全文获取类型
收费全文 | 426024篇 |
免费 | 7495篇 |
国内免费 | 1384篇 |
专业分类
电工技术 | 7963篇 |
综合类 | 394篇 |
化学工业 | 65202篇 |
金属工艺 | 14677篇 |
机械仪表 | 12204篇 |
建筑科学 | 12453篇 |
矿业工程 | 968篇 |
能源动力 | 11405篇 |
轻工业 | 45826篇 |
水利工程 | 3410篇 |
石油天然气 | 1855篇 |
武器工业 | 13篇 |
无线电 | 56241篇 |
一般工业技术 | 80350篇 |
冶金工业 | 75252篇 |
原子能技术 | 5678篇 |
自动化技术 | 41012篇 |
出版年
2021年 | 2997篇 |
2020年 | 2093篇 |
2019年 | 2719篇 |
2018年 | 4351篇 |
2017年 | 4409篇 |
2016年 | 4703篇 |
2015年 | 3928篇 |
2014年 | 6285篇 |
2013年 | 20478篇 |
2012年 | 10898篇 |
2011年 | 15551篇 |
2010年 | 12030篇 |
2009年 | 13544篇 |
2008年 | 14627篇 |
2007年 | 14982篇 |
2006年 | 13289篇 |
2005年 | 12380篇 |
2004年 | 11906篇 |
2003年 | 11603篇 |
2002年 | 11258篇 |
2001年 | 11411篇 |
2000年 | 10512篇 |
1999年 | 10963篇 |
1998年 | 24172篇 |
1997年 | 17752篇 |
1996年 | 14038篇 |
1995年 | 11124篇 |
1994年 | 9885篇 |
1993年 | 9452篇 |
1992年 | 7212篇 |
1991年 | 6876篇 |
1990年 | 6472篇 |
1989年 | 6177篇 |
1988年 | 5924篇 |
1987年 | 4947篇 |
1986年 | 4889篇 |
1985年 | 6096篇 |
1984年 | 5729篇 |
1983年 | 4915篇 |
1982年 | 4589篇 |
1981年 | 4551篇 |
1980年 | 4285篇 |
1979年 | 4155篇 |
1978年 | 3851篇 |
1977年 | 4608篇 |
1976年 | 6162篇 |
1975年 | 3198篇 |
1974年 | 3068篇 |
1973年 | 2945篇 |
1972年 | 2351篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
Kexin Jiao Laurence J. Walsh Sao Ivanovski Pingping Han 《International journal of molecular sciences》2021,22(9)
Periodontitis is a chronic complex inflammatory disease associated with a destructive host immune response to microbial dysbiosis, leading to irreversible loss of tooth-supporting tissues. Regeneration of functional periodontal soft (periodontal ligament and gingiva) and hard tissue components (cementum and alveolar bone) to replace lost tissues is the ultimate goal of periodontal treatment, but clinically predictable treatments are lacking. Similarly, the identification of biomarkers that can be used to accurately diagnose periodontitis activity is lacking. A relatively novel category of molecules found in oral tissue, circular RNAs (circRNAs) are single-stranded endogenous, long, non-coding RNA molecules, with covalently circular-closed structures without a 5’ cap and a 3’ tail via non-classic backsplicing. Emerging research indicates that circRNAs are tissue and disease-specific expressed and have crucial regulatory functions in various diseases. CircRNAs can function as microRNA or RNA binding sites or can regulate mRNA. In this review, we explore the biogenesis and function of circRNAs in the context of the emerging role of circRNAs in periodontitis pathogenesis and the differentiation of periodontal cells. CircMAP3K11, circCDK8, circCDR1as, circ_0062491, and circ_0095812 are associated with pathological periodontitis tissues. Furthermore, circRNAs are expressed in periodontal cells in a cell-specific manner. They can function as microRNA sponges and can form circRNA–miRNA–mRNA networks during osteogenic differentiation for periodontal-tissue (or dental pulp)-derived progenitor cells. 相似文献
23.
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
24.
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
25.
Cybernetics and Systems Analysis - The authors propose a method for solving the problem of approach of controlled objects in dynamic game problems with a terminal payoff function. The method is... 相似文献
26.
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
27.
Romero-Garcés A. Salles De Freitas R. Marfil R. Vicente-Chicote C. Martínez J. Inglés-Romero J. F. Bandera A. 《Multimedia Tools and Applications》2022,81(3):3603-3628
Multimedia Tools and Applications - The design of robots capable of operating autonomously in changing and unstructured environments, requires using complex software architectures in which,... 相似文献
28.
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
29.
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
30.
Belcher Calvin H. Zheng Baolong MacDonald Benjamin E. Langlois Eric D. Lehman Benjamin Pearce Charles Delaney Robert Apelian Diran Lavernia Enrique J. Monson Todd C. 《Journal of Materials Science》2022,57(9):5518-5532
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic... 相似文献