全文获取类型
收费全文 | 619497篇 |
免费 | 9022篇 |
国内免费 | 2471篇 |
专业分类
电工技术 | 11205篇 |
综合类 | 847篇 |
化学工业 | 92512篇 |
金属工艺 | 22840篇 |
机械仪表 | 18072篇 |
建筑科学 | 16132篇 |
矿业工程 | 2320篇 |
能源动力 | 16073篇 |
轻工业 | 57988篇 |
水利工程 | 5748篇 |
石油天然气 | 7378篇 |
武器工业 | 56篇 |
无线电 | 77532篇 |
一般工业技术 | 118646篇 |
冶金工业 | 115794篇 |
原子能技术 | 11857篇 |
自动化技术 | 55990篇 |
出版年
2021年 | 4385篇 |
2019年 | 4087篇 |
2018年 | 6714篇 |
2017年 | 6855篇 |
2016年 | 7310篇 |
2015年 | 5381篇 |
2014年 | 9014篇 |
2013年 | 28183篇 |
2012年 | 15305篇 |
2011年 | 21753篇 |
2010年 | 16798篇 |
2009年 | 19230篇 |
2008年 | 20337篇 |
2007年 | 20704篇 |
2006年 | 18264篇 |
2005年 | 16943篇 |
2004年 | 16688篇 |
2003年 | 16255篇 |
2002年 | 15685篇 |
2001年 | 15704篇 |
2000年 | 14773篇 |
1999年 | 15484篇 |
1998年 | 36215篇 |
1997年 | 26255篇 |
1996年 | 20373篇 |
1995年 | 15904篇 |
1994年 | 14108篇 |
1993年 | 13838篇 |
1992年 | 10226篇 |
1991年 | 9819篇 |
1990年 | 9369篇 |
1989年 | 9077篇 |
1988年 | 8599篇 |
1987年 | 7509篇 |
1986年 | 7502篇 |
1985年 | 8803篇 |
1984年 | 8200篇 |
1983年 | 7280篇 |
1982年 | 6830篇 |
1981年 | 6830篇 |
1980年 | 6564篇 |
1979年 | 6325篇 |
1978年 | 6055篇 |
1977年 | 7081篇 |
1976年 | 9519篇 |
1975年 | 5146篇 |
1974年 | 4970篇 |
1973年 | 4895篇 |
1972年 | 4051篇 |
1971年 | 3544篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Nicholas Caffes David B. Kurland Volodymyr Gerzanich J. Marc Simard 《International journal of molecular sciences》2015,16(3):4973-4984
Ischemic and hemorrhagic strokes are associated with severe functional disability and high mortality. Except for recombinant tissue plasminogen activator, therapies targeting the underlying pathophysiology of central nervous system (CNS) ischemia and hemorrhage are strikingly lacking. Sur1-regulated channels play essential roles in necrotic cell death and cerebral edema following ischemic insults, and in neuroinflammation after hemorrhagic injuries. Inhibiting endothelial, neuronal, astrocytic and oligodendroglial sulfonylurea receptor 1–transient receptor potential melastatin 4 (Sur1–Trpm4) channels and, in some cases, microglial KATP (Sur1–Kir6.2) channels, with glibenclamide is protective in a variety of contexts. Robust preclinical studies have shown that glibenclamide and other sulfonylurea agents reduce infarct volumes, edema and hemorrhagic conversion, and improve outcomes in rodent models of ischemic stroke. Retrospective studies suggest that diabetic patients on sulfonylurea drugs at stroke presentation fare better if they continue on drug. Additional laboratory investigations have implicated Sur1 in the pathophysiology of hemorrhagic CNS insults. In clinically relevant models of subarachnoid hemorrhage, glibenclamide reduces adverse neuroinflammatory and behavioral outcomes. Here, we provide an overview of the preclinical studies of glibenclamide therapy for CNS ischemia and hemorrhage, discuss the available data from clinical investigations, and conclude with promising preclinical results that suggest glibenclamide may be an effective therapeutic option for ischemic and hemorrhagic stroke. 相似文献
102.
Muntasir Hashim Farnoosh Farhad David Smyth‐Boyle Robert Akid Xiang Zhang Philip J. Withers 《工业材料与腐蚀》2019,70(11):2009-2019
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits. 相似文献
103.
104.
105.
106.
107.
108.
Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant. 相似文献
109.
In this work was investigated the effect of the addition of barium titanate (BaTiO3) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO3‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10?8 S m?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO3 ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (102 Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (Tg) values in the range 125–180 °C. An increase of 7 °C in Tg was observed after the incorporation of 0.5 wt% of BaTiO3 into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO3. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry 相似文献
110.
Wireless Personal Communications - In this article compact multiple input multiple output (MIMO) antenna with triple notch at the ultra-wideband application having two identical monopole antennas... 相似文献