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   5404篇
  免费   409篇
  国内免费   3篇
电工技术   15篇
综合类   1篇
化学工业   1921篇
金属工艺   37篇
机械仪表   104篇
建筑科学   201篇
矿业工程   11篇
能源动力   133篇
轻工业   1765篇
水利工程   49篇
石油天然气   37篇
无线电   182篇
一般工业技术   650篇
冶金工业   142篇
原子能技术   7篇
自动化技术   561篇
  2024年   17篇
  2023年   91篇
  2022年   348篇
  2021年   394篇
  2020年   207篇
  2019年   232篇
  2018年   234篇
  2017年   231篇
  2016年   269篇
  2015年   195篇
  2014年   290篇
  2013年   426篇
  2012年   405篇
  2011年   426篇
  2010年   318篇
  2009年   311篇
  2008年   267篇
  2007年   239篇
  2006年   173篇
  2005年   130篇
  2004年   111篇
  2003年   86篇
  2002年   77篇
  2001年   40篇
  2000年   46篇
  1999年   46篇
  1998年   33篇
  1997年   24篇
  1996年   20篇
  1995年   12篇
  1994年   14篇
  1993年   13篇
  1992年   10篇
  1991年   7篇
  1990年   4篇
  1989年   17篇
  1988年   7篇
  1987年   11篇
  1986年   4篇
  1985年   6篇
  1984年   6篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1980年   3篇
  1978年   4篇
  1977年   2篇
  1976年   1篇
  1972年   1篇
排序方式: 共有5816条查询结果,搜索用时 0 毫秒
81.
Plant-derived products and their extracted compounds have been used in folk medicine since early times. Zimbro or common juniper (Juniperus communis) is traditionally used to treat renal suppression, acute and chronic cystitis, bladder catarrh, albuminuria, leucorrhea, and amenorrhea. These uses are mainly attributed to its bioactive composition, which is very rich in phenolics, terpenoids, organic acids, alkaloids, and volatile compounds. In the last few years, several studies have analyzed the huge potential of this evergreen shrub, describing a wide range of activities with relevance in different biomedical discipline areas, namely antimicrobial potential against human pathogens and foodborne microorganisms, notorious antioxidant and anti-inflammatory activities, antidiabetic, antihypercholesterolemic and antihyperlipidemic effects, and neuroprotective action, as well as antiproliferative ability against cancer cells and the ability to activate inductive hepato-, renal- and gastroprotective mechanisms. Owing to these promising activities, extracts and bioactive compounds of juniper could be useful for the development of new pharmacological applications in the treatment of several acute and chronic human diseases.  相似文献   
82.
Putrescine (Put) is the starting point of the polyamines (PAs) pathway and the most common PA in higher plants. It is synthesized by two main pathways (from ornithine and arginine), but recently a third pathway from citrulline was reported in sesame plants. There is strong evidence that Put may play a crucial role not only in plant growth and development but also in the tolerance responses to the major stresses affecting crop production. The main strategies to investigate the involvement of PA in plant systems are based on the application of competitive inhibitors, exogenous PAs treatments, and the most efficient approaches based on mutant and transgenic plants. Thus, in this article, the recent advances in understanding the role of this metabolite in plant growth promotion and protection against abiotic and biotic stresses will be discussed to provide an overview for future research.  相似文献   
83.
84.
Neural Computing and Applications - Artificial neural networks have been proposed in medical research as an alternative to some regression models such as the generalized linear models, being the...  相似文献   
85.

Nowadays, the stability and the safe cover and closure of soft tailings has become one of the most challenging topics in geotechnical and environmental engineering. For appropriate analysis and modelling, geotechnical properties of tailings should be well defined. Due to low strength, viscous nature and poor trafficability, as well as due to the specific geometrical properties of fine particles and pore water chemistry in tailings, different test methods and their modification and improvements must be used for valid and reliable characterisation of tailings. This paper analyses and compares the results of different field test methods, piezocone penetration test (CPTu), flat dilatometer test (DMT) and field vane test (FVT), performed on the red gypsum sludge and complementary laboratory tests. CPTu and DMT measurements were evaluated using procedures developed for soils and the obtained mechanical properties were compared with those measured in the laboratory. The significant distinctions between different test methods and different empirical correlations were analysed taking into account differences in index properties of soils and the red gypsum sludge. Based on analysis, some modifications of conventional empirical correlations were proposed for field tests results interpretation and sludge characterisation. The obtained data also show the advantages and limitations of some conventional methods and prove the need for further development in that field of geotechnical investigation.

  相似文献   
86.
The proximate composition and fatty acid content of spinach were determined in two processing stages. Crude protein and ash content were 2.89% and 1.96%, respectively. The total lipid content was 0-61%. The predominant fatty acids were palmitic (16:0), hexadecadienoic (16:2), hexadecenoic (16:1), stearic and hexadecatrienoic (18:0 and 16:3), oleic (18:1), linoleic (18:2) and linolenic (18:3). Little loss was observed as a result of processing. Soluble protein content showed losses of up to 87% during processing.  相似文献   
87.
88.
This study presents the first application of a high-resolution magic angle spinning 1H NMR approach to elucidate the metabolic effects of a hypercholesterolemic condition and two high-fiber diets based on rye and wheat bread, respectively, in intact pig liver biopsy samples. Standard 1D and spin-echo 1H spectra were acquired on a total of 20 biopsy samples, and 2D total correlation spectroscopy experiments were carried out on selected samples for assignment of the observed resonances. Principal component analyses and partial least-squares regression discriminant analysis revealed differences in the hepatic lipid content and choline-containing compounds between normal and hypercholesterolemic pigs. In addition, the results demonstrated that the liver metabolite profile of hypercholesterolemic pigs fed a high-fiber rye bread differed from that of pigs fed high-fiber wheat bread with respect to both the lipoprotein fractions and the choline-containing compounds. These findings suggest that earlier reports on high-fiber rye diet-induced effects on plasma HDL/LDL content partially can be ascribed to effects on liver cholesterol metabolism and that the hepatic phospholipase pathways of phosphatidylcholine breakdown are affected by the high-fiber rye diet.  相似文献   
89.
Spin crossover (SCO) complexes sensitively react on changes of the environment by a change in the spin of the central metallic ion making them ideal candidates for molecular spintronics. In particular, the composite of SCO complexes and ferromagnetic (FM) surfaces would allow spin-state switching of the molecules in combination with the magnetic exchange interaction to the magnetic substrate. Unfortunately, when depositing SCO complexes on ferromagnetic surfaces, spin-state switching is blocked by the relatively strong interaction between the adsorbed molecules and the surface. Here, the Fe(II) SCO complex [FeII(Pyrz)2] (Pyrz = 3,5-dimethylpyrazolylborate) with sub-monolayer thickness in contact with a passivated FM film of Co on Au(111) is studied. In this case, the molecules preserve thermal spin crossover and at the same time the high-spin species show a sizable exchange interaction of > 0.9 T with the FM Co substrate. These observations provide a feasible design strategy in fabricating SCO-FM hybrid devices.  相似文献   
90.
High resolution 1H NMR has been applied to monitor the changes in the composition of natural mango juice subjected to spoilage and to microbial contamination with Penicillium expansum. A vast number of compounds undergoing changes upon these processes have been identified and their variations followed throughout time (132 h). Besides the formation of typical fermentation products (e.g. acetate, lactic acid, acetoin and isopropanol/2,3-butanediol) and the utilization of the major sugars (sucrose, glucose and fructose), there were changes in organic acids (e.g. decreases of quinic and shikimic acids with formation of 3,4,5-trihydroxycyclohexane acid in spoiled juice, and decreases of citric and malic acids in contaminated juice), amino acids (decreases of alanine, leucine, isoleucine and valine), and less abundant components such as oligosaccharides and aromatic compounds. The possibility of using these changes as early indicators of natural spoilage or P. expansum contamination is discussed.  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