全文获取类型
收费全文 | 61443篇 |
免费 | 993篇 |
国内免费 | 1103篇 |
专业分类
电工技术 | 1473篇 |
技术理论 | 3篇 |
综合类 | 843篇 |
化学工业 | 5838篇 |
金属工艺 | 1901篇 |
机械仪表 | 3125篇 |
建筑科学 | 4936篇 |
矿业工程 | 3623篇 |
能源动力 | 446篇 |
轻工业 | 10217篇 |
水利工程 | 2207篇 |
石油天然气 | 1707篇 |
武器工业 | 242篇 |
无线电 | 7057篇 |
一般工业技术 | 13699篇 |
冶金工业 | 1645篇 |
原子能技术 | 554篇 |
自动化技术 | 4023篇 |
出版年
2023年 | 428篇 |
2022年 | 525篇 |
2021年 | 468篇 |
2020年 | 415篇 |
2019年 | 471篇 |
2018年 | 505篇 |
2015年 | 449篇 |
2014年 | 962篇 |
2013年 | 871篇 |
2012年 | 4687篇 |
2011年 | 5632篇 |
2010年 | 1675篇 |
2009年 | 1347篇 |
2008年 | 4270篇 |
2007年 | 3924篇 |
2006年 | 3445篇 |
2005年 | 3147篇 |
2004年 | 2573篇 |
2003年 | 2356篇 |
2002年 | 2110篇 |
2001年 | 1784篇 |
2000年 | 1565篇 |
1999年 | 1005篇 |
1998年 | 656篇 |
1997年 | 593篇 |
1996年 | 590篇 |
1995年 | 647篇 |
1994年 | 627篇 |
1993年 | 489篇 |
1992年 | 633篇 |
1991年 | 696篇 |
1990年 | 735篇 |
1989年 | 670篇 |
1988年 | 697篇 |
1987年 | 834篇 |
1986年 | 763篇 |
1985年 | 782篇 |
1984年 | 747篇 |
1983年 | 661篇 |
1982年 | 720篇 |
1981年 | 722篇 |
1980年 | 535篇 |
1979年 | 377篇 |
1977年 | 316篇 |
1976年 | 385篇 |
1975年 | 353篇 |
1974年 | 359篇 |
1972年 | 313篇 |
1967年 | 369篇 |
1965年 | 393篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
该文通过研究国内外相关的句法分析算法与理论,再结合维吾尔语自身的特点对基于规则的维吾尔语句法分析方法进行讨论,由于维吾尔语作为一种自然语言,具有自然语言所共有的一些规则,发现国外经典的句法分析方法同样适合于维吾尔语的句法分析,本论文主要讨论了自项向下的的自动句法分析方法。 相似文献
992.
993.
Dang TN Wilkinson L Anand A 《IEEE transactions on visualization and computer graphics》2010,16(6):1044-1052
An ongoing challenge for information visualization is how to deal with over-plotting forced by ties or the relatively limited visual field of display devices. A popular solution is to represent local data density with area (bubble plots, treemaps), color (heatmaps), or aggregation (histograms, kernel densities, pixel displays). All of these methods have at least one of three deficiencies:1) magnitude judgments are biased because area and color have convex downward perceptual functions, 2) area, hue, and brightness have relatively restricted ranges of perceptual intensity compared to length representations, and/or 3) it is difficult to brush or link to individual cases when viewing aggregations. In this paper, we introduce a new technique for visualizing and interacting with datasets that preserves density information by stacking overlapping cases. The overlapping data can be points or lines or other geometric elements, depending on the type of plot. We show real-dataset applications of this stacking paradigm and compare them to other techniques that deal with over-plotting in high-dimensional displays. 相似文献
994.
Born S Wiebel A Friedrich J Scheuermann G Bartz D 《IEEE transactions on visualization and computer graphics》2010,16(6):1329-1338
Stream surfaces are an intuitive approach to represent 3D vector fields. In many cases, however, they are challenging objects to visualize and to understand, due to a high degree of self-occlusion. Despite the need for adequate rendering methods, little work has been done so far in this important research area. In this paper, we present an illustrative rendering strategy for stream surfaces. In our approach, we apply various rendering techniques, which are inspired by the traditional flow illustrations drawn by Dallmann and Abraham \& Shaw in the early 1980s. Among these techniques are contour lines and halftoning to show the overall surface shape. Flow direction as well as singularities on the stream surface are depicted by illustrative surface streamlines. ;To go beyond reproducing static text book images, we provide several interaction features, such as movable cuts and slabs allowing an interactive exploration of the flow and insights into subjacent structures, e.g., the inner windings of vortex breakdown bubbles. These methods take only the parameterized stream surface as input, require no further preprocessing, and can be freely combined by the user. We explain the design, GPU-implementation, and combination of the different illustrative rendering and interaction methods and demonstrate the potential of our approach by applying it to stream surfaces from various flow simulations. ; 相似文献
995.
Paine SW Barton P Bird J Denton R Menochet K Smith A Tomkinson NP Chohan KK 《Journal of molecular graphics & modelling》2010,29(4):529-537
In silico models that predict the rate of human renal clearance for a diverse set of drugs, that exhibit both active secretion and net re-absorption, have been produced using three statistical approaches. Partial Least Squares (PLS) and Random Forests (RF) have been used to produce continuous models whereas Classification And Regression Trees (CART) has only been used for a classification model. The best models generated from either PLS or RF produce significant models that can predict acids/zwitterions, bases and neutrals with approximate average fold errors of 3, 3 and 4, respectively, for an independent test set that covers oral drug-like property space. These models contain additional information on top of any influence arising from plasma protein binding on the rate of renal clearance. Classification And Regression Trees (CART) has been used to generate a classification tree leading to a simple set of Renal Clearance Rules (RCR) that can be applied to man. The rules are influenced by lipophilicity and ion class and can correctly predict 60% of an independent test set. These percentages increase to 71% and 79% for drugs with renal clearances of < 0.1 ml/min/kg and > 1 ml/min/kg, respectively. As far as the authors are aware these are the first set of models to appear in the literature that predict the rate of human renal clearance and can be used to manipulate molecular properties leading to new drugs that are less likely to fail due to renal clearance. 相似文献
996.
The molecular structures, molecular orbitals, atomic charges, electronic absorption spectra, and infrared (IR) and Raman spectra of a series of substituted metal-free phthalocyanine compounds with four (1, 3, 5, 7) or eight (2, 4, 6, 8) methoxyl (1, 2, 5, 6) or methylthio groups (3, 4, 7, 8) on the nonperipheral (1-4) or peripheral positions (5-8) of the phthalocyanine ring are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The calculated structural parameters and simulated electronic absorption and IR spectra are compared with the X-ray crystallography structures and the experimentally observed electronic absorption and IR spectra of the similar molecules, and good agreement between the calculated and experimental results is found. The substitution of the methoxyl or methylthio groups at the nonperipheral positions of the phthalocyanine ring has obvious effects on the molecular structure and spectroscopic properties of the metal-free phthalocyanine. Nonperipheral substitution has a more significant influence than peripheral substitution. The substitution effect increases with an increase in the number of substituents. The methylthio group shows more significant influence than the methoxyl group, despite the stronger electron-donating property of the methoxyl group than the methylthio group. The octa-methylthio-substituted metal-free phthalocyanine compounds have nonplanar structures whose low-lying occupied molecular orbitals and electronic absorption spectra are significantly changed by the substituents. The present systematical study will be helpful for understanding the relationship between structures and properties in phthalocyanine compounds and designing phthalocyanines with typical properties. 相似文献
997.
998.
随着计算机技术的飞速发展,并行计算机用户环境的设计日益成为一个至关重要的问题;并行计算机用户环境的优劣将直接影响到高性能计算机的发展和应用;论文就MPMD型微机群并行计算机的开机方式进行了有意义的改进;MPMD型微机群并行计算机在开启时,需经人工按压开关开启各个节点,多达64个;改进后系统利用MCS-51单片机系统,在实验的基础上确定了开启节点的最佳时间段,实现了利用微处理器开肩多节点的程控开关,可方便地实现了多节点的自动安全连续启动. 相似文献
999.
在玩家热切的期盼下,《成吉思汗2》开启内测。继《成吉思汗》中六大职业,又推出十字军、圣火使、刺客、近卫军、隐修士、僧侣六个全新的职业。今天,便来简单介绍一下僧侣这个新兴职业。 相似文献
1000.
从iPhone的问世,到Android平台的崛起,互联网手持设备开始疯狂增长。从当初0-9的数字按键到现在全触摸屏,已经发生巨大变化。 相似文献