全文获取类型
收费全文 | 60401篇 |
免费 | 6037篇 |
国内免费 | 3253篇 |
专业分类
电工技术 | 4324篇 |
技术理论 | 6篇 |
综合类 | 4454篇 |
化学工业 | 9729篇 |
金属工艺 | 3260篇 |
机械仪表 | 3696篇 |
建筑科学 | 5185篇 |
矿业工程 | 1851篇 |
能源动力 | 1662篇 |
轻工业 | 5484篇 |
水利工程 | 1205篇 |
石油天然气 | 3453篇 |
武器工业 | 547篇 |
无线电 | 6877篇 |
一般工业技术 | 6804篇 |
冶金工业 | 2411篇 |
原子能技术 | 745篇 |
自动化技术 | 7998篇 |
出版年
2024年 | 307篇 |
2023年 | 1237篇 |
2022年 | 2245篇 |
2021年 | 3005篇 |
2020年 | 2426篇 |
2019年 | 1807篇 |
2018年 | 2060篇 |
2017年 | 2170篇 |
2016年 | 1912篇 |
2015年 | 2729篇 |
2014年 | 3298篇 |
2013年 | 3872篇 |
2012年 | 4297篇 |
2011年 | 4542篇 |
2010年 | 3783篇 |
2009年 | 3455篇 |
2008年 | 3484篇 |
2007年 | 3206篇 |
2006年 | 3137篇 |
2005年 | 2610篇 |
2004年 | 1699篇 |
2003年 | 1533篇 |
2002年 | 1525篇 |
2001年 | 1365篇 |
2000年 | 1307篇 |
1999年 | 1312篇 |
1998年 | 988篇 |
1997年 | 824篇 |
1996年 | 759篇 |
1995年 | 617篇 |
1994年 | 532篇 |
1993年 | 368篇 |
1992年 | 313篇 |
1991年 | 219篇 |
1990年 | 183篇 |
1989年 | 159篇 |
1988年 | 93篇 |
1987年 | 77篇 |
1986年 | 57篇 |
1985年 | 43篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 17篇 |
1980年 | 23篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1959年 | 10篇 |
1953年 | 1篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
101.
采用微软公司Microsoft Excel的规划求解功能,可以快速准确地进行玻璃料方的计算,从而大大提高工作效率.本文以平板玻璃料方为例,对玻璃料方的电子计算机计算原理作介绍,并对利用Excel电子表格的规划求解功能进行玻璃料方计算的过程进行介绍. 相似文献
102.
Ying Ding Chunqing Wang Yanhong Tian Binbin Zhang 《Metallurgical and Materials Transactions A》2006,37(12):1017-1025
in-situ transmission electron microscopy (TEM) tensile tests on as-cast and aged 63Sn37Pb solder alloys were conducted, and the fracture
behavior in nanometer scale ahead of the crack tip was inspected and discussed. Results show that the fracture was completed
by connecting the discontinuous cracks or voids. Dislocation behavior was concentrated along the grain boundaries for as-cast
samples, and displayed mainly as dislocation climb. The crack was intergranular dominated under the lower strain rate. While
remarkable mutual dislocation emission was detected in the aged solder. Transgranular cracks were dominant in the fractured
area, and they propagated by linking up with the nanometer scale cracks ahead of the crack tips under the effective promotion
of the inverse dislocation emission. At the same time, the partial interphase or intergranular cracks in the thinned area
were also found. Under this condition, a new critical stress intensity factor K
c
′ to define the mutual dislocation emission was proposed. 相似文献
103.
Wang Xuegang Yan Fengjie Yan Qian Li Xingeng 《Frontiers of Materials Science in China》2007,1(2):225-227
An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel
pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer
(EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base
metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base
metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the
mechanical properties of the joint are similar around the pipe. 相似文献
104.
压密注浆及其在地基加固中的应用 总被引:1,自引:0,他引:1
在简单介绍了压密注浆工法的加固机理、影响被加固土体强度的因素的基础上,结合工程实例介绍了压缩注浆工法的工程应用情况。 相似文献
105.
Tian Yang Lipson S. O'Brien J.D. Deppe D.G. 《Photonics Technology Letters, IEEE》2005,17(11):2244-2246
We report on the demonstration of optically pumped photonic crystal lasers with InAs quantum dot active regions operating at room temperature near 1310 nm. Absorbed threshold pump powers as low as 25 /spl mu/W are observed. We also extract a characteristic temperature of 17 K, which is attributed to limitations caused by surface recombination. 相似文献
106.
Enhancing echo cancellation via estimation of delay 总被引:2,自引:0,他引:2
Youhong Lu Fowler R. Tian W. Thompson L. 《Signal Processing, IEEE Transactions on》2005,53(11):4159-4168
The advent of packetized audio transmission, such as voice over IP (VoIP), has resulted in challenging requirements for echo cancellation technology. One key aspect of this technology is the need to characterize, quickly and accurately, the echo paths in the transmission media. Echo paths consist of a constant time delay with no echo signal and active regions in which the echo signal is present. When an adaptive filter echo cancellation algorithm is used, its performance can be greatly increased, and its complexity can be reduced if it is only applied to the active regions. This requires an algorithm to estimate the constant delay and locate the active regions. Traditionally, delay estimation has been based on direct application of cross-correlation. This method has poor performance because the input signals are highly correlated and has a high implementation cost because many cross-correlation lags have to be computed for longer time delays. The delay estimation addressed in this paper has two major advantages over the traditional methods. The first is that it has improved performance because the input signals are processed to have less correlation. The second is that the implementation cost is significantly reduced because fewer cross-correlation lags are computed, and an efficient method to estimate lags is created. 相似文献
107.
J. Chen J. B. Xu K. Xue J. An N. Ke W. Cao H. B. Xia J. Shi D. C. Tian 《Microelectronics Reliability》2005,45(1):137-142
Transition-metal compound TiC60 thin films were grown by co-deposition from two separated sources of fullerene C60 powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C60 structure with certain amount of sp3 bonds and a rough surface with a large number of nanoclusters. z–V tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm2 and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC60 thin films can be ascribed to structural variation of C60 in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C60 matrix. 相似文献
108.
109.
110.
Xiaojun Xie Yonghong Cheng Hong Wang Qian Wang Xiaolin Chen Caixin Sun 《Ceramics International》2008,34(4):689-693
In the ideal A2B2O6O′ pyrochlore structure, the x-value of O atom position is a variable parameter. In Bi1.5ZnNb1.5−xTaxO7 (BZNT) cubic pyrochlores, the x-values alter with the different compositions of Nb/Ta. In this work, a series of initial models for BZNT were established by analyzing X-ray diffraction data. Then three structure modifying methods, including Rietveld refinement, Rietveld refinement with energy and geometry optimization based on quantum mechanics, were employed to obtain the precise models using Materials Studio. Moreover, the reflectivities of BZNT were computed by quantum mechanical simulation based on the refined models. Comparing the simulation results from different modifying models with the experimental results, it is found that Rietveld refinement with energy optimization is the most accurate method for BZNT pyrochlores. According to the simulation results, the different reflectivities correspond well with various x-values of O atom positions in BZNT pyrochlores. 相似文献