全文获取类型
收费全文 | 21150篇 |
免费 | 1345篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 363篇 |
综合类 | 53篇 |
化学工业 | 4582篇 |
金属工艺 | 611篇 |
机械仪表 | 517篇 |
建筑科学 | 939篇 |
矿业工程 | 129篇 |
能源动力 | 444篇 |
轻工业 | 2837篇 |
水利工程 | 163篇 |
石油天然气 | 52篇 |
无线电 | 1273篇 |
一般工业技术 | 5327篇 |
冶金工业 | 1683篇 |
原子能技术 | 197篇 |
自动化技术 | 3342篇 |
出版年
2023年 | 254篇 |
2022年 | 197篇 |
2021年 | 453篇 |
2020年 | 389篇 |
2019年 | 359篇 |
2018年 | 700篇 |
2017年 | 721篇 |
2016年 | 793篇 |
2015年 | 631篇 |
2014年 | 897篇 |
2013年 | 1623篇 |
2012年 | 997篇 |
2011年 | 1196篇 |
2010年 | 1033篇 |
2009年 | 941篇 |
2008年 | 1048篇 |
2007年 | 1032篇 |
2006年 | 738篇 |
2005年 | 605篇 |
2004年 | 517篇 |
2003年 | 502篇 |
2002年 | 497篇 |
2001年 | 408篇 |
2000年 | 362篇 |
1999年 | 291篇 |
1998年 | 608篇 |
1997年 | 419篇 |
1996年 | 344篇 |
1995年 | 281篇 |
1994年 | 212篇 |
1993年 | 202篇 |
1992年 | 145篇 |
1991年 | 125篇 |
1990年 | 112篇 |
1989年 | 94篇 |
1988年 | 104篇 |
1987年 | 85篇 |
1986年 | 74篇 |
1985年 | 179篇 |
1984年 | 180篇 |
1983年 | 114篇 |
1982年 | 122篇 |
1981年 | 149篇 |
1980年 | 118篇 |
1979年 | 94篇 |
1978年 | 95篇 |
1977年 | 106篇 |
1976年 | 151篇 |
1975年 | 89篇 |
1974年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
141.
K. Fröhlich 《e & i Elektrotechnik und Informationstechnik》2002,119(1):15-21
It is discussed to what extent tools, provided by modern information technology, reasonably improve the performance of high voltage circuit breakers in transmission systems of electric power. Controlled switching, properly applied, has a high potential to increase life expectancy of the breaker itself and of the adjacent equipment. Power quality can also be improved. The technical advantage of controlled switching is beyond doubt, although the economic benefits are not easily quantified. In terms of breaker intelligence, another very important aspect is condition diagnosis. In particular a model based diagnosis seems to point to the future. Condition diagnosis giving maintainance requirements and pre-warning of impending failures should facilitate the tasks of the operating personnel. As a conclusion it can be stated that more intelligence of circuit breakers would be useful. 相似文献
142.
Students (N = 167) from the 4th, 8th, and 11th grades sorted meals, listed on individual cards, according to whether they would or would not eat them. Students were told to either consider eating the meals at home or at school. Forty-two different meals were selected from a pool of unique meals created by students in a previous study. The meals differed in head component, the presence or absence of vegetables, and the number of different foodstuffs. On average, approximately half of the meals were deemed acceptable, but older students accepted more meals than younger ones, boys accepted more meals than girls, and meals to be consumed at home were accepted more than those to be consumed at school. In addition, students tended to accept meals comprised of a small number of foodstuffs that did not contain vegetables. The also chose more meat-based meals over those containing fish or soup. These results suggest that students have rather unique food preferences that do not correspond well with nutritional standards. In order to address this problem we recommended that students be given more good choices in the school cafeteria through the introduction of a two-meal system and salad bars. 相似文献
143.
Droplet formation on Si surfaces bombarded by 10 keV beams from a liquid metal indium ion source has been observed. It has been verified that excess indium is transported in the ion beam, probably in the form of charged droplets. SIMS, SEM and RBS techniques have been used to study the distribution of droplets at the surface. At the specified ion source operating conditions, equilibrium droplet coverage is of the order of 25%. Individual droplets have an average diameter of 0.35 ωm and an average height of 2.2 nm. At a bombardment current density of 0.1 mA cm?2, equilibrium coverage is reached in about 1 s. 相似文献
144.
The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0°C and the concentration of CO2 was < 1 ppm or 350 ppm. Different amounts of sodium chloride (0–70 μg/cm2) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X‐ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCl is very corrosive towards AZ91. However, the NaCl‐induced corrosion is inhibited by ambient concentrations of CO2. Exposure in the absence of CO2 gives rise to heavy pitting, with brucite, Mg(OH)2, being the dominant corrosion product. In the presence of CO2 a layer of hydrated magnesium hydroxy carbonate, Mg5(CO3)4(OH)2 · 5 H2O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments. 相似文献
145.
C. Schönbauer Dipl.-Ing. 《e & i Elektrotechnik und Informationstechnik》2003,120(10):304-306
The new law for the support of electricity produced by renewable sources in Austria (Ökostromgesetz) which came into force with the beginning of 2003, shows its impacts already after the first months. Investments into wind power have increased considerably. These will be accompanied by activities for electricity production by biomass and biogas. The 4%-target quota will probably be reached earlier than the 2008 target period of the law. 相似文献
146.
北电网络提供的Contivity解决方案不仅可以使用户建立各种类型的VPN,而且还可以把这些VPN集成到未来的融合话音和数据的网络中。该方案已实现了安全路由选择;可通过多种技术支持鉴权功能,从而实现安全接入;允许用户使用其各自的安全性配置文件设置;其设计中没有“后门”,重点介绍了Contivity 2700网关的主要特征及其优势。 相似文献
147.
Zusammenfassung Aufgrund von Eingangs- und Ausgangsst?rungen des Me?systems sowie einer endlichen Frequenzaufl?sung treten stets systematische
(Bias-) und zuf?llige Fehler bei gemessenen Frequenzg?ngen und deren Varianzen auf. Auf solchen Frequenzg?ngen und Varianzen
beruhende Sch?tzungen der modalen Parameter sind damit ebenfalls systematisch verzerrt. Um die Genauigkeit und Sicherheit
der modalen Parameter zu erh?hen, wird ein Sch?tzverfahren vorgestellt, in dem der Einflu? der Biasfehler auf die Sch?tzung
n?herungsweise in einer diagonalen Wichtungsmatrix berücksichtigt wird. Es wird gezeigt, da? die systematischen Fehler Einflu?
auf die Absch?tzung der statistischen Sicherheit der modalen Parameter haben. Anhand zweier Beispiele wird die Wirksamkeit
des Sch?tzverfahrens demonstriert.
Prof. Dr.-Ing. Dr.-Ing. E.h.H.K. T?nshoff: Dipl.-Ing.Z. Liu, Institut für Fertigungstechnik und Spanende Werkzeugmaschinen (IFW), Universit?t Hannover. 相似文献
148.
149.
Y. Romanyshyn S. Guimond H. Kuhlenbeck S. Kaya R. P. Blum H. Niehus S. Shaikhutdinov V. Simic-Milosevic N. Nilius H.-J. Freund M. V. Ganduglia-Pirovano R. Fortrie J. Döbler J. Sauer 《Topics in Catalysis》2008,50(1-4):106-115
Oxidation catalysts are modeled by oxide single crystals, thin oxide films, as well as supported oxide nanoparticles. We characterize the surface of those materials using a variety of surface sensitive techniques including scanning tunneling microscopy and spectroscopy, photoelectron spectroscopy, infrared spectroscopy, and thermal desorption spectroscopy. We find temperature dependent structural transformations from V2O5(001) to V2O3(0001) via V6O13(001). V2O3(0001) is found to be vanadyl terminated in an oxygen ambient and it loses the vanadyl termination after electron bombardment. It is shown that the concentration of vanadyl groups controls the selectivity of the methanol oxy-dehydrogenation towards formaldehyde. A proposal for the mechanism is made. The results on single crystalline thin films are compared with similar measurements on deposited vanadia nanoparticles. The experimental results are correlated with theoretical calculations and models. 相似文献
150.