全文获取类型
收费全文 | 508851篇 |
免费 | 7136篇 |
国内免费 | 1482篇 |
专业分类
电工技术 | 9969篇 |
综合类 | 1310篇 |
化学工业 | 72925篇 |
金属工艺 | 17169篇 |
机械仪表 | 14046篇 |
建筑科学 | 12105篇 |
矿业工程 | 1931篇 |
能源动力 | 12796篇 |
轻工业 | 43668篇 |
水利工程 | 4434篇 |
石油天然气 | 6168篇 |
武器工业 | 19篇 |
无线电 | 63577篇 |
一般工业技术 | 92122篇 |
冶金工业 | 111907篇 |
原子能技术 | 8403篇 |
自动化技术 | 44920篇 |
出版年
2021年 | 3427篇 |
2019年 | 3253篇 |
2018年 | 5787篇 |
2017年 | 5893篇 |
2016年 | 6431篇 |
2015年 | 4609篇 |
2014年 | 7026篇 |
2013年 | 21369篇 |
2012年 | 12974篇 |
2011年 | 17398篇 |
2010年 | 12698篇 |
2009年 | 14633篇 |
2008年 | 15252篇 |
2007年 | 15165篇 |
2006年 | 13671篇 |
2005年 | 15285篇 |
2004年 | 14423篇 |
2003年 | 13617篇 |
2002年 | 12174篇 |
2001年 | 12530篇 |
2000年 | 11439篇 |
1999年 | 12431篇 |
1998年 | 35322篇 |
1997年 | 24244篇 |
1996年 | 18590篇 |
1995年 | 13809篇 |
1994年 | 12153篇 |
1993年 | 11936篇 |
1992年 | 8212篇 |
1991年 | 7942篇 |
1990年 | 7738篇 |
1989年 | 7494篇 |
1988年 | 7179篇 |
1987年 | 5911篇 |
1986年 | 6101篇 |
1985年 | 7007篇 |
1984年 | 6225篇 |
1983年 | 5752篇 |
1982年 | 5266篇 |
1981年 | 5627篇 |
1980年 | 5103篇 |
1979年 | 4815篇 |
1978年 | 4679篇 |
1977年 | 6024篇 |
1976年 | 8285篇 |
1975年 | 4038篇 |
1974年 | 3827篇 |
1973年 | 3801篇 |
1972年 | 3177篇 |
1971年 | 2801篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Technical Physics Letters - Specific features of monitoring the state of a flowing medium by method of nuclear magnetic resonance (NMR) are considered. An approach to studying the state of a... 相似文献
142.
Fominski V. Yu. Nevolin V. N. Fominski D. V. Romanov R. I. Gritskevich M. D. 《Technical Physics Letters》2020,46(1):83-86
Technical Physics Letters - We present the results of a comparative investigation of the friction and wear characteristics of MoSx and MoSex coatings in an oxidizing medium (argon–air... 相似文献
143.
Detailed study on fusion characteristics of rigid poly(vinyl chloride) nanocomposites: The comparison of using multiple regression analysis and artificial neural network
下载免费PDF全文
![点击此处可从《乙烯基与添加剂工艺杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Fusion behavior of poly(vinyl chloride) (PVC) compounds plays an important role in the development of physical properties of processed material. The fusion characteristics in PVC processing are governed by material variables that affect the fusion with some interactions. In this research, the aim was to characterize the effects of formulation ingredients on fusion characteristics of PVC. Four material parameters, including the contents of nanoclay (NC), azodicarbonamide, calcium stearate, and processing aid, are proposed as affecting variables. The fusion time (FT) as well as fusion factor (FF) are considered fusion indicators and are experimentally determined in some different levels of affecting parameters. The multivariable regression analysis (MRA) and the Artificial Neural Network (ANN) modeling are considered as two analytical methods. The regression analysis result for the FT denotes, in part, significant linear and quadratic effects of NC and also its significant interactions with azodicarbonamide and calcium stearate, whereas that of FF indicates only a linear effect of NC. ANN modeling is performed with a three‐layer (input, hidden, and output) neural network. The results of the comparison of the MRA and ANN predictions with experimental values are reported as the correlation coefficient (R2), mean‐square error, and mean absolute percentage error for both FF and FT parameters. The obtained values clearly denote that the ANN results are more precise and especially more general than those of MRA. However, in the case of FT, improvement of the ANN modeling is much greater than that of FF. J. VINYL ADDIT. TECHNOL., 21:147–155, 2015. © 2014 Society of Plastics Engineers 相似文献
144.
An explicit extraction of the retinal vessel is a standout amongst the most significant errands in the field of medical imaging to analyze both the ophthalmological infections, for example, Glaucoma, Diabetic Retinopathy (DR), Retinopathy of Prematurity (ROP), Age-Related Macular Degeneration (AMD) as well as non retinal sickness such as stroke, hypertension and cardiovascular diseases. The state of the retinal vasculature is a significant indicative element in the field of ophthalmology. Retinal vessel extraction in fundus imaging is a difficult task because of varying size vessels, moderately low distinction, and presence of pathologies such as hemorrhages, microaneurysms etc. Manual vessel extraction is a challenging task due to the complicated nature of the retinal vessel structure, which also needs strong skill set and training. In this paper, a supervised technique for blood vessel extraction in retinal images using Modified Adaboost Extreme Learning Machine (MAD-ELM) is proposed. Firstly, the fundus image preprocessing is done for contrast enhancement and in-homogeneity correction. Then, a set of core features is extracted, and the best features are selected using “minimal Redundancy-maximum Relevance (mRmR).” Later, using MAD-ELM method vessels and non vessels are classified. DRIVE and DR-HAGIS datasets are used for the evaluation of the proposed method. The algorithm’s performance is assessed based on accuracy, sensitivity and specificity. The proposed technique attains accuracy of 0.9619 on the DRIVE database and 0.9519 on DR-HAGIS database, which contains pathological images. Our results show that, in addition to healthy retinal images, the proposed method performs well in extracting blood vessels from pathological images and is therefore comparable with state of the art methods. 相似文献
145.
Ugur Gezer Ebru E. Y?rüker Metin Keskin Cemil Burak Kulle Yoganiranjana Dharuman Stefan Holdenrieder 《International journal of molecular sciences》2015,16(12):29654-29662
Circulating nucleic acids (CNAs) are under investigation as a liquid biopsy in cancer as potential non-invasive biomarkers, as stable structure in circulation nucleosomes could be valuable sources for detection of cancer-specific alterations in histone modifications. Our interest is in histone methylation marks with a focus on colorectal cancer, one of the leading cancers respective the incidence and mortality. Our previous work included the analysis of trimethylations of lysine 9 on histone 3 (H3K9me3) and of lysine 20 on histone 4 (H4K20me3) by chromatin immuno- precipitation-related PCR in circulating nucleosomes. Here we asked whether global immunologic measurement of histone marks in circulation could be a suitable approach to show their potential as biomarkers. In addition to H3K9me3 and H4K20me3 we also measured H3K27me3 in plasma samples from CRC patients (n = 63) and cancer free individuals (n = 40) by ELISA-based methylation assays. Our results show that of three marks, the amounts of H3K27me3 (p = 0.04) and H4K20me3 (p < 0.001) were significantly lower in CRC patients than in healthy controls. For H3K9me3 similar amounts were measured in both groups. Areas under the curve (AUC) in receiver operating characteristic (ROC) curves indicating the power of CRC detection were 0.620 for H3K27me3, 0.715 for H4K20me3 and 0.769 for the combination of both markers. In conclusion, findings of this preliminary study reveal the potential of blood-based detection of CRC by quantification of histone methylation marks and the additive effect of the marker combination. 相似文献
146.
147.
148.
149.
150.
Verbovitskii Yu. V. Denis R. V. Shtender V. V. Zavalii I. Yu. 《Powder Metallurgy and Metal Ceramics》2015,54(3-4):220-226
Powder Metallurgy and Metal Ceramics - Multiphase La 2 MgNi 9 alloys are synthesized by induction melting. The crystalline structures of all phases in the alloys are determined with X-ray... 相似文献