全文获取类型
收费全文 | 80854篇 |
免费 | 8029篇 |
国内免费 | 4450篇 |
专业分类
电工技术 | 5125篇 |
技术理论 | 5篇 |
综合类 | 5774篇 |
化学工业 | 12719篇 |
金属工艺 | 4741篇 |
机械仪表 | 5312篇 |
建筑科学 | 6271篇 |
矿业工程 | 2476篇 |
能源动力 | 2469篇 |
轻工业 | 6387篇 |
水利工程 | 1854篇 |
石油天然气 | 3967篇 |
武器工业 | 821篇 |
无线电 | 9511篇 |
一般工业技术 | 9485篇 |
冶金工业 | 3598篇 |
原子能技术 | 1166篇 |
自动化技术 | 11652篇 |
出版年
2024年 | 407篇 |
2023年 | 1354篇 |
2022年 | 2519篇 |
2021年 | 3468篇 |
2020年 | 2671篇 |
2019年 | 2276篇 |
2018年 | 2596篇 |
2017年 | 2772篇 |
2016年 | 2624篇 |
2015年 | 3450篇 |
2014年 | 4271篇 |
2013年 | 5156篇 |
2012年 | 5842篇 |
2011年 | 6013篇 |
2010年 | 5434篇 |
2009年 | 5270篇 |
2008年 | 4984篇 |
2007年 | 4770篇 |
2006年 | 4402篇 |
2005年 | 3645篇 |
2004年 | 2802篇 |
2003年 | 2602篇 |
2002年 | 2759篇 |
2001年 | 2442篇 |
2000年 | 1752篇 |
1999年 | 1546篇 |
1998年 | 1040篇 |
1997年 | 846篇 |
1996年 | 777篇 |
1995年 | 667篇 |
1994年 | 474篇 |
1993年 | 384篇 |
1992年 | 323篇 |
1991年 | 225篇 |
1990年 | 172篇 |
1989年 | 133篇 |
1988年 | 117篇 |
1987年 | 67篇 |
1986年 | 69篇 |
1985年 | 37篇 |
1984年 | 34篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1977年 | 10篇 |
1970年 | 7篇 |
1959年 | 8篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
啤酒酵母菌种用液体石蜡技术保藏具有设备简单、操作方便,成活率高,变异少,优良种性能保持较长时间的优点,实用价值高。本文从液体石蜡保藏菌种的机理、保藏效果、保藏等具体技术操作及其使用方法都作了较为详细的介绍,相信能为啤酒菌种的保藏带来较大的好处。 相似文献
23.
24.
A practical resource management method that can significantly reduce cochannel interference (CCI) and improve spectrum utilisation in FH-OFDMA packet-based cellular networks is presented. The proposed method seeks an effective combination of dynamic resource allocation with fractional coding and bit loading to respectively minimise CCI and maximise system throughput for a desired performance. 相似文献
25.
数字图书馆是图书馆发展的主要方向。在我国,数字图书馆建设存在一些问题。探索解决问题的方法和途径,是摆在我们面前的一项任务。 相似文献
26.
Shinsook Yoon Mi-Kyoung Kim In-Young Lee Mikyung Yun Jeong E. Nam Shin 《Journal of Industrial and Engineering Chemistry》2008,14(6):759-764
We have developed a mutant strain derived from Agrobacterium sp. ATCC 31750, which produces a water-soluble polysaccharide having potential utility to the food, feed, pharmaceutical and cosmetic industries. A high concentration of product (15 g/L) is obtained by 48 h cultivation of the mutant strain under optimized fermentation conditions. The water-soluble polysaccharide obtained from cultures of the mutant strain beta82 has Glc:Man:Gal in approximate molar ratios of 5.8:6.7:1.0. The molecular weight of the polysaccharide was determined to be approximately 1000 kDa by HPSEC analysis. Linkage analysis contained 3-Glcp, 3-Manp, terminal Glcp and terminal Manp, as well as a small proportion of 3- and 3,4-Galp, and 4,6-Manp residues. Based on analyses using FT-IR and 13C NMR spectrometers, most glycosidic bonds joining these sugar residues are of the α-type, and acetyl groups are apparently attached to the polymer chain at random. 相似文献
27.
Yun‐Seok Cho Bheong‐Uk Lee Kye‐Heon Oh 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1211-1217
BACKGROUND: Environmental contamination by nitroaromatic compounds such as 2,4,6‐trinitrotoluene (TNT), hexahydro‐1,3,5‐trinitro‐1,3,5‐s‐triazine (RDX), atrazine, and/or simazine (TRAS) generated as waste from military and agricultural activities is a serious worldwide problem. Microbiological treatment of these compounds is an attractive method because many explosives and herbicides are biodegradable and the process can be made cost‐effective. We explored the feasibility of using cultures of Pseudomonas putida HK‐6 for simultaneous degradation of TRAS with the aim of microbial application in wastewater treatment in bench‐scale bioreactors. RESULTS: Experiments were conducted to study the effects of supplemental carbons, nitrogens, and Tween‐80 on the degradation of Ps. putida HK‐6 in media containing TRAS as target substrate(s). The most effective TRAS degradation was shown in the presence of molasses. Addition of nitrogen sources produced a delayed effect for the target substrate(s). Tween‐80 enhanced the degradation of target substrate(s). Simultaneous degradation of these compounds proceeded to completion within the given period. CONCLUSIONS: Ps. putida HK‐6 was capable of growth with TRAS, and the effects of supplements on TRAS degradation and simultaneous TRAS degradation were evaluated in bench‐scale bioreactors. The results of this study have practical applications in the processes of industrial waste stream treatment where the disposal of TRAS may be problematic. Copyright © 2008 Society of Chemical Industry 相似文献
28.
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
29.
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
30.
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