全文获取类型
收费全文 | 1443篇 |
免费 | 8篇 |
专业分类
电工技术 | 4篇 |
综合类 | 1篇 |
化学工业 | 125篇 |
金属工艺 | 4篇 |
机械仪表 | 17篇 |
建筑科学 | 8篇 |
矿业工程 | 2篇 |
能源动力 | 4篇 |
轻工业 | 36篇 |
水利工程 | 1篇 |
石油天然气 | 5篇 |
武器工业 | 1篇 |
无线电 | 66篇 |
一般工业技术 | 94篇 |
冶金工业 | 1022篇 |
原子能技术 | 5篇 |
自动化技术 | 56篇 |
出版年
2021年 | 4篇 |
2018年 | 4篇 |
2016年 | 8篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 11篇 |
2011年 | 19篇 |
2010年 | 7篇 |
2009年 | 12篇 |
2008年 | 18篇 |
2007年 | 14篇 |
2006年 | 17篇 |
2005年 | 20篇 |
2004年 | 13篇 |
2003年 | 20篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 34篇 |
1998年 | 296篇 |
1997年 | 166篇 |
1996年 | 127篇 |
1995年 | 76篇 |
1994年 | 52篇 |
1993年 | 53篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 20篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1978年 | 9篇 |
1977年 | 38篇 |
1976年 | 71篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1971年 | 4篇 |
1968年 | 5篇 |
1959年 | 3篇 |
1955年 | 5篇 |
排序方式: 共有1451条查询结果,搜索用时 15 毫秒
1.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
2.
AJ Dunipace EJ Brizendine ME Wilson W Zhang BP Katz GK Stookey 《Canadian Metallurgical Quarterly》1998,128(8):1392-1400
On the basis of observations that endemic fluorosis occurs more often in malnourished populations, a series of studies tested the hypothesis that deficient dietary intake of calcium, protein or energy affects fluoride metabolism so that the margin of safe fluoride exposure may be reduced. The objective of the investigation was to determine whether changes in fluoride metabolism in nutritionally deficient rats resulted in manifestation of any extraskeletal toxic fluoride effects not observed in healthy animals. This investigation included two studies, one that monitored the effect of calcium deficiency on the effects of chronic fluoride exposure, and a second study that observed fluoride effects in rats that were deficient either in protein or in energy and total nutrient intake. Control and experimental rats received drinking water containing 0, 0.26 (5), 0.79 (15) or 2.63 (50) mmol fluoride/L (mg/L) for 16 or 48 wk. Control rats were fed optimal diets and experimental rats were fed diets deficient in calcium (Study 1) or protein (Study 2). An additional group of experimental rats (Study 2) was provided with a restricted amount of diet; thus these rats were deficient in energy and total nutrient intake. The intake, excretion and retention of fluoride were monitored; after the rats were killed, tissue fluoride levels and biochemical markers of tissue function were analyzed. Bone marrow cells were harvested from some of the rats, after 48 wk of treatment, for determining the frequency of sister chromatid exchange, a marker of genetic damage. Although there were significant differences among fluoride treatment groups in fluoride excretion and retention that resulted in significantly greater fluoride levels in tissues of the experimental rats, we were unable to detect any harmful, extraskeletal biochemical, physiologic or genetic effects of fluoride in the nutritionally deficient rats. 相似文献
3.
4.
PURPOSE: The etiology of voiding dysfunction was determined in men after a cerebrovascular accident who were at risk for obstructive uropathy to evaluate whether the cause of voiding dysfunction could be predicted by the type (obstructive or irritative) or onset of symptoms. MATERIALS AND METHODS: We evaluated 38 men with complaints of voiding dysfunction following a cerebrovascular accident. All patients were of the age when bladder outlet obstruction secondary to benign prostatic hyperplasia would otherwise be prevalent. After a comprehensive history and physical examination, all patients underwent multichannel urodynamic studies at a medium fill rate (20 to 50 ml. per minute). Findings were classified by the Abrams-Griffiths nomogram as obstruction, no obstruction or equivocal. RESULTS: Mean patient age was 70 years (range 54 to 87). Patients were grouped according to the presenting voiding complaints (purely irritative in 42%, purely obstructive in 34% or mixed in 24%). In 34 patients (89%) the onset of symptoms paralleled the occurrence of the cerebrovascular accident. Detrusor hyperreflexia was noted in 82% of the patients. There was no statistically significant difference in the occurrence of detrusor hyperreflexia among the 3 symptom groups (Fisher's exact test). Pressure-flow analysis clearly showed obstruction in 24 patients (63%), no obstruction in 9 (24%) and equivocal results in 5 (13%) according to the nomogram. There was no statistically significant difference in the incidence of obstruction among the 3 symptom groups (Fisher's exact test). CONCLUSIONS: Presenting symptoms did not predict the urodynamic findings of bladder outlet obstruction or detrusor hyperreflexia. The significant incidence of onset of symptoms after stroke suggests that the cerebrovascular accident induced voiding dysfunction in the face of preexisting bladder outlet obstruction may exacerbate the symptoms of the latter condition or vice versa. 相似文献
5.
S Cohrs G Herrendorf J Wiltfang A Rodenbeck J Kinkelbur L Adler G Hajak 《Canadian Metallurgical Quarterly》1996,146(13-14):366-368
10 patients with obstructive sleep apnea syndrome (OSAS) have been treated with the new surgical procedure functional palatoraphy and modified genioplasty. 5 months after surgery 7 patients with an apnea hypopnea index under 10 were cured. Three therapy refractory patients were all overweight with a body mass index of more than 29 kg/m2. Excessively overweight patients should therefore not be operated. Following the selection criteria we introduced an effective new treatment method for OSAS. 相似文献
6.
General formulae are derived for the reflection of insolation from finite plane surfaces unto tilted sensors. These results are reduced to various special cases which are compared to known results when possible. Both circular and rectangular geometries are considered. 相似文献
7.
8.
L Fr?yland DK Asiedu H Vaagenes A Garras O Lie GK Totland RK Berge 《Canadian Metallurgical Quarterly》1995,36(12):2529-2540
The mechanism behind the hypolipidemic effect of tetradecylthioacetic acid (CMTTD, a non-beta-oxidizable 3-thia fatty acid) was studied in hamsters fed a high cholesterol diet (2%), which resulted in hyperlipidemia. Treating hyperlipidemic hamsters with CMTTD resulted in a progressive hypocholesterolemic and hypotriacylglycerolemic effect. Decreased plasma cholesterol was followed by a 39% and 30% reduction in VLDL-cholesterol and LDL-cholesterol, respectively. In contrast, the HDL-cholesterol content was not affected, thus decreasing the VLDL-cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol ratios. 3-Hydroxy-3-methylglutaryl- (HMG) CoA reductase activity and its mRNA level were unchanged after CMTTD administration. Also, the LDL receptor and LDL receptor-related protein (LRP-4) mRNAs were unchanged. The decrease in plasma triacylglycerol was accompanied by a 45% and 56% reduction in VLDL-triacylglycerol and LDL-triacylglycerol, respectively. The hypolipidemic effect of CMTTD was followed by a 1.4-fold increase in mitochondrial fatty acid oxidation and a 2.3-fold increase in peroxisomal fatty acid oxidation. CMTTD treatment led to an accumulation of dihomo-gamma-linolenic acid (20:3n-6) in liver, plasma, very low density lipoprotein, and heart. Noteworthy, CMTTD accumulated more in the heart, plasma, and VLDL particles compared to the liver, and in the VLDL particle alpha-linolenic acid (18:3n-3) decreased whereas eicosatetraenoic acid (20:4n-3) increased. In addition, linoleic acid (18:2n-6) and the total amount of polyunsaturated fatty acids decreased, the latter mainly due to a decrease in n-6 fatty acids. The present data show that CMTTD was detected in plasma and incorporated into VLDL, liver, and heart. The relative incorporation (mol%) of CMTTD was heart > VLDL > liver. In conclusion, CMTTD causes both a hypocholesterolemic and hypotriacylglycerolemic effect in hyperlipidemic hamsters. 相似文献
9.
RA Reinhardt MP Masada GK Johnson LM DuBois GJ Seymour AC Allison 《Canadian Metallurgical Quarterly》1993,20(7):514-519
Interleukin (IL)-1 alpha and beta are cytokines which can mediate inflammatory, bone resorbing, and reparative effects in the periodontium, but few longitudinal data exist exploring their role following periodontal therapy. This study examined gingival crevicular fluid (GCF) concentrations of IL-1 alpha and IL-1 beta at sites with shallow sulci (SS) or inflamed moderate/advanced pockets (M/AP) before and 6 months after treatment with closed scaling/root planing (SC/RP) or papillary flap debridement (PFD), all in the same subject (n = 14 patients). No significant differences were noted in IL-1 alpha or beta concentrations (determined with two-site enzyme-linked immunosorbent assays) between SS and M/AP sites at baseline. While both therapies improved clinical parameters of periodontal disease, IL-1 alpha concentration increased significantly (p < 0.05) in M/AP-PFD sites 6 months after treatment, but were unchanged in other groups. IL-1 beta concentrations were numerically lower after therapy, except for a significant increase (p < 0.05) in M/AP-PFD sites. These data suggest that surgical wound healing in an inflamed, plaque-infected site (M/AP-PFD) results in prolonged production of IL-1, which may be a reflection of the extent of tissue trauma and delayed wound healing. In spite of increased IL-1 levels, these sites demonstrated significant short-term improvement in clinical attachment level (+ 1.8 mm, p < or = 0.001) postoperatively. 相似文献
10.
M Adler Z Girsh-Solomonovich B Raikhlin-Eisenkraft 《Canadian Metallurgical Quarterly》1993,124(10):616-8, 667
A 15-year-old girl took 3 g of isoniazid (15 tablets) in a suicide attempt and was brought unconscious to the emergency room. She was in respiratory failure, with seizures that could not be stopped with diazepam. Severe metabolic acidosis with normal serum lactate developed (pH 6.85), but did not improve after infusion of bicarbonate. Intravenous administration of pyridoxine led to prompt cessation of the seizures and to gradual improvement of acid-base status. She recovered consciousness after several hours and was discharged a week later. 相似文献