全文获取类型
收费全文 | 3447篇 |
免费 | 512篇 |
国内免费 | 65篇 |
专业分类
电工技术 | 15篇 |
综合类 | 82篇 |
化学工业 | 945篇 |
金属工艺 | 41篇 |
机械仪表 | 48篇 |
建筑科学 | 32篇 |
矿业工程 | 4篇 |
能源动力 | 27篇 |
轻工业 | 2132篇 |
水利工程 | 8篇 |
石油天然气 | 7篇 |
武器工业 | 2篇 |
无线电 | 75篇 |
一般工业技术 | 289篇 |
冶金工业 | 38篇 |
原子能技术 | 3篇 |
自动化技术 | 276篇 |
出版年
2024年 | 37篇 |
2023年 | 120篇 |
2022年 | 224篇 |
2021年 | 294篇 |
2020年 | 184篇 |
2019年 | 223篇 |
2018年 | 179篇 |
2017年 | 169篇 |
2016年 | 165篇 |
2015年 | 152篇 |
2014年 | 163篇 |
2013年 | 213篇 |
2012年 | 191篇 |
2011年 | 172篇 |
2010年 | 133篇 |
2009年 | 112篇 |
2008年 | 125篇 |
2007年 | 114篇 |
2006年 | 134篇 |
2005年 | 129篇 |
2004年 | 91篇 |
2003年 | 100篇 |
2002年 | 75篇 |
2001年 | 63篇 |
2000年 | 56篇 |
1999年 | 46篇 |
1998年 | 59篇 |
1997年 | 40篇 |
1996年 | 40篇 |
1995年 | 35篇 |
1994年 | 29篇 |
1993年 | 31篇 |
1992年 | 28篇 |
1991年 | 18篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4024条查询结果,搜索用时 457 毫秒
31.
Ebony A. Monson Donna R. Whelan Karla J. Helbig 《International journal of molecular sciences》2021,22(9)
Lipid droplets (LDs) have traditionally been thought of as solely lipid storage compartments for cells; however, in the last decade, they have emerged as critical organelles in health and disease. LDs are highly dynamic within cells, and their movement is critical in organelle–organelle interactions. Their dynamics are known to change during cellular stress or nutrient deprivation; however, their movement during pathogen infections, especially at very early timepoints, is under-researched. This study aimed to track LD dynamics in vitro, in an astrocytic model of infection. Cells were either stimulated with a dsRNA viral mimic, poly I:C, or infected with the RNA virus, Zika virus. Individual LDs within infected cells were analysed to determine displacement and speed, and average LD characteristics for multiple individual cells calculated. Both LD displacement and mean speed were significantly enhanced in stimulated cells over a time course of infection with an increase seen as early as 2 h post-infection. With the emerging role for LDs during innate host responses, understanding their dynamics is critical to elucidate how these organelles influence the outcome of viral infection. 相似文献
32.
Agata Wawrzkiewicz-Jaowiecka Anna Lalik Graa Soveral 《International journal of molecular sciences》2021,22(10)
The gonadal steroids, including androgens, estrogens and progestogens, are involved in the control of body fat distribution in humans. Nevertheless, not only the size and localization of the fat depots depend on the sex steroids levels, but they can also highly affect the functioning of adipose tissue. Namely, the gonadocorticoids can directly influence insulin signaling, lipid metabolism, fatty acid uptake and adipokine production. They may also alter energy balance and glucose homeostasis in adipocytes in an indirect way, e.g., by changing the expression level of aquaglyceroporins. This work presents the recent advances in understanding the molecular mechanism of how the gonadal steroids influence the functioning of adipose tissue leading to a set of detrimental metabolic consequences. Special attention is given here to highlighting the sexual dimorphism of adipocyte functioning in terms of health and disease. Particularly, we discuss the molecular background of metabolic disturbances occurring in consequence of hormonal imbalance which is characteristic of some common endocrinopathies such as the polycystic ovary syndrome. From this perspective, we highlight the potential drug targets and the active substances which can be used in personalized sex-specific management of metabolic diseases, in accord with the patient’s hormonal status. 相似文献
33.
To date, it has been reliably shown that the lipid bilayer/water interface can be thoroughly characterized by a sophisticated so-called “dynamic molecular portrait”. The latter reflects a combination of time-dependent surface distributions of various physicochemical properties, inherent in both model lipid bilayers and natural multi-component cell membranes. One of the most important features of biomembranes is their mosaicity, which is expressed in the constant presence of lateral inhomogeneities, the sizes and lifetimes of which vary in a wide range—from 1 to 103 nm and from 0.1 ns to milliseconds. In addition to the relatively well-studied macroscopic domains (so-called “rafts”), the analysis of micro- and nanoclusters (or domains) that form an instantaneous picture of the distribution of structural, dynamic, hydrophobic, electrical, etc., properties at the membrane-water interface is attracting increasing interest. This is because such nanodomains (NDs) have been proven to be crucial for the proper membrane functioning in cells. Therefore, an understanding with atomistic details the phenomena associated with NDs is required. The present mini-review describes the recent results of experimental and in silico studies of spontaneously formed NDs in lipid membranes. The main attention is paid to the methods of ND detection, characterization of their spatiotemporal parameters, the elucidation of the molecular mechanisms of their formation. Biological role of NDs in cell membranes is briefly discussed. Understanding such effects creates the basis for rational design of new prospective drugs, therapeutic approaches, and artificial membrane materials with specified properties. 相似文献
34.
Emad Karrar Isam A. Mohamed Ahmed Muhammad Faisal Manzoor Frederick Sarpong Wei Wei Xingguo Wang 《European Journal of Lipid Science and Technology》2021,123(3):2000104
Cucurbitaceae family seeds are mostly discarded as agro-industrial wastes. Gurum (Citrullus lanatus var. colocynthoide) is an underutilized wild cucurbit plant, closely related to desert watermelon, which is grown abundantly in some African countries. Gurum seeds can play a significant role in health and nutrition due to their high oil content. This review describes the nutritional composition of gurum seeds and their oil profile. Gurum seeds are a good source of oil (27–35.5%), fiber (26–31%), crude protein (15–18%), and carbohydrates (14–17%). Gurum seeds oil is extracted by supercritical CO2 (SFE), screw press, and solvent extraction techniques. The gurum seeds oil is composed of unsaturated fatty acids with a high proportion of linoleic acid (C18:2) and oleic acid (C18:1). Gurum seeds oil contains various bioactive compounds, such as tocopherols, phytosterols, and polyphenols. It is reported that solvent extraction gives a higher yield than the screw press and SFE, but the SFE is preferred due to safety issues. More studies are required for producing better quality gurum seeds oil by using novel extraction techniques that can increase oil yield. 相似文献
35.
Amy?Richards Chakra?WijesunderaEmail author Phil?Salisbury 《Journal of the American Oil Chemists' Society》2005,82(12):869-874
Lipid oxidation is a major factor affecting flavor quality and shelf life of vegetable oils. Oxidative stability is therefore
an important criterion by which oils are judged for usefulness in various food applications. In this study a method based
on headspace analysis was developed to evaluate relative oxidative stability of canola oils. The method does not require the
use of chemicals, involves minimal sample preparation, and can be performed on a relatively small sample size in comparison
with traditional wet chemical methods. Canola oils freshly extracted in the laboratory from different seed samples were subjected
to accelerated oxidation and analyzed for PV by standard methods and headspace volatiles by solid phase microextraction/GC-MS.
Forward stepwise regression analysis of the data revealed a relationship between PV and headspace concentration of the volatile
lipid oxidation products hexanal and trans,trans-2,4-heptadienal. The PV calculated using this formula correlated (R
2=0.73) with those measured by conventional methods.
Presented in part at the 96th Annual Meeting of the AOCS, 1–4 May 2005, Salt Lake City, UT. 相似文献
36.
Extraction of Lipids from Municipal Wastewater Plant Microorganisms for Production of Biodiesel 总被引:2,自引:0,他引:2
Stephen Dufreche R. Hernandez T. French D. Sparks M. Zappi E. Alley 《Journal of the American Oil Chemists' Society》2007,84(2):181-187
Municipal wastewater treatment plants in the USA produce over 6.2 × 106 t of dried sewage sludge every year. This microorganism-rich sludge is often landfilled or used as fertilizer. Recent restrictions
on the use of sewage sludge, however, have resulted in increased disposal problems. Extraction of lipids from sludge yields
an untapped source of cheap feedstock for biodiesel production. Solvents used for extraction in this study include n-hexane, methanol, acetone, and supercritical CO2. The gravimetric yield of oil was low for nonpolar solvents, but use of polar solvents gave a considerably increased yield;
however, the percentage of saponifiable material was less. Extraction of lipids with a mixture of n-hexane, methanol, and acetone gave the largest conversion to biodiesel compared with other solvent systems, 4.41% based on
total dry weight of sludge. In situ transesterification of dried sludge resulted in a yield of 6.23%. If a 10% dry weight
yield of fatty acid methyl esters is assumed, the amount of biodiesel available for production in the USA is 1.4 × 106 m3/year. Outfitting 50% of municipal wastewater plants for lipid extraction and transesterification could result in enough biodiesel
production to replace 0.5% of the national petroleum diesel demand (0.7 × 106 m3). 相似文献
37.
Dennis J. O’Brien Gerard E. Senske 《Journal of the American Oil Chemists' Society》1994,71(9):947-950
Utilization of lipids containing eicosapentaenoic acid (EPA) produced by microorganisms requires processes for their efficient
recovery from microbial cells. Recovery of EPA from mycelia of the fungusPythium irregulare by solvent extraction with hexane-isopropanol (HIP) in a pilot-plant colloid mill was investigated. Extraction efficiencies
of 96% for lipid and EPA were achieved with a 3∶2 (vol/vol) HIP mixture by milling wet, filtered mycelia for 5 min at a solvent/dry
solids ratio of 100 L/kg. The process yielded a crude extract that contained up to 96% lipid and an EPA content as high as
24% (with no selectivity for EPA). 相似文献
38.
Vanesa Losada Jorge Barros‐Velzquez Jos M. Gallardo Santiago P. Aubourg 《European Journal of Lipid Science and Technology》2004,106(12):844-850
Slurry ice is a biphasic system consisting of small spherical ice crystals surrounded by seawater at subzero temperature. Its effect on lipid damage (hydrolysis and oxidation) was evaluated during the chilled storage of a fatty fish species, sardine (Sardina pilchardus). Slurry ice treatment was checked alone and in combination with ozone and compared to traditional flake icing during a 22‐day storage. Different lipid damage indices (free fatty acids, FFA; peroxide value, PV; thiobarbituric acid index, TBA‐i; fluorescent compounds, FR) were checked and compared to sensory assessment and nucleotide degradation (K value). According to lipid hydrolysis (FFA) and oxidation (PV and FR) developments, slurry ice showed an inhibitory effect (p <0.05) on lipid damage during storage, as well as an inhibition of nucleotide autolytic degradation. Ozonised slurry ice did not provide differences (p >0.05) from slurry ice alone when considering lipid hydrolysis, nucleotide degradation and some lipid oxidation indices (PV and FR), although a higher (p <0.05) TBA‐i was observed at day 22 of storage when compared to flake ice and slurry ice treatments. However, a lower (p <0.05) fluorescence development was observed for fish treated under ozonised slurry ice when compared to traditionally iced fish. Sensory assessment showed a higher shelf life for fish samples treated under ozonised slurry ice than for their counterparts under slurry ice (15 d versus 12 d), while flake icing led to a far shorter shelf life (5 d). According to sensory and biochemical (lipid matter and nucleotide) analysis, slurry ice has proved to be a promising technology for damage inhibition and quality retention in a fatty fish species such as sardine. Ozonised slurry ice was also shown to be useful, since a longer shelf life was obtained in the present experiment and a pro‐oxidant effect of ozone on sardine lipids was not proved. 相似文献
39.
针对高维数据导致的维数灾难问题,提出了一种基于面向分类准则的维数约简方法。所提准则使每个训练样本在特征空间中与同类样本尽可能接近,而与异类样本尽可能疏远。首先对每个训练样本定义同类样本加权平均距离和异类样本加权平均距离。然后基于上述两个概念分别定义总体同类距离和总体异类距离。以最小化总体同类距离和最大化总体异类距离为目的提出了面向分类的准则(Classification Oriented Criterion,COC)。最后,基于面向分类的准则推导出了一种新的维数约简方法。在公共人脸数据库ORL和Yale上的实验表明所提方法性能优于有代表性的维数约简方法。 相似文献
40.
该文以现代汉语(特别是网络搜索词)中的名名组合为主要研究对象,探索一种基于规则的汉语名名组合的自动释义方法。其研究步骤为: (1)利用《现代汉语语义词典》中名词的语义类别,来建立名名组合的语义类组合模式;(2)在“生成词库论”中物性角色思想的指导下,用名名组合中某个名词的施成角色或功能角色作为释义动词,来揭示这两个名词之间的语义关系;(3)以语义类组合模式为单位构建名名组合的释义模板,并汇集成名名搭配数据库;(4)利用《知网》资源,来获取具体名词的施成角色和功能角色,建立汉语名词知识库。在这两个数据库的基础上,我们初步实现了一个汉语名名组合的自动释义程序。 相似文献