全文获取类型
收费全文 | 92495篇 |
免费 | 8436篇 |
国内免费 | 6061篇 |
专业分类
电工技术 | 2918篇 |
技术理论 | 1篇 |
综合类 | 5616篇 |
化学工业 | 23423篇 |
金属工艺 | 7475篇 |
机械仪表 | 4737篇 |
建筑科学 | 3406篇 |
矿业工程 | 2485篇 |
能源动力 | 2250篇 |
轻工业 | 5609篇 |
水利工程 | 1342篇 |
石油天然气 | 2985篇 |
武器工业 | 700篇 |
无线电 | 11368篇 |
一般工业技术 | 15845篇 |
冶金工业 | 3434篇 |
原子能技术 | 1164篇 |
自动化技术 | 12234篇 |
出版年
2024年 | 341篇 |
2023年 | 1788篇 |
2022年 | 2838篇 |
2021年 | 3449篇 |
2020年 | 3017篇 |
2019年 | 2793篇 |
2018年 | 2489篇 |
2017年 | 3037篇 |
2016年 | 3358篇 |
2015年 | 3542篇 |
2014年 | 4858篇 |
2013年 | 5198篇 |
2012年 | 5749篇 |
2011年 | 7650篇 |
2010年 | 5721篇 |
2009年 | 6424篇 |
2008年 | 5506篇 |
2007年 | 6189篇 |
2006年 | 5400篇 |
2005年 | 4808篇 |
2004年 | 3953篇 |
2003年 | 3581篇 |
2002年 | 3034篇 |
2001年 | 1997篇 |
2000年 | 1913篇 |
1999年 | 1554篇 |
1998年 | 1217篇 |
1997年 | 963篇 |
1996年 | 904篇 |
1995年 | 689篇 |
1994年 | 654篇 |
1993年 | 484篇 |
1992年 | 381篇 |
1991年 | 312篇 |
1990年 | 228篇 |
1989年 | 202篇 |
1988年 | 128篇 |
1987年 | 109篇 |
1986年 | 121篇 |
1985年 | 67篇 |
1984年 | 45篇 |
1983年 | 47篇 |
1982年 | 53篇 |
1981年 | 31篇 |
1980年 | 42篇 |
1979年 | 32篇 |
1978年 | 12篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
3GPP关于3G演进(LTE)的工作情况 总被引:1,自引:0,他引:1
随着新技术的不断出现以及移动通信理念的变革,为了把握新一轮的技术浪潮,保持在移动通信领域的领导地位,2004年底3GPP启动了关于3G演进型系统,即LTE的研究与标准化工作,并且计划在2007年发布第一个版本的系统规范。目前,该项目已经进行了将近一年的时间,各个方面的研究都取得了一定的进展。本文简要介绍了该项目的背景情况,目前的进展和相关的趋势。 相似文献
52.
Kurjenniemi Janne Hämäläinen Seppo Ristaniemi Tapani 《Wireless Personal Communications》2003,27(4):337-351
In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out. 相似文献
53.
54.
介绍了3G技术在国内外的发展情况,阐述了发展趋势,对3G技术的分类和所采用的主流技术、标准化情况进行了论述,并对CDMA2000,WCDMA和TD-SCDMA三种3G的三大主流应用技术标准进行比较分析。 相似文献
55.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
56.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
57.
Mitsuo Miyazawa Hideki Kawazoe Mitsuro Hyakumachi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(6):620-625
The microbial transformation of l‐menthol ( 1 ) was investigated by using 12 isolates of soil‐borne plant pathogenic fungi, Rhizoctonia solani (AG‐1‐IA Rs24, Joichi‐2, RRG97‐1; AG‐1‐IB TR22, R147, 110.4; AG‐1‐IC F‐1, F‐4, P‐1; AG‐1‐ID RCP‐1, RCP‐3, and RCP‐7) as a biocatalyst. Rhizoctonia solani F‐1, F‐4 and P‐1 showed 89.7–99.9% yields of converted product from 1 , RCP‐1, RCP‐3, and RCP‐7 26.0–26.9% and the other isolates 0.1–12.0%. In the cases of F‐1, F‐4 and P‐1, substrate 1 was converted to (?)‐(1S,3R,4S,6S)‐6‐hydroxymenthol ( 2 ), (?)‐(1S,3R,4S)‐1‐hydroxymenthol ( 3 ) and (+)‐(1S,3R,4R,6S)‐6,8‐dihydroxymenthol ( 4 ), which was a new compound. Substrate 1 was converted to 2 and/or 3 by RRG97‐1, 110.4, RCP‐1, RCP‐3 and RCP‐7. The structures of the metabolic products were elucidated on the basis of their spectral data. In addition, metabolic pathways of the biotransformation of 1 by Rhizoctonia solani are discussed. Finally, from the main component analysis and the differences in the yields of converted product from 1 , the 12 isolates of Rhizoctonia solani were divided into three groups based on an analysis of the metabolites. Copyright © 2003 Society of Chemical Industry 相似文献
58.
This paper describes the methodology for simulating a reprographic ink with a ceramic ink based on a commercially available zirconia powder for direct ceramic ink-jet printing. Of over-riding importance was matching viscosity and this was tested systematically by using a mineral oil–hexane binary system. Of secondary importance was adjustment of the pressure defect behind the nozzle to compensate for small differences in surface tension. The inks tested in the wide array print-head were based on low electrical conductivity liquids to avoid damage to the electroding system. The organic binder for the zirconia ink was paraffin wax and the dispersant was a hydroxystearic acid based polyester. 相似文献
59.
60.