全文获取类型
收费全文 | 1755145篇 |
免费 | 54278篇 |
国内免费 | 21946篇 |
专业分类
电工技术 | 54453篇 |
技术理论 | 45篇 |
综合类 | 32584篇 |
化学工业 | 321262篇 |
金属工艺 | 82073篇 |
机械仪表 | 61658篇 |
建筑科学 | 71197篇 |
矿业工程 | 22857篇 |
能源动力 | 59028篇 |
轻工业 | 123627篇 |
水利工程 | 20878篇 |
石油天然气 | 59773篇 |
武器工业 | 3121篇 |
无线电 | 228711篇 |
一般工业技术 | 303530篇 |
冶金工业 | 141707篇 |
原子能技术 | 37127篇 |
自动化技术 | 207738篇 |
出版年
2022年 | 17579篇 |
2021年 | 28489篇 |
2020年 | 21467篇 |
2019年 | 22295篇 |
2018年 | 23278篇 |
2017年 | 23675篇 |
2016年 | 29688篇 |
2015年 | 30305篇 |
2014年 | 45261篇 |
2013年 | 106656篇 |
2012年 | 55061篇 |
2011年 | 67931篇 |
2010年 | 61706篇 |
2009年 | 69428篇 |
2008年 | 61142篇 |
2007年 | 57559篇 |
2006年 | 62568篇 |
2005年 | 54163篇 |
2004年 | 51108篇 |
2003年 | 50256篇 |
2002年 | 48394篇 |
2001年 | 43658篇 |
2000年 | 42461篇 |
1999年 | 41321篇 |
1998年 | 38855篇 |
1997年 | 37249篇 |
1996年 | 35887篇 |
1995年 | 32359篇 |
1994年 | 30035篇 |
1993年 | 28627篇 |
1992年 | 27211篇 |
1991年 | 23771篇 |
1990年 | 23898篇 |
1989年 | 22768篇 |
1988年 | 21052篇 |
1987年 | 19165篇 |
1986年 | 18323篇 |
1985年 | 21521篇 |
1984年 | 22020篇 |
1983年 | 19952篇 |
1982年 | 19063篇 |
1981年 | 19087篇 |
1980年 | 17672篇 |
1979年 | 18217篇 |
1978年 | 17463篇 |
1977年 | 16679篇 |
1976年 | 16727篇 |
1975年 | 15777篇 |
1974年 | 15314篇 |
1973年 | 15382篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
131.
132.
Changbai Long Ning Ji Li Yang Wenjie Zhou Kun Zheng Wei Ren Laijun Liu 《Journal of the European Ceramic Society》2021,41(6):3369-3378
With co-substitution of (Li0.5Sm0.5) at A site and W at B site, the electrical properties of modified Ca0.92(Li0.5Sm0.5)0.08Bi2Nb2-xWxO9 [(CLS)BN-xW, x = 0, 0.015 and 0.03] piezoceramics with ultrahigh Curie temperature (TC) of > 930 °C were enhanced dramatically. The increased resistivity induced by the co-substitution ensure them to be polarized under an enough high field. Combined with the increase of spontaneous ferroelectric polarization (PS), the significant enhancements in the piezoelectric, dielectric and ferroelectric properties can be obtained in the composition x = 0.015. Furthermore, the piezoelectric activity (d33) and bulk resistivity (ρb) of (CLS)BN-0.015 W can be further enhanced at an appropriate sintering temperature. This optimum composition sintered at 1170 °C shows ultrahigh TC of ~948 °C, d33 of ~17.3 pC/N and ρb of ~6.9 MΩ cm at 600 °C, which are comparable to those of the reported high-temperature Aurivillius piezoceramics with TC > 850 °C. 相似文献
133.
Castro Mateus B. Souza Raphael R. N. Junior Agord M. P. Lima Eduardo R. Manera Leandro T. 《Analog Integrated Circuits and Signal Processing》2021,109(3):647-656
Analog Integrated Circuits and Signal Processing - This paper presents the complete design of a phase locked loop-based clock synthesizer for reconfigurable analog-to-digital converters. The... 相似文献
134.
Zhang Qi Wang Yujing Zhang Xueling Song Jun Li Yinlei Wu Xuehong Yuan Kunjie 《Journal of Materials Science》2022,57(14):7208-7224
Journal of Materials Science - Form-stable composite phase change materials (C-PCMs) prepared by microencapsulation method and porous matrix adsorption method need for compression molding after... 相似文献
135.
136.
Catalysis Letters - An environmentally benign process for synthesizing 4-methoxyphenol through methylation of hydroquinone using polystyrene immobilized Bronsted acidic ionic liquid is presented.... 相似文献
137.
138.
磁声发射(MAE)是铁磁性材料磁化过程中产生的声发射信号,在构件应力检测和微观损伤检测中有着广泛的应用。针对MAE信号非稳态、复杂性、衰减性等特点,提出海鸥算法结合变分模态分解(SOA-VMD)的去噪方法,为克服海鸥算法求解过程中易陷入局部最优解问题,利用柯西变异算子产生随机迭代过程,使改进算法即柯西变异海欧算法(CVSOA)跳出早熟收敛。采用以幅值谱熵为适应度函数,优化VMD算法中分解模态个数K和二次惩戒因子α ![]()
![]()
两个参数,将含噪声的MAE信号进行VMD分解重构。经仿真信号和实际检测信号分析表明,改进后的CVSOA-VMD算法全局寻优能力和去噪性能优于传统的SOA-VMD算法,降噪后的MAE信号特征值对于不同应力下均方根、偏斜度特征值的重复性更好,可靠性更高。 相似文献
139.
Alison Willette Benjamin Fallen Hem Bhandari Carl Sams Feng Chen Virginia Sykes Chris Smallwood Kristin Bilyeu Zenglu Li Vincent Pantalone 《Journal of the American Oil Chemists' Society》2021,98(8):861-869
Soybean oil hydrogenation alters the linolenic acid molecule to prevent the oil from becoming rancid, however, health reports have indicated trans-fat caused by hydrogenation, is not generally regarded as safe. Typical soybeans contain approximately 80 g kg−1 to 120 g kg−1 linolenic acid and 240 g kg−1 of oleic acid. In an effort to accommodate the need for high-quality oil, the United Soybean Board introduced an industry standard for a high oleic acid greater than 750 g kg−1 and linolenic acid less than 30 g kg−1 oil. By combing mutations in the soybean plant at four loci, FAD2-1A and FAD2-1B, oleate desaturase genes and FAD3A and FAD3C, linoleate desaturase genes, and seed oil will not require hydrogenation to prevent oxidation and produce high-quality oil. In 2017 and 2018, a study comparing four near-isogenic lines across multiple Tennessee locations was performed to identify agronomic traits associated with mutations in FAD3A and FAD3C loci, while holding FAD2-1A and FAD2-1B constant in the mutant (high oleic) state. Soybean lines were assessed for yield and oil quality based on mutations at FAD2-1 and FAD3 loci. Variations of wild-type and mutant genotypes were compared at FAD3A and FAD3C loci. Analysis using a generalized linear mixed model in SAS 9.4, indicated no yield drag or other negative agronomic traits associated with the high oleic and low linolenic acid genotype. All four mutations of fad2-1A, fad2-1B, fad3A, and fad3C were determined as necessary to produce a soybean with the new industry standard (>750 g kg−1 oleic and <30 g kg−1 linolenic acid) in a maturity group-IV-Late cultivar for Tennessee growers. 相似文献
140.
Corey Andrews Yiting Xu Michael Kirberger Jenny J. Yang 《International journal of molecular sciences》2021,22(1)
Calmodulin (CaM) is an important intracellular protein that binds Ca2+ and functions as a critical second messenger involved in numerous biological activities through extensive interactions with proteins and peptides. CaM’s ability to adapt to binding targets with different structures is related to the flexible central helix separating the N- and C-terminal lobes, which allows for conformational changes between extended and collapsed forms of the protein. CaM-binding targets are most often identified using prediction algorithms that utilize sequence and structural data to predict regions of peptides and proteins that can interact with CaM. In this review, we provide an overview of different CaM-binding proteins, the motifs through which they interact with CaM, and shared properties that make them good binding partners for CaM. Additionally, we discuss the historical and current methods for predicting CaM binding, and the similarities and differences between these methods and their relative success at prediction. As new CaM-binding proteins are identified and classified, we will gain a broader understanding of the biological processes regulated through changes in Ca2+ concentration through interactions with CaM. 相似文献