全文获取类型
收费全文 | 143182篇 |
免费 | 6853篇 |
国内免费 | 3557篇 |
专业分类
电工技术 | 4862篇 |
技术理论 | 4篇 |
综合类 | 6654篇 |
化学工业 | 21145篇 |
金属工艺 | 8179篇 |
机械仪表 | 6926篇 |
建筑科学 | 6782篇 |
矿业工程 | 1897篇 |
能源动力 | 2825篇 |
轻工业 | 7956篇 |
水利工程 | 2491篇 |
石油天然气 | 3031篇 |
武器工业 | 497篇 |
无线电 | 16902篇 |
一般工业技术 | 23964篇 |
冶金工业 | 5066篇 |
原子能技术 | 1047篇 |
自动化技术 | 33364篇 |
出版年
2024年 | 277篇 |
2023年 | 971篇 |
2022年 | 1844篇 |
2021年 | 2555篇 |
2020年 | 1822篇 |
2019年 | 1608篇 |
2018年 | 15952篇 |
2017年 | 15051篇 |
2016年 | 11682篇 |
2015年 | 3113篇 |
2014年 | 3243篇 |
2013年 | 3875篇 |
2012年 | 7011篇 |
2011年 | 13608篇 |
2010年 | 12067篇 |
2009年 | 9022篇 |
2008年 | 10306篇 |
2007年 | 11027篇 |
2006年 | 3433篇 |
2005年 | 4048篇 |
2004年 | 3233篇 |
2003年 | 3181篇 |
2002年 | 2809篇 |
2001年 | 2005篇 |
2000年 | 1711篇 |
1999年 | 1404篇 |
1998年 | 1127篇 |
1997年 | 920篇 |
1996年 | 853篇 |
1995年 | 716篇 |
1994年 | 614篇 |
1993年 | 462篇 |
1992年 | 354篇 |
1991年 | 289篇 |
1990年 | 192篇 |
1989年 | 155篇 |
1988年 | 140篇 |
1987年 | 75篇 |
1986年 | 60篇 |
1985年 | 42篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1959年 | 39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
71.
Service composition for generic service graphs 总被引:1,自引:0,他引:1
Service composition is a promising approach to multimedia service provisioning, due to its ability to dynamically produce new multimedia content, and to customize the content for individual client devices. Previous research work has addressed various aspects of service composition such as composibility, QoS-awareness, and load balancing. However, most of the work has focused on applications where data flow from a single source is processed by intermediate services and then delivered to a single destination. In this paper, we address the service composition problem for multimedia services that can be modeled as directed acyclic graphs (DAGs). We formally define the problem and prove its NP hardness. We also design a heuristic algorithm to solve the problem. Our simulation results show that the algorithm is effective at finding low-cost composition solutions, and can trade off computation overhead for better results. When compared with a hop-by-hop approach for service composition, our algorithm can find composition solutions that aress 10% smaller in cost, even when the hop-by-hop approach uses exhaustive searches. 相似文献
72.
Gert Schubring 《NTM》2003,11(2):90-99
Enno Heeren Dirksen (1788–1850) was one of several mathematicians originating from Eastern Frisia at the end of the eighteenth
century to acquire prominence in neohumanist reformed Prussia. While striving—like so many of his contemporaries—for more
rigour in the foundations of calculus, his work is significant due to his unusual emphasis on the semiotic aspects of the
basic concepts. As a clear-sighted propagator of Cauchy's conceptual innovations in Germany, his achievements in improving
sign expressions of such concepts enabled him to clarify hitherto not differentiated multiple limit processes—although less
successfully in constructive concept formation itself.
The contribution is based on the analysis of Dirksen's published texts and on the numerous texts which remained drafts for
his projected voluminousOrganon der gesamten Analysis.
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
Menso Folkerts zum 60. Geburtstag gewidmet 相似文献
73.
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
74.
实时操作系统DSP/BIOS在DSP开发中的应用 总被引:2,自引:0,他引:2
本文介绍了RTOS(实时操作系统)DSP/BIOS在DSP的开发设计中的应用。在简述了DSP的一般模型后,论述了RTOS在DSP/BIOS外设管理,实时性能分析以及程序流程控制中的应用。 相似文献
75.
76.
概述了Windows2000即插即用系统组成及其实现过程,结合实例介绍了Windows2000设备驱动程序如何支持用户即插即用的功能。 相似文献
77.
采用四组分法从辽河减压渣油中分离出胶质、沥青质,分别考察了它们在分散型催化剂作用下的临氢热反应行为。结果表明,胶质、沥青质一方面要裂化生成较轻的产物;另一方面也要发生缩合反应生成较重的反应产物以及甲苯不溶物。渣油在临氢热反应过程中,沥青质是生焦的主要来源,其次才是胶质。比较了热反应生成的沥青质与原生沥青质之间以及热反应生成的胶质与原生胶质之间化学组成的区别,结果表明,反应生成的沥青质和胶质较原生的沥青质和胶质分子结构缩合程度高,并且反应苛刻度越高,缩合程度也越高。 相似文献
78.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
79.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
80.