全文获取类型
收费全文 | 452596篇 |
免费 | 86930篇 |
国内免费 | 53734篇 |
专业分类
电工技术 | 41509篇 |
技术理论 | 31篇 |
综合类 | 36583篇 |
化学工业 | 70654篇 |
金属工艺 | 38455篇 |
机械仪表 | 23939篇 |
建筑科学 | 33709篇 |
矿业工程 | 21446篇 |
能源动力 | 15711篇 |
轻工业 | 36236篇 |
水利工程 | 11817篇 |
石油天然气 | 30122篇 |
武器工业 | 5764篇 |
无线电 | 58440篇 |
一般工业技术 | 61551篇 |
冶金工业 | 21001篇 |
原子能技术 | 3956篇 |
自动化技术 | 82336篇 |
出版年
2024年 | 3673篇 |
2023年 | 8544篇 |
2022年 | 12102篇 |
2021年 | 16076篇 |
2020年 | 16309篇 |
2019年 | 24300篇 |
2018年 | 26598篇 |
2017年 | 28556篇 |
2016年 | 27342篇 |
2015年 | 29212篇 |
2014年 | 30526篇 |
2013年 | 32265篇 |
2012年 | 32650篇 |
2011年 | 30858篇 |
2010年 | 27150篇 |
2009年 | 23308篇 |
2008年 | 21126篇 |
2007年 | 20210篇 |
2006年 | 20220篇 |
2005年 | 18236篇 |
2004年 | 15918篇 |
2003年 | 13754篇 |
2002年 | 12923篇 |
2001年 | 11468篇 |
2000年 | 11505篇 |
1999年 | 12345篇 |
1998年 | 10284篇 |
1997年 | 8930篇 |
1996年 | 8456篇 |
1995年 | 7645篇 |
1994年 | 6312篇 |
1993年 | 5030篇 |
1992年 | 4463篇 |
1991年 | 3325篇 |
1990年 | 2557篇 |
1989年 | 2233篇 |
1988年 | 1752篇 |
1987年 | 803篇 |
1986年 | 636篇 |
1985年 | 440篇 |
1984年 | 309篇 |
1983年 | 202篇 |
1982年 | 254篇 |
1981年 | 198篇 |
1980年 | 157篇 |
1976年 | 225篇 |
1975年 | 203篇 |
1972年 | 235篇 |
1971年 | 127篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
铁煤集团大兴矿(以下简称"大兴矿")2019年产240万t,井田位于铁法煤田的西南角,火成岩侵入及地质构造复杂,煤层破坏程度严重[1-2]。受火成岩影响,煤层瓦斯含量大幅增加[3-4],渗透性能差,力学强度低,煤的含水率低,自然发火期较短,是煤与瓦斯突出矿井。在采煤过程中,防治自然发火是重中之重,综采设备在设计初期未考虑实施灭火的操作空间,为此,笔者提出通过改造综采设备增加实施灭火的操作空间,降低出现自然发火灾害时防治的难度,保证采煤安全。 相似文献
53.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018) 下载免费PDF全文
54.
Because of heat amount is different from peripheral to central of friction welding interface, which is leaded to vary the characterizations along that interface. Current study, respectively, focused on the effect of different friction pressure on micro-structural and mechanical properties of that friction welding joint interface. Presently, these friction pressures are 110, 130, 150 and 170 MPa while kept all other conditions constant. The effects of different friction pressure on welding interface characterization were investigated by EDX, SEM, tensile, compression, impact and hardness tests. The tensile tests carried out on the standardized test piece with diameter 6 mm and 8 mm, thus, compression tests were extracted from the positions of 0°, 45° 90° with test specimen of 4 mm diameter and 6.5 mm length at weld center. Whereas, the impact test pieces were picked up in two positions, the first one is symmetrical, which it obtained to the respect of the rotation axis and the interface, on the other hand, the second one is non-symmetrical with the axis of rotation and symmetrical to the interface, for making the notch head coincide with the center of the welded joint, The obtained results showed that with reducing of friction pressure will present lack of bonding increasing from peripheral toward the welding center, which will responsible on reducing of the mechanical properties such as tensile, compression and impact strength. 相似文献
55.
目的研究蛋类礼盒包装结构的缓冲性能。方法以蛋类尺寸为基础,建立可发性聚乙烯(expandable polyethylene. EPE)缓冲单元结构和组合结构,进行静态仿真分析和实验验证,比较结构在形状、叠合层数、组合形式等参数变化时的载荷与位移。结果结构层数变化相同时,单元结构的极限载荷从143N增加到236 N,组合结构的极限载荷从224 N增加到476 N,均呈近线性增长。结论蛋类礼盒包装中,组合结构的承载能力优于单元结构,通过单元结构的组合,可满足不同蛋类的包装要求。 相似文献
56.
57.
ABSTRACT In this study, effect of calcium and gypsum on scheelite and fluorite was investigated using sodium oleate as collector. Micro-flotation and contact angle results showed that the adsorption of calcium could inhibit the hydrophobicity of scheelite and fluorite. Moreover, sulfate could enhance the inhibition. FT-IR results showed that calcium could be priori precipitated into calcium oleate and adsorb on mineral surface. The adsorption of calcium could increase the scheelite potential to IEP, while it showed limited effect on fluorite potential. However, the interaction of calcium on scheelite and fluorite in gypsum solution was more complex than that in calcium solution. 相似文献
58.
Guoxiang
Zhang Junyu Xiang 《International journal for numerical methods in engineering》2020,121(15):3339-3361
A new eight-node conforming quadrilateral element with high-order completeness, denoted as QH8-C1, is proposed in this article. First, expressions for the interpolation displacement function satisfying the requirements for high-order completeness in the global coordinate system are constructed. Second, the displacement function expression in global coordinates is transformed into isoparametric coordinates, and the relationships between the two series of coefficients for the two kinds of displacement function expressions are found. Third, the displacement function expression is modified to satisfy the requirements of nodal freedom and interelement boundary continuity. The key to the new element construction is the derivation of the linear relationship expressions among 12 coefficients of element displacement interpolation polynomials in the global and isoparametric coordinate systems. As a result, the relationship between quadratic completeness and interelement continuity is explicitly given, and a proof of the completeness and the continuity was conducted to theoretically guarantee the validity of the derivation results. Furthermore, in order to verify the correctness of the theoretical work, nine numerical examples were performed. The computation results from these examples demonstrate that QH8-C1 exhibited excellent performance, including high simulation accuracy, fast convergence, insensitivity to mesh distortion, and monotonic convergence. 相似文献
59.
Chuntao Lan Haiyang Zou Longfei Wang Meng Zhang Shuang Pan Ying Ma Yiping Qiu Zhong Lin Wang Zhiqun Lin 《Advanced materials (Deerfield Beach, Fla.)》2020,32(47):2005481
Despite recent rapid advances in metal halide perovskites for use in optoelectronics, the fundamental understanding of the electrical-poling-induced ion migration, accounting for many unusual attributes and thus performance in perovskite-based devices, remain comparatively elusive. Herein, the electrical-poling-promoted polarization potential is reported for rendering hybrid organic–inorganic perovskite photodetectors with high photocurrent and fast response time, displaying a tenfold enhancement in the photocurrent and a twofold decrease in the response time after an external electric field poling. First, a robust meniscus-assisted solution-printing strategy is employed to facilitate the oriented perovskite crystals over a large area. Subsequently, the electrical poling invokes the ion migration within perovskite crystals, thus inducing a polarization potential, as substantiated by the surface potential change assessed by Kelvin probe force microscopy. Such electrical-poling-induced polarization potential is responsible for the markedly enhanced photocurrent and largely shortened response time. This work presents new insights into the electrical-poling-triggered ion migration and, in turn, polarization potential as well as into the implication of the latter for optoelectronic devices with greater performance. As such, the utilization of ion-migration-produced polarization potential may represent an important endeavor toward a wide range of high-performance perovskite-based photodetectors, solar cells, transistors, scintillators, etc. 相似文献
60.