全文获取类型
收费全文 | 10640篇 |
免费 | 428篇 |
国内免费 | 231篇 |
专业分类
电工技术 | 225篇 |
综合类 | 278篇 |
化学工业 | 1010篇 |
金属工艺 | 304篇 |
机械仪表 | 408篇 |
建筑科学 | 422篇 |
矿业工程 | 184篇 |
能源动力 | 116篇 |
轻工业 | 392篇 |
水利工程 | 94篇 |
石油天然气 | 513篇 |
武器工业 | 30篇 |
无线电 | 667篇 |
一般工业技术 | 746篇 |
冶金工业 | 5151篇 |
原子能技术 | 56篇 |
自动化技术 | 703篇 |
出版年
2024年 | 24篇 |
2023年 | 94篇 |
2022年 | 177篇 |
2021年 | 268篇 |
2020年 | 195篇 |
2019年 | 153篇 |
2018年 | 173篇 |
2017年 | 166篇 |
2016年 | 162篇 |
2015年 | 239篇 |
2014年 | 256篇 |
2013年 | 354篇 |
2012年 | 329篇 |
2011年 | 386篇 |
2010年 | 321篇 |
2009年 | 287篇 |
2008年 | 364篇 |
2007年 | 316篇 |
2006年 | 306篇 |
2005年 | 266篇 |
2004年 | 153篇 |
2003年 | 136篇 |
2002年 | 129篇 |
2001年 | 117篇 |
2000年 | 146篇 |
1999年 | 317篇 |
1998年 | 1622篇 |
1997年 | 981篇 |
1996年 | 639篇 |
1995年 | 389篇 |
1994年 | 346篇 |
1993年 | 363篇 |
1992年 | 80篇 |
1991年 | 86篇 |
1990年 | 76篇 |
1989年 | 82篇 |
1988年 | 68篇 |
1987年 | 63篇 |
1986年 | 72篇 |
1985年 | 50篇 |
1984年 | 4篇 |
1983年 | 14篇 |
1982年 | 24篇 |
1981年 | 31篇 |
1980年 | 32篇 |
1978年 | 13篇 |
1977年 | 126篇 |
1976年 | 280篇 |
1975年 | 10篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
贵港航运枢纽二期工程通过优化设计,重新调整施工进度计划,压缩施—工期,采用了许多先进的施工技术措施,诸如,在截流施工技术上,采用上游戗堤单向立堵,下游紧跟推进技术措施;在围堰堰体基岩防渗帷幕钻孔灌浆施工中,采用了右岸提前预进占,提前钻孔灌浆施工措施;水上部分钻孔灌浆采用在浮桶上投设钻孔灌浆平台的新措施等.通过以上措施,实现了两个枯水期的工程一个枯水期完成,使二期工程提前一年完工,早日实现了枢纽经济效益和社会效益的发挥. 相似文献
62.
63.
考虑Hopfield模型中假态之间的布尔逻辑关系,提出利用IPA模型对神经网络中的假态进行抑制,并和原网络的性能进行了比较,结果表明:改进后的网络性能比Hopfield模型和IPA模型均有较大提高。 相似文献
64.
KR Porter PL Summers D Dubois B Puri W Nelson E Henchal JJ Oprandy CG Hayes 《Canadian Metallurgical Quarterly》1993,48(3):440-446
A polymerase chain reaction (PCR) assay was developed to rapidly detect and identify West Nile (WN) virus. The RNA from seven isolates of WN virus from six countries and four other flaviviruses (Kunjin, Japanese encephalitis, St. Louis encephalitis, and yellow fever viruses) was reverse-transcribed (RT) and amplified by PCR. The nucleotide sequences of the amplified products were determined by a rapid, automated DNA sequencing method. The WN virus RT/PCR assay detected the target gene segment of sequencing method. The WN virus RT/PCR assay detected the target gene segment of isolates from both the African-Middle Eastern group and the Indian group with a sensitivity of approximately 0.05 pg of viral RNA. Kunjin virus was the only other flavivirus tested that produced a band of the appropriate size. Five of seven WN virus isolates showed 92-98% homology in the nucleotide sequence of their PCR products. The sequence of one isolate was virtually identical to the published sequence of the Nigerian isolate (99.5% homology). No correlation was established between the degree of nucleotide homology, geographic location, time of isolation, or source of the isolates. 相似文献
65.
66.
无线数据通信网发展趋势 总被引:1,自引:0,他引:1
无线数据通信具有两大发展趋势,即低速的广域移动数据网及高速的局域无线数据网。本文介绍了其技术特点、应用情况和市场前景,分析了无线数据通信传输技术、网络结构和媒质接入控制等问题。 相似文献
67.
SD Walter SE Birnie LD Marrett SM Taylor D Reynolds J Davies JJ Drake M Hayes 《Canadian Metallurgical Quarterly》1994,84(3):367-376
OBJECTIVES: Our objectives were (1) to describe an analysis of the spatial pattern of cancer incidence in Ontario and (2) to discuss the quality of data in the Ontario Cancer Registry with respect to the accuracy of local cancer rates. METHODS: Cancer incidence rates were calculated for 22 cancer sites in 49 counties of Ontario during 1976 to 1986. Capture-recapture methods were used to estimate completeness of case registration, and completeness of residence information was also assessed. Spatial autocorrelation was used in measuring the geographic pattern of incidence rates. Comparisons were also made between sexes and with earlier data from 1966 to 1975. RESULTS: The quality of the geographic data in the registry appeared good, and corrections for incomplete or inaccurate registration had little impact. About one third of the sex-site combinations showed some evidence of spatial patterning in the cancer rate. Particularly strong regional variation was noted for cancers of the stomach, lung, uterus, and prostate. CONCLUSIONS: The analysis revealed a number of cancers with significant spatial patterning of risk. Further work is needed to relate the cancer data to other information on potential life-style and environmental factors. 相似文献
68.
The fabric and faces of threat, and the expediency and efficiency in the communication of threat, are examined with a threat appraisal model. This model is empirically tested on an ongoing communication challenge, the issuance of terror alerts by the United States' Department of Homeland Security (DHS), focusing on how threat is appraised by both the conservative and liberal audiences. Findings showed a shared view by the DHS and conservative audiences on the levels and nature of threats; liberal audiences thought otherwise. Though there appeared to be a consensus between the conservative and liberal audiences on the efficacy of threat communication, more internal consistency within DHS is needed to optimise its effectiveness. 相似文献
69.
RD Spruell ER Ferguson JJ Clymer WV Vicente CP Murrah WL Holman 《Canadian Metallurgical Quarterly》1995,41(3):M636-M641
Intravascular perfluorochemical (PFC) emulsions together with a high oxygen (O2) tension may increase the delivery of dissolved O2 to useful levels. A severely anemic model of cardiopulmonary bypass (CPB) was used to test the hypothesis that a novel PFC emulsion (PFCE; Oxygent [Alliance Pharmaceutical Corp., San Diego, CA] 90% w/v perflubron) used at a high PO2 during bypass delivers sufficient O2 to ameliorate hypoxic myocardial contractile dysfunction. Acutely anemic dogs (N = 42; hematocrit = 15.8 +/- 0.6% [mean +/- SEM] before CPB and 10.9 +/- 0.1% during CPB) were divided into four groups. Group 1 was a control (n = 12). As CPB was initiated, groups 2 (n = 10), 3 (n = 10), and 4 (n = 10) had 1.35 g PFC.kg-1, 2.7 g PFC.kg-1, or 5.4 g PFC.kg-1 added via the venous return cannula. Pre-CPB and post-CPB cardiac function was measured by the first derivative of left ventricular pressure (dP/dtmax). The dP/dtmax on separation from CPB was: group 1, 619 +/- 96; group 2, 738 +/- 56; group 3, 782 +/- 101; and group 4, 828 +/- 100 (p < 0.05 groups 3 and 4 versus group 1). Mortality during the first hour after separation from CPB was higher in group 1 than in PFCE treated dogs; however, this trend did not attain statistical significance (p < 0.065). The PFC dose was higher in survivors than in nonsurvivors (2.6 +/- 0.4 g PFC.kg-1 versus 1.2 +/- 0.5 g PFC.kg-1; p < 0.05). A PFCE used at a high PO2 provides sufficient physically dissolved O2 to relieve myocardial hypoxic injury in a severely anemic model of CPB. Current PFCEs are effective O2 carriers. This finding suggests that they can be used as a temporary erythrocyte substitute to diminish the need for allogeneic transfusions during cardiac operations. 相似文献
70.