全文获取类型
收费全文 | 2054篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 39篇 |
综合类 | 1篇 |
化学工业 | 176篇 |
金属工艺 | 20篇 |
机械仪表 | 23篇 |
建筑科学 | 24篇 |
矿业工程 | 2篇 |
能源动力 | 13篇 |
轻工业 | 116篇 |
水利工程 | 8篇 |
石油天然气 | 7篇 |
武器工业 | 2篇 |
无线电 | 235篇 |
一般工业技术 | 168篇 |
冶金工业 | 1081篇 |
原子能技术 | 3篇 |
自动化技术 | 161篇 |
出版年
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 22篇 |
2013年 | 37篇 |
2012年 | 36篇 |
2011年 | 32篇 |
2010年 | 15篇 |
2009年 | 29篇 |
2008年 | 40篇 |
2007年 | 53篇 |
2006年 | 38篇 |
2005年 | 44篇 |
2004年 | 32篇 |
2003年 | 51篇 |
2002年 | 42篇 |
2001年 | 43篇 |
2000年 | 33篇 |
1999年 | 65篇 |
1998年 | 360篇 |
1997年 | 205篇 |
1996年 | 129篇 |
1995年 | 100篇 |
1994年 | 79篇 |
1993年 | 77篇 |
1992年 | 32篇 |
1991年 | 31篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 30篇 |
1986年 | 16篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 27篇 |
1978年 | 7篇 |
1977年 | 30篇 |
1976年 | 65篇 |
1975年 | 10篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 5篇 |
排序方式: 共有2079条查询结果,搜索用时 15 毫秒
41.
During the examination of the colon by fibre-optic colonoscopy in 200 consecutive patients it was possible to reach the caecum or suspected lesion in 80% of cases. Careful bowel preparation, sedation and detailed attention to techniques described are necessary for safe and successful performance of this procedure. In 85% of examinations, colonoscopy produced positive results including the definition of uncertain radiological lesions in 45 patients, finding of a cause for rectal bleeding not shown on barium studies in 15 patients, the assessment of inflammatory bowel disease in 28 patients, and the removal of polyps in 40 patients. Important was the finding of a normal colon in 49 cases, which obviated unnecessary surgery. Colonic perforation occurred in 2 patients. The limitations and complications of the procedure must be realised, but it is concluded that the colonoscope provides a valuable and effective means of diagnosis and therapy of lesions in the large bowel. 相似文献
42.
43.
44.
Inasmuch as precise correlations of light- and electronmicroscopy are crucial for understanding biostructure, it seemed necessary to bring together the advantages of the glyoxylic acid (GA) method (for inducing monoamine fluorescence) and electron microscopy. A combined fluorescence and electron microscope method using GA is introduced. The brain is perfused by 2% GA in Krebs-Ringer bicarbonate buffer (pH 7.0) and this solution is followed by 4% paraformaldehyde containing 0.5% glutaraldehyde in Sorensen's phosphate buffer (pH 7.4). Sections are cut by cryostat or by vitratome and incubated in 2% GA in phosphate buffer (pH 7.0). Using fluorescence microscopy, features of interest are sketched and/or photographed. Afterwards, the same or subsequent section is processed for electron microscopy. Since axons of catecholamine-containing neurons (as well as their perikarya and terminals) are visualized by GA, the recommended procedure expands the range of studies concerning monoamine neurons that can now be carried out effectively. 相似文献
45.
46.
47.
48.
Milk response to concentrate supplementation of high producing dairy cows grazing at two pasture allowances 总被引:4,自引:0,他引:4
Twenty multiparous Holstein cows (four ruminally cannulated) in five 4 x 4 Latin squares with 21-d periods were used to study the effect of concentrate supplementation when grazed at two pasture allowances. The four dietary treatments resulted from the combination of two pasture allowance targets (low, 25 vs. high, 40 kg of dry matter/cow per day) and two concentrate supplementation levels (zero vs. 1 kg of concentrate/4 kg of milk). Concentrate supplementation decreased pasture dry matter intake 2.0 kg/d at the low pasture allowance (17.5 vs. 15.5 kg/d) and 4.4 kg/d at the high pasture allowance (20.5 vs. 16.1 kg/d). Substitution rate was lower at the low pasture allowance (0.26 kg pasture/kg concentrate) than at the high pasture allowance (0.55 kg of pasture/kg of concentrate). Total dry matter intake of both supplemented treatments averaged 24.4 kg/d. Milk production of both supplemented treatments averaged 29.8 kg/d, but was increased with higher pasture allowance in the unsupplemented treatments (19.1 vs. 22.2 kg/d). Milk response to concentrate supplementation was 1.36 and 0.96 kg of milk/kg of concentrate for the low and high pasture allowances, respectively. Concentrate supplementation reduced milk fat percentage but increased milk protein percentage. Rumen pH and NH3-N concentration were decreased with concentrate supplementation. Substitution rate was likely related to both negative associative effects in the rumen (reductions in rumen pH, rate of pasture digestion, and NDF digestibility) and reductions in grazing time. The latter was more important, quantitatively explaining at least 80% of the reduction in pasture dry matter intake observed. 相似文献
49.
介绍了RSB-D35自调匀整并条机的特性。与无自调匀整器的双头并条机相比,RSB—D 35并条机生产效率高,纱线质量好,可提高后道加工的经济效益。 相似文献
50.
D S Lough L D Muller R S Kensinger T F Sweeney L C Griel 《Journal of dairy science》1988,71(5):1161-1169
Four early lactation Holstein cows (44 to 105 d postpartum) were used in a 4 X 4 Latin square experiment in a 2 X 2 factorial arrangement of treatments to study effects of added dietary fat and/or bovine somatotropin on performance and metabolism. Treatments were: 1) control diet plus placebo injection; 2) 5% added dietary fat (hydrolyzed blend of animal and vegetable fat) + placebo injection; 3) control diet + 50 IU bovine somatotropin/d; and 4) 5% added dietary fat + 50 IU bovine somatotropin/d. Dietary fat reduced dry matter intake (21.6 vs. 22.7 kg/d) and elevated plasma triglycerides (34.7 vs. 29.2 mg/100 ml). Injection of somatotropin lowered blood urea nitrogen, increased plasma free fatty acids, and increased plasma somatotropin. Milk production, milk fat percent, and 4% FCM production were increased by the injection of somatotropin. Milk protein percent was decreased (3.30 vs. 3.44%) with added fat and tended to be lower with somatotropin. The percentage of short-chain fatty acids (C6 to C14) in milk fat decreased with added fat while the percentage of stearic and oleic acids in milk fat increased. Production responses for fat plus somatotropin and somatotropin treatments were similar. Under the conditions of this study, the addition of dietary fat with injection of somatotropin had little effect on production parameters compared with that found with somatotropin alone. 相似文献