全文获取类型
收费全文 | 436226篇 |
免费 | 34245篇 |
国内免费 | 19273篇 |
专业分类
电工技术 | 26014篇 |
技术理论 | 47篇 |
综合类 | 30654篇 |
化学工业 | 71224篇 |
金属工艺 | 24994篇 |
机械仪表 | 27083篇 |
建筑科学 | 33724篇 |
矿业工程 | 13310篇 |
能源动力 | 11996篇 |
轻工业 | 30043篇 |
水利工程 | 8415篇 |
石油天然气 | 26572篇 |
武器工业 | 3412篇 |
无线电 | 49302篇 |
一般工业技术 | 48927篇 |
冶金工业 | 22656篇 |
原子能技术 | 4491篇 |
自动化技术 | 56880篇 |
出版年
2024年 | 1745篇 |
2023年 | 6591篇 |
2022年 | 11952篇 |
2021年 | 16721篇 |
2020年 | 12457篇 |
2019年 | 10147篇 |
2018年 | 11715篇 |
2017年 | 13296篇 |
2016年 | 12106篇 |
2015年 | 16707篇 |
2014年 | 21254篇 |
2013年 | 25839篇 |
2012年 | 27952篇 |
2011年 | 31074篇 |
2010年 | 27378篇 |
2009年 | 26092篇 |
2008年 | 25615篇 |
2007年 | 24498篇 |
2006年 | 24666篇 |
2005年 | 21409篇 |
2004年 | 14529篇 |
2003年 | 12817篇 |
2002年 | 12041篇 |
2001年 | 10641篇 |
2000年 | 10454篇 |
1999年 | 11099篇 |
1998年 | 8835篇 |
1997年 | 7538篇 |
1996年 | 7071篇 |
1995年 | 5848篇 |
1994年 | 4724篇 |
1993年 | 3321篇 |
1992年 | 2625篇 |
1991年 | 1993篇 |
1990年 | 1582篇 |
1989年 | 1268篇 |
1988年 | 1062篇 |
1987年 | 694篇 |
1986年 | 551篇 |
1985年 | 386篇 |
1984年 | 296篇 |
1983年 | 231篇 |
1982年 | 189篇 |
1981年 | 132篇 |
1980年 | 146篇 |
1979年 | 78篇 |
1978年 | 49篇 |
1977年 | 55篇 |
1976年 | 82篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Jun-Fa Mao Zheng-Fan Li 《Microwave Theory and Techniques》1992,40(4):637-644
A new method for analysis of the time response of multiconductor transmission lines with frequency-dependent losses is presented. This method can solve the time response of various kinds of transmission lines with arbitrary terminal networks. Particularly, it can analyze nonuniform lines with frequency-dependent losses, for which no effective method for analyzing their time response exists. This method starts from the frequency-domain telegrapher's equations. After decoupling and inversely Fourier transforming, then a set of decoupled time-domain equations including convolutions are given. These equations can be solved with the characteristic method. The results obtained with this method are stable and accurate. Two examples are given to illustrate the application of this method to various multiconductor transmission lines 相似文献
72.
带隔板底水油藏油井临界产量计算公式 总被引:25,自引:9,他引:16
本给出了带隔板底水油藏油井的监界产量计算公式,它适用于所有带隔板底水油藏的油井。 相似文献
73.
In this study, the effect and side-effect of epidural injection with lappaconitine compound for post-operative analgesia was observed. One hundred and twenty patients were randomly divided into 4 groups. Lappaconitine compound (LB) consisted of 12 mg of lappaconitine and 22.5 mg of bupivacaine, was given to group A (the group of observation), and lappaconitine 12 mg, bupivacaine 22.5 mg and morphine 2 mg to group B, C and D respectively for control. All were given by epidural injection with single blind method during post-operative pain of incision operation. Result showed that the initiating of analgesia was quicker in group A and C than that in group B and D, and the efficacy was group D > A > C > B. There was significant difference between group A and B in the above two parameters, P < 0.01 and P < 0.05. The analgisia maintenence time of single injection was D > A > B > C, that of group D was significantly longer than that of group A (P < 0.01). It indicated that the epidural injection with LB was more rapid and potent than that with lappaconitine alone in post-operative analgesia, and the former had no side-effect, it was safer than morphine. 相似文献
74.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。 相似文献
75.
76.
This investigation focuses on the correlation between the crystallographic orientation of grains with respect to magnetic
properties in Co-Cr films. Based on a distribution measured for the (0002) crystallographic pole densities, modified formulae
describing the texture were used to calculate the coercivity Hc, the squareness ratio Rs (Mr⊥/TMs) and the anisotropy field
Ha for Co-Cr films. In general, calculated values for the coercive force He agreed well with the measured values. The calculated
Rs⊥. values were much larger than the measured ones, however, indicating that the influence of the demagnetizing field and
the magnetostriction on the orientation of the magnetization cannot be neglected.
On leave from Institute of Computing Technology, Academia Sinica, P.O.Box 2704-6, Beijing, P.R. China. 相似文献
77.
Code-division multiple-access (CDMA) implemented with direct-sequence spread spectrum (DS/SS) signaling is a promising multiplexing technique for cellular telecommunications services. The efficiency of a direct-sequence spread-spectrum code-division multiple-access (DS-CDMA) system depends heavily on the shape of the spectrum of the spread signal. Maximum efficiency is obtained with an ideal brick-wall bandpass spectrum. There are two approaches toward achieving such a spectrum. One is to use a simple spreader that produces a broad spectrum and then follow it with a precise, high order filter to band limit the spectrum. A second approach, which is the approach taken in this paper, is to use a spreader that produces a spectrum close to the ideal spectrum and then employ a simple filter to control the out-of-band power. The proposed spreader/despreader is based on a simple hybrid function and can be easily implemented. An analysis provides a compact expression for the signal-to-noise ratio (SNR) of a RAKE receiver. The expression includes the effects of baseband, intermediate frequency (IF) and RF filtering as well as the effects of the spectral densities of the spreading/despreading functions. The analysis shows that the proposed spreader/despreader yields superior performance over a conventional pseudo noise (PN) spreading/despreading mechanism 相似文献
78.
Min-Shiang Hwang Chih-Wei Lin Cheng-Chi Lee 《Electronics letters》2002,38(23):1429-1431
An authenticated multiple-key agreement protocol is proposed. The protocol is not only secure against the unknown-key attack but also more efficient than other protocols. 相似文献
79.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
80.
Network fault identification is an important network management function, which is closely related to fault management and has an impact on other network management functions such as configuration management, and performance management. This paper investigates fault surveillance and fault identification mechanisms for a transparent optical network in which data travels optically from the source node to the destination node without going through any optical-to-electrical (O/E) or electrical-to-optical (E/O) conversion. Mechanisms and algorithms are proposed to detect and isolate faults such as fiber cuts, laser, receiver, or router failures. These mechanisms allow nonintrusive device monitoring without requiring any prior knowledge of the actual protocols being used in the data transmission 相似文献