全文获取类型
收费全文 | 35196篇 |
免费 | 3860篇 |
国内免费 | 2163篇 |
专业分类
电工技术 | 2313篇 |
技术理论 | 1篇 |
综合类 | 3309篇 |
化学工业 | 5271篇 |
金属工艺 | 965篇 |
机械仪表 | 2116篇 |
建筑科学 | 2160篇 |
矿业工程 | 652篇 |
能源动力 | 1228篇 |
轻工业 | 2162篇 |
水利工程 | 519篇 |
石油天然气 | 898篇 |
武器工业 | 463篇 |
无线电 | 3703篇 |
一般工业技术 | 4999篇 |
冶金工业 | 1396篇 |
原子能技术 | 333篇 |
自动化技术 | 8731篇 |
出版年
2024年 | 201篇 |
2023年 | 594篇 |
2022年 | 922篇 |
2021年 | 1054篇 |
2020年 | 1275篇 |
2019年 | 1118篇 |
2018年 | 1049篇 |
2017年 | 1314篇 |
2016年 | 1443篇 |
2015年 | 1467篇 |
2014年 | 2128篇 |
2013年 | 2318篇 |
2012年 | 2544篇 |
2011年 | 2890篇 |
2010年 | 2098篇 |
2009年 | 2175篇 |
2008年 | 1838篇 |
2007年 | 2167篇 |
2006年 | 1897篇 |
2005年 | 1527篇 |
2004年 | 1295篇 |
2003年 | 1189篇 |
2002年 | 984篇 |
2001年 | 774篇 |
2000年 | 690篇 |
1999年 | 595篇 |
1998年 | 524篇 |
1997年 | 453篇 |
1996年 | 365篇 |
1995年 | 339篇 |
1994年 | 293篇 |
1993年 | 221篇 |
1992年 | 185篇 |
1991年 | 157篇 |
1990年 | 134篇 |
1989年 | 126篇 |
1988年 | 110篇 |
1987年 | 81篇 |
1986年 | 68篇 |
1985年 | 81篇 |
1984年 | 97篇 |
1983年 | 108篇 |
1982年 | 111篇 |
1981年 | 47篇 |
1980年 | 37篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 18篇 |
1959年 | 5篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
The general mixed μ problem has been shown to be NP hard, so that the exact solution of the general problem is computationally intractable, except for small problems. In this paper we consider not the general problem, but a particular special case of this problem, the rank one mixed μ problem. We show that for this case the mixed μ problem is equivalent to its upper bound (which is convex), and it can in fact be computed easily (and exactly). This special case is shown to be equivalent to the so-called ‘affine parameter variation’ problem (for a polynomial with perturbed coefficients) which has been examined in detail in the literature, and for which several celebrated ‘Kharitonov-type’ results have been proven. 相似文献
103.
This article is the second of two papers that review the field of spatially sensitive social scientific research into the links between social status and transport disadvantage. The first paper undertook a comprehensive review of the social scientific and transport planning literature to mark the level of development in the field and identify conceptual and methodological issues and constraints in this field of inquiry. The present article supports the advancement of socially and geographically sensitive transport research by opportunities for the development of more sophisticated spatial analytical methodologies. The approach we present is able to account for factors not previously addressed in either social or transport planning research, in particular the temporal dimensions of transport service accessibility. The article articulates the methodology through an empirical case study of socio-spatial transport disadvantage within the Gold Coast City. The article demonstrates that there are important theoretical and practical lessons to be gained for researchers and policy makers in addressing the social dimensions of transport and infrastructure provision. Further, the article argues that an attentiveness to new ways of combining and representing social and transport data-sets can promote policy relevant empirical social inquiry. The article also contributes in a productive way to the empirical knowledge of Australia's sixth-largest metropolitan area, which is often overlooked by urban scholars. 相似文献
104.
利用独立分量分析法去除地震噪声 总被引:2,自引:0,他引:2
独立分量分析(ICA)作为盲源分离(BSS)的一种新方法,是分解观测数据中独立信息的有力工具。以往的ICA算法一般假设噪声可以忽略不计,而实际的观测数据中又常常包含一些加性噪声。对于加性噪声的影响不能忽略的情况下,改进的ICA算法首先利用非零时间滞后协方差,应用两步特征值分解法(EVD)可成功地去除部分加性噪声的影响;再利用ICA算法就能更好地分离出原信号。本文通过对地震理论模型和实际资料的试验,说明改进的ICA算法能够有效地克服加性噪声对常规ICA算法的影响,能够分离出地震资料中的有效信号,从而实现利用独立分量分析压制地震资料噪声的目的。 相似文献
105.
应用水文过河缆道测验在传统水文测验中是一种行之有效的测验手段。本文主要结合黄河水文近年来开展的水文测报水平升级活动和现代化建设过程中取得的成功经验,分析说明水文过河缆道建设施工过程中的质量控制措施和方法。 相似文献
106.
107.
E. GLASER 《Journal of microscopy》2005,218(1):1-5
It is well known that the estimation of an object's volume by means of serial cross-sections, the so-called Cavalieri method, yields an unbiased estimate. But by itself it provides no means by which to estimate how precise this estimate is unless the shape of the volume is fully known beforehand. This knowledge can only be partially determined from the serial section information that is collected. Methods have been developed that claim to surmount this difficulty by using the serial section data to create a mathematical model of the volume's shape properties. The model then is used to estimate (predict) the precision of the volume estimate (its CE) from the single set of data available. Unfortunately, the theory underlying the model is flawed and so the model itself amounts to no more than an unsubstantiated guess about the shape of the volume. Therefore, the precision of the volume estimates that one obtains from the method is only as good as the model and this cannot be ascertained from the single set of acquired data. In this letter I explain the inadequacies of the modelling method. I suggest that it be used only with caution, if at all. Instead I suggest two alternative ways to predict the CE, one that is based upon a rule-of-thumb approach to the object's shape, and another that is based upon spectral analysis of the measurement function and that is easy to implement with available computer software. 相似文献
108.
在后工业时代,建筑设计已经冲破了西方思维所惯用的二元对立方式的约束,呈现出日新月异的景象,建筑表皮的创作尤为突出。这个住宅设计是从四维分解到四维连续的一种大胆尝试,并引入拓扑学的基本方法处理动态空间。 相似文献
109.
Charbel Farhat Ulrich Hetmaniuk 《International journal for numerical methods in engineering》2002,54(9):1309-1332
We present a fictitious domain decomposition method for the fast solution of high‐frequency acoustic scattering problems characterized by a partially axisymmetric sound‐soft scatterer. We apply this method to the solution of various mockup submarine problems, and highlight its computational advantages and intrinsic parallelism. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
110.
农业重组微生物生物安全研究进展 总被引:2,自引:2,他引:0
综述了近年来农业重组微生物的研究现状和进展 ,详细介绍农业重组微生物环境释放的监控方法以及对环境的冲击作用 ,对一些有关生物安全研究的热点问题进行了探讨 相似文献