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   1253篇
  免费   26篇
电工技术   104篇
综合类   2篇
化学工业   168篇
金属工艺   35篇
机械仪表   26篇
建筑科学   27篇
能源动力   31篇
轻工业   107篇
水利工程   1篇
石油天然气   6篇
无线电   147篇
一般工业技术   168篇
冶金工业   308篇
原子能技术   24篇
自动化技术   125篇
  2023年   4篇
  2021年   14篇
  2020年   5篇
  2019年   8篇
  2018年   20篇
  2017年   11篇
  2016年   23篇
  2015年   11篇
  2014年   27篇
  2013年   54篇
  2012年   47篇
  2011年   37篇
  2010年   48篇
  2009年   37篇
  2008年   47篇
  2007年   40篇
  2006年   40篇
  2005年   42篇
  2004年   33篇
  2003年   37篇
  2002年   22篇
  2001年   29篇
  2000年   29篇
  1999年   40篇
  1998年   122篇
  1997年   76篇
  1996年   38篇
  1995年   46篇
  1994年   31篇
  1993年   24篇
  1992年   14篇
  1991年   14篇
  1990年   9篇
  1989年   21篇
  1988年   15篇
  1987年   7篇
  1986年   14篇
  1985年   11篇
  1984年   13篇
  1983年   16篇
  1982年   15篇
  1981年   9篇
  1980年   16篇
  1979年   8篇
  1978年   7篇
  1977年   9篇
  1976年   13篇
  1975年   5篇
  1974年   5篇
  1970年   4篇
排序方式: 共有1279条查询结果,搜索用时 109 毫秒
1.
2.
Recent growth of renewable energy generations with natural variability, such as photovoltaic generation and wind turbine generation, would make the demand and supply control in a whole power system more difficult, and therefore, alternatives for demand and supply regulation resources would be required. The authors focus on cogeneration system (CGS) as one of regulation resources. In order to procure adequate volume of regulation capability, an aggregator coordinates a number of CGSs efficiently and flexibly considering the wide variety of electricity/thermal demands of CGS owners. This paper proposes a novel optimal operation strategy of CGS coordinated by the aggregator considering the energy balance and operation cost of individual CGS owner. This paper also demonstrates the availability of CGSs for regulation capability by numerical case studies in which the actual consumption profile is employed.  相似文献   
3.
The present study investigated whether delaying the first feeding of colostrum affected ileum and colon mucosa-associated microbiota in calves. Twenty-seven male Holstein calves were randomly assigned to 1 of 3 groups, fed colostrum at 45 min, 6 h, and 12 h after birth, respectively. Ileum and colon mucosa were collected at 51 h after birth, and their associated microbial profiles were assessed using amplicon sequencing. Both ileum and colon mucosa-associated microbiota were predominated by genus Escherichia-Shigella. The negative correlation between the molar proportion of short-chain fatty acids (SCFA) and ileum mucosa-associated opportunistic pathogens, and the positive correlation between the molar proportion of SCFA and colon mucosa-associated beneficial bacteria, suggest that SCFA might play an important role in maintaining the gut health of 2-d-old calves. A higher relative abundance of ileum mucosa-associated Enterococcus and Streptococcus was detected when the first colostrum feeding was delayed for 12 h. The relative abundance of colon mucosa-associated Lactobacillus tended to be lower in calves fed colostrum 12 h than those under the other 2 treatments, whereas that of Faecalibacterium tended to be lower in calves fed colostrum immediately after birth than those fed colostrum 6 and 12 h after birth, respectively. Our findings suggest that delayed first colostrum feeding affects the establishment of ileum and colon mucosa-associated bacteria, which may have long-term effects on gut health of calves.  相似文献   
4.
Numerous phytoplankton species in Lake Kasumigaura were shown to comprise the Spring bloom in 1980. The predominant phytoplankton species that appeared during the Spring bloom belonged to 28 genera. A few species among them increased at any time to form a phytoplankton pulse, but the few species of phytoplankters that comprised a phytoplankton pulse did not exclude completely other phytoplankters. During the Spring bloom, one pulse was replaced by another pulse composed of a new grouping of different species. Throughout these replacements by natural selection in the bloom were numerous other species by phytoplankters at levels of abundance somewhat less than those which formed phytoplankton pulse.  相似文献   
5.
6.
7.
We carried out a study of neutrino detection at the experimental fast reactor JOYO using a 0.76 tons gadolinium loaded liquid scintillator detector. The detector was set up on the ground level at 24.3 m from the JOYO reactor core of 140 MW thermal power. The measured neutrino event rate from reactor on-off comparison was 1.11±1.24(stat.)±0.46(syst.) events/day. Although the statistical significance of the measurement was not enough, backgrounds in such a compact detector at the ground level were studied in detail and MC simulations were found to describe the data well. A study for improvement of the detector for future such experiments is also shown.  相似文献   
8.
Obesity-related metabolic abnormalities, including adipokine imbalance and chronic inflammation, are involved in liver carcinogenesis. Chemerin, a novel adipokine, plays a critical role in adipogenesis, energy metabolism, and inflammation. We evaluated the impact of serum chemerin levels on liver functional reserves in hepatocellular carcinoma (HCC) patients and on the recurrence and prognosis of HCC. This study included 44 patients with any stage of HCC who underwent curative treatment at Gifu Municipal Hospital (Gifu, Japan) between 2006 and 2007. Recurrence-free survival and overall survival were estimated using the Kaplan-Meier method. Serum albumin levels (Pearson’s correlation coefficient; r = 0.3110, p = 0.0399), platelet counts (r = 0.4159, p = 0.0050), and prothrombin times (r = 0.3775, p = 0.0115) were significantly correlated with serum chemerin levels in patients with HCC, and they were inversely correlated with Child-Pugh scores (r = −0.3732, p = 0.0126), serum alanine aminotransferase levels (r = −0.3864, p = 0.0105), and total bilirubin levels (r = −0.4023, p = 0.0068). Among these variables, a multiple comparison test identified that platelet counts and total bilirubin levels were associated with serum chemerin levels (p < 0.0083). No significant correlation was found between serum chemerin levels and recurrence-free survival (p = 0.3691) or overall survival (p = 0.7916). In HCC patients, serum chemerin concentrations were correlated with liver functional reserves and platelet counts, but not with recurrence or prognosis.  相似文献   
9.
The boron concentration profiles around prior austenite grain boundaries in Fe-0.05C-0.5Mo-0.001B (mass pct) are examined using aberration-corrected STEM-EELS. In order to obtain the precise distribution of boron around the boundaries, tilt series measurements with thin specimens (<30 nm) are performed and the EEL spectra are analyzed by principal component analysis (PCA) and multivariate curve resolution (MCR). The boron concentration profile changes with the cooling rate from the solid solution temperature. The concentration at grain boundaries is maximized at a medium rate (30 °C/s), where the concentration reaches 8 at. pct, and it decreases at a larger (250 °C/s) or smaller (5 °C/s) rate. On the other hand, the boron distribution becomes wider as the cooling rate becomes smaller. The current results suggest that the boron segregation in the alloy is formed by the “non-equilibrium segregation mechanism.”  相似文献   
10.
Polypeptide hydrogels were prepared by cross-linking of hydrophobically-modified poly[N5-(2-hydroxyethyl) l-glutamine] having alkyl side chains –CnH2n+1. Chain length of the alkyl group was n = 8, 16, and 18, and their mole fractions in the polypeptide were varied in the range of 0.05–0.16. Shape memory ability of the prepared polypeptide hydrogels was investigated. After deformation at 60 °C, the hydrogel was cooled in order to fix the temporary deformed shape. It was found that crystallization of the alkyl side chains did not occur, and the fixation ability of the hydrogel at 0 °C was low. In the subsequent heating process, the deformed temporary shape spontaneously recovered to the original shape gradually with increasing temperature, in other words, the shape recovery ratio varied with depending on the recovery temperature. From these observations, it was proposed that the shape fixation of the polypeptide hydrogel was achieved by strong segregation of the hydrophobic alkyl chains at low temperature, and the shape recovery of the deformed hydrogel was accompanied by the gradual decrease of the segregation strength with the temperature increase.  相似文献   
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