全文获取类型
收费全文 | 95798篇 |
免费 | 9875篇 |
国内免费 | 5981篇 |
专业分类
电工技术 | 4258篇 |
技术理论 | 1篇 |
综合类 | 8207篇 |
化学工业 | 16642篇 |
金属工艺 | 8977篇 |
机械仪表 | 7666篇 |
建筑科学 | 5793篇 |
矿业工程 | 3810篇 |
能源动力 | 3374篇 |
轻工业 | 10628篇 |
水利工程 | 2674篇 |
石油天然气 | 4097篇 |
武器工业 | 1104篇 |
无线电 | 8655篇 |
一般工业技术 | 11876篇 |
冶金工业 | 4653篇 |
原子能技术 | 1564篇 |
自动化技术 | 7675篇 |
出版年
2024年 | 349篇 |
2023年 | 1566篇 |
2022年 | 2478篇 |
2021年 | 3150篇 |
2020年 | 3406篇 |
2019年 | 3093篇 |
2018年 | 3010篇 |
2017年 | 3711篇 |
2016年 | 3804篇 |
2015年 | 3974篇 |
2014年 | 5643篇 |
2013年 | 6722篇 |
2012年 | 7221篇 |
2011年 | 7404篇 |
2010年 | 5336篇 |
2009年 | 5302篇 |
2008年 | 4851篇 |
2007年 | 6070篇 |
2006年 | 5399篇 |
2005年 | 4471篇 |
2004年 | 3772篇 |
2003年 | 3228篇 |
2002年 | 2835篇 |
2001年 | 2386篇 |
2000年 | 2111篇 |
1999年 | 1751篇 |
1998年 | 1440篇 |
1997年 | 1294篇 |
1996年 | 1179篇 |
1995年 | 909篇 |
1994年 | 760篇 |
1993年 | 612篇 |
1992年 | 519篇 |
1991年 | 383篇 |
1990年 | 361篇 |
1989年 | 246篇 |
1988年 | 208篇 |
1987年 | 111篇 |
1986年 | 127篇 |
1985年 | 100篇 |
1984年 | 88篇 |
1983年 | 62篇 |
1982年 | 60篇 |
1981年 | 26篇 |
1980年 | 38篇 |
1979年 | 18篇 |
1978年 | 9篇 |
1975年 | 11篇 |
1959年 | 15篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
61.
62.
电器外壳制品形状结构复杂,有两处侧凸(孔)较难处理。通过对矩形孔内侧凸的结构分析,在其局部设计了分型面,避免了使用侧向抽芯机构;对侧孔部位设计了斜顶杆侧向抽芯机构,其结构简单、紧凑。模具采用一模二腔、平衡式布局,采用经扁推杆由制品内部进料的潜伏式浇口,S型流道。在NX 8.0中完成了模具结构设计。经实践证明,该模具结构合理,产品合格。 相似文献
63.
We model developable surfaces by wrapping a planar figure around cones and cylinders. Complicated developables can be constructed by successive mappings using cones and cylinders of different sizes and shapes. We also propose an intuitive control mechanism, which allows a user to select an arbitrary point on the planar figure and move it to a new position. Numerical techniques are then used to find a cone or cylinder that produces the required mapping. Several examples demonstrate the effectiveness of our technique. 相似文献
64.
The identification rate of UHF RFID system was restricted by multipath propagation effects.The system identification performance was studied considering the correlation coefficient between forward and reverse channels.Based on the generalized Rician fading channel model,the analytical expression of identification rate was derived under independent,full correlation and correlation cases.Compared with the existing analysis,the proposed uniform calculation formula of identification rate was for any correlation coefficient and kinds of channel conditions.The numerical computation and Monte-carlo simulations show that the influences of different correlation coefficients,channel conditions,sensitivity and distance on the identification rate. 相似文献
65.
以钙系生料釉为基础,引入结晶剂CuO、MnO2制备无铅CuO-MnO2系金属光泽釉;结合XRD、SEM-EDS进行物相组成定性分析和显微结构表征,系统探究外加TiO2、V2O5以及玻璃粉对金属光泽釉釉面分相的影响。研究表明:一定量的TiO2、V2O5引入能有效促进釉面的分相,将玻璃粉部分替换基础釉中的钾长石能使得釉熔体的高温粘度降低,并进一步加剧釉面分相,促进CuMn2O4铜锰尖晶石在釉层表面的析出和富集;当TiO2引入量为2%,V2O5引入量为1%,玻璃粉引入量为25%(同为质量分数)时,金属光泽釉釉面效果最佳。 相似文献
66.
When a mission arrives at a random time and lasts for a duration, it becomes an interesting problem to plan replacement policies according to the health condition and repair history of the operating unit, as the reliability is required at mission time and no replacement can be done preventively during the mission duration. From this viewpoint, this paper proposes that effective replacement policies should be collaborative ones gathering data from time of operations, mission durations, minimal repairs and maintenance triggering approaches. We firstly discuss replacement policies with time of operations and random arrival times of mission durations, model the policies and find optimum replacement times and mission durations to minimize the expected replacement cost rates analytically. Secondly, replacement policies with minimal repairs and mission durations are discussed in a similar analytical way. Furthermore, the maintenance triggering approaches, i.e., replacement first and last, are also considered into respective replacement policies. Numerical examples are illustrated when the arrival time of the mission has a gamma distribution and the failure time of the unit has a Weibull distribution. In addition, simple case illustrations of maintaining the production system in glass factories are given based on the assumed data. 相似文献
67.
68.
Enhanced gravity, or centrifugal, separators have revolutionised gold processing over the past decades, significantly increasing the recovery of fine (−100 μm) free gold. One of the main drawbacks of centrifugal gravity concentrators is the large volume of water required (even if it is all recycled). With water becoming an ever increasingly important “commodity”, reducing this is of importance both from an environmental and a monetary point of view. This work investigated operating a laboratory scale Knelson Concentrator with a dry feed and using air as the fluidising medium. The feed used was a synthetic mixture of tungsten and quartz, used to mimic a gold ore. The response surface method and central composite design techniques were used to design the experiments and to model the results, with the experimental variables being the bowl speed (G-Level), air fluidising pressure and the feed rate. The models corresponded well to the experimental results, indicating that for this experimental setup, the optimal conditions were a bowl G-Level of 40 G, a feed rate of 220 g/min and an air fluidising pressure of 8 psi. 相似文献
69.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
70.
Antoine Depoorter Carmen Kalalian Corinne Emmelin Chantal Lorentz Christian George 《Indoor air》2021,31(3):682-692
People spend approximately 80% of their time indoor, making the understanding of the indoor chemistry an important task for safety. The high surface-area-to-volume ratio characteristic of indoor environments leads the semi-volatile organic compounds (sVOCs) to deposit on the surfaces. Using a long path absorption photometer (LOPAP), this work investigates the formation of nitrous acid (HONO) through the photochemistry of adsorbed nitrate anions and its enhancement by the presence of furfural. Using a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS), this work also investigates the surface emissions of VOCs from irradiated films of furfural and a mix of furfural and nitrate anions. Among the emitted VOCs, 2(5H)-furanone/2-Butenedial was observed at high concentrations, leading to maleic anhydride formation after UV irradiation. Moreover, the addition of potassium nitrate to the film formed NOx and HONO concentrations up to 10 ppb, which scales to ca. 4 ppb for realistic indoor conditions. This work helps to understand the high levels of HONO and NOx measured indoors. 相似文献