全文获取类型
收费全文 | 339704篇 |
免费 | 3425篇 |
国内免费 | 1051篇 |
专业分类
电工技术 | 6329篇 |
综合类 | 2452篇 |
化学工业 | 44915篇 |
金属工艺 | 17228篇 |
机械仪表 | 13931篇 |
建筑科学 | 7367篇 |
矿业工程 | 1968篇 |
能源动力 | 6421篇 |
轻工业 | 18827篇 |
水利工程 | 3720篇 |
石油天然气 | 4524篇 |
武器工业 | 7篇 |
无线电 | 41623篇 |
一般工业技术 | 68922篇 |
冶金工业 | 53987篇 |
原子能技术 | 4830篇 |
自动化技术 | 47129篇 |
出版年
2021年 | 1357篇 |
2020年 | 1025篇 |
2019年 | 1388篇 |
2018年 | 22005篇 |
2017年 | 21593篇 |
2016年 | 14843篇 |
2015年 | 2628篇 |
2014年 | 3084篇 |
2013年 | 8583篇 |
2012年 | 9586篇 |
2011年 | 21679篇 |
2010年 | 19142篇 |
2009年 | 16861篇 |
2008年 | 17969篇 |
2007年 | 20469篇 |
2006年 | 6109篇 |
2005年 | 9969篇 |
2004年 | 8181篇 |
2003年 | 7728篇 |
2002年 | 6111篇 |
2001年 | 5587篇 |
2000年 | 5278篇 |
1999年 | 5640篇 |
1998年 | 15904篇 |
1997年 | 10505篇 |
1996年 | 8144篇 |
1995年 | 5928篇 |
1994年 | 5169篇 |
1993年 | 5169篇 |
1992年 | 3504篇 |
1991年 | 3372篇 |
1990年 | 3292篇 |
1989年 | 3122篇 |
1988年 | 2836篇 |
1987年 | 2294篇 |
1986年 | 2362篇 |
1985年 | 2676篇 |
1984年 | 2376篇 |
1983年 | 2127篇 |
1982年 | 1955篇 |
1981年 | 2098篇 |
1980年 | 1827篇 |
1979年 | 1703篇 |
1978年 | 1691篇 |
1977年 | 2059篇 |
1976年 | 2749篇 |
1975年 | 1455篇 |
1974年 | 1395篇 |
1973年 | 1340篇 |
1972年 | 1129篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
Nathan M. Wilbur Antin M. O'Sullivan Kerry T. B. MacQuarrie Tommi Linnansaari R. Allen Curry 《河流研究与利用》2020,36(5):769-783
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems. 相似文献
65.
This work developed a computational methodology to evaluate and compare standard fire exposures such as those outlined in ASTM E119 with real fire exposures and determine the difference in the temperature rise of a rail car floor assembly. The real fire exposures simulated in this work were identified in a review of incidents and consisted of a constantly-fed diesel fuel spill, a localized trash fire, and a gasoline spill simulated from a collision of the railcar with an automobile. These realistic fire exposures were applied to a variety of exemplar rail cars representative of single-level and bi-level passenger cars. These floor assembly models exposed to realistic fires were simulated in Fire Dynamics Simulator (FDS). The thermal exposure at the underside of railcar provided by FDS was coupled with a thermal model in ABAQUS, which provided the evolution of temperature in different components of the floor assembly. The standard scenarios were simulated for 2 hours instead of the typical 30 minutes to identify the appropriate exposure duration in ASTM E119, which can better represent a real fire scenario. The average and maximum temperatures predicted at the unexposed surface for both scenarios were compared with the threshold values given in NFPA 130. 相似文献
66.
Dr. Li Di Prof. Per Artursson Dr. Alex Avdeef Prof. Leslie Z. Benet Prof. J. Brian Houston Dr. Manfred Kansy Edward H. Kerns Prof. Hans Lennernäs Dr. Dennis A. Smith Prof. Kiyohiko Sugano 《ChemMedChem》2020,15(20):1862-1874
Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients. 相似文献
67.
Vu Hoa T. Nguyen Manh B. Vu Tan M. Le Giang H. Pham Trang T. T. Nguyen Trinh Duy Vu Tuan A. 《Topics in Catalysis》2020,63(11-14):1046-1055
Topics in Catalysis - Nano Fe-BTC/graphene oxide (GO) composites were successfully synthesized by hydrothermal treatment with a microwave-assisted method. Samples were characterized by X-ray... 相似文献
68.
H. Cherfouh O. Fellahi T. Hadjersi B. Marsan 《International Journal of Hydrogen Energy》2018,43(6):3431-3440
This work aims at developing a new composite material based on nanosized semiconducting CuInS2 (CIS) particles combined with silicon nanowires grown on a silicon substrate (SiNWs/Si) for photoelectrochemical (PEC)-splitting of water. The CIS particles were prepared via a colloidal method using N-methylimidazole (NMI) as the solvent and an annealing treatment. The SiNWs were obtained by chemical etching of silicon (100) substrates assisted by a metal. The CIS/SiNWs/Si composite material was obtained by deposition of an aliquot of a suspension of CIS particles onto the SiNWs/Si substrate, using spin coating followed by a drying step. The XRD pattern demonstrated that CuInS2 grows in the tetragonal/chalcopyrite phase, while SiNWs/Si presents a cubic structure. The SEM images show semi-spherical particles (~10 nm) distributed on the surface of silicon nanowires (~10 μm). The EIS measurements reveal n-type conductivity for CIS, SiNWs/Si and CIS/SiNWs/Si materials, which could favour the oxidation reaction of water molecules. 相似文献
69.
70.
A. V. Kozlov I. A. Portnykh V. I. Pastukhov 《The Physics of Metals and Metallography》2018,119(4):396-401
The influence of the temperature gradient over the thickness of the cladding of a fuel element of a fast-neutron reactor on the migration of point defects formed in the cladding material due to neutron irradiation has been studied. It has been shown that, under the action of the temperature gradient, the flux of vacancies onto the inner surface of the cladding is higher than the flux of interstitial atoms, which leads to the formation of a specific concentration profile in the cladding with a vacancy-depleted zone near the inner surface. The experimental results on the spatial distribution of pores over the cladding thickness have been presented with which the data on the concentration profiles and vacancy fluxes have been compared. 相似文献