全文获取类型
收费全文 | 112614篇 |
免费 | 10533篇 |
国内免费 | 6284篇 |
专业分类
电工技术 | 7361篇 |
技术理论 | 3篇 |
综合类 | 10286篇 |
化学工业 | 17570篇 |
金属工艺 | 6216篇 |
机械仪表 | 7129篇 |
建筑科学 | 8280篇 |
矿业工程 | 2841篇 |
能源动力 | 3028篇 |
轻工业 | 9953篇 |
水利工程 | 2271篇 |
石油天然气 | 4977篇 |
武器工业 | 1005篇 |
无线电 | 13562篇 |
一般工业技术 | 11826篇 |
冶金工业 | 4746篇 |
原子能技术 | 1723篇 |
自动化技术 | 16654篇 |
出版年
2024年 | 469篇 |
2023年 | 1570篇 |
2022年 | 3150篇 |
2021年 | 4173篇 |
2020年 | 3269篇 |
2019年 | 2768篇 |
2018年 | 3002篇 |
2017年 | 3325篇 |
2016年 | 3147篇 |
2015年 | 4304篇 |
2014年 | 5613篇 |
2013年 | 6549篇 |
2012年 | 7647篇 |
2011年 | 8138篇 |
2010年 | 7576篇 |
2009年 | 7416篇 |
2008年 | 7398篇 |
2007年 | 7004篇 |
2006年 | 6862篇 |
2005年 | 5787篇 |
2004年 | 4450篇 |
2003年 | 4044篇 |
2002年 | 4674篇 |
2001年 | 4107篇 |
2000年 | 2927篇 |
1999年 | 2218篇 |
1998年 | 1405篇 |
1997年 | 1247篇 |
1996年 | 1129篇 |
1995年 | 899篇 |
1994年 | 719篇 |
1993年 | 530篇 |
1992年 | 455篇 |
1991年 | 309篇 |
1990年 | 250篇 |
1989年 | 186篇 |
1988年 | 169篇 |
1987年 | 121篇 |
1986年 | 61篇 |
1985年 | 69篇 |
1984年 | 59篇 |
1983年 | 46篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1959年 | 13篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Environmental factors such as oxygen, temperature, and microbial species may have significant effects on decomposition of biodegradable polymers. A representative biodegradable, thermoplastic polymer, poly(3‐hydroxybutyrate‐co‐hydroxyvalerate) (PHBV), was decomposed in an aqueous medium under controlled laboratory conditions by soil microbes for the intrinsic degradation kinetics and the effects of the environmental factors on polymer biodegradation. The amount of proteins, including the PHBV depolymerases, that attached to the polymer surfaces was quite constant during the period of significant mass loss of the polymer specimens. The microbial polymer degradation followed a zero‐order rate model, so the residual mass fraction of PHBV films declined linearly with time. The mixed aerobic microbial organisms from fertile soil showed a higher activity of polymer degradation than an aerobic PHBV‐producing bacterium and the mixed anaerobes in the same soil. The mixed anaerobic microorganisms from barren soil decomposed the polymer at a slower rate than the anaerobes from fertile soil, and this was attributed to fewer microbial cells in the barren soil instead of the difference in the microbial species. The temperature effect on PHBV degradation can be described with an Arrhenius equation, and the activation energy is around 16 kcal/mol. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 205–213, 2003 相似文献
62.
63.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
64.
随机激光器的最新进展 总被引:5,自引:2,他引:3
综述了近年来随机激光器的最新研究结果,包括随机激光产生的机制,随机增益介质的制备方法,随机激光器的激励与发光特性和随机激光理论。最后,介绍了随机激光器的应用前景。 相似文献
65.
66.
Qi Wang Mosa Ali Abu-Rgheff 《Wireless Communications, IEEE》2006,13(6):68-76
In the all-IP wireless networks beyond the third generation, mobility management can be effectively achieved by applying mobile IP (MIP) and the session initiation protocol (SIP) jointly. Nevertheless, an efficient combination of both protocols remains an open research issue. Conventional hybrid MIP-SIP mobility architectures operate MIP and SIP almost independently, resulting in significant redundant costs. This article investigates the representative hybrid MIP-SIP architectures and explores the joint optimizations between MIP and SIP for a more cost-efficient mobility support whilst utilizing their complementary power. Two novel design approaches are presented. The first approach culminates in a tightly integrated architecture, which merges the redundant mobility entities in MIP and SIP to yield maximum system efficiency. The other approach leads to a loosely integrated architecture, where necessary interactions are introduced between MIP and SIP mobility servers while their physical entities are kept intact. Major mobility procedures, including location update, session setup and handoff, are discussed in these architectures. The analytical results demonstrate that both proposed architectures outperform typical hybrid MIP-SIP architectures in terms of clear-cut reduced signaling costs 相似文献
67.
68.
关于我国钢铁工业发展战略的思考 总被引:2,自引:0,他引:2
21世纪初是世界经济发展的重大战略机遇期,如何抓住机遇加快发展,是中国钢铁行业应认真思考的问题。十一五我国钢铁工业的发展,靠什么来拉动,还能靠大规模的投资吗?目前我们还不能生产的双高产品怎么办,靠花钱能买来技术吗?靠市场能换来核心产品吗?值得深思。当今,我们思考的不仅应考虑个别企业的生存问题,而更应考虑的是钢铁行业整体的长远发展问题,即 相似文献
69.
70.