全文获取类型
收费全文 | 62671篇 |
免费 | 5961篇 |
国内免费 | 2826篇 |
专业分类
电工技术 | 4045篇 |
技术理论 | 4篇 |
综合类 | 3874篇 |
化学工业 | 10324篇 |
金属工艺 | 3601篇 |
机械仪表 | 4262篇 |
建筑科学 | 4870篇 |
矿业工程 | 2087篇 |
能源动力 | 1952篇 |
轻工业 | 4480篇 |
水利工程 | 1280篇 |
石油天然气 | 3249篇 |
武器工业 | 584篇 |
无线电 | 6934篇 |
一般工业技术 | 7595篇 |
冶金工业 | 2944篇 |
原子能技术 | 828篇 |
自动化技术 | 8545篇 |
出版年
2024年 | 316篇 |
2023年 | 1155篇 |
2022年 | 1959篇 |
2021年 | 2780篇 |
2020年 | 2120篇 |
2019年 | 1877篇 |
2018年 | 2133篇 |
2017年 | 2253篇 |
2016年 | 2055篇 |
2015年 | 2729篇 |
2014年 | 3470篇 |
2013年 | 4050篇 |
2012年 | 4655篇 |
2011年 | 4833篇 |
2010年 | 4208篇 |
2009年 | 3954篇 |
2008年 | 3736篇 |
2007年 | 3463篇 |
2006年 | 3326篇 |
2005年 | 2754篇 |
2004年 | 1967篇 |
2003年 | 1752篇 |
2002年 | 1770篇 |
2001年 | 1522篇 |
2000年 | 1220篇 |
1999年 | 1174篇 |
1998年 | 794篇 |
1997年 | 633篇 |
1996年 | 597篇 |
1995年 | 518篇 |
1994年 | 372篇 |
1993年 | 315篇 |
1992年 | 244篇 |
1991年 | 175篇 |
1990年 | 140篇 |
1989年 | 89篇 |
1988年 | 102篇 |
1987年 | 47篇 |
1986年 | 60篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 12篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1970年 | 6篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
2.
本文提出新型布线算法,集李氏迷宫法与线搜索法的长处为一体,以饱和带法进行动态排序,以线搜索法确定借孔位置,然后用李氏法进行单层布线,获得最佳路径,从而达到线型好,布通率高的效果。 相似文献
3.
Min Chan Kim Dong Won Lee Chang Kyun Choi 《Korean Journal of Chemical Engineering》2008,25(6):1239-1244
When a horizontal homogeneous solid is melted from below, convection can be induced in a thermally unstable melt layer. In
this study the onset of buoyancy-driven convection during time-dependent melting is investigated by using similarly transformed
disturbance equations. The critical Rayleigh numbers based on the melt-layer thickness are found numerically for various conditions.
For small superheats, the present predictions approach the well known results of classical Rayleigh-Bénard problems, that
is, critical Rayleigh numbers are located between 1,296 and 1,708, regardless of the Prandtl number. However, for high superheats
the critical Rayleigh number increases with an increase in phase change rate but with decrease in Prandtl number. 相似文献
4.
Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles. 相似文献
5.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
6.
Shu‐Li Sun Jing Ma Nan Lv 《International Journal of Adaptive Control and Signal Processing》2008,22(10):932-948
Based on the optimal fusion estimation algorithm weighted by scalars in the linear minimum variance sense, a distributed optimal fusion Kalman filter weighted by scalars is presented for discrete‐time stochastic singular systems with multiple sensors and correlated noises. A cross‐covariance matrix of filtering errors between any two sensors is derived. When the noise statistical information is unknown, a distributed identification approach is presented based on correlation functions and the weighted average method. Further, a distributed self‐tuning fusion filter is given, which includes two stage fusions where the first‐stage fusion is used to identify the noise covariance and the second‐stage fusion is used to obtain the fusion state filter. A simulation verifies the effectiveness of the proposed algorithm. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
7.
Dong Zhang 《Korean Journal of Chemical Engineering》2008,25(5):1205-1207
Ceria-zirconia solid particles have been recognized as a key material of the automotive exhaust catalysts since they can release
and uptake oxygen owing to the rapid reversible oxidation states of cerium between Ce3+ and Ce4+. Several methods have recently been described to prepare the CeO2-ZrO2 solid particles used in the catalysts. In this paper, a new coprecipitation method is used to prepare the CeO2-ZrO2 solid particles. The Ce-Zr alcogel is dried and calcined in flowing N2 not in flowing air under atmospheric pressure. The results show that the ceria-zirconia sample calcined at 650 °C has high
surface area over 90 m2g−1, which drops to 40 m2g−1 following treatment at 900°C. 相似文献
8.
防治水泥稳定碎石基层沥青路面裂缝的措施浅析 总被引:3,自引:0,他引:3
水泥稳定碎石基层沥青路面裂缝产生的原因复杂 ,但非荷载型裂缝更为主要。防治水泥稳定碎石基层沥青路面的裂缝应该从设计和施工两方面考虑 ,其中由结构、材料组成设计 ,以及施工工艺出发控制水泥稳定碎石基层本身的收缩也是一项重要措施。 相似文献
9.
For the first time, the surface metal on nonalloyed ohmic electrodes is found to significantly change the profiles of gate grooves, when resist openings are employed to monitor drain current during wet-chemical gate recess for sub-micron InAlAs/lnGaAs heterojunction field-effect transistors (HFETs). The surface metal of Ni enhances the etching rate in comparison with that in the absence of electrodes by a factor of 4 and 10, laterally and vertically, which is favorable to fabricate deep gate grooves with small side etching. The Pt surface metal, however, leads to preferential etching of InGaAs over InAlAs, which can be useful to realize large side etching. The existence of an electrochemistry-related etching component, which arises when the ohmic electrodes are present during recess etching, is considered to be responsible for these behaviors 相似文献
10.
Kwang Soo Lee In Soo Park & Dong Sun Lee 《International Journal of Food Science & Technology》1996,31(1):7-13
The aim of this study was to design a modified atmosphere package for a mixed vegetable salad consisting of 75 g of cut carrot, 55 g of cut cucumber, 20 g of sliced garlic and 50 g of whole green pepper. Respiration data of all the components were combined with film permeability data to predict package atmospheres and design optimal packages for experimental testing for improved shelf-life of the produce. The optimal package avoided minimum O2 and maximum CO2 tolerance limits, and chilling injury temperatures for any component. A pouch form package made of 27 mm low density polyethylene developed a modified atmosphere of 2.0–2.1% O2 and 5.5–5.7% CO2 , which was beneficial for all components and provided better quality retention than other test packages. 相似文献