全文获取类型
收费全文 | 50240篇 |
免费 | 3860篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 1580篇 |
综合类 | 421篇 |
化学工业 | 14966篇 |
金属工艺 | 865篇 |
机械仪表 | 1072篇 |
建筑科学 | 1613篇 |
矿业工程 | 236篇 |
能源动力 | 657篇 |
轻工业 | 7342篇 |
水利工程 | 447篇 |
石油天然气 | 190篇 |
武器工业 | 5篇 |
无线电 | 1557篇 |
一般工业技术 | 8440篇 |
冶金工业 | 8144篇 |
原子能技术 | 142篇 |
自动化技术 | 6457篇 |
出版年
2023年 | 901篇 |
2022年 | 638篇 |
2021年 | 1433篇 |
2020年 | 1295篇 |
2019年 | 1319篇 |
2018年 | 1881篇 |
2017年 | 1705篇 |
2016年 | 1965篇 |
2015年 | 1820篇 |
2014年 | 2019篇 |
2013年 | 3970篇 |
2012年 | 2474篇 |
2011年 | 2169篇 |
2010年 | 2219篇 |
2009年 | 2188篇 |
2008年 | 1658篇 |
2007年 | 1573篇 |
2006年 | 1075篇 |
2005年 | 947篇 |
2004年 | 864篇 |
2003年 | 782篇 |
2002年 | 674篇 |
2001年 | 525篇 |
2000年 | 449篇 |
1999年 | 526篇 |
1998年 | 2542篇 |
1997年 | 1744篇 |
1996年 | 1220篇 |
1995年 | 794篇 |
1994年 | 623篇 |
1993年 | 776篇 |
1992年 | 357篇 |
1991年 | 325篇 |
1990年 | 301篇 |
1989年 | 329篇 |
1988年 | 293篇 |
1987年 | 298篇 |
1986年 | 300篇 |
1985年 | 305篇 |
1984年 | 294篇 |
1983年 | 274篇 |
1982年 | 288篇 |
1981年 | 349篇 |
1980年 | 321篇 |
1979年 | 252篇 |
1977年 | 424篇 |
1976年 | 770篇 |
1975年 | 250篇 |
1974年 | 235篇 |
1973年 | 424篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
I Frías MT Caldeira JR Pérez-Casti?eira JP Navarro-Avi?ó FA Culia?ez-Maciá O Kuppinger H Stransky M Pagés A Hager R Serrano 《Canadian Metallurgical Quarterly》1996,8(9):1533-1544
The plasma membrane (PM) H(+)-ATPase has been proposed to play important transport and regulatory roles in plant physiology, including its participation in auxin-induced acidification in coleoptile segments. This enzyme is encoded by a family of genes differing in tissue distribution, regulation, and expression level. A major expressed isoform of the maize PM H(+)-ATPase (MHA2) has been characterized. RNA gel blot analysis indicated that MHA2 is expressed in all maize organs, with highest levels being in the roots. In situ hybridization of sections from maize seedlings indicated enriched expression of MHA2 in stomatal guard cells, phloem cells, and root epidermal cells. MHA2 mRNA was induced threefold when nonvascular parts of the coleoptile segments were treated with auxin. This induction correlates with auxin-triggered proton extrusion by the same part of the segments. The PM H(+)-ATPase in the vascular bundies does not contribute significantly to auxin-induced acidification, is not regulated by auxin, and masks the auxin effect in extracts of whole coleoptile segments. We conclude that auxin-induced acidification in coleoptile segments most often occurs in the nonvascular tissue and is mediated, at least in part, by increased levels of MHA2. 相似文献
62.
M Pan J Suárez de Lezo A Medina M Romero E Hernández J Segura F Melian F Wangüemert M Landin F Benítez M Amat F Velasco A Torres 《Canadian Metallurgical Quarterly》1997,80(10):1336-1338
Two hundred twenty-eight patients with successful coronary stent implantation were randomized either to protamine administration and femoral sheath removal (group I, n = 117) or no heparin neutralization and delayed sheath removal (group II, n = 111). The hospital stay after treatment was shorter in patients receiving protamine; therefore, protamine use for neutralizing circulating heparin may be safely administered immediately after stent implantation. 相似文献
63.
Dr.-Ing. Ch. Dörnemann Prof. Dr.-Ing. E. Handschin 《Electrical Engineering (Archiv fur Elektrotechnik)》1992,76(1):33-40
Übersicht Der Betriebszustand eines Verteilungsnetzes wird durch die Strombelastung aller Betriebsmittel beschrieben. Mit Hilfe einer statischen Estimationsmethode werden aus einzelnen Messungen und der Kenntnis der Verbrauchsdaten typische Verbraucherkurven (TVK) berechnet, die das elektrische Verhalten verschiedener Verbrauchergruppen widerspiegeln. Auf dieser Basis ist eine betriebsmittelbezogene Lastmodellierung an beliebigen Betriebsmitteln in Abhängigkeit der Verbraucherzusammensetzung unter Berücksichtigung externer Einflüsse wie der Temperatur möglich. Die so gewonnenen Belastungsverläufe erlauben eine Beschreibung des Netzzustands in den Verteilungsnetzen.
Bus load modelling in distribution systems
Contents The operating state of a distribution system is determined by the bus load current. Based on individual substation measurements and the load composition typical load curves are calculated using statistical estimation theory. These typical load curves describe the electrical behaviour of the different load types (e.g. household, storage heating, commerce etc.). As soon as the typical load curves are determined it is possible to calculate the bus load current in any substation taking external influences such as temperature into consideration. The bus load current serve as load models which completely describe the operating state of the distribution system.相似文献
64.
1. 45 myopes (-3.0 to -6.0 D) were examined before and 1 and 6 months after photorefractive keratectomy (PRK). Visual acuity (VA) was tested using Snellen and logMAR charts. Contrast sensitivity (CS) was measured using a computerized system. 2. Preoperative best corrected VA (BCVA) in myopes was significantly lower in comparison with a control group using logMAR charts only. A reduction of BCVA by both methods at 1. month and its return after 6 months nearly to original values was noted. 3. Significantly lower values of CS were found in patients before PRK compared to the control group. After 1 and 6 months stayed the values on preoperative level. 相似文献
65.
66.
67.
68.
S Knecht M Deppe EB Ringelstein M Wirtz H Lohmann B Dr?ger T Huber H Henningsen 《Canadian Metallurgical Quarterly》1998,29(6):1155-1159
BACKGROUND AND PURPOSE: Since functional transcranial Doppler ultrasonography (fTCD) allows convenient and fully automated quantification of language lateralization, it seems ideal for longitudinal studies of perfusion changes during deterioration as well as recovery of language functions. However, during serial examinations, the technical, stochastic, and physiological variabilities of cerebral blood flow velocities (CBFV) have to be considered. Therefore, before fTCD is accepted as a tool for evaluation of changes in lateralization in the diseased state, its reliability in healthy subjects needs to be determined. METHODS: We performed fTCD during a word generation task based on a previously validated technique with automated calculation of the averaged CBFV differences in the middle cerebral arteries providing an index of lateralization (LI). RESULTS: (1) The accuracy of the LI as assessed by the confidence interval was better than 1% of the mean hemispheric difference. (2) On repeated examination, LIs obtained from 10 subjects showed a high test-retest reproducibility (Pearson product moment correlation coefficient r = 0.95, P < 0.0001). (3) On 10 repeated assessments of LI in the same subject, no practice effects were detected. CONCLUSIONS: Functional TCD is a suitable and very robust tool for the longitudinal quantitative measurement of cerebral language lateralization. 相似文献
69.
70.