全文获取类型
收费全文 | 31069篇 |
免费 | 3353篇 |
国内免费 | 1964篇 |
专业分类
电工技术 | 2405篇 |
技术理论 | 1篇 |
综合类 | 2439篇 |
化学工业 | 4541篇 |
金属工艺 | 1852篇 |
机械仪表 | 2050篇 |
建筑科学 | 2756篇 |
矿业工程 | 901篇 |
能源动力 | 873篇 |
轻工业 | 2163篇 |
水利工程 | 750篇 |
石油天然气 | 1527篇 |
武器工业 | 360篇 |
无线电 | 3899篇 |
一般工业技术 | 3541篇 |
冶金工业 | 1313篇 |
原子能技术 | 450篇 |
自动化技术 | 4565篇 |
出版年
2024年 | 138篇 |
2023年 | 546篇 |
2022年 | 1075篇 |
2021年 | 1582篇 |
2020年 | 1125篇 |
2019年 | 929篇 |
2018年 | 1048篇 |
2017年 | 1066篇 |
2016年 | 904篇 |
2015年 | 1375篇 |
2014年 | 1696篇 |
2013年 | 1912篇 |
2012年 | 2190篇 |
2011年 | 2357篇 |
2010年 | 2250篇 |
2009年 | 1968篇 |
2008年 | 1923篇 |
2007年 | 1828篇 |
2006年 | 1677篇 |
2005年 | 1395篇 |
2004年 | 1033篇 |
2003年 | 1052篇 |
2002年 | 1160篇 |
2001年 | 1037篇 |
2000年 | 745篇 |
1999年 | 582篇 |
1998年 | 385篇 |
1997年 | 299篇 |
1996年 | 238篇 |
1995年 | 203篇 |
1994年 | 158篇 |
1993年 | 141篇 |
1992年 | 99篇 |
1991年 | 53篇 |
1990年 | 46篇 |
1989年 | 47篇 |
1988年 | 33篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1959年 | 6篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
51.
52.
均匀设计法在烷基糖苷合成中的应用 总被引:2,自引:0,他引:2
在烷基糖苷的合成反应中,影响糖苷得率的因素很多,且各因素之间又存在着相互牵制作用。为了探索合成的最佳条件,我们采用了均匀实验设计法。实验证明:它特别适用于多因素多水平的实验设计,同时减少了实验的次数,降低了实验的费用,提高了工作效率。 相似文献
53.
Y. Xiang Y. B. Zhao G. W. Wei 《International journal for numerical methods in engineering》2002,55(8):947-971
Part 2 of this series of two papers presents the applications of the discrete singular convolution (DSC) algorithm. The main purpose of this paper is to explore the utility, test the accuracy and examine the convergence of the proposed approach for the vibration analysis of rectangular plates with internal supports. Both partial internal line supports and complex internal supports are considered for 21 square plates of various combinations of edge support conditions. The effects of different size, shape and topology of the internal supports and different boundary conditions on the vibration response of plates are investigated. The partial internal line supports may vary from a central point support to a full range of cross or diagonal line supports. Several closed‐loop supports, such as ring, square and rhombus, and their combinations are studied for complex internal supports. Convergence and comparison studies are carried out to establish the correctness and accuracy of the DSC algorithm. The DSC results are compared with those in the available literature obtained by using other methods. Numerical results indicate that the DSC algorithm exhibits controllable accuracy for plate analysis and shows excellent flexibility in handling complex geometries, boundary conditions and support conditions. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
54.
55.
煤层物性测井评价方法初探 总被引:6,自引:1,他引:5
依据煤岩的赋存方式和结构特点,利用电阻率和井径测井资料在不同煤质结构的煤层所表现的差异性,建立了2个指标(即深侧向电阻率与微球电阻率之间的比值,井径与钻头之间的比值)对煤质结构进行了准确的识别。用多元回归的概率模型建立了煤岩镜质反射率的测井计算模式,其结果与已有的煤心分析数据对比,两者具有较好的一致性。在综合分析的基础上,对煤层的重要物性参数煤阶、煤质结构进行了测井评价。 相似文献
56.
Xiang‐Dan Li Zhen‐Xin Zhong Sang‐Hoon Han Seung Hee Lee Myong‐Hoon Lee 《Polymer International》2005,54(2):406-411
From chloromethylated polyimide, a useful starting material for modification of aromatic polyimides, a thermocurable transparent polyimide having acrylate side groups was prepared. In the presence of 1,8‐diazabicyclo[5,4,0]undec‐7‐ene, chloromethylated polyimide was esterified with acrylic acid to synthesize poly(imide methylene acrylate). The polymer was soluble in organic solvent, which makes it possible to prepare a planar film by spin coating. The polymer film became insoluble after thermal treatment at 230 °C for 30 min. Optical transparency of the film at 400 nm (for 1 µm thickness) was higher than 98 % and not affected by further heating at 230 °C for 250 min. Adhesion properties measured by the ASTM D3359‐B method ranged from 4B to 5B. Preliminary results of planarization testing showed a high degree of planarization (DOP) value (>0.53). These properties demonstrate that poly(imide methylene acrylate) could be utilized as a thermocurable transparent material in fabricating display devices such as TFT‐LCD. Copyright © 2004 Society of Chemical Industry 相似文献
57.
Aimin Xiang Zhongjie Du Qinghua Zeng Chen Zhang Hangquan Li 《Polymer International》2005,54(10):1366-1370
This paper presents recent efforts on the preparation of flexible polyhedral particles via concentrated emulsion templating polymerization in which the hydrophilic monomer (acrylamide) and hydrophobic monomer (butyl acrylate) are polymerized simultaneously in the continuous and dispersed phase, respectively. Such templating polymerization has been enhanced in our systems owing to the introduction of acrylamide monomer and their higher polymerization rate in continuous phase as compared with butyl acrylate in dispersed phase. Diffusion between the different phases was also inhibited. Furthermore, the stability of the concentrated emulsion and the molecular weight of the produced poly(butyl acrylate) were found to be significantly affected by the amount of redox initiator. The morphology of the particles could be controlled by varying the volume fraction of the dispersed phase and the polyhedral particles were achieved at higher volume fraction. Copyright © 2005 Society of Chemical Industry 相似文献
58.
A block‐oriented approximate feedback linearization for control of a pneumatic cylinder positioning system is introduced and a rather detailed discussion is presented on the uncertain linearization residual characterization. It is shown that making use of the characterized gain–phase information of the linearized system leads to a more reasonable trade‐off between performance and stability in the QFT control design and thus results in high control performance. Simulation and experimental results are shown. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
59.
In this paper, a methodology is developed to use data acquisition derived from condition monitoring and standard diagnosis for rehabilitation purposes of transformers. The interpretation and understanding of the test data are obtained from international test standards to determine the current condition of transformers. In an attempt to ascertain monitoring priorities, the effective test methods are selected for transformer diagnosis. In particular, the standardization of diagnostic and analytical techniques are being improved that will enable field personnel to more easily use the test results and will reduce the need for interpretation by experts. In addition, the advanced method has the potential to reduce the time greatly and increase the accuracy of diagnostics. The important aim of the standardization is to develop the multiple diagnostic models that combine results from the different tests and give an overall assessment of reliability and maintenance for transformers. 相似文献
60.
研究了用固体润滑石墨、碳化硅、二硫化钼等填料改性的聚苯硫醚 (PPS)涂层的耐磨性能。实验结果表明 ,聚苯硫醚复合涂层具有优良的耐磨性 ;加入适量 ( 3 0 % )的石墨、碳化硅等固体润滑剂 (石墨 :碳化硅 =2∶3 ) ,可以有效提高涂层的耐磨性能 ,而二硫化钼和三氧化二铬的减摩效果更佳 相似文献