全文获取类型
收费全文 | 40567篇 |
免费 | 3119篇 |
国内免费 | 1033篇 |
专业分类
电工技术 | 1501篇 |
技术理论 | 3篇 |
综合类 | 1354篇 |
化学工业 | 7957篇 |
金属工艺 | 1910篇 |
机械仪表 | 2540篇 |
建筑科学 | 2000篇 |
矿业工程 | 489篇 |
能源动力 | 1399篇 |
轻工业 | 3117篇 |
水利工程 | 400篇 |
石油天然气 | 884篇 |
武器工业 | 171篇 |
无线电 | 5947篇 |
一般工业技术 | 6919篇 |
冶金工业 | 2488篇 |
原子能技术 | 484篇 |
自动化技术 | 5156篇 |
出版年
2024年 | 168篇 |
2023年 | 636篇 |
2022年 | 1064篇 |
2021年 | 1605篇 |
2020年 | 1159篇 |
2019年 | 1033篇 |
2018年 | 1253篇 |
2017年 | 1242篇 |
2016年 | 1364篇 |
2015年 | 1412篇 |
2014年 | 1913篇 |
2013年 | 2431篇 |
2012年 | 2612篇 |
2011年 | 2968篇 |
2010年 | 2385篇 |
2009年 | 2311篇 |
2008年 | 2270篇 |
2007年 | 1891篇 |
2006年 | 1725篇 |
2005年 | 1554篇 |
2004年 | 1340篇 |
2003年 | 1124篇 |
2002年 | 1143篇 |
2001年 | 993篇 |
2000年 | 900篇 |
1999年 | 871篇 |
1998年 | 1073篇 |
1997年 | 761篇 |
1996年 | 714篇 |
1995年 | 518篇 |
1994年 | 383篇 |
1993年 | 336篇 |
1992年 | 240篇 |
1991年 | 201篇 |
1990年 | 162篇 |
1989年 | 172篇 |
1988年 | 126篇 |
1987年 | 99篇 |
1986年 | 88篇 |
1985年 | 59篇 |
1984年 | 54篇 |
1983年 | 45篇 |
1982年 | 49篇 |
1981年 | 34篇 |
1980年 | 50篇 |
1979年 | 20篇 |
1977年 | 35篇 |
1976年 | 37篇 |
1975年 | 21篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Joongsuk Park Cam Nguyen 《Microwave and Wireless Components Letters, IEEE》2002,12(6):221-222
A new compact millimeter-wave distance-measurement sensor prototype has been developed. The sensor is a step-frequency radar implemented using coherent heterodyne technique. It operates in Ka-band (26.5-40 GHz) and is realized using MICs and MMICs. The sensor transmits sinusoidal signals of incremental frequencies and demodulates the received signals into base-band I/Q signals for processing. Experimental results show that the sensor is capable of measuring distance with less than 0.2 inch of absolute error and a low transmitted power of only -20±3 dBm 相似文献
72.
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
73.
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
74.
A two-dimensional finite element model was constructed to analyze the simulated mechanical behavior of a cantilevered fixed partial denture. The variations of the models were made by altering the degree of bone support, the number of splinted abutments, and the length of the pontics. High stress concentrations were observed around the connectors of the fixed prosthesis and the tooth closest to the cantilever. Reduced bone support increased the deflection and stress concentrations. There was reduction in displacement and stress concentration when the teeth were splinted together. To improve the prognosis of the fixed partial denture cantilever, the number of abutments should be increased and the number of pontics decreased. 相似文献
75.
76.
Calculation of Mass Attenuation Coefficients of Beta Particles 总被引:1,自引:0,他引:1
Yi C.Y.; Han H.S.; Cho W.K.; Park U.J.; Jun J.S.; Chai H.S. 《Radiation protection dosimetry》1998,78(3):221-229
77.
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
78.
We address the problem of determining the topology and bridge-capacity assignments for a network connecting a number of token rings via source-routing bridges. The objective is to minimize the cost of bridge installations while meeting the network users' performance requirements. The problem is modeled as a mixed 0–1 integer program. A comparison is given between two solution algorithms: a simulated annealing algorithm using the flow-deviation algorithm for each routing subproblem, and a drop algorithm using the simplex method for the same subproblems to provide benchmark solutions. In the former algorithm, the routing subproblem is formulated as a nonlinear program with penalty functions to model node and link capacity constraints, and in the latter as a multicommodity flow model with the same capacity constraints. Computational results show that the simulated-annealing/flow-deviation algorithm produced substantially better solutions than the LP-based drop algorithm. 相似文献
79.
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
80.