全文获取类型
收费全文 | 37043篇 |
免费 | 3563篇 |
国内免费 | 2274篇 |
专业分类
电工技术 | 4841篇 |
技术理论 | 10篇 |
综合类 | 4581篇 |
化学工业 | 3990篇 |
金属工艺 | 943篇 |
机械仪表 | 1441篇 |
建筑科学 | 5012篇 |
矿业工程 | 1933篇 |
能源动力 | 1752篇 |
轻工业 | 2191篇 |
水利工程 | 1653篇 |
石油天然气 | 3264篇 |
武器工业 | 244篇 |
无线电 | 2284篇 |
一般工业技术 | 3229篇 |
冶金工业 | 1950篇 |
原子能技术 | 678篇 |
自动化技术 | 2884篇 |
出版年
2024年 | 57篇 |
2023年 | 382篇 |
2022年 | 772篇 |
2021年 | 1206篇 |
2020年 | 1172篇 |
2019年 | 905篇 |
2018年 | 882篇 |
2017年 | 1054篇 |
2016年 | 1295篇 |
2015年 | 1399篇 |
2014年 | 2269篇 |
2013年 | 2383篇 |
2012年 | 2648篇 |
2011年 | 2916篇 |
2010年 | 2251篇 |
2009年 | 2290篇 |
2008年 | 2129篇 |
2007年 | 2518篇 |
2006年 | 2277篇 |
2005年 | 2003篇 |
2004年 | 1654篇 |
2003年 | 1437篇 |
2002年 | 1302篇 |
2001年 | 1022篇 |
2000年 | 881篇 |
1999年 | 743篇 |
1998年 | 545篇 |
1997年 | 452篇 |
1996年 | 404篇 |
1995年 | 326篇 |
1994年 | 268篇 |
1993年 | 173篇 |
1992年 | 146篇 |
1991年 | 129篇 |
1990年 | 116篇 |
1989年 | 96篇 |
1988年 | 95篇 |
1987年 | 45篇 |
1986年 | 27篇 |
1985年 | 23篇 |
1984年 | 29篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1964年 | 10篇 |
1961年 | 9篇 |
1960年 | 9篇 |
1959年 | 9篇 |
1955年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Age-related macular degeneration (AMD) is the major reason for blindness in the industrialized world with limited treatment options. Important pathogenic pathways in AMD include oxidative stress and vascular endothelial growth factor (VEGF) secretion. Due to their bioactivities, fucoidans have recently been suggested as potential therapeutics. This review gives an overview of the recent developments in this field. Recent studies have characterized several fucoidans from different species, with different molecular characteristics and different extraction methods, in regard to their ability to reduce oxidative stress and inhibit VEGF in AMD-relevant in vitro systems. As shown in these studies, fucoidans exhibit a species dependency in their bioactivity. Additionally, molecular properties such as molecular weight and fucose content are important issues. Fucoidans from Saccharina latissima and Laminaria hyperborea were identified as the most promising candidates for further development. Further research is warranted to establish fucoidans as potential therapeutics for AMD. 相似文献
62.
The coal and biomass coupling power generation technology is considered as a promising technology for energy conservation and emission reduction. In this paper, a novel coal and biomass indirect coupling system is proposed based on the technology of biomass gasification and co-combustion of coal and gasification gas. For the sake of comparison, a coal and biomass direct coupling system is also introduced based on the technology of co-combustion of coal and biomass. The process of the direct and the indirect coupling system is simulated. The thermodynamic and economic performances of two systems are analyzed and compared. The simulation indicates that the thermodynamic performance of the indirect coupling system is slightly worse, but the economic performance is better than that of the direct coupling system. When the blending ratio of biomass is 20%, the energy and exergy efficiencies of the indirect coupling system are 42.70% and 41.14%, the internal rate of return (IRR) and discounted payback period (DPP) of the system are 25.68% and 8.56 years. The price fluctuation of fuels and products has a great influence on the economic performance of the indirect coupling system. The environmental impact analysis indicates that the indirect coupling system can inhibit the propagation of NOx and reduce the environmental cost. 相似文献
63.
Neil Gerard Quigley Dr. Stefano Tomassi Dr. Francesco Saverio di Leva Dr. Salvatore Di Maro Dr. Frauke Richter Dr. Katja Steiger Prof. Dr. Susanne Kossatz Prof. Dr. Luciana Marinelli Dr. Johannes Notni 《Chembiochem : a European journal of chemical biology》2020,21(19):2836-2843
αvβ6 Integrin is an epithelial transmembrane protein that recognizes latency-associated peptide (LAP) and primarily activates transforming growth factor beta (TGF-β). It is overexpressed in carcinomas (most notably, pancreatic) and other conditions associated with αvβ6 integrin-dependent TGF-β dysregulation, such as fibrosis. We have designed a trimeric Ga-68-labeled TRAP conjugate of the αvβ6-specific cyclic pentapeptide SDM17 (cyclo[RGD-Chg-E]-CONH2) to enhance αvβ6 integrin affinity as well as target-specific in-vivo uptake. Ga-68-TRAP(SDM17)3 showed a 28-fold higher αvβ6 affinity than the corresponding monomer Ga-68-NOTA-SDM17 (IC50 of 0.26 vs. 7.4 nM, respectively), a 13-fold higher IC50-based selectivity over the related integrin αvβ8 (factors of 662 vs. 49), and a threefold higher tumor uptake (2.1 vs. 0.66 %ID/g) in biodistribution experiments with H2009 tumor-bearing SCID mice. The remarkably high tumor/organ ratios (tumor-to-blood 11.2; -to-liver 8.7; -to-pancreas 29.7) enabled high-contrast tumor delineation in PET images. We conclude that Ga-68-TRAP(SDM17)3 holds promise for improved clinical PET diagnostics of carcinomas and fibrosis. 相似文献
64.
65.
The formation mechanism of an internal crack was clarified from the viewpoint of the crystallography and thermal expansion. An inverse pole figure map obtained by EBSD pattern showed that the crack propagated along the grain boundaries having high ∑ values within the columnar zone. After the crack initiation, these positions were considered to undergo cracking followed by propagation toward the equiaxed side. Near the termination position, the grains ahead of crack propagation had a Schmid factor higher than 0.45 consuming elastic strain energy. Thermal expansion measurements showed that the grain with (0 0 1) orientation had the largest expansion while that with (0 1 1) the smallest. The grain boundaries neighboring the combination of (0 0 1) and (0 1 1) grains had the largest thermal stress. Therefore, thermal stress contributed to the initiation of cracking. It was thus proposed to enlarge the equiaxed zone to prevent cracking by discontinuing the crack propagation. 相似文献
66.
Seung-Hwan Lee Jin-Myung Choi Jae-Hong Lim Jozeph Park Jin-Seong Park 《Ceramics International》2018,44(2):1978-1983
The thermoelectric properties of aluminum-doped tin oxide (ATO) thin films synthesized by thermal atomic layer deposition (ALD) were studied with respect to the aluminum concentration. The overall aluminum content in each layer was modulated by adjusting the relative number of tin oxide (SnO2) and aluminum oxide (Al2O3) growth cycles, where a sequential process involving n cycles of SnO2 growth followed by 1 cycle of Al2O3 deposition was performed (building up a super-cycle). The electrical conductivity (620 S/cm), free carrier concentration (1.23x1021 cm-3), and power factor (0.49 mW/K2m) increase until their maximum values are reached when the Al content is approximately 1.50 at% of the cations, and decrease as more Al is added in. On the other hand, the Seebeck coefficient decreases monotonically as the Al content increases up to about 2.88 at%, and begins to increase with further Al doping. Here the thermoelectric efficiency is therefore determined primarily by the free carrier concentration, while the Seebeck coefficient appears to be influenced by the overall crystal structure. 相似文献
67.
通过对磷酸二铵生产造粒特性分析,高压中速磨粉机原理分析,结合实践生产中的工艺需求,利用高压中速磨粉系统将颗粒状不合格品磨成细粉后添加进系统重新喷浆造粒,提高返料添加量,减少不合格品的产生,腾空仓库有限货位,以获取更大的经济价值。 相似文献
68.
He Qi Ruzhong Zuo Jing-feng Li Longtu Li 《Journal of the European Ceramic Society》2018,38(16):5341-5347
A morphotropic phase boundary (MPB) between rhombohedral (R) and tetragonal (T) phases was identified in a few (0.9-x)NaNbO3-0.1BaTiO3-xABO3 (x?=?0–0.05) lead-free systems. Critical roles of R-phase inducers were specially evaluated in terms of phase boundary position, microstructure and piezoelectric responses. The results indicate not only the tolerance factor of the ABO3 additive but also its ferroelectricity and corresponding volume change would influence the formation of phase boundary and further determine dielectric and ferroelectric responses. The piezoelectric coefficient d33 of MPB compositions was compared with theoretically-calculated d33-cal according to d33?=?2Pr·ε33·Q33, demonstrating that the piezoelectric response of these systems should be determined by combined effects of the phase coexistence, nano-scale domains and particularly enhanced dielectric responses. The largest d33 ~305 pC/N, the highest ε33T/εo ~2815 and the lowest Pr ~14.7 μC/cm2 were achieved in the MPB composition with 3.75% SrZrO3. These experimental results provide a valuable reference for designing new NaNbO3-based lead-free piezoelectric materials. 相似文献
69.
Sang Moon Lee Nong Xu John R. Grace Anwu Li C. Jim Lim Sung Su Kim Farzam Fotovat Achim Schaadt Robin J. White 《Journal of the European Ceramic Society》2018,38(1):211-219
NaA zeolite membranes were synthesised in the secondary growth hydrothermal method based on the seeding of the inner surface of a ceramic α-alumina tube. The impacts of crystallisation time and zeolite precursor concentration (in H2O) were investigated. The structure and stability of the prepared NaA zeolite membranes were also investigated with operating temperatures, times and pressures. The results indicate that the optimal synthesis gel molar composition was 3Na2O: 2SiO2: Al2O3: 200H2O. This led to cubic-shaped NaA zeolite which showed good stability. The optimal NaA zeolite membrane had H2O and CH3OH fluxes of 2.77 and 0.19 kg/m2h, with H2O/H2 and CH3OH/H2 separation factors of ∞ and 0.09 at a temperature of 30 °C. The NaA zeolite membrane had high thermal stability, but poor separation performance at high temperature (240 °C). The results suggested that the H2 permeation flux is significantly influenced by preferential adsorption of vapour in the NaA zeolite membrane. 相似文献
70.
以高速摄影技术作为主要研究手段,研究钢轨交流闪光焊接过程过梁爆破特征,并结合热成像系统采集焊接过程温度场,以此为数据基础定量分析了钢轨交流闪光焊接过梁爆破特征. 结果表明,钢轨交流脉动闪光焊接工艺模式下,加速闪光阶段具有几个阶段中最高的闪光频次46.93次/s,脉动闪光阶段具有最低的闪光频次11.07次/s;连续闪光阶段闪光烈度为0.009 2 mm/次,是几个阶段中最强的,脉动阶段的闪光烈度最弱,为0.003 8 mm/次;从闪光加热因子来看,脉动阶段最高,符合了该阶段积累热量的主要目的;加速闪光阶段最低,是由于该阶段为了制造保护气氛产生的气化过梁带走了较多的热量;从闪光均匀度看,闪光最不均匀的阶段是闪平阶段,最均匀的阶段是脉动阶段,这恰恰说明了两待焊端面的微观平行情况在闪平阶段最差、脉动阶段最佳. 相似文献