全文获取类型
收费全文 | 1842779篇 |
免费 | 57277篇 |
国内免费 | 23067篇 |
专业分类
电工技术 | 57534篇 |
技术理论 | 42篇 |
综合类 | 32002篇 |
化学工业 | 331462篇 |
金属工艺 | 84934篇 |
机械仪表 | 66473篇 |
建筑科学 | 77791篇 |
矿业工程 | 23823篇 |
能源动力 | 60615篇 |
轻工业 | 130492篇 |
水利工程 | 21940篇 |
石油天然气 | 61377篇 |
武器工业 | 3402篇 |
无线电 | 236281篇 |
一般工业技术 | 317899篇 |
冶金工业 | 162163篇 |
原子能技术 | 37806篇 |
自动化技术 | 217087篇 |
出版年
2022年 | 18987篇 |
2021年 | 30698篇 |
2020年 | 22948篇 |
2019年 | 23577篇 |
2018年 | 25084篇 |
2017年 | 26045篇 |
2016年 | 31167篇 |
2015年 | 32115篇 |
2014年 | 47345篇 |
2013年 | 109576篇 |
2012年 | 59149篇 |
2011年 | 72650篇 |
2010年 | 65183篇 |
2009年 | 72495篇 |
2008年 | 64954篇 |
2007年 | 61191篇 |
2006年 | 65465篇 |
2005年 | 57276篇 |
2004年 | 52532篇 |
2003年 | 51005篇 |
2002年 | 49612篇 |
2001年 | 45378篇 |
2000年 | 44483篇 |
1999年 | 44328篇 |
1998年 | 46819篇 |
1997年 | 42385篇 |
1996年 | 39386篇 |
1995年 | 34688篇 |
1994年 | 32147篇 |
1993年 | 30593篇 |
1992年 | 28329篇 |
1991年 | 24700篇 |
1990年 | 24596篇 |
1989年 | 23384篇 |
1988年 | 21736篇 |
1987年 | 19716篇 |
1986年 | 18890篇 |
1985年 | 22045篇 |
1984年 | 22289篇 |
1983年 | 20195篇 |
1982年 | 19267篇 |
1981年 | 19326篇 |
1980年 | 17902篇 |
1979年 | 18434篇 |
1978年 | 17623篇 |
1977年 | 17143篇 |
1976年 | 17728篇 |
1975年 | 15943篇 |
1974年 | 15441篇 |
1973年 | 15509篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Haitang Yang Zilong Lu Bixiong Bie Zeyu Fu Jianling Yue Xiaozhong Huang 《Ceramics International》2019,45(9):11395-11402
SiCf/PyC/SiC and SiCf/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiCf/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiCf/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiCf/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B2O3 molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B2O3, the SiCf/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO2 grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiCf/PyC/SiC and SiCf/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale. 相似文献
993.
Adem Sreedhar I. Neelakanta Reddy Qui Thanh Hoai Ta Gitae Namgung Eunbin Cho Jin-Seo Noh 《Ceramics International》2019,45(6):6985-6993
In this paper, novel morphology correlation between silver nanowires (AgNWs) and cobalt (Co)-doped ZnO (Co-ZnO) flake-like thin films (nanowire/flake-like) has been proposed for enhanced photoelectrochemical (PEC) water splitting activity. Here in, high-quality AgNWs/Co-ZnO heterostructures enabled superior visible light water splitting activity compared to the pure ZnO and AgNWs/ZnO. To address the strategic effect of AgNWs coupling and transition metal (Co-2?at%) doping into the ZnO host lattice, we have carried out the X-ray diffraction, field emission scanning microscopy, X-ray photoelectron spectroscopy, UV–Vis transmittance, water contact angle and PEC analyses. In this way, PEC water splitting activity was mainly examined by linear sweep voltammetry (I-V), amperometric I-t and photoconversion efficiency (η) studies. The experimental results provide clear evidence of morphology correlation between AgNWs and Co-ZnO flake-like structures for strong visible light absorption. Specifically, AgNWs/Co-ZnO composites exhibited significant enhancement in the photocurrent density (7.0?×?10?4 A/cm2) than AgNWs/ZnO (3.2?×?10?4 A/cm2) and pure ZnO (1.5?×?10?6 A/cm2). As a result, detailed AgNWs/Co-ZnO geometry has great potential for photoconversion efficiency (0.73%). In a word, the merits of controllable AgNWs/Co-ZnO heterostructure are proposed to improve the visible light harvesting and charge carrier generation for energy conversion devices. 相似文献
994.
Nassar Sabry S. Faragallah Osama S. El-Bendary Mohsen A. M. 《Wireless Personal Communications》2021,119(1):37-61
Wireless Personal Communications - Due to the widely spreading of fake news utilizing image manipulation and its bad effects, this paper investigates efficient image contents verification and... 相似文献
995.
Metallurgist - Kinetics of austenite grain growth within a heat-affected zone is studied for low carbon low-alloy steels of different alloying composition. The effect of Ti/N ratio on the metal... 相似文献
996.
997.
Steffen Vojacek Lukas Schulig Nathalie Wössner Norman Geist Prof. Dr. Walter Langel Prof. Dr. Manfred Jung Prof. Dr. Dennis Schade Prof. Dr. Andreas Link 《ChemMedChem》2019,14(8):853-864
Indoles are privileged structures in medicinal and bioorganic chemistry that are particularly well suited to serve as platforms for diversity. Among many other therapeutic areas, the indole scaffold has been used to design aromatic compounds useful to interfere with enzymes engaged in the regulation of substrate acylation status, such as sirtuins. However, the planarity of the indole ring is not necessarily optimal for all target enzymes, especially when functionalization with aromatic side chains is required. Replacement of flat scaffolds by nonplanar molecular cores dominated by sp3 hybridization is a common strategy to avoid the disadvantages associated with poor solubility and high promiscuity, while covering less-well-explored areas of chemical space. Thus, we synthesized fragment-like tetrahydroindoles suitable for fragment-based drug discovery as well as a well-characterized small library intended as multipurpose screening compounds. For proof of principle, these compounds were screened against sirtuins 1–3, enzymes known to be addressable by indoles. We found that 2,6,6-trimethyl-4-oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxamides are potent and selective SIRT2 inhibitors. Compound 16 t displayed an IC50 value of 0.98 μm and could serve as exquisite starting point for hit-to-lead profiling. 相似文献
998.
999.
Parsania P. H. Sankhavara Dharmesh B. Chopda Jalpa Patel Jignesh P. 《Polymer Bulletin》2020,77(6):3111-3128
Polymer Bulletin - Jute and glass composites of epoxy resin of (2E, 6E)-bis(4-hydroxybenzylidene)cyclohexanone (EBHBC) were prepared by compressing molding technique using three different hardeners... 相似文献
1000.
Palmitoleic acid has been classified as an insulin-sensitizing lipokine, but evidence for this from human studies has been inconsistent. We hypothesized that this is related to either the types of samples or conditions under which samples are collected. We measured plasma palmitoleic acid and total free fatty acids (FFA) using ultra-performance liquid chromatography in blood samples collected from 34 adults under a variety of conditions. We collected duplicate samples of adipose (n = 10), FFA (n = 9), and very low density lipoprotein triacylglycerol (VLDL-TAG) (n = 7) to measure the palmitoleic acid as a percentage of total fatty acids. We tested whether the percentage of palmitoleic acid was correlated with insulin resistance, as measured by homeostatic model of insulin resistance (HOMA-IR). Adipose stearoyl-coenzyme A desaturase 1 (SCD-1) protein was measured by capillary Western blotting. FFA-palmitoleic acid percentage increased as a function of total FFA and was greater (p < 0.005) in females than males. Adipose palmitoleic acid percentage was greater in females than males (p < 0.001), as was adipose SCD-1. Palmitoleic acid was greater in femoral fat than in abdominal fat in both females and males (p < 0.001), and correlated positively with HOMA-IR only in females. The test–retest reliability values for percentage palmitoleic acid were 7 ± 10% for adipose, 24 ± 26% for VLDL, and 53 ± 31% for FFA. Because FFA-palmitoleic acid percentage varies as a function of total FFA, investigators should re-evaluate how palmitoleic acid data is presented. The positive relationship between adipose palmitoleic acid and HOMA-IR in females suggests that it is not a potent insulin-sensitizing lipokine in humans. 相似文献