全文获取类型
收费全文 | 247022篇 |
免费 | 25366篇 |
国内免费 | 14946篇 |
专业分类
电工技术 | 19949篇 |
技术理论 | 5篇 |
综合类 | 20364篇 |
化学工业 | 35496篇 |
金属工艺 | 15308篇 |
机械仪表 | 17105篇 |
建筑科学 | 20809篇 |
矿业工程 | 8289篇 |
能源动力 | 7173篇 |
轻工业 | 17703篇 |
水利工程 | 5951篇 |
石油天然气 | 12298篇 |
武器工业 | 2835篇 |
无线电 | 29770篇 |
一般工业技术 | 25151篇 |
冶金工业 | 9802篇 |
原子能技术 | 2875篇 |
自动化技术 | 36451篇 |
出版年
2024年 | 1029篇 |
2023年 | 3600篇 |
2022年 | 7781篇 |
2021年 | 10717篇 |
2020年 | 7958篇 |
2019年 | 6186篇 |
2018年 | 6916篇 |
2017年 | 8042篇 |
2016年 | 7150篇 |
2015年 | 10953篇 |
2014年 | 13692篇 |
2013年 | 16271篇 |
2012年 | 19029篇 |
2011年 | 19906篇 |
2010年 | 18470篇 |
2009年 | 17690篇 |
2008年 | 17307篇 |
2007年 | 16510篇 |
2006年 | 15043篇 |
2005年 | 12141篇 |
2004年 | 8345篇 |
2003年 | 7032篇 |
2002年 | 6672篇 |
2001年 | 5880篇 |
2000年 | 4800篇 |
1999年 | 4056篇 |
1998年 | 2636篇 |
1997年 | 2231篇 |
1996年 | 2027篇 |
1995年 | 1706篇 |
1994年 | 1384篇 |
1993年 | 923篇 |
1992年 | 726篇 |
1991年 | 545篇 |
1990年 | 445篇 |
1989年 | 382篇 |
1988年 | 278篇 |
1987年 | 175篇 |
1986年 | 152篇 |
1985年 | 63篇 |
1984年 | 66篇 |
1983年 | 36篇 |
1982年 | 51篇 |
1981年 | 54篇 |
1980年 | 59篇 |
1979年 | 33篇 |
1978年 | 17篇 |
1976年 | 17篇 |
1959年 | 15篇 |
1951年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
31.
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
32.
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
33.
Because of its ability to change optical absorption dynamically by applied electric field, nickel oxide (NiO) is a promising anodic material in smart windows, which can improve energy conversion efficiency in construction buildings. Although many works have achieved high electrochromic performance with different method. The underlying mechanism is still not fully investigated. In this article, we prepared the NiO films with large specific surface area and high stability by electron beam evaporation. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to figure out the surface morphology and composition of as-deposited films. Afterwards, the electrochemical properties and optical performance of the prepared NiO films were investigated. On this basis, the origin of surface charge was fully analyzed by cyclic voltammetry and diffusion coefficient test. These experimental and theoretical results firmly confirm that both the surface reaction and capacitive effect bring about the excellent EC performance in NiO films. These results not only provide clear evidence about electrochemical kinetics in NiO films, but also offer some useful guidelines for the design of EC materials with higher performance and longer stability. 相似文献
34.
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
35.
Electronic Commerce Research - We consider a platform providing free content for users and earning profit from the sale of advertising. The platform can collect and analyze personal data to... 相似文献
36.
37.
38.
Virtual Reality - BRICKxAR is a novel augmented reality (AR) instruction method for construction toys such as LEGO®. With BRICKxAR, physical LEGO construction is guided by virtual bricks.... 相似文献
40.
为了提升大型载货车、专用车用变速箱分离机构分离性能,满足大离合器盘分离需求,设计出一种分离机构.该机构通过机械原理实现放大输入端推力来满足离合器摩擦片分离.该分离机构结构简单、成本低廉,值得推广. 相似文献