exist only in the atmosphere-liquid interface region
by means of liquid adsorption, and electric field could help form the oriented molecular film.
__________
Translated from Journal of Fudan University (Natural Science), 2005, 44(4) (in Chinese) 相似文献
199.
Mine K. Kubota N. Morimoto F. Sanada M. Zhang Qi 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(3):253-255
This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance 相似文献
200.
Xu Baowen Zhang Weifeng 《电子科学学刊(英文版)》2002,19(4)
The users' interest can be mined from the web cache and can be used widely. The interest can be specialized by the two-tuple (term, weight) in the simple interest model, in which the association relations are not mined, and then the interest cannot be associated in expressing the users' interest. Based on analyzing the WWW cache model, this letter brings forward a two-dimensional interest model and gives the interrelated methods on how to store the two-dimensional interest model effectively. 相似文献