全文获取类型
收费全文 | 3739篇 |
免费 | 604篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 3篇 |
综合类 | 110篇 |
化学工业 | 1407篇 |
金属工艺 | 21篇 |
机械仪表 | 127篇 |
建筑科学 | 4篇 |
轻工业 | 2245篇 |
水利工程 | 1篇 |
石油天然气 | 8篇 |
无线电 | 100篇 |
一般工业技术 | 327篇 |
冶金工业 | 5篇 |
原子能技术 | 13篇 |
自动化技术 | 20篇 |
出版年
2024年 | 25篇 |
2023年 | 107篇 |
2022年 | 134篇 |
2021年 | 304篇 |
2020年 | 180篇 |
2019年 | 249篇 |
2018年 | 195篇 |
2017年 | 174篇 |
2016年 | 174篇 |
2015年 | 218篇 |
2014年 | 173篇 |
2013年 | 246篇 |
2012年 | 299篇 |
2011年 | 339篇 |
2010年 | 220篇 |
2009年 | 207篇 |
2008年 | 165篇 |
2007年 | 203篇 |
2006年 | 165篇 |
2005年 | 133篇 |
2004年 | 101篇 |
2003年 | 88篇 |
2002年 | 73篇 |
2001年 | 40篇 |
2000年 | 26篇 |
1999年 | 28篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有4391条查询结果,搜索用时 46 毫秒
1.
Bernette Maria Oosterlaken Heiner Friedrich Gijsbertus de With 《Microscopy research and technique》2022,85(1):412-417
Transmission electron microscopy (TEM) is an important analysis technique to visualize (bio)macromolecules and their assemblies, including collagen fibers. Many protocols for TEM sample preparation of collagen involve one or more washing steps to remove excess salts from the dispersion that could hamper analysis when dried on a TEM grid. Such protocols are not standardized and washing times as well as washing solvents vary from procedure to procedure, with each research group typically having their own protocol. Here, we investigate the influence of washing with water, ethanol, but also methanol and 2-propanol, for both mineralized and unmineralized collagen samples via a protocol based on centrifugation. Washing with water maintains the hydrated collagen structure and the characteristic banding pattern can be clearly observed. Conversely, washing with ethanol results in dehydration of the fibrils, often leading to aggregation of the fibers and a less obvious banding pattern, already within 1 min of ethanol exposure. As we show, this process is fully reversible. Similar observations were made for methanol and propanol. Based on these results, a standardized washing protocol for collagenous samples is proposed. 相似文献
2.
Angiotensin I‐converting enzyme inhibitory and Ca‐binding activities of peptides prepared from tuna cooking juice and spleen proteases 下载免费PDF全文
Jirawadee Kasiwut Wirote Youravong Pittaya Adulyatham Nualpun Sirinupong 《International Journal of Food Science & Technology》2015,50(2):389-395
Tuna cooking juice is a by‐product from the tuna canning industry. In this study, tuna cooking juice was hydrolysed by proteases extracted from the spleen. Tuna cooking juice showed the highest ACE inhibitory and Ca‐binding activities after hydrolysis for 270 and 180 min, respectively. The hydrolysate was further fractionated by ultrafiltration. The permeate exhibited highest ACE inhibitory and Ca‐binding activities when passed through 1 and 5 kDa cut‐off membranes, respectively. Gel filtration chromatography was used to determine the MW of bioactive peptides that exhibited highest ACE inhibitory and Ca‐binding activities. Those peptides that exhibited highest ACE inhibitory and Ca‐binding activities were the MW range of 238–829 Da and 1355–1880 Da, respectively. These results suggest that the tuna cooking juice and the spleen protease extract are a potential source of bioactive peptides that can be utilised as bioactive ingredients in functional food and nutraceuticals. 相似文献
3.
Marta Gabasa Marselina Arshakyan Alejandro Llorente Lourdes Chuli-Peris Irina Pavelescu Antoni Xaubet Javier Pereda Jordi Alcaraz 《International journal of molecular sciences》2020,21(22)
Pro-inflammatory cytokines like interleukin-1β (IL-1β) are upregulated during early responses to tissue damage and are expected to transiently compromise the mechanical microenvironment. Fibroblasts are key regulators of tissue mechanics in the lungs and other organs. However, the effects of IL-1β on fibroblast mechanics and functions remain unclear. Here we treated human pulmonary fibroblasts from control donors with IL-1β and used Atomic Force Microscopy to unveil that IL-1β significantly reduces the stiffness of fibroblasts concomitantly with a downregulation of filamentous actin (F-actin) and alpha-smooth muscle (α-SMA). Likewise, COL1A1 mRNA was reduced, whereas that of collagenases MMP1 and MMP2 were upregulated, favoring a reduction of type-I collagen. These mechanobiology changes were functionally associated with reduced proliferation and enhanced migration upon IL-1β stimulation, which could facilitate lung repair by drawing fibroblasts to sites of tissue damage. Our observations reveal that IL-1β may reduce local tissue rigidity by acting both intracellularly and extracellularly through the downregulation of fibroblast contractility and type I collagen deposition, respectively. These IL-1β-dependent mechanical effects may enhance lung repair further by locally increasing pulmonary tissue compliance to preserve normal lung distension and function. Moreover, our results support that IL-1β provides innate anti-fibrotic protection that may be relevant during the early stages of lung repair. 相似文献
4.
氦氖激光对人胚腱细胞生长分泌的影响 总被引:2,自引:0,他引:2
目的 阐明氦氖激光促进人胚腱细胞增殖及分泌胶原的机制。方法 将传代培养的人胚腱细胞分为对照组、照射1日组、照射3日组及照射5日组。在氦氖激光照射的不同时相点,分别测定细胞DNA含量,cAMP水平及胶原分泌量。结果 在氦氖激光作用早期(1-3日),细胞cAMP水平与DNA合成均呈明显升高(P<0.05),细胞内信使物质合成及细胞增殖加快,但胶原分泌无变化,而在氦氖激光作用晚期(3-5日),当cAMP水平及DNA合成都不再改变时,腱细胞分泌胶原量显著增加(P<0.01)。结论 氦氖激光可能通过作用于cAMP蛋白激酶A信号转导系统,从而调控人胚腱细胞增殖及胶原分泌。提示临床应用氛氖激光促进肌腱愈合宜从早期开始,并且需要照射足够长的时间。 相似文献
5.
Tadashi Hano Michiaki Matsumoto Takahisa Kawazu Takaaki Ohtake 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,62(1):60-63
The extraction equilibria of various di- and tripeptides with di-2-ethylhexylphosphoric acid (D2EHPA) were studied at low pH values. The complex extracted to organic phase consisted of one molecule of peptide and two molecules of D2EHPA dimer. The extraction constants of the peptides correlated well with the distribution coefficients of peptides between 1-octanol and water, which is a measure of hydrophobicity. The permeation rates of peptides through an emulsion liquid membrane were examined by using D2EHPA as a carrier, Span 80 as an emulsifier and kerosene as a diluent. The rates varied considerably with peptide type, depending upon the hydrophobicity. 相似文献
6.
7.
Auguste Commeyras Hlne Collet Laurent Boiteau Jacques Taillades Odile Vandenabeele‐Trambouze Herv Cottet Jean‐Philippe Biron Raphaël Plasson Louis Mion Olivier Lagrille Herv Martin Franck Selsis Michel Dobrijevic 《Polymer International》2002,51(7):661-665
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry. 相似文献
8.
E Aida Pea‐Ramos Youling L Xiong Guillermo E Arteaga 《Journal of the science of food and agriculture》2004,84(14):1908-1918
Whey protein isolate (WPI) was hydrolysed for 1 h using Alcalase, Protamex and Flavourzyme. Native WPI, hydrolysed WPI and two commercial WPI hydrolysates were subjected to fractionation by size exclusion chromatography. Antioxidant activity of WPI fractions was measured with a liposome‐oxidising system (50 µM FeCl3/0.1 µM ascorbate, pH 7.0). Lipid oxidation was measured as thiobarbituric acid‐reactive substances (TBARS). Gel electrophoresis and amino acid analysis were run to identify the peptide composition. The influence of amino acid composition on antioxidant activity was evaluated using multivariate analysis methods (correlation analysis, principal component analysis, multiple linear regression and discriminant analysis). TBARS assays indicated the presence of antioxidant activity in all protein fractions, including non‐hydrolysed WPI. For native and hydrolysed WPI samples the first fraction (> 45 kDa) showed a higher TBARS inhibition effect (24–27%) when compared with lower‐molecular‐weight fractions and hydrolysate mixtures. In contrast, for commercial WPI hydrolysates a higher inhibitory effect was found in most of the lower‐molecular‐weight fractions (30–55%). The ability of WPI fractions to delay lipid oxidation was found to be related to the prevalence of histidine and hydrophobic amino acids. Copyright © 2004 Society of Chemical Industry 相似文献
9.
Hu Kai Yang Xianjin Cai Yanli Cui Zhenduo Wei Qiang 《Frontiers of Materials Science in China》2007,1(3):229-236
A hydroxyapatite (HA)/collagen (COL) composite coating on NiTi shape memory alloy (SMA) was prepared by eletrochemical deposition
(ELD) in modified simulated body fluid (MSBF). To draw comparisons of physical characteristics and bioactivity of the composite
coating, the HA/COL composite coating was also prepared by chemically biomimetic growth (BG) and the ELD coating was re-soaked
in MSBF again for further biomimetic growth (called EBG method in this paper). It was indicated that the c-axis of HA crystals
was oriented parallel to the longitudinal direction of the COL fibril in BG and EBG coating, which could not found in ELD
coating. The EBG method could induce a denser, thicker and better crystallized HA/COL coating. The cell culture test indicated
that the BG coating presented better cell biocompatibility. 相似文献
10.