全文获取类型
收费全文 | 118273篇 |
免费 | 4326篇 |
国内免费 | 2207篇 |
专业分类
电工技术 | 3107篇 |
技术理论 | 3篇 |
综合类 | 4772篇 |
化学工业 | 16533篇 |
金属工艺 | 6906篇 |
机械仪表 | 5326篇 |
建筑科学 | 5135篇 |
矿业工程 | 1612篇 |
能源动力 | 1976篇 |
轻工业 | 6198篇 |
水利工程 | 1907篇 |
石油天然气 | 2381篇 |
武器工业 | 330篇 |
无线电 | 13276篇 |
一般工业技术 | 20221篇 |
冶金工业 | 4375篇 |
原子能技术 | 570篇 |
自动化技术 | 30178篇 |
出版年
2024年 | 251篇 |
2023年 | 684篇 |
2022年 | 1192篇 |
2021年 | 1664篇 |
2020年 | 1254篇 |
2019年 | 1001篇 |
2018年 | 15351篇 |
2017年 | 14437篇 |
2016年 | 10898篇 |
2015年 | 2056篇 |
2014年 | 2039篇 |
2013年 | 2196篇 |
2012年 | 5320篇 |
2011年 | 11592篇 |
2010年 | 10278篇 |
2009年 | 7441篇 |
2008年 | 8681篇 |
2007年 | 9586篇 |
2006年 | 2038篇 |
2005年 | 2997篇 |
2004年 | 2400篇 |
2003年 | 2208篇 |
2002年 | 1574篇 |
2001年 | 948篇 |
2000年 | 1013篇 |
1999年 | 875篇 |
1998年 | 745篇 |
1997年 | 655篇 |
1996年 | 606篇 |
1995年 | 477篇 |
1994年 | 396篇 |
1993年 | 296篇 |
1992年 | 219篇 |
1991年 | 178篇 |
1990年 | 144篇 |
1989年 | 131篇 |
1988年 | 98篇 |
1987年 | 56篇 |
1986年 | 47篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1960年 | 30篇 |
1959年 | 36篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
在语音时域挑选剩余可懂度低的可用置换集合,置换集合是语音TDS系统中不可缺少的重要环节,本文给出了可用置换选取的条件、客观评价标准和方法。 相似文献
173.
用数值方法对泊松方程求解时,往往要对迭代的中间结果作适当的压缩处理,以加快收敛速度和避免溢出。本文提出一种单一指数因子的非线性压缩法。一维数值模拟结果表明,平衡态时不必进行压缩处理。而在非平衡态时,最佳指数压缩因子的大小与杂质浓度有关。参考本文给出的数值计算结果,根据给定器件的杂质浓度分布,选定一最佳指数压缩因子,可以使泊松方程的数值求解过程具有最快的收敛速度。 相似文献
174.
175.
椭球反射镜膜厚均匀性 总被引:2,自引:1,他引:1
本文分析了椭球反射镜膜层厚度均匀性对反射率的影响,从理论上得到膜厚计算公式。根据计算的膜厚分布设计了遮蔽板,获得较好的反射特性。 相似文献
176.
Wireless ATM networks require efficient mobility management to cope with frequent mobile handoff and rerouting of connections. Although much attention has been given in the literature to network architecture design to support wide-area mobility in public ATM networks, little has been done to the important issue of user mobility estimation and prediction to improve the connection reliability and bandwidth efficiency of the underlying system architecture. This paper treats the problem by developing a hierarchical user mobility model that closely represents the movement behavior of a mobile user, and that, when used with appropriate pattern matching and Kalman filtering techniques, yields an accurate location prediction algorithm, HLP, or hierarchical location prediction, which provides necessary information for advance resource reservation and advance optimal route establishment in wireless ATM networks 相似文献
177.
The effect of transverse stitching on the stresses in the adhesive is investigated using an adhesive sandwich model with nonlinear adhesive properties and a transverse stitching model for adhesive bonded composite single-lap and double-lap joints. Numerical results indicate that, among all stitching parameters, thread pretension and stitch density have significant effect on the peel stresses in the adhesive; increase in the thread pretension and the stitch density leads to a decrease in peel stress in the adhesive, while an increase in other parameters generally results in a negligible reduction in peel stress. The effect of stitching was found to be negligible on the shear stresses in the adhesive. Thus it is concluded that stitching is effective for the joints where peel stresses are critical and ineffective for those where shear stresses are critical. 相似文献
178.
提出底敞口充气浮箱的结构和概念。经模型模拟试验研究分析,经典浮力定律可用于这种浮箱的浮力计算;其动充气状况还具有一定的允许伤损面积。它的研究将为水陆两用车辆增大浮力,缩小外形,提高水上自下而上能力和潜驶潜伏提供具有诱惑力的工程应用前景。 相似文献
179.
180.
Plasminogen activator-inhibitor C-1 (PAI-1) plays a critical role in the regulation of fibrinolysis, serving as the primary inhibitor of tissue-type plasminogen activator. Elevated levels of PAI-1 are a risk factor for recurrent myocardial infarction, and locally increased PAI-1 expression has been described in atherosclerotic human arteries. Recent studies have shown that the administration of angiotensin converting enzyme inhibitors reduces the risk of recurrent myocardial infarction in selected patients. Since angiotensin II (Ang II) has been reported to induce PAI-1 production in cultured astrocytes, we have hypothesized that one mechanism that may contribute to the beneficial effect of angiotensin converting enzyme inhibitors is an effect on fibrinolytic balance. In the present study, we examined the interaction of Ang II with cultured bovine aortic endothelial cells (BAECs) and the effects of this peptide on the production of PAI-1. 125I-Ang II was found to bind to BAECs in a saturable and specific manner, with an apparent Kd of 1.4 nM and Bmax of 74 fmol per mg of protein. Exposure of BAECs to Ang II induced dose-dependent increases in PAI-1 antigen in the media and in PAI-1 mRNA levels. Induction of PAI-1 mRNA expression by Ang II was not inhibited by pretreating BAECs with either Dup 753 or [Sar1, Ile8]-Ang II, agents that are known to compete effectively for binding to the two major angiotensin receptor subtypes. These data indicate that Ang II regulates the expression of PAI-1 in cultured endothelial cells and that this response is mediated via a pharmacologically distinct form of the angiotensin receptor. 相似文献