全文获取类型
收费全文 | 61823篇 |
免费 | 5463篇 |
国内免费 | 3040篇 |
学科分类
工业技术 | 70326篇 |
出版年
2024年 | 312篇 |
2023年 | 1085篇 |
2022年 | 1750篇 |
2021年 | 2556篇 |
2020年 | 1827篇 |
2019年 | 1520篇 |
2018年 | 1729篇 |
2017年 | 1921篇 |
2016年 | 1707篇 |
2015年 | 2335篇 |
2014年 | 2821篇 |
2013年 | 3474篇 |
2012年 | 3739篇 |
2011年 | 3984篇 |
2010年 | 3607篇 |
2009年 | 3342篇 |
2008年 | 3463篇 |
2007年 | 3320篇 |
2006年 | 3342篇 |
2005年 | 2853篇 |
2004年 | 1999篇 |
2003年 | 1805篇 |
2002年 | 1922篇 |
2001年 | 1696篇 |
2000年 | 1463篇 |
1999年 | 1626篇 |
1998年 | 1896篇 |
1997年 | 1466篇 |
1996年 | 1272篇 |
1995年 | 944篇 |
1994年 | 789篇 |
1993年 | 601篇 |
1992年 | 454篇 |
1991年 | 350篇 |
1990年 | 232篇 |
1989年 | 210篇 |
1988年 | 193篇 |
1987年 | 125篇 |
1986年 | 89篇 |
1985年 | 81篇 |
1984年 | 36篇 |
1983年 | 27篇 |
1982年 | 43篇 |
1981年 | 30篇 |
1980年 | 42篇 |
1979年 | 8篇 |
1977年 | 70篇 |
1976年 | 143篇 |
1955年 | 5篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
3.
总结了住宅设计的发展,概括了住宅各个功能区的特点。通过设计的实例说明了各不同功能区的设计,成果可供进一步的研究参考。 相似文献
4.
电信企业信息化的实质就是赋予电信企业精细化的企业资源整合能力,本以此认识为出发点,通过定义基本的信息化业务元素,需求参数和基本信息处理机制,构建出带有行业共性的电信企业信息化统一模型,该模型针对目前电信企业信息化中常见的和潜在的问题提供了有效的解决措施。 相似文献
5.
6.
阴,阳离子聚合物地层内凝胶化改善水驱效果的研究 总被引:9,自引:1,他引:8
研究了一杆阴离子聚合物(Ac530)和一种阳离子聚合物(Mb581)在水溶液中形成凝胶的条件和过程、凝胶化学结构、形态、稳定性和力学性能。在模拟地层的二维微观模型内观测了两种聚合物驱替渗流、相逼、形成凝胶、凝胶封堵大孔道的机理。在亲水填砂模型内测定了阴、阳离子聚合物凝胶体系降低渗透率的能力。 相似文献
7.
8.
本文就利用诸如蛋白石这样的疏松多孔矿料同灰土构成的混合料,在路面结构中表现出的独特有效的抗冻作用机理作了深入分析,并结合足尺试验数据加以验证。阐述了所谓多孔板体结构的概念、机制和材料组成要求。 相似文献
9.
10.
BACKGROUND: The enterococci have become important nosocomial pathogens. They can cause multiple site infections and enterococcal bacteremia becomes more frequently associated with a high mortality rate. Previous studies of enterococcal bacteremia showed a variety of results. To establish the significance and importance of enterococci as nosocomial pathogens in this hospital, to characterize their clinical pictures and to search for the risk factors for mortality, this retrospective study was performed. METHODS: There were 208 cases of enterococcal bacteremia which occurred from 1988 to 1992. Twenty-seven cases had no medical charts, dismissing possibility of evaluation. Finally, 181 cases of enterococcal bacteremia were analysed. RESULTS: One hundred and eighteen episodes were nosocomial infections. Polymicrobial bacteremia occurred in 68.5% of the patients and the most common co-isolate was Pseudomonas aeruginosa. Those patients (78.5%) with underlying diseases and malignancies were the most common underlying problems. The portal of entry could be found in 69.6 percent of patients, with the gastrointestinal tract the most common sources. Antimicrobial susceptibility testing showed high gentamicin resistance rate (89.5%), and ampicillin still had about 80 percent sensitivity rate. The group who received specific antibiotic therapy for enterococcus showed lower mortality (36.4% versus 47.6%). Only one case had infective endocarditis. Forty-nine patients suffered from septic shock, the cause of 30 deaths. Totally 75 patients died during hospitalization. Besides sepsis, another major cause of death was their underlying diseases itself. CONCLUSIONS: Enterococci have no doubt become important nosocomial pathogens and enterococcal bacteremia were associated with high mortality, especially in elderly patients with underlying diseases such as malignancy or diabetes. When clinically dealing with sepsis from the gastrointestinal or biliary tract, especially when previous cephalosporins therapy showed no response, the possibility of enterococcal bacteremia should always be considered. 相似文献