全文获取类型
收费全文 | 25916篇 |
免费 | 2112篇 |
国内免费 | 902篇 |
专业分类
电工技术 | 1348篇 |
技术理论 | 1篇 |
综合类 | 1474篇 |
化学工业 | 4691篇 |
金属工艺 | 1387篇 |
机械仪表 | 1362篇 |
建筑科学 | 1945篇 |
矿业工程 | 591篇 |
能源动力 | 907篇 |
轻工业 | 1705篇 |
水利工程 | 370篇 |
石油天然气 | 1367篇 |
武器工业 | 124篇 |
无线电 | 3188篇 |
一般工业技术 | 3344篇 |
冶金工业 | 1446篇 |
原子能技术 | 330篇 |
自动化技术 | 3350篇 |
出版年
2024年 | 67篇 |
2023年 | 406篇 |
2022年 | 730篇 |
2021年 | 1078篇 |
2020年 | 750篇 |
2019年 | 690篇 |
2018年 | 733篇 |
2017年 | 818篇 |
2016年 | 779篇 |
2015年 | 960篇 |
2014年 | 1291篇 |
2013年 | 1626篇 |
2012年 | 1648篇 |
2011年 | 1795篇 |
2010年 | 1470篇 |
2009年 | 1506篇 |
2008年 | 1387篇 |
2007年 | 1291篇 |
2006年 | 1391篇 |
2005年 | 1194篇 |
2004年 | 868篇 |
2003年 | 771篇 |
2002年 | 775篇 |
2001年 | 563篇 |
2000年 | 554篇 |
1999年 | 624篇 |
1998年 | 589篇 |
1997年 | 475篇 |
1996年 | 459篇 |
1995年 | 350篇 |
1994年 | 289篇 |
1993年 | 195篇 |
1992年 | 176篇 |
1991年 | 118篇 |
1990年 | 90篇 |
1989年 | 74篇 |
1988年 | 91篇 |
1987年 | 50篇 |
1986年 | 44篇 |
1985年 | 22篇 |
1984年 | 29篇 |
1983年 | 13篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 4篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Spatial ability has been recognized as one of the most important factors affecting the mathematical performance of students. Previous studies on spatial learning have mainly focused on developing strategies to shorten the problem-solving time of learners for very specific learning tasks. Such an approach usually has limited effects on improving the mathematical performance of students. In this study, a cognitive analysis approach is proposed for developing spatial learning tools by taking game characteristics into consideration. Moreover, the validation of the cognitive components of the spatial sense test for constructing two different kinds of intervention is verified, and the effects of the interventions are compared. To evaluate the performance of the proposed approach, an experiment was conducted on the mathematics course of an elementary school. The experimental results show that the spatial learning tool promotes not only the learning achievement, but also the spatial sense of the students. 相似文献
942.
Lixin Yang Xiaoyun Mi Jiangang Su Xiyan Zhang Zhaohui Bai Nengli Wang Jun Lin 《Journal of Materials Science: Materials in Electronics》2018,29(10):7941-7951
YVO4:Bi3+,Ln3+ (Ln?=?Dy, Sm, Eu) phosphors were successful synthesized by microwave sintering method, and characterized by X-ray powder diffraction, scanning electron microscope, photoluminescence spectra, lifetime, quantum efficiency and general structure analysis system structure refinement. Refinement results indicated that the introduced ions occupy the sites of Y3+. Under 275 nm excitation, the luminescent intensity of YVO4:Bi3+ samples reach the maximum when Bi3+ concentration is 0.02, the broad excitation spectrum of YVO4:Bi3+ has a strongest peak at near 343 nm. Doped Bi3+ can effectively improve the emission intensity of YVO4:Ln3+. The energy transfer mechanism of Bi3+?→?Ln3+ was dipole-quadrupole mechanism of electric multipole interaction. The critical distance (Rc) between Ln3+ and Bi3+ were calculated by concentration quenching method. Emitting color of YVO4:Bi3+,Ln3+ phosphors were tunable by adjusting Ln3+ content. In a word, the material has a good application prospects on light emitting diodes. 相似文献
943.
近远场地震中土工格栅加筋土挡墙抗震特性的振动台试验研究 总被引:2,自引:0,他引:2
地震中土工格栅加筋土挡墙的动态行为与抗震机理的认识还尚不清楚。采用叠层剪切型模型土箱开展大型振动台试验,基于量纲理论π定理的Froude常数设计试验模型,考虑近远场地震动影响,采用汶川地震中松潘远场波、什邡近场波和Taft中远场地震波,测试墙体加速度、加筋回填土加速度、墙体侧向变形、加筋区与非加筋区回填土表面震陷、加筋区填土超静孔隙水压力以及土工格栅应变特性,得出远场和中远场地震波对加筋结构产生了强烈的宏观反应特征,而近场波对加筋区填土超静孔隙水压力的微观反应影响显著,加速度和沉降反应特征表明土工格栅为柔性挡土墙提供了较强的抗震能力,格栅应变分布特征揭示了柔性挡土墙上受力分布规律。研究结果将为土工格栅加筋土挡墙抗震安全设计和工程施工提供依据。 相似文献
944.
Using Computational Intelligence Algorithms to Solve the Coalition Structure Generation Problem in Coalitional Skill Games 下载免费PDF全文
Coalitional skill games (CSGs) are a simple model of cooperation in an uncertain environment where each agent has a set of skills that are required to accomplish a variety of tasks and each task requires a set of skills to be completed, but each skill is very hard to be quantified and can only be qualitatively expressed. Thus far, many computational questions surrounding CSGs have been studied. However, to the best of our knowledge, the coalition structure generation problem (CSGP), as a central issue of CSGs, is extremely challenging and has not been well solved. To this end, two different computational intelligence algorithms are herein evaluated: binary particle swarm optimization (BPSO) and binary differential evolution (BDE). In particular, we develop the two stochastic search algorithms with two-dimensional binary encoding and corresponding heuristic for individual repairs. After that, we discuss some fundamental properties of the proposed heuristic. Finally, we compare the improved BPSO and BDE with the state-of-the-art algorithms for solving CSGP in CSGs. The experimental results show that our algorithms can find the same near optimal solutions with the existing approaches but take extremely short time, especially under the large problem size. 相似文献
945.
946.
Mohammad A. Rahman Biing-Ming Su Elliot Band Mojahedul Islam 《Journal of surfactants and detergents》2011,14(3):333-338
An efficient procedure for the regioselective synthesis of secondary alcohol alkoxylates from 2,2,4-trimethyl-1,3-pentanediol
(TMPD) is described. TMPD was reacted with propylene oxide followed by ethylene oxide in the presence of a catalytic amount
of alkali metal hydroxide to form secondary alcohol alkoxylates. Instead of a mixture of compounds resulting from the reaction
of TMPD and propylene oxide, the primary hydroxyl group of the TMPD reacted to form predominantly 2,2,4-trimethyl-3-hydroxypentylpropoxylate
as the major product. On further ethoxylation the less hindered secondary hydroxyl group of the 2,2,4-trimethyl-3-hydroxypentylpropoxylate
reacted predominantly. 13C NMR indicated that the secondary hydroxyl group (96.2 mol%) of TMPD remained unreacted during alkoxylation. 相似文献
947.
Encapsulationof lycopene from watermelon in calcium‐alginate microparticles using an optimised inverse‐gelation method by response surface methodology 下载免费PDF全文
Giovana B. Celli Alyne G. Teixeira Tamunoemi G. Duke Marianne Su‐Ling Brooks 《International Journal of Food Science & Technology》2016,51(6):1523-1529
Lycopene exhibits strong antioxidant activity due to its unsaturated molecular bonds, which also contributes to its susceptibility for degradation. Encapsulation techniques can reduce lycopene degradation, increasing its potential applications in functional foods and nutraceuticals. The objective of this study was to optimise the encapsulation of lycopene from watermelon in alginate microparticles using the inverse gelation method. Box–Behnken design was used for the optimisation of three variables: concentrations of alginate (w/v %) and CaCl2 (g L?1), and gelation time (min). Two types of alginate were investigated (low viscosity and high viscosity) and optimised separately using encapsulation efficiency and loading capacity as responses. Results indicated that the models had a good fit to the experimental data and the optimal conditions varied depending on the type of alginate. In general, particles prepared with low‐viscosity alginate exhibited higher encapsulation efficiency and loading capacity and could be used for further research. 相似文献
948.
The application of hydrocolloid gel particles is potentially useful in food, chemical, and pharmaceutical industries. Alginate gel particles are one of the more commonly used hydrocolloid gel particles due to them being biocompatible, nontoxic, biodegradable, cheap, and simple to produce. They are particularly valued for their application in encapsulation. Encapsulation in alginate gel particles confers protective benefits to cells, DNA, nutrients, and microbes. Slow release of flavors, minerals, and drugs can also be achieved by encapsulation in gel particles. The particle size and shape of the gel particles are crucial for specific applications. In this review, current methods of producing alginate gel particles will be discussed, taking into account their advantages, disadvantages, scalability, and impact on particle size. The physical properties of alginate gel particles will determine the effectiveness in different application conditions. This review will cover the current understanding of the alginate biopolymer, gelation mechanisms and factors affecting release properties, gel strength, and rheology of the alginate gel particle systems. 相似文献
949.
Su Won Park Soo Jin Lee You Sin Sim Jin Young Choi Eun Young Park Bong Soo Noh 《Food science and biotechnology》2017,26(2):311-317
The purpose of this study was to analyze ethanol content in soy sauce using mass spectrometry (MS) with electronic nose (e-nose) to determine if MS e-nose can replace gas chromatographic analysis for halal certification. Gas chromatography–flame ionization detector (GC-FID), the standard method of ethanol content, was used to analyze 24 different kinds of soy sauce. Ethanol was detected from 13 soy sauce samples in the concentration range of 0.0004–1.7wt%. The MS e-nose data were analyzed by discriminant function analysis (DFA). Based on an addition method, the results were more than 96.6% accurate when the ethanol concentrations were greater than 0.5%. A high correlation between the first score of the DFA plot and the ethanol concentration was observed. Thus, mass spectrometry based on e-nose is an efficient method for determining ethanol as a primary screening tool for halal certification. 相似文献
950.
The antioxidant activities and nutritional properties of Jeonyak made with beef bone stock and gelatin were investigated. Traditional Jeonyak (J1) was prepared with beef bone stock, whereas modified Jeonyak was made with gelatin and honey (J2) or with gelatin and oligosaccharides (J3). All 3 kinds of Jeonyak had antioxidant activities and J1 had the highest activity. The α-glucosidase inhibitory activity was measured to investigate the antidiabetic effect and J3 had the highest inhibitory activity of 80.47%. Glycine was the most abundant amino acid in all 3 kinds of Jeonyak. Both traditional and modified Jeonyaks have antioxidative and antidiabetic effects, suggesting that Jeonyak can be used as an effective traditional functional food. 相似文献