全文获取类型
收费全文 | 200032篇 |
免费 | 2666篇 |
国内免费 | 611篇 |
专业分类
电工技术 | 3470篇 |
综合类 | 152篇 |
化学工业 | 29199篇 |
金属工艺 | 8063篇 |
机械仪表 | 6078篇 |
建筑科学 | 4856篇 |
矿业工程 | 1305篇 |
能源动力 | 5138篇 |
轻工业 | 17191篇 |
水利工程 | 2298篇 |
石油天然气 | 4040篇 |
武器工业 | 8篇 |
无线电 | 23105篇 |
一般工业技术 | 40142篇 |
冶金工业 | 37270篇 |
原子能技术 | 5092篇 |
自动化技术 | 15902篇 |
出版年
2021年 | 1625篇 |
2019年 | 1589篇 |
2018年 | 2587篇 |
2017年 | 2660篇 |
2016年 | 2795篇 |
2015年 | 1813篇 |
2014年 | 3097篇 |
2013年 | 8978篇 |
2012年 | 5091篇 |
2011年 | 7061篇 |
2010年 | 5625篇 |
2009年 | 6385篇 |
2008年 | 6476篇 |
2007年 | 6541篇 |
2006年 | 5600篇 |
2005年 | 5251篇 |
2004年 | 5028篇 |
2003年 | 4900篇 |
2002年 | 4539篇 |
2001年 | 4668篇 |
2000年 | 4592篇 |
1999年 | 4739篇 |
1998年 | 11383篇 |
1997年 | 8136篇 |
1996年 | 6420篇 |
1995年 | 4688篇 |
1994年 | 4279篇 |
1993年 | 4082篇 |
1992年 | 3230篇 |
1991年 | 3085篇 |
1990年 | 2877篇 |
1989年 | 2957篇 |
1988年 | 2837篇 |
1987年 | 2405篇 |
1986年 | 2310篇 |
1985年 | 2721篇 |
1984年 | 2507篇 |
1983年 | 2354篇 |
1982年 | 2095篇 |
1981年 | 2211篇 |
1980年 | 2033篇 |
1979年 | 2126篇 |
1978年 | 2121篇 |
1977年 | 2367篇 |
1976年 | 3193篇 |
1975年 | 1836篇 |
1974年 | 1764篇 |
1973年 | 1773篇 |
1972年 | 1447篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
K.M. Srinivasamurthy Jagadeesha Angadi V S.P. Kubrin Shiddaling Matteppanavar D.A. Sarychev P. Mohan Kumar Haileeyesus Workineh Azale B. Rudraswamy 《Ceramics International》2018,44(8):9194-9203
Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni2+ substitution effect in Co1-xNixFe2O4 (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni2+ concentration. The M-H loops reveals that saturation magnetization(Ms), coercive field(Hc) remanence magnetization(Mr) and magnetron number(ηB) decreases significantly with increasing Ni2+ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(Hc) is found strongly dependent on the concentration of Ni2+ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni2+ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application. 相似文献
82.
83.
Radiochemistry - Azathioprine, an antitumor agent, was labeled with 99mTc using stannous chloride dihydrate as a reducing agent. Factors such as the amounts of the reducing agent and substrate, pH,... 相似文献
84.
Effect of Supports and Promoters on the Performance of Ni-Based Catalysts in Ethanol Steam Reforming
Thanh Khoa Phung Thong Le Minh Pham Anh-Nga T. Nguyen Khanh B. Vu Ha Ngoc Giang Tuan-Anh Nguyen Thanh Cong Huynh Hong Duc Pham 《化学工程与技术》2020,43(4):672-688
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process. 相似文献
85.
Dr. Vlastimil Jirasko Dr. Nils-Alexander Lakomek Dr. Susanne Penzel Dr. Marie-Laure Fogeron Prof. Dr. Ralf Bartenschlager Prof. Dr. Beat H. Meier Dr. Anja Böckmann 《Chembiochem : a European journal of chemical biology》2020,21(10):1453-1460
Proton-detected 100 kHz magic-angle-spinning (MAS) solid-state NMR is an emerging analysis method for proteins with only hundreds of microgram quantities, and thus allows structural investigation of eukaryotic membrane proteins. This is the case for the cell-free synthesized hepatitis C virus (HCV) nonstructural membrane protein 4B (NS4B). We demonstrate NS4B sample optimization using fast reconstitution schemes that enable lipid-environment screening directly by NMR. 2D spectra and relaxation properties guide the choice of the best sample preparation to record 2D 1H-detected 1H,15N and 3D 1H,13C,15N correlation experiments with linewidths and sensitivity suitable to initiate sequential assignments. Amino-acid-selectively labeled NS4B can be readily obtained using cell-free synthesis, opening the door to combinatorial labeling approaches which should enable structural studies. 相似文献
86.
N. Bartsch M. Girard A. Wilde T. Bruhn O. Kappenstein B. Vieth C. Hutzler A. Luch 《乙烯基与添加剂工艺杂志》2019,25(Z2):E12-E27
The thermo‐oxidative stability of widely used polymer additives has been investigated. A comparative analytical approach with classic and innovative decomposition models for polymer additives was conducted and the results supported using quantum‐chemical calculations. Unique pyrolysis products of the analytes were compiled utilizing pyrolysis online coupled to gas chromatography followed by mass spectrometric detection (Pyr‐GC–MS). The pyrolysis was either performed under inert conditions or in an oxygen‐containing atmosphere. Squalane was applied as polymer‐mimicking liquid next to low density polyethylene (LDPE) and polyamide 6 (PA 6) as matrices for 10 selected additives. The additives included in this study range from antioxidants and plasticizers to processing aids. These were selected to address a range of application in consumer products and to cover different chemical classes. The toxicological relevance of additives and potential breakdown products was considered. Consequently, degradation of sterically hindered antioxidants, diarylamines, and a trimellitic acid derivative was investigated. The findings were used to predict the behavior of consumer products made of polymeric materials entailing additives. The level of Antioxidant 2246 [2‐tert‐butyl‐6‐[(3‐tert‐butyl‐2‐hydroxy‐5‐methylphenyl)methyl]‐4‐methylphenol] and one of its predicted decomposition products was determined in baby bottle nipples made of natural rubber [2‐tert‐butyl‐4‐methylphenol] utilizing the complementary technique of gas chromatography coupled to tandem mass spectrometry (GC–MS/MS). This study provides a comprehensive characterization of important polymer additives and enables the prioritization of degradation products for further risk assessment. J. VINYL ADDIT. TECHNOL., 25:E12–E27, 2019. © 2018 The Authors. Journal of Vinyl and Additive Technology published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers 相似文献
87.
88.
89.
Locke Davenport Huyer Serena Mandla Yufeng Wang Scott B. Campbell Bess Yee Christian Euler Benjamin F. Lai A. Dawn Bannerman Dawn S. Y. Lin Miles Montgomery Kayla Nemr Timothy Bender Slava Epelman Radhakrishnan Mahadevan Milica Radisic 《Advanced functional materials》2021,31(6):2003341
Itaconate (ITA) is an emerging powerhouse of innate immunity with therapeutic potential that is limited in its ability to be administered in a soluble form. A library of polyester materials that incorporate ITA into polymer backbones resulting in materials with inherent immunoregulatory behavior is developed. Harnessing hydrolytic degradation release from polyester backbones, ITA polymers result in the mechanism specific immunoregulatory properties on macrophage polarization in vitro. In a functional assay, the polymer-released ITA inhibits bacterial growth on acetate. Translation to an in vivo model of biomaterial associated inflammation, intraperitoneal injection of ITA polymers demonstrate a rapid resolution of inflammation in comparison to a control polymer silicone, demonstrating the value of sustained biomimetic presentation of ITA. 相似文献
90.
Ci̇velekler Ebru Okur Volkan D. Afacan Kamil B. 《Bulletin of Engineering Geology and the Environment》2021,80(7):5589-5607
Bulletin of Engineering Geology and the Environment - Local soil characteristics play a key role in determining soil-structure interaction and reliability of the superstructure behavior under... 相似文献