全文获取类型
收费全文 | 154948篇 |
免费 | 6655篇 |
国内免费 | 3366篇 |
专业分类
电工技术 | 4531篇 |
技术理论 | 11篇 |
综合类 | 6450篇 |
化学工业 | 23855篇 |
金属工艺 | 8689篇 |
机械仪表 | 7560篇 |
建筑科学 | 8389篇 |
矿业工程 | 2677篇 |
能源动力 | 3225篇 |
轻工业 | 7919篇 |
水利工程 | 2432篇 |
石油天然气 | 4920篇 |
武器工业 | 571篇 |
无线电 | 17556篇 |
一般工业技术 | 25245篇 |
冶金工业 | 6274篇 |
原子能技术 | 1081篇 |
自动化技术 | 33584篇 |
出版年
2024年 | 267篇 |
2023年 | 1189篇 |
2022年 | 2038篇 |
2021年 | 2705篇 |
2020年 | 2146篇 |
2019年 | 1878篇 |
2018年 | 16113篇 |
2017年 | 15389篇 |
2016年 | 11818篇 |
2015年 | 3381篇 |
2014年 | 3653篇 |
2013年 | 4286篇 |
2012年 | 7586篇 |
2011年 | 14001篇 |
2010年 | 12290篇 |
2009年 | 9367篇 |
2008年 | 10495篇 |
2007年 | 11474篇 |
2006年 | 4136篇 |
2005年 | 4659篇 |
2004年 | 3481篇 |
2003年 | 3224篇 |
2002年 | 2519篇 |
2001年 | 1891篇 |
2000年 | 1986篇 |
1999年 | 2137篇 |
1998年 | 1905篇 |
1997年 | 1550篇 |
1996年 | 1490篇 |
1995年 | 1126篇 |
1994年 | 1068篇 |
1993年 | 735篇 |
1992年 | 570篇 |
1991年 | 471篇 |
1990年 | 334篇 |
1989年 | 265篇 |
1988年 | 251篇 |
1987年 | 149篇 |
1986年 | 107篇 |
1985年 | 81篇 |
1984年 | 39篇 |
1982年 | 40篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1959年 | 38篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
972.
本文用照相法测定了锚式搅拌槽中高粘度流体的流型和速度分布.利用最小二乘法获得速度分布拟合方程以及槽中剪切率γ和耗散能Φ分布方程.比较了槽壁区域剪切率和全槽平均剪切率、Metzner常数k_S和搅拌器特性参数C_3,指出k_S是表征槽中高剪切区域剪切率大小的特征量,C_3表征了全槽平均剪切率的大小.对于均匀剪切场,两者是一致的.可以用单位体积剪切率分布系数φ_V来描述槽中剪切率分布的均匀程度.本文还研究了Re数对速度分布流型的影响,发现在低Re数下,流型是对称的.高Re数下,流型则不对称. 相似文献
973.
974.
本试验研究了新型黄腐酸环保肥料在樱桃番茄上的冲施效果。采用单因素随机区组试验设计,共设六个处理:300mg/mL、120mg/mL、75mg/mL、54mg/mL、43mg/mL、0mg/mL(对照)。试验结果表明,冲施新型黄腐酸环保肥料后,樱桃番茄品质明显改善,产量显著增加。75mg/mL效果最好,120mg/mL次之。在改善果实品质方面,75mg/mL提高可溶性固形物、可溶性总糖、可溶性蛋白、果实干重方面均达显著水平;其中,可溶性固形物、可溶性总糖的提高达极显著水平。在提高产量方面,75mg/mL效果最好,达极显著水平,与对照相比,提高28.34%。另外,75mg/mL处理在改善光合作用能力方面,显著增加叶面积并显著提高叶绿素含量,为植株健壮生长奠定了基础。 相似文献
975.
For a biped pole-climbing robot (BiPCR) with grippers, it is an essential demand to determine the target grasp configuration for climbing and transiting between poles, with the graspable region as a priori knowledge. The graspable region on the target pole is critically important for climbing path planning and motion control. To efficiently compute the graspable region for a BiPCR, we propose a novel binary approximating method in this paper. This method may also be applied to generate the three-dimensional (3-D) workspace of a manipulator with constant orientation. The grasping problem and the concept of graspable region for a BiPCR are first introduced. The binary approximating method and the corresponding algorithms are then presented to generate the graspable region. Additional constraints on a biped climbing robot with five degrees of freedom (DoFs) are presented as a supplement to the algorithm. A series of comprehensive simulations are conducted with the five-DoF and six-DoF climbing robots to verify the effectiveness of the proposed method. Finally, the dexterity of biped climbing robots with different DoFs is discussed. 相似文献
976.
Extracting significant features from high-dimension and small sample size biological data is a challenging problem. Recently, Micha? Draminski proposed the Monte Carlo feature selection (MC) algorithm, which was able to search over large feature spaces and achieved better classification accuracies. However in MC the information of feature rank variations is not utilized and the ranks of features are not dynamically updated. Here, we propose a novel feature selection algorithm which integrates the ideas of the professional tennis players ranking, such as seed players and dynamic ranking, into Monte Carlo simulation. Seed players make the feature selection game more competitive and selective. The strategy of dynamic ranking ensures that it is always the current best players to take part in each competition. The proposed algorithm is tested on 8 biological datasets. Results demonstrate that the proposed method is computationally efficient, stable and has favorable performance in classification. 相似文献
977.
以高纯天然石膏为原料,加压水热法制备高品质硫酸钙晶须。采用常规分析方法、XRD和扫描电镜等手段分析和表征石膏原料和硫酸钙晶须产品。结果表明,制备硫酸钙晶须的最优条件为:料浆质量分数为6.0%,转晶剂氯化镁加入量为石膏质量的0.05%,硫酸加入量为水体积的1.0%,反应时间为4.0 h,快速过滤干燥即得硫酸钙晶须产品。分析结果表明:硫酸钙晶须长度最大为280.4 μm,最小为19.59 μm,平均长度为80 μm;硫酸钙晶须直径最大为5.86 μm,最小为0.20 μm,平均直径为2.67 μm;通过统计分析可知,长径比范围为10~80。 相似文献
978.
采用酸溶法测定并比较几种典型的火山灰质掺合料的火山灰活性,探讨其火山灰反应程度对浆体强度的影响。试验结果表明,硅灰的火山灰活性最大,明显高于煤矸石和粉煤灰;煤矸石和Ⅱ级磨细粉煤灰的火山灰活性比Ⅰ级分选粉煤灰较大;酸溶法测定的煤矸石或硅灰的火山灰活性误差较大,活性偏低;掺合料火山灰的活性与其浆体强度有一定相关性。 相似文献
979.
980.
Hadi Shahriar Shahhoseini Ehsan Saleh Kandzi Morteza Mollajafari 《The Journal of supercomputing》2014,67(1):31-46
Parallel machines are extensively used to increase computational speed in solving different scientific problems. Various topologies with different properties have been proposed so far and each one is suitable for specific applications. Pyramid interconnection networks have potentially powerful architecture for many applications such as image processing, visualization, and data mining. The major advantage of pyramids which is important for image processing systems is hierarchical abstracting and transferring the data toward the apex node, just like the human being vision system, which reach to an object from an image. There are rapidly growing applications in which the multidimensional datasets should be processed simultaneously. For such a system, we need a symmetric and expandable interconnection network to process data from different directions and forward them toward the apex. In this paper, a new type of pyramid interconnection network called Non-Flat Surface Level (NFSL) pyramid is proposed. NFSL pyramid interconnection networks constructed by L-level A-lateral-base pyramids that are named basic-pyramids. So, the apex node is surrounded by the level-one surfaces of NFSL that are the first nearest level of nodes to apex in the basic pyramids. Two topologies which are called NFSL-T and NFSL-Q originated from Trilateral-base and Quadrilateral-base basic-pyramids are studied to exemplify the proposed structure. To evaluate the proposed architecture, the most important properties of the networks are determined and compared with those of the standard pyramid networks and its variants. 相似文献