全文获取类型
收费全文 | 12134篇 |
免费 | 913篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 184篇 |
综合类 | 4篇 |
化学工业 | 3179篇 |
金属工艺 | 305篇 |
机械仪表 | 387篇 |
建筑科学 | 346篇 |
矿业工程 | 27篇 |
能源动力 | 479篇 |
轻工业 | 2295篇 |
水利工程 | 131篇 |
石油天然气 | 78篇 |
无线电 | 732篇 |
一般工业技术 | 2000篇 |
冶金工业 | 1117篇 |
原子能技术 | 81篇 |
自动化技术 | 1726篇 |
出版年
2024年 | 36篇 |
2023年 | 133篇 |
2022年 | 390篇 |
2021年 | 619篇 |
2020年 | 409篇 |
2019年 | 538篇 |
2018年 | 548篇 |
2017年 | 585篇 |
2016年 | 537篇 |
2015年 | 394篇 |
2014年 | 528篇 |
2013年 | 949篇 |
2012年 | 804篇 |
2011年 | 858篇 |
2010年 | 587篇 |
2009年 | 631篇 |
2008年 | 568篇 |
2007年 | 493篇 |
2006年 | 397篇 |
2005年 | 289篇 |
2004年 | 256篇 |
2003年 | 246篇 |
2002年 | 210篇 |
2001年 | 156篇 |
2000年 | 150篇 |
1999年 | 151篇 |
1998年 | 346篇 |
1997年 | 242篇 |
1996年 | 196篇 |
1995年 | 124篇 |
1994年 | 109篇 |
1993年 | 94篇 |
1992年 | 59篇 |
1991年 | 40篇 |
1990年 | 39篇 |
1989年 | 52篇 |
1988年 | 43篇 |
1987年 | 29篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1977年 | 11篇 |
1976年 | 32篇 |
1975年 | 11篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Adelino Santos 《计算机科学技术学报》1993,8(3):67-79
CoMEdiA is a groupware tool which enables co-authors to cooperatively produce hypermedia documents.CoMEdiA allows co-authors to communicate their ideas,drafts,guidelines,constraints and annotations to other co-authors.In uses a mix of communication patterns,media and document organization to enable co-authors to keep on exchanging information(remotely or face-to-face),improving passages and modifying notes until a final document is achieved.We did not concentrate on th depth but on the breath of the features.Our efforts were on integrating and corrdinating concepts from collaboration,multimedia and hyper organization rather than on making a specialized system in any of them.We began with the text medium and are now including bitmaps and raster images.Later sound and video will also be integrated.In this paper we describe and sustain the available capacites. 相似文献
63.
64.
Pertussis in Massachusetts, 1981-1991: incidence, serologic diagnosis, and vaccine effectiveness 总被引:1,自引:0,他引:1
CD Marchant AM Loughlin SM Lett CW Todd LH Wetterlow R Bicchieri S Higham P Etkind E Silva GR Siber 《Canadian Metallurgical Quarterly》1994,169(6):1297-1305
Massachusetts provides diphtheria-tetanus toxoid-pertussis (DTP) vaccine, and since 1980 has monitored pertussis with a statewide diagnostic service. The incidence of bacteriologically confirmed pertussis was 104.5 per 100,000 person-years in 1-month-old infants and declined progressively thereafter. Infants < 6 months old experienced disproportionate morbidity: 44% of bacteriologically confirmed pertussis, 64% of hospitalizations, and 71% of hospital days. Most children with pertussis had received < 3 DTP doses during childhood, whereas 87% of adolescents with pertussis had received > or = 4 doses. Serodiagnosis by single serum anti-pertussis toxin antibody ELISA increased the incidence of confirmed pertussis in persons 11-19 years old from 3.0 to 12.9 per 100,000 and in persons > or = 20 years old from 0.16 to 0.56 per 100,000. Bacteriologic methods underestimate pertussis incidence, but a single serum anti-pertussis toxin antibody ELISA is a practical method for population-based diagnosis in adolescents and adults. 相似文献
65.
Orestes E. Alarcón Ricardo E. medrano Pcter P. Gillis 《Metallurgical and Materials Transactions A》1994,25(5):961-968
To fully characterize the mechanical behavior of ceramics, it is useful to study their response to both tensile and bending
tests. In this investigation, a quantitative comparison is made between tensile and bending results from (circularly) cylindrical
glass rods of borosilicate glass and of fused silica. These experimental results show that in each material, the Weibull exponentm is approximately the same for both types of test. The fractured samples clearly showed that all failures initiated at surface-located
flaws. The stress level at which the probability of fracture in tension equals 50 Pct was determined; the maximum tensile
stress for 50 Pct probability of fracture in bending was also determined. The ratio of these two stresses was predicted previously
from simple, theoretical considerations based upon the applicability of the Weibull function and on the distribution of defects
in the specimens. This theoretical result is inconsistent with the experimental observations in view of the fractography.
Therefore, it is concluded that failure in the materials tested is not satisfactorily described by Weibull statistics. 相似文献
66.
Cristiane Vieira Helm Alicia de Francisco Salete Aparecida Gaziola Ricardo Francisco Fornazier Georgia Bertoni Pompeu Ricardo Antunes Azevedo 《Food Biotechnology》2005,18(3):327-341
Barley (Hordeum vulgare L.) has had an important impact on human nutrition. Hull-less barley is a genetically improved type that has been widely used in recent years. Six Brazilian hull-less barley varieties (IAC-IBON 214-82; IAC 8612-421; IAC 8501-31; IAC 8501-12; IAPAR 39-ACUMAI; IAC 8501-22) were analyzed for storage protein constituents, amino acid contents, and similarity among the hull-less barley varieties. Albumins, globulins, prolamins I and II, and glutelins were extracted and separated by SDS-PAGE. The total protein amino acid contents of the flour were also determined for each variety by TLC and HPLC. Variations in intensity and appearance and disappearance of protein bands were observed among the varieties suggesting genetic variability. However, the amino acid profile did not indicate any major variations in the amino acid concentrations. The high lysine and threonine total concentrations detected in the seeds of the hull-less barley varieties encouraged an investigation into the regulation of amino acid metabolism and storage protein synthesis. 相似文献
67.
68.
Ricardo Lima Author Vitae Author Vitae Claudio Reineri Author Vitae Author Vitae 《Computers & Electrical Engineering》2008,34(6):520-530
This paper presents a novel concept for power quality hardware and software architecture. Software tools related to detection, classification and characterization of power quality events can be integrated into a Distribution Control Center in which the interconnection between different subsystems is being carried out through the Internet allowing flexibility to the system. This system is implemented using wavelet analysis applied in all proposed algorithms. Different power quality events are taken as examples to illustrate the capabilities of the proposed method. The obtained results reveal that the proposed architecture is feasible to be implemented as an integral part of a control center system.The proposed system has the property of fast and accurate detection and classification of any power quality disturbance event and introduces a new PQ index determination that allows characterizing any type of disturbance including the non-periodic signals. 相似文献
69.
70.
We present the design and realization of cylindrical dielectric resonators operating in the 40–60 GHz frequency range, designed
for the measurement of the surface resistance and of the surface reactance shift in High-T
c Superconductors (HTS) thin films in a dc magnetic field. The resonators are single tone, based on the TE
011 mode, and multiple tone, the latter allowing in principle to exploit the simultaneous determination of the surface impedance
at different frequencies. As an application example, we report the temperature and field dependencies of the effective surface
impedance of some cuprate superconductors thin films. The results are compared with those obtained through the use of a standard
metal cavity with a similar Q-factor and operating in the same frequency range. The comparison highlights a superior stability and a higher sensitivity,
resulting in an increase of about two orders of magnitude in the resolution of the surface impedance measurement. By contrast,
the dissipative part of the superconducting transition (above T/T
c = 0.97) is better studied with the metal cavity. We also present measurements in the vortex state in YBaCa2Cu3O7−δ and Tl2Ba2CaCu2O8+x
that show significantly different physics.
PACS: 74.25 Nf. 相似文献