全文获取类型
收费全文 | 351841篇 |
免费 | 4011篇 |
国内免费 | 1369篇 |
专业分类
电工技术 | 5965篇 |
综合类 | 2563篇 |
化学工业 | 49580篇 |
金属工艺 | 14818篇 |
机械仪表 | 11044篇 |
建筑科学 | 8639篇 |
矿业工程 | 1496篇 |
能源动力 | 8789篇 |
轻工业 | 25973篇 |
水利工程 | 3593篇 |
石油天然气 | 3707篇 |
武器工业 | 16篇 |
无线电 | 45168篇 |
一般工业技术 | 68233篇 |
冶金工业 | 56100篇 |
原子能技术 | 5634篇 |
自动化技术 | 45903篇 |
出版年
2021年 | 2290篇 |
2020年 | 1656篇 |
2019年 | 2045篇 |
2018年 | 17389篇 |
2017年 | 16310篇 |
2016年 | 13217篇 |
2015年 | 2942篇 |
2014年 | 4413篇 |
2013年 | 12306篇 |
2012年 | 9616篇 |
2011年 | 18176篇 |
2010年 | 15244篇 |
2009年 | 13710篇 |
2008年 | 15436篇 |
2007年 | 16346篇 |
2006年 | 7956篇 |
2005年 | 8231篇 |
2004年 | 7787篇 |
2003年 | 8159篇 |
2002年 | 7106篇 |
2001年 | 7153篇 |
2000年 | 6611篇 |
1999年 | 6931篇 |
1998年 | 18344篇 |
1997年 | 12589篇 |
1996年 | 9674篇 |
1995年 | 7187篇 |
1994年 | 6432篇 |
1993年 | 6383篇 |
1992年 | 4431篇 |
1991年 | 4323篇 |
1990年 | 4124篇 |
1989年 | 3926篇 |
1988年 | 3809篇 |
1987年 | 3243篇 |
1986年 | 3151篇 |
1985年 | 3438篇 |
1984年 | 3103篇 |
1983年 | 2998篇 |
1982年 | 2789篇 |
1981年 | 2733篇 |
1980年 | 2624篇 |
1979年 | 2437篇 |
1978年 | 2237篇 |
1977年 | 2847篇 |
1976年 | 3891篇 |
1975年 | 1874篇 |
1974年 | 1825篇 |
1973年 | 1763篇 |
1972年 | 1539篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
In this paper, we propose a routing algorithm called minimum fusion Steiner tree (MFST) for energy efficient data gathering with aggregation (fusion) in wireless sensor networks. Different from existing schemes, MFST not only optimizes over the data transmission cost, but also incorporates the cost for data fusion, which can be significant for emerging sensor networks with vectorial data and/or security requirements. By employing a randomized algorithm that allows fusion points to be chosen according to the nodes' data amounts, MFST achieves an approximation ratio of 5/4log(k + 1), where k denotes the number of source nodes, to the optimal solution for extremely general system setups, provided that fusion cost and data aggregation are nondecreasing against the total input data. Consequently, in contrast to algorithms that only excel in full or nonaggregation scenarios without considering fusion cost, MFST can thrive in a wide range of applications 相似文献
32.
The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation. 相似文献
33.
Yu. V. Baldokhin V. V. Vavilova P. Ya. Kolotyrkin Yu. K. Kovneristyi N. A. Palii A. S. Solomatin 《Inorganic Materials》2003,39(6):562-567
Mössbauer effect measurements and physicochemical analysis demonstrate that annealing of amorphous Fe–P–Mn alloys leads to the formation of a nanocrystalline structure. 相似文献
34.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
35.
36.
This article presents a graph-theoretic method for constructing low-density parity-check (LDPC) codes from connected graphs without the requirement of large girth. This method is based on finding a set of paths in a connected graph, which satisfies the constraint that any two paths in the set are either disjoint or cross each other at one and only one vertex. Two trellis-based algorithms for finding these paths are devised. Good LDPC codes of practical lengths are constructed and they perform well with iterative decoding. 相似文献
37.
38.
In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %. 相似文献
39.
Zs. T
kei D. Kelleher B. Mebarki T. Mandrekar S. Guggilla K. Maex 《Microelectronic Engineering》2003,70(2-4):358-362
Passivated single damascene copper SiO2 damascene lines were evaluated in combination with TiSiN and Ta(N)/Ta diffusion barriers. Leakage current, breakdown and time-dependent dielectric breakdown properties were investigated on a wafer level basis for temperatures ranging between room temperature and 150 °C. It is found that the leakage performance of the wafers with a TiSiN barrier is better at room temperature, but at 150 °C the performance levels out with Ta(N)/Ta. Time-dependent dielectric breakdown measurements at 150 °C show that the lifetime of the interconnect is higher with the selected Ta(N)/Ta barrier than for TiSiN. 相似文献
40.
Many organisations use decision models in their processes such as tables or trees to provide decision support to their operational
divisions. For example, in fault management, customer contact centre operators usually use a decision model in the form of
prescribed interviews. Based on the answers given by customers, the operator navigates through the decision model to reach
an assessment of the problem. In order to achieve customer satisfaction and operational excellence, it is very important to
constantly monitor the performance of a decision model not only on an overall level, but also on the level of individual decisions.
In this paper we present a configurable business process analytics tool, known as the intelligent Universal Service Management
System, that constantly monitors decision data and is capable of optimising the decisions based on high-level business objectives.
We explain the various features of the software and show how it can be used to optimise decision processes. We also show how
we can easily provide a customised version to monitor the performance of provision processes. 相似文献