全文获取类型
收费全文 | 96358篇 |
免费 | 8306篇 |
国内免费 | 4258篇 |
专业分类
电工技术 | 5542篇 |
技术理论 | 10篇 |
综合类 | 5905篇 |
化学工业 | 16051篇 |
金属工艺 | 5495篇 |
机械仪表 | 5912篇 |
建筑科学 | 7146篇 |
矿业工程 | 2630篇 |
能源动力 | 2901篇 |
轻工业 | 7106篇 |
水利工程 | 1753篇 |
石油天然气 | 4961篇 |
武器工业 | 729篇 |
无线电 | 11891篇 |
一般工业技术 | 12646篇 |
冶金工业 | 4902篇 |
原子能技术 | 986篇 |
自动化技术 | 12356篇 |
出版年
2024年 | 461篇 |
2023年 | 1766篇 |
2022年 | 3120篇 |
2021年 | 4299篇 |
2020年 | 3318篇 |
2019年 | 2619篇 |
2018年 | 3023篇 |
2017年 | 3091篇 |
2016年 | 3109篇 |
2015年 | 3903篇 |
2014年 | 4835篇 |
2013年 | 5590篇 |
2012年 | 6139篇 |
2011年 | 6739篇 |
2010年 | 5637篇 |
2009年 | 5369篇 |
2008年 | 5228篇 |
2007年 | 4732篇 |
2006年 | 4544篇 |
2005年 | 3936篇 |
2004年 | 2949篇 |
2003年 | 2668篇 |
2002年 | 2408篇 |
2001年 | 2141篇 |
2000年 | 2266篇 |
1999年 | 2577篇 |
1998年 | 2250篇 |
1997年 | 1809篇 |
1996年 | 1750篇 |
1995年 | 1450篇 |
1994年 | 1256篇 |
1993年 | 848篇 |
1992年 | 678篇 |
1991年 | 489篇 |
1990年 | 416篇 |
1989年 | 379篇 |
1988年 | 267篇 |
1987年 | 191篇 |
1986年 | 143篇 |
1985年 | 105篇 |
1984年 | 79篇 |
1983年 | 52篇 |
1982年 | 60篇 |
1981年 | 48篇 |
1980年 | 43篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 23篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
Whispering-gallery-like modes in square resonators 总被引:1,自引:0,他引:1
Wei-Hua Guo Yong-Zhen Huang Qiao-Yin Lu Li-Juan Yu 《Quantum Electronics, IEEE Journal of》2003,39(9):1106-1110
The mode frequencies and field distributions of whispering-gallery (WG)-like modes of square resonators are obtained analytically, which agree very well with the numerical results calculated by the FDTD technique and Pade approximation method. In the analysis, a perfect electric wall for the transverse magnetic mode or perfect magnetic wall for the transverse electric mode is assumed at the diagonals of the square resonators, which not only provides the transverse mode confinement, but also requires the longitudinal mode number to be an even integer. The WG-like modes of square resonators are nondegenerate modes with high-quality factors, which make them suitable for fabricating single-mode low-threshold semiconductor microcavity lasers. 相似文献
13.
14.
15.
一类Feistel密码的线性分析 总被引:5,自引:0,他引:5
该文提出一种新的求取分组密码线性偏差上界的方法,特别适用于密钥线性作用的Feistel密码.该分析方法的思路是,首先对密码体制线性偏差进行严格的数学描述,分别给出密码线性偏差与轮函数F及S盒的线性偏差的数学关系;然后通过求取线性方程组最小重量解,确定密码线性偏差的上界. 相似文献
16.
This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem. 相似文献
17.
To determine three‐dimensional fiber orientation states in injection‐molded short‐fiber composites, a confocal laser scanning microscope (CLSM) is used. Since the CLSM optically sections the specimen, more than two images of the cross sections on and below the surface of the composite can be obtained. Three‐dimensional fiber orientation states can be determined by using geometric parameters of fiber images obtained from two parallel cross sections. For experiments, carbon‐fiber‐reinforced polystyrene is examined by the CLSM and geometric parameters of fibers on each cross‐sectional plane are measured by an image analysis. In order to describe fiber orientation states compactly, orientation tensors are determined at different positions of the prepared specimen. Three‐dimensional orientation states are obtained without any difficulty by determining the out‐of‐plane angles utilizing fiber images on two parallel planes acquired by the CLSM. Orientation states are different at different positions and show the shell–core structure along the thickness of the specimen. Fiber orientation tensors are predicted by a numerical analysis and the numerically predicted orientation states show good agreement with measured ones. However, some differences are found at the end of cavity. They may result from the fountain flow effects, which are not considered in the numerical analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 500–509, 2003 相似文献
18.
对己二腈工业反应器提出了两釜串联带回流的模型,通过模拟计算得出模型的级间返混系数 f=6的结论。该模型能较好地预测工业反应器中物料组分浓度变化和气、液两相的流动特性;指出了现工业反应器的鼓泡中和段体积偏小是造成己二酸浓度偏高的关键;提出了可以通过增加串连一个鼓泡预反应段的改造方案,能有效地降低己二酸的浓度,从7%降至4%左右,从而能较好地减缓腐蚀和结焦。 相似文献
19.
20.
Ki Hyun Kim Yong Hoon Kang Byoungho Lee 《Photonics Technology Letters, IEEE》1997,9(12):1610-1612
A photorefractive volume hologram was recorded and probed using light diffracted from a tapered optical fiber as a reference beam. A single-mode fiber (SMF) was chemically etched and tapered to give a complicated beam pattern, and it is shown that the tapered optical fiber can be utilized to increase the storage density of the volume hologram. Spatial selectivity of the volume hologram with this method was increased by two times compared to the normal SMF referencing, which is due to the fact that the complicated beam pattern has little correlation with its shifted version 相似文献