全文获取类型
收费全文 | 18583篇 |
免费 | 1768篇 |
国内免费 | 893篇 |
专业分类
电工技术 | 1148篇 |
综合类 | 1300篇 |
化学工业 | 3289篇 |
金属工艺 | 805篇 |
机械仪表 | 955篇 |
建筑科学 | 1094篇 |
矿业工程 | 418篇 |
能源动力 | 726篇 |
轻工业 | 1683篇 |
水利工程 | 369篇 |
石油天然气 | 479篇 |
武器工业 | 99篇 |
无线电 | 2360篇 |
一般工业技术 | 2170篇 |
冶金工业 | 1641篇 |
原子能技术 | 254篇 |
自动化技术 | 2454篇 |
出版年
2024年 | 41篇 |
2023年 | 166篇 |
2022年 | 373篇 |
2021年 | 519篇 |
2020年 | 378篇 |
2019年 | 398篇 |
2018年 | 430篇 |
2017年 | 447篇 |
2016年 | 456篇 |
2015年 | 644篇 |
2014年 | 812篇 |
2013年 | 1148篇 |
2012年 | 1126篇 |
2011年 | 1173篇 |
2010年 | 1082篇 |
2009年 | 1030篇 |
2008年 | 1041篇 |
2007年 | 1018篇 |
2006年 | 949篇 |
2005年 | 776篇 |
2004年 | 726篇 |
2003年 | 839篇 |
2002年 | 1085篇 |
2001年 | 905篇 |
2000年 | 521篇 |
1999年 | 400篇 |
1998年 | 416篇 |
1997年 | 345篇 |
1996年 | 249篇 |
1995年 | 200篇 |
1994年 | 139篇 |
1993年 | 155篇 |
1992年 | 100篇 |
1991年 | 98篇 |
1990年 | 82篇 |
1989年 | 72篇 |
1988年 | 65篇 |
1987年 | 41篇 |
1986年 | 41篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 46篇 |
1982年 | 52篇 |
1981年 | 50篇 |
1980年 | 43篇 |
1979年 | 36篇 |
1977年 | 61篇 |
1976年 | 54篇 |
1975年 | 40篇 |
1972年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
101.
Given a stability region of a polytope of polynomials, the edge theorem can be used to verify certain root-clustering properties of the polytope. The authors consider the inverse problem; starting with a polytope of real polynomials, they present a result that allows the construction of the smallest set of regions in the complex plane which characterizes its zero location 相似文献
102.
King Abby C.; Taylor C. Barr; Haskell William L.; DeBusk Robert F. 《Canadian Metallurgical Quarterly》1989,8(3):305
Evaluated 120 healthy, sedentary, middle-aged adults randomly assigned to either a 6-mo home-based aerobic exercise training program or to an assessment-only control condition. Adherence across the 6-mo period by the exercise group was demonstrated by self-report and heart rate microprocessor methods to exceed 75%. A 14-item Likert rating scale was used to measure a variety of psychological variables. Significant between-groups differences favoring the exercise group were found on scale items closely associated with actual physical changes that occurred with exercise (satisfaction with shape/appearance, perceived fitness). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
ABSTRACT: This study determined the efficacy and safety of ozonation in degrading aflatoxin in corn. Ozonation (10 to 12 wt%) reduced aflatoxin levels by 92% and no reversion to the parent compound was observed. Ozonation had minimal effect on fatty acids of uncontaminated corn, but had significant effect on fatty acids of contaminated corn. Crude extracts showed no mutagenic potential in the Ames assay using TA98 and TA100. Clean-up using hexane increased their mutagenic potentials. Clean-up using Mycosep columns increased the mutagenic potentials 18 to 617%. Hexane extracts from ozone-treated contaminated corn had lower inhibitory effect. This suggested that a fat-soluble mutagen is being formed or natural inhibitors of mutagenicity are being destroyed. 相似文献
104.
Compact conical antennas for wide-band coverage 总被引:7,自引:0,他引:7
A broadband antenna with a vertically polarized, omnidirectional electric field is studied. The design of the antenna and its feeding system in the wide frequency range from 20 to 1000 MHz is described and the driving-point impedance determined. Also calculated are the voltage standing-wave ratio (VSWR) and the input impedance of a transmission line connected to the antenna. More efficient operation at low frequencies is obtained by adding a length of transmission line to form a resonant section with the antenna. The effect of the different properties of the earth's surface on the field pattern is treated in a companion paper 相似文献
105.
介绍了ADSS光缆的力学计算,给出了光缆弧垂、张力、应变和悬长等计算公式,并对普遍采用的“悬链线”和“抛物线”两种计算方法加以比较。 相似文献
106.
Kok Wai Wong Chun Che Fung Eren H. Gedeon T. 《IEEE transactions on instrumentation and measurement》2003,52(6):1865-1869
Fuzzy rule-based systems have been very popular in many engineering applications. In mineral engineering, fuzzy rules are normally constructed using some fuzzy rule extraction techniques to establish the determination model in predicting the d50c of hydrocyclones. However, when generating fuzzy rules from the available information, it may result in a sparse fuzzy rule base. The use of more than one input variable is also common in hydrocyclone data analysis. This paper examines the application of fuzzy interpolation to resolve the problems using sparse fuzzy rule bases, and to perform analysis of fuzzy interpolation in multidimensional input spaces. 相似文献
107.
108.
M. E. Fitzpatrick M. T. Hutchings J. E. King D. M. Knowles P. J. Withers 《Metallurgical and Materials Transactions A》1995,26(12):3191-3198
The effects of a thermal residual stress field on fatigue crack growth in a silicon carbide particle-reinforced aluminum alloy
have been measured. Stress fields were introduced into plates of material by means of a quench from a solution heat-treatment
temperature. Measurements using neutron diffraction have shown that this introduces an approximately parabolic stress field
into the plates, varying from compressive at the surfaces to tensile in the center. Long fatigue cracks were grown in specimens
cut from as-quenched plates and in specimens which were given a stress-relieving overaging heat treatment prior to testing.
Crack closure levels for these cracks were determined as a function of the position of the crack tip in the residual stress
field, and these are shown to differ between as-quenched and stress-relieved samples. By monitoring the compliance of the
specimens during fatigue cycling, the degree to which the residual stresses close the crack has been evaluated.
formerly Research Student, Department of Materials Science and Metallurgy, University of Cambridge
formerly Lecturer, Department of Materials Science and Metallurgy, University of Cambridge
This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the
1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint
TMS-SMD/ASM-MSD Composite Materials Committee. 相似文献
109.
This paper considers determination of the optimal number of periodic preventive maintenance operations during the warranty period. The hazard rate after preventive maintenance lies between as good as new and as bad as old. After minimal repair, the hazard rate of the system remains unchanged. Free and modified warranty policies are considered with a numerical example using the Weibull case. 相似文献
110.
Very high-order microring resonator filters for WDM applications 总被引:6,自引:0,他引:6
B.E. Little S.T. Chu P.P. Absil J.V. Hryniewicz F.G. Johnson F. Seiferth D. Gill V. Van O. King M. Trakalo 《Photonics Technology Letters, IEEE》2004,16(10):2263-2265
High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications. 相似文献