全文获取类型
收费全文 | 185109篇 |
免费 | 17922篇 |
国内免费 | 9637篇 |
专业分类
电工技术 | 12926篇 |
技术理论 | 12篇 |
综合类 | 13248篇 |
化学工业 | 29520篇 |
金属工艺 | 10497篇 |
机械仪表 | 12109篇 |
建筑科学 | 15364篇 |
矿业工程 | 5816篇 |
能源动力 | 5561篇 |
轻工业 | 12627篇 |
水利工程 | 3836篇 |
石油天然气 | 10368篇 |
武器工业 | 1785篇 |
无线电 | 22052篇 |
一般工业技术 | 20819篇 |
冶金工业 | 7831篇 |
原子能技术 | 2283篇 |
自动化技术 | 26014篇 |
出版年
2024年 | 754篇 |
2023年 | 3098篇 |
2022年 | 5891篇 |
2021年 | 8562篇 |
2020年 | 6417篇 |
2019年 | 5110篇 |
2018年 | 5598篇 |
2017年 | 6374篇 |
2016年 | 5467篇 |
2015年 | 8164篇 |
2014年 | 10117篇 |
2013年 | 11873篇 |
2012年 | 13550篇 |
2011年 | 14295篇 |
2010年 | 12603篇 |
2009年 | 11835篇 |
2008年 | 11361篇 |
2007年 | 10490篇 |
2006年 | 10065篇 |
2005年 | 8473篇 |
2004年 | 5701篇 |
2003年 | 4565篇 |
2002年 | 4219篇 |
2001年 | 3671篇 |
2000年 | 3675篇 |
1999年 | 3793篇 |
1998年 | 3065篇 |
1997年 | 2610篇 |
1996年 | 2393篇 |
1995年 | 2072篇 |
1994年 | 1660篇 |
1993年 | 1182篇 |
1992年 | 948篇 |
1991年 | 751篇 |
1990年 | 547篇 |
1989年 | 473篇 |
1988年 | 389篇 |
1987年 | 256篇 |
1986年 | 169篇 |
1985年 | 96篇 |
1984年 | 62篇 |
1983年 | 40篇 |
1982年 | 70篇 |
1981年 | 47篇 |
1980年 | 50篇 |
1979年 | 26篇 |
1978年 | 5篇 |
1965年 | 3篇 |
1959年 | 18篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
972.
NADPH diaphorase histochemistry is commonly used to identify cells containing nitric oxide synthase (NOS), the enzyme catalyzing the production of nitric oxide from L-arginine. NADPH diaphorase activity and NOS immunostaining was demonstrated in different cells of the vertebrate retina; photoreceptors, horizontal cells, amacrine cells, ganglion cells, and Müller cells. However, the physiological role of nitric oxide (NO) in the retina has yet to be elucidated. In this study, we tested the assumption that NADPH diaphorase activity in the retinas of rabbits and rats depended on the state of visual adaptation. In the rabbit, light adaptation enhanced NADPH diaphorase activity in amacrine cells and practically eliminated it in horizontal cells. Dark adaptation induced the opposite effects; the NADPH diaphorase activity was reduced in amacrine cells and enhanced in horizontal cells. Retinas from eyes that were injected intravitreally with L-glutamate exhibited a pattern of NADPH diaphorase activity that was similar to that seen in dark-adapted retinas. In rats, the NADPH diaphorase activity of amacrine and horizontal cells exhibited adaptation dependency similar to that of the rabbit retina. But, the most pronounced effect of dark adaptation in the rat's retina was an enhancement of NADPH diaphorase activity in Müller cells, especially of the endfoot region. Assuming that NADPH diaphorase activity is a marker for NOS, these findings suggest that NO production in the mammalian retina is modulated by the level of ambient illumination and support the notion that NO plays a physiological role in the retina. 相似文献
973.
In this paper, two new representation schemes called the Branched Gaussian Image (BGI) and the Hierarchical Extended Gaussian Image (HEGI) are proposed. They can be used for uniquely representing both concave and convex, two-dimensional figures and three-dimensional objects. The representation by the Branched Gaussian Image involves several Gaussian spheres connected by branches where the traversing directions might be different. Examples showing how the use of the BGI enables us to achieve the mapping and inverse mapping of concave polygons and polyhedra uniquely are presented. The Gaussian spheres in the BGI can be organized into a tree-like hierarchical structure known as the Hierarchical Extended Gaussian Image. A general procedure for mapping a polygon or polyhedron to its HEGI representation is described. An approach for reconstructing concave polygons from Branched Gaussian Images is presented. The reconstruction of a concave polyhedron from its Hierarchical Extended Gaussian Images by using an iterative method or a closed-form method for each convex component is also described. 相似文献
974.
975.
在高速气流粉碎作用下PVC的力化学降解及形态变化的研究 总被引:4,自引:0,他引:4
通过GPT、FT-IR、SEM和力学性能测试,研究了在高速气流作用下聚氯乙烯(PVC)的力化学降解反应、颗粒形态和微晶结构变化及其对PVC物理、力学性能的影响。实验结果表明,经过高速气流处理PVC,分子量将有所降低,晶体结构发生变化,颗粒尺寸和表观密度降低,比表面积增大,加工性能和力学性能得到明显改善。 相似文献
976.
C_MPS的设计与实现 总被引:1,自引:0,他引:1
元程序设计系统是进行元程序设计的有效工具。C_MPS(CMetaProgra-mming System)是我们在PC机上开发的C语言的元程序设计系统,本文介绍了该系统的设计思想和实现技术。 相似文献
977.
氯丁橡胶的溶液接枝反应研究 总被引:3,自引:1,他引:2
本文研究了引发剂过氧化苯甲酰的用量对CR接技MMA-AA反应的单体转化率、接枝率及接枝胶的粘度、剥离强度等的影响,并用红外光谱和元素和元素分析对反应产物进行了表征.结果表明,体系中存在接枝、降解、交联三种反应,在不同的配方和工艺条件下,三种反应的反应程度不同. 相似文献
978.
Void formation and growth in a class of compressible solids 总被引:1,自引:0,他引:1
A new class of compressible elastic solids, which includes the Blatz-Ko material as a special case, is proposed. A closed-form solution is constructed and studied for a bifurcation problem modeling void formation in this class of compressible elastic solids. The relation between the void-formation condition and the material parameters is obtained analytically. An energy comparison of the void-formation deformation and the homogeneous expansion deformation is carried out. 相似文献
979.
Chao M. Huang Dong Zhu Xu Yuren Waltraud M. Kriven Chao Y. Yuh 《Materials Science and Engineering: A》1996,220(1-2)
A composite of O′SiAlON (Si2-xAlxN2-xO1+x, with x 0.14) reinforced with 20 vol.% SiC monofilaments was fabricated by hot-pressing, at 1600°C, for 2 h under 34 MPa pressure. The mechanical and interfacial properties of the composites, as-fabricated as well as post-oxidized, were, investigated. The composite exhibited a significant improvement in ultimate flexure strength (640 MPa) and work of fracture (42 kJ m−2) compared with that (350 MPa and 1.8 kJ m−2, respectively) of the monolithic material. These mechanical properties were slightly increased after the composite was heat treated for 24 h in air at 1200 and 1300°C. However, the composite exhibited a significant degradation in ultimate strength, while the work of fracture (WOF) remained unchanged after exposure in air at temperatures beyond 1400°C. The as-fabricated composite revealed a low interfacial shear strength (6.2 MPa) and a frictional sliding stress (3.2 MPa). After the composite was oxidized at elevated temperatures, the interfacial bonding and sliding stresses were reduced to noticeable extents, resulting from the degradation of the carbon coating layer of the SiC monofilaments. 相似文献
980.
Cleavage fracture in an Al-Li alloy 8090 总被引:1,自引:0,他引:1
Jiang Daming Wang Yinong Hong Bande Lei Tingquan Sun Fenglian 《Journal of Materials Science Letters》1996,15(18):1597-1600