全文获取类型
收费全文 | 1537篇 |
免费 | 65篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 64篇 |
综合类 | 14篇 |
化学工业 | 138篇 |
金属工艺 | 31篇 |
机械仪表 | 47篇 |
建筑科学 | 15篇 |
矿业工程 | 5篇 |
能源动力 | 25篇 |
轻工业 | 26篇 |
水利工程 | 12篇 |
石油天然气 | 12篇 |
武器工业 | 7篇 |
无线电 | 70篇 |
一般工业技术 | 155篇 |
冶金工业 | 831篇 |
原子能技术 | 4篇 |
自动化技术 | 161篇 |
出版年
2023年 | 8篇 |
2022年 | 28篇 |
2021年 | 22篇 |
2020年 | 31篇 |
2019年 | 19篇 |
2018年 | 28篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 33篇 |
2013年 | 59篇 |
2012年 | 53篇 |
2011年 | 38篇 |
2010年 | 31篇 |
2009年 | 35篇 |
2008年 | 28篇 |
2007年 | 36篇 |
2006年 | 18篇 |
2005年 | 23篇 |
2004年 | 20篇 |
2003年 | 14篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 29篇 |
1998年 | 261篇 |
1997年 | 128篇 |
1996年 | 97篇 |
1995年 | 64篇 |
1994年 | 56篇 |
1993年 | 50篇 |
1992年 | 6篇 |
1991年 | 17篇 |
1990年 | 18篇 |
1989年 | 23篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 20篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 27篇 |
1976年 | 68篇 |
1974年 | 4篇 |
1973年 | 2篇 |
排序方式: 共有1617条查询结果,搜索用时 15 毫秒
121.
Disturbed eating behaviour and disturbed body experience are important features for the differential diagnosis of eating disorders from other disorders. Eating disorders occur mainly in young females. The one-year prevalence of anorexia nervosa is 0.4% and that of bulimia nervosa 1.5% among young females. To motivate patients for treatment it is important to discuss physical problems and the high risk of severe complications with them. It is difficult to motivate patients for treatment, because anorexia nervosa patients deny their illness and bulimia nervosa patients are ashamed and hide their disturbed eating behaviour. The treatment of anorexia nervosa consists of two partly overlapping phases: normalizing the eating pattern to improve weight restoration and psychotherapeutic treatment for underlying emotional problems. Family therapy is effective for patients younger than 18 years with a short duration of illness. Cognitive behaviour therapy is the most important form of treatment for bulimia nervosa. 相似文献
122.
EF Hoffenberg P Kozlowski TA Salerno R Deslauriers 《Canadian Metallurgical Quarterly》1996,62(1):135-143
Methylguanidine, guanidinoacetic acid and guanidinosuccinic acid are endogenous substances in body tissues. Extremely high levels of these substances are known to be related to the pathogenesis of epilepsy and renal failure such as uremia. In this study it was demonstrated that methylguanidine, guanidinoacetic acid and guanidinosuccinic acid, and arginine generate hydroxyl radicals in aqueous solution. These findings suggest that a high level of guanidino compounds accumulating near or within cells such as neurons (in an epileptogenic focus) or nephrons (in uremic patients) may cause free radical damage leading to these clinical disorders. Arginine may have a similar role in the pathogenesis of hyperarginemia. 相似文献
123.
MJ Lizak EF Secchi JW Lee S Sato E Kubo Y Akagi PF Kador 《Canadian Metallurgical Quarterly》1998,39(13):2688-2695
PURPOSE: To investigate flux through the polyol pathway in the dog lens by 19F-nuclear magnetic resonance (19F-NMR) spectroscopy, using 3-fluoro-3-deoxy-D-glucose (3-FG) as a substrate. METHODS: 3-FG metabolism was monitored by 19F-NMR analysis. Dog lenses were incubated in Dulbecco's modified Eagle's medium containing 10 mM 3-FG. Enzymatic reductase and dehydrogenase activities were spectrophotometrically determined, whereas the analyses of 3-FG metabolites were conducted by 19F-NMR analysis. Aldose reductase (AR) was immunohistochemically localized in dog lens with antibodies raised against dog kidney AR. RESULTS: 19F-NMR spectra indicate that incubation of purified dog lenses AR with 3-FG results in the formation of 3-fluoro-3-deoxy-D-sorbitol (3-FS) and that incubation of dog liver sorbitol dehydrogenase (SDH) with 3-FS results in the formation of 3-fluoro-3-deoxy-D-fructose (3-FF). This confirms that 3-FG is metabolized to 3-FF by the polyol pathway enzymes. The affinity (Km) of AR for 3-FG is approximately 20-fold better than that for D-glucose, whereas the Km of SDH for 3-FS was fourfold less than for D-sorbitol. 3-FG in cultured dog lenses is metabolized primarily to 3-FS; however, small amounts of 3-FF and 3-fluoro-3-deoxy-D-gluconic acid (3-FGA) are also formed. 3-FS formation was reduced by the AR inhibitor AL 1576, and 3-FF formation was eliminated by the SDH inhibitor CP-166,572. In dog lens epithelial cells cultured with 3-FG, only 3-FS is formed. Similarly, only 3-FS is formed when lens capsule containing primarily epithelial lens contaminated with superficial epithelial cells was incubated in 3-FG. Similar incubation of the remaining cortex resulted primarily in the formation of 3-FS and 3-FGA. This enzymatic distribution was confirmed by spectrophotometric activity analysis and the immunohistochemical localization of AR. CONCLUSIONS: The data confirm that flux through the polyol pathway primarily results in sorbitol accumulation. The absence of fructose and gluconic acid from cultured lens epithelium suggests that the epithelial cells primarily contain AR, whereas differentiated fiber cells also contain SDH and glucose dehydrogenase. 相似文献
124.
125.
The objective of this work was to study the gastric emptying (GE) of liquids in fasted and sucrose-fed rats with toxic hepatitis induced by acetaminophen. The GE of three test meals (saline, glucose and mayonnaise) was evaluated in Wistar rats. For each meal, the animals were divided into two groups (N = 24 each). Group I was fed a sucrose diet throughout the experiment (66 h) while group II was fasted. Forty-two hours after the start of the experiment, each group was divided into two subgroups (N = 12 each). Subgroup A received a placebo and subgroup B was given acetaminophen (1 g/kg). Twenty-four hours later, the GE of the three test meals was assessed and blood samples were collected to measure the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and acetaminophen. In group IB, the mean AST and ALT values were 515 and 263 IU/l, respectively, while for group IIB they were 4014 and 2472 IU/l, respectively. The mean serum acetaminophen levels were higher in group IIB (120 micrograms/ml) than in group IB (87 micrograms/ml). The gastric retention values were significantly higher in group IIB than in group IIA for all three test meals: saline, 51 vs 35%; glucose, 52 vs 38% and mayonnaise, 51 vs 29% (median values). The correlation between gastric retention and AST levels was significant (P < 0.05) for group IIB for the three test meals: r = 0.73, 0.67 and 0.68 for saline, glucose and mayonnaise, respectively. We conclude that GE is altered in rats with hepatic lesions induced by acetaminophen, and that these alterations may be related to the liver cell necrosis caused by the drug. 相似文献
126.
Guo J.-I. Yen J.-C. Pai H.-F. 《Vision, Image and Signal Processing, IEE Proceedings -》2002,149(4):237-243
The authors propose a voice over Internet protocol (VoIP) technique with a new hierarchical data security protection (HDSP) scheme. The proposed HDSP scheme can maintain the voice quality degraded from packet loss and preserve high data security. It performs both the data inter-leaving on the inter-frame of voice for achieving better error recovery of voices suffering from continuous packet loss, and the data encryption on the intra-frame of voice for achieving high data security, which are controlled by a random bit-string sequence generated from a chaotic system. To demonstrate the performance of the proposed HDSP scheme, we have successfully verified and analysed the proposed approach through software simulation and statistical measures on several test voices 相似文献
127.
128.
129.
130.
Role of magnesium in cast aluminium alloy matrix composites 总被引:1,自引:0,他引:1
B. C. Pai Geetha Ramani R. M. Pillai K. G. Satyanarayana 《Journal of Materials Science》1995,30(8):1903-1911
Wetting between the dispersoid and the matrix alloy is the foremost requirement during the preparation of metal matrix composites (MMC) especially with the casting/liquid metal processing technique. The basic principles involved in improving wetting fall under three categories: (i) increasing the surface energies of the solids, (ii) decreasing the surface tension of the liquid matrix alloy, and (iii) decreasing the solid/liquid interfacial energy at the dispersoid matrix interface. The presence of magnesium, a powerful surfactant as well as a reactive element, in the aluminium alloy matrix seems to fulfil all the above three requirements. The role played by magnesium during the synthesis of aluminium alloy matrix composites with dispersoids such as zircon (ZrSiO4), zirconia (ZrO2), titania (TiO2), silica (SiO2), graphite, aluminium oxide (Al2O3) and silicon carbide (SiC), has been analysed. The important role played by the magnesium during the composite synthesis is the scavenging of the oxygen from the dispersoid surface, thus thinning the gas layer and improving wetting and reaction-aided wetting with the surface of the dispersoid. The combinations of magnesium and aluminium seem to have some synergistic effect on wetting. 相似文献