全文获取类型
收费全文 | 1685642篇 |
免费 | 43610篇 |
国内免费 | 11035篇 |
专业分类
电工技术 | 40559篇 |
技术理论 | 2篇 |
综合类 | 12251篇 |
化学工业 | 296378篇 |
金属工艺 | 69762篇 |
机械仪表 | 49786篇 |
建筑科学 | 55732篇 |
矿业工程 | 13311篇 |
能源动力 | 53205篇 |
轻工业 | 134873篇 |
水利工程 | 17993篇 |
石油天然气 | 41136篇 |
武器工业 | 813篇 |
无线电 | 212349篇 |
一般工业技术 | 312621篇 |
冶金工业 | 206547篇 |
原子能技术 | 34948篇 |
自动化技术 | 188021篇 |
出版年
2021年 | 19246篇 |
2020年 | 15242篇 |
2019年 | 18698篇 |
2018年 | 20185篇 |
2017年 | 20229篇 |
2016年 | 26303篇 |
2015年 | 22988篇 |
2014年 | 35294篇 |
2013年 | 96429篇 |
2012年 | 44904篇 |
2011年 | 58555篇 |
2010年 | 50481篇 |
2009年 | 57913篇 |
2008年 | 53634篇 |
2007年 | 50602篇 |
2006年 | 52302篇 |
2005年 | 45714篇 |
2004年 | 46710篇 |
2003年 | 45979篇 |
2002年 | 44721篇 |
2001年 | 41748篇 |
2000年 | 39839篇 |
1999年 | 39300篇 |
1998年 | 58889篇 |
1997年 | 47951篇 |
1996年 | 41433篇 |
1995年 | 34812篇 |
1994年 | 32280篇 |
1993年 | 31597篇 |
1992年 | 27458篇 |
1991年 | 24609篇 |
1990年 | 24679篇 |
1989年 | 23707篇 |
1988年 | 22230篇 |
1987年 | 20364篇 |
1986年 | 19871篇 |
1985年 | 23125篇 |
1984年 | 22998篇 |
1983年 | 20882篇 |
1982年 | 19680篇 |
1981年 | 19790篇 |
1980年 | 18404篇 |
1979年 | 18934篇 |
1978年 | 18102篇 |
1977年 | 18656篇 |
1976年 | 21095篇 |
1975年 | 16255篇 |
1974年 | 15748篇 |
1973年 | 15825篇 |
1972年 | 13308篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Yang Yang Yibei Zhou Juan Ren Qiaoji Zheng Kwok Ho Lam Dunmin Lin 《Journal of the European Ceramic Society》2018,38(2):557-566
Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO3-xCaHfO3 was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO3 (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d33~400 pC/N), inverse piezoelectric coefficient (d33*~547 pm/V) and planar electromechanical coupling factor (kp~58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response. 相似文献
992.
Crossover designs are an extremely useful tool to investigators, and group sequential methods have proven highly proficient at improving the efficiency of parallel group trials. Yet, group sequential methods and crossover designs have rarely been paired together. One possible explanation for this could be the absence of a formal proof of how to strongly control the familywise error rate in the case when multiple comparisons will be made. Here, we provide this proof, valid for any number of initial experimental treatments and any number of stages, when results are analyzed using a linear mixed model. We then establish formulae for the expected sample size and expected number of observations of such a trial, given any choice of stopping boundaries. Finally, utilizing the four-treatment, four-period TOMADO trial as an example, we demonstrate that group sequential methods in this setting could have reduced the trials expected number of observations under the global null hypothesis by over 33%. 相似文献
993.
994.
Prof. Michael Murray Dr. Ariane Roseblade Dr. Yongjuan Chen Kirsi Bourget Dr. Tristan Rawling 《ChemMedChem》2020,15(2):247-255
Targeting the tumor cell mitochondrion could produce novel anticancer agents. We designed an aryl−urea fatty acid ( 1 g ; 16({[4-chloro-3-(trifluoromethyl)phenyl]carbamoyl}amino)hexadecanoic acid) that disrupted the mitochondrion and decreased MDA-MB-231 breast cancer cell viability. To optimize the aryl−ureas the present study evaluated mitochondrial targeting by 1 g analogues containing alkyl chains between 10–17 carbons. Using the dye JC-1, the C12−C17 analogues efficiently disrupted the mitochondrial membrane potential (IC50s 3.5±1.2 to 7.6±1.1 μM) and impaired ATP production; shorter analogues were less active. 7-Aminoactinomycin D/annexin V staining and flow cytometry showed that these agents activated the killing mechanisms of necrosis and apoptosis to varying extents (7-aminoactinomycin D/annexin V staining ratios 4.3–6.0). Indeed, 1 g and its C17 analogue preferentially activated necrosis and apoptosis, respectively (ratios 2.1 and 16). Taken together, alkyl chain length is a determinant of mitochondrial targeting by aryl−ureas and can be varied to develop analogues that activate apoptosis or necrosis in a regulated fashion. 相似文献
995.
The solvent-dependent polymorphism of the active pharmaceutical ingredient (API) carbamazepine is interpreted from calculations of the solid-state and API-solvent intermolecular interactions. These simulations suggested that apolar solute-solute interactions could be disrupted by apolar solvents. In contrast, the polar solute-solute interactions were found to be easily disrupted by polar and protic solvents. This is consistent with experimental observations that the crystallization of the metastable form II is more dominant in apolar solvents. The Mercury program remains the gold standard in terms of usability; however, further expansion into more complex simulation techniques could make this package of even greater use in pharmaceutical manufacturing workflows. 相似文献
996.
Ajit Sharma Doan Van Thuan Thanh-Dong Pham Mai Hung Thanh Tung Nguyen Thi Thanh Truc Dai-Viet N. Vo 《化学工程与技术》2020,43(4):752-761
FeO-doped TiO2 nanoparticle photocatalysts were immobilized onto the surface of fibrous activated carbon (ACF) via a sol-gel process. As an adsorbent and photocatalyst, FeO-TiO2 on immobilized ACFs (FeO-TiO2/ACF) greatly improved the photocatalysis rate of hydrogen production as compared with pure TiO2 and ACF-TiO2 under UV irradiation and visible light. The addition of ACFs surface significantly reduced the photogenerated pairs of electrons-hole recombination, thereby promoting the photocatalysis action of doped photo-metal oxides of FeO-TiO2. Co-doping of FeO onto the lattice of the TiO2 approach can improve the absorption activity of visible light through photo-metal oxide of TiO2 and further enhance hydrogen production under visible light. The photocatalytic fabrics (FeO-TiO2/ACF) were effortlessly split out from the experimental solution for re-utilization and exhibited high stability even after five complete regeneration cycles. 相似文献
997.
Radiochemistry - Leaching of uranium and REEs with oxalic acid from the Egyptian Abu-Tartur phosphate rock (PR) was studied. The effect exerted on the leaching process by oxalic acid concentration,... 相似文献
998.
Burdin D. A. Savel’ev D. V. Ekonomov N. A. Chashin D. V. Fetisov Yu. K. 《Technical Physics Letters》2020,46(5):487-490
Technical Physics Letters - The magnetoelectric (ME) effect in a planar amorphous ferromagnet–piezoelectric lead zirconate titanate (PZT) composite structure can be effectively excited by... 相似文献
999.
1000.