全文获取类型
收费全文 | 85421篇 |
免费 | 1071篇 |
国内免费 | 413篇 |
专业分类
电工技术 | 791篇 |
综合类 | 2325篇 |
化学工业 | 11771篇 |
金属工艺 | 4829篇 |
机械仪表 | 3089篇 |
建筑科学 | 2190篇 |
矿业工程 | 570篇 |
能源动力 | 1246篇 |
轻工业 | 3810篇 |
水利工程 | 1275篇 |
石油天然气 | 343篇 |
无线电 | 9360篇 |
一般工业技术 | 16682篇 |
冶金工业 | 2794篇 |
原子能技术 | 267篇 |
自动化技术 | 25563篇 |
出版年
2023年 | 30篇 |
2022年 | 82篇 |
2021年 | 90篇 |
2020年 | 76篇 |
2019年 | 89篇 |
2018年 | 14517篇 |
2017年 | 13450篇 |
2016年 | 10031篇 |
2015年 | 637篇 |
2014年 | 315篇 |
2013年 | 354篇 |
2012年 | 3222篇 |
2011年 | 9509篇 |
2010年 | 8364篇 |
2009年 | 5613篇 |
2008年 | 6835篇 |
2007年 | 7844篇 |
2006年 | 151篇 |
2005年 | 1248篇 |
2004年 | 1150篇 |
2003年 | 1202篇 |
2002年 | 571篇 |
2001年 | 115篇 |
2000年 | 196篇 |
1999年 | 78篇 |
1998年 | 83篇 |
1997年 | 59篇 |
1996年 | 71篇 |
1995年 | 27篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 39篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1969年 | 27篇 |
1968年 | 44篇 |
1967年 | 37篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Channapatna Gopalkrishna Raghavendra Raghu Srivatsa Marasandra Prakash Vignesh Nayak Panemangalore 《ETRI Journal》2021,43(4):650-659
Multi-carrier waveforms have several advantages over single-carrier waveforms for radar communication. Employing multi-carrier complementary phase-coded (MCPC) waveforms in radar applications has recently attracted significant attention. MCPC radar signals take advantage of orthogonal frequency division multiplexing properties, and several authors have explored the use of MCPC signals and the difficulties associated with their implementation. The sidelobe level and peak-to-mean-envelope-power ratio (PMEPR) are the key issues that must be addressed to improve the performance of radar signals. We propose a scheme that applies pattern-based scaling and geometric progression methods to enhance sidelobe and PMEPR levels in MCPC radar signals. Numerical results demonstrate the improvement of sidelobe and PMEPR levels in the proposed scheme. Additionally, autocorrelations are obtained and analyzed by applying the proposed scheme in extensive simulation experiments. 相似文献
2.
3.
Flow phenomena of three-dimensional conducting Casson fluid through a stretching sheet are proposed in the present investigation with the impact of the magnetic parameter in a permeable medium. The adaptation of particular transformations is useful to modify the governing equations into their nondimensional as well as the ordinary form. However, these transformed equations are nonlinear and approximate analytical methods for the solution of the complex form of governing equations. In particular, the Adomian decomposition method is proposed for the solution. The behavior of several variables, such as the magnetic and porous matrix, on the flow profile as well as the rate of shear stress, are discussed via graphs and tables. The conformity of the current result with the earlier study shows a road map for further investigation. The major concluding remarks are; the retardation in the velocity distribution is rendered due to an increase in the Casson parameter moreover, the Casson parameter favors in reducing the rate of shear stress coefficient in magnitude. 相似文献
4.
Chattopadhyay Arup Kumar Nag Amitava Singh Jyoti Prakash 《Multimedia Tools and Applications》2022,81(24):34969-34999
Multimedia Tools and Applications - A secret sharing scheme partitions a secret into a set of shares and distributes them among the eligible participants, with each participant receiving one share... 相似文献
5.
6.
Avneet Kaur Neha Bhardwaj Amanpreet Kaur Km Abida Tejo Prakash Nagaraja Amjad Ali Ranjana Prakash 《Journal of the American Oil Chemists' Society》2021,98(2):139-147
Epoxidized methyl esters (EMO) with their high oxirane ring reactivity, acts as a raw material in the synthesis of various industrial chemicals including polymers, stabilizers, plasticizers, glycols, polyols, carbonyl compounds, biolubricants etc. EMO has been generally quantified by the gas chromatography (GC) and high-performance liquid chromatography (HPLC) techniques. Taking into the account of the limitations of these techniques, two qHNMR-based equations have been proposed for the quantification of EMO in the mixture of EMO and methylesters (MO). The validity of the proposed method was determined using standard mixtures of MO and EMO having different molar concentrations. The developed equations have been applied on the samples of EMO prepared from oleic acid in two-step process viz., esterification followed by epoxidation. The qHNMR-based EMO quantification showed acceptable agreement with the results obtained from HPLC analysis. 相似文献
7.
8.
The complexity and uncertainties associated with mining operations often lead to deviations from short-term plans. A proactive approach will predict such deviations and help minimise opportunity losses, providing economic and operational gains. This paper presents an optimisation tool as a dynamic shovel allocation decision-maker for mining operation simulation models. The objectives of the optimisation tool are to provide shovel allocations to mining faces in order to maximise production, meet desired head grade and tonnage at the crushers, and minimise shovel movements. This paper presents the development and implementation of the optimisation tool with an iron ore mine case study. 相似文献
9.
Yavuz Emre Arslan Yusuf Furkan Galata Tugba Sezgin Arslan Burak Derkus 《Journal of materials science. Materials in medicine》2018,29(8):127
In this study, we aimed at fabricating decellularized bovine myocardial extracellular matrix-based films (dMEbF) for cardiac tissue engineering (CTE). The decellularization process was carried out utilizing four consecutive stages including hypotonic treatment, detergent treatment, enzymatic digestion and decontamination, respectively. In order to fabricate the dMEbF, dBM were digested with pepsin and gelation process was conducted. dMEbF were then crosslinked with N-hydroxysuccinimide/1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (NHS/EDC) to increase their durability. Nuclear contents of native BM and decellularized BM (dBM) tissues were determined with DNA content analysis and agarose-gel electrophoresis. Cell viability on dMEbF for 3rd, 7th, and 14th days was assessed by MTT assay. Cell attachment on dMEbF was also studied by scanning electron microscopy. Trans-differentiation capacity of human adipose-derived mesenchymal stem cells (hAMSCs) into cardiomyocyte-like cells on dMEbF were also evaluated by histochemical and immunohistochemical analyses. DNA contents for native and dBM were, respectively, found as 886.11?±?164.85 and 47.66?±?0.09?ng/mg dry weight, indicating a successful decellularization process. The results of glycosaminoglycan and hydroxyproline assay, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), performed in order to characterize the extracellular matrix (ECM) composition of native and dBM tissue, showed that the BM matrix was not damaged during the proposed method. Lastly, regarding the histological study, dMEbF not only mimics native ECM, but also induces the stem cells into cardiomyocyte-like cells phenotype which brings it the potential of use in CTE. 相似文献
10.