全文获取类型
收费全文 | 198962篇 |
免费 | 2477篇 |
国内免费 | 633篇 |
专业分类
电工技术 | 4188篇 |
综合类 | 126篇 |
化学工业 | 26361篇 |
金属工艺 | 7601篇 |
机械仪表 | 5497篇 |
建筑科学 | 4011篇 |
矿业工程 | 747篇 |
能源动力 | 4759篇 |
轻工业 | 14404篇 |
水利工程 | 1701篇 |
石油天然气 | 2786篇 |
武器工业 | 7篇 |
无线电 | 27624篇 |
一般工业技术 | 37555篇 |
冶金工业 | 46077篇 |
原子能技术 | 3703篇 |
自动化技术 | 14925篇 |
出版年
2021年 | 1247篇 |
2020年 | 964篇 |
2019年 | 1316篇 |
2018年 | 2204篇 |
2017年 | 2158篇 |
2016年 | 2251篇 |
2015年 | 1548篇 |
2014年 | 2708篇 |
2013年 | 8139篇 |
2012年 | 4599篇 |
2011年 | 6300篇 |
2010年 | 5075篇 |
2009年 | 5919篇 |
2008年 | 6316篇 |
2007年 | 6361篇 |
2006年 | 5773篇 |
2005年 | 5438篇 |
2004年 | 5374篇 |
2003年 | 5177篇 |
2002年 | 4753篇 |
2001年 | 5134篇 |
2000年 | 4647篇 |
1999年 | 5279篇 |
1998年 | 15694篇 |
1997年 | 10299篇 |
1996年 | 7828篇 |
1995年 | 5854篇 |
1994年 | 5082篇 |
1993年 | 5079篇 |
1992年 | 3415篇 |
1991年 | 3272篇 |
1990年 | 3251篇 |
1989年 | 3060篇 |
1988年 | 2800篇 |
1987年 | 2246篇 |
1986年 | 2310篇 |
1985年 | 2645篇 |
1984年 | 2339篇 |
1983年 | 2085篇 |
1982年 | 1924篇 |
1981年 | 2062篇 |
1980年 | 1804篇 |
1979年 | 1681篇 |
1978年 | 1668篇 |
1977年 | 2048篇 |
1976年 | 2732篇 |
1975年 | 1422篇 |
1974年 | 1367篇 |
1973年 | 1313篇 |
1972年 | 1117篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
Firebrand production from structure combustion becomes a key factor in the magnitude of how quickly a large outdoor fire may spread. Post‐fire disaster investigations suggest that attached building components, such as wood fencing assemblies are known to be prone to ignition in these fires, and may provide pathways to structure ignition. Here, a comparison of ignition results from full‐scale fencing assembly experiments conducted using a full‐scale wind tunnel facility, to mock‐ups of full‐scale fencing assemblies using the recently developed experimental capability at the National Research Institute of Fire and Disaster (NRIFD) are discussed. In both experimental facilities, the fencing assemblies were exposed to firebrand showers using custom built continuous feed firebrand generators with size and mass distributions similar to those generated from structure combustion. Similar ignition behaviors were observed between the full‐scale fencing assemblies and the mock‐up of full‐scale fencing assemblies. Additional experiments are required for other fencing assembly types to further verify these important findings. 相似文献
82.
The present work concentrates on some physical investigation of the undoped and Cr doped SnO2 thin films deposited onto precleaned glass substrates by the spray pyrolysis system. The physical properties of the undoped and Cr doped SnO2 thin films were investigated by the X-ray diffraction (XRD), atomic force electron microscope (AFM), field emission scanning electron microscope (FESEM), four-probe method and double beam spectrophotometer. The undoped and Cr doped SnO2 films display a polycrystalline nature with orthorhombic crystal structure. The linear optical constants energy gap Eg, refractive index n, absorption coefficient α, static refractive index no, oscillation energy Eo, dispersion energy Ed and the Urbach energy of the undoped and Cr doped SnO2 thin films were evaluated. The investigated films exhibit a direct energy gap and their values decrease with the increasing of Cr doping content while the Urbach energy follows a reverse behavior. On the other hand, the nonlinear optical constants (third-order nonlinear susceptibility and nonlinear refractive index n2) have been increased with increasing the Cr doping content. Finally, it has been found that the sheet resistance and conductivity of the synthesized thin films were enhanced by increasing the Cr doping content. The 5?wt% Cr doped SnO2 thin film has a high value of the figure of merit among other films. 相似文献
83.
Improvement of 19F MR image uniformity in a mouse model of cellular therapy using inductive coupling
Park Bu S. Ma Ge Koch William T. Rajan Sunder S. Mastromanolis Manuel Lam Johnny Sung Kyung McCright Brent 《Magma (New York, N.Y.)》2019,32(1):15-23
Magnetic Resonance Materials in Physics, Biology and Medicine - Improve 19F magnetic resonance imaging uniformity of perfluorocarbon (PFC)-labeled cells by using a secondary inductive resonator... 相似文献
84.
Strength of Materials - We apologize to the authors and readers for these technical lapses made by the journal staff. 相似文献
85.
Pashayev A. M. Tagiyev B. H. Tagiyev O. B. Majidova V. T. Sadikhov I. Z. 《Semiconductors》2019,53(2):210-214
Semiconductors - The results of measuring the electrical conductivity of layered crystals (GaSe, GaTe, and their solid solutions) and cubic crystals (Ga2Se3) in strong electric fields (up to 5... 相似文献
86.
Legka T. M. Mika T. M. Milman Yu. V. Korzhova N. P. Voskoboynik I. V. Mordovets N. M. 《Powder Metallurgy and Metal Ceramics》2019,57(11-12):716-722
Powder Metallurgy and Metal Ceramics - A fragment of the Al corner in the ternary Al–Ge–Mg phase diagram has been constructed. Experimental methods have shown that the tie-line of the L... 相似文献
87.
Measurement Techniques - The design, principle of operation, and budget of errors of a laser interference oil manometer developed at the Mendeleev All-Russia Research Institute of Metrology (VNIIM)... 相似文献
88.
Trisha T. C. Lin 《International journal of human-computer interaction》2019,35(2):99-108
Past social TV (STV) system user studies usually tested a small number of trialists in lab settings in Western countries. This Asian research took a mix method approach (interview, observation, and web survey) to examine the attitudes of 76 young adults’ experiences of using a multiscreen STV system. The results show that the majority of participants preferred shifting and complementary patterns when using STV. Their favorite feature was multiscreen video teleportation via QR codes. Nearly half of participants agreed that sociability features of the STV system could facilitate their perceived social presence and sense of community, which increased adoption intention. Additionally, text messaging was selected as the preferred mode for social interactions during video viewing. Although most participants liked the user-friendly design to upload and share videos conveniently, age has a negative association with users’ receptiveness of the user generated video channel creation and aggregation feature. 相似文献
89.
90.
Journal of Applied Electrochemistry - We have developed a methodology for electrohydrodynamic printing of a nitric oxide (NO) sensor. The primary features of this amperometric methodology include... 相似文献