全文获取类型
收费全文 | 23401篇 |
免费 | 3681篇 |
国内免费 | 2730篇 |
专业分类
化学 | 13025篇 |
晶体学 | 191篇 |
力学 | 1058篇 |
综合类 | 106篇 |
数学 | 1850篇 |
物理学 | 7065篇 |
无线电 | 6517篇 |
出版年
2024年 | 72篇 |
2023年 | 626篇 |
2022年 | 667篇 |
2021年 | 920篇 |
2020年 | 982篇 |
2019年 | 885篇 |
2018年 | 773篇 |
2017年 | 737篇 |
2016年 | 1027篇 |
2015年 | 1079篇 |
2014年 | 1284篇 |
2013年 | 1591篇 |
2012年 | 1950篇 |
2011年 | 1904篇 |
2010年 | 1394篇 |
2009年 | 1311篇 |
2008年 | 1449篇 |
2007年 | 1327篇 |
2006年 | 1305篇 |
2005年 | 1166篇 |
2004年 | 791篇 |
2003年 | 716篇 |
2002年 | 716篇 |
2001年 | 548篇 |
2000年 | 493篇 |
1999年 | 603篇 |
1998年 | 479篇 |
1997年 | 466篇 |
1996年 | 440篇 |
1995年 | 383篇 |
1994年 | 314篇 |
1993年 | 273篇 |
1992年 | 214篇 |
1991年 | 185篇 |
1990年 | 184篇 |
1989年 | 125篇 |
1988年 | 93篇 |
1987年 | 63篇 |
1986年 | 60篇 |
1985年 | 65篇 |
1984年 | 33篇 |
1983年 | 33篇 |
1982年 | 31篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1977年 | 3篇 |
1957年 | 2篇 |
1942年 | 2篇 |
1930年 | 2篇 |
1916年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
钒酸钇晶体及其在光纤通信中的应用 总被引:3,自引:2,他引:1
钒酸钇(YVO4)晶体具有良好的机械和物理特性,近年在光纤通信器件制造生产中得到了广泛的应用。本文介绍了基于YVO4晶体为材料的隔离器、环行器和交叉波分复用的功能及其原理结构。 相似文献
122.
Yiran He 《Journal of Global Optimization》2007,39(3):419-426
The existence of global error bound for convex inclusion problems is discussed in this paper, including pointwise global error
bound and uniform global error bound. The existence of uniform global error bound has been carefully studied in Burke and
Tseng (SIAM J. Optim. 6(2), 265–282, 1996) which unifies and extends many existing results. Our results on the uniform global
error bound (see Theorem 3.2) generalize Theorem 9 in Burke and Tseng (1996) by weakening the constraint qualification and
by widening the varying range of the parameter. As an application, the existence of global error bound for convex multifunctions
is also discussed. 相似文献
123.
基于约束优化的联想记忆模型学习算法 总被引:1,自引:1,他引:0
本文提出了一种对称互连神经元网络的学习策略,利用全局约束优化方法确定连接权。优化过程采用了梯度下降技术。这种学习算法可以保证训练样本成为系统的稳定吸引子,并且具有优化意义上的最大吸引域。本文讨论了网络的存储容量,训练样本的渐近稳定性和吸引域大小。计算机实验结果说明了学习算法的优越性。 相似文献
124.
Fabrication of bamboo-shaped GaN nanorods 总被引:1,自引:0,他引:1
H. Li J.Y. Li M. He X.L. Chen Z. Zhang 《Applied Physics A: Materials Science & Processing》2002,74(4):561-562
Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder
diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area
electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated
that the nanorods were single-crystal wurtzite GaN.
Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001 相似文献
125.
126.
The optical logic-operated moire,which is proposed on the basis of optical logicoperation,is a new method to obtain specific moire beat pattern.Its advantages lie in the ca-pability to select carrier-free,sharpened fringes with high contrast.The experimental methodand results of the application of the optical logic-operared moire in moire topography are pre-sented in this paper. 相似文献
127.
128.
PZT铁电薄膜的制备及电学性能研究 总被引:6,自引:1,他引:5
使用硝酸锆作锆源的溶胶-凝胶方法制备PZT铁电薄膜。他们的电学性能被测试包括电滞回线,电流I(t)特性,漏电流,矫顽场疲劳和老化。测到的PZT薄膜剩余极化8.2μC/cm~2,矫顽场68kV/cm.簿膜的寿命可超过10~(11)周期。 相似文献
129.
Dynamic oxide voltage relaxation spectroscopy 总被引:3,自引:0,他引:3
Mingzhen Xu Changhua Tan Yandong He Xiaowei Liu Yangyuan Wang 《Electron Devices, IEEE Transactions on》1996,43(4):628-635
A new method for trap characterization of oxidized silicon is described. The Dynamic Oxide Voltage Relaxation Spectroscopy (DOVRS) is an improved version of the formerly proposed Oxide Voltage Relaxation Spectroscopy (OVRS) technique which applies a periodic long duration constant current for tunneling injection. It has been demonstrated that the new technique can be used not only to separate and identify the oxide trap from interface trap, but also to separate and determine the centroid from the oxide trap density generated in the MOS system by the tunneling current stress. In the pulse constant current mode, the OVRS measurement can be completed instead of using the double current-voltage technique. Thus the new method results in more accurate and quicker measurements of the oxide trap centroid. Analytical expressions for computing the paramaters of the interface and oxide traps are derived. The effect of the channel carrier mobility on the spectroscopy is also considered. Two types of oxide and two types of interface traps were observed at a pulse constant Fowler-Nordheim current stress by the new method of DOVRS 相似文献
130.
Time-varying adaptive filters for evoked potential estimation 总被引:4,自引:0,他引:4
Xiao-Hu Yu Zhen-Ya He Yi-Sheng Zhang 《IEEE transactions on bio-medical engineering》1994,41(11):1062-1071
Adaptive implementation of an optimal time-varying filter (TVF) for evoked potential (EP) estimation is addressed here. A data-adaptive scheme is used, which converges asymptotically to the optimal TVF solution. Two basic adaptive TVF's (ATVF's) are first introduced, namely least mean square (LMS) ATVF and recursive least-squares (RLS) ATVF. The latter converges much faster than the former. Since the basic ATVF's usually require a relatively large set of response trials to get a meaningful solution, a reduced-order ATVF is further presented and the corresponding LMS and RLS (including a fast RLS) adaptive algorithms are developed. To save memory, a truncated Fourier expansion is suggested to express approximately the time-sequenced weight-vectors of the ATVF's, resulting in a simplified reduced-order ATVF. Finally, extensive simulations are provided to confirm the superior performance of the ATVF's. The present ATVF's can be used as prefilters for latency-corrected average (LCA) processing to obtain more informative estimates of EP signals 相似文献