全文获取类型
收费全文 | 28306篇 |
免费 | 2353篇 |
国内免费 | 1018篇 |
专业分类
电工技术 | 1682篇 |
技术理论 | 1篇 |
综合类 | 1598篇 |
化学工业 | 5059篇 |
金属工艺 | 1485篇 |
机械仪表 | 1487篇 |
建筑科学 | 2148篇 |
矿业工程 | 663篇 |
能源动力 | 984篇 |
轻工业 | 1881篇 |
水利工程 | 437篇 |
石油天然气 | 1513篇 |
武器工业 | 150篇 |
无线电 | 3428篇 |
一般工业技术 | 3633篇 |
冶金工业 | 1531篇 |
原子能技术 | 343篇 |
自动化技术 | 3654篇 |
出版年
2024年 | 116篇 |
2023年 | 499篇 |
2022年 | 847篇 |
2021年 | 1268篇 |
2020年 | 883篇 |
2019年 | 809篇 |
2018年 | 815篇 |
2017年 | 954篇 |
2016年 | 895篇 |
2015年 | 1070篇 |
2014年 | 1425篇 |
2013年 | 1782篇 |
2012年 | 1773篇 |
2011年 | 1955篇 |
2010年 | 1578篇 |
2009年 | 1597篇 |
2008年 | 1510篇 |
2007年 | 1366篇 |
2006年 | 1512篇 |
2005年 | 1272篇 |
2004年 | 935篇 |
2003年 | 828篇 |
2002年 | 835篇 |
2001年 | 596篇 |
2000年 | 569篇 |
1999年 | 662篇 |
1998年 | 616篇 |
1997年 | 496篇 |
1996年 | 479篇 |
1995年 | 368篇 |
1994年 | 304篇 |
1993年 | 206篇 |
1992年 | 185篇 |
1991年 | 122篇 |
1990年 | 100篇 |
1989年 | 76篇 |
1988年 | 92篇 |
1987年 | 50篇 |
1986年 | 46篇 |
1985年 | 27篇 |
1984年 | 33篇 |
1983年 | 21篇 |
1982年 | 27篇 |
1981年 | 12篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Eu~(3+)-doped hydrocalumites (Eu~(3+)-doped CaAl-LDH) were prepared in an ethanol/water media. Various techniques, including inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), and fluorescent spetctra (FL), etc., were employed to study the structure, composition,and fluorescence of samples. Compositional analyses reveal that the contents of all the elements calculated from the chemical formula are close to that of the actual found from measurement. XRD results suggest that the samples with different molar ratios of Ca~(2+)/(Al~(3+)+Eu~(3+)) present typical layered structure. Moreover, all the samples exhibit monoclinic structure. Fluorescent spectra show strong red emissions ascribed to~5D_0→~7F_J(J=1, 2) transitions of Eu3+ions for all the Eu~(3+)-doped hydrocalumites,revealing that the hydrocalumite is favorable for the emission of Eu~(3+). The Eu~(3+)-doped hydrocalumite may be a latent fluorescent material applied in biological or medical fields in consideration of the biocompatibility of Ca~(2+) ions and fluorescent property of Eu~(3+) ions. 相似文献
992.
993.
Su Mingzhou Wang Huimeng Zhou Qiaoling Chen Chang 《Powder Metallurgy and Metal Ceramics》2019,58(5-6):278-284
Powder Metallurgy and Metal Ceramics - The space holder technique was widely used in manufacturing high melting-point porous metals. Corn powders with a smaller size (11.4 μm on average) than... 相似文献
994.
995.
Lu Yang Guangwei Wu Fanyue Meng Huomiao Ran Wenbing Yin Wei Li Xiaoqing Liu 《International journal of molecular sciences》2022,23(7)
The strategies of genetic dereplication and manipulation of epigenetic regulators to activate the cryptic gene clusters are effective to discover natural products with novel structure in filamentous fungi. In this study, a combination of genetic dereplication (deletion of pesthetic acid biosynthetic gene, PfptaA) and manipulation of epigenetic regulators (deletion of histone methyltransferase gene PfcclA and histone deacetylase gene PfhdaA) was developed in plant endophytic fungus Pestalotiopsis fici. The deletion of PfptaA with PfcclA and/or PfhdaA led to isolation of 1 novel compound, pestaloficiol X (1), as well as another 11 known compounds with obvious yield changes. The proposed biosynthesis pathway of pestaloficiol X was speculated using comparative analysis of homologous biosynthetic gene clusters. Moreover, phenotypic effects on the conidial development and response to oxidative stressors in the mutants were explored. Our results revealed that the new strain with deletion of PfcclA or PfhdaA in ΔPfptaA background host can neutralise the hyperformation of conidia in the PfptaA mutant, and that the ΔPfptaA ΔPfhdaA mutant was generally not sensitive to oxidative stressors as much as the ΔPfptaA ΔcclA mutant in comparison with the single mutant ΔPfptaA or the parental strains. This combinatorial approach can be applied to discover new natural products in filamentous fungi. 相似文献
996.
在确定的函数关系(数学模型)中,因变量(输出量)随自变量(输入量)的变化规律完全由数学逻辑所确定,自变量到因变量的传递系数(灵敏系数)也可由因变量的标准差和自变量的标准差之比所决定,而与自变量的来历(测量的或者给定的)没有关系[1].本文根据这一基本原理,采用模拟自变量随机变化的方法,成功计算了手持式激光测距仪的测距固定偏差和比例偏差系数的测量不确定度,从而计算出测距标准差综合评定的扩展不确定度,同时解决了复杂的数学模型中多个输入量到输出量的灵敏系数和输出量的不确定度的计算问题. 相似文献
997.
Comparison of the Antimicrobial and Sanitizer Resistance of Salmonella Isolates from Chicken Slaughter Processes in Korea 下载免费PDF全文
So Youn Youn Ok Mi Jeong Byung Kook Choi Suk Chan Jung Min Su Kang 《Journal of food science》2017,82(3):711-717
Salmonella is a foodborne pathogen worldwide. Outbreaks of Salmonella are commonly associated with consumption of contaminated foods such as poultry products. Therefore, the objective of this study was to determine the occurrence, biofilm formation, antibiotic resistance, and sanitizer resistance of Salmonella enterica isolated from chicken carcasses. A total of 318 samples were collected from 15 chicken slaughterhouses in 8 provinces of Korea. They were then examined for Salmonella contamination. S. enterica isolates were tested for their susceptibilities to 15 antimicrobials by broth microdilution method. Their biofilm formation ability and resistance to sanitizers were also evaluated. Eighty‐two isolates of S. enterica were obtained from the 318 samples. There were 14 serotypes and 2 untypable isolates. Fifty‐seven (69.5%) isolates were resistant to at least one antibiotic while 30 (36.6%) isolates were resistant to 5 or more antibiotics. Two S. Senftenberg and 3 S. Montevideo isolates exhibited considerable biofilm formation ability (A600>0.2) following incubation in Luria‐Bertani (LB) broth for 48 h. Biofilm cell survival and recovery growth assay after sanitization showed that most isolates were highly susceptible to 2.5% lactic acid and 0.1% cetylpyridinium chloride. Therefore, lactic acid and cetylpyridinium chloride might be alternatively or additionally used in addition to chlorine‐based sanitizers that are frequently used to reduce Salmonella contamination of chicken carcasses. Our results provide basic information on the distribution of Salmonella serotypes in chicken slaughterhouses. This study also highlights the necessity to improve farming practices and use antimicrobial agents cautiously. This study also suggests that sanitization during the slaughtering process might be necessary to reduce Salmonella contamination of chicken carcasses. 相似文献
998.
999.
1000.