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   208245篇
  免费   4921篇
  国内免费   1920篇
电工技术   4889篇
技术理论   5篇
综合类   1965篇
化学工业   33593篇
金属工艺   9337篇
机械仪表   6974篇
建筑科学   6476篇
矿业工程   1659篇
能源动力   5335篇
轻工业   19323篇
水利工程   2146篇
石油天然气   4459篇
武器工业   174篇
无线电   23171篇
一般工业技术   37874篇
冶金工业   34494篇
原子能技术   4532篇
自动化技术   18680篇
  2022年   1532篇
  2021年   2529篇
  2020年   1787篇
  2019年   2057篇
  2018年   3585篇
  2017年   3577篇
  2016年   3436篇
  2015年   2846篇
  2014年   4146篇
  2013年   9307篇
  2012年   6492篇
  2011年   8338篇
  2010年   6511篇
  2009年   7333篇
  2008年   7234篇
  2007年   7125篇
  2006年   6239篇
  2005年   7658篇
  2004年   6359篇
  2003年   5884篇
  2002年   5351篇
  2001年   5078篇
  2000年   4587篇
  1999年   4632篇
  1998年   10717篇
  1997年   7690篇
  1996年   5931篇
  1995年   4503篇
  1994年   3788篇
  1993年   3699篇
  1992年   2699篇
  1991年   2614篇
  1990年   2486篇
  1989年   2476篇
  1988年   2410篇
  1987年   2142篇
  1986年   2086篇
  1985年   2376篇
  1984年   2190篇
  1983年   2017篇
  1982年   1885篇
  1981年   1949篇
  1980年   1807篇
  1979年   1816篇
  1978年   1776篇
  1977年   2108篇
  1976年   2687篇
  1975年   1557篇
  1974年   1549篇
  1973年   1607篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell.  相似文献   
4.
Mangiferin (MGF) is a phenolic compound isolated from mango, but its poor solubility significantly limits its use. In this study, MGF was embedded into the inner aqueous phase of W1/O/W2 emulsions. Firstly, the dissolution method of MGF was determined. MGF remained stable in solution with pH 13 at 30 min, and its solubility reached 10 mg mL−1. When the pH of MGF solutions was adjusted from pH 13 to pH 6, MGF did not immediately crystallise, providing sufficient time to construct the MGF-loaded W1/O/W2 emulsions. Subsequently, the MGF-loaded W1/O/W2 emulsions were constructed using polyglycerol polyricinoleate (PGPR) and calcium caseinate (CAS). The formation and stability of the W1/O/W2 emulsions were investigated. The MGF-loaded W1/O/W2 emulsions stabilised with 1% PGPR and 1% – 3% CAS exhibited a low viscosity, limited loading capacity, and poor stability. Conversely, the MGF-loaded W1/O/W2 emulsions stabilised by 3%PGPR–3%CAS exhibited optimal loading capacity (encapsulation efficiency = 95.31% and loading efficiency = 0.91%) and stability, which was attributed to the fact that high viscosity and gel state retarded the migration of inner aqueous phase. These results indicated that the W1/O/W2 emulsions stabilised by PGPR and CAS may be a potential alternative for encapsulating mangiferin.  相似文献   
5.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
6.
With the continuous development of bionics, such as, geckos and virginia creeper with both superhydrophobic and super-adhesive, the surface wetting and super-adhesive properties of various porous materials have attracted extensive attention of the scientific and medical communities. Here, the honeycomb polyurethane (PU) porous films with strong adhesion were successfully prepared by microphase separation method and the effects of growth parameters on their microstructure and adhesive strength to ice were investigated. It was found that a high relative humidity (e.g., 100%) and a low solution concentration (e.g., 2%) facilitated the formation of ordered honeycomb PU porous films, and as-prepared PU pores with average pore diameter as small as 5 μm are better ordered and more uniform than these in related documents. Although the contact angle of water droplets on the surface of PU porous films increased from the premodification value of 85–130° to more than 160° after surface modification with polydopamine (PDA), the corresponding rolling angle remained approximately constant (180°), indicating that the surface of PU porous films has strong adhesion similar to geckos and virginia creeper. Furthermore, at lower temperature, the PU porous films exhibited the high adhesive strength of 142.13 kPa on ice, which was strongly dependent on the porous microstructures and surface compositions. The improved adhesive behavior to ice of honeycomb PU porous films modified with PDA provides new strategies for surface modification of materials and potential applications in medical domain.  相似文献   
7.
Fine-grained few-shot learning is a difficult task in image classification. The reason is that the discriminative features of fine-grained images are often located in local areas of the image, while most of the existing few-shotlearning image classification methods only use top-level features and adopt a single measure. In that way, the localfeatures of the sample cannot be learned well. In response to this problem, ensemble relation network with multi-level measure (ERN-MM) is proposed in this paper. It adds the relation modules in the shallow feature space tocompare the similarity between the samples in the local features, and finally integrates the similarity scores from thefeature spaces to assign the label of the query samples. So the proposed method ERN-MM can use local details andglobal information of different grains. Experimental results on different fine-grained datasets show that the proposedmethod achieves good classification performance and also proves its rationality.  相似文献   
8.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  相似文献   
9.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  相似文献   
10.
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