全文获取类型
收费全文 | 772658篇 |
免费 | 10666篇 |
国内免费 | 2102篇 |
专业分类
电工技术 | 14106篇 |
综合类 | 731篇 |
化学工业 | 116007篇 |
金属工艺 | 32669篇 |
机械仪表 | 24691篇 |
建筑科学 | 18684篇 |
矿业工程 | 4201篇 |
能源动力 | 19639篇 |
轻工业 | 65161篇 |
水利工程 | 8182篇 |
石油天然气 | 14683篇 |
武器工业 | 49篇 |
无线电 | 85651篇 |
一般工业技术 | 152918篇 |
冶金工业 | 144092篇 |
原子能技术 | 15840篇 |
自动化技术 | 68122篇 |
出版年
2021年 | 6269篇 |
2020年 | 4636篇 |
2019年 | 5819篇 |
2018年 | 15365篇 |
2017年 | 15554篇 |
2016年 | 13553篇 |
2015年 | 7595篇 |
2014年 | 12054篇 |
2013年 | 32757篇 |
2012年 | 20678篇 |
2011年 | 31474篇 |
2010年 | 25979篇 |
2009年 | 27838篇 |
2008年 | 28206篇 |
2007年 | 29149篇 |
2006年 | 20733篇 |
2005年 | 21298篇 |
2004年 | 19458篇 |
2003年 | 18920篇 |
2002年 | 17641篇 |
2001年 | 17225篇 |
2000年 | 16149篇 |
1999年 | 16794篇 |
1998年 | 42793篇 |
1997年 | 30527篇 |
1996年 | 23491篇 |
1995年 | 17588篇 |
1994年 | 15429篇 |
1993年 | 15115篇 |
1992年 | 11083篇 |
1991年 | 10580篇 |
1990年 | 10269篇 |
1989年 | 10095篇 |
1988年 | 9569篇 |
1987年 | 8419篇 |
1986年 | 8315篇 |
1985年 | 9384篇 |
1984年 | 8830篇 |
1983年 | 7966篇 |
1982年 | 7464篇 |
1981年 | 7689篇 |
1980年 | 7298篇 |
1979年 | 7114篇 |
1978年 | 7001篇 |
1977年 | 8315篇 |
1976年 | 10950篇 |
1975年 | 6209篇 |
1974年 | 5813篇 |
1973年 | 5881篇 |
1972年 | 4982篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms. 相似文献
32.
Castro Mateus B. Souza Raphael R. N. Junior Agord M. P. Lima Eduardo R. Manera Leandro T. 《Analog Integrated Circuits and Signal Processing》2021,109(3):647-656
Analog Integrated Circuits and Signal Processing - This paper presents the complete design of a phase locked loop-based clock synthesizer for reconfigurable analog-to-digital converters. The... 相似文献
33.
34.
Krzysztof M. Tokarz Wojciech Wesoowski Barbara Tokarz Wojciech Makowski Anna Wysocka Roman J. Jdrzejczyk Karolina Chrabaszcz Kamilla Malek Anna Kostecka-Gugaa 《International journal of molecular sciences》2021,22(2)
Grass pea (Lathyrus sativus) is a leguminous plant of outstanding tolerance to abiotic stress. The aim of the presented study was to describe the mechanism of grass pea (Lathyrus sativus L.) photosynthetic apparatus acclimatisation strategies to salinity stress. The seedlings were cultivated in a hydroponic system in media containing various concentrations of NaCl (0, 50, and 100 mM), imitating none, moderate, and severe salinity, respectively, for three weeks. In order to characterise the function and structure of the photosynthetic apparatus, Chl a fluorescence, gas exchange measurements, proteome analysis, and Fourier-transform infrared spectroscopy (FT-IR) analysis were done inter alia. Significant differences in the response of the leaf and stem photosynthetic apparatus to severe salt stress were observed. Leaves became the place of harmful ion (Na+) accumulation, and the efficiency of their carboxylation decreased sharply. In turn, in stems, the reconstruction of the photosynthetic apparatus (antenna and photosystem complexes) activated alternative electron transport pathways, leading to effective ATP synthesis, which is required for the efficient translocation of Na+ to leaves. These changes enabled efficient stem carboxylation and made them the main source of assimilates. The observed changes indicate the high plasticity of grass pea photosynthetic apparatus, providing an effective mechanism of tolerance to salinity stress. 相似文献
35.
Glass and Ceramics - An analysis of the specific mechanisms of the influence of the state of the grain structure on the thermoelectric properties (electrical resistivity and total thermal... 相似文献
36.
Bosyakova N. A. Pomortsev S. A. Gizatullin R. G. Klyosov Yu. L. Laptov S. V. Kashcheev I. D. Zemlyanoi K. G. 《Refractories and Industrial Ceramics》2021,62(4):381-383
Refractories and Industrial Ceramics - Technology for producing alumina-periclase-carbon refractories of the brands APUK-D and APU-D is developed and implemented. Use of complex antioxidant and... 相似文献
37.
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
38.
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
39.
Multimedia Tools and Applications - In this paper, a hashing based watermarking technique for the protection and authentication of document image is proposed. Message Digest 5 (MD5) hashing is... 相似文献
40.
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