全文获取类型
收费全文 | 152247篇 |
免费 | 20348篇 |
国内免费 | 9874篇 |
专业分类
电工技术 | 13769篇 |
技术理论 | 15篇 |
综合类 | 18918篇 |
化学工业 | 11700篇 |
金属工艺 | 4831篇 |
机械仪表 | 11260篇 |
建筑科学 | 14092篇 |
矿业工程 | 5059篇 |
能源动力 | 6616篇 |
轻工业 | 4978篇 |
水利工程 | 9532篇 |
石油天然气 | 7824篇 |
武器工业 | 2124篇 |
无线电 | 12496篇 |
一般工业技术 | 12891篇 |
冶金工业 | 4813篇 |
原子能技术 | 1596篇 |
自动化技术 | 39955篇 |
出版年
2025年 | 1643篇 |
2024年 | 3905篇 |
2023年 | 3636篇 |
2022年 | 4885篇 |
2021年 | 5448篇 |
2020年 | 5923篇 |
2019年 | 5194篇 |
2018年 | 4765篇 |
2017年 | 5725篇 |
2016年 | 6618篇 |
2015年 | 6795篇 |
2014年 | 8777篇 |
2013年 | 9360篇 |
2012年 | 10353篇 |
2011年 | 10975篇 |
2010年 | 8675篇 |
2009年 | 8918篇 |
2008年 | 8919篇 |
2007年 | 10029篇 |
2006年 | 8654篇 |
2005年 | 7601篇 |
2004年 | 6146篇 |
2003年 | 5336篇 |
2002年 | 4189篇 |
2001年 | 3495篇 |
2000年 | 3022篇 |
1999年 | 2326篇 |
1998年 | 1965篇 |
1997年 | 1616篇 |
1996年 | 1509篇 |
1995年 | 1334篇 |
1994年 | 1082篇 |
1993年 | 768篇 |
1992年 | 635篇 |
1991年 | 501篇 |
1990年 | 402篇 |
1989年 | 331篇 |
1988年 | 206篇 |
1987年 | 135篇 |
1986年 | 104篇 |
1985年 | 105篇 |
1984年 | 108篇 |
1983年 | 48篇 |
1982年 | 67篇 |
1981年 | 35篇 |
1980年 | 49篇 |
1979年 | 47篇 |
1978年 | 18篇 |
1959年 | 18篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
基于复杂地形上三角网数字地面模型的建立 总被引:4,自引:0,他引:4
蒋红斐 《计算机应用与软件》1998,15(4):62-66
本文提出了一种生成三角网数字地面模型的新方法,它首先利用凸多边形的性质与凸锥的特性来将离散点连成一三角网,计算工作特别快速有效;其次在三角网形成过程中,能将特征信息线作为三角形的边参加构网并采用了优化手段来优化三角网的现状。该方法能有效地限制狭长三角形的出现,并使生成的三角网能密贴地面,真实反映出地表形状。与其它算法相比,该方法具有思路简单明了、成网速度快、编程容易及成网质量高的特点。实际应用表明 相似文献
102.
Perturbation Analysis of Multiclass Stochastic Fluid Models 总被引:1,自引:5,他引:1
Gang Sun Christos G. Cassandras Christos G. Panayiotou 《Discrete Event Dynamic Systems》2004,14(3):267-307
We use a stochastic fluid model (SFM) to capture the operation of finite-capacity queueing systems with multiple customer classes. We derive gradient estimators for class-dependent loss and workload related performance metrics with respect to any one of several threshold parameters used for buffer control. These estimators are shown to be unbiased and directly observable from a sample path without any knowledge of underlying stochastic characteristics of the traffic processes. This renders them computable in on-line environments and easily implementable in settings such as communication networks. 相似文献
103.
刘海滨 《中国矿业大学学报(英文版)》2004,14(1)
On the basis of analysis and selection of factors influencing operation cost of coal resources development, fuzzy set method and artificial neural network (ANN) were adopted to set up the classification analysis model of coal resources. The collected samples were classified by using this model. Meanwhile, the pattern recognition model for classifying of the coal resources was built according to the factors influencing operation cost. Based on the results achieved above, in the light of the theory of information diffusion, the calculation model for operation cost of coal resources development has been presented and applied in practice, showing that these models are reasonable. 相似文献
104.
事故预测模型的建立与应用 总被引:3,自引:2,他引:3
阐述了事故发生的时序随机平稳性,采用最小二乘法进行相关分析,建立了事故频数与年序数之间的回归预测模型,应用事故预测模型,对某单位15年事故进行了相关分析与计算,预测了未来年度该单位可能发生的事故频数,及其预测区间.对该事故预测模型的应用进行了简单的说明. 相似文献
105.
活齿端面谐波齿轮啮合状态的几何模型 总被引:1,自引:1,他引:1
活齿端面谐波齿轮是综合现有的谐波齿轮传动和活齿传动的优点而发明的一种新型传动装置.可以在保留现有谐波齿轮传动所有优点的基础上.大幅度地提高所传递的功率。建立了描写活齿端面谐波齿轮啮合状态的几何模型.并利用该几何模型推导出了活齿端面谐波齿轮实现连续传动的条件。 相似文献
106.
A solution is given to the urgent problem of high-efficiency control of complex hierarchical distributed integrated industrial complexes by developing a unified functional target approach to synthesizing their control systems utilizing information technologies and the creation of means for constructing a conceptual model of the subject domain. 相似文献
107.
We propose a method for the recalculation of dynamic stresses from a photoelastic model to a real solid in plane problems of the mechanics of orthotropic bodies. To estimate the accuracy of the method, we recalculate stresses for a problem with known theoretical solution. 相似文献
108.
This paper introduces a measuring method of early lateral energy fraction in the scale model experiments. According to the interference principle of half wave length making the high frequency figure-8 directional microphone. With the signal-processing technique, a receiving and analyzing system, for the measurements of lateral energy fraction in the scale model is realized. 相似文献
109.
This article considers a structured latent curve model for multiple repeated measures. In a structured latent curve model, a smooth nonlinear function characterizes the mean response. A first-order Taylor polynomial taken with regard to the mean function defines elements of a restricted factor matrix that may include parameters that enter nonlinearly. Similar to factor scores, random coefficients are combined with the factor matrix to produce individual latent curves that need not follow the same form as the mean curve. Here the associations between change characteristics in multiple repeated measures are studied. A factor analysis model for covariates is included as a means of relating latent covariates to the factors characterizing change in different repeated measures. An example is provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
110.
The algorithm is divided into two steps. The first step pre-locates the blank by aligning its centre of gravity and approximate normal vector with those of destination surfaces, with largest overlap of projections of two objects on a plane perpendicular to the normal vector. The second step is optimizing an objective function by means of gradient-simulated annealing algorithm to get the best matching of a set of distributed points on the blank and destination surfaces. An example for machining… 相似文献