全文获取类型
收费全文 | 1505篇 |
免费 | 80篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 12篇 |
综合类 | 2篇 |
化学工业 | 386篇 |
金属工艺 | 11篇 |
机械仪表 | 14篇 |
建筑科学 | 80篇 |
能源动力 | 40篇 |
轻工业 | 145篇 |
水利工程 | 10篇 |
石油天然气 | 1篇 |
无线电 | 133篇 |
一般工业技术 | 242篇 |
冶金工业 | 137篇 |
原子能技术 | 9篇 |
自动化技术 | 366篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 33篇 |
2020年 | 40篇 |
2019年 | 40篇 |
2018年 | 47篇 |
2017年 | 42篇 |
2016年 | 68篇 |
2015年 | 32篇 |
2014年 | 73篇 |
2013年 | 87篇 |
2012年 | 99篇 |
2011年 | 112篇 |
2010年 | 73篇 |
2009年 | 81篇 |
2008年 | 85篇 |
2007年 | 74篇 |
2006年 | 65篇 |
2005年 | 68篇 |
2004年 | 59篇 |
2003年 | 51篇 |
2002年 | 53篇 |
2001年 | 25篇 |
2000年 | 21篇 |
1999年 | 32篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 27篇 |
1995年 | 15篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1963年 | 2篇 |
1959年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有1588条查询结果,搜索用时 15 毫秒
11.
The 4-alkoxybenzoic acids are well-known liquid crystals showing several mesophases(nematic,smectic C phase or both)depending on the alkoxy chain length and whereby the rigid core of the mesogen is formed by intermolecular hydrogen bonds.In this paper it is shown that the thermal behaviour of lanthanide salts of 4-hexyloxybenzoic acids depends on the lanthanide ion(Ln=La,Pr,Nd,Sm,Eu).The lanthanum(Ⅲ)and praseodymium(Ⅲ)4-hexyloxybenzoates exhibit a smectic A mesophase.No mesophase is found for the corresponding compounds of heavier lanthanides.The thermal properties of the lanthanide(Ⅲ)4-hexyloxybenzoates were investigated by differential scanning calorimetry(DSC),polarising thermo-optical microscopy and synchrotron X-ray radiation. 相似文献
12.
Adrian Maxim Ramin Poorfard Bart DeCanne 《电子设计应用》2007,(8):82-84,85,91
CMOS技术是把L波段卫星调谐器、解调器和其它功能整合至低成本、高效能单芯片的关键。本文将探讨新型低中频和传统零中频DBS调谐器架构在单芯片DBS射频前端设计中的优缺点。 相似文献
13.
14.
J Schramlová K Blazek B Otová M Bartácková D Hulínská 《Canadian Metallurgical Quarterly》1997,43(5):195-199
The antiphlogistic Ibuprofen incorporated in liposomes caused a decrease of the inflammatory edema induced by Carrageenan in the distal part of the rat's hind leg after both the intramuscular and percutaneous administration. The antiphlogistic effect of free Ibuprofen in the cream was weaker. Intramuscular administration of empty liposomes slowed down in the initial stages the development of inflammation and slightly diminished the size of edema. 相似文献
15.
Y Panis J Belghiti D Valla JP Benhamou F Fékété 《Canadian Metallurgical Quarterly》1994,115(3):276-281
BACKGROUND: In Budd-Chiari syndrome (BCS) treated by portosystemic shunt, postoperative shunt thrombosis is associated with high morbidity and mortality rates. The aim of this study was to determine factors associated with shunt thrombosis. METHODS: From 1985 to 1991, 25 patients underwent portosystemic shunt for BCS. According to the patency of the shunt during the postoperative period and follow-up, patients were divided into two groups including 17 patients with patent shunt and 8 (32%) with shunt thrombosis. RESULTS: In patients with patent shunt, actuarial survival rate at 5 years was 87% versus 38% in patients with shunt thrombosis (p < 0.05). Duration of symptoms before operation was higher in patients with shunt thrombosis than in patients with patent shunt (315 +/- 483 vs 109 +/- 168 days, p < 0.05). In patients with patent shunt, extensive fibrosis or cirrhosis was observed in 3 of 17 (18%) versus in 5 of 8 (63%) of patients with shunt thrombosis (p < 0.05). Shunt thrombosis was observed in 3 of 3 patients (100%) with the combination of myeloproliferative disorder, duration of symptoms more than 100 days, and cirrhosis versus 0 of 6 (0%) patients without this combination (p < 0.05). CONCLUSIONS: In acute form of BCS (with short history of the disease and absence of extensive fibrosis or cirrhosis), early portal decompression is mandatory, with low risk of shunt thrombosis and good long-term results. In chronic form of BCS, the risk of shunt thrombosis is high and long-term results are bad; in these patients, orthotopic liver transplantation must be considered. 相似文献
16.
The possible flow measurement error due to heating or cooling of exhaust gases in the Single‐Burning‐Item (SBI) test is estimated from numerical experiments. It is illustrated that there is no one‐to‐one correspondence between the velocity profile shape and the instantaneous Reynolds number, due to the time‐dependent temperature and density profile evolution in the exhaust gas pipe. A non‐ambiguous relation is found between the velocity profile shape and an ‘effective’ Reynolds number, based on the turbulent viscosity. Maximum variations of the velocity correction factors, relating the mean velocity to the velocity on the pipe axis, are found to be in the order of 2% for limiting circumstances for the SBI test. The primary effect is caused by instantaneous Reynolds number variations. The effect of heating or cooling of the flow by the hot or cold pipe is noticeable, too. The statements are proved to be valid independent of the computational grid, the turbulence model and the time steps taken to obtain the numerical solutions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
17.
18.
Bart Deronde Walter Debruyn Eric Gontier Erwin Goor Tim Jacobs Sara Verbeiren 《International journal of remote sensing》2014,35(7):2402-2420
Throughout the VEGETATION programme, the Flemish Institute for Technological Research (VITO) uninterruptedly hosted the prime user segment of both VEGETATION 1 and VEGETATION 2 multispectral instruments on board the Satellite Pour l’Observation de la Terre 4 (SPOT 4) and SPOT 5 satellites. Operational since the launch of SPOT 4 in March 1998, and foreseen to continue at least until the end of the SPOT 5 mission (anticipated in spring 2014), this user segment comprises a processing facility (PF), actively receiving, processing, correcting, archiving, and distributing the VEGETATION data and derived added-value products. First and foremost, the VEGETATION programme has been serving the needs of operational users – both institutional and commercial – requesting data in near-real time. However, scientific and educational users too benefited significantly, in particular from VEGETATION’s unique time series of the Earth’s land cover, and more specifically the vegetation cover. Over the years, the centralized archive houses processed data covering the equivalent of 11,000 times the Earth’s surface, and delivered more than 50 terapixels to around 10.000 users. As such, VEGETATION’s mission is a prime example of what Europe wants to achieve through the Global Monitoring for Environment and Security (GMES) initiative: truly operational services providing reliable and up-to-date information.This article describes the processing facility, the way the data and products are archived, the different dissemination channels as well as the data policy adopted and the users served. One of the recent evolutions, the development of an entirely new product distribution facility (PDF), implemented as part of the Project for On-Board Autonomy – Vegetation (PROBA-V) user segment is discussed. 相似文献
19.
The enantioselective hydrogenation of ethyl pyruvate to (S)-ethyl lactate over cinchonine- and -isocinchonine-modified Pt/Al2O3 catalysts was studied as a function of modifier concentration and reaction temperature. The maximum enantioselectivities obtained under the applied mild conditions were 89% ee using cinchonine (0.014 mmoldm–3, 1 bar H2, 23°C, 6% AcOH in toluene), and 76% ee in the case of -isocinchonine (0.14 mmoldm–3, 1 bar H2, –10°C, 6% AcOH in toluene). Since -isocinchonine of rigid structure exists only in anti-open conformation these data provide additional experimental evidence to support the former suggestion concerning the dominating role of anti-open conformation in these cinchona-modified enantioselective hydrogenations. 相似文献
20.
Symmetries in constraint problems present an opportunity for reducing search. This paper presents Lightweight Dynamic Symmetry Breaking, an automatic symmetry breaking method that is efficient enough to be used as a default, since it never yields a major slowdown while often giving major performance improvements. This is achieved by automatically exploiting certain kinds of symmetry that are common, can be compactly represented, easily and efficiently processed, automatically detected, and lead to large reductions in search. Moreover, the method is easy to implement and integrate in any constraint system. Experimental results show the method is competitive with the best symmetry breaking methods without risking poor performance. 相似文献