全文获取类型
收费全文 | 28664篇 |
免费 | 3683篇 |
国内免费 | 2665篇 |
专业分类
电工技术 | 1903篇 |
技术理论 | 3篇 |
综合类 | 2924篇 |
化学工业 | 4830篇 |
金属工艺 | 1359篇 |
机械仪表 | 1194篇 |
建筑科学 | 2536篇 |
矿业工程 | 848篇 |
能源动力 | 1123篇 |
轻工业 | 1200篇 |
水利工程 | 852篇 |
石油天然气 | 1469篇 |
武器工业 | 357篇 |
无线电 | 3186篇 |
一般工业技术 | 4217篇 |
冶金工业 | 905篇 |
原子能技术 | 658篇 |
自动化技术 | 5448篇 |
出版年
2024年 | 153篇 |
2023年 | 665篇 |
2022年 | 820篇 |
2021年 | 1039篇 |
2020年 | 1144篇 |
2019年 | 1025篇 |
2018年 | 1035篇 |
2017年 | 1225篇 |
2016年 | 1283篇 |
2015年 | 1318篇 |
2014年 | 1787篇 |
2013年 | 2086篇 |
2012年 | 2062篇 |
2011年 | 2278篇 |
2010年 | 1750篇 |
2009年 | 1670篇 |
2008年 | 1635篇 |
2007年 | 1849篇 |
2006年 | 1573篇 |
2005年 | 1394篇 |
2004年 | 1166篇 |
2003年 | 953篇 |
2002年 | 801篇 |
2001年 | 699篇 |
2000年 | 543篇 |
1999年 | 505篇 |
1998年 | 382篇 |
1997年 | 363篇 |
1996年 | 316篇 |
1995年 | 246篇 |
1994年 | 216篇 |
1993年 | 173篇 |
1992年 | 155篇 |
1991年 | 121篇 |
1990年 | 114篇 |
1989年 | 105篇 |
1988年 | 74篇 |
1987年 | 49篇 |
1986年 | 47篇 |
1985年 | 47篇 |
1984年 | 40篇 |
1983年 | 32篇 |
1982年 | 22篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
束东良 《有色冶金设计与研究》2006,27(5):35-39
多层建筑的斜屋面结构,应建立合理的结构模型,选用合理的结构方案,在采用结构软件设计时,一定要正确采用倾斜构件沿水平或垂直方向的荷载。 相似文献
52.
鄂尔多斯西缘前陆盆地巨厚黄土地区地震采集技术 总被引:2,自引:2,他引:0
鄂尔多斯西缘前陆盆地表层地质地貌极其复杂,有巨厚黄土区、黄土-沙漠区及山前砾石-黄土区,独特的黄土地貌使得地震采集面临着诸多技术难题。根据以往巨厚黄土地区地震采集经验,采用多种方法系统地开展黄土表层结构精细调查,深入研究黄土地球物理特征及激发因素与表层黄土结构之间的关系,优选激发井位和井深,确保了激发效果;采用小道距、三线小线距、高密度空间采样技术,获得了高信噪比、高分辨率地震资料。研究表明,巨厚黄土地区地震采集时应优选激发井位和岩性,合理选择激发井深;坚持多深井组合激发、单井药量不宜过大总药量要大两项基本原则;采用高密度采样技术,提高采集资料的覆盖次数和信噪比。图10表1参15 相似文献
53.
54.
张曙辉 《水利与建筑工程学报》2002,8(3):15-20
使用进口或国产核子密度仪测定土坝及土堤压实干密度具有操作简便、快速之优点。通过对不同的土质进行了现场核子密度仪与环刀法测定干密度的对比试验后 ,证明核子密度仪在测定土的干密度时 ,用环刀法测定并进行校核是必要和重要的 相似文献
55.
在启动大规模的现代化建设的进程中,应对发展中听中型城市实施“休克疗法”,强调性终止城市发展的无序而缓慢的自然进程。选择短暂的“回归”或“中断”历史的调整时,应以能否适当地的历史文化特质从而把握当代的发展机遇为依据。 相似文献
56.
JUJUN JULIANTY† PANFILO BELO‡ ELVEDA SMITH‡ LUCY McPROUD‡ 《International Journal of Food Science & Technology》1994,29(3):315-320
Four levels of egg white powder (EWP), 0, 1.5, 3.0 and 4.5%, were added to fisfc cracker formulation consisting of tapioca starch, fish paste, and water. the mixture was extruded through a single screw extruder, and the extrudate was cut, dried, heated in a microwave, and the degrees of expansion, bulk density, colour and protein content were measured.
The addition of 1.5 and 3.0% EWP had no significant effect ( P < 0.01) on diametral and longitudinal expansion, however, 4.5% EWP significantly ( P < 0.01) reduced them. Bulk density and protein content of the final product increased as the percentage of EWP increased in the formulation. the total colour difference measurement showed a significant increase ( P < 0.01) in brown colouration at 4.5% EWP. 相似文献
The addition of 1.5 and 3.0% EWP had no significant effect ( P < 0.01) on diametral and longitudinal expansion, however, 4.5% EWP significantly ( P < 0.01) reduced them. Bulk density and protein content of the final product increased as the percentage of EWP increased in the formulation. the total colour difference measurement showed a significant increase ( P < 0.01) in brown colouration at 4.5% EWP. 相似文献
57.
Fracture toughness and fatigue crack propagation (FCP) of plain and modified anhydride-cured epoxy resin (EP) were studied at ambient temperature. Liquid carboxyl-terminated acrylonitrile-butadiene (CTBN) and silicon (SI) rubber dispersions were used as tougheners for the EP. The morphology of the modified EP was characterized by dynamic mechanical analysis (DMA) and by scanning electron microscopy (SEM). The fracture toughness, Kc, of the compositions decreased with increasing deformation rate. Kc of the EP was slightly improved by CTBN addition and practically unaffected by incorporation of the SI dispersion when tests were performed at low cross-head speed, v. Both modifiers improved Kc at high v, and also the resistance to FCP, by shifting the curves to higher stress intensity factor ranges, ΔK, by comparison with the plain EP. It was established that both fracture and fatigue performance rely on the compliance, JR, at the rubbery plateau, and thus on the apparent molecular mass between crosslinks, Mc. The failure mechanisms were less dependent upon the loading mode (fracture, fatigue), but differed basically for the various modifiers. Rubber-induced cavitation and shear yielding of the EP were dominant for CTBN, whereas crack bifurcation and branching controlled the cracking in SI-modified EP. The simultaneous use of both modifiers resulted in a synergistic effect for both the fracture toughness at high deformation rate and the FCP behavior. 相似文献
58.
A. N. Iyer U. Balachandran L. R. Motowidlo J. G. Hoehn P. Haldar 《Journal of Electronic Materials》1994,23(11):1087-1091
Pb0.4Bi1.8Sr2Ca2.2Cu3Ox (Bi-2223) precursor powder was prepared by a solid-state reaction of carbonates and oxides of lead, bismuth, strontium, calcium,
and copper, and the powder was then used to fabricate silver-clad tapes by the powder-in-tube technique. Transport critical
current density (Jc) values>4×104 A/cm2 at 77K and 2×105 A/cm2 at 4.2 and 27K have been achieved in short tape samples. Long lengths of tape were tested by winding them into pancake coils.
Recently, we fabricated a test magnet by stacking ten pancake coils, each containing three 16m lengths of rolled tape, and
tested it at 4.2, 27 and 77K. A maximum generated field of 2.6 T was measured in zero applied field at 4.2K and the test magnet
generated significant self-field in background fields up to 20 T. The results are discussed in this paper. 相似文献
59.
A. Goyal E. D. Specht Z. L. Wang D. M. Kroeger J. A. Sutliff J. E. Tkaczyk J. A. Deluca L. Masur G. N. Riley 《Journal of Electronic Materials》1994,23(11):1191-1197
Microstructural origins for reduced weak-link behavior in high-Jc melt-processed YBCO, spray pyrolyzed thick films of Tl-1223, metallic precursor Y-124 polycrystalline powder-in-tube (PIT)
wires and PIT Bi-2212/2223 are discussed. Since the materials studied are the highest Jc, polycrystalline, high-Tc superconductors fabricated worldwide, the results provide important guidelines for further improvements in superconducting
properties, thereby enabling practical applications of these materials. It is found that strongly linked current flow within
domains of melt-processed 123 occurs effectively through a single crystal path. In c-axis oriented, polycrystalline Tl-1223
thick films, local in-plane texture has been found to play a crucial role in the reduced weak-link behavior. Formation of
“colonies” of grains with a common c-axis and modest in-plane misorientation was observed. Furthermore, a colony boundary
in general has a varying misorientation along the boundary. Large regions comprised primarily of low angle boundaries were
observed. Percolative transport through a network of such small angle boundaries appears to provide the nonweak-linked current
path. Although powder-in-tube BSCCO 2212 and 2223 also appear to have a “colony” microstructure, there are some important
differences. Colonies in BSCCO consist of stacks of grains with similar c-axis orientation in contrast to colonies in Tl-1223
films where few grains are stacked on top of one another. Furthermore, most grains within a colony in BSCCO have the same
lateral dimensions as that of the colony, resulting largely largely in “twist” boundaries. Further microstructural characterization
of high-Jc PIT 2212 and 2223 is currently underway. In the case of Y-124 wires, weak macroscopic in-plane texture is found. Additional
measurements are underway to determine if a sharper, local in-plane texture also exists. It is found that in three of the
four types of superconductors studied, reduced weak-link behavior can be ascribed to some degree of biaxial alignment between
grains, either on a “local” or a “global” scale. 相似文献
60.
ZHANG Zu-fan DU Hui-ping JIANG Ze Chongqing University of Posts Telecommunications Chongqing China University of Electronic Science Technology of China Chengdu China 《中国邮电高校学报(英文版)》2006,13(4):29-33
1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar… 相似文献