全文获取类型
收费全文 | 132365篇 |
免费 | 12901篇 |
国内免费 | 7597篇 |
专业分类
电工技术 | 9278篇 |
技术理论 | 11篇 |
综合类 | 9860篇 |
化学工业 | 20234篇 |
金属工艺 | 7996篇 |
机械仪表 | 8719篇 |
建筑科学 | 10728篇 |
矿业工程 | 4708篇 |
能源动力 | 4064篇 |
轻工业 | 8766篇 |
水利工程 | 2840篇 |
石油天然气 | 7841篇 |
武器工业 | 1369篇 |
无线电 | 15553篇 |
一般工业技术 | 14204篇 |
冶金工业 | 6001篇 |
原子能技术 | 1710篇 |
自动化技术 | 18981篇 |
出版年
2024年 | 697篇 |
2023年 | 2338篇 |
2022年 | 4518篇 |
2021年 | 6380篇 |
2020年 | 4789篇 |
2019年 | 3829篇 |
2018年 | 4257篇 |
2017年 | 4760篇 |
2016年 | 4175篇 |
2015年 | 6005篇 |
2014年 | 7559篇 |
2013年 | 8729篇 |
2012年 | 9917篇 |
2011年 | 10425篇 |
2010年 | 9410篇 |
2009年 | 8574篇 |
2008年 | 8259篇 |
2007年 | 7663篇 |
2006年 | 6977篇 |
2005年 | 5793篇 |
2004年 | 4005篇 |
2003年 | 3441篇 |
2002年 | 3637篇 |
2001年 | 2952篇 |
2000年 | 2357篇 |
1999年 | 2357篇 |
1998年 | 1664篇 |
1997年 | 1421篇 |
1996年 | 1418篇 |
1995年 | 1108篇 |
1994年 | 842篇 |
1993年 | 610篇 |
1992年 | 466篇 |
1991年 | 366篇 |
1990年 | 267篇 |
1989年 | 212篇 |
1988年 | 200篇 |
1987年 | 113篇 |
1986年 | 90篇 |
1985年 | 46篇 |
1984年 | 49篇 |
1983年 | 30篇 |
1982年 | 36篇 |
1981年 | 24篇 |
1980年 | 42篇 |
1979年 | 20篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1959年 | 14篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
利用高酸值餐饮废油脂制备生物柴油 总被引:8,自引:0,他引:8
以高酸值餐饮废油脂为原料,在酯化反应后再经两步酯交换反应制备生物柴油。在酯化反应中添加吸水剂可降低油脂的酸值,经一次酯化反应即可将油脂的酸值降至2m g/g左右,满足酯交换反应的要求。考察了酯化反应中吸水剂的添加方式、种类及其用量对酯化反应的影响,以及酯交换催化剂的种类及用量对脂肪酸甲酯(FAME)收率和产物组成的影响。实验结果表明,以凹凸棒土为吸水剂(用量为餐饮废油脂中游离脂肪酸质量的3%),且在酯化反应30m in时加入,酯化效果较好;以质量比为1∶1的NaOH和KOH混合物为催化剂进行两步酯交换反应时,催化剂的最佳用量依次为1.00%和0.75%(质量分数,基于油脂的质量),FAME收率最高达到96.33%。 相似文献
103.
To reduce the receiver complexity of the space-time bit-interleaved coded modulation (ST-BICM) scheme, this letter describes a turbo-type iterative structure consisting of a modified Gaussian approximation (MGA) detector and an a posteriori probability (APP) decoder. Utilizing the characteristics of the interleaving and the central limited theoretic, the MGA detector first assumes the superposition of the transmitted signals as a Gaussian random variable. Then, P most significant signal combinations are identified to calculate the log-likelihood ratio of each bit. Without any pre-process on the received signals, the proposed method is free of matrix inverse operation and can be applied in systems with more transmit antennas than receive antennas. Furthermore, the performance of the MGA approaches that of the optimal detection 相似文献
104.
105.
一种改进的共同进化遗传算法及其应用 总被引:2,自引:0,他引:2
将共同进化遗传算法应用于临床营养决策优化中,虽然取得了一定成果,但算法中仍存在早熟现象、局部搜索能量弱等问题,为此提出一种改进的共同进化模型。算法使用新的子群体划分方法和交叉算子,引入精英保留策略、信息交换原则和小生境技术。通过对糖尿病营养治疗的仿真表明,改进后的算法在保证群体多样性和避免早熟现象的前提下,提高了算法的局部和全局寻优能力,且膳食配方中营养素达标率符合要求,满足专家建议的糖尿病饮食需求。 相似文献
106.
107.
Transient performance study of a brushless doubly fed twin stator induction generator 总被引:2,自引:0,他引:2
This paper presents theoretical, simulation, and experimental study of the brushless doubly fed twin stator induction generator (BDFTSIG) dynamics under vector control based on the orientation on the power machine stator flux. A complex transfer function is derived which links the control current and power winding current space vectors in the field coordinates. Based on this result, the transient response of the BDFTSIG to step changes in the control current is examined theoretically. The oscillatory transients are explained in detail and linked to control flux transients triggered whenever operation point of the generator is changed. Furthermore, BDFTSIG operation with closed loop control of the power machine active and reactive powers is examined theoretically and experimentally. It is shown that in the closed loop operation, the system damping may be reduced so that the PI controller gains must be properly selected to achieve a good transient response. 相似文献
108.
For the purpose of remediation of soils polluted by heavy metals, the use of some strong synthetic chelating agents such as ethylenediaminetetraacetic acid (EDTA) has been proposed. However, EDTA would not be considered as the preferential choice for the remediation of soil polluted with heavy metals like copper because of its nonbiodegradability and permanent residence in the natural environment. In the present work, some novel environmentally benign chelating agents, glucosamine hydrochloride, chito-oligosaccharide and
-asparaginic-N,N-diacetic acid (ASDA) were screened to find alternatives to EDTA by investigating the elution of copper from vermiculite with these reagents and comparing their effectiveness with EDTA. The effects of suspension contact time, reagent concentration and equilibrium pH of the solution on the removal of copper were examined. A stoichiometric amount of EDTA can quantitatively remove copper in both acidic and neutral conditions. Chito-oligosaccharide was a slightly less-effective reagent under acidic conditions compared to EDTA, and an amount well in excess of stoichiometry is required to achieve the maximum removal of copper from vermiculite. Glucosamine hydrochloride shows a relatively weak ability for the liberation of copper. The elution behavior of ASDA was equivalent to EDTA in acidic and neutral media. It was concluded that ASDA is the best substitute for EDTA because of its similar high complexing ability and superior biodegradability. 相似文献
109.
Haiquan Guo Shiquan Tao 《IEEE sensors journal》2007,7(3):323-328
Palladium-doped silica nanocomposites were synthesized via a sol-gel technique combined with a template of Triton X-100 micelle. The freshly prepared sol sample of Pd-doped silica nanocomposites was investigated by TEM. Determined from the TEM image, the sizes of the Pd nanoparticles are narrowly distributed, which are around 30 nm in diameter. The prepared sol solution of the sample was injected into a Tygon Microbore Autoanalysis tubing. After 14 days gelatinization, a transparent porous optical fiber was obtained. The response of the fiber to hydrogen gas was tested by using a fiber-optic spectrometric method. The palladium-doped silica nanocomposite fiber is sensitive upon exposure to hydrogen gas and the response is reversible. This palladium-doped silica nanocomposite fiber can be applied as a new kind of hydrogen gas sensor 相似文献
110.
根据生产实践 ,结合PLC的技术特点和 385m2 凯利式叶滤机的电气联锁特性 ,阐述了应用PLC技术 ,可进一步提高 385m2 凯利式叶滤机的运转率和自动化水平。 相似文献