全文获取类型
收费全文 | 54541篇 |
免费 | 5519篇 |
国内免费 | 2923篇 |
专业分类
电工技术 | 3818篇 |
技术理论 | 2篇 |
综合类 | 3573篇 |
化学工业 | 8820篇 |
金属工艺 | 2994篇 |
机械仪表 | 3423篇 |
建筑科学 | 4257篇 |
矿业工程 | 1596篇 |
能源动力 | 1662篇 |
轻工业 | 4878篇 |
水利工程 | 994篇 |
石油天然气 | 2493篇 |
武器工业 | 446篇 |
无线电 | 6815篇 |
一般工业技术 | 7217篇 |
冶金工业 | 2408篇 |
原子能技术 | 624篇 |
自动化技术 | 6963篇 |
出版年
2024年 | 203篇 |
2023年 | 1124篇 |
2022年 | 1865篇 |
2021年 | 2717篇 |
2020年 | 2163篇 |
2019年 | 1682篇 |
2018年 | 1979篇 |
2017年 | 1980篇 |
2016年 | 1876篇 |
2015年 | 2413篇 |
2014年 | 2994篇 |
2013年 | 3569篇 |
2012年 | 3996篇 |
2011年 | 4223篇 |
2010年 | 3530篇 |
2009年 | 3312篇 |
2008年 | 3129篇 |
2007年 | 2764篇 |
2006年 | 2636篇 |
2005年 | 2196篇 |
2004年 | 1532篇 |
2003年 | 1385篇 |
2002年 | 1266篇 |
2001年 | 1121篇 |
2000年 | 1145篇 |
1999年 | 1083篇 |
1998年 | 944篇 |
1997年 | 760篇 |
1996年 | 718篇 |
1995年 | 558篇 |
1994年 | 489篇 |
1993年 | 333篇 |
1992年 | 284篇 |
1991年 | 209篇 |
1990年 | 177篇 |
1989年 | 161篇 |
1988年 | 94篇 |
1987年 | 74篇 |
1986年 | 67篇 |
1985年 | 47篇 |
1984年 | 30篇 |
1983年 | 20篇 |
1982年 | 28篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 8篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1959年 | 10篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Boundary element analysis of thermal stress intensity factors for interface griffith and cusp cracks
Kang Yong Lee
Woon Cheon Baik
《Engineering Fracture Mechanics》1994,47(6):909-918The thermal stress intensity factors for interface cracks of Griffith and symmetric lip cusp types under vertical uniform heat flow in a finite body are calculated by the boundary element method. The boundary conditions on the crack surfaces are insulated or fixed to constant temperature. The relationship between the stress intensity factors and the displacements on the nodal point of a crack-tip element is derived. The numerical values of the thermal stress intensity factors for an interface Griffith crack in an infinite body are compared with the previous solutions. The thermal stress intensity factors for a symmetric lip cusp interface crack in a finite body are calculated with respect to various effective crack lengths, configuration parameters, material property ratios and the thermal boundary conditions on the crack surfaces. Under the same outer boundary conditions, there are no appreciable differences in the distribution of thermal stress intensity factors with respect to each material property. However, the effect of crack surface thermal boundary conditions on the thermal stress intensity factors is considerable. 相似文献
92.
介绍了一种日常参数智能控制器的研制及研制过程中的几个重要问题的解决方法。特别是用于城市照明及美化城市的彩灯的开、关时间智能控制方面,给出了依据当地绝对时间、经度、纬度进行昼夜时间计算的方法,使之在不接光电传感器情况下可跟踪季节的昼夜变化。控制系统采用89C2051单片机,配有时钟日历芯片DS12887,系统体积小、功能强、可靠性高。 相似文献
93.
Ki Hyun Kim Yong Hoon Kang Byoungho Lee 《Photonics Technology Letters, IEEE》1997,9(12):1610-1612
A photorefractive volume hologram was recorded and probed using light diffracted from a tapered optical fiber as a reference beam. A single-mode fiber (SMF) was chemically etched and tapered to give a complicated beam pattern, and it is shown that the tapered optical fiber can be utilized to increase the storage density of the volume hologram. Spatial selectivity of the volume hologram with this method was increased by two times compared to the normal SMF referencing, which is due to the fact that the complicated beam pattern has little correlation with its shifted version 相似文献
94.
DH Kang CL Coe DO McCarthy NN Jarjour EA Kelly RR Rodriguez WW Busse 《Canadian Metallurgical Quarterly》1997,17(8):481-487
T cell cytokines play an important role in mediating airway inflammation in asthma. The predominance of a Th2 cytokine profile, particularly interleukin (IL)-4 and IL-5, is associated with the pathogenesis and course of asthma. The aim of this study was to test the hypothesis that a stressful life event alters the pattern of cytokine release in asthmatic individuals. Thirteen healthy controls and 21 asthmatic adolescents gave blood samples three times over a semester: midsemester, during the week of final examinations, and 2-3 weeks after examinations. Interferon-gamma (IFN-gamma), IL-2, IL-4, and IL-5 were measured from supernatants of cells stimulated with PHA/PMA for 24 h. Cells from asthmatic subjects released significantly more IL-5 during the examination and postexamination periods, whereas cells from healthy controls released significantly more IL-2 during the midsemester and examination periods, thereby indicating a bias for a Th2-like pattern in asthmatics and a Th1-like pattern in healthy controls. IL-4 and IL-5 production showed a marked decrease during and after examinations in healthy controls, whereas this decline was absent in asthmatics. The ratios of IFN-gamma:IL-4 and IFN-gamma:IL-5 also revealed significant changes in the profile of cytokine release across the semester. These results indicate differential cytokine responses in asthmatics that may become pronounced during periods of cellular activation. 相似文献
95.
96.
气体引射器流体动力特性实验研究 总被引:5,自引:3,他引:2
在实验装置上对气体引射器计算基本公式进行了实测验证,分析了理论特性曲线的可信度。通过实验,获得一些参数对引射器工况的影响规律。 相似文献
97.
In order to modify the continuous network of eutectic cementite normally found in low alloy white cast irons into a dispersive distribution, strategies of controlling the morphology of eutectic cementite by additives are discussed. Qualitative arguments are presented and applied to the development of a complex modifier REAINTi. With the addition of this modifier to low carbon white cast irons nearly one fifth of the original eutectic cementite network can be modified into blocky particles in the plane of polish, and one third into isolated irregular ones. The experimental data shows that Ti(CN) may act as an effective nucleant or a grain refiner for eutectic cementite. The modification effects of rare earth elements are attributed to their abilities to purify the melt, promote divorced eutectic growth and refine the microstructure. Aluminium contributes to the modification by its purification effect. 相似文献
98.
CA/PAN中空纤维血浆分离膜的结构与性能 总被引:4,自引:2,他引:2
本研究以CA及PAN的共混溶液,通过干-湿法纺丝制取中空纤维,利用共混高聚物各组分在凝固剂中相分离速度的差异,形成具有稳定结构的中空纤维孔膜,该膜用于分离血液中的血浆成分具有良好效果。讨论了成型条件及添加剂等对膜结构、性能的影响,用SEM及图相分析仪、MAP压汞仪及DSC等分析手段,对膜的微孔结构、形态、孔尺寸及中空纤维膜的血浆通量和水通量等进行了系统的考查。 相似文献
99.
2Mbit/s高速信令链路在移动通信七号信令网中的应用 总被引:1,自引:0,他引:1
通过对2Mbit/s高速信令链路原理、特点的介绍,阐明了该技术在现阶段使用的实际意义,并给出了2Mbit/s高速信令链路在移动通信七号信令网中的应用。 相似文献
100.
软X射线不仅能引起红细胞表面电荷的变化,同时也能导致淋巴细胞和血小板表面电荷下降,表现为照射后它们的电泳率下降。低剂量范围内,这种电荷的变化是暂时性的,照后4小时降到最低点,24小时后恢复到对照的水平。细胞电泳率的下降与辐射剂量相关。淋巴细胞是一个复杂的细胞群,正常状态下,按细胞在电场中泳动速度的快慢,可分为两个组分:快峰为T细胞,慢峰为B细胞。软X射线照射以后,T和B细胞的电泳率皆减慢,频数分布峰值下降,离散度加大。血小板成分单一,电泳率较一致。 从照射浓集的血小板再加回自身血浆中电泳率的下降较照射血浆再加到血小板中的电泳率下降大得多;受照射的血小板在磷酸缓冲液中电泳率下降较在血浆悬液中严重得多;2000 rad照后,悬浮于血浆中的血小板电泳率能恢复,而悬浮于磷酸缓冲液中则不能恢复,三个方面来看,血浆中可能存在抗辐射因子。超氧化物岐化酶能有效地预防血小板电泳率的下降,从而可阻止血小板的凝聚。 相似文献