全文获取类型
收费全文 | 86841篇 |
免费 | 7350篇 |
国内免费 | 4949篇 |
专业分类
电工技术 | 4632篇 |
技术理论 | 3篇 |
综合类 | 7266篇 |
化学工业 | 14861篇 |
金属工艺 | 6124篇 |
机械仪表 | 4316篇 |
建筑科学 | 8934篇 |
矿业工程 | 4115篇 |
能源动力 | 3814篇 |
轻工业 | 5937篇 |
水利工程 | 2742篇 |
石油天然气 | 3807篇 |
武器工业 | 1301篇 |
无线电 | 6435篇 |
一般工业技术 | 11149篇 |
冶金工业 | 6355篇 |
原子能技术 | 1462篇 |
自动化技术 | 5887篇 |
出版年
2024年 | 283篇 |
2023年 | 969篇 |
2022年 | 2118篇 |
2021年 | 2636篇 |
2020年 | 2740篇 |
2019年 | 2233篇 |
2018年 | 2172篇 |
2017年 | 2882篇 |
2016年 | 3095篇 |
2015年 | 3067篇 |
2014年 | 4901篇 |
2013年 | 5157篇 |
2012年 | 5981篇 |
2011年 | 6459篇 |
2010年 | 4954篇 |
2009年 | 5164篇 |
2008年 | 4533篇 |
2007年 | 6099篇 |
2006年 | 5278篇 |
2005年 | 4667篇 |
2004年 | 3919篇 |
2003年 | 3547篇 |
2002年 | 2951篇 |
2001年 | 2473篇 |
2000年 | 2101篇 |
1999年 | 1682篇 |
1998年 | 1329篇 |
1997年 | 1114篇 |
1996年 | 1002篇 |
1995年 | 815篇 |
1994年 | 670篇 |
1993年 | 487篇 |
1992年 | 378篇 |
1991年 | 278篇 |
1990年 | 241篇 |
1989年 | 184篇 |
1988年 | 125篇 |
1987年 | 69篇 |
1986年 | 63篇 |
1985年 | 62篇 |
1984年 | 42篇 |
1983年 | 32篇 |
1982年 | 27篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1975年 | 13篇 |
1959年 | 12篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
61.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended. 相似文献
62.
Yang Aiying Wang Ziyu Zhang Zhaoyi Chen Zhangyuan Wu Deming 《电子科学学刊(英文版)》2003,20(6):461-466
A 10Gbit/s recirculating system is configured with Chirped Fiber Bragg Grating (CFBG) for the dispersion compensation. For the first time, the transmission distance in the loop reaches 1000km with bit error rate of 10-9. The effect of the group delay ripple of the fiber grating is also investigated in the recirculating systems, and it is shown that the transmission distance is limited to 4 cycles (4×167.1km ) in the loop with the power penalty fluctuation below 1.0dB. Thus the group delay ripple should be reduced to allow for the wavelength drift of±5GHz. At the end of this letter, the principles are given for designing long haul recirculating systems with dispersion compensation CFBG. 相似文献
63.
渤海湾盆地石油地质储量和产量增长趋势的预测 总被引:3,自引:1,他引:2
渤海湾盆地的石油地质储量发现过程具有明显的渐进性、阶段性和长期性,石油产量的增长也具有一定的起伏性,用一个周期的单旋回哈伯特模型难以预测其发展趋势。通过分析渤海湾盆地的勘探开发历程,结合新一轮常规油气资源评价的结果,分别采用4个和3个哈伯特旋回拟合石油地质储量发现和产量增长曲线。预测结果显示,2005-2015年渤海湾盆地处于石油地质储量发现高峰期,2015年左右其石油产量达到高峰,之后处于下降趋势。实践证明,利用多旋回哈伯特模型对具有“多峰”特征的石油地质储量和产量的未来趋势进行预测是一种有效的方法。 相似文献
64.
用矾土作为主原料,选择适当结合剂和添加剂,引入微粉技术,采用真空炼泥等工艺手段,研制成低水分抗热震高铝可塑料。该制品用作热媒加热炉衬里,显示出良好的耐高温和耐热冲击性能。 相似文献
65.
新型壳聚糖/纳米二氧化硅杂化材料的制备与性能 总被引:10,自引:5,他引:5
在纳米S iO2颗粒表面引入羟丙基氯活性基团,得到功能化S iO2颗粒,再将羟丙基氯化的S iO2颗粒交联固定在壳聚糖上,制备了一种新型的壳聚糖/纳米S iO2杂化材料(简称杂化材料);通过傅里叶变换红外光谱、透射电镜、扫描电镜方法对杂化材料进行表征,采用热重(TG)分析研究杂化材料的热性能;考察了杂化材料的沉降速率和对金属离子Ca2+和M g2+的吸附能力。电镜分析结果表明,杂化材料微粒为纳米尺度的无机S iO2加强化的微粒,S iO2颗粒分散在材料中,形成均匀的表面;TG分析结果表明,杂化材料的热性能有所提高;沉降实验测得壳聚糖和杂化材料作为吸附剂的沉降时间分别为130.3,68.5s,表明杂化材料的沉降速率比壳聚糖的沉降速率快了近一倍;杂化材料对金属离子Ca2+和M g2+的吸附量分别可达到0.289 3,1.445 6mm ol/g。 相似文献
66.
67.
Ben-Jye Chang 《Telecommunication Systems》2006,33(4):333-352
3G Wideband CDMA systems adopt the Orthogonal Variable Spreading Factor code tree as the channelization codes management for
achieving high data rate transmission in personal multimedia communications. It assigns a single channelization code for each
accepted connection. Nevertheless, it wastes the system capacity when the required rate is not powers of two of the basic
rate. One good solution is to assign multiple codes for each accepted connection but it causes two inevitable drawbacks: long
handoff delay and new call setup delay due to high complexity of processing with multiple channelization codes, and high cost
of using more number of rake combiners. Especially, long handoff delay may result in more call dropping probability and higher
Grade of Service, which will degrade significantly the utilization and revenue of the 3G cellular systems. Therefore, we propose
herein an adaptive efficient codes determination algorithm based on the Markov Decision Process analysis approach to reduce
the waste rate and reassignments significantly while providing fast handoff. Numerical results demonstrate that the proposed
approach yields several advantages, including the lowest GOS, the least waste rate, and the least number of reassignments.
Meanwhile, the optimal number of rake combiners is also analyzed in this paper.
This research was supported in part by the National Science Council of Taiwan, ROC, under contract NSC-93-2213-E-324-018. 相似文献
68.
Effect of Strain Rate on Discontinuous Flow and Mechanical Characteristics of High-Nitrogenous Steel
Experimental study on the effect of strain rate on discontinuous flow and mechanical characteristics of the high-nitrogenous steel Kh23AG19F has been performed. Within the range of strain rates from 4.62 · 10-5 to 1.85 · 10 -4 s-1, discontinuous flow, reflected by serration on the tensile diagram, is chiefly determined by intergranular deformation mechanisms. Under strain rates over 1.85 · 10-2 s-1, combined deformation modes prevail, which cause a change in the character of discontinuous flow and transform a serrated tensile diagram into a wavy graph, with the yield stress of steel increased significantly. 相似文献
69.
Ludmil Drenchev Jerzy Sobczak Rajiv Asthana Savko Malinov 《Journal of Computer-Aided Materials Design》2003,10(1):35-54
Ordered porosity metal materials belong to a relatively new class of porous materials named gasars. This paper presents a mathematical model of the complex physical phenomena in the production of gasars. Analyses for heat transfer, solidification kinetics and gas diffusion were coupled to describe the formation of unique gasar structure. Several criterial functions were introduced to provide significant quantitative information about the relationship between the operating technological parameters and the final structure. The computational outcomes of the numerical simulation were compared with the characteristics of real gasar ingots. The model was applied to determine the boundary conditions that would provide approximately constant physical conditions on the solidification front. The structure sensitiveness of gasars with respect to the different technological parameters is discussed. 相似文献
70.
中国石化北京燕化石油化工股份有限公司动力事业部二供水车间电气改造完成后,能源实时监控与信息管理系统出现线路名称不统一、电流互感系数变比不起作用、数据查询功能及统计报表数据的准确性等问题,严重地影响系统的使用。通过对比分析,找到了出现问题的实质,对源代码进行修改,问题得到了解决。同时也成功地解决了其他部门遇到相类似的问题。 相似文献