全文获取类型
收费全文 | 3785篇 |
免费 | 188篇 |
国内免费 | 25篇 |
专业分类
电工技术 | 51篇 |
综合类 | 16篇 |
化学工业 | 810篇 |
金属工艺 | 89篇 |
机械仪表 | 138篇 |
建筑科学 | 161篇 |
矿业工程 | 13篇 |
能源动力 | 266篇 |
轻工业 | 582篇 |
水利工程 | 36篇 |
石油天然气 | 36篇 |
武器工业 | 3篇 |
无线电 | 293篇 |
一般工业技术 | 709篇 |
冶金工业 | 180篇 |
原子能技术 | 59篇 |
自动化技术 | 556篇 |
出版年
2024年 | 15篇 |
2023年 | 64篇 |
2022年 | 152篇 |
2021年 | 187篇 |
2020年 | 163篇 |
2019年 | 168篇 |
2018年 | 209篇 |
2017年 | 183篇 |
2016年 | 182篇 |
2015年 | 120篇 |
2014年 | 151篇 |
2013年 | 331篇 |
2012年 | 230篇 |
2011年 | 232篇 |
2010年 | 193篇 |
2009年 | 219篇 |
2008年 | 212篇 |
2007年 | 174篇 |
2006年 | 116篇 |
2005年 | 88篇 |
2004年 | 72篇 |
2003年 | 63篇 |
2002年 | 39篇 |
2001年 | 26篇 |
2000年 | 37篇 |
1999年 | 40篇 |
1998年 | 48篇 |
1997年 | 42篇 |
1996年 | 27篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 12篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1971年 | 2篇 |
1970年 | 4篇 |
1967年 | 3篇 |
排序方式: 共有3998条查询结果,搜索用时 15 毫秒
1.
2.
Telecommunication Systems - This paper proposes two algorithms for hybrid (Analog–Digital) beamforming in a single-user millimeter-wave (mm-wave) multi-input multi-output (MIMO) systems under... 相似文献
3.
4.
Karim Gharbi Louise Matthews James Bron Ron Roberts Alan Tinch Michael Stear 《Journal of the Royal Society Interface》2015,12(110)
Sea lice threaten the welfare of farmed Atlantic salmon and the sustainability of fish farming across the world. Chemical treatments are the major method of control but drug resistance means that alternatives are urgently needed. Selective breeding can be a cheap and effective alternative. Here, we combine experimental trials and diagnostics to provide a practical protocol for quantifying resistance to sea lice. We then combined quantitative genetics with epidemiological modelling to make the first prediction of the response to selection, quantified in terms of reduced need for chemical treatments. We infected over 1400 young fish with Lepeophtheirus salmonis, the most important species in the Northern Hemisphere. Mechanisms of resistance were expressed early in infection. Consequently, the number of lice per fish and the ranking of families were very similar at 7 and 17 days post infection, providing a stable window for assessing susceptibility to infection. The heritability of lice numbers within this time window was moderately high at 0.3, confirming that selective breeding is viable. We combined an epidemiological model of sea lice infection and control on a salmon farm with genetic variation in susceptibility among individuals. We simulated 10 generations of selective breeding and examined the frequency of treatments needed to control infection. Our model predicted that substantially fewer chemical treatments are needed to control lice outbreaks in selected populations and chemical treatment could be unnecessary after 10 generations of selection. Selective breeding for sea lice resistance should reduce the impact of sea lice on fish health and thus substantially improve the sustainability of Atlantic salmon production. 相似文献
5.
Muhammad Sheeraz Mamoon Ur Rashid Asad Ali Fazli Akram Ho Jeong Lee Jin San Choi Jong-Seong Bae Yong Soo Kim Young-Han Shin Chang Won Ahn Tae Heon Kim 《Journal of the European Ceramic Society》2021,41(10):5155-5162
We demonstrate the structural evolution of polymorphic phases in Al2O3-inserted SrMnO3 ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO3 ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO3 and the secondary hexagonal SrAl2O4 phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO3 phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al2O3-inserted SrMnO3 compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO3. 相似文献
6.
7.
8.
OA al-Swayeh MS al-Humayyd AA Mustafa AS al-Tuwaijri RS al-Rashed AT Ali 《Canadian Metallurgical Quarterly》1997,12(7):481-489
Recent evidence suggests that oxygen-derived free radicals are involved in mediating gastric microvascular and parenchymal cell injuries induced by ischaemia and reperfusion. Therefore, the effect of the locally acting anti-ulcer drug, sucralfate, was studied on ischaemia and reperfusion (e.g. induced gastric lesions, intraluminal bleeding, changes in vascular permeability and non-protein sulfhydryl levels in the rat stomach). Allopurinol was used as a known standard antioxidant drug. Rats were subjected to 30 min of gastric ischaemia in the presence of 100 mmol/L hydrochloric acid and reperfusion periods of 15, 30 or 60 min duration. The gastric lesions were assessed microscopically under an inverted microscope. The vascular permeability was quantified by measuring the extravasated Evans blue in the stomach. There were significantly greater numbers of gastric lesions, intraluminal bleeding and leakage of Evans blue during all reperfusion periods as compared with those of ischaemia, with maximum effects occurring at 60 min following reperfusion. Pretreatment with sucralfate (31.25-250 mg/kg, p.o.) or allopurinol (12.5-50 mg/kg, i.p.) 30 min before the procedure, dose-dependently reduced the gastric lesions, intraluminal bleeding, and decreased the vascular permeability induced by ischaemia and reperfusion. Furthermore, sucralfate dose-dependently reverses the ischaemia and reperfusion-induced depletion of mucosal non-protein sulfhydryl levels and inhibited the superoxide radical production in both cell-free xanthine-xanthine oxidase and in the stimulated polymorphonuclear cellular systems. These results suggest that the protection produced by sucralfate against gastric injury may be due to its antioxidant effects. 相似文献
9.
The aim of this paper is to give a general quantitative requirement which the loop gain must satisfy in order to stabilize a given unstable (possibly nonlinear and time-varying) plant, namely that the gain must exceed one. 相似文献
10.
Effect of flexure induced transverse crack and self-healing on chloride diffusivity of reinforced mortar 总被引:2,自引:0,他引:2
Mustafa Şahmaran 《Journal of Materials Science》2007,42(22):9131-9136
Cracks in reinforced concrete are unavoidable. Durability is of increasing concern in the concrete industry, and it is significantly
affected by the presence of cracks. The corrosion of reinforcing steel due to chloride ions in deicing salts or sea-water
is a major cause of premature deterioration of reinforced concrete structures. Although, it is generally recognized that cracks
accelerate the ingress of chlorides in concrete, a lack of consensus on this subject does not yet allow reliable quantification
of their effects. The present work studies the relationship between crack widths and chloride diffusivity. Flexural load was
introduced to generate cracks of width ranging between 29 and 390 μm. As crack width was increased, the effective diffusion
coefficient was also increased, thus reducing the initiation period of corrosion process. For cracks with widths less than
135 μm, the effect of crack widths on the effective diffusion coefficient of mortar was found to be marginal, whereas for
crack widths higher than 135 μm the effective diffusion coefficient increased rapidly. Therefore, the effect of crack width
on chloride penetration was more pronounced when the crack width is higher than 135 μm. Results also indicate that the relation
between the effective diffusion coefficient and crack width was found to be power function. In addition, a significant amount
of self-healing was observed within the cracks with width below 50 μm subjected to NaCl solution exposure. The present research
may provide insight into developing design criteria for a durable concrete and in predicting service life of a concrete structures. 相似文献