全文获取类型
收费全文 | 41459篇 |
免费 | 5297篇 |
国内免费 | 2603篇 |
专业分类
电工技术 | 3689篇 |
技术理论 | 4篇 |
综合类 | 3103篇 |
化学工业 | 6138篇 |
金属工艺 | 2407篇 |
机械仪表 | 2933篇 |
建筑科学 | 3020篇 |
矿业工程 | 1649篇 |
能源动力 | 1193篇 |
轻工业 | 3468篇 |
水利工程 | 1151篇 |
石油天然气 | 1904篇 |
武器工业 | 514篇 |
无线电 | 5069篇 |
一般工业技术 | 4632篇 |
冶金工业 | 1953篇 |
原子能技术 | 535篇 |
自动化技术 | 5997篇 |
出版年
2024年 | 287篇 |
2023年 | 940篇 |
2022年 | 2011篇 |
2021年 | 2614篇 |
2020年 | 1985篇 |
2019年 | 1466篇 |
2018年 | 1668篇 |
2017年 | 1975篇 |
2016年 | 1670篇 |
2015年 | 2408篇 |
2014年 | 2880篇 |
2013年 | 3223篇 |
2012年 | 3599篇 |
2011年 | 3575篇 |
2010年 | 2983篇 |
2009年 | 2563篇 |
2008年 | 2487篇 |
2007年 | 2148篇 |
2006年 | 1706篇 |
2005年 | 1353篇 |
2004年 | 937篇 |
2003年 | 751篇 |
2002年 | 716篇 |
2001年 | 615篇 |
2000年 | 493篇 |
1999年 | 396篇 |
1998年 | 336篇 |
1997年 | 294篇 |
1996年 | 261篇 |
1995年 | 208篇 |
1994年 | 179篇 |
1993年 | 119篇 |
1992年 | 112篇 |
1991年 | 69篇 |
1990年 | 53篇 |
1989年 | 55篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1973年 | 5篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Synthesis of Dimethyl Carbonate from Methanol and Carbon dioxide using Potassium Methoxide as Catalyst under Mild Conditions 总被引:2,自引:0,他引:2
Pd-supported on WO3–ZrO2 (W/Zr atomic ratio=0.2) calcined at 1073 K was found to be highly active and selective for gas-phase oxidation of ethylene to acetic acid in the presence of water at 423 K and 0.6 MPa. Contact time dependence demonstrated that acetic acid is formed via acetaldehyde formed by a Wacker-type reaction, not through ethanol by hydration of ethylene. 相似文献
102.
Min Zhou Dezheng Wang Xianchun Liu Ning Xiang Xiexian Guo Runsheng Zhai 《Catalysis Letters》1989,3(1):37-47
TPD/Exchange from CO/Re(001) in a gas ambience showed that the absolute rate of desorption depends on the gas pressure and has a first plus second order rate law. It is proposed that desorption is a two step process from the adsorbed state to a stable intermediate which is itself weakly adsorbed. 相似文献
103.
和田菟丝子在不同寄主中有效成分含量的测定研究 总被引:1,自引:0,他引:1
采用高效液相色谱法(HPLC)对和田菟丝子中槲皮素和山萘酚进行了定量测定。测定寄主为胡麻植物的菟丝子中槲皮素含量为0 239 mg·g-1,山萘酚的含量为0 347 mg·g-1 ;寄主为苜蓿的菟丝子中槲皮素含量为0 103 mg·g-1,山萘酚的含量为0 068 mg·g-1。和田菟丝子寄主不同,其槲皮素和山萘酚的含量不同,应结合寄主植物研究其有效成分。 相似文献
104.
通过n-乙酰化保护氨基,氯磺酸与氨水反应在氨基对位形成磺酰胺阻塞基团,再经脱乙酰基,氯化,水解脱阻塞基团,合成2,6-二氯-3-甲基苯胺得到目标产物。与经典文献方法相比,用盐酸代替氢氧化钠脱除乙酰基,用氯酸钠和浓盐酸代替双氧水和浓盐酸或氯气的氯化方法,合成过程中省略了中间产物的分离步骤,以间甲苯胺计总摩尔收率从20%提高到了60.8%,产品纯度大于99.5%。 相似文献
105.
A new design of the liquid crystal lenticular (LCL) lens array with interlaced electrodes is proposed to realize an auto-stereoscopic 3D display. The structure of interlaced electrodes aims to generate a desired non-uniform electric filed to improve the focusing ability of the LCL-lens array with lower voltage drives. This paper is organized as first to describe the design criteria of a lenticular lens sheet for wide extended graphics array LCD panel. Based on the designed lenticular lens array, an LCL-lens array with proposed interlaced electrodes is next designed. The fabrication and the detailed structure are given. A series of experiments are then conducted and successfully verify the focusing capability and desired 3D display functions, that is, to separate two images to right and left eyes. Also, the developed auto-stereoscopic 3D display is able to adapt to varied viewer locations with favorable imaging quality. 相似文献
106.
Jian-Ruei Chen Paul C.-P. Chao Che-Hung Tsai Wei-Dar Chen 《Microsystem Technologies》2014,20(8-9):1583-1595
A new image acquisition system module for extracting signals of high-resolution short wave infrared (SWIR) from a focal plane array (FPA) is presented in this study. The short wave infrared (SWIR—with wavelength about 900–1,700 nm) images have been proven its unique values in many applications such as military, semiconductor inspection and aviation security. The designs for the SWIR data acquisition system module consists of digitization and acquisition of FPA signals, design of synchronous dynamic random access memory controller and real-time image signal transformation and display. Three major steps involved towards a successful SWIR module—(1) Selection of hardware ICs according to specification for the FPA; (2) Design of a timing generator for the image acquisition system to control FPA and other ICs by Verilog HDL programming; (3) Integrate the individual modules on a PCB. The SWIR image output signals are successfully generated in the format of National Television System Committee (NSTC), which can be displayed on a common NTSC monitor, flat panel displays with an AV input terminal or a CRT display in a favorable speed of frame rate at 30 per second. 相似文献
107.
108.
Jia Bing Dai Xing Yuan Zhang Jing Chao Chen Yan Bai 《Journal of Coatings Technology and Research》2007,4(3):283-288
A novel core–shell type fluorinated acrylic and siliconated polyurethane (FSiPUA) hybrid emulsion was prepared by seeded emulsion
polymerization using siliconated polyurethane (SiPU) as a seed and forming the structure with SiPU as a shell and the copolymer
of butyl acrylate (BA) with 2,2,2-trifluoroethylmethacrylate (TFEMA) as a core. SiPU was synthesized using isophorone diisocyanate
(IPDI), polytetramethylene ether glycol (PTMG), polypropylene glycol (PPG), dihydroxybutyl-terminated polydimethylsiloxane
(PDMS), dimethylol propionic acid (DMPA), 1,6-hexanediol (HDO) and triethylamine (TEA). The contents of siloxane and fluorine
were determined according to the feed ratio. Fourier transform infrared spectroscopy (FTIR) was used to identify the chain
structure of SiPU and FSiPUA. Investigation of transmission electron microscopy (TEM) confirmed the core–shell structure of
FSiPUA emulsion and gave the particle size at about 50 nm. The measurement results of water contact angles and the solvent
absorptions in water and n-octane for cured films showed that the water and the oil repellency for FSiPUA had been improved significantly with a suitable
content of fluorine and siloxane. 相似文献
109.
Solutions of rare earth modifier (RES) and epoxy chloropropane (ECP) grafting modification method were used for the surface treatment of aramid fiber. Tensile properties of both the aramid/epoxy composites and single fibers were tested. The effects of RES concentration on tensile properties of aramid/epoxy composites were investigated in detail to explore an optimum amount of rare earth elements in solution for modifying aramid fiber. The fracture surface morphologies of tensile specimens were observed and analyzed with the aid of SEM. The experimental results show that rare earth treatment is superior to ECP grafting treatment in promoting interfacial adhesion between the aramid fiber and epoxy matrix. Meanwhile, the tensile strengths of single fibers were almost not affected by RES treatment. The optimum performance is obtained when the content of rare earth elements is 0.5 wt %. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1037–1041, 2004 相似文献
110.
In this paper, we will extend the strict maximum principle preserving flux limiting technique developed for one dimensional scalar hyperbolic conservation laws to the two-dimensional scalar problems. The parametrized flux limiters and their determination from decoupling maximum principle preserving constraint is presented in a compact way for two-dimensional problems. With the compact fashion that the decoupling is carried out, the technique can be easily applied to high order finite difference and finite volume schemes for multi-dimensional scalar hyperbolic problems. For the two-dimensional problem, the successively defined flux limiters are developed for the multi-stage total-variation-diminishing Runge–Kutta time-discretization to improve the efficiency of computation. The high order schemes with successive flux limiters provide high order approximation and maintain strict maximum principle with mild Courant-Friedrichs-Lewy constraint. Two dimensional numerical evidence is given to demonstrate the capability of the proposed approach. 相似文献