全文获取类型
收费全文 | 81293篇 |
免费 | 7703篇 |
国内免费 | 3972篇 |
专业分类
电工技术 | 5058篇 |
技术理论 | 7篇 |
综合类 | 5727篇 |
化学工业 | 13604篇 |
金属工艺 | 4519篇 |
机械仪表 | 4981篇 |
建筑科学 | 6699篇 |
矿业工程 | 2466篇 |
能源动力 | 2571篇 |
轻工业 | 6084篇 |
水利工程 | 1623篇 |
石油天然气 | 3919篇 |
武器工业 | 759篇 |
无线电 | 9328篇 |
一般工业技术 | 9653篇 |
冶金工业 | 3604篇 |
原子能技术 | 998篇 |
自动化技术 | 11368篇 |
出版年
2024年 | 420篇 |
2023年 | 1560篇 |
2022年 | 2840篇 |
2021年 | 3793篇 |
2020年 | 2887篇 |
2019年 | 2374篇 |
2018年 | 2539篇 |
2017年 | 2968篇 |
2016年 | 2598篇 |
2015年 | 3463篇 |
2014年 | 4218篇 |
2013年 | 5078篇 |
2012年 | 5464篇 |
2011年 | 5638篇 |
2010年 | 5094篇 |
2009年 | 4828篇 |
2008年 | 4620篇 |
2007年 | 4114篇 |
2006年 | 4072篇 |
2005年 | 3464篇 |
2004年 | 2448篇 |
2003年 | 2185篇 |
2002年 | 2311篇 |
2001年 | 2004篇 |
2000年 | 1736篇 |
1999年 | 1824篇 |
1998年 | 1499篇 |
1997年 | 1215篇 |
1996年 | 1208篇 |
1995年 | 945篇 |
1994年 | 817篇 |
1993年 | 592篇 |
1992年 | 489篇 |
1991年 | 384篇 |
1990年 | 274篇 |
1989年 | 238篇 |
1988年 | 179篇 |
1987年 | 127篇 |
1986年 | 96篇 |
1985年 | 66篇 |
1984年 | 57篇 |
1983年 | 40篇 |
1982年 | 33篇 |
1981年 | 29篇 |
1980年 | 32篇 |
1979年 | 22篇 |
1978年 | 9篇 |
1976年 | 12篇 |
1959年 | 8篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
51.
Hoksung Yau Yunpeng Pan Leyuan Shi 《Automation Science and Engineering, IEEE Transactions on》2008,5(2):349-360
This paper addresses the general single-machine earliness-tardiness problem with distinct release dates, due dates, and unit costs. The aim of this research is to obtain an exact nonpreemptive solution in which machine idle time is allowed. In a hybrid approach, we formulate and then solve the problem using dynamic programming (DP), while incorporating techniques from branch-and-bound (BB). This approach (DP-BB) has been proven to be effective in solving certain types of scheduling problems. We further propose a new adaptation of the approach to a general problem with a nonregular objective function. To address some shortcomings of DP-BB, we also apply a BB approach in which partial dynamic programming dominance (BB-PDP) is exploited. Computational experiments were conducted with randomly generated test instances in order to evaluate the effectiveness of the two approaches. The results clearly showed that our new approaches can solve all the instances with up to 40 jobs and most of the instances with 50 jobs, which outperforms those frequently used approaches in scheduling research. 相似文献
52.
Environmentally responsive hydrogels have become attractive research subjects for many applications. In this work, a series of pH‐sensitive and color‐changing nanoparticles (nanogels) with core–shell structures were synthesized. The cores were blue latex particles synthesized by a miniemulsion technique with styrene and methacrylic acid as monomers and Neozapon Blue 807 as a dye. The shell was a pH‐sensitive polymer that was precipitation‐polymerized onto the core from 2‐(diethylamino) ethyl methacrylate with N,N′‐methylenebisacrylamide, poly(propylene glycol) diacrylate, and divinylbenzene as crosslinking agents. In the resultant latexes, the color was observed to change from deep blue to pale blue as the pH of the system was changed from a high of 10 to a low of 3. The synthesized latexes and particles (gels) were then characterized with an ultraviolet–visible spectrometer, dynamic light scattering, Fourier transform infrared, and nuclear magnetic resonance. Atomic force microscopy was also used to investigate the different morphologies of the particles after the synthesized latexes were dried at different pH values. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
53.
We present the synthesis and characterization of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) cylindrical brushes, their pH responsiveness, and the corresponding quaternized analog, poly{[2-(methacryloyloxy)ethyl] trimethylammonium iodide} (PMETAI) brushes. PDMAEMA brushes were prepared by atom transfer radical polymerization (ATRP) using the grafting-from strategy. Initiating efficiencies of the ATRP processes were determined by cleaving the side-chains and gel permeation chromatography (GPC) analysis. Due to the slow initiation and steric hindrance, the initiating efficiency is only around 50%. The PDMAEMA brushes show worm-like structures and pH responsiveness, as proven by dynamic light scattering (DLS), atomic force microscopy (AFM), and cryogenic transmission electron microscopy (cryo-TEM) measurements. Strong cationic polyelectrolyte PMETAI brushes were produced by quaternization of the PDMAEMA brushes. AFM and cryo-TEM images showed similar worm-like morphologies for the PMETAI brushes. The PMETAI brushes collapsed in solution with high concentration of monovalent salt, as proven by DLS and AFM results. 相似文献
54.
Han‐Lang Wu Chen‐Chi M. Ma Chun‐Chieh Lin Yie‐Chan Chiu Chih‐Yuan Chen Chin‐Lung Chiang 《应用聚合物科学杂志》2008,107(5):3236-3243
Poly(arylene ether benzonitrile) (PAEBN) was synthesized with 2,6‐dichlorobenzonitrile and biphenol. PAEBNs with various molecular weights (MWs), 1,640,000 and 185,000 g/mol, were synthesized by control of the stoichiometry of the monomers and were blended with sulfonated poly(ether ether ketone) (SPEEK). The effects of MW on the water uptake, swelling, methanol permeability, and proton conductivity of the SPEEK/PAEBN blend membranes were investigated. The molecular mobility of the SPEEK/PAEBN blends was also examined in this study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
55.
56.
Conventional cancer therapies, the second leading cause of death worldwide, result in serious side effects and, at best, merely extend the patient''s lifespan by a few years. Searching for effective prevention is of high priority in both basic and clinical sciences. In recent decades natural products have been considered to be an important source of cancer chemopreventive agents. Red wine polyphenols, which consisted of various powerful antioxidants such as flavonoids and stilbenes, have been implicated in cancer prevention and that promote human health without recognizable side effects. Since resveratrol, a major component of red wine polyphenols, has been studied and reviewed extensively for its chemopreventive activity to interfere with the multi-stage carcinogenesis, this review focuses on recent progress in studies on cancer chemopreventive activities of red wine polyphenol extracts and fractions as well as other red wine polyphenols, like procyanidin B5 analogues and myricetin. 相似文献
57.
58.
依据丰满漉域的水文气象资料,计算丰满流域可能最大暴雨,推求白丰区间的可能最大洪水并进行成果合理性分析. 相似文献
59.
60.
对37名骨密度(BD)低下的飞行员(实验组)和BD正常的48名飞行员、100名地面人员(正常对照组)进行了BD和血清TT_3、TT_4、TSH IRMA、CT、PTH、E_2和T放射免疫测定。结果显示,实验组BD均值明显低于对照组(p<0.01),血清TT_3、TT_4、CT、E_2(女性)和T(男性)均值与对照组比较,大多数年龄存在着显著或非常显著差异(p<0.05或p<0.01)。同时对飞行人员BD与几种内分泌激素关系进行了探讨。 相似文献