全文获取类型
收费全文 | 1057篇 |
免费 | 157篇 |
国内免费 | 107篇 |
专业分类
电工技术 | 30篇 |
综合类 | 102篇 |
化学工业 | 135篇 |
金属工艺 | 26篇 |
机械仪表 | 31篇 |
建筑科学 | 24篇 |
矿业工程 | 8篇 |
能源动力 | 33篇 |
轻工业 | 104篇 |
水利工程 | 21篇 |
石油天然气 | 18篇 |
武器工业 | 8篇 |
无线电 | 171篇 |
一般工业技术 | 162篇 |
冶金工业 | 21篇 |
原子能技术 | 48篇 |
自动化技术 | 379篇 |
出版年
2024年 | 1篇 |
2023年 | 20篇 |
2022年 | 44篇 |
2021年 | 55篇 |
2020年 | 51篇 |
2019年 | 48篇 |
2018年 | 41篇 |
2017年 | 52篇 |
2016年 | 62篇 |
2015年 | 62篇 |
2014年 | 65篇 |
2013年 | 76篇 |
2012年 | 69篇 |
2011年 | 67篇 |
2010年 | 59篇 |
2009年 | 59篇 |
2008年 | 73篇 |
2007年 | 43篇 |
2006年 | 39篇 |
2005年 | 43篇 |
2004年 | 49篇 |
2003年 | 43篇 |
2002年 | 42篇 |
2001年 | 29篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有1321条查询结果,搜索用时 15 毫秒
11.
The antioxidant vitamin E, -tocopherol, was tested as a candidate elicitor of alterable antiherbivory in soybean plants against cabbage looper larvae. Although a nonspecific antioxidant, vitamin E proved elicitory to the involved sulfhydryl-dependent receptor-energy transducer protein in soybean plasma membrane. Effects of -tocopherol were dependent on dosage, time, and space in the plant. The observed elicited effects were all decreases in herbivory. The best negative phytochemical correlate of looper feeding was the percentage of increased total HPLC peak area of extractables from elicited as compared to nonelicited leaves. Some specific compounds, e.g., glyceollins, were quantitatively major components of the total profile of secondary metabolites. 相似文献
12.
Y. F. Zhou S. Xie X. W. Ge C. H. Chen K. Amine 《Journal of Applied Electrochemistry》2004,34(11):1119-1125
An admixture of commercial liquid electrolyte (LB302, 1 M solution of LiPF6 in 1:1 EC/DEC) and methyl methacrylate (MMA) was enclosed in CR2032 cells. The assembled cells were then -ray-irradiated using configurations of half cells and full cells. Through this in situ irradiation polymerization process, we obtained rechargeable lithium ion cells with poly(methyl methacrylate) (PMMA) based gel polymer electrolytes (GPE). Galvanostatic cycling, AC impedance spectroscopy, and cyclic voltammetry were employed to investigate the electrochemical properties of the cells and the gel polymer electrolyte. This PMMA-based gel polymer electrolyte was found to exhibit a high ionic conductivity (at least 10–3 S cm–1) at room temperature. Due to a significant increase in the charge transfer resistance between the GPE and the cathode, the cell impedance of a PMMA-based lithium ion cell is greater than that of a liquid-electrolyte-based cell. The discharge capacity of a LiNi0.8Co0.2O2/GPE/graphite is approximately 145 mAh g–1 for the first cycle and decreases to123 mAh g–1 after 20 cycles. In addition, a large initial cell impedance (LICI) was observed in the irradiated positive half cell. In this paper, we propose a possible mechanism related to the detachment of the PMMA layer from the lithium electrode. This detachment of the PMMA layer from the lithium electrode has not been explicitly discussed previously. 相似文献
13.
首先对文献[3]所提出的门限密钥分割方案进行了整理分析,具体分析了其动态性,然后在此基础上提出了一种新的基于ElGamal公钥体制的动态(k,n)门限密钥托管方案。该方案具有如下特点:(1)可以防止闽下信道攻击;(2)在监听过程中,监听机构可以对托管代理交给其的子密钥进行验证;(3)解决了“一次监听,永久监听问题”;(4)具有动态性质。 相似文献
14.
在定数截尾缺失数据样本下,研究了不可修k/N(G)系统的可靠性指标评估问题。将经典估计方法和Bayes方法相结合得到了部件的平均寿命、系统可靠度及平均寿命等可靠性指标的Bayes估计。最后利用随机模拟例子说明了本研究方法的正确性和可行性。 相似文献
15.
The catalytic activity and selectivity of heterodonor phosphine rhodium catalysts prepared in situ were tested in the hydroformylation of functional alkenes (ethyl acrylate, methyl methacrylate, styrene, 4-vinyl-1-cyclohexene, dicyclopentadiene and cis-1,2,3,6-tetrahydrophthalic anhydride). Systematic variation of the heterodonor atom in the ortho position of the ligand showed that the heterodonor atom has a significant influence on the activities and selectivities of the reaction. However, the activity seems to depend mainly on the modifying ligand, and the regioselectivity mainly on the substrate (i.e., the structure and functionality of the alkene). Nevertheless, regioselective control is only obtained through synergy between the substrate and the catalyst. Clear regiocontrol was observed in the hydroformylation of ,-unsaturated esters and styrene with an in situ formed o-(thiomethylphenyl)diphenylphosphine rhodium catalyst. 相似文献
16.
并行计算机系统互连网络的拓扑性质对系统功能的实现起着重要的作用。为了衡量基于[k]元[n]方体网络构建的并行计算机系统的容错能力,研究了边故障模型下[k]元[n]方体网络中[k]元[(n-1)]方体子网络的可靠性。当[k(k≥3)]为奇数时,分别在固定划分模式和灵活划分模式下得出了[k]元[n]方体网络中不同数目的[k]元[(n-1)]方体子网络保持无故障状态的平均失效时间的计算公式,并通过仿真实验验证了理论结果的精确性。研究表明,当[k]为奇数的[k]元[n]方体网络中有边故障发生时,相比固定划分模式,在灵活划分模式下不同数目的[k]元[(n-1)]方体子网络保持无故障状态的平均失效时间更大。 相似文献
17.
分类是数据挖掘和数据分析中最有应用价值的技术之一。传统的积极学习方法需要预先对模型空间进行假设,并且没有充分考虑到实例之间的相关性,其泛化能力将会受到一定程度的影响。针对上述问题,提出了一种基于新型映射关系的局部加权回归方法 MLWR。该算法首先找出测试样本在训练集中的近邻样本,然后建立测试样本和近邻样本的回归函数,根据建立的回归模型和近邻样本的标签,计算得到测试样本的标签。实验与当前流行的多种分类方法在UCI的9个数据集上进行测试。实验结果表明我们的方法能有效地提高分类精度,对较大样本数据也有较好的适用性。 相似文献
18.
Embedding of paths have attracted much attention in the parallel processing. Many-to-many communication is one of the most central issues in various interconnection networks. A graph G is globally two-equal-disjoint path coverable if for any two distinct pairs of vertices (u,v) and (w,x) of G, there exist two disjoint paths P and Q satisfied that (1) P (Q, respectively) joins u and v (w and x, respectively), (2) |P|=|Q|, and (3) V(PQ)=V(G). The Matching Composition Network (MCN) is a family of networks which two components are connected by a perfect matching. In this paper, we consider the globally two-equal-disjoint path cover property of MCN. Applying our result, the Crossed cube CQn, the Twisted cube TQn, and the Möbius cube MQn can all be proven to be globally two-equal-disjoint path coverable for n5. 相似文献
19.
Abstract. In this paper two problems on the class of k -trees, a subclass of the class of chordal graphs, are considered: the fast reordering problem and the isomorphism problem. An O(log
2
n) time parallel algorithm for the fast reordering problem is described that uses O(nk(n-k)/\kern -1ptlog n) processors on a CRCW PRAM proving membership in the class NC for fixed k . An O(nk(k+1)!) time sequential algorithm for the isomorphism problem is obtained representing an improvement over the O(n
2
k(k+1)!) algorithm of Sekharan (the second author) [10]. A parallel version of this sequential algorithm is presented that runs in
O(log
2
n) time using O((nk((k+1)!+n-k))/log n) processors improving on a parallel algorithm of Sekharan for the isomorphism problem [10]. Both the sequential and parallel
algorithms use a concept introduced in this paper called the kernel of a k -tree. 相似文献
20.
基于无秩树自动机的信息抽取技术研究 总被引:1,自引:0,他引:1
针对目前基于网页结构的信息抽取方法的缺陷,提出了一种基于无秩树自动机的信息抽取技术,其核心思想是通过将结构化(半结构化)文档转换成无秩树,然后利用(k,l)-contextual树构造样本自动机,依据树自动机接收和拒绝状态来对网页进行数据的抽取.该方法充分利用结构,依托树自动机将传统的以单一结构途径的信息抽取方法与文法推理原则相结合,得到信息抽取规则.实验结果表明,该方法与同类抽取方法相比在准确率、召回率以及抽取所需时间上均有所提高. 相似文献