全文获取类型
收费全文 | 1856篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 30篇 |
综合类 | 2篇 |
化学工业 | 95篇 |
金属工艺 | 14篇 |
机械仪表 | 6篇 |
建筑科学 | 26篇 |
矿业工程 | 1篇 |
能源动力 | 22篇 |
轻工业 | 21篇 |
水利工程 | 13篇 |
石油天然气 | 1篇 |
无线电 | 129篇 |
一般工业技术 | 126篇 |
冶金工业 | 1286篇 |
原子能技术 | 5篇 |
自动化技术 | 97篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 3篇 |
2014年 | 14篇 |
2013年 | 35篇 |
2012年 | 19篇 |
2011年 | 17篇 |
2010年 | 22篇 |
2009年 | 35篇 |
2008年 | 26篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 19篇 |
2004年 | 12篇 |
2003年 | 20篇 |
2002年 | 10篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 62篇 |
1998年 | 433篇 |
1997年 | 222篇 |
1996年 | 167篇 |
1995年 | 86篇 |
1994年 | 74篇 |
1993年 | 72篇 |
1992年 | 23篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 21篇 |
1986年 | 29篇 |
1985年 | 35篇 |
1984年 | 20篇 |
1983年 | 21篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 31篇 |
1976年 | 54篇 |
1973年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有1874条查询结果,搜索用时 8 毫秒
81.
Microwave Studies on Strontium Ferrite Based Absorbers 总被引:1,自引:0,他引:1
Single layer microwave absorbers based on strontium ferrite-epoxy composites have been fabricated and their reflection loss characteristics studied in the X-band (8–12.4 GHz) of microwave frequencies. Permittivity (r – jr) and permeability (r – jr) of Co and Ti added strontium ferrite SrCo
x
Ti
x
Fe12 – 2x
O19 (x = 0.1 to 0.9 in steps of 0.2), have been measured. Thickness of the absorber is an important criterion influencing the absorption characteristics. Composites of 3 mm thickness are found to absorb over a reasonable range of X-band frequencies. A minimum reflection loss of –36.5 dB is observed for the composite with x = 0.3. 相似文献
82.
R Fuhrer C Dufouil TC Antonucci MJ Shipley C Helmer JF Dartigues 《Canadian Metallurgical Quarterly》1999,149(2):116-126
The possible modifying effect of social relations on the association between depression and mortality was examined in a community-based cohort study. A total of 3,777 randomly selected persons 65 years of age and older in southwest France were followed over a 5-year period from 1988 in the Personnes Agees Quid (PAQUID). At study entry, the prevalence of elevated depressive symptomatology was 12.9% for men and 14.7% for women, and the reported relative isolation was 14.1% for men and 26.0% for women. During a total of 16,984 person-years of follow-up, 849 deaths occurred. Among participants with high levels of depressive symptomatology, the age-adjusted mortality rate ratio was 2.10 (95% confidence interval 1.7-2.7) in men and 1.76 (95% confidence interval 1.4-2.3) in women. When compared with individuals with the most connections, men and women with few social network connections were also at increased risk of mortality: age-adjusted rate ratio = 2.69 (95% confidence interval 1.9-3.8) for men and 1.56 (95% confidence interval 1.0-2.4) for women. Satisfaction with social support had a small but nonsignificant effect on mortality risk. For women, the excess risks due to depressive symptoms and few network connections are observed only in the 65- to 74-year age group, after adjusting for health and health behaviors. Social relations did not significantly modify the depression-mortality associations for either men or women, although the depression-mortality effect was reduced by 12.8% in men. The latter findings do not appear to be compatible with the buffering hypothesis, whereby we would expect social relations to decrease the depression-mortality association. Nonetheless, there are independent effects from these two factors, and older men who are depressed and not socially connected are at increased risk of dying earlier. 相似文献
83.
Theoretical and experimental design considerations for single-mode-crossing switches at the wavelength of 1.32 μm are presented. The dependence of extinction ratio on branch angle for the extended electrodes and the estimation of fabrication tolerances of the crossing channel structure are discussed. It is also shown that crossing channel devices required a precise control of fabrication parameters 相似文献
84.
FN Rehman M Audeh ES Abrams PW Hammond M Kenney TC Boles 《Canadian Metallurgical Quarterly》1999,27(2):649-655
A flexible chemistry for solid phase attachment of oligonucleotides is described. Oligonucleotides bearing 5'-terminal acrylamide modifications efficiently co-polymerize with acrylamide monomers to form thermally stable DNA-containing polyacrylamide co-polymers. Co-polymerization attachment is specific for the terminal acrylamide group. Stable probe-containing layers are easily fabricated on supports bearing exposed acrylic groups, including plastic microtiter plates and silanized glass. Attachment can be accomplished using standard polyacrylamide gel recipes and polymerization techniques. Supports having a high surface density of hybridizable oligonucleotide (approximately 200 fmol/mm2) can be produced. 相似文献
85.
P Chanbancherd AE Brown R Trichavaroj P Tienamporn P Puthakird N Limpairojn TC VanCott MS de Souza 《Canadian Metallurgical Quarterly》1999,37(3):804-806
Dried blood spot (DBS) specimens were assessed as an alternative to plasma for human immunodeficiency virus type 1 (HIV-1) serotyping by V3 loop peptide enzyme immunoassay. Nested PCR capable of distinguishing HIV-1 subtypes B and E was used as the reference standard. Ninety-two percent of DBS samples were typeable as either HIV-1 subtype B or E. Serotype results with DBS and plasma were identical for 254 of 257 specimens. A simple DBS collection method provides a convenient alternative for conducting HIV-1 serotype surveillance while retaining sensitivity and specificity. 相似文献
86.
The dependence of interconnection delays on several different methods has been examined for GaAs-based VLSI. 相似文献
87.
88.
High Strength Low Alloy (HSLA) steel exhibits good ductility at low temperatures down to 77 K in both ferrite-pearlite and
dual-phase structures. The instantaneous strain-rate sensitivity (m) increases with decreasing temperature and reaches a maximum at 100 K. This peak temperature is much lower than that for
plain carbon steels. The post-uniform elongation, which is more sensitively dependent onm, shows only slight increase around 100 K. The effect ofm on the post-uniform elongation is probably mitigated by the increasing dependence ofm on strain rate above 180 K. The uniform elongation, normally associated with the strain hardening characteristics of the
material, also shows some increase around 100 K. Therefore, both strain-hardening and strain-rate hardening are responsible
for the enhanced ductility of HSLA steel around 100 K. 相似文献
89.
90.