全文获取类型
收费全文 | 554681篇 |
免费 | 93338篇 |
国内免费 | 58585篇 |
专业分类
电工技术 | 48755篇 |
技术理论 | 52篇 |
综合类 | 46164篇 |
化学工业 | 85622篇 |
金属工艺 | 43715篇 |
机械仪表 | 30042篇 |
建筑科学 | 41012篇 |
矿业工程 | 24341篇 |
能源动力 | 18489篇 |
轻工业 | 44935篇 |
水利工程 | 14466篇 |
石油天然气 | 34717篇 |
武器工业 | 6655篇 |
无线电 | 69391篇 |
一般工业技术 | 70333篇 |
冶金工业 | 26169篇 |
原子能技术 | 5207篇 |
自动化技术 | 96539篇 |
出版年
2024年 | 3999篇 |
2023年 | 9788篇 |
2022年 | 15072篇 |
2021年 | 19966篇 |
2020年 | 19127篇 |
2019年 | 25955篇 |
2018年 | 28658篇 |
2017年 | 30862篇 |
2016年 | 29732篇 |
2015年 | 32818篇 |
2014年 | 35461篇 |
2013年 | 38492篇 |
2012年 | 39559篇 |
2011年 | 38906篇 |
2010年 | 34534篇 |
2009年 | 30485篇 |
2008年 | 28415篇 |
2007年 | 26787篇 |
2006年 | 26316篇 |
2005年 | 23390篇 |
2004年 | 19864篇 |
2003年 | 17318篇 |
2002年 | 16334篇 |
2001年 | 14576篇 |
2000年 | 13936篇 |
1999年 | 14094篇 |
1998年 | 11464篇 |
1997年 | 9951篇 |
1996年 | 9308篇 |
1995年 | 8327篇 |
1994年 | 6740篇 |
1993年 | 5302篇 |
1992年 | 4642篇 |
1991年 | 3471篇 |
1990年 | 2740篇 |
1989年 | 2441篇 |
1988年 | 1940篇 |
1987年 | 865篇 |
1986年 | 720篇 |
1985年 | 507篇 |
1984年 | 349篇 |
1983年 | 270篇 |
1982年 | 283篇 |
1981年 | 230篇 |
1980年 | 197篇 |
1976年 | 272篇 |
1975年 | 222篇 |
1972年 | 250篇 |
1971年 | 136篇 |
1960年 | 207篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
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
93.
Yuhua Cheng Chih-Hung Chen Matloubian M. Deen M.J. 《Electron Devices, IEEE Transactions on》2002,49(3):400-408
High-frequency (HF) AC and noise modeling of MOSFETs for radio frequency (RF) integrated circuit (IC) design is discussed. A subcircuit RF model incorporating the HF effects of parasitics is presented. This model is compared with the measured data for both y parameter and fT characteristics. Good model accuracy is achieved against measurements for a 0.25 μm RF CMOS technology. The HF noise predictivity of the model is also examined with measured data. Furthermore, a methodology to extract the channel thermal noise of MOSFETs from HF noise measurements is presented. By using the extracted channel thermal noise, any thermal noise models can be verified directly. Several noise models including the RF model discussed in this paper have been examined, and the results show that the RF model can predict the channel thermal noise better than the other models 相似文献
94.
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
95.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method 相似文献
96.
LDD方法在提高电路工作电压中的应用研究 总被引:1,自引:0,他引:1
研究了利用轻掺杂漏结构来制作高电源电压器件的工艺方法。分析了LDD结构参数对器件击穿特性的影响,并结合实验结果对N^-区的注入剂量,长度及引入的串联电阻进行了优化设计。 相似文献
97.
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
98.
NMOS器件两次沟道注入杂质分布和阈电压计算 总被引:1,自引:1,他引:0
分别考虑了深浅两次沟道区注入杂质在氧化扩散过程中对表面浓度的贡献。对两次注入杂质的扩散分别提取了扩散系数的氧化增强系数、氧化衰减系数和有效杂地系数,给出了表面浓度与工艺参数之间的模拟关系式,以峰值浓度为强反型条件计算了开启电压,文章还给出了开启电压、氧化条件、不同注入组合之间的关系式。 相似文献
99.
对油管漏失进行定量测试的方法确定具体漏失位置。方法运用双频道回声探仪探测动液面的原理和工作方法,根据油管漏失形成的死油坏在测试曲线上出现特殊波位置判断油管漏失位置。结果:经过70多井次的现场试验,该方法具有较高的准确性和可靠性。结论:利用特殊波可以有效监测油管漏失,并具有推广使用价值。 相似文献
100.
埋地管道涂层检测技术现状 总被引:3,自引:0,他引:3
李继华 《石油化工腐蚀与防护》1998,15(4):4-6,52
文章对各种埋地管道涂层检测技术进行了综述,并指出了各种技术的优缺点及应用前景. 相似文献