全文获取类型
收费全文 | 288894篇 |
免费 | 22020篇 |
国内免费 | 11074篇 |
专业分类
电工技术 | 15391篇 |
技术理论 | 31篇 |
综合类 | 17429篇 |
化学工业 | 50182篇 |
金属工艺 | 16872篇 |
机械仪表 | 18427篇 |
建筑科学 | 22864篇 |
矿业工程 | 9523篇 |
能源动力 | 7954篇 |
轻工业 | 16659篇 |
水利工程 | 4778篇 |
石油天然气 | 20256篇 |
武器工业 | 2234篇 |
无线电 | 31459篇 |
一般工业技术 | 34374篇 |
冶金工业 | 15267篇 |
原子能技术 | 2857篇 |
自动化技术 | 35431篇 |
出版年
2024年 | 1217篇 |
2023年 | 4675篇 |
2022年 | 7916篇 |
2021年 | 11438篇 |
2020年 | 8524篇 |
2019年 | 7266篇 |
2018年 | 8166篇 |
2017年 | 9215篇 |
2016年 | 8023篇 |
2015年 | 11167篇 |
2014年 | 13770篇 |
2013年 | 16443篇 |
2012年 | 17749篇 |
2011年 | 19397篇 |
2010年 | 16747篇 |
2009年 | 15901篇 |
2008年 | 15438篇 |
2007年 | 15084篇 |
2006年 | 15972篇 |
2005年 | 14146篇 |
2004年 | 9045篇 |
2003年 | 7903篇 |
2002年 | 7304篇 |
2001年 | 6483篇 |
2000年 | 7097篇 |
1999年 | 8498篇 |
1998年 | 6845篇 |
1997年 | 5821篇 |
1996年 | 5450篇 |
1995年 | 4507篇 |
1994年 | 3757篇 |
1993年 | 2628篇 |
1992年 | 2136篇 |
1991年 | 1601篇 |
1990年 | 1173篇 |
1989年 | 933篇 |
1988年 | 759篇 |
1987年 | 523篇 |
1986年 | 389篇 |
1985年 | 265篇 |
1984年 | 183篇 |
1983年 | 120篇 |
1982年 | 130篇 |
1981年 | 86篇 |
1980年 | 70篇 |
1979年 | 24篇 |
1978年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
962.
J2EE(Java 2平台企业版)是当前建立和开发各种Web应用的主流平台,MVC(模型-视图-控制)体系结构是当今设计交互式应用的事实标准.文中结合MVC在J2EE Web中的应用,通过电子政务系统开发实践,提出了一个具体的实现方案,描述了应用系统设计,给出了表示层、控制层、代理层、业务逻辑层、数据访问层和数据存储层等层次的明确划分,阐述了各层的功能作用以及层与层之间的关系,并针对具体业务给出了实现的部分具体内容,为在J2EE环境下开发结构良好、易于维护、易于扩展的Web应用提供了可行方案. 相似文献
963.
The technique of using a coarse model obtained from layout-level synthesis of radio frequency components in neural inverse space mapping (NISM) optimisation technique is proposed. Layout-level synthesis is based on a combination of segmented lump-circuit modelling, nonlinear mapping using neural network (NN) and circuit-level optimisation. The circuit model based on the electromagnetic (EM) simulation describes the important parameters and parasitic parameters and serves as a high-quality coarse model in applying NISM. In implementation of NISM optimisation, trained NN is introduced as a buffer space between the original coarse model space and the fine model space, where the subset of the coarse model space is completely different from that of the fine model space. Stoer-Bulirsch adaptive frequency sampling (S-B AFS) technique is used in frequency sweep of the fine model to further reduce the computing time. An application design of low-temperature ceramic cofired filter is used to demonstrate the proposed technique. Synthesis and optimisation results of the filter meet the design specifications. 相似文献
964.
A globally convergent algorithm for transportation continuous network design problem 总被引:2,自引:0,他引:2
The continuous network design problem (CNDP) is characterized by a bilevel programming model, in which the upper level problem
is generally to minimize the total system cost under limited expenditure, while at the lower level the network users make
choices with regard to route conditions following the user equilibrium principle. In this paper, the bilevel programming model
for CNDP is transformed into a single level convex programming problem by virtue of an optimal-value function tool and the
relationship between System Optimum (SO) and User Equilibrium (UE). By exploring the inherent nature of the CNDP, the optimal-value
function for the lower level user equilibrium problem is proved to be continuously differentiable and its derivative in link
capacity enhancement can be obtained efficiently by implementing user equilibrium assignment subroutine. However, the reaction
(or response) function between the upper and lower level problem is implicit and its gradient is difficult to obtain. Although,
here we approximately express the gradient with the difference concept at each iteration, based on the method of successive
averages (MSA), we propose a globally convergent algorithm to solve the single level convex programming problem. Comparing
with widely used heuristic algorithms, such as sensitivity analysis based (SAB) method, the proposed algorithm needs not strong
hypothesis conditions and complex computation for the inverse matrix. Finally, a numerical example is presented to compare
the proposed method with some existing algorithms. 相似文献
965.
The self-assembly of various nanostructures is recently attracting a great deal of research attention. In this paper, we demonstrate that a palladium chloride aqueous solution, mixed with a proper ammonia solution, can produce Tetra-amminepalladous chloride (Pd(NH3)4Cl2·H2O) nanowires. These nanowires can spontaneously form the two-dimensional hexagon-oriented Pd(NH3)4Cl2·H2O arrays on mica surfaces. We can control the length and height of these nanowires by adjusting their deposit time on the mica substrate. This method can be potentially used in making sensors or in making templates to wire and position nanodevices. 相似文献
966.
967.
土体中毛细水压力的研究 总被引:1,自引:0,他引:1
该文从毛细水产生负孔隙水压力概念入手 ,对较难确定的孔隙水压力系数以及较抽象的地下连续墙时效稳定分析等问题进行了定量计算 ,以期对工程实践有一定的指导作用 相似文献
968.
文本索引词项相对权重计算方法与应用 总被引:4,自引:0,他引:4
文本索引词权重计算方法决定了文本分类的准确率。该文提出一种文本索引词项相对权重计算方法,即文本索引词项权重根据索引词项在该文本中的出现频率与在整个文本空间出现的平均频率之间的相对值进行计算。该方法能有效地提高索引词对文本内容识别的准确性。 相似文献
969.
硫含量对钴钼型耐硫脱氧剂的脱氧活性影响 总被引:2,自引:0,他引:2
研究了工艺气中硫含量对钴钼型耐硫脱氧剂脱氧活性的影响。通过常压微反 -色谱装置测定脱氧剂的本征脱氧活性 ,加压原粒度反应器测定脱氧剂的表观脱氧活性 ,结合实际经验确定了耐硫脱氧剂所需的最低硫含量。还讨论了温度、压力、空速对耐硫脱氧剂脱氧活性的影响。结果表明 ,耐硫脱氧剂完全能满足耐硫变换工艺的要求 ,而且有耐硫变换的作用 ,并对耐硫变换催化剂起到保护作用 相似文献
970.
The ears of lizards are highly directional. The directionality is generated by strong acoustical coupling of the eardrums.
A simple lumped-parameter model of the ear followed by binaural comparisons has been shown to perform successful phonotaxis
in robot implementations. However, such a model will produce localization errors in the form of response bias if the ears
are asymmetrical. We have evaluated how large errors are generated by asymmetry using simulations of the ear model in Mathematica
5.2. The study shows that the effect of asymmetry is minimal around the most directional frequency of the ear, but that biases
reduce the useful bandwidth of localization.
This work was presented in part at the First European Workshop on Artificial Life and Robotics, Vienna, Austria, July 12–13,
2007 相似文献