全文获取类型
收费全文 | 36660篇 |
免费 | 4965篇 |
国内免费 | 2421篇 |
专业分类
电工技术 | 3396篇 |
技术理论 | 3篇 |
综合类 | 2752篇 |
化学工业 | 5116篇 |
金属工艺 | 2030篇 |
机械仪表 | 2609篇 |
建筑科学 | 2637篇 |
矿业工程 | 1440篇 |
能源动力 | 1052篇 |
轻工业 | 3183篇 |
水利工程 | 1056篇 |
石油天然气 | 1528篇 |
武器工业 | 484篇 |
无线电 | 4512篇 |
一般工业技术 | 3891篇 |
冶金工业 | 2446篇 |
原子能技术 | 475篇 |
自动化技术 | 5436篇 |
出版年
2024年 | 263篇 |
2023年 | 844篇 |
2022年 | 1834篇 |
2021年 | 2376篇 |
2020年 | 1783篇 |
2019年 | 1318篇 |
2018年 | 1483篇 |
2017年 | 1816篇 |
2016年 | 1497篇 |
2015年 | 2166篇 |
2014年 | 2596篇 |
2013年 | 2872篇 |
2012年 | 3226篇 |
2011年 | 3205篇 |
2010年 | 2638篇 |
2009年 | 2237篇 |
2008年 | 2180篇 |
2007年 | 1849篇 |
2006年 | 1437篇 |
2005年 | 1144篇 |
2004年 | 786篇 |
2003年 | 625篇 |
2002年 | 618篇 |
2001年 | 517篇 |
2000年 | 364篇 |
1999年 | 292篇 |
1998年 | 486篇 |
1997年 | 340篇 |
1996年 | 251篇 |
1995年 | 185篇 |
1994年 | 164篇 |
1993年 | 137篇 |
1992年 | 76篇 |
1991年 | 50篇 |
1990年 | 43篇 |
1989年 | 54篇 |
1988年 | 34篇 |
1987年 | 22篇 |
1986年 | 28篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 22篇 |
1976年 | 48篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
分片汇接的网状网结构是江苏省本地电话网的基本框架,而汇接局和连接汇接局的传输系统则是网路规划与通信建设的重点。 相似文献
32.
DT Netscher S Sharma J Thornby M Peltier A Lyos M Fater A Mosharrafa 《Canadian Metallurgical Quarterly》1997,100(1):206-219
As we began to see increasing numbers of women concerned about their gel-filled breast implants, we became aware that we could not advise them with any degree of confidence what they might expect in terms of aesthetic result after implant removal. We decided to review the records and outcomes over a 2-year period of a number of patients who underwent implant removal. Eighty-five consecutive patients were reviewed, 69 of whom had undergone cosmetic augmentation and 16 of whom had breast reconstruction with silicone gel implant(s). Thirty-nine of the 69 cosmetic augmentation patients had removal of implants alone, and 27 had removal accompanied by mastopexy. Three had reaugmentation with saline-filled implants; one had replacement with saline-filled implants. Fifteen of the 16 reconstruction patients underwent autogenous tissue transfer. Preoperative and postoperative photographs of all patients were mixed randomly and rated by two independent raters in four aesthetic categories on a five-point scoring system. Repeatability was measured several weeks later, when each rater scored randomly selected photographs from this patient pool. The patients also performed their own outcome evaluations by means of questionnaire. We discovered that cosmetic augmentation patients who undergo implant removal only often suffer adverse aesthetic results. The postremoval appearance of many cosmetic augmentation patients actually will be improved over their preoperative appearance when mastopexy is performed in conjunction with implant removal. The study demonstrated that patients with certain body types could expect a particular outcome; i.e., women with asthenic builds and older patients with lax, striated breast skin generally had unsatisfactory aesthetic outcomes with implant removal only. Patients selected for autogenous breast reconstruction had favorable results, with extended latissimus dorsi and TRAM flaps yielding equally good outcomes. The study allows us to offer patients an optimistic view of postoperative results following breast implant removal. We have begun to advise selected patients that implant removal accompanied by mastopexy provides a more pleasing aesthetic outcome than implant removal alone. 相似文献
33.
Two near-infrared spectroscopy (NIRS) methods are available for measuring changes (Delta) in total cerebral hemoglobin concentration (CHC): 1) a continuous measurement of the changes in total hemoglobin concentration (Delta[Hb]tot) and 2) the difference between two absolute measurements of CHC, each derived from a small, controlled change in inspired O2 fraction. This paper investigates the internal consistency of these two methods by using an experimental and theoretical comparison. NIRS was used to measure [Hb]tot in five newborn piglets before and after a change in arterial PCO2. Delta[Hb]tot demonstrated a low coefficient of variation of 2.8 +/- 2.8 (SD) % which allowed changes in CO2-cerebral blood volume reactivity to be clearly discriminated. However, a high coefficient of variation of 22.8 +/- 3.5% on the DeltaCHC measurements obscured any CO2 reactivity changes. A theoretical analysis demonstrates the effects of optical pathlength, background absorption, scatter, and blood vessel diameter on both methods. For more accurate monitoring of CHC, individual measurements of optical pathlength and more accurate pulse oximetry are required. 相似文献
34.
35.
北京市部分学校教室采光照明现状分析 总被引:8,自引:2,他引:6
近年来我国学生视力不良检出率居高不下,并且呈现明显上升趋势,已经到了极为严重的程度.学校教室的采光照明问题是保护学生视力健康的重要部分.2004年我国重新修订了国家标准〈建筑照明设计标准〉GB50034-2004.本文对北京市部分大中小学校进行采光照明的调查分析,结果显示,北京市学校教室采光照明问题十分严重,与国家标准要求差距很大,在被调查的39间教室中,窗地面积比达标率为20.5%,课桌面照度达标率为25.6%,黑板照度达标率为零. 相似文献
36.
Ming-Jer Chen Kum-Chang Chao Tzuen-Hsi Huang Jyh-Min Tsaur 《Electron Device Letters, IEEE》1992,13(12):654-657
The buried-type p-channel LDD MOSFETs biased at high positive gate voltage exhibit novel characteristics: (1) the ratio of the drain to gate currents is about 1×10-3 to 5×10-3; and (2) the gate and drain currents both are functions of only the gate voltage minus the n-well bias. Such characteristics are addressed based on the formation of the surface n + inversion layer due to the punchthrough of the buried channel to the underlying shallow p-n junction. The measured gate current is due to the Fowler-Nordheim tunneling of electrons from this inversion layer surface and the holes generated within the high-field oxide constitute the drain current. The n+ inversion layer surface potential is found to be equal to the n-well bias plus 0.55 V. As a result, both the oxide field and the gate and drain currents are independent of drain voltage 相似文献
37.
38.
39.
以某工程钻爆参数为例,阐述了在地下工程掘进施工中,应用回归分析法建立钻爆参数的相关模型,并利用此模型帮助建立某断面钻爆方案. 相似文献
40.