首页 | 官方网站   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   486441篇
  免费   23909篇
  国内免费   11222篇
工业技术   521572篇
  2023年   4760篇
  2022年   7387篇
  2021年   12666篇
  2020年   9787篇
  2019年   8973篇
  2018年   11633篇
  2017年   12731篇
  2016年   11838篇
  2015年   13262篇
  2014年   17413篇
  2013年   25011篇
  2012年   23355篇
  2011年   26513篇
  2010年   22536篇
  2009年   22308篇
  2008年   21977篇
  2007年   21488篇
  2006年   21469篇
  2005年   19209篇
  2004年   13621篇
  2003年   12410篇
  2002年   11463篇
  2001年   10693篇
  2000年   10918篇
  1999年   12364篇
  1998年   16666篇
  1997年   12683篇
  1996年   10651篇
  1995年   8542篇
  1994年   7274篇
  1993年   6404篇
  1992年   5050篇
  1991年   4536篇
  1990年   4017篇
  1989年   3721篇
  1988年   3571篇
  1987年   2961篇
  1986年   2903篇
  1985年   3065篇
  1984年   2833篇
  1983年   2636篇
  1982年   2407篇
  1981年   2335篇
  1980年   2399篇
  1979年   2370篇
  1978年   2367篇
  1977年   2478篇
  1976年   2871篇
  1975年   2182篇
  1973年   2155篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
This study aimed to determine the main bioactive components of Cornus officinalis vinegar (COV) and assess the effects of COV on the body weight (BW) and hepatic steatosis in a nonalcoholic fatty liver disease (NAFLD) mouse model. Seven-week-old KM female mice were divided into five treatment groups: (1) Normal control (NC) group, (2) high fat diet (HFD) group, (3) low concentration treatment group (3.5% COV), (4) medium concentration treatment group (5.0% COV), and (5) high concentration treatment group (6.5% COV). Mice in the NC group were fed with a normal chow diet, and those in the other four groups were fed with a HFD known for causing obesity for 10 weeks. Then, mice in the three COV treatment groups were orally administered with COV once a day for 6 weeks. Results showed that the contents of loganin and morroniside in COV reached 16.82 and 51.17 µg/ml, respectively, and COV also contained multiple organic acids. COV significantly reduced BW, abdominal fat weight, liver weight, and the levels of glucose, triglyceride, and low-density lipoprotein cholesterol of serum and increased the levels of high-density lipoprotein cholesterol of serum (< 0.05). COV also improved the liver function and anti-oxidant activity of liver (< 0.05). COV treatments increased the interleukin-10 expression and reduced the tumor necrosis factor-α expression in the liver tissue of NAFLD mice (< 0.05). Histopathological observation revealed that COV suppressed hepatic lipid accumulation and steatosis. The results suggest that COV may contribute to the alleviation of NAFLD and obesity.  相似文献   
42.
Zhang  Jiawei  Li  Chen  Rahaman  Md Mamunur  Yao  Yudong  Ma  Pingli  Zhang  Jinghua  Zhao  Xin  Jiang  Tao  Grzegorzek  Marcin 《Artificial Intelligence Review》2022,55(4):2875-2944

Microorganisms such as bacteria and fungi play essential roles in many application fields, like biotechnique, medical technique and industrial domain. Microorganism counting techniques are crucial in microorganism analysis, helping biologists and related researchers quantitatively analyze the microorganisms and calculate their characteristics, such as biomass concentration and biological activity. However, traditional microorganism manual counting methods, such as plate counting method, hemocytometry and turbidimetry, are time-consuming, subjective and need complex operations, which are difficult to be applied in large-scale applications. In order to improve this situation, image analysis is applied for microorganism counting since the 1980s, which consists of digital image processing, image segmentation, image classification and suchlike. Image analysis-based microorganism counting methods are efficient comparing with traditional plate counting methods. In this article, we have studied the development of microorganism counting methods using digital image analysis. Firstly, the microorganisms are grouped as bacteria and other microorganisms. Then, the related articles are summarized based on image segmentation methods. Each part of the article is reviewed by methodologies. Moreover, commonly used image processing methods for microorganism counting are summarized and analyzed to find common technological points. More than 144 papers are outlined in this article. In conclusion, this paper provides new ideas for the future development trend of microorganism counting, and provides systematic suggestions for implementing integrated microorganism counting systems in the future. Researchers in other fields can refer to the techniques analyzed in this paper.

  相似文献   
43.
MgAl2O4 transparent ceramics were shaped by a commonly used polyacrylic acid (PAA), which acted as both dispersant and gelling agent. The spinel slurries were prepared by ball-milling MgAl2O4 powder, PAA, and water in an attrition mill. The gelling of slurries happened at room temperature in air atmosphere without any other organic additive. The gelling mechanism was the formation of chelates between Mg2+ and carboxyl groups (-COO) of PAA. The frequency-based testing method was applied to investigate the gelling process of the as-prepared slurry. In addition, a novel in situ characterization method based on a modified indentation testing was invented to better understand the strengthening of the wet green body with time and to guide when demolding could be carried out. After sintering, transparent MgAl2O4 ceramics with high in-line transmittance were resulted.  相似文献   
44.
In the current research on intensity-modulation and direct-detection optical orthogonal frequency division multiplexing ( IMDD-OOFDM ) system, effective channel compensation is a key factor to improve system performance. In order to improve the efficiency of channel compensation, a deep learning-based symbol detection algorithm is proposed in this paper for IMDD-OOFDM system. Firstly, a high-speed data streams symbol synchronization algorithm based on a training sequence is used to ensure accurate symbol synchronization. Then the traditional channel estimation and channel compensation are replaced by an echo state network (ESN) to restore the transmitted signal. Finally, we collect the data from the system experiment and calculate the signal-to-noise ratio (SNR). The analysis of the SNR optimized by the ESN proves that the ESN-based symbol detection algorithm is effective in compensating nonlinear distortion.  相似文献   
45.
建盏工艺在我国有着十分悠久的历史,最早可以追溯到宋代,因茶而诞生,在当时是人们进行斗茶最理想的工具,因此有着十分广泛的群众基础,在当时和后世都有着特别广泛的应用。建盏烧制工艺十分独特,其中包含着十分丰富的内涵,也有很多注意事项。基于此,本文着重探讨建盏烧制技艺以及相关内容,希望本文的分析能够为继承和弘扬我国传统文化、传统工艺做出贡献。  相似文献   
46.
47.
Conversion of LCO (light cycle oil) to BTX (benzene, toluene, and xylene) is an economically valuable method for refineries. However, this approach still faces difficulties as the main reactions are not clearly understood. Here we study the detailed hydrocracking pathway of typical reactants, 1-methylnaphthalene and tetralin, through molecular simulations and experiments to improve our understanding of the conversion process of LCO to BTX. Molecular simulations demonstrate that the rate-determining step is the isomerization pathway of six-membered ring to five-membered ring in tetralin as its activation energy (ΔEa) is the highest among all the reactions and the order of ΔEa of reactions is isomerization > ring-opening ≈ side-chain cleavage. The results of experiments show that with the increase in reaction depth, i.e., through a high temperature (350 – 370 °C) and low LHSV (4.5 – 6.0 h−1), isomerization, ring-opening, and side-chain  cleavage reactions occurred, thus improving the selectivity and yield of alkyl aromatics.  相似文献   
48.
49.
Feng  Yingrui  Hu  Kang  Zhang  Min  Ding  Wei  Kong  Xiangkai  Sheng  Zhigao  Liu  Qiangchun 《Journal of Materials Science》2022,57(1):204-216
Journal of Materials Science - Rationally designing microwave absorption materials with highly efficient and tunable bandwidth is in great demand but remains a huge challenge. In this study,...  相似文献   
50.
Inorganic Materials - We have studied the effect of isothermal holding of a melt containing 78 mol % Bi2O3 and 22 mol % SiO2 and various melt cooling schedules on the morphology, microstructure,...  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-23

京公网安备 11010802026262号