全文获取类型
收费全文 | 23702篇 |
免费 | 1322篇 |
国内免费 | 59篇 |
专业分类
电工技术 | 312篇 |
综合类 | 26篇 |
化学工业 | 4900篇 |
金属工艺 | 881篇 |
机械仪表 | 1298篇 |
建筑科学 | 426篇 |
矿业工程 | 6篇 |
能源动力 | 864篇 |
轻工业 | 1850篇 |
水利工程 | 91篇 |
石油天然气 | 16篇 |
无线电 | 3655篇 |
一般工业技术 | 4628篇 |
冶金工业 | 3478篇 |
原子能技术 | 291篇 |
自动化技术 | 2361篇 |
出版年
2024年 | 22篇 |
2023年 | 275篇 |
2022年 | 400篇 |
2021年 | 683篇 |
2020年 | 470篇 |
2019年 | 497篇 |
2018年 | 699篇 |
2017年 | 661篇 |
2016年 | 768篇 |
2015年 | 602篇 |
2014年 | 940篇 |
2013年 | 1389篇 |
2012年 | 1456篇 |
2011年 | 1790篇 |
2010年 | 1298篇 |
2009年 | 1332篇 |
2008年 | 1211篇 |
2007年 | 937篇 |
2006年 | 813篇 |
2005年 | 709篇 |
2004年 | 638篇 |
2003年 | 586篇 |
2002年 | 594篇 |
2001年 | 518篇 |
2000年 | 439篇 |
1999年 | 507篇 |
1998年 | 1272篇 |
1997年 | 755篇 |
1996年 | 596篇 |
1995年 | 390篇 |
1994年 | 280篇 |
1993年 | 284篇 |
1992年 | 121篇 |
1991年 | 121篇 |
1990年 | 92篇 |
1989年 | 108篇 |
1988年 | 108篇 |
1987年 | 84篇 |
1986年 | 67篇 |
1985年 | 66篇 |
1984年 | 36篇 |
1983年 | 31篇 |
1982年 | 38篇 |
1981年 | 38篇 |
1980年 | 45篇 |
1979年 | 15篇 |
1977年 | 72篇 |
1976年 | 154篇 |
1975年 | 19篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Bongsoo Lee Gang-Guk Choi Yoon-E. Choi Minji Sung Min S. Park Ji-Won Yang 《Korean Journal of Chemical Engineering》2014,31(6):1036-1042
Microalgae-derived biomass has been considered as the most promising candidate for next generation biofuel due to its sustainability and biodegradability. In this study, microalgal strain Chlamydmonas reinhardtii was randomly mutagenized by using a chemical mutagen, ethyl methane sulfonate (EMS) to create mutants showing enhanced lipid production. We identified three random mutants that displayed high lipid production in the screening using Nile red staining. Among those, mutant #128 was selected as candidate for further studies. Our flow cytometry and confocal microscopy analysis revealed that mutant #128 contains larger and more abundant lipid bodies than that of wild-type. Moreover, mutant #128 showed 1.4-fold increased fatty acid methyl ester (FAME) content compared to wild-type under nitrogen depleted condition. In addition, mutant #128 grew faster and accumulated more biomass, resulting in high lipid production. 2D gel electrophoresis and MALDI-TOF analysis used for gene targeting revealed that β-subunit of mitochondrial ATP Synthase and two-component response regulator PilR may be involved in enhanced characteristics of mutant #128. These results show the possibilities of EMS mediated random mutagenesis in generation of mutants to produce high amount of lipid as well as further study for molecular mechanism of mutants. 相似文献
972.
Paik Bu-Geun Park Il-Ryong Kim Ki-Sup Lee Kurnchul Kim Min-Jae Kim Kyoung-Youl 《Journal of Mechanical Science and Technology》2017,31(9):4227-4235
Journal of Mechanical Science and Technology - The main objective of the present study is to design a bubble collecting section for use in ventilated supercavitation experiments. The large amounts... 相似文献
973.
Hyejin Yang Young-Chul Lee Kyoung-Sik Han Harjinder Singh Minseok Yoon Ji-Hae Park Chang-Won Cho Suengmok Cho 《Food chemistry》2013
Kiwifruit is one of the most popular fruits worldwide, and it has various biological properties, including antioxidant, anti-allergic, and cardiovascular protective effects. The peel of kiwifruit, which is a by-product of processing, is a good source of flavonoids; however, its bioactivity has not been widely investigated. In this study, we evaluated the hypnotic effects of green (GRPE, Actinidia deliciosa) and gold (GOPE, Actinidia chinensis) kiwifruit peel ethanol extracts and their solvent fractions, and the possible underlying mechanisms. Oral GRPE and GOPE administration (125–1000 mg/kg) produced a dose-dependent decrease in sleep latency and an increase in sleep duration in pentobarbital-treated mice. Among three different solvent fractions of GRPE and GOPE, ethyl acetate (EA) fractions had the greatest effect on sleep duration at 250 mg/kg. The total flavonoid contents of solvent fractions were proportional to sleep duration. Like diazepam (a GABAA–benzodiazepine (BZD) receptor agonist), the hypnotic effects of GRPE, GOPE, and their EA fractions were fully inhibited by flumazenil (a GABAA–BZD receptor antagonist). These results suggest that potentiation effects of GRPE and GOPE on pentobarbital-induced sleep in mice may be modulated by a GABAergic mechanism. 相似文献
974.
975.
Su-Yun Lyu Ai Hyang Shin Dug Ryong Hahn Won-Bong Park 《Food science and biotechnology》2012,21(5):1445-1450
Reactive oxygen species (ROS) are continuously produced in aerobic organisms. Overproduction of ROS is known to play a crucial role in the pathogenesis of many cardiovascular diseases, including atherosclerosis and hypertension. Superoxide dismutase (SOD) and catalase (CAT) play critical roles on the removal of excess ROS. In the present study, we investigated the antioxidant activity of cyanidins from ogapy (Acanthopanax divaricatus var. albeofructus, ADA) fruits against oxidative stress in hydrogen peroxide (H2O2)-pretreated U937 macrophages, and explored the plausibility of the therapeutic effect of cyanidins on atherosclerosis. As a result, H2O2 generation and lipid peroxidation induced by H2O2-pretreatment was decreased by the treatment of cyanidins in U937 macrophages. In addition, increased activity of SOD and CAT was shown in H2O2-pretreated cells when treated with cyanidins. Overall, the results obtained in this study showed that cyanidin 3-galactoside and cyanidin 3-lathyroside from ADA fruits could protect macrophages against the damaging effects of H2O2 treatment. 相似文献
976.
Composite joints are often the weakest elements in composite structures. In this paper, we propose a modified version of the damage zone theory based on the yield strain ratio. We use this framework to predict failure loads for various adhesive joints. Thick aluminum-to-aluminum joint specimens with eight different adhesive lengths and four adhesive thicknesses were manufactured and tested. The strengths of different adhesive lengths could be predicted to within 15.4% using the damage zone ratio method. In addition, the strengths of joints that feature different adhesive thicknesses were predicted to within 16.3% using the damage zone ratio method. 相似文献
977.
Relva C. Buchanan Eusiuk Park Rajesh Surana Harshani Tennakone Kirthi Tennakone 《Journal of Electroceramics》2011,26(1-4):116-121
High electromechanical strains have been developed in this study in Barium Titanate ceramics, suitably doped with Nd and Zr to form a controlled concentration gradient, leading to a dome-like structure on sintering. Compacted pellets constituted of layers of barium titanate powder of varying minor amounts of Nd and Zr powders, incorporated as nitrates precursors, acquire this dome shape on sintering at 1300?C1320oC and cooling to the ambient temperature, the result of the residual thermoelastic strain. The dome structures exhibit high electromechanical responses, and the piezoelectric coefficients (deduced from electric field induced strains measurements in dome-up and dome-down positions) are also found to be exceptionally high. These Nd and Zr doped barium titanate structures could find applications as an environmentally benign material for fabrication of high displacement functionally graded electromechanical actuators in a single sintering step process. 相似文献
978.
Hydrogenated amorphous silicon films were grown on to thermally oxidized silicon wafers by Radio Frequency magnetron sputtering, and SiNx and Al2O3 capping layers were used to control the residual thermal stress. After annealing, a comparison of the silicon films with and without capping layers indicates that tensile stress induced by the capping layer enhances the crystallinity of the annealed amorphous silicon film. The stress is due to the mismatch between the coefficients of thermal expansion for the capping layer and amorphous silicon film. These results highlight the potential of thermal stress as a means to alter the crystallization in thin film architectures and suggest that even larger effects can be obtained with suitable choices of capping layer chemistry. 相似文献
979.
Seungkeun Park Byeong-Gwon Kang 《Communications, IEEE Transactions on》2009,57(8):2198-2203
This letter presents an alternative derivation of the Case IV of Pawula F-function and an approximation for the corresponding probability density function (pdf) in the presence of the Tikhonov distributed phase error. The pdf of Case IV is used to obtain new upper bounds for the conditional and average symbol-error probabilities of M-ary phase shift keying with phase error over additive white Gaussian noise channels. Numerical results demonstrate the validity of the upper bounds. 相似文献
980.
Irisappan Ganesh Sambandam Ravikumar Si Jae Park Seung Hwan Lee Soon Ho Hong 《Korean Journal of Chemical Engineering》2013,30(7):1443-1447
The malate-pyruvate conversion pathway is catalyzed by two malic enzyme isomers, MaeA and MaeB. qRT-PCR was carried out under malate and pyruvate supplemented conditions to understand the dynamics of maeA and maeB gene expression. maeA expression was elevated by malate, and maeB expression was inhibited by levels of both malate and pyruvate higher than 0.1 mM. Green fluorescent protein (GFP) reporter plasmids were also constructed by integration of the maeA/maeB promoter with the gfp gene. We showed that maeA driven GFP expression was positively and negatively correlated with extracellular malate and pyruvate induction. In contrast, no significant changes in maeB driven GFP expression were observed under both malate and pyruvate supplemented conditions. 相似文献