全文获取类型
收费全文 | 49293篇 |
免费 | 4764篇 |
国内免费 | 2766篇 |
专业分类
电工技术 | 2539篇 |
技术理论 | 4篇 |
综合类 | 5158篇 |
化学工业 | 6240篇 |
金属工艺 | 1894篇 |
机械仪表 | 2980篇 |
建筑科学 | 6501篇 |
矿业工程 | 2324篇 |
能源动力 | 1354篇 |
轻工业 | 3525篇 |
水利工程 | 2001篇 |
石油天然气 | 2705篇 |
武器工业 | 326篇 |
无线电 | 5557篇 |
一般工业技术 | 5361篇 |
冶金工业 | 2631篇 |
原子能技术 | 862篇 |
自动化技术 | 4861篇 |
出版年
2024年 | 162篇 |
2023年 | 787篇 |
2022年 | 1196篇 |
2021年 | 1582篇 |
2020年 | 1434篇 |
2019年 | 1334篇 |
2018年 | 1271篇 |
2017年 | 1416篇 |
2016年 | 1617篇 |
2015年 | 1741篇 |
2014年 | 2735篇 |
2013年 | 2608篇 |
2012年 | 3228篇 |
2011年 | 3480篇 |
2010年 | 2670篇 |
2009年 | 2898篇 |
2008年 | 2692篇 |
2007年 | 3340篇 |
2006年 | 3010篇 |
2005年 | 2649篇 |
2004年 | 2316篇 |
2003年 | 2104篇 |
2002年 | 1796篇 |
2001年 | 1473篇 |
2000年 | 1284篇 |
1999年 | 1055篇 |
1998年 | 770篇 |
1997年 | 683篇 |
1996年 | 604篇 |
1995年 | 510篇 |
1994年 | 416篇 |
1993年 | 355篇 |
1992年 | 279篇 |
1991年 | 191篇 |
1990年 | 198篇 |
1989年 | 174篇 |
1988年 | 132篇 |
1987年 | 108篇 |
1986年 | 75篇 |
1985年 | 72篇 |
1984年 | 59篇 |
1983年 | 33篇 |
1982年 | 24篇 |
1981年 | 36篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1975年 | 20篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
作为太赫兹技术中的重要组成部分,太赫兹脉冲焦平面成像一经问世就引起了行业内的广泛关注,人们引入了各种方法去提升此成像技术的测量性能,同时也尝试将此成像技术应用于不同的工业和基础研究领域。本文综述了近年来人们对太赫兹脉冲焦平面成像的技术改良和应用研究,包括提升成像系统的空间分辨率、信噪比、信息获取能力,以及将此成像技术应用于光谱识别检测、超表面器件功能验证、太赫兹特殊光束测量、太赫兹表面波观测等,希望该综述能够推动太赫兹脉冲焦平面成像的进一步技术革新和应用拓展。 相似文献
32.
《岩石力学与岩土工程学报(英文版)》2020,12(6):1214-1225
With rapid development of infrastructures like tunnels and open excavations in Shanghai, investigations on deeper soils have become critically important. Most of the existing laboratory works were focused on the clayey strata up to Layer 6 in Shanghai, i.e. at depth of up to 40 m. In this paper, Layers 7, 9, and 11, which were mostly formed of sandy soils at depth of up to 150 m, were experimentally investigated with respect to physico-mechanical behaviors. The stress–strain behaviors were analyzed by the consolidated drained/undrained (CD/CU) triaxial tests under monotonic loading. One-dimensional (1D) oedometer tests were performed to investigate the consolidation properties of the sandy soils. Specimens were prepared at three different relative densities for each layer. Also, the micro-images and particle size analyzers were used to analyze the shape and size of the sand grains. The influences of grain size, density, and angularity on the stress–strain behaviors and compressibility were also studied. Compared to the other layers, Layer 11 had the smallest mean grain size (D50), highest compressibility, and lowest shear strength. In contrast, Layer 9 had the largest mean grain size, lowest compressibility, and highest shear strength. Layer 7 was of intermediate mean grain size, exhibiting more compressibility and less shear strength than that of Layer 9. Also, the critical state parameters and maximum dilatancy rate of different layers were discussed. 相似文献
33.
34.
35.
Haibo Zhang Guohua Geng Kang Li Cheng Liu Yuqing Hou 《Journal of Modern Optics》2018,65(20):2278-2289
Cone-beam X-ray luminescence computed tomography (CB-XLCT) is an attractive hybrid imaging modality, and it has the potential of monitoring the metabolic processes of nanophosphors-based drugs in vivo. However, the XLCT imaging suffers from a severe ill-posed problem. In this work, a sparse nonconvex Lp (0?p?1) regularization was utilized for the efficient reconstruction for early detection of small tumour in CB-XLCT imaging. Specifically, we transformed the non-convex optimization problem into an iteratively reweighted scheme based on the L1 regularization. Further, an iteratively reweighted split augmented lagrangian shrinkage algorithm (IRW_SALSA-Lp) was proposed to efficiently solve the non-convex Lp (0?p?1) model. We studied eight different non-convex p-values (1/16, 1/8, 1/4, 3/8, 1/2, 5/8, 3/4, 7/8) in both 3D digital mouse experiments and in vivo experiments. The results demonstrate that the proposed non-convex methods outperform L2 and L1 regularization in accurately recovering sparse targets in CB-XLCT. And among all the non-convex p-values, our Lp(1/4?p?1/2) methods give the best performance. 相似文献
36.
Fresh and frozen-thawed (F-T) pork meats were classified by Vis–NIR hyperspectral imaging. Eight optimal wavelengths (624, 673, 460, 588, 583, 448, 552 and 609 nm) were selected by successive projections algorithm (SPA). The first three principal components (PCs) obtained by principal component analysis (PCA) accounted for over 99.98% of variance. Gray-level-gradient co-occurrence matrix (GLGCM) was applied to extract 45 textural features from the PC images. The correct classification rate (CCR) was employed to evaluate the performance of the partial least squares-discriminate analysis (PLS-DA) models, by using (A) the reflected spectra at full wavelengths and (B) those at the optimal wavelengths, (C) the extracted textures based on the PC images, and (D) the fused variables combining spectra at the optimal wavelengths and textures. The results showed that the best CCR of 97.73% was achieved by applying (D), confirming the high potential of textures for fresh and F-T meat discrimination. 相似文献
37.
文章中主要采用有机溶剂萃取法(OSE)对高浓度石油污染土壤进行修复,经过精馏操作,有效回收原油,建立脱附等温曲线,研究了石油污染物在土壤-有机溶剂两相间的迁移规律。 相似文献
38.
39.
考察了双河油田双河联、江河联注入水堵塞地层的因素;膨胀性黏土,悬浮固体颗粒。细菌及悬浮污油。含膨胀性黏土的双河南、双河北及不含膨胀性黏土的双江岩心粉,在注入水中相对于地层水中的体积膨胀度分别为14.5%、11.1%及0.02%;注入100PV不含悬浮颗粒的等体积比地层水、注入水混合水使双河、双江岩心渗透率分别下降7%和4%、9%和7%。注入水中悬浮颗粒引起岩心渗透率下降,粒径越大、颗粒浓度越大、注入量越大,则渗透率越低。在粒径2.1μm或颗粒浓度3mg/L前后下降幅度变化较大。注入水中硫酸盐还原菌引起岩心渗透率下降,含菌量越大则渗透率开始下降时的注水量越小,注入含菌50个/L的水100PV使岩心渗透率下降7%。岩心对注水合油量敏感,注入含油量20mg/L的水50PV使岩心渗透率下降20%。在岩心注水实验中渗透率下降最严重的是双河南岩心,其次是双河北岩心.江河岩心较轻,注入精细过滤水的双河北岩心渗透率下降大大减少.说明悬浮固体是造成注水堵塞的主要因素。为了解除双河油田注水井的堵塞,研制了含黏土稳定剂、缓蚀剂、铁离子稳定剂、互溶剂的土酸液,与南阳油田使用的低伤害酸液一起,用于1口注水井的解堵,效果良好。图7表4参5。 相似文献
40.