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   97337篇
  免费   5669篇
  国内免费   5229篇
电工技术   4548篇
技术理论   5篇
综合类   9870篇
化学工业   13146篇
金属工艺   5718篇
机械仪表   3536篇
建筑科学   4979篇
矿业工程   1360篇
能源动力   2894篇
轻工业   6113篇
水利工程   2268篇
石油天然气   4321篇
武器工业   848篇
无线电   8183篇
一般工业技术   15200篇
冶金工业   2571篇
原子能技术   2253篇
自动化技术   20422篇
  2024年   88篇
  2023年   451篇
  2022年   782篇
  2021年   997篇
  2020年   1469篇
  2019年   1308篇
  2018年   1431篇
  2017年   1371篇
  2016年   1926篇
  2015年   2543篇
  2014年   4473篇
  2013年   5262篇
  2012年   4594篇
  2011年   5258篇
  2010年   4365篇
  2009年   5757篇
  2008年   5769篇
  2007年   6143篇
  2006年   5662篇
  2005年   4699篇
  2004年   4069篇
  2003年   3925篇
  2002年   3937篇
  2001年   2966篇
  2000年   3343篇
  1999年   3077篇
  1998年   2571篇
  1997年   2450篇
  1996年   2583篇
  1995年   2746篇
  1994年   2471篇
  1993年   1509篇
  1992年   1546篇
  1991年   1075篇
  1990年   800篇
  1989年   709篇
  1988年   668篇
  1987年   387篇
  1986年   248篇
  1985年   389篇
  1984年   420篇
  1983年   437篇
  1982年   342篇
  1981年   410篇
  1980年   276篇
  1979年   114篇
  1978年   115篇
  1977年   74篇
  1976年   43篇
  1975年   57篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Stream ciphers based on linear feedback shift register (LFSR) are suitable for constrained environments, such as satellite communications, radio frequency identification devices tag, sensor networks and Internet of Things, due to its simple hardware structures, high speed encryption and lower power consumption. LFSR, as a cryptographic primitive, has been used to generate a maximum period sequence. Because the switching of the status bits is regular, the power consumption of the LFSR is correlated in a linear way. As a result, the power consumption characteristics of stream cipher based on LFSR are vulnerable to leaking initialization vectors under the power attacks. In this paper, a new design of LFSR against power attacks is proposed. The power consumption characteristics of LFSR can be masked by using an additional LFSR and confused by adding a new filter Boolean function and a flip-flop. The design method has been implemented easily by circuits in this new design in comparison with the others.  相似文献   
42.
Composites play important role in dental filling by controlling shrinkage along with correction in teeth's shape and position. Rehabilitation of severely worn dentition can be achieved using mechanically strong composites. This study aims to synthesize zirconia-based composites to be used as dental fillers. Effect of microwave powers (100–900?W) along with Fe3O4 doping are studied on the structural, mechanical and magnetic properties of stabilized zirconia. SEM and TEM reveal formation of spherical nanoparticles with diameter of ~30?nm. XRD results shows phase pure tetragonal zirconia (t-ZrO2) at microwave power of 500?W without any post heat treatment. Crystallite size calculated from XRD data (~23?nm) matches well with the previously reported value for stabilization of t-ZrO2. Microwave energy dissipation results in stresses causing volume shrinkage leading to monoclinic to tetragonal phase transformation with higher X-ray density and hardness of ~1347HV. VSM results show ferromagnetic response with low coercivity (600Oe) value and saturation magnetization (~2emu/g). It is worth mentioning here that this is one of its kind study reporting synthesis of room temperature stabilized Fe3O4 doped zirconia composites at microwave power of 500?W. Antibacterial studies reveal inhibition zone of ~32?mm against bacillus bacteria suggesting their potential use as dental filler.  相似文献   
43.
Xin-Na Geng  Danyu Bai 《工程优选》2019,51(8):1301-1323
This article addresses the no-wait flowshop scheduling problem with simultaneous consideration of common due date assignment, convex resource allocation and learning effect in a two machine setting. The processing time of each job can be controlled by its position in a sequence and also by allocating extra resource, which is a convex function of the amount of a common continuously divisible resource allocated to the job. The objective is to determine the optimal common due date, the resource allocation and the schedule of jobs such that the total earliness, tardiness and common due date cost (the total resource consumption cost) are minimized under the constraint condition that the total resource consumption cost (the total earliness, tardiness and common due date cost) is limited. Polynomial time algorithms are developed for two versions of the problem.  相似文献   
44.
45.
The removal of methylene blue (MB) from aqueous solutions using sulfuric acid modified Cupressus semperirens cones (H2SO4-CSC), was investigated. Results showed that a pH value of 12 was favorable for the adsorption of MB and that the moisture and ash yields are suitable for industrial exploitation. A high porosity value was found, 68.1%. In agreement with its low content of basicity compared to its acidity, the H2SO4-CSC absorbent had an acidic behavior. Rate constants of pseudo-first-order, pseudo-second-order, and nth kinetic model were determined to analyze the dynamic of the biosorption process; they showed that adsorption kinetics followed a pseudo-second-order and nth kinetic models. Ionic strength was shown to have a negative impact on the biosorption of MB onto H2SO4-CSC. The Sips isotherm model was found to be the most relevant to describe MB biosorption onto H2SO4-CSC with a correlation factor R2?>?0.999. The biosorption capacity of H2SO4-CSC was found to be 460?mg?g?1 at 10°C and 590?mg?g?1 at 25°C, confirming biosorbent efficiency for the removal of MB dye from aqueous solutions. Thermodynamic parameters indicated that the biosorption process of MB was endothermic and more effective at high temperatures. The values of ΔG° and ΔH° confirmed that the biosorption of MB onto H2SO4-CSC was spontaneous and endothermic in nature. An irregular increase in randomness at the H2SO4-CSC–solution interface during the biosorption process was suggested by the positive values of ΔS°.  相似文献   
46.
The correct separation of chromosomes during mitosis is necessary to prevent genetic instability and aneuploidy, which are responsible for cancer and other diseases, and it depends on proper centrosome duplication. In a recent study, we found that Smy2 can suppress the essential role of Mps2 in the insertion of yeast centrosome into the nuclear membrane by interacting with Eap1, Scp160, and Asc1 and designated this network as SESA (S my2, E ap1, S cp160, A sc1). Detailed analysis showed that the SESA network is part of a mechanism which regulates translation of POM34 mRNA. Thus, SESA is a system that suppresses spindle pole body duplication defects by repressing the translation of POM34 mRNA. In this study, we performed a genome-wide screening in order to identify new members of the SESA network and confirmed Dhh1 as a putative member. Dhh1 is a cytoplasmic DEAD-box helicase known to regulate translation. Therefore, we hypothesized that Dhh1 is responsible for the highly selective inhibition of POM34 mRNA by SESA.  相似文献   
47.
The segmentation of specific tissues in an MR brain image for quantitative analysis can assist the disease diagnosis and medical research. Therefore, a robust and accurate method for automatic segmentation is necessary. Atlas-based-method is a common and effective method of automatic segmentation where an atlas refers to a pair of image consist of an intensity image and its corresponding label image. Apart from the general multi-atlas-based methods, which propagate labels through the single atlas then fuse them, we proposed a hybrid atlas forest based on confidence-weighted probability matrix to consider the atlases set as a whole and treat each voxel differently. In the framework, we first register the atlas to the image space of target and calculate the confidence of voxels in the registered atlas. Then, a confidence-weighted probability matrix is generated and it augments to the intensity image of the atlas or target for providing spatial information of the target tissue. Third, a hybrid atlas forest is trained to gather the features and correlation information among the atlases in the dataset. Finally, the segmentation of the target tissues is predicted by the trained hybrid atlas forest. The segment performance and the components efficiency of the proposed method are evaluated on the two public datasets. Based on the experiment results and quantitative comparisons, our method can gather spatial information and correlation among the atlases to obtain an accurate segmentation.  相似文献   
48.
RNA can be modified in over 100 distinct ways, and these modifications are critical for function. Pseudouridine synthases catalyse pseudouridylation, one of the most prevalent RNA modifications. Pseudouridine synthase 7 modifies a variety of substrates in Saccharomyces cerevisiae including tRNA, rRNA, snRNA, and mRNA, but the substrates for other budding yeast Pus7 homologues are not known. We used CRISPR-mediated genome editing to disrupt Candida albicans PUS7 and find absence leads to defects in rRNA processing and a decrease in cell surface hydrophobicity. Furthermore, C. albicans Pus7 absence causes temperature sensitivity, defects in filamentation, altered sensitivity to antifungal drugs, and decreased virulence in a wax moth model. In addition, we find C. albicans Pus7 modifies tRNA residues, but does not modify a number of other S. cerevisiae Pus7 substrates. Our data suggests C. albicans Pus7 is important for fungal vigour and may play distinct biological roles than those ascribed to S. cerevisiae Pus7.  相似文献   
49.
A series of inorganic yellow pigments with general formula Y_(4-x)A_xMoO_(9+δ)(A = Ta, Tb), where x = 0,0.05,0.1,0.2, 0.4 for Ta and χ = 0, 0.005, 0.01.0.03, 0.05 for Tb,were synthesized by a conventional ceramic method at 1400 ℃ for 6 h in air. The samples were characterized by XRD,EDS,XPS,SEM,TG-DSC,UV-vis-NIR reflectance spectroscopy and CIE L*a*b* color scales. It is found that the substitution of A(A = Ta, Tb) for Y~(3+) in Y_4 MoO_9 decreases the NIR reflectance of the pigment samples, but the developed pigments Y_(4-x)A_xMoO_(9+δ)(A = Ta, Tb) still exhibit impressive NIR solar reflectance. The brighter yellow color of inorganic pigments Y_(4-x)A_xMoO_(9+δ)(A = Ta, Tb) is available when x is about 0.1 for Ta and 0.01 for Tb. The results make them a series of potential candidates as ecological yellow pigments because of their high reflectance, lightness, intense coloration and excellent thermal and chemical stability.  相似文献   
50.
游惠明 《中国油脂》2021,46(6):98-101
为探明不同种源地香叶树作为油料树种的开发价值,采集了全国6省20县市的香叶树果实,对香叶树全果、果肉及籽的油脂含量及脂肪酸组成进行了分析,并采用ward法对不同种源地香叶树籽油脂肪酸进行了聚类分析。结果表明:香叶树全果、果肉以及籽的平均油脂含量分别为43.31%、42.38%及46.12%;全果油脂肪酸组成以月桂酸、油酸和癸酸为主;果肉油以油酸和棕榈酸为主;而籽油则以月桂酸和癸酸为主,月桂酸含量为53.20%~70.30%,月桂酸和癸酸总含量达76.40%~90.10%;聚类分析将不同种源地香叶树分为3大类,云南省、贵州省及广西省的香叶树属低月桂酸类型,福建省、江西省及湖南省的香叶树属中高月桂酸型。香叶树可作为生产中碳链脂肪酸的新晋树种,福建省的香叶树籽油脂含量高,且籽油中月桂酸含量高,作为中碳链脂肪酸的原料地具有明显的开发优势。  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