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   3573篇
  免费   281篇
  国内免费   101篇
电工技术   195篇
技术理论   1篇
综合类   185篇
化学工业   707篇
金属工艺   198篇
机械仪表   187篇
建筑科学   297篇
矿业工程   84篇
能源动力   183篇
轻工业   167篇
水利工程   49篇
石油天然气   185篇
武器工业   18篇
无线电   352篇
一般工业技术   505篇
冶金工业   202篇
原子能技术   24篇
自动化技术   416篇
  2024年   9篇
  2023年   65篇
  2022年   77篇
  2021年   135篇
  2020年   110篇
  2019年   100篇
  2018年   116篇
  2017年   135篇
  2016年   116篇
  2015年   118篇
  2014年   152篇
  2013年   208篇
  2012年   246篇
  2011年   218篇
  2010年   196篇
  2009年   199篇
  2008年   177篇
  2007年   166篇
  2006年   198篇
  2005年   173篇
  2004年   102篇
  2003年   116篇
  2002年   89篇
  2001年   61篇
  2000年   98篇
  1999年   109篇
  1998年   94篇
  1997年   61篇
  1996年   67篇
  1995年   73篇
  1994年   51篇
  1993年   21篇
  1992年   30篇
  1991年   19篇
  1990年   10篇
  1989年   13篇
  1988年   6篇
  1987年   4篇
  1986年   4篇
  1985年   3篇
  1984年   4篇
  1982年   5篇
  1980年   1篇
排序方式: 共有3955条查询结果,搜索用时 15 毫秒
101.
泥沙与鄱阳湖水环境   总被引:3,自引:0,他引:3  
分析并讨论了鄱阳湖泥沙的来源及其对鄱阳湖水环境质量的影响。  相似文献   
102.
通过实验探索利用双氧水对大豆油进行脱色的工艺操作方法。经对脱色后油脂的各项理化指标及在贮藏过程中的变化情况进行测定表明,用双氧水对大豆油进行脱色是可行的。  相似文献   
103.
The LOR (LURP-one related) family genes encode proteins containing a conserved LOR domain. Several members of the LOR family genes are required for defense against Hyaloperonospora parasitica (Hpa) in Arabidopsis. However, there are few reports of LOR genes in response to abiotic stresses in plants. In this study, a genome-wide survey and expression levels in response to abiotic stresses of 36 LOR genes from Glycine max were conducted. The results indicated that the GmLOR gene family was divided into eight subgroups, distributed on 14 chromosomes. A majority of members contained three extremely conservative motifs. There were four pairs of tandem duplicated GmLORs and nineteen pairs of segmental duplicated genes identified, which led to the expansion of the number of GmLOR genes. The expansion patterns of the GmLOR family were mainly segmental duplication. A heatmap of soybean LOR family genes showed that 36 GmLOR genes exhibited various expression patterns in different tissues. The cis-acting elements in promoter regions of GmLORs include abiotic stress-responsive elements, such as dehydration-responsive elements and drought-inducible elements. Real-time quantitative PCR was used to detect the expression level of GmLOR genes, and most of them were expressed in the leaf or root except that GmLOR6 was induced by osmotic and salt stresses. Moreover, GmLOR4/10/14/19 were significantly upregulated after PEG and salt treatments, indicating important roles in the improvement of plant tolerance to abiotic stress. Overall, our study provides a foundation for future investigations of GmLOR gene functions in soybean.  相似文献   
104.
Growth performance is an important economic trait in chicken. MicroRNAs (miRNAs) have been shown to play important roles in various biological processes, but their functions in chicken growth are not yet clear. To investigate the function of miRNAs in chicken growth, breast muscle tissues of the two-tail samples (highest and lowest body weight) from Recessive White Rock (WRR) and Xinghua Chickens (XH) were performed on high throughput small RNA deep sequencing. In this study, a total of 921 miRNAs were identified, including 733 known mature miRNAs and 188 novel miRNAs. There were 200, 279, 257 and 297 differentially expressed miRNAs in the comparisons of WRRh vs. WRRl, WRRh vs. XHh, WRRl vs. XHl, and XHh vs. XHl group, respectively. A total of 22 highly differentially expressed miRNAs (fold change > 2 or < 0.5; p-value < 0.05; q-value < 0.01), which also have abundant expression (read counts > 1000) were found in our comparisons. As far as two analyses (WRRh vs. WRRl, and XHh vs. XHl) are concerned, we found 80 common differentially expressed miRNAs, while 110 miRNAs were found in WRRh vs. XHh and WRRl vs. XHl. Furthermore, 26 common miRNAs were identified among all four comparisons. Four differentially expressed miRNAs (miR-223, miR-16, miR-205a and miR-222b-5p) were validated by quantitative real-time RT-PCR (qRT-PCR). Regulatory networks of interactions among miRNAs and their targets were constructed using integrative miRNA target-prediction and network-analysis. Growth hormone receptor (GHR) was confirmed as a target of miR-146b-3p by dual-luciferase assay and qPCR, indicating that miR-34c, miR-223, miR-146b-3p, miR-21 and miR-205a are key growth-related target genes in the network. These miRNAs are proposed as candidate miRNAs for future studies concerning miRNA-target function on regulation of chicken growth.  相似文献   
105.
In the current study, the lipid-shell and polymer-core hybrid nanoparticles (lpNPs) modified by Arg–Gly–Asp(RGD) peptide, loaded with curcumin (Cur), were developed by emulsification-solvent volatilization method. The RGD-modified hybrid nanoparticles (RGD–lpNPs) could overcome the poor water solubility of Cur to meet the requirement of intravenous administration and tumor active targeting. The obtained optimal RGD-lpNPs, composed of PLGA (poly(lactic-co-glycolic acid))–mPEG (methoxyl poly(ethylene- glycol)), RGD–polyethylene glycol (PEG)–cholesterol (Chol) copolymers and lipids, had good entrapment efficiency, submicron size and negatively neutral surface charge. The core-shell structure of RGD–lpNPs was verified by TEM. Cytotoxicity analysis demonstrated that the RGD–lpNPs encapsulated Cur retained potent anti-tumor effects. Flow cytometry analysis revealed the cellular uptake of Cur encapsulated in the RGD–lpNPs was increased for human umbilical vein endothelial cells (HUVEC). Furthermore, Cur loaded RGD–lpNPs were more effective in inhibiting tumor growth in a subcutaneous B16 melanoma tumor model. The results of immunofluorescent and immunohistochemical studies by Cur loaded RGD–lpNPs therapies indicated that more apoptotic cells, fewer microvessels, and fewer proliferation-positive cells were observed. In conclusion, RGD–lpNPs encapsulating Cur were developed with enhanced anti-tumor activity in melanoma, and Cur loaded RGD–lpNPs represent an excellent tumor targeted formulation of Cur which might be an attractive candidate for cancer therapy.  相似文献   
106.
A synthetic ureido mixture prepared from the reaction of 4,4′‐diphenylmethane disocynanate (MDI) and cyclohexylamine without using any harmful organic solvents, has been used as a nucleating agent (PNA) for polyamide 6 (PA6). The effect of PNA on the crystallization and mechanical properties of PA6 has been studied by means of differential scanning calorimetry (DSC), polarized optical microscopy (POM), tensile test, melt flow index (MFI), and X‐ray diffraction (XRD). The results show that PNA is an effective nucleation agent for PA6. PNA affects the nucleation mechanism of PA6, and substantially accelerates the crystallization rate of PA6 and gives rise to smaller crystal size. In comparison with PA6, the crystallization temperature (Tc) of PA6/PNA (100/0.5) increases 21.3°C and the degree of sub‐cooling (ΔTc) decreases 23.7°C. Furthermore, because of the heterogeneous nucleation induced by PNA, the spherulites of PA6 become even and tiny based on POM observation. Polymorph transform has been obtained from XRD analysis. The virgin PA6 is free of γ‐phase crystals, presented as α‐phase crystals in this study, but γ‐phase crystal appears after the introduction of PNA. The mechanical and thermal properties of PA6 are obviously improved by the addition of PNA. POLYM. ENG. SCI., 55:2011–2017, 2015. © 2015 Society of Plastics Engineers  相似文献   
107.
研究了利用低价含硫化合物的强配位能力和还原性及它作为助剂催化引发氯化钴的羰化反应的工艺条件,以便在较低的CO压力下合成四羰基钴盐。对几种常见含硫化合物的引发反应效果进行了对比。结果表明少量的含硫化合物可以引发钴盐的羰化反应,过多的添加则会阻断氯苄羰化反应的催化作用。  相似文献   
108.
Poly(methyl methacrylate), which is prepared by polymerization of methyl methacrylate (MMA), is widely used in the fabrication of polymer optical fiber and devices. In this article, a dielectric measurement method was proposed to monitor the polymerization process. The measurement result is compared with that obtained by the traditional Abbe's refractometer method. By monitoring the dielectric behaviors of polymerization system, the correlation between dielectric properties of reacting bulk and conversion of MMA was established. The influence of reactive temperature, reactive time, conversion rate of prepolymerization, and oxygen environment was discussed. It was shown that the gel effect occurred at 2 h at the reactive temperature of 50°C when the conversion of prepolymer was about 24% with the absence of oxygen. The conversion rate obtained by Abbe's refractometer method was larger than that measured by dielectric method in the reaction metaphase. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   
109.
《计算机在化工中的应用》课程建设与教学   总被引:1,自引:1,他引:1  
介绍了武汉科技大学化学工程与技术学院《计算机在化工中的应用》课程建设与教学实施情况,总结了该门课程的教学心得。教学实践表明,该课程内容实用,深受学生欢迎。  相似文献   
110.
以武汉科技大学化学工程与技术学院化学工程与工艺专业为例,介绍了优化培养计划、在专业理论教学中融入计算机应用和在实践教学强中融入计算机应用等强化化工专业本科生计算机应用能力培养的具体措施。指出化工专业本科生计算机应用能力的培养是一项系统工程,光靠低年级开设的那几门计算机课程是不够的,在高年级阶段还要继续强化计算机应用能力的培养。  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