全文获取类型
收费全文 | 105757篇 |
免费 | 9789篇 |
国内免费 | 6281篇 |
专业分类
电工技术 | 4237篇 |
技术理论 | 4篇 |
综合类 | 12222篇 |
化学工业 | 16156篇 |
金属工艺 | 8426篇 |
机械仪表 | 6035篇 |
建筑科学 | 19796篇 |
矿业工程 | 3983篇 |
能源动力 | 2888篇 |
轻工业 | 5594篇 |
水利工程 | 2703篇 |
石油天然气 | 5075篇 |
武器工业 | 984篇 |
无线电 | 6252篇 |
一般工业技术 | 12066篇 |
冶金工业 | 4642篇 |
原子能技术 | 753篇 |
自动化技术 | 10011篇 |
出版年
2024年 | 208篇 |
2023年 | 1382篇 |
2022年 | 2522篇 |
2021年 | 3069篇 |
2020年 | 3055篇 |
2019年 | 2558篇 |
2018年 | 2376篇 |
2017年 | 3027篇 |
2016年 | 3242篇 |
2015年 | 3503篇 |
2014年 | 6350篇 |
2013年 | 5643篇 |
2012年 | 7374篇 |
2011年 | 8116篇 |
2010年 | 6227篇 |
2009年 | 6743篇 |
2008年 | 6129篇 |
2007年 | 7279篇 |
2006年 | 6724篇 |
2005年 | 5861篇 |
2004年 | 4874篇 |
2003年 | 4403篇 |
2002年 | 3715篇 |
2001年 | 3059篇 |
2000年 | 2584篇 |
1999年 | 2152篇 |
1998年 | 1667篇 |
1997年 | 1454篇 |
1996年 | 1148篇 |
1995年 | 1027篇 |
1994年 | 983篇 |
1993年 | 645篇 |
1992年 | 596篇 |
1991年 | 480篇 |
1990年 | 391篇 |
1989年 | 282篇 |
1988年 | 218篇 |
1987年 | 113篇 |
1986年 | 77篇 |
1985年 | 91篇 |
1984年 | 73篇 |
1983年 | 68篇 |
1982年 | 85篇 |
1981年 | 26篇 |
1980年 | 67篇 |
1979年 | 23篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1959年 | 12篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
《Ceramics International》2019,45(8):9799-9806
(Nb1-xTax)4AlC3 (x = 0–0.5) ceramics were prepared by the hot press sintering method. The XRD results show that the second phase (Nb1-xTax)C is formed when the Ta content increases to 25 mol%. The SEM micrographs show that (Nb1-xTax)C has a core/rim structure, whose formation mechanism was also investigated. Substituting some Ta for Nb can significantly improve the mechanical properties of Nb4AlC3. (Nb0.75Ta0.25)4AlC3 exhibits an excellent fracture toughness of 8.3 ± 0.3 MPa m1/2 at room temperature (RT). The highest Young's modulus (349 ± 16 GPa) and Vickers hardness (4.5 ± 0.3 GPa) at RT are exhibited by the (Nb0.5Ta0.5)4AlC3 sample, which correlate to increases of 18% and 80%, respectively, compared with those of Nb4AlC3. The flexural strengths of (Nb0.5Ta0.5)4AlC3 are 439 ± 18 MPa at RT and 344 ± 22 MPa at 1100 °C, which correlate to increases of 27% and 45%, respectively, compared with those of Nb4AlC3. The solid solution of Ta and the formation of (Nb1-xTax)C are beneficial to the strengthening of Nb4AlC3. The coefficient of thermal expansion (CTE) increases slightly from 7.08 × 10−6 K−1 for Nb4AlC3 to 7.24 × 10−6 K−1 for (Nb0.75Ta0.25)4AlC3 at 25–1400 °C. The thermal conductivity of (Nb0.75Ta0.25)4AlC3 (28.4–29.8 W/m·K) is higher than that of Nb4AlC3 (18.1–21.2 W/m·K) over the whole test range (25–1000 °C). Owing to their excellent mechanical and thermal properties, Ta-doped Nb4AlC3 ceramics have good potential as structural materials. 相似文献
102.
Dapeng Wang Qingzhao Wang Zhiming Wang Huanying Jiang Zhao Zhang Peng Liu Chao Xu Longyang Gao 《Ceramics International》2019,45(9):11578-11583
Glass fibre is a random network structure composed of [SiO4] tetrahedra. The structure contains a large number of defects, which act as crack initiation points. Under tensile stress, cracks undergo crack initiation, stable propagation, failure propagation, and fracture, and the stress that begins after unstable propagation is called the critical fracture stress. When the stress is less than the critical value, the crack is subject to the force of chemical bonds during the crack propagation process, and crack arrest occurs. When the stress is greater than the critical value, the glass fibre will undergo destructive fracture. In this paper, long-term tensile tests were carried out on glass fibre and a glass fibre composite under different constant tensile stress conditions. The fracture times of the glass fibre and glass fibre composite under different tensile stresses were obtained, the critical fracture stress of glass fibre was inferred, and the fracture mechanism was explained. 相似文献
103.
Chahid Ayouch El-Hassan Essoufi Mouhcine Tilioua 《Computers & Mathematics with Applications》2019,77(5):1347-1357
The present paper deals with global existence of weak solutions of a time-space fractional Landau–Lifshitz–Bloch equation involving the weak Caputo derivative and a fractional Laplacian. We use Faedo–Galerkin method with some commutator estimates in order to prove global existence of weak solutions for the model. The uniqueness is also discussed in a special one dimensional case. 相似文献
104.
Shi-Jin Feng Ming-Qing Peng Hong-Xin Chen Zhang-Long Chen 《Geotextiles and Geomembranes》2019,47(3):282-294
In this study, analytical solution for degradable organic contaminant transport through a composite liner consisting of a geomembrane (GMB) layer, a geosynthetic clay liner (GCL) and an attenuation layer (AL) is derived by the separation of variables method. The transient contaminant transport in the whole composite liner can be well described avoiding some weird phenomena in existing analytical solutions. The results of parametric study show that GCL has significant effect on improving the barrier efficiency especially for scenarios with high leachate head. The biodegradation and adsorption in GCL have significant influence on the contaminant transport through the composite liner when the half-life of contaminant in GCL is less than 5 years. Otherwise, the effect can be neglected. 相似文献
105.
Hydrolytic stability is an essential requirement for polyurethanes (PUs) that are used in highly humid and aqueous environments. In this study, hydrolysis-resistant PU elastomers (PUEs) are synthesized based on hydrophobic bio-based polyfarnesene diol (PFD), which contains unique “bottle brushes” structure (with long branched hydrocarbon side chains). The effect of hard segment (HS) content, ranging from 30 to 50%, on the morphology and properties of PUEs is investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, tensile, water absorption, and contact angle measurements. The results show that there are prominent phase separations in the synthesized PUEs. The PUEs show a three-stage degradation process and two Tg, one is at about −66 °C and the other 61 °C, which are related to the soft segment and HS, respectively. Water contact angles of PUEs increase from 98.6 to 105.2° with the increasing of PFD structural unit fraction. After being immersed in deionized water for 30 days, PUEs show no significant degradation of both tensile strength and elongation at break, and mass changes of all samples are less than 0.5%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47673. 相似文献
106.
Samson I. Eze Chidinma C. Ezeofor Nkiru V. Mmadubuike Francis K. Ojo 《Petroleum Science and Technology》2019,37(15):1830-1838
The abstraction of crude oil molecules from aqueous solution (produced water) and from real petroleum polluted water (collected from River State, Nigeria) by Dialium guineense Seed Husk (DGSH) and its ammonium sulfate functionalized form (AS-DGSH) was studied using a batch technique. The sorbents were characterized using Fourier transform infrared (FTIR), BET surface area analysis and the Scanning electron microscopy (SEM). Crude oil characterization revealed a light crude oil based on the API gravity of 35.60. The Langmuir and Freundlich models gave good fits for crude oil sorption on DGSH and AS-DGSH respectively. The sorbents were found to remove over 50% of crude oil from the real polluted water at the natural pH of 6.1 and showed increase in removal with increase in sorbent dose. The potential of DGSH and its ammonium sulfate modified derivative as effective low cost sorbents for oil spill treatment was established. 相似文献
107.
《Ceramics International》2019,45(15):18614-18622
Low ionic conductivity at room temperature and poor interfacial compatibility are the main obstacles to restrain the practical application of polymer solid electrolytes. In this work, lanthanum zirconate (LZO) fibers were prepared by electrospinning method and used for the first time as fillers in sandwich polypropylene carbonate (PPC)-based solid electrolyte. Meanwhile, a graphite coating was applied on one surface of the composite solid electrolyte (CSE) membrane. The results show that the LZO fibers significantly increases the room-temperature electrochemical performance of the CSE, and the graphite coating enhances the interfacial compatibility between electrolyte and lithium anode. Furthermore, an ultra-thin PPC-LZO CSE with a total thickness of 22 μm was prepared and used in NCM622/CSE/Li solid-state cell, which shows an initial discharge capacity of 165.6 mAh/g at the current density of 0.5C and a remaining capacity of 113.0 mAh/g after 250 cycles at room temperature. Rise to 1C, the cell shows an initial discharge capacity of 154.2 mAh/g with a remaining capacity of 95.6 mAh/g after 250 cycles. This ultra-thin CSE is expected to be widely applied in high energy-density solid-state battery with excellent room-temperature electrochemical performances. 相似文献
108.
109.
110.
In this paper, the nonreciprocal properties of a novel kind of 1D magnetized plasma photonic crystals(MPPCs) with the Fibonacci sequence are investigated. The isolation of the proposed 1D MPPCs is also used to analyze the nonreciprocal properties. Compared to the conventional 1D MPPCs with periodic structure, the nonreciprocal performance can be significantly improved.The effects of several parameters of the proposed 1D MPPCs on the nonreciprocal properties are studied by the transfer matrix method, which includes the incident angle, order of the Fibonacci sequence, plasma frequency, plasma cyclotron frequency and plasma filling factor. The obtained results show that the nonreciprocal propagation properties can be improved by increasing the values of the plasma cyclotron frequency and incident angle, but they will worsen by blindly increasing the order of the Fibonacci sequence, plasma frequency and filling factor of plasma.The peaks of transmittance also are obviously reduced. In addition, the value of isolation will increase with increasing the incident angle, order of Fibonacci sequence, plasma frequency and plasma filling factor. However, when the plasma cyclotron frequency is increased, the value of isolation will be increased at lower frequencies, but is almost unchanged at higher frequencies. 相似文献