全文获取类型
收费全文 | 602686篇 |
免费 | 69332篇 |
国内免费 | 46990篇 |
专业分类
电工技术 | 51957篇 |
技术理论 | 5篇 |
综合类 | 63816篇 |
化学工业 | 76831篇 |
金属工艺 | 41648篇 |
机械仪表 | 42664篇 |
建筑科学 | 47447篇 |
矿业工程 | 25790篇 |
能源动力 | 15641篇 |
轻工业 | 62898篇 |
水利工程 | 19680篇 |
石油天然气 | 23165篇 |
武器工业 | 9416篇 |
无线电 | 62960篇 |
一般工业技术 | 51581篇 |
冶金工业 | 25563篇 |
原子能技术 | 9490篇 |
自动化技术 | 88456篇 |
出版年
2024年 | 3654篇 |
2023年 | 9883篇 |
2022年 | 22751篇 |
2021年 | 29173篇 |
2020年 | 21419篇 |
2019年 | 15008篇 |
2018年 | 16276篇 |
2017年 | 19156篇 |
2016年 | 16911篇 |
2015年 | 26434篇 |
2014年 | 33461篇 |
2013年 | 39036篇 |
2012年 | 49040篇 |
2011年 | 51248篇 |
2010年 | 48575篇 |
2009年 | 46298篇 |
2008年 | 47722篇 |
2007年 | 46639篇 |
2006年 | 40509篇 |
2005年 | 33321篇 |
2004年 | 23767篇 |
2003年 | 15998篇 |
2002年 | 14880篇 |
2001年 | 13527篇 |
2000年 | 11300篇 |
1999年 | 5821篇 |
1998年 | 3000篇 |
1997年 | 2380篇 |
1996年 | 2294篇 |
1995年 | 1895篇 |
1994年 | 1487篇 |
1993年 | 1186篇 |
1992年 | 993篇 |
1991年 | 729篇 |
1990年 | 593篇 |
1989年 | 561篇 |
1988年 | 408篇 |
1987年 | 277篇 |
1986年 | 216篇 |
1985年 | 137篇 |
1984年 | 124篇 |
1983年 | 94篇 |
1982年 | 87篇 |
1981年 | 122篇 |
1980年 | 190篇 |
1979年 | 115篇 |
1965年 | 18篇 |
1964年 | 10篇 |
1959年 | 106篇 |
1951年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
61.
Chuncheng Wei Zhen Liu Yun Wu Yeqing Liu Heng Zhang Peng Wang Qiyan Sun Lijuan Zhou 《Ceramics International》2021,47(13):18693-18698
Laminated Si3N4/SiCw ceramics were successfully prepared by tape casting and hot-pressing. Its mechanical properties were measured and the impact resistance was discussed. The toughness of the laminated Si3N4/SiCw ceramics was 13.5 MPa m1/2, which was almost 1.6 times that of Si3N4/SiCw composite ceramics, namely 8.5 MPa m1/2. Moreover, the indentation strength of laminated Si3N4/SiCw ceramics was not sensitive to increasing indentation loads and exhibited a rising R-curve behaviour, indicating that the laminated Si3N4/SiCw ceramics had excellent impact resistance. The improved toughness and impact resistance of laminated Si3N4/SiCw ceramics was attributed to the residual stress caused by a thermal expansion coefficient mismatch between the different layers, resulting in crack deflection and bridging of SiC whiskers in the interface layer, thus consuming a large amount of fracture work. 相似文献
63.
Katja F. Hellendahl Felix Kaspar Dr. Xinrui Zhou Zhaoyi Yang Prof. Dr. Zhen Huang Prof. Dr. Peter Neubauer Dr. Anke Kurreck 《Chembiochem : a European journal of chemical biology》2021,22(11):2002-2009
Selenium-modified nucleosides are powerful tools to study the structure and function of nucleic acids and their protein interactions. The widespread application of 2-selenopyrimidine nucleosides is currently limited by low yields in established synthetic routes. Herein, we describe the optimization of the synthesis of 2-Se-uridine and 2-Se-thymidine derivatives by thermostable nucleoside phosphorylases in transglycosylation reactions using natural uridine or thymidine as sugar donors. Reactions were performed at 60 or 80 °C and at pH 9 under hypoxic conditions to improve the solubility and stability of the 2-Se-nucleobases in aqueous media. To optimize the conversion, the reaction equilibria in analytical transglycosylation reactions were studied. The equilibrium constants of phosphorolysis of the 2-Se-pyrimidines were between 5 and 10, and therefore differ by an order of magnitude from the equilibrium constants of any other known case. Hence, the thermodynamic properties of the target nucleosides are inherently unfavorable, and this complicates their synthesis significantly. A tenfold excess of sugar donor was needed to achieve 40−48 % conversion to the target nucleoside. Scale-up of the optimized conditions provided four Se-containing nucleosides in 6–40 % isolated yield, which compares favorably to established chemical routes. 相似文献
64.
65.
Juan Ding Yong He Shenhe Fu Xiangsheng Xie Haowen Liang Jianying Zhou 《Journal of the Society for Information Display》2022,30(2):159-167
Illumination is essential for modern life as colorful world is perceived by human visionary system. Display technology has been developing rapidly in recent decades, and the basic principle is related to the way that the image is illuminated and light is emanated. Traditional illumination is provided by different types of light sources, and the display image is visible in large viewing space until the emanating light decays to zero. This work proposes and demonstrates a novel illumination scheme for a display in which the displaying images are visible only in specific spatial regions. The directional backlight ensures the image propagating to specific direction while imaging visibility can be controlled to terminate abruptly at certain distance from the display screen while exerting no influence to nearby regions. The working principle for such an illumination scheme is the use of the modulated coherent directional backlight through an axicon lens. It is shown that the illumination scheme can robustly deliver carried image information to the designated viewing region. This new illumination scheme has many advantages over conventional illumination, including its usage for personal display, very lower energy consumption, as well as minimizing light hazard pollution. 相似文献
66.
Myelodysplastic syndromes (MDS) are highly heterogeneous myeloid neoplasms, and a large number of
patients are difficult to diagnose and classify by blood and bone marrow examination. As a surface marker of
granulocyte, studies have shown CD10 can be used to define the degree of granulocyte maturation in MDS patients.
However, whether it can be used for differential diagnosis of MDS and other hematological diseases remains
inconclusive. To explore the value of CD10 for differential diagnosis of MDS, 60 newly diagnosed MDS, 20 aplastic
anemia (AA) patients, and 35 iron-deficient anemia (IDA) patients were selected for this study. Bone marrow (BM)
specimens were processed for surface marker analysis and labeled with pre-conjugated monoclonal antibodies. Stained
cells were detected by flow cytometry. Our results indicated that CD10-positive granulocytes were significantly
decreased in BM of MDS patients than AA and IDA patients, and the level of CD10-positive mature granulocytes was
not associated with the clinical stages of malignancy. Receiver operating characteristic (ROC) areas under the curve
(AUC) of CD10-positive granulocytes was 0.86 and 0.85, respectively, in MDS patients than the IDA group and AA
group with good specificity and sensitivity. Further, CD10-positive granulocytes were increased after effective
treatment. In conclusion, we found the decrease in CD10-positive granulocytes has a differential diagnostic value of MDS. 相似文献
67.
68.
69.
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
70.