全文获取类型
收费全文 | 245530篇 |
免费 | 3396篇 |
国内免费 | 440篇 |
专业分类
电工技术 | 4341篇 |
综合类 | 261篇 |
化学工业 | 38934篇 |
金属工艺 | 9427篇 |
机械仪表 | 7486篇 |
建筑科学 | 5842篇 |
矿业工程 | 1415篇 |
能源动力 | 5417篇 |
轻工业 | 25040篇 |
水利工程 | 2545篇 |
石油天然气 | 4982篇 |
武器工业 | 32篇 |
无线电 | 25531篇 |
一般工业技术 | 46046篇 |
冶金工业 | 46410篇 |
原子能技术 | 5982篇 |
自动化技术 | 19675篇 |
出版年
2021年 | 2178篇 |
2019年 | 2210篇 |
2018年 | 3707篇 |
2017年 | 3643篇 |
2016年 | 3916篇 |
2015年 | 2439篇 |
2014年 | 4209篇 |
2013年 | 10805篇 |
2012年 | 6641篇 |
2011年 | 8998篇 |
2010年 | 7014篇 |
2009年 | 7665篇 |
2008年 | 8111篇 |
2007年 | 8173篇 |
2006年 | 7280篇 |
2005年 | 6389篇 |
2004年 | 6107篇 |
2003年 | 5841篇 |
2002年 | 5671篇 |
2001年 | 5411篇 |
2000年 | 5117篇 |
1999年 | 5092篇 |
1998年 | 12402篇 |
1997年 | 8783篇 |
1996年 | 6711篇 |
1995年 | 5381篇 |
1994年 | 4761篇 |
1993年 | 4636篇 |
1992年 | 3660篇 |
1991年 | 3387篇 |
1990年 | 3614篇 |
1989年 | 3471篇 |
1988年 | 3274篇 |
1987年 | 2892篇 |
1986年 | 2935篇 |
1985年 | 3374篇 |
1984年 | 3226篇 |
1983年 | 2913篇 |
1982年 | 2735篇 |
1981年 | 2807篇 |
1980年 | 2708篇 |
1979年 | 2626篇 |
1978年 | 2679篇 |
1977年 | 2939篇 |
1976年 | 3799篇 |
1975年 | 2366篇 |
1974年 | 2237篇 |
1973年 | 2361篇 |
1972年 | 1964篇 |
1971年 | 1839篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
P.A. Luque H.E. Garrafa-Gálvez O. Nava A. Olivas M.E. Martínez-Rosas A.R. Vilchis-Nestor A. Villegas-Fuentes M.J. Chinchillas-Chinchillas 《Ceramics International》2021,47(17):23861-23874
In this work, tin dioxide (SnO2) Nanoparticles (NPs) were synthesized through green synthesis, using Citrus × paradisi extract as a stabilizing (capping). The extract concentrations used were 1, 2 and 4% in relation to the aqueous solution. The resulting SnO2 NPs were used for the degradation of Methyl Orange (MO), Methylene Blue (MB) and Rhodamine B (RhB), under both solar and UV radiation. The NPs were characterized via Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM-SAED), the Brunauer-Emmett-Teller (BET) theory, Ultraviolet to Visible spectroscopy (UV–Vis), and Photoluminescence spectroscopy (PL); while the photocatalytic degradation was evaluated using UV-VIS. The results showed that the Citrus × paradisi extract is a good medium for the formation of SnO2 NPs. These NPs presented quasi-spherical morphology, particle sizes of 4–8 nm, with a rutile phase crystalline structure, and with banned gap of 2.69 at 3.28 eV. The NPs had excellent photocatalytic properties under solar radiation, degrading 100% of the OM in 180 min. Furthermore, under UV radiation, 100% degradation of the three dyes was achieved in a short time; 20 min for MO, and 60 min for MB and RhB. Therefore, green synthesis is a feasible medium for the formation of SnO2 NPs with good photocatalytic properties. 相似文献
52.
Dresvyannikov A. F. Petrova E. V. Akhmetova A. N. Kashfrazieva L. I. Tverdov I. D. 《Glass Physics and Chemistry》2021,47(5):489-495
Glass Physics and Chemistry - The scientific foundations for the synthesis of precursors of nanostructured oxide systems Al2O3–ZrO2–MxOy (M = Mg, Y) are developed. The processes... 相似文献
53.
Dr. Chungsik Kim Mintesinot Kassu Dr. Kenneth P. Smith Prof. James E. Kirby Prof. Roman Manetsch 《ChemMedChem》2021,16(18):2775-2780
Pyrazole-thiazole core-containing compound KP-40 and 20 novel derivatives were designed and synthesized through traditional SAR analysis. These molecules displayed adjunctive activity with meropenem against Gram-negative bacteria evidenced by a range of fractional inhibitory concentration (FIC=0.5–0.25) and minimum adjunctive concentration (MAC=128–32 μM) values. Of this series of molecules, four compounds displayed notable adjunctive potential, with FIC and MAC values of 0.25 and 32 μM, respectively. Moreover, the solubility of these compounds was improved to an acceptable range. Further analysis using our “in house” permeation and efflux multi parameter optimization (PEMPO) algorithm revealed key physicochemical properties that may be critical for the development of active Gram-negative antibacterials. Taking PEMPO scores into consideration prior to executing synthesis of analogs may be a simple, yet rapid and effective strategy that can be used in conjunction with traditional SAR approaches to aid in the design of potent Gram-negative antibacterials. 相似文献
54.
Samuel J. Bunce Yiming Wang Sheena E. Radford Andrew J. Wilson Carol K. Hall 《American Institute of Chemical Engineers》2021,67(3):e17101
Determining the structure of the (oligomeric) intermediates that form during the self-assembly of amyloidogenic peptides is challenging because of their heterogeneous and dynamic nature. Thus, there is need for methodology to analyze the underlying molecular structure of these transient species. In this work, a combination of fluorescence quenching, photo-induced crosslinking (PIC) and molecular dynamics simulation was used to study the assembly of a synthetic amyloid-forming peptide, Aβ16-22. A PIC amino acid containing a trifluormethyldiazirine (TFMD) group—Fmoc(TFMD)Phe—was incorporated into the sequence (Aβ*16–22). Electrospray ionization ion-mobility spectrometry mass-spectrometry (ESI-IMS-MS) analysis of the PIC products confirmed that Aβ*16–22 forms assemblies with the monomers arranged as anti-parallel, in-register β-strands at all time points during the aggregation assay. The assembly process was also monitored separately using fluorescence quenching to profile the fibril assembly reaction. The molecular picture resulting from discontinuous molecule dynamics simulations showed that Aβ16-22 assembles through a single-step nucleation into a β-sheet fibril in agreement with these experimental observations. This study provides detailed structural insights into the Aβ16-22 self-assembly processes, paving the way to explore the self-assembly mechanism of larger, more complex peptides, including those whose aggregation is responsible for human disease. 相似文献
55.
The base and nucleotide excision repair pathways (BER and NER, respectively) are two major mechanisms that remove DNA lesions formed by the reactions of genotoxic intermediates with cellular DNA. It is generally believed that small non-bulky oxidatively generated DNA base modifications are removed by BER pathways, whereas DNA helix-distorting bulky lesions derived from the attack of chemical carcinogens or UV irradiation are repaired by the NER machinery. However, existing and growing experimental evidence indicates that oxidatively generated DNA lesions can be repaired by competitive BER and NER pathways in human cell extracts and intact human cells. Here, we focus on the interplay and competition of BER and NER pathways in excising oxidatively generated guanine lesions site-specifically positioned in plasmid DNA templates constructed by a gapped-vector technology. These experiments demonstrate a significant enhancement of the NER yields in covalently closed circular DNA plasmids (relative to the same, but linearized form of the same plasmid) harboring certain oxidatively generated guanine lesions. The interplay between the BER and NER pathways that remove oxidatively generated guanine lesions are reviewed and discussed in terms of competitive binding of the BER proteins and the DNA damage-sensing NER factor XPC-RAD23B to these lesions. 相似文献
56.
Abulyazied Dalia E. Alturki Asma M. Youness Rasha A. Abomostafa H. M. 《Journal of Inorganic and Organometallic Polymers and Materials》2021,31(10):4077-4092
Journal of Inorganic and Organometallic Polymers and Materials - In this work, a borosilicate glass sample (5SiO2–45B2O3–20Na2O–25CaO–5Ag2O) was added to nano-sized... 相似文献
57.
Semiconductors - Nanoheterostructures based on titanium dioxide synthesized by the sol–gel technique are studied. Microscopy, X-ray diffraction, optical spectroscopy, and electron-spin... 相似文献
58.
Tarasova E. A. Khazanova S. V. Golikov O. L. Puzanov A. S. Obolensky S. V. Zemlyakov V. E. 《Semiconductors》2021,55(12):895-898
Semiconductors - The paper presents the results of modeling the electrophysical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (pHEMT) structures via... 相似文献
59.
Nefedov E. I. Zayarnyi V. P. Ponomarev I. N. 《Journal of Communications Technology and Electronics》2021,66(4):420-426
Journal of Communications Technology and Electronics - Mathematical models are developed for planar symmetric slot antennas (SAs) with constant slot width using a tensor Green function that takes... 相似文献
60.