全文获取类型
收费全文 | 164867篇 |
免费 | 13621篇 |
国内免费 | 7247篇 |
专业分类
电工技术 | 9826篇 |
技术理论 | 7篇 |
综合类 | 10557篇 |
化学工业 | 22821篇 |
金属工艺 | 7760篇 |
机械仪表 | 8619篇 |
建筑科学 | 11121篇 |
矿业工程 | 3925篇 |
能源动力 | 3779篇 |
轻工业 | 12253篇 |
水利工程 | 3333篇 |
石油天然气 | 5592篇 |
武器工业 | 1278篇 |
无线电 | 16169篇 |
一般工业技术 | 16789篇 |
冶金工业 | 26450篇 |
原子能技术 | 1891篇 |
自动化技术 | 23565篇 |
出版年
2024年 | 716篇 |
2023年 | 2411篇 |
2022年 | 4347篇 |
2021年 | 5823篇 |
2020年 | 4288篇 |
2019年 | 3360篇 |
2018年 | 4206篇 |
2017年 | 4901篇 |
2016年 | 4720篇 |
2015年 | 6039篇 |
2014年 | 7140篇 |
2013年 | 8325篇 |
2012年 | 11030篇 |
2011年 | 11674篇 |
2010年 | 9275篇 |
2009年 | 8669篇 |
2008年 | 8521篇 |
2007年 | 8227篇 |
2006年 | 7544篇 |
2005年 | 9086篇 |
2004年 | 6650篇 |
2003年 | 5322篇 |
2002年 | 4104篇 |
2001年 | 3518篇 |
2000年 | 2750篇 |
1999年 | 2926篇 |
1998年 | 7676篇 |
1997年 | 5172篇 |
1996年 | 3812篇 |
1995年 | 2509篇 |
1994年 | 1905篇 |
1993年 | 1725篇 |
1992年 | 776篇 |
1991年 | 706篇 |
1990年 | 565篇 |
1989年 | 505篇 |
1988年 | 485篇 |
1987年 | 329篇 |
1986年 | 274篇 |
1985年 | 226篇 |
1984年 | 115篇 |
1983年 | 101篇 |
1982年 | 162篇 |
1981年 | 202篇 |
1980年 | 226篇 |
1979年 | 74篇 |
1978年 | 99篇 |
1977年 | 610篇 |
1976年 | 1320篇 |
1975年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
91.
92.
93.
We extend the definition of the classical Jacobi polynomials withindexes α, β>−1 to allow α and/or β to be negative integers. We show that the generalized Jacobi polynomials, with indexes corresponding to the number of boundary conditions in a given partial differential equation, are the natural basis functions for the spectral approximation of this partial differential equation. Moreover, the use of generalized Jacobi polynomials leads to much simplified analysis, more precise error estimates and well conditioned algorithms.Mathematics subject classification 1991. 65N35, 65N22, 65F05, 35J05 相似文献
94.
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
95.
In this paper, we consider the problem of designing optimal asynchronous wake-up schedules to facilitate distributed power management and neighbor discovery in multihop wireless networks. We first formulate it as a block design problem and derive the fundamental trade-offs between wake-up latency and the average duty cycle of a node. After the theoretical foundation is laid, we then devise a neighbor discovery and schedule bookkeeping protocol that can operate on the optimal wake-up schedule derived. To demonstrate the usefulness of asynchronous wake-up, we investigate the efficiency of neighbor discovery and the application of on-demand power management, which overlays a desirable communication schedule over the wake-up schedule mandated by the asynchronous wake-up mechanism. Simulation studies demonstrate that the proposed asynchronous wake-up protocol has short discovery time which scales with the density of the network; it can accommodate various traffic characteristics and loads to achieve an energy savings that can be as high as 70 percent, while the packet delivery ratio is comparable to that without power management. 相似文献
96.
97.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
98.
99.
Li Junling Zheng Tinglu Han Zhaping 《中国炼油与石油化工》2006,(3):57-60
The method for refining the straight-run diesel fuel was studied in laboratory scale in order to make the acid number of diesel fraction comply with the standard while removing the naphthenic acids contained in diesel without causing environmental pollution. After comparing the effect of refining using three solvents, the isopropyl alcohol-HOA was specified as the best solvent. Meanwhile, the relationship between the acid number of diesel fraction and the amount of solvent used and the relationship between the concentration of solvent and temperature and the stability of diesel in terms of its acid number were also investigated. Experimental results had shown that when the mass fraction of the HOA-IPA solvent was 20% at a dosage of 17 mL of the solvent and a temperature of 30℃, the acid number of the refined diesel fraction was 0.015 mg KOH/g with a good stability of acidity in the diesel fraction, 相似文献
100.
在海上石油平台CFD11项目中,首次使用了含沙探测系统,对平台上工艺流程中沙子的含量做出检测。含沙探测系统由探头、计算单元和数据处理单元/操作系统组成,安装非常方便,操作也很简单,探测结果非常有利于海洋石油平台的设备保护。 相似文献