全文获取类型
收费全文 | 345188篇 |
免费 | 6725篇 |
国内免费 | 985篇 |
专业分类
电工技术 | 5879篇 |
综合类 | 473篇 |
化学工业 | 57830篇 |
金属工艺 | 13386篇 |
机械仪表 | 9841篇 |
建筑科学 | 8976篇 |
矿业工程 | 2077篇 |
能源动力 | 8227篇 |
轻工业 | 34690篇 |
水利工程 | 3607篇 |
石油天然气 | 7353篇 |
武器工业 | 30篇 |
无线电 | 34452篇 |
一般工业技术 | 67487篇 |
冶金工业 | 60582篇 |
原子能技术 | 7919篇 |
自动化技术 | 30089篇 |
出版年
2021年 | 3631篇 |
2020年 | 2700篇 |
2019年 | 3096篇 |
2018年 | 5456篇 |
2017年 | 5310篇 |
2016年 | 5829篇 |
2015年 | 4120篇 |
2014年 | 6354篇 |
2013年 | 15929篇 |
2012年 | 9840篇 |
2011年 | 12742篇 |
2010年 | 10302篇 |
2009年 | 11320篇 |
2008年 | 11654篇 |
2007年 | 11304篇 |
2006年 | 9791篇 |
2005年 | 8940篇 |
2004年 | 8156篇 |
2003年 | 7813篇 |
2002年 | 7828篇 |
2001年 | 7402篇 |
2000年 | 6991篇 |
1999年 | 7088篇 |
1998年 | 17763篇 |
1997年 | 12987篇 |
1996年 | 9961篇 |
1995年 | 7431篇 |
1994年 | 6685篇 |
1993年 | 6512篇 |
1992年 | 4784篇 |
1991年 | 4745篇 |
1990年 | 4515篇 |
1989年 | 4564篇 |
1988年 | 4476篇 |
1987年 | 3837篇 |
1986年 | 3815篇 |
1985年 | 4519篇 |
1984年 | 4263篇 |
1983年 | 3865篇 |
1982年 | 3646篇 |
1981年 | 3845篇 |
1980年 | 3674篇 |
1979年 | 3555篇 |
1978年 | 3611篇 |
1977年 | 4236篇 |
1976年 | 5620篇 |
1975年 | 3314篇 |
1974年 | 3122篇 |
1973年 | 3182篇 |
1972年 | 2710篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Reliable prediction of flooding conditions is needed for sizing and operating packed extraction columns. Due to the complex interplay of physicochemical properties, operational parameters and the packing-specific properties, it is challenging to develop accurate semi-empirical or rigorous models with a high validity range. State of the art models may therefore fail to predict flooding accurately. To overcome this problem, a data-driven model based on Gaussian processes is developed to predict flooding for packed liquid-liquid and high-pressure extraction columns. The optimized Gaussian process for the liquid-liquid extraction column results in an average absolute relative error (AARE) of 15.23 %, whereas the algorithm for the high-pressure extraction column results in an AARE of 13.68 %. Both algorithms can predict flooding curves for different packing geometries and chemical systems precisely. 相似文献
32.
Wireless Networks - Orthogonal frequency-division multiplexing with random multiple access (OFDRMA) is discussed for down-link communications, whereby a single base-station transmits information... 相似文献
33.
N.A. Zhuk M.G. Krzhizhanovskaya N.A. Sekushin V.V. Kharton B.A. Makeev V.A. Belyy R.I. Korolev 《Ceramics International》2021,47(14):19424-19433
The solid solutions based on the pyrochlore-type system Bi2MgNb2-xTaxO9 were formed in the compositional range х = 0–2.0 (Bi1·6Mg0·8Nb1.6-tTatO7.2, t = 0–1.6). The Rietveld method was used to refine the structure for Bi2MgNb2-xTaxO9 (x = 0, 1.0, 2.0). The increasing tantalum content led to the slight decrease in the cubic unit cell parameters from 10.56934 (4) Å for x = 0 and 10.54607 (3) Å for x = 2 (sp.gr. Fd-3m:2). At the same time, tantalum additions suppressed grain growth in the pyrochlore ceramics during sintering and made it possible to obtain materials with an average grain size of 1–2 μm (Bi1·6Mg0·8Ta1·6O7.2). The increase in the Ta5+ concentration led to the decrease in the dielectric permeability from 104 (Bi1·6Mg0·8Nb1·6O7.2) to 20 (Bi1·6Mg0·8Ta1·6O7.2) at room temperature, while the dielectric loss tangent remained lower than 0.002, which is due to the small grain size and the high porosity of the samples. An increase in temperature has practically no effect on the values of the dielectric permittivity in the entire frequency range. The samples have weak through conductivity. The activation energies of electrical conductivity varied in the range of 0.84–1.00 eV, and the less tantalum, the lower the activation energy. The electrical properties of the samples at 200 Hz to 1 MHz are described by the simplest parallel scheme. 相似文献
34.
Celia Nieto Milena A. Vega Eva M. Martín del Valle 《International journal of molecular sciences》2021,22(6)
Ferroptosis is gaining followers as mechanism of selective killing cancer cells in a non-apoptotic manner, and novel nanosystems capable of inducing this iron-dependent death are being increasingly developed. Among them, polydopamine nanoparticles (PDA NPs) are arousing interest, since they have great capability of chelating iron. In this work, PDA NPs were loaded with Fe3+ at different pH values to assess the importance that the pH may have in determining their therapeutic activity and selectivity. In addition, doxorubicin was also loaded to the nanoparticles to achieve a synergist effect. The in vitro assays that were performed with the BT474 and HS5 cell lines showed that, when Fe3+ was adsorbed in PDA NPs at pH values close to which Fe(OH)3 begins to be formed, these nanoparticles had greater antitumor activity and selectivity despite having chelated a smaller amount of Fe3+. Otherwise, it was demonstrated that Fe3+ could be released in the late endo/lysosomes thanks to their acidic pH and their Ca2+ content, and that when Fe3+ was co-transported with doxorubicin, the therapeutic activity of PDA NPs was enhanced. Thus, reported PDA NPs loaded with both Fe3+ and doxorubicin may constitute a good approach to target breast tumors. 相似文献
35.
Zagidullin S. Kh. Dolganov V. L. Lozhkin I. G. 《Chemical and Petroleum Engineering》2022,57(9-10):765-769
Chemical and Petroleum Engineering - The hydrodynamics of oxidation towers used for bitumen production were studied using a model tower having transparent walls. Experiments were carried out in two... 相似文献
36.
37.
Ib Holzmeister Jan Weichhold Jürgen Groll Hala Zreiqat Uwe Gbureck 《Journal of the American Ceramic Society》2021,104(7):3554-3561
In this study, the hydraulic reactivity and cement formation of baghdadite (Ca3ZrSi2O9) was investigated. The material was synthesized by sintering a mixture of CaCO3, SiO2, and ZrO2 and then mechanically activated using a planetary mill. This leads to a decrease in particle and crystallite size and a partial amorphization of baghdadite as shown by X-ray powder diffraction (XRD) and laser diffraction measurements. Baghdadite cements were formed by the addition of water at a powder to liquid ratio of 2.0 g/ml. Maximum compressive strengths were found to be ~2 MPa after 3-day setting for a 24-h ground material. Inductively coupled plasma mass spectrometry (ICP-MS) measurements showed an incongruent dissolution profile of set cements with a preferred dissolution of calcium and only marginal release of zirconium ions. Cement formation occurs under alkaline conditions, whereas the unground raw powder leads to a pH of 11.9 during setting, while prolonged grinding increased pH values to approximately 12.3. 相似文献
38.
Precipitation of calcium deficient hydroxyapatite nanoparticles in an environmentally benign manner by using only dilute solutions of calcium hydroxide and phosphoric acid without pH adjustment and addition of other chemicals, and water, being the only by-product was investigated by using continuous flow Vortex Reactor (VR) and Semi-Batch Reactor (SBR). The effect of hydrodynamics by changing the Reynolds number of the jets providing residence times of 8.4 ms to 4.37 s for VR, and by changing the stirrer speed between 100 rpm (Re = 2656) and 1000 rpm (Re = 26560) for SBR, on the particle size, particle size distribution, and morphology of the particles was investigated for both systems. It has been shown that it is possible to produce pure phase hydroxyapatite nanoparticles in the desired morphology by changing production system, without resorting to additives. While VR produced rod-like particles with the crystallite size around 4 nm, SBR produced spherical particles with the crystallite size of around 5 nm. 相似文献
39.
Journal of Low Temperature Physics - This study modeled and investigated the magnetocaloric effect in Ni2MnGa Heusler alloy characterized by its magnetic entropy change (ΔSm) and its... 相似文献
40.
Alawiya Reslan Juliano G. Haddad Liadrine Moukendza Koundi Philippe Desprs Jean-Loup Bascands Gilles Gadea 《International journal of molecular sciences》2021,22(5)
Mosquito-borne Zika virus (ZIKV) became a real threat to human health due to the lack of vaccine and effective antiviral treatment. The virus has recently been responsible for a global outbreak leading to millions of infected cases. ZIKV complications were highlighted in adults with Guillain–Barré syndrome and in newborns with increasing numbers of congenital disorders ranging from mild developmental delays to fatal conditions. The ability of ZIKV to establish a long-term infection in diverse organs including the kidneys has been recently documented but the consequences of such a viral infection are still debated. Our study aimed to determine whether the efficiency of ZIKV growth in kidney cells relates to glucose concentration. Human kidney HK-2 cells were infected with different ZIKV strains in presence of normal and high glucose concentrations. Virological assays showed a decrease in viral replication without modifying entry steps (viral binding, internalization, fusion) under high glucose conditions. This decrease replication was associated with a lower virus progeny and increased cell viability when compared to ZIKV-infected HK-2 cells in normal glucose concentration. In conclusion, we showed for the first time that an elevated glucose level influences ZIKV replication level with an effect on kidney cell survival. 相似文献