全文获取类型
收费全文 | 75160篇 |
免费 | 4349篇 |
国内免费 | 2276篇 |
专业分类
电工技术 | 3275篇 |
综合类 | 3725篇 |
化学工业 | 8854篇 |
金属工艺 | 2887篇 |
机械仪表 | 3182篇 |
建筑科学 | 3485篇 |
矿业工程 | 1495篇 |
能源动力 | 1182篇 |
轻工业 | 5403篇 |
水利工程 | 1504篇 |
石油天然气 | 1179篇 |
武器工业 | 470篇 |
无线电 | 5011篇 |
一般工业技术 | 6434篇 |
冶金工业 | 22921篇 |
原子能技术 | 554篇 |
自动化技术 | 10224篇 |
出版年
2024年 | 208篇 |
2023年 | 721篇 |
2022年 | 1195篇 |
2021年 | 1582篇 |
2020年 | 1064篇 |
2019年 | 816篇 |
2018年 | 1729篇 |
2017年 | 1942篇 |
2016年 | 2016篇 |
2015年 | 2166篇 |
2014年 | 2129篇 |
2013年 | 2368篇 |
2012年 | 4694篇 |
2011年 | 5067篇 |
2010年 | 3073篇 |
2009年 | 3130篇 |
2008年 | 3031篇 |
2007年 | 2887篇 |
2006年 | 2567篇 |
2005年 | 4966篇 |
2004年 | 3724篇 |
2003年 | 3068篇 |
2002年 | 1863篇 |
2001年 | 1673篇 |
2000年 | 872篇 |
1999年 | 990篇 |
1998年 | 6317篇 |
1997年 | 3961篇 |
1996年 | 2624篇 |
1995年 | 1542篇 |
1994年 | 1154篇 |
1993年 | 1153篇 |
1992年 | 291篇 |
1991年 | 337篇 |
1990年 | 333篇 |
1989年 | 297篇 |
1988年 | 310篇 |
1987年 | 231篇 |
1986年 | 202篇 |
1985年 | 175篇 |
1984年 | 72篇 |
1983年 | 81篇 |
1982年 | 127篇 |
1981年 | 178篇 |
1980年 | 197篇 |
1979年 | 64篇 |
1978年 | 98篇 |
1977年 | 608篇 |
1976年 | 1319篇 |
1975年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
Da-Wang Tan Zhen-Yong Lao Zhan Zhang Wei-Ming Guo Shi-Kuan Sun Hua-Tay Lin 《Journal of the American Ceramic Society》2021,104(6):2860-2867
B4C-TiB2 ceramics (TiB2 ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B4C-TiB2 without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB2 grains. The interface of the rim between TiB2 and B4C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B4C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B2 rim around the TiB2 core may occur as a result of the solid solution and dissolution-precipitation between TiB2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB2 content increased, alongside the decreased hardness. B4C-30 vol% TiB2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m1/2. 相似文献
2.
3.
飞机从一个航段飞向下一个航段时,需要对下个航段是否激活进行判断.提出了一种新的飞行计划航段自动激活方法,通过获取飞机当前位置及其磁差,并结合临近的3个航路点对应位置的磁差经纬度,分别计算3个航路点与飞机位置对应的磁航向角,通过磁航向角之间做差进行比较,进而判断是否被激活.算法推导完成后,通过基于模型的系统工程工具SCADE SUITE进行了建模,并结合杰普逊航图进行了实际数据采样与仿真.仿真结果表明:该航段自动激活方法能够有效稳定地激活下一航段,比传统方法计算简便,方法实用有效.已在实际飞行中成功应用,达到了预期效果. 相似文献
4.
Chengkai Li Zheyi Zhang Haifei Zhan Zhuoqun Zheng Jingshuai Bai Yuantong Gu 《大分子材料与工程》2021,306(10):2100292
Low-dimensional carbon nanostructures are ideal nanofillers to reinforce the mechanical performance of polymer nanocomposites due to their excellent mechanical properties. Through molecular dynamics simulations, the mechanical performance of poly(vinyl alchohol) (PVA) nanocomposites reinforced with a single-layer diamond – diamane is investigated. It is found the PVA/diamane exhibits similar interfacial strengths and pull-out characteristics with the PVA/bilayer-graphene counterpart. Specifically, when the nanofiller is fully embedded in the nanocomposite, it is unable to deform simultaneously with the PVA matrix due to the weak interfacial load transfer efficiency, thus the enhancement effect is not significant. In comparison, diamane can effectively promote the tensile properties of the nanocomposite when it has a laminated structure as it deforms simultaneously with the matrix. With this configuration, the interlayer sp3 bonds endows diamane with a much higher resistance under compression and shear tests, thus the nanocomposite can reach very high compressive and shear stress. Overall, enhancement on the mechanical interlocking at the interface as triggered by surface functionalization is only effective for the fully embedded nanofiller. This work provides a fundamental understanding of the mechanical properties of PVA nanocomposites reinforced by diamane, which can shed lights on the design and preparation of next generation high-performance nanocomposites. 相似文献
5.
Klimis?S.?NtalianisEmail author Anastasios?D.?Doulamis Nikolaos?D.?Doulamis Nikos?E.?Mastorakis Athanasios?S.?Drigas 《Journal of Signal Processing Systems》2015,80(2):153-161
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation. 相似文献
7.
Wojciech Jó?wicki Anna A. Bro?yna Jerzy Siekiera Andrzej T. Slominski 《International journal of molecular sciences》2015,16(2):3783-3803
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape. 相似文献
8.
9.
Klaus Reinhardt Hans Georg Breunig Aisada Uchugonova Karsten K?nig 《Journal of the Royal Society Interface》2015,12(110)
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype. 相似文献
10.
Lü Qing Xu Bin Yu Yang Zhan Wei Zhao Yu Zheng Jun Ji Jian 《Bulletin of Engineering Geology and the Environment》2021,80(8):6513-6525
Bulletin of Engineering Geology and the Environment - Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability... 相似文献