全文获取类型
收费全文 | 8032篇 |
免费 | 630篇 |
国内免费 | 233篇 |
专业分类
电工技术 | 439篇 |
技术理论 | 1篇 |
综合类 | 541篇 |
化学工业 | 1358篇 |
金属工艺 | 326篇 |
机械仪表 | 435篇 |
建筑科学 | 536篇 |
矿业工程 | 216篇 |
能源动力 | 215篇 |
轻工业 | 724篇 |
水利工程 | 140篇 |
石油天然气 | 490篇 |
武器工业 | 73篇 |
无线电 | 713篇 |
一般工业技术 | 946篇 |
冶金工业 | 715篇 |
原子能技术 | 57篇 |
自动化技术 | 970篇 |
出版年
2024年 | 25篇 |
2023年 | 111篇 |
2022年 | 197篇 |
2021年 | 292篇 |
2020年 | 209篇 |
2019年 | 193篇 |
2018年 | 246篇 |
2017年 | 260篇 |
2016年 | 242篇 |
2015年 | 291篇 |
2014年 | 396篇 |
2013年 | 505篇 |
2012年 | 502篇 |
2011年 | 557篇 |
2010年 | 456篇 |
2009年 | 420篇 |
2008年 | 433篇 |
2007年 | 409篇 |
2006年 | 447篇 |
2005年 | 320篇 |
2004年 | 238篇 |
2003年 | 224篇 |
2002年 | 200篇 |
2001年 | 214篇 |
2000年 | 182篇 |
1999年 | 199篇 |
1998年 | 271篇 |
1997年 | 197篇 |
1996年 | 135篇 |
1995年 | 114篇 |
1994年 | 99篇 |
1993年 | 78篇 |
1992年 | 44篇 |
1991年 | 33篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 2篇 |
1974年 | 3篇 |
排序方式: 共有8895条查询结果,搜索用时 15 毫秒
101.
102.
The different melting temperatures of N‐methyl morpholine N‐oxide (NMMO) hydrates in the cellulose–NMMO hydrate solution may be explained by the rather different crystal structures of NMMO hydrates, which are determined by the amount of the hydrates. The preparative process of cellulose–NMMO hydrate solution may result in cellulose structural change from cellulose I to cellulose II, depending on the amount of the hydrate. Mixtures of cellulose and NMMO hydrate in a blender was changed from the granules to slurry with increasing mixing time at 60–70°C, which is below the melting point of the NMMO hydrate. In the case of 15 wt % cellulose–NMMO hydrate granules, which were made by mixing for 20 min, the melting points of various NMMO hydrates were obtained as 77.8°C (n = 0.83), 70.2°C (n = 0.97), and 69.7°C (n = 1.23), respectively, depending on the hydrate number. However, the melting points of cellulose–NMMO hydrate slurry and solution were shifted lower than those of cellulose granules, while the mixing time of slurry and solution are 25 and 35 min, respectively. These melting behaviors indicate instantaneous liquefaction of the NMMO hydrate and the diffusion of the NMMO hydrate into cellulose during mixing in a blender. When cellulose was completely dissolved in NMMO hydrate, the crystal structure of cellulose showed only cellulose II structure. In the cellulose–NMMO products of granules or slurry obtained by high‐speed mixing, which is a new preparation method, they still retained the original cellulose I structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1687–1697, 2004 相似文献
103.
Fabrication and characterization of PFSI/ePTFE composite proton exchange membranes of polymer electrolyte fuel cells 总被引:1,自引:0,他引:1
PFSI/ePTFE composite proton exchange membranes were fabricated by impregnating perfluorosulfonic acid resin (PFSI resin, Nafion) into chemically modified expanded PTFE (ePTFE) matrix. Chemical modification of sodium-naphthalene treatment and N-methylol acrylamide (NMA) grafting decreased the contact angle of the as-received ePTFE from 125 ± 0.5° to 67 ± 0.5°, effectively converting the as-received hydrophobic ePTFE to a hydrophilic ePTFE matrix. The composite membrane fabricated with the hydrophilic ePTFE have higher impregnated PFSI loading, much lower porosity and better PTFE/PFSI interface contact, as compared to the composite membranes with the as-received ePTFE. This leads to much lower gas permeability and significantly improves the durability under an accelerated dry/wet cycle test. The fuel cell made from the PFSI/ePTFE composite membranes with hydrophilic ePTFE showed superior performance as compared to that with the composite membrane made from the as-received ePTFE and Nafion 211 membrane. 相似文献
104.
灭多威在棉花及土壤中降解动态及残留量研究 总被引:6,自引:0,他引:6
按生产上常规用量,每亩喷施20%灭多威乳油60毫升防治二代棉铃虫,施药后7天在棉叶上及14天在土壤中其降解率分别为98.81%及88.09%;半衰期分别的1.56天及4.98天。防治二、三、四代棉铃虫,按有效剂量施药6次,有效成分72克/亩,棉籽和土壤中的最大残留量分别为0.023及0.084微克/克;再加大50%用量,有效成分108克/亩,最大残留量仅为0.034及0.214微克/克。结果表明,灭多威在棉叶上及土壤中降解较迅速,常规用量下,对棉籽及土壤污染较轻。 相似文献
105.
106.
果酸脂质体的制备、检测及应用 总被引:3,自引:0,他引:3
以大豆卵磷脂为包封材料 ,用反相蒸发法制备果酸脂质体。并用透射电子显微镜表征了其形态结构 ,证实其直径在1 0 0纳米~ 2 0 0纳米之间。研究了果酸浓度对包封率 ,稳定剂浓度对脂质体稳定性的影响。结果表明 ,果酸浓度为 0 .3mg/ml时可以得到较好的包封率 ,丙二醇的适宜浓度是 5 % -1 5 % ,最终将脂质体应用于化妆品中 ,并证明是可行的 相似文献
107.
研究了硫调型氯丁橡胶乳液聚合中转化率对产晶结构与性能的影响.结果表明,随单体转化率的提高,聚合物的凝胶量及其交联密度增大,致使断链速度减慢,所得断链胶的门尼粘度上升,残存凝胶量增加,分子支化程度增大,分子量分布变宽,焦烧时间缩短。而相应硫化胶的拉伸强度、撕裂强度、冲击弹性和硬度等提高,扯断伸长率和永久变形下降。这些变化一般在转化率为80——85%时有明显转折.综合考虑产量与质量,聚合转化率控制在82±2%较为适宜。 相似文献
108.
The present work investigates the relationships between the microstructural state and fracture properties in commercial polypropylene‐based materials. In this case an isopolypropylene homopolymer and three ethylene propylene block copolymers (EPBC) with different ethylene content (EC) have been studied. A variety of morphologies were obtained by a combination of several processing methods (injection molding, injection molding‐annealing, and compression molding) and thickness. Fracture behavior of deeply double‐edged notched specimens was evaluated by scanning electron microscopy (SEM) and by the essential work of fracture (EWF) method, analyzing the influence of processing, thickness (t), EC, and orientation respect to melt flow direction (MD and TD). The testing direction and EC are the most relevant variables that affect the ability of the crack tip to deform plastically during the crack propagation, determining the final fracture behavior. The fracture parameters obtained with the EWF method, specific EWF, we, and plastic item, βwp, have proved to be very sensitive to the processing induced morphology, finding interesting relationships between such morphologies (characterized by crystallinity index, orientation level, and skin/core ratio) and the fracture parameters of the plaques. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2714–2724, 2006 相似文献
109.
针对目前测量分析、弱信号检测的需求,以STM32F107和AD9958为核心实现了一种高分辨率幅度、频率、相位的双路信号源。首先对直接数字合成(Direct Digital Synthesis,DDS)工作原理进行介绍,重点分析了杂散的主要来源,并设计LC椭圆低通滤波器对杂散进行抑制。设计输出电路使信号源满足低频需求,并可直接用于驱动负载。最后采用STM32F107和VC6.0搭建了配置平台,对信号源波形灵活控制。 相似文献
110.
木又青 《网络安全技术与应用》2014,(9):213-213
当今社会疗养院建设快速推进,疗养院卫生信息化发展极为迅速.那么疗养院怎样根据自身情况,提高疗养院整体管理水平、规范各项医疗工作,已成为一个迫切需要解决的问题.这就要求疗养院必须提高自己的自身信息化建设水平,必须跟上社会卫生信息化建设步伐.本文对疗养院信息化建设的基本情况、遇到的主要问题及其今后发展的趋势进行了探讨.以促进疗养院信息化建设迅速健康的发展. 相似文献