首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   601篇
  免费   38篇
电工技术   6篇
综合类   3篇
化学工业   138篇
金属工艺   4篇
机械仪表   9篇
建筑科学   20篇
能源动力   23篇
轻工业   77篇
水利工程   2篇
石油天然气   4篇
无线电   32篇
一般工业技术   153篇
冶金工业   47篇
原子能技术   2篇
自动化技术   119篇
  2024年   2篇
  2023年   9篇
  2022年   24篇
  2021年   26篇
  2020年   13篇
  2019年   24篇
  2018年   27篇
  2017年   27篇
  2016年   24篇
  2015年   16篇
  2014年   30篇
  2013年   48篇
  2012年   48篇
  2011年   67篇
  2010年   25篇
  2009年   29篇
  2008年   38篇
  2007年   29篇
  2006年   27篇
  2005年   15篇
  2004年   15篇
  2003年   8篇
  2002年   12篇
  2001年   4篇
  2000年   7篇
  1999年   8篇
  1998年   7篇
  1997年   8篇
  1995年   5篇
  1994年   1篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1988年   2篇
  1986年   3篇
  1985年   4篇
  1982年   1篇
  1980年   1篇
  1978年   1篇
排序方式: 共有639条查询结果,搜索用时 9 毫秒
91.
92.
93.
Ip injections of epinephrine (20, 40, 80, and 160 μg/kg) and amphetamine (.1, .2, and .4 mg/kg) were administered to 27 male Long-Evans hooded rats with various forms of hepatic denervation. Results suggest that the major component of hepatic metabolic afferent fibers travels from the liver, through the celiac ganglion, and into the esophageal vagal trunks where they ascend to the brain. The anorexic action of amphetamine appears to result from a centrally induced sympathetic action on the liver. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
94.
The specific contact resistivity (ρC) for aluminum (Al), silver (Ag) and indium (In) metallic contacts on CuInS2 thin films was determined from I-V measurements, with the purpose of having the most appropriate ohmic contact for TCO/CdS/CuInS2 solar cells; ρC was measured using the transmission line method (TLM) for the metallic contacts evaporated on CuInS2 thin films deposited by spray pyrolysis with ratios x=[Cu]/[In]=1.0, 1.1, 1.3 and 1.5 in the spray solution. The results show that In contacts have the lowest ρC values for CuInS2 samples grown with x=1.5. The minimum ρC was 0.26 Ω cm2 for the In contacts. This value, although not very low, will allow the fabrication of CuInS2 solar cells with a small series resistance.  相似文献   
95.
The power system capacity adequacy has public good features that cannot be entirely solved by electricity markets. Regulatory intervention is then necessary and established methods have been used to assess adequacy and help regulators to fix this market failure. In regional electricity markets, transmission interconnections play an important role in contributing to adequacy. However, the adequacy problem and related policy are typically considered at a national level. This paper presents a simple model to study how the interconnection capacity interacts with generation adequacy. First results indicate that increasing interconnection capacity between systems improves adequacy up to a certain level; further increases do not procure additional adequacy improvements. Furthermore, besides adequacy improvement, increasing transmission capacity under asymmetric adequacy criteria or national system characteristics could create several concerns about externalities. These results imply that regional coordination of national adequacy policies is essential to internalise adequacy of cross-border effects.  相似文献   
96.
97.
Ethanol tolerance, ATPase activity and the lipid composition of the plasma membrane to study potential relationship among them were examined in five different wine yeast strains. Yeast cells were subjected to ethanol stress (4% v/v). Principal component analysis of the results revealed that the wine yeasts studied can be distinguished in terms of ATPase activity and oleic acid (C18:1), and palmitoleic acid (C16:1), in plasma membrane. Multiple regression analysis was used to identify a potential influence of some components of the plasma membrane on ethanol tolerance and ATPase activity. Based on the results, the ergosterol, oleic acid and palmitoleic acid are highly correlated with ATPase activity and ethanol tolerance. Ethanol tolerance and the ATPase activity of the plasma membrane were correlated at the 96.64% level with the oleic acid and ergosterol in plasma membrane. The Saccharomyces cerevisiae var. capensis flor yeast strain, which exhibited the highest ergosterol concentration in plasma membrane when grown in the presence of 4% v/v ethanol, was found to be the most ethanol-tolerant.  相似文献   
98.
The main objective of this study was to evaluate the risk factors for late embryonic loss (LEL) in supplemented grazing dairy cows. Additional objectives were to assess the incidence of LEL and its association with the reproductive performance of cows. A data set containing productive, reproductive, and health records of 13,551 lactations was used. A retrospective case-control study involving 631 cows with LEL (cases) and 2,524 controls (4 controls per case within each study year) was run. A case of LEL was defined when the embryo had no heartbeat or there was evidence of detached membranes or floating structures including embryo remnants by ultrasonography (US) at 28 to 42 d post-artificial insemination (AI), whereas a non-case was defined as a cow diagnosed with positive pregnancy by US 28 to 42 d post-AI and reconfirmed as pregnant 90 ± 7 d post-AI. Four controls per case were randomly selected from the non-cases with a temporal matching criterion (±3 d around the date of the fecundating AI of the case). Multivariable logistic models were offered with the following predictors: year of LEL (2011 through 2015), season of LEL (summer vs. fall vs. winter vs. spring), parity (1 vs. 2 vs. ≥3), uterine disease (UD), non-uterine disease (NUD), body condition score at parturition, body condition score at 28 to 42 d post-AI (BCS-LEL), days in milk (DIM), and daily milk yield (MY). Statistical significance was set at P < 0.05 and a tendency was set at P ≤ 0.10. We found that 4.7, 22, and 23% of cows had LEL, UD, and NUD, respectively. Cases tended to have higher daily MY than controls (32.5 vs. 31.8 kg); also, cases had much longer calving to pregnancy interval (226 vs. 118 d), lower hazard of pregnancy [hazard ratio = 0.39, 95% confidence interval (CI) = 0.35–0.43], and higher odds for non-pregnancy [odds ratio (OR) = 2.89, 95% CI = 2.37–3.54] than controls. We found that the odds for LEL increased with parity number (OR = 2.48, 95% CI = 1.99–3.08 for parity ≥3) and with BCS-LEL <2.50 (OR = 1.81, 95% CI = 1.33–2.47). Conversely, the odds for LEL decreased with BCS-LEL >3.00 (OR = 0.70, 95% CI = 0.53–0.91). The odds for LEL increased with UD (OR = 1.23, 95% CI = 1.01–1.49), NUD (OR = 1.24, 95% CI = 1.01–1.54), DIM (OR = 1.03, 95% CI = 1.00–1.05), and daily MY (OR = 1.14, 95% CI = 1.04–1.25) in univariable models only. Finally, the odds for LEL were not associated with year, season, DIM, and body condition score at parturition. In conclusion, LEL is associated with extended calving to pregnancy interval, and among its risk factors are parity number and BCS-LEL.  相似文献   
99.
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号