全文获取类型
收费全文 | 20636篇 |
免费 | 2516篇 |
国内免费 | 1487篇 |
专业分类
电工技术 | 2763篇 |
综合类 | 2715篇 |
化学工业 | 410篇 |
金属工艺 | 781篇 |
机械仪表 | 3547篇 |
建筑科学 | 599篇 |
矿业工程 | 447篇 |
能源动力 | 305篇 |
轻工业 | 224篇 |
水利工程 | 300篇 |
石油天然气 | 337篇 |
武器工业 | 580篇 |
无线电 | 4350篇 |
一般工业技术 | 2041篇 |
冶金工业 | 337篇 |
原子能技术 | 174篇 |
自动化技术 | 4729篇 |
出版年
2024年 | 94篇 |
2023年 | 272篇 |
2022年 | 499篇 |
2021年 | 530篇 |
2020年 | 658篇 |
2019年 | 509篇 |
2018年 | 538篇 |
2017年 | 748篇 |
2016年 | 853篇 |
2015年 | 957篇 |
2014年 | 1264篇 |
2013年 | 1173篇 |
2012年 | 1593篇 |
2011年 | 1596篇 |
2010年 | 1183篇 |
2009年 | 1251篇 |
2008年 | 1251篇 |
2007年 | 1532篇 |
2006年 | 1372篇 |
2005年 | 1101篇 |
2004年 | 870篇 |
2003年 | 819篇 |
2002年 | 659篇 |
2001年 | 582篇 |
2000年 | 514篇 |
1999年 | 389篇 |
1998年 | 295篇 |
1997年 | 280篇 |
1996年 | 248篇 |
1995年 | 205篇 |
1994年 | 178篇 |
1993年 | 130篇 |
1992年 | 92篇 |
1991年 | 68篇 |
1990年 | 57篇 |
1989年 | 71篇 |
1988年 | 52篇 |
1987年 | 27篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 10篇 |
1956年 | 5篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Voigt线型及其精确快速算法 总被引:1,自引:1,他引:0
通过把上半复平面分为4个区,并在每一区利用不同近似,建立了一种精确快速计算Voigt函数、修正的Voigt函数和Voigt函数偏导数的算法,其最大相对误差小于5×10-4.该算法是Line-by-Line大气透过率/辐射强度计算及其相关应用的有效算法. 相似文献
32.
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
33.
34.
35.
普通的最小平方反褶积只有在子波为最小相位脉冲和反射序列为白噪声的假设下才是成立的,而对于混合相位未知脉冲来说,这种最小平方反褶积就不再适用了。本文提出一种适合于有限长度混合相位未知脉冲的最小平方反褶积方法。运用此法只需预先估计一个混合相位子波的长度。合成数据的试验结果表明,该方法有较好的效果,且对预先估计出的子波长度不敏感。文中还证明混合相位未知脉冲最小平方反褶积等效于一种有间隙的平滑误差滤波器的作用,而这种有间隙的平滑误差滤波又可分解为一个前向多步预测误差滤波与一个后向多步预测误差滤波之和。可以预计这种新的反滤积方法将在地震数据处理中得到有效的应用。 相似文献
36.
阐述静态电子轨道衡诸多优点;工作原理、允许误差及误差分配;轨道衡的结构组成部分、解析各部分的工作特性及技术指标要求;合理选配及推荐实例. 相似文献
37.
One of the most frequently cited reasons for conducting a meta-analysis is the increase in statistical power that it affords a reviewer. This article demonstrates that fixed-effects meta-analysis increases statistical power by reducing the standard error of the weighted average effect size (T?.) and, in so doing, shrinks the confidence interval around T?.. Small confidence intervals make it more likely for reviewers to detect nonzero population effects, thereby increasing statistical power. Smaller confidence intervals also represent increased precision of the estimated population effect size. Computational examples are provided for 3 effect-size indices: d (standardized mean difference), Pearson's r, and odds ratios. Random-effects meta-analyses also may show increased statistical power and a smaller standard error of the weighted average effect size. However, the authors demonstrate that increasing the number of studies in a random-effects meta-analysis does not always increase statistical power. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
38.
Sanghoon Lee Chris Podilchuk Vidhya Krishnan Alan C. Bovik 《The Journal of VLSI Signal Processing》2003,34(1-2):149-166
By exploiting new human-machine interface techniques, such as visual eyetrackers, it should be possible to develop more efficient visual multimedia services associated with low bandwidth, dynamic channel adaptation and robust visual data transmission. In this paper, we introduce foveation-based error resilience and unequal error protection techniques over highly error-prone mobile networks. Each frame is spatially divided into foveated and background layers according to perceptual importance. Perceptual importance is determined either through an eye tracker or by manually selecting a region of interest. We attempt to improve reconstructed visual quality by maintaining the high visual source throughput of the foveated layer using foveation-based error resilience and error correction using a combination of turbo codes and ARQ (automatic reQuest). In order to alleviate the degradation of visual quality, a foveation based bitstream partitioning is developed. In an effort to increase the source throughput of the foveated layer, we develop unequal delay-constrained ARQ (automatic reQuest) and rate compatible punctured turbo codes where the punctual pattern of RCPC (rate compatible punctured convolutional) codes in H.223 Annex C is used. In the simulation, the visual quality is significantly increased in the area of interest using foveation-based error resilience and unequal error protection; (as much as 3 dB FPSNR (foveal peak signal to noise ratio) improvement) at 40% packet error rate. Over real-fading statistics measured in the downtown area of Austin, Texas, the visual quality is increased up to 1.5 dB in PSNR and 1.8 dB in FPSNR at a channel SNR of 5 dB. 相似文献
39.
Chuxiang Li Jianhua Lu Jun Gu Ming L. Liou 《The Journal of VLSI Signal Processing》2003,33(3):277-285
In this paper, error-resilient schemes are proposed to support robust video transmission for digital terrestrial TV broadcasting (DTTB). In particular, a temporal error concealment incorporated with a low-complexity block-matching is developed, achieving an effective reception of predictive pictures in harsh terrestrial environment. Special algorithms are also designed for isolated I-pictures. Moreover, combined with an intra/inter case prediction, an adaptive error concealment scheme is further contrived to fit for different error conditions. Extensive simulations have been conducted under various DTTB channel conditions, even with a very high packet error rate, to verify the effectiveness of the proposed schemes. 相似文献
40.
N. V. Khovanov 《Measurement Techniques》2007,50(3):255-258
A Bayesian model is proposed based on randomizing the systematic errors of the instruments. Conditions are identified under
which the randomization reduces the expected bias in estimating a measured quantity.
__________
Translated from Izmeritel’naya Tekhnika, No. 3, pp. 22–25, March, 2007. 相似文献