全文获取类型
收费全文 | 194705篇 |
免费 | 21516篇 |
国内免费 | 14543篇 |
专业分类
电工技术 | 16696篇 |
技术理论 | 1篇 |
综合类 | 19478篇 |
化学工业 | 26147篇 |
金属工艺 | 13009篇 |
机械仪表 | 13895篇 |
建筑科学 | 14909篇 |
矿业工程 | 7846篇 |
能源动力 | 5115篇 |
轻工业 | 18536篇 |
水利工程 | 5270篇 |
石油天然气 | 8214篇 |
武器工业 | 2382篇 |
无线电 | 21444篇 |
一般工业技术 | 18356篇 |
冶金工业 | 7958篇 |
原子能技术 | 2796篇 |
自动化技术 | 28712篇 |
出版年
2024年 | 1096篇 |
2023年 | 3075篇 |
2022年 | 7055篇 |
2021年 | 9179篇 |
2020年 | 6624篇 |
2019年 | 4828篇 |
2018年 | 5259篇 |
2017年 | 6177篇 |
2016年 | 5616篇 |
2015年 | 8811篇 |
2014年 | 10597篇 |
2013年 | 12823篇 |
2012年 | 15214篇 |
2011年 | 16122篇 |
2010年 | 15071篇 |
2009年 | 14928篇 |
2008年 | 14742篇 |
2007年 | 14468篇 |
2006年 | 12648篇 |
2005年 | 10548篇 |
2004年 | 7370篇 |
2003年 | 5518篇 |
2002年 | 5101篇 |
2001年 | 4554篇 |
2000年 | 3779篇 |
1999年 | 2322篇 |
1998年 | 1325篇 |
1997年 | 1124篇 |
1996年 | 945篇 |
1995年 | 791篇 |
1994年 | 627篇 |
1993年 | 491篇 |
1992年 | 385篇 |
1991年 | 308篇 |
1990年 | 257篇 |
1989年 | 233篇 |
1988年 | 170篇 |
1987年 | 100篇 |
1986年 | 94篇 |
1985年 | 45篇 |
1984年 | 43篇 |
1983年 | 32篇 |
1982年 | 30篇 |
1981年 | 40篇 |
1980年 | 55篇 |
1979年 | 24篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1959年 | 35篇 |
1951年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Tao Feng Mingde Tong Shuotian Yao Hejun Li Shifeng Wen Hongjiao Lin 《Journal of the European Ceramic Society》2021,41(1):158-166
Composites based on hafnium carbide and reinforced with continuous naked carbon fiber with and without PyC interface were prepared at low temperature by precursor infiltration and pyrolysis and chemical vapor deposition method. The microstructure, mechanical property, cyclic ablation and fiber bundle push-in tests of the composites were investigated. The results show that after three times ablation cycles, the bending strength of samples without PyC interface decreased by 63.6 %; the bending strength of samples with PyC interface only decreased by 37.8 %. The force displacement curve of the samples with PyC interface presented a well pseudoplastic deformation state. The mechanical behavior difference of two kinds of composites was due to crucial function of PyC interface phase including protection of fiber and weakening of fiber/matrix interface. 相似文献
12.
Fenqi Du Dongmei Yang Yue Sun Yang Jiao Feng Teng Haibo Fan 《Ceramics International》2021,47(4):4963-4971
Ultrawide band gap semiconductor materials have attracted considerable attention in recent years owing to their great potential in the photocatalytic field. In this study, Zn-doped Ga2O3 nanofibers with various concentrations were synthesized via electrospinning; they exhibited a superior photocatalytic degradation performance of rhodamine B dye compared to that of undoped Ga2O3 nanofibers. The Zn dopant replaced Ga sites via replacement doping, which could increase the concentration of oxygen vacancies and lead to enhanced photocatalytic properties. When the Zn concentration increased, a Ga2O3/ZnGa2O4 hybrid structure formed, which could further enhance the photocatalytic performance. The separation of photogenerated carriers due to Zn doping and heterojunctions were the primary causes of the enhanced photocatalytic performance. This study provides experimental data for the fabrication of high-performance photocatalysts based on Ga2O3 nanomaterials. 相似文献
13.
药物相互作用改变了剂量效应关系,可能会降低疗效或增加毒性,是临床应用中合并用药治疗时重要的考虑因素。预测具有临床意义的药物相互作用是药物研发过程中获益风险评估的重要环节。本文概述了药物研发过程中药物相互作用研究的目的和意义,体内和体外研究的主要内容;梳理分析了2020年国家药品监督管理局(National Medical Products Administration, NMPA)和美国食品药品监督管理局(Food and Drug Administration, FDA)批准上市的新药药物相互作用研究情况,旨在为我国药物研发过程中药物相互作用研究及其监管审评提供参考。 相似文献
14.
15.
Shuhai Liu Ming Han Xiaolong Feng Qiuhong Yu Long Gu Longfei Wang Yong Qin Zhong Lin Wang 《Advanced functional materials》2021,31(17):2010339
Utilizing inner-crystal piezoelectric polarization charges to control carrier transport across a metal-semiconductor or semiconductor–semiconductor interface, piezotronic effect has great potential applications in smart micro/nano-electromechanical system (MEMS/NEMS), human-machine interfacing, and nanorobotics. However, current research on piezotronics has mainly focused on systems with only one or rather limited interfaces. Here, the statistical piezotronic effect is reported in ZnO bulk composited of nanoplatelets, of which the strain/stress-induced piezo-potential at the crystals’ interfaces can effectively gate the electrical transport of ZnO bulk. It is a statistical phenomenon of piezotronic modification of large numbers of interfaces, and the crystal orientation of inner ZnO nanoplatelets strongly influence the transport property of ZnO bulk. With optimum preferred orientation of ZnO nanoplatelets, the bulk exhibits an increased conductivity with decreasing stress at a high pressure range of 200–400 MPa, which has not been observed previously in bulk. A maximum sensitivity of 1.149 µS m−1 MPa−1 and a corresponding gauge factor of 467–589 have been achieved. As a statistical phenomenon of many piezotronic interfaces modulation, the proposed statistical piezotronic effect extends the connotation of piezotronics and promotes its practical applications in intelligent sensing. 相似文献
16.
Recently, the successful synthesis of wafer-scale single-crystal graphene, hexagonal boron nitride (hBN), and MoS2 on transition metal surfaces with step edges boosted the research interests in synthesizing wafer-scale 2D single crystals on high-index substrate surfaces. Here, using hBN growth on high-index Cu surfaces as an example, a systematic theoretical study to understand the epitaxial growth of 2D materials on various high-index surfaces is performed. It is revealed that hBN orientation on a high-index surface is highly dependent on the alignment of the step edges of the surface as well as the surface roughness. On an ideal high-index surface, well-aligned hBN islands can be easily achieved, whereas curved step edges on a rough surface can lead to the alignment of hBN along with different directions. This study shows that high-index surfaces with a large step density are robust for templating the epitaxial growth of 2D single crystals due to their large tolerance for surface roughness and provides a general guideline for the epitaxial growth of various 2D single crystals. 相似文献
17.
Qianying Hoo Xiaohu Wang Feng Yuan Xuewei Cao Tiewa Cao Maolin Zhang 《Journal of the European Ceramic Society》2021,41(6):3816-3822
Jingdezhen is famous for its bluish white (Qingbai) porcelains of the Song Dynasty, and those decorated with iron spots are distinctive among them. Herein, iron spots on a bluish white porcelain were investigated using a series of microscopic and spectroscopic characterizations. We found the decreasing iron content from more than 8 wt% to about 2 wt% during the glaze color transition from rusty to brown and finally into green, which built a connection on the coloring mechanism of iron-rich crystallized glaze and celadon glaze. We identified the rare ε-Fe2O3, a promising magnetic material, in both the dark brown crystals and the triangular crystals in the rusty area, which is its first discovery among bluish white porcelains. Based on these findings, we discussed the coloring mechanism of iron-spot decoration along with the physical form of the iron oxide crystals, indicating the partially reducing atmosphere during firing process. 相似文献
18.
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
19.
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
20.