全文获取类型
收费全文 | 2587篇 |
免费 | 56篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 52篇 |
综合类 | 1篇 |
化学工业 | 597篇 |
金属工艺 | 51篇 |
机械仪表 | 56篇 |
建筑科学 | 137篇 |
矿业工程 | 21篇 |
能源动力 | 60篇 |
轻工业 | 220篇 |
水利工程 | 8篇 |
石油天然气 | 7篇 |
武器工业 | 1篇 |
无线电 | 185篇 |
一般工业技术 | 393篇 |
冶金工业 | 494篇 |
原子能技术 | 28篇 |
自动化技术 | 339篇 |
出版年
2022年 | 20篇 |
2021年 | 37篇 |
2019年 | 30篇 |
2018年 | 51篇 |
2017年 | 38篇 |
2016年 | 39篇 |
2015年 | 36篇 |
2014年 | 46篇 |
2013年 | 175篇 |
2012年 | 83篇 |
2011年 | 107篇 |
2010年 | 92篇 |
2009年 | 97篇 |
2008年 | 98篇 |
2007年 | 81篇 |
2006年 | 91篇 |
2005年 | 69篇 |
2004年 | 49篇 |
2003年 | 39篇 |
2002年 | 59篇 |
2001年 | 33篇 |
2000年 | 45篇 |
1999年 | 40篇 |
1998年 | 83篇 |
1997年 | 53篇 |
1996年 | 44篇 |
1995年 | 34篇 |
1994年 | 46篇 |
1993年 | 39篇 |
1992年 | 35篇 |
1991年 | 28篇 |
1990年 | 22篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1986年 | 27篇 |
1985年 | 36篇 |
1984年 | 49篇 |
1983年 | 38篇 |
1982年 | 22篇 |
1981年 | 46篇 |
1980年 | 44篇 |
1979年 | 42篇 |
1978年 | 31篇 |
1977年 | 30篇 |
1976年 | 39篇 |
1975年 | 24篇 |
1974年 | 31篇 |
1973年 | 27篇 |
1972年 | 20篇 |
1970年 | 27篇 |
排序方式: 共有2650条查询结果,搜索用时 15 毫秒
81.
Bioequivalence of Docosahexaenoic Acid from Different Algal Oils in Capsules and in a DHA-Fortified Food 总被引:4,自引:0,他引:4
Arterburn LM Oken HA Hoffman JP Bailey-Hall E Chung G Rom D Hamersley J McCarthy D 《Lipids》2007,42(11):1011-1024
Docosahexaenoic acid (DHA), a long-chain omega-3 fatty acid, is important for eye and brain development and ongoing visual, cognitive, and cardiovascular health. Unlike fish-sourced oils, the bioavailability of DHA from vegetarian-sourced (algal) oils has not been formally assessed. We assessed bioequivalence of DHA oils in capsules from two different algal strains versus bioavailability from an algal-DHA-fortified food. Our 28-day randomized, placebo-controlled, parallel group study compared bioavailability of (a) two different algal DHA oils in capsules ("DHASCO-T" and "DHASCO-S") at doses of 200, 600, and 1,000 mg DHA per day (n = 12 per group) and of (b) an algal-DHA-fortified food (n = 12). Bioequivalence was based on changes in plasma phospholipid and erythrocyte DHA levels. Effects on arachidonic acid (ARA), docosapentaenoic acid-n-6 (DPAn-6), and eicosapentaenoic acid (EPA) were also determined. Both DHASCO-T and DHASCO-S capsules produced equivalent DHA levels in plasma phospholipids and erythrocytes. DHA response was dose-dependent and linear over the dose range, plasma phospholipid DHA increased by 1.17, 2.28 and 3.03 g per 100 g fatty acid at 200, 600, and 1,000 mg dose, respectively. Snack bars fortified with DHASCO-S oil also delivered equivalent amounts of DHA on a DHA dose basis. Adverse event monitoring revealed an excellent safety and tolerability profile. Two different algal oil capsule supplements and an algal oil-fortified food represent bioequivalent and safe sources of DHA. 相似文献
82.
Shigeng Li Kausick Auddy Peter Barber Tara J. Hansen Jisheng Ma Hans‐Conrad zur Loye Harry J. Ploehn 《Polymer Engineering and Science》2012,52(9):1888-1902
This study used in situ polymerization to prepare polyethylene terephthalate (PET) nanocomposites incorporating Ethoquad‐modified montmorillonite (eMMT), unmodified hectorite (HCT), or phenyl hectorite (phHCT) particles to study the impact of platelet surface chemistry and loading on thermal, mechanical, and gas barrier properties. eMMT platelets reduced the PET crystallization rate without altering the ultimate degree of crystallinity. In contrast, HCT and phHCT platelets accelerated the polymer's crystallization rate and increased its crystallinity. DMA results for thermally‐quenched samples showed that as T increased past glass transition temperature (Tg), HCT and phHCT nanocomposites (and control PET) manifested precipitous drops in G′ followed by increasing G′ due to cold crystallization; in contrast, eMMT nanocomposites had much higher G′ values around Tg. This provides direct evidence of eMMT reinforcement in thermally‐quenched eMMT nanocomposites. These results suggest that eMMT has a strong, favorable interaction with PET, possibly through Ethoquad‐PET entanglement. HCT and phHCT have a fundamentally different interaction with PET that increases crystallization rate and Tg by 11 to 17°C. Water barrier improvement in eMMT nanocomposites agrees with previously published oxygen barrier results and can be rationalized in terms of a tortuous path gas barrier model. POLYM. ENG. SCI., 52:1888–1902, 2012. © 2012 Society of Plastics Engineers 相似文献
83.
84.
Flame Assisted Chemical Vapor Deposition (FACVD), a novel technique that shows an enormous potential in porous oxides deposition, was employed for the first time aiming to obtain hydroxyapatite (HA) coatings on 316 L stainless steel metallic substrates. Calcium acetate and ammonium phosphate diluted in ethanol were employed as precursor salts. A Ca/P molar ratio of 1.66 was employed in precursor solution, which is equivalent to stoichiometric hydroxyapatite. A porous coating, formed by an open and interconnected network, was observed by scanning electronic microscopy (SEM) and associated with homogenous reactions. Thickness of hydroxyapatite coating was 412 ± 3 μm. X-ray diffraction (XRD) analysis indicated the presence of crystalline coatings, mainly constituted by hydroxyapatite phase and traces of tricalcium phosphate (β-TCP). Carbonate in the hydroxyapatite coatings was identified by Fourier transform-infrared (FTIR) spectroscopy. 相似文献
85.
86.
G. Schmidl G. Andrä J. Bergmann A. Gawlik I. Höger S. Anders F. Schmidl V. Tympel F. Falk 《Journal of Materials Science》2013,48(12):4177-4182
CW-diode laser crystallization of amorphous silicon (a-Si) deposited by sputtering or by electron beam evaporation onto different substrates (glass without or with SiNx or SiO2 intermediate layers) is investigated. The resulting grain sizes and orientations are characterized by electron backscatter diffraction, optical microscopy, and x-ray diffraction. We demonstrate that 200 nm thick sputtered a-Si layers can be crystallized on all of the used substrates to result in grains from 1 up to 100 μm in size, depending on the laser irradiation parameters (intensity, exposure time). Electron beam evaporated a-Si films can be crystallized only on sputtered SiNx intermediate layers to result in grains of 100 μm in size. Similar crystallographic film properties follow from laser treatment if the product of laser peak intensity and square root of exposure time is kept constant, independent of the scan velocity used. A high fraction of preferred (100)-oriented silicon grains can only be observed for samples with crystallites less than 10 μm in size. 相似文献
87.
89.
Maria M. Mendes-Pinto Amy M. LaFountain Mary Caswell Stoddard Richard O. Prum Harry A. Frank Bruno Robert 《Journal of the Royal Society Interface》2012,9(77):3338-3350
Light absorption by carotenoids is known to vary substantially with the shape or conformation of the pigment molecule induced by the molecular environment, but the role of interactions between carotenoid pigments and the proteins to which they are bound, and the resulting impact on organismal coloration, remain unclear. Here, we present a spectroscopic investigation of feathers from the brilliant red scarlet ibis (Eudocimus ruber, Threskiornithidae), the orange-red summer tanager (Piranga rubra, Cardinalidae) and the violet-purple feathers of the white-browed purpletuft (Iodopleura isabellae, Tityridae). Despite their striking differences in colour, all three of these feathers contain canthaxanthin (β,β-carotene-4,4′-dione) as their primary pigment. Reflectance and resonance Raman (rR) spectroscopy were used to investigate the induced molecular structural changes and carotenoid–protein interactions responsible for the different coloration in these plumage samples. The results demonstrate a significant variation between species in the peak frequency of the strong ethylenic vibration (ν1) peak in the rR spectra, the most significant of which is found in I. isabellae feathers and is correlated with a red-shift in canthaxanthin absorption that results in violet reflectance. Neither polarizability of the protein environment nor planarization of the molecule upon binding can entirely account for the full extent of the colour shift. Therefore, we suggest that head-to-tail molecular alignment (i.e. J-aggregation) of the protein-bound carotenoid molecules is an additional factor. 相似文献
90.
Battery cells being electrically disconnected resulting from degradation, mechanical stress, or corrosion can lead to hazardous situations during operation of electric vehicles or storage systems in stationary applications. The mentioned errors can be acceptable in some cases when cells or cell strings are connected in parallel, but the failure is to be detected in order to guarantee the reliable and safe operation of the battery system. A method enabling the estimation whether individual battery cells are faulty (cell error or electrically disconnected) by evaluating the mean impedance and capacity information of cell groups is introduced and validated. 相似文献