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   38834篇
  免费   2902篇
  国内免费   114篇
电工技术   947篇
综合类   877篇
化学工业   12070篇
金属工艺   740篇
机械仪表   636篇
建筑科学   1324篇
矿业工程   133篇
能源动力   969篇
轻工业   4523篇
水利工程   266篇
石油天然气   162篇
武器工业   7篇
无线电   2326篇
一般工业技术   5749篇
冶金工业   6246篇
原子能技术   244篇
自动化技术   4631篇
  2023年   696篇
  2022年   827篇
  2021年   1380篇
  2020年   1111篇
  2019年   1071篇
  2018年   1157篇
  2017年   1103篇
  2016年   1219篇
  2015年   1140篇
  2014年   1478篇
  2013年   2213篇
  2012年   1672篇
  2011年   1895篇
  2010年   1782篇
  2009年   1887篇
  2008年   1379篇
  2007年   1198篇
  2006年   914篇
  2005年   993篇
  2004年   1107篇
  2003年   962篇
  2002年   973篇
  2001年   775篇
  2000年   560篇
  1999年   582篇
  1998年   2085篇
  1997年   1363篇
  1996年   986篇
  1995年   687篇
  1994年   542篇
  1993年   659篇
  1992年   301篇
  1991年   355篇
  1990年   311篇
  1989年   279篇
  1988年   275篇
  1987年   251篇
  1986年   265篇
  1985年   264篇
  1984年   209篇
  1983年   198篇
  1982年   191篇
  1981年   225篇
  1980年   197篇
  1979年   156篇
  1978年   110篇
  1977年   199篇
  1976年   273篇
  1975年   145篇
  1973年   182篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
SUMMARY-The development of food mixtures containing vegetable protein concentrates, minerals, and vitamins represents an important approach to the problem of protein-calorie malnutrition of preschool children in many parts of the world. In Brazil, soy flour is the most readily available good-quality protein for this purpose. Protein efficiency-ratio studies in rats demonstrated that soy flour with a PER value of 1.99 was available in large quantities. Accordingly, a formula containing 19.50% soy flour, 4.50% nonfat milk powder, 32.28% corn starch, 39.00% sucrose, and 4.72% vitamins and minerals was thoroughly tested as an infant food. The PER value of the protein in rats was 2.31. Amino acid assay demonstrated that the protein compared favorably with the essential amino acid pattern of the FAO/WHO reference protein (FAO/WHO, 196.5) except for methionine-cystine, The formula was well accepted and tolerated by children and adults. Average nitrogen absorption and retention of the formula as the sole food of malnourished children were 72.68 and 23.82%; values for milk protein were 80.17 and 30.13%. Average nitrogen absorption and retention were 63.4 and 22.0% when the formula provided one-half (15 g) of the daily protein for normal children consuming a typical diet of the region, comparing favorably with values of 69.3 and 21.3% for milk protein.  相似文献   
994.
The commenter corrects and comments on a few results reported in the paper by H. Takagi (see ibid., vol.COM-35, p.248-50, Feb. 1987). In addition, it is shown how these results can be utilized to give the average message delay for token passing protocols where each network station is allowed to send a maximum of one fixed-length packet per cycle (known as chaining discipline)  相似文献   
995.
The performance of polymer solar cells (PSC) strongly depends on the 3D morphological organization of the donor and acceptor compounds within the bulk heterojunction active layer. The technique of electron tomography is a powerful tool for studying 3D morphology of the layers composed of poly(3‐hexylthiophene) (P3HT) and a fullerene derivative ([6,6]‐phenyl‐C61‐butyric acid methyl ester; PCBM), especially to quantify the amount and distribution of fibrillar P3HT nanocrystals throughout the volume of the active layer. In this study, electron tomography is used to characterize P3HT/PCBM layers with different blend compositions, both before and after thermal annealing. The power conversion efficiency of the corresponding PSCs is strongly dependent on the overall crystallinity of P3HT and the way P3HT crystals are distributed throughout the thickness of the active layer.  相似文献   
996.
997.
A primary mechanistic hypothesis by which ambient air particles have a significant negative impact on human health is via the induction of pulmonary inflammatory responses mediated through the generation of reactive oxygen species (ROS). Development of a biosensor for the assessment of particulate ROS activity would be a significant advance in air pollution monitoring. The objective of this study was to evaluate whether air particulates interact directly with protective enzymes involved in oxidative stress responses. We performed enzyme activity assays on four enzymes involved in oxidative stress responses (Cu/Zn superoxide dismutase, Mn superoxide dismutase, glutathione peroxidase, and glutathione reductase) in the presence of particles of varying toxicities and found distinctive inhibition patterns. On the basis of these findings, we suggest a strategy for an enzyme bioassay that could be used to assess the potential of particles to generate ROS-induced responses.  相似文献   
998.
999.
The science space in a state school in Natal city was built using a composite consisting of gypsum, EPS (expanded polystyrene), shredded tire, cement and water. Mechanical and thermal resistances were evaluated. Inside the blocks, three types of fillings (EPS plates, aluminum cans and 500 mL bottles of mineral water) were placed in order to obtain a walls with higher thermal resistance, but also to give it an ecologically correct order, considering that both the tire and the EPS occupy a large space in landfills and require years to be degraded when released into the environment. Compression tests were conducted according to the rules. The experiments demonstrated that the temperature difference between the internal and external surfaces on the walls reached levels above 12.0 ℃. It was also demonstrated that the proposed composite has adequate mechanical strength to be used for sealing walls. The proposed use of the composite can contribute to reduce the significant housing deficit of Brazil, producing popular houses at low cost and with little time to work.  相似文献   
1000.
Conventional chemotherapy (CT) is associated with severe side effects and inducible resistance, making it difficult to meet clinical requirements, forcing the development of new multifunctional prodrugs for precision medicine. In recent decades, researchers and clinicians have focused on developing of multifunctional chemotherapeutic prodrugs with tumor-targeting capability, activatable and traceable chemotherapeutic activity, as a powerful tool to improve theranostic outcomes in cancer treatment. The conjugates of near-infrared (NIR) organic fluorophores and chemotherapy reagents create an exciting avenue for real-time monitoring of drug delivery and distribution, as well as the combination of chemotherapy and photodynamic therapy (PDT). Therefore, there are great opportunities for researchers to conceive and exploit multifunctional prodrugs that can visualize chemo-drugs release and tumor treatment in vivo. In this review, the design strategy and the recent progress of multifunctional organic chemotherapeutic prodrugs for activating NIR fluorescence imaging-guided therapy are described and discussed in detail. Finally, the prospects and challenges of multifunctional chemotherapeutic prodrugs for NIR fluorescence imaging-guided therapy are provided.  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