全文获取类型
收费全文 | 47696篇 |
免费 | 1094篇 |
国内免费 | 1069篇 |
专业分类
电工技术 | 901篇 |
综合类 | 374篇 |
化学工业 | 7410篇 |
金属工艺 | 3384篇 |
机械仪表 | 1621篇 |
建筑科学 | 1225篇 |
矿业工程 | 273篇 |
能源动力 | 1598篇 |
轻工业 | 2976篇 |
水利工程 | 449篇 |
石油天然气 | 1503篇 |
武器工业 | 16篇 |
无线电 | 4566篇 |
一般工业技术 | 11483篇 |
冶金工业 | 7646篇 |
原子能技术 | 837篇 |
自动化技术 | 3597篇 |
出版年
2022年 | 382篇 |
2021年 | 556篇 |
2020年 | 435篇 |
2019年 | 542篇 |
2018年 | 905篇 |
2017年 | 857篇 |
2016年 | 942篇 |
2015年 | 773篇 |
2014年 | 1091篇 |
2013年 | 2807篇 |
2012年 | 1740篇 |
2011年 | 2267篇 |
2010年 | 1819篇 |
2009年 | 2090篇 |
2008年 | 1877篇 |
2007年 | 2023篇 |
2006年 | 1659篇 |
2005年 | 1405篇 |
2004年 | 1326篇 |
2003年 | 1275篇 |
2002年 | 1301篇 |
2001年 | 1323篇 |
2000年 | 1094篇 |
1999年 | 1083篇 |
1998年 | 2221篇 |
1997年 | 1775篇 |
1996年 | 1521篇 |
1995年 | 1036篇 |
1994年 | 803篇 |
1993年 | 817篇 |
1992年 | 628篇 |
1991年 | 595篇 |
1990年 | 533篇 |
1989年 | 494篇 |
1988年 | 381篇 |
1987年 | 406篇 |
1986年 | 372篇 |
1985年 | 389篇 |
1984年 | 319篇 |
1983年 | 311篇 |
1982年 | 310篇 |
1981年 | 301篇 |
1980年 | 354篇 |
1979年 | 349篇 |
1978年 | 305篇 |
1977年 | 421篇 |
1976年 | 645篇 |
1975年 | 311篇 |
1974年 | 300篇 |
1973年 | 314篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C?s??1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050?mm. 相似文献
32.
Hong Wei Li Li Ya‐Li Ma Ru‐Xue Liu Shuang‐Yan Meng Li‐Tong Niu Zhe Zhang Zhi‐Wang Yang 《火与材料》2019,43(7):868-879
Through the simple precipitation of palygorskite (PGS) by zinc borate (ZB) (to make PGS@ZB) and the decoration of PGS@ZB by dodecylamine (N), a novel organic‐inorganic@inorganic hybrid flame retardant of PGS@ZB‐N was prepared and was incorporated with ethylene vinyl acetate copolymer (EVA) to improve its flame retardance. The structure and morphology of PGS@ZB‐N were characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), and scanning electron microscopy (SEM), and it was confirmed that the PGS@ZB‐N hybrid had been successfully prepared. The flame retardancy and burning behavior of EVA/PGS@ZB‐N/EG (EG = expandable graphite) composite were studied through thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL‐94 (by the vertical burning test), and cone calorimeter test (CCT) characterizations. The prepared EVA/PGS@ZB‐N/EG composite obtained an LOI value of 41.2% with the addition of 30 wt% PGS@ZB‐N/EG. It was found that EVA/PGS@ZB‐N/EG was protected through a gas phase and condensed phase alternating synergistic effect mechanism. 相似文献
33.
The hippocampus is crucial in learning, memory and emotion processing, and is involved in the development of different neurological and neuropsychological disorders. Several epigenetic factors, including DNA methylation, histone modifications and non-coding RNAs, have been shown to regulate the development and function of the hippocampus, and the alteration of epigenetic regulation may play important roles in the development of neurocognitive and neurodegenerative diseases. This review summarizes the epigenetic modifications of various cell types and processes within the hippocampus and their resulting effects on cognition, memory and overall hippocampal function. In addition, the effects of exposure to radiation that may induce a myriad of epigenetic changes in the hippocampus are reviewed. By assessing and evaluating the current literature, we hope to prompt a more thorough understanding of the molecular mechanisms that underlie radiation-induced epigenetic changes, an area which can be further explored. 相似文献
34.
Qiuping Wang Bojan Šarkanj Jasna Jurasovic Yusuf Chisti Michael Sulyok Jiashun Gong Sarote Sirisansaneeyakul Draženka Komes 《International Journal of Food Science & Technology》2019,54(5):1541-1549
Theabrownins (TB) are polymeric phenolic compounds associated with the multiple bioactivities of Pu-erh tea, a post-fermented Chinese dark tea. High-TB instant Pu-erh tea was produced via a novel submerged fermentation (SF) using Aspergillus tubingensis and compared with samples produced commercially via the conventional solid-state fermentation (SSF). Viable microorganisms and microbial toxins, especially aflatoxins B1, G1, B2, G2, cyclopiazonic acid, fumonisins B1, B2, B3 and ochratoxin A, were below the detection limit in all samples. Fewer microbial metabolites were found in SF instant tea compared with the SSF teas. Based on an adult consuming 1 g of instant Pu-erh tea daily, the dietary intake of investigated elements was below the safe limits recommended by various authorities. Tasters viewed the instant tea infusions as very mild, smooth, mellow and full. This suggested that submerged fermentation using A. tubingensis offers a speedy and safe alternative to commercial production of instant Pu-erh tea. 相似文献
35.
36.
37.
38.
Popular biorthogonal wavelet filters via a lifting scheme and its application in image compression 总被引:2,自引:0,他引:2
Cheng L. Liang D.L. Zhang Z.H. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(4):227-232
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image. 相似文献
39.
In colloidal suspensions of silica, particles undergo constant collisions. By controlling various parameters, the repulsive barrier can be reduced, thereby substantially increasing the number of collision‐induced dimerization events. Xia and co‐workers report on p. 1627 that the dimers could be arrested and then permanently fixed by introducing a small amount of fresh tetraethylorthosilicate into the colloidal suspension, with monodisperse dimer yields of up to 50 %. This yield could be increased to 80 % by centrifugation in a density gradient medium. When fresh tetraethylorthosilicate is introduced into a colloidal suspension of silica spheres, it hydrolyzes and condenses in situ to arrest and fix the dimers resulting from constant collisions between the spheres. By optimizing the experimental parameters (including the length of aging time) and the diameter of the silica spheres, as well as the concentrations of counterions, water, and ammonia, it is possible to routinely produce monodisperse dimers with a yield as high as 50 %. When combined with centrifugation using a density gradient medium, the yield of such dimers could be further increased to 80 %. It is believed that this method will provide a simple and versatile approach to the high‐volume production of dimers from spherical colloids composed of different materials. These dimers may find widespread use in a range of applications such as fabrication of photonic crystals and fundamental studies related to colloidal science. 相似文献
40.
Hyun‐Cheol Kim Charalampos Z. Patrikakis Nikos Minogiannis Pantelis N. Karamolegkos Alex Lambiris Kyuheon Kim 《ETRI Journal》2006,28(4):411-424
This paper presents a multimedia streaming platform for efficiently transmitting MPEG‐4 content over IP networks. The platform includes an MPEG‐4 compliant streaming server and client, supporting object‐based representation of multimedia scenes, interactivity, and advanced encoding profiles defined by the ISO standard. For scalability purposes, we employ an application‐layer multicast scheme for media transmission using overlay networks. The overlay network, governed by the central entity of the network distribution manager, is dynamically deployed according to a set of pre‐defined criteria. The overlay network supports both broadcast delivery and video‐on‐demand content. The multimedia streaming platform is standards‐compliant and utilizes widespread multimedia protocols such as MPEG‐4, real‐time transport protocol, real‐time transport control protocol, and real‐time streaming protocol. The design of the overlay network was architected with the goal of transparency to both the streaming server and the client. As a result, many commercial implementations that use industry‐standard protocols can be plugged into the architecture relatively painlessly and can enjoy the benefits of the platform. 相似文献