全文获取类型
收费全文 | 71464篇 |
免费 | 8130篇 |
国内免费 | 4416篇 |
专业分类
电工技术 | 5425篇 |
技术理论 | 4篇 |
综合类 | 6064篇 |
化学工业 | 10869篇 |
金属工艺 | 4077篇 |
机械仪表 | 4658篇 |
建筑科学 | 6120篇 |
矿业工程 | 2255篇 |
能源动力 | 2170篇 |
轻工业 | 6650篇 |
水利工程 | 1630篇 |
石油天然气 | 3392篇 |
武器工业 | 782篇 |
无线电 | 8578篇 |
一般工业技术 | 7343篇 |
冶金工业 | 2621篇 |
原子能技术 | 714篇 |
自动化技术 | 10658篇 |
出版年
2024年 | 413篇 |
2023年 | 1547篇 |
2022年 | 3098篇 |
2021年 | 4170篇 |
2020年 | 2881篇 |
2019年 | 2245篇 |
2018年 | 2416篇 |
2017年 | 2565篇 |
2016年 | 2218篇 |
2015年 | 3393篇 |
2014年 | 4061篇 |
2013年 | 4546篇 |
2012年 | 5404篇 |
2011年 | 5572篇 |
2010年 | 4852篇 |
2009年 | 4634篇 |
2008年 | 4478篇 |
2007年 | 4065篇 |
2006年 | 3713篇 |
2005年 | 3096篇 |
2004年 | 2247篇 |
2003年 | 2061篇 |
2002年 | 2274篇 |
2001年 | 1866篇 |
2000年 | 1365篇 |
1999年 | 1088篇 |
1998年 | 714篇 |
1997年 | 599篇 |
1996年 | 511篇 |
1995年 | 443篇 |
1994年 | 357篇 |
1993年 | 256篇 |
1992年 | 201篇 |
1991年 | 174篇 |
1990年 | 118篇 |
1989年 | 83篇 |
1988年 | 64篇 |
1987年 | 48篇 |
1986年 | 37篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 12篇 |
1980年 | 30篇 |
1979年 | 10篇 |
1978年 | 2篇 |
1959年 | 2篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
In this research, the three‐dimensional structural and colorimetric modeling of three‐dimensional woven fabrics was conducted for accurate color predictions. One‐hundred forty single‐ and double‐layered woven samples in a wide range of colors were produced. With the consideration of their three‐dimensional structural parameters, three‐dimensional color prediction models, K/S‐, R‐, and L*a*b*‐based models, were developed through the optimization of previous two‐dimensional models which have been reported to be the three most accurate models for single‐layered woven structures. The accuracy of the new three‐dimensional models was evaluated by calculating the color differences ΔL*, ΔC*, Δh°, and ΔECMC(2:1) between the measured and the predicted colors of the samples, and then the error values were compared to those of the two‐dimensional models. As a result, there has been an overall improvement in color predictions of all models with a decrease in ΔECMC(2:1) from 10.30 to 5.25 units on average after the three‐dimensional modeling. 相似文献
52.
Jialin Sun Jun Zhao Xiuying Ni Feng Gong Zuoli Li 《Journal of the European Ceramic Society》2018,38(9):3096-3103
This work investigates the critical roles of two-step sintering (TSS) and laminated structure on the sintering behavior and mechanical properties of functionally graded WC-TiC-Al2O3 nanostructured composite materials doped with Cr3C2/VC. Results show that excellent mechanical properties are achieved for tailored TSS conditions with a hardness of 27.91?±?2.3?GPa and a flexural strength of 1423.3?±?23.5?MPa. The desirable mechanical properties are attributed to the suppressed grain growth without densification deterioration. TSS is more effective in facilitating the favorable dispersion of secondary phase toughening nano-particulates in a WC matrix than conventional sintering (CS). Cr3C2/VC dopant plays an important role in maximizing and shifting the temperature range of the kinetic window for WC-Al2O3 composites. Al2O3 crack deflection, transgranular Al2O3, microcracking, WC crack bridging and plate-like WC crack deflection are the major toughening mechanisms. Residual surface compressive stress induced by the graded structure is also an appreciated contribution to the improvement of mechanical properties. 相似文献
53.
54.
55.
56.
Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers (HCTs) during direct shear of infilled joints under constant normal stiffness (CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using three-dimensional (3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients (JRCs) of 8–10 and 18–20 with the ratios of infill thickness to asperity height (t/a) equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness. 相似文献
57.
This paper considers a novel distributed iterative learning consensus control algorithm based on neural networks for the control of heterogeneous nonlinear multiagent systems. The system's unknown nonlinear function is approximated by suitable neural networks; the approximation error is countered by a robust term in the control. Two types of control algorithms, both of which utilize distributed learning laws, are provided to achieve consensus. In the provided control algorithms, the desired reference is considered to be an unknown factor and then estimated using the associated learning laws. The consensus convergence is proven by the composite energy function method. A numerical simulation is ultimately presented to demonstrate the efficacy of the proposed control schemes. 相似文献
58.
Semiconductors - The performance of InGaN/GaN multiple quantum well (MQW) solar cells with five different Si-doping concentrations, namely 0, 4 × 1017 cm–3, 1 × 1018 cm–3, 3... 相似文献
59.
60.
Qiuping Wang Bojan Šarkanj Jasna Jurasovic Yusuf Chisti Michael Sulyok Jiashun Gong Sarote Sirisansaneeyakul Draženka Komes 《International Journal of Food Science & Technology》2019,54(5):1541-1549
Theabrownins (TB) are polymeric phenolic compounds associated with the multiple bioactivities of Pu-erh tea, a post-fermented Chinese dark tea. High-TB instant Pu-erh tea was produced via a novel submerged fermentation (SF) using Aspergillus tubingensis and compared with samples produced commercially via the conventional solid-state fermentation (SSF). Viable microorganisms and microbial toxins, especially aflatoxins B1, G1, B2, G2, cyclopiazonic acid, fumonisins B1, B2, B3 and ochratoxin A, were below the detection limit in all samples. Fewer microbial metabolites were found in SF instant tea compared with the SSF teas. Based on an adult consuming 1 g of instant Pu-erh tea daily, the dietary intake of investigated elements was below the safe limits recommended by various authorities. Tasters viewed the instant tea infusions as very mild, smooth, mellow and full. This suggested that submerged fermentation using A. tubingensis offers a speedy and safe alternative to commercial production of instant Pu-erh tea. 相似文献