全文获取类型
收费全文 | 283319篇 |
免费 | 5342篇 |
国内免费 | 885篇 |
专业分类
电工技术 | 5033篇 |
综合类 | 209篇 |
化学工业 | 41514篇 |
金属工艺 | 10137篇 |
机械仪表 | 8162篇 |
建筑科学 | 7012篇 |
矿业工程 | 950篇 |
能源动力 | 7840篇 |
轻工业 | 26168篇 |
水利工程 | 2517篇 |
石油天然气 | 3332篇 |
武器工业 | 20篇 |
无线电 | 35509篇 |
一般工业技术 | 55539篇 |
冶金工业 | 55933篇 |
原子能技术 | 5188篇 |
自动化技术 | 24483篇 |
出版年
2021年 | 2879篇 |
2020年 | 2221篇 |
2019年 | 2712篇 |
2018年 | 4632篇 |
2017年 | 4612篇 |
2016年 | 4774篇 |
2015年 | 3301篇 |
2014年 | 5249篇 |
2013年 | 14143篇 |
2012年 | 8192篇 |
2011年 | 10412篇 |
2010年 | 8407篇 |
2009年 | 9232篇 |
2008年 | 9707篇 |
2007年 | 9537篇 |
2006年 | 8206篇 |
2005年 | 7209篇 |
2004年 | 6960篇 |
2003年 | 7148篇 |
2002年 | 6617篇 |
2001年 | 6922篇 |
2000年 | 6360篇 |
1999年 | 6816篇 |
1998年 | 18693篇 |
1997年 | 12875篇 |
1996年 | 9418篇 |
1995年 | 7137篇 |
1994年 | 6311篇 |
1993年 | 6317篇 |
1992年 | 4277篇 |
1991年 | 4165篇 |
1990年 | 3981篇 |
1989年 | 3743篇 |
1988年 | 3647篇 |
1987年 | 3098篇 |
1986年 | 3018篇 |
1985年 | 3294篇 |
1984年 | 3022篇 |
1983年 | 2862篇 |
1982年 | 2712篇 |
1981年 | 2630篇 |
1980年 | 2558篇 |
1979年 | 2338篇 |
1978年 | 2159篇 |
1977年 | 2813篇 |
1976年 | 4064篇 |
1975年 | 1790篇 |
1974年 | 1746篇 |
1973年 | 1698篇 |
1972年 | 1470篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
81.
ABSTRACTIn this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory. 相似文献
82.
Madhu H. C. Edachery Vimal Lijesh K. P. Perugu Chandra Shekhar Kailas Satish V. 《Metallurgical and Materials Transactions A》2020,51(8):4086-4099
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result... 相似文献
83.
Manoj Karakoti Ritu Jangra Sandeep Pandey Pawan Singh Dhapola Sunil Dhali Suman Mahendia Pramod K Singh Nanda Gopal Sahoo 《International Journal of Applied Ceramic Technology》2020,17(4):1899-1908
This study deals with the utility of mini spray dryer process to improve the dispersibility, of graphene oxide(GO) and its application for high-performance supercapacitor. Initially, the neutral solution of GO was obtained using the modified Hummer's method. After this, the prepared GO solution was processed by mini spray dryer to obtain a more purified, lighter, and dispersed form of GO which is named as spray dryer processed GO (SPGO). The SPGO thus obtained showed excellent dispersibility behavior with various solvents, which is not found in case of conventional oven drying. Furthermore, utility of SPGO and its reduced form (r-SPGO) for supercapacitor applications have been investigated. Results obtained from the cyclic voltammetry(CV) analysis, impedance, and charge-discharge behavior of supercapacitor fabricated using r-SPGO shows enhanced features. Therefore, the simple spray dried GO and its reduced form, that is, r-SPGO can be utilized as a potential candidate for the supercapacitor application. Herein, as synthesized SPGO exhibited the specific capacitance of 12.07 and 37.6 F/g with PVA-H3PO4 and 1 mol/L H3PO4, respectively, at a scan rate of 5 mV/s. On the other hand, reduced form of SPGO, that is, r-SPGO showed the specific capacitance of 27.16 and 230 F/g with PVA-H3PO4 and 1 mol/L H3PO4, respectively. 相似文献
84.
Daniel T. Payne Mandeep K. Chahal V clav B&rcaron ezina Whitney A. Webre Katsuhiko Ariga Francis D Souza Jan Labuta Jonathan P. Hill 《Frontiers of Chemical Science and Engineering》2020,14(1):28
Chiral 1,1’-binaphthyl-linked diporphyrin ‘tweezers’ (R)-1/(S)-1 and the corresponding zinc(II) complexes (R)-2/(S)-2 were prepared as chiral host molecules, and their utility for chiral analyses (especially enantiomeric excess (ee) determinations) were evaluated. Tris(1-n-dodecyl)porphyrins were used for the first time as the interacting units. Host capabilities of the diporphyrin tweezers were investigated by titrations with (R,R)- and (S,S)-cyclohexane-1,2-diamine (CHDA). The host molecules could be used as multichannel probes of ee by using UV-vis, circular dichroism (CD), fluorescence emission and 1H nuclear magnetic resonance (1H-NMR) methods. Chiral configurations could also be differentiated using CD or 1H-NMR spectroscopy. All three optical techniques give good resolution of ee with reasonable sensitivity considering the low concentrations used (ca. 10−6 mol·L−1). The ee determination of CHDA enantiomers using NMR spectroscopy is also possible because of the reasonably well separated resonances in the case of (R,R)- and (S,S)-CHDA. Non-metallated (R)-1/(S)-1 hosts could not be used to detect chiral information in a strongly acidic chiral guest. This work demonstrates the utility of 1,1’-binapthyl-linked chiral hosts for chiral analysis of ditopically interacting enantiomers. 相似文献
85.
Konstantinos Spyrou Matteo Calvaresi Evmorfia K. Diamanti Theodoros Tsoufis Dimitrios Gournis Petra Rudolf Francesco Zerbetto 《Advanced functional materials》2015,25(2):263-269
Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”. 相似文献
86.
87.
Esteban Vera Pingitore María Silvina Juárez Tomás Birgitt Wiese 《Drug development and industrial pharmacy》2015,41(6):942-952
Context: The administration of pharmabiotics is a promising alternative to antimicrobial drugs for the treatment and/or prevention of female urogenital infections.Objective: To design pharmabiotic formulations including bioactive ingredients of microbial origin combined with non-microbial substances and then to evaluate the stability of the combinations during freeze-drying and storage.Materials and methods: Different formulations including Lactobacillus gasseri CRL 1263, Lactobacillus salivarius CRL 1328, salivaricin CRL 1328 (a bacteriocin) and non-microbial compounds (lactose, inulin and ascorbic acid) were assayed, and the ingredients were freeze-dried together or separately. The formulations were stored in gelatin capsules at 4?°C for 360?d.Results: The viability of lactobacilli was affected to different extents depending on the strains and on the formulations assayed. L. salivarius and ascorbic acid were successfully combined only after the freeze-drying process. Salivaricin activity was not detected in formulations containing L. gasseri. However, when combined with ascorbic acid, lactose, inulin or L. salivarius, the bacteriocin maintained its activity for 360?d. The selected microorganisms proved to be compatible for their inclusion in multi-strain formulations together with lactose, inulin and ascorbic acid. Salivaricin could be included only in a L. salivarius CRL 1328 single-strain formulation together with non-microbial substances.Conclusions: This study provides new insights into the design of urogenital pharmabiotics combining beneficial lactobacilli, salivaricin CRL 1328 and compounds with different functionalities. 相似文献
88.
Emma Layton Anna-Marie Fairhurst Sam Griffiths-Jones Richard K. Grencis Ian S. Roberts 《International journal of molecular sciences》2020,21(23)
In eukaryotes, microRNAs (miRNAs) have roles in development, homeostasis, disease and the immune response. Recent work has shown that plant and mammalian miRNAs also mediate cross-kingdom and cross-domain communications. However, these studies remain controversial and are lacking critical mechanistic explanations. Bacteria do not produce miRNAs themselves, and therefore it is unclear how these eukaryotic RNA molecules could function in the bacterial recipient. In this review, we compare and contrast the biogenesis and functions of regulatory RNAs in eukaryotes and bacteria. As a result, we discovered several conserved features and homologous components in these distinct pathways. These findings enabled us to propose novel mechanisms to explain how eukaryotic miRNAs could function in bacteria. Further understanding in this area is necessary to validate the findings of existing studies and could facilitate the use of miRNAs as novel tools for the directed remodelling of the human microbiota. 相似文献
89.
90.