全文获取类型
收费全文 | 61851篇 |
免费 | 7313篇 |
国内免费 | 4240篇 |
学科分类
工业技术 | 73404篇 |
出版年
2024年 | 159篇 |
2023年 | 1006篇 |
2022年 | 2101篇 |
2021年 | 3108篇 |
2020年 | 2234篇 |
2019年 | 1764篇 |
2018年 | 1934篇 |
2017年 | 2160篇 |
2016年 | 2045篇 |
2015年 | 2985篇 |
2014年 | 3716篇 |
2013年 | 4394篇 |
2012年 | 5232篇 |
2011年 | 5330篇 |
2010年 | 4843篇 |
2009年 | 4585篇 |
2008年 | 4337篇 |
2007年 | 4183篇 |
2006年 | 3772篇 |
2005年 | 2963篇 |
2004年 | 2111篇 |
2003年 | 1528篇 |
2002年 | 1480篇 |
2001年 | 1159篇 |
2000年 | 915篇 |
1999年 | 718篇 |
1998年 | 511篇 |
1997年 | 392篇 |
1996年 | 358篇 |
1995年 | 315篇 |
1994年 | 224篇 |
1993年 | 161篇 |
1992年 | 142篇 |
1991年 | 100篇 |
1990年 | 75篇 |
1989年 | 68篇 |
1988年 | 45篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 19篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
本文采用QuEChERS技术结合超高效液相色谱-串联质谱(UHPLC-MS/MS)技术建立同时检测丙烯酰胺(AA)、亚硝胺(NAs)和杂环胺(HAAs)含量的方法,用于分析热加工肉制品中产生的胺类物质。结果表明:该方法检测出的三类成分20种胺类物质在相应浓度范围内显示出良好的线性关系(R2>0.991),检测限和定量限分别为0.01~1.6 ng/g和0.03~4.8 ng/g,日内回收率介于66.3%~116.5%之间,日内精密度介于0.78%~9.0%之间。每个胺类物的5×LOQ加标水平计算的日间精度范围为3.4%~9.4%。该方法应用于煎烤的四种肉制品中AA、NAs和HAAs的分析,共检测出9种胺类物质,浓度范围为0.03~31.26 ng/g。 相似文献
5.
6.
Qian-Yun Han Fang Liu Yuan-Ying Ni 《International Journal of Food Science & Technology》2022,57(2):920-930
The gene sequence coding for the membrane-bound polyphenol oxidase (mPPO) with a length of 1761 bp was cloned by PCR method and shown to contain one highly conserved sequence encoding a di-copper-binding region. The predicted three-dimensional structure of mPPO indicated that the active site was located near two copper ions and composed of a typical bundle of four α-helices. Each of the two catalytic copper ions was coordinated with three histidine residues in the hydrophobic pocket, yielding His 180, His 201, His 210, His 332, His 336 and His 366. Docking studies showed that 4-methylcatechol and chlorogenic acid have different binding models due to different ligand sizes and binding sites in the active centre, and it was found that the smaller compound exhibited a higher affinity for mPPO. Molecular dynamic simulation results indicated that Phe 353 is important in controlling enzymatic activity through influencing substrate coordination in the active site. 相似文献
7.
Qing Li Jun Wang Jie Ma Meng Ni Fan Yang Peng Liu Kuo Yang Lee Hsing-I Hsiang Deyuan Shen Dingyuan Tang 《Journal of the American Ceramic Society》2022,105(5):3375-3381
High-efficiency Yb:Y2O3 laser ceramics were fabricated using the vacuum-sintering plus hot isostatic pressing (HIP) without sintering additives. High-purity well-dispersed nanocrystalline Yb:Y2O3 powder was synthesized using a modified co-precipitation method in-house. The green bodies were first vacuum sintered at a temperature as low as 1430°C and then HIPed at 1450°C. Finally, the samples were air annealed at 800°C for 10 h. Although no sintering aids were used, full density of the samples with excellent optical homogeneity and an inline transmission of 80% at 400 nm could be obtained. Moreover, photodarkening phenomenon was not detected in the ceramics. Preliminary laser experiment with the fabricated ceramics in a two-mirror cavity has demonstrated 32 W continuous-wave (CW) output at ∼1077 nm with an optical-to-optical conversion efficiency of 58.2%. To the best of our knowledge, this is so far the highest CW output power and optical-to-optical conversion efficiency achieved with the Yb3+-doped sesquioxide ceramics in a simple two-mirror cavity. 相似文献
8.
Ya-Nan Yang Yin-Ning Zhou Bo Ouyang Yi-Yang Wu Xi-Bao Zhang Zheng-Hong Luo 《American Institute of Chemical Engineers》2022,68(5):e17645
The computational fluid dynamics (CFD) and kinetic-based moment methods coupled approach is adopted to simulate the bulk copolymerization of styrene–acrylonitrile (SAN) in a stirred tank reactor. Numerical simulations are carried out to investigate the impacts of impeller speed, monomer ratio, initiator ratio, and initial reaction temperature on the copolymerization process and product properties. Particularly, the Chaos theory is selected as a criterion for evaluating the occurrence of the thermal runaway. The Flory's and Stockmayer's distributions are employed to calculate chain length distribution and copolymer composition distribution of copolymer. The simulation results highlight that the appearance of thermal runaway can be postponed by properly increasing the rotation speed, decreasing the initiator loadings, initial acrylonitrile contents and initial reactor temperature. Furthermore, significant differences exist in the product properties that predicted by the ideal and non-ideal models, which demonstrates that the temperature heterogeneity plays a crucial role in SAN copolymerization. This study could offer references for the safe operation and design of polymerization processes. 相似文献
9.
在国内,火花放电原子发射光谱分析广泛使用类型标准化进行方法校正。在国外,标准和文献中鲜见使用此方法的相关论述。类型标准化主要采用平移校正和转动校正两种方式,哪种方式更加合理也鲜见报道。国外设备类型标准化的默认设置优先采用转动校正方式,相关国内标准对最优校正方式的规定尚不明确,此默认设置的合理性有待探讨。实验选用低合金钢20CrNi2Mo、R407标准样品和不锈钢317L、0Cr18Ni9标准样品,引用国内相关标准,以正确度临界差为评判依据,模拟类型标准化样品和待测样品“十分接近”和“接近”两种情况下平移校正和转动校正的数据正确度。经数据统计分析,平移校正分析结果均满足要求,转动校正结果在“接近”情况下部分元素不满足要求。结合相关国家标准中元素含量范围和精密度数据进行分析,通过计算允许最大偏倚量并制作曲线图方式展开分析,得出如下结论:在满足文中类型标准化控制要点前提下,分析设置更适合于采用平移校正方式。 相似文献