全文获取类型
收费全文 | 49165篇 |
免费 | 3969篇 |
国内免费 | 2883篇 |
专业分类
电工技术 | 1309篇 |
技术理论 | 1篇 |
综合类 | 2991篇 |
化学工业 | 9240篇 |
金属工艺 | 9470篇 |
机械仪表 | 2800篇 |
建筑科学 | 3859篇 |
矿业工程 | 1512篇 |
能源动力 | 2359篇 |
轻工业 | 2171篇 |
水利工程 | 818篇 |
石油天然气 | 2604篇 |
武器工业 | 416篇 |
无线电 | 4443篇 |
一般工业技术 | 7438篇 |
冶金工业 | 2114篇 |
原子能技术 | 446篇 |
自动化技术 | 2026篇 |
出版年
2024年 | 265篇 |
2023年 | 861篇 |
2022年 | 1317篇 |
2021年 | 1551篇 |
2020年 | 1585篇 |
2019年 | 1464篇 |
2018年 | 1385篇 |
2017年 | 1790篇 |
2016年 | 1682篇 |
2015年 | 1769篇 |
2014年 | 2693篇 |
2013年 | 2829篇 |
2012年 | 3348篇 |
2011年 | 3824篇 |
2010年 | 2943篇 |
2009年 | 2906篇 |
2008年 | 2523篇 |
2007年 | 3021篇 |
2006年 | 3081篇 |
2005年 | 2439篇 |
2004年 | 2098篇 |
2003年 | 1836篇 |
2002年 | 1539篇 |
2001年 | 1318篇 |
2000年 | 1191篇 |
1999年 | 914篇 |
1998年 | 753篇 |
1997年 | 597篇 |
1996年 | 518篇 |
1995年 | 447篇 |
1994年 | 333篇 |
1993年 | 314篇 |
1992年 | 269篇 |
1991年 | 167篇 |
1990年 | 126篇 |
1989年 | 106篇 |
1988年 | 54篇 |
1987年 | 28篇 |
1986年 | 30篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1959年 | 6篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
We consider a structural approach to the consensus building problem in multi‐group multi‐layer (MGML) distributed sensor networks (DSNs) common in many natural and engineering applications. From among the possible network structures, we focus on bipartite graph structure as it represents a typical MGML structure and has a wide applicability in the real world. We establish exact conditions for consensus and derive a precise relationship between the consensus value and the degree distribution of nodes in a bipartite MGML DSN. We also demonstrate that for subclasses of connectivity patterns, convergence time and simple characteristics of network topology can be captured by explicit algebra. Direct inference of the convergence behavior of consensus strategies from MGML DSN structure is the main contribution of this paper. The insights gained from our analysis facilitate the design and development of large‐scale DSNs that meet specific performance criteria. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
942.
Tan S Chan WM Wai MS Hui LK Hui VW James AE Yeung LY Yew DT 《Microscopy research and technique》2011,74(12):1192-1198
Different doses of ketamine (10 mg/kg, 20 mg/kg, 30 mg/kg, 40 mg/kg, 50 mg/kg, and 60 mg/kg) were injected i.p. (I.P.), respectively, to male ICR mice to determine the optimal dosage for chronic administration. At and above 40 mg/kg I.P. injection, mice had almost no hindlimb movement during swimming test. Subsequently, 30 mg/kg was used as the dose for the study in the toxicity of long-term ketamine administration on urinary bladder and sperm motility. The treatment group were subdivided into two (n = 10 each group); one received daily ketamine treatment i.p. for 3 months and another group for 6 months. Corresponding number of mice in control groups (n = 5 each group) received saline injection instead of ketamine. Terminal dUTP nick and labeling (TUNEL) study and Sirius red staining were carried out on the sectioned slides of the urinary bladders to study the degree of apoptosis in both epithelium and muscular layers of the urinary bladder and the relative thickness of the muscular layers in this organ was also computed. Apoptosis in the bladder epithelium was observed initially in the 3-month ketamine treated mice and the number of apoptotic cells was significantly different (P < 0.05) between the 3-month and 6-month ketamine treated mice and the control. The relative thickness of muscular layers in the bladder wall also decreased significantly (P < 0.05) when the 6-month treated mice and the control were compared. Sirius red staining revealed increase of collagen in the urinary bladder of the treated mice, most evidently 6 months after ketamine treatment. In addition, the sperm motility was studied and there was a statistically significant difference between the control and ketamine treated groups in the percentages of sperms which were motile (P < 0.05). This suggested that the chronic administration of ketamine affected the genital system as well. 相似文献
943.
944.
945.
Gigabit home networks represent a key technology to make the Future Internet success a reality. Consumers will require networks to be simple to install, without the need of any new wire and with green consideration. To make this network ubiquitous, seamless and robust, a technology independent MAC layer will ensure its global control and provide connectivities to any number of devices the user wishes to connect to it in any room. In order to make this vision comes true, substantial progress is required in the fields of protocol design and in systems architectures. For this goal, we introduce a new convergence layer denoted inter-MAC, which provides a common infrastructure to the home network, Among the inter-MAC functionalities, we focused the interest on the path selection mechanism including the green aspect. To improve quality of service, reduce energy consumption and radiofrequency devices number, we define a new path selection protocol based on several metrics. We present some preliminary results obtained on an experimental test bed. 相似文献
946.
介绍我国建造在透水覆盖层上土石坝渗流量观测的现状;提出考虑技术、经济、效果、运行以及对环境影响等因素的渗流量观测设计方案的综合评价方法;实例分析表明该方法考虑因素比较全面,处理得当,易于操作,结论合理。 相似文献
947.
黄土类地层综合降水试验及优化设计 总被引:1,自引:1,他引:0
根据南水北调中线穿黄工程Ⅰ标渠道及进口段场地水文地质条件,通过单井降水试验和生产性群井降水试验的降水资料,采取以管井为主,井点及明排为辅的综合性降水施工方法,成功地将渠道内地下水位降至基础设计标高以下.保证了渠道边坡稳定,达到了黄土类弱透水、高地下水位地层降水、渠道高边坡开挖和衬砌施工的目的.所得降水试验及设计成果为今... 相似文献
948.
曹康建 《水利与建筑工程学报》2011,9(3):83-86,102
喷射混凝土技术,已经成为地下工程和岩土工程支护中最有效的支护手段之一,它可以配合其它支护构件或单独地作为结构的永久性支护.结合钢纤维喷射混凝土单层衬砌的研究现状、单层衬砌支护机理以及湿喷钢纤维混凝土的力学特性等,介绍了在宜昌-巴东高速公路峡口隧道斜井中的应用,对同类工程具有一定的借鉴作用. 相似文献
949.
IEEE 802.11网络中的BSS切换不可避免地产生丢包问题,这会造成网络性能严重下降,进而限制了移动环境下WLAN的广泛应用。为了降低切换过程中的丢包率,本文提出了一种在数据链路层、由无线链路事件触发的用户空间平滑切换机制,并且在基于嵌入式Linux平台的无线AP上进行了实现。大量的实验结果表明,在无需对当前IEEE 802.11协议进行改动的前提下,新切换机制可以保证在允许的时延范围内,较大地降低丢包率,提高网络性能,并且可以支持平滑漫游。改进的平滑切换机制独立于驱动,具有良好的可移植性,可以在现有AP上增量添加,而无需更改STA,降低了升级成本。 相似文献
950.
以MEMS红外气敏传感器为应用目标,采用MEMS技术设计和制作一种二维金属亚波长孔阵列结构红外辐射源。探讨了不同厚度SU-8膜对金属/电介质/金属(M/D/M)二维金属亚波长孔阵列结构在中远红外波段透射特性的影响。设计并制作了Au/SU-8/Au的M/D/M结构,测试采用傅里叶变换红外光谱仪器。同时对M/D/M结构不同电介质层情况下的中远红外波段透射特性进行了模拟。实验结果表明,SU-8厚度在小于1μm时,透射强度远大于厚度1μm以上的结构,且有透射强度最大值出现(SU-8厚度为360nm),同时,随着SU-8厚度的增加,透射谱峰值呈现规律性红移。 相似文献