全文获取类型
收费全文 | 6207篇 |
免费 | 628篇 |
国内免费 | 471篇 |
专业分类
电工技术 | 543篇 |
综合类 | 585篇 |
化学工业 | 648篇 |
金属工艺 | 382篇 |
机械仪表 | 518篇 |
建筑科学 | 440篇 |
矿业工程 | 163篇 |
能源动力 | 108篇 |
轻工业 | 824篇 |
水利工程 | 259篇 |
石油天然气 | 121篇 |
武器工业 | 62篇 |
无线电 | 560篇 |
一般工业技术 | 460篇 |
冶金工业 | 685篇 |
原子能技术 | 86篇 |
自动化技术 | 862篇 |
出版年
2024年 | 44篇 |
2023年 | 108篇 |
2022年 | 197篇 |
2021年 | 332篇 |
2020年 | 208篇 |
2019年 | 123篇 |
2018年 | 148篇 |
2017年 | 167篇 |
2016年 | 148篇 |
2015年 | 277篇 |
2014年 | 346篇 |
2013年 | 405篇 |
2012年 | 453篇 |
2011年 | 458篇 |
2010年 | 482篇 |
2009年 | 469篇 |
2008年 | 447篇 |
2007年 | 448篇 |
2006年 | 407篇 |
2005年 | 317篇 |
2004年 | 217篇 |
2003年 | 135篇 |
2002年 | 120篇 |
2001年 | 134篇 |
2000年 | 107篇 |
1999年 | 49篇 |
1998年 | 142篇 |
1997年 | 99篇 |
1996年 | 57篇 |
1995年 | 36篇 |
1994年 | 25篇 |
1993年 | 33篇 |
1992年 | 11篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 9篇 |
1976年 | 24篇 |
1975年 | 2篇 |
1965年 | 2篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有7306条查询结果,搜索用时 31 毫秒
21.
22.
LA Cole E Acuna T Isozaki GE Palomaki RO Bahado-Singh MO Mahoney 《Canadian Metallurgical Quarterly》1997,17(12):1125-1133
Recent articles by Cuckle et al., Canick et al., and Isozaki et al. have evaluated urine beta-core fragment as a screening test for Down syndrome in second-trimester pregnancies. They found over four-fold elevation of beta-core fragment levels in Down syndrome pregnancies, and between 62 and 88 per cent detection of this trisomy at a 5 per cent false-positive rate. Urine beta-core fragment may be a superior screening test for Down syndrome pregnancies. In the present study, urinary total oestriol has been evaluated as a marker to use in combination with beta-core fragment in screening for Down syndrome pregnancies. The two markers were evaluated separately in relation to the urine creatinine concentration. To amplify screening performance, we evaluated the ratio of beta-core fragment to total oestriol levels (creatinine-independent). beta-core fragment and total oestriol levels were determined (normalized to creatinine, ng/mg creatinine) in urine samples from 480 unaffected and 12 Down syndrome pregnancies, collected consecutively at a single prenatal diagnosis centre. The median beta-core fragment level in Down syndrome cases was 4.5 MOM. Fifty-eight per cent of Down syndrome cases had beta-core fragment levels exceeding the 95th centile of unaffected pregnancies. The median total oestriol level in Down syndrome cases was 0.33 MOM. Forty-two per cent of Down syndrome cases had total oestriol levels exceeding the 95th centile of unaffected pregnancies. We investigated the ratio of the two determinants (beta-core fragment, ng/ml divided by total oestriol, ng/ml) in our sample set. The median beta-core fragment:total oestriol ratio in Down syndrome cases was 13 MOM. Seventy-five per cent of Down syndrome cases had a ratio exceeding the 95th and the 99.5th centile of unaffected pregnancies. Total oestriol complements beta-core fragment in urine screening for Down syndrome pregnancies. A test measuring the ratio of the two urine determinants may be a significant improvement over current serum methods for detecting Down syndrome. 相似文献
23.
24.
25.
26.
MO Makinde 《Canadian Metallurgical Quarterly》1993,40(8):582-586
Dilution procedures using tritiated water and Evans blue dye (T 1824) were applied to estimate total body water and plasma volume in small ruminants, pigs and cockerels during the two different seasons in Zimbabwe. The amounts of total body water (TBW) obtained were between 60% to 85% of the body weight in sheep and goats, 40% to 60% in pigs and 63% to 75% in cockerels. TBW values were significantly higher (P < 0.05) in the small ruminants than in pigs and observed age differences were significant (P < 0.05) in the small ruminants. There were significant (P < 0.05) seasonal differences in the total body water mean values but nonsignificant (P > 0.05) differences in the plasma volume mean values for the domestic species investigated. 相似文献
27.
28.
The research was conducted to evaluate the effects of cellulose and polyester fibers on the properties of porous asphalt mixes, using the tests of draindown, abrasion, volumetric properties, rutting, and moisture damage. Images of scanning electron microscopy and X-ray computerized tomography were adopted to identify the microstructure of the fiber and inner stone skeleton of porous asphalt. The influence of rutting parameter (G*/sin δ) of asphalt modified by different fibers on the rutting resistance of the mixes was investigated. Based upon MOHR-COULOMB theory, the cohesion and the angle of internal friction of the mixes were derived from both indirect tension and unconfined compression strength. The experimental results indicate that fibers mainly stabilize asphalt binder and thicken asphalt film around aggregates. Furthermore, they result in the improved mechanical strength of porous asphalt mixes at high temperature slightly. From comparison analysis, cellulose fibers appear to perform better than polyester fibers in porous asphalt mixes. 相似文献
29.
RA Bayoumi MS Nur-E-Kamal M Tadayyon KK Mohamed BH Mahboob MM Qureshi MS Lakhani MO Awaad J Kaeda TJ Vulliamy L Luzzatto 《Canadian Metallurgical Quarterly》1996,46(3):136-141
Operational skills involved in controlling a motor vehicle were measured in two groups of very healthy elderly drivers and a young control group to test the hypothesis that there are age-related declines in operational performance that may influence driver safety. An actual behind-the-wheel, standardized road test was employed using a motor vehicle equipped with sensors to record speed, braking activity, and lane position, as well as direction and magnitude of front-wheel and eye-movement excursions. The data from these sensors were used as dependent measures of operational performance. Older drivers made fewer steering and eye-movement excursions and drifted across the center line more frequently than the young control group. Younger drivers drove significantly faster and executed more braking applications than did their older counterparts. The motor-vehicle operational performance of older healthy drivers was related to visual-spatial attentional declines and the useful field of vision associated with the normal aging process. 相似文献
30.