全文获取类型
收费全文 | 8269篇 |
免费 | 824篇 |
国内免费 | 591篇 |
专业分类
电工技术 | 118篇 |
综合类 | 716篇 |
化学工业 | 2210篇 |
金属工艺 | 1052篇 |
机械仪表 | 185篇 |
建筑科学 | 356篇 |
矿业工程 | 283篇 |
能源动力 | 277篇 |
轻工业 | 783篇 |
水利工程 | 801篇 |
石油天然气 | 405篇 |
武器工业 | 45篇 |
无线电 | 211篇 |
一般工业技术 | 862篇 |
冶金工业 | 1020篇 |
原子能技术 | 260篇 |
自动化技术 | 100篇 |
出版年
2024年 | 28篇 |
2023年 | 144篇 |
2022年 | 288篇 |
2021年 | 323篇 |
2020年 | 354篇 |
2019年 | 312篇 |
2018年 | 288篇 |
2017年 | 343篇 |
2016年 | 379篇 |
2015年 | 316篇 |
2014年 | 535篇 |
2013年 | 612篇 |
2012年 | 805篇 |
2011年 | 706篇 |
2010年 | 512篇 |
2009年 | 434篇 |
2008年 | 363篇 |
2007年 | 440篇 |
2006年 | 429篇 |
2005年 | 373篇 |
2004年 | 309篇 |
2003年 | 238篇 |
2002年 | 220篇 |
2001年 | 170篇 |
2000年 | 148篇 |
1999年 | 98篇 |
1998年 | 73篇 |
1997年 | 64篇 |
1996年 | 53篇 |
1995年 | 52篇 |
1994年 | 38篇 |
1993年 | 51篇 |
1992年 | 32篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 3篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有9684条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(64):27516-27526
It is extremely desirable to develop high hydrogen evolution activity and stable visible-light-driven photocatalysts. The sluggish oxidation process and holes accumulation are the main obstacles to high catalysis activity and photo-stability. An efficient γ-NiOOH/ZnCdS photocatalyst was prepared by in-situ hydrothermal method. The γ-NiOOH nanosheets distribute on ZnCdS nanospheres surface and accelerate holes transfer. The hydrogen evolution rate is up to 48.60 mmol g?1 h?1 under visible-light illumination (λ = 400–780 nm), about 10.8 times of pure ZnCdS (4.50 mmol g?1 h?1) and 1.8 times of general β-NiOOH modified ZnCdS (27.40 mmol g?1 h?1). And apparent quantum yield of γ-NiOOH/ZCS-100 is up to 18.23% (400 nm). The carrier lifetime extends from 5.50 ns (ZnCdS) to 6.10 ns (γ-NiOOH/ZCS), examined by steady photoluminescence and time-resolved photoluminescence. Moreover, the γ-NiOOH/ZCS photocatalyst has exhibited excellent photo-stability even after one-year of storage. The γ-NiOOH nanosheets can be an excellent co-catalyst on accelerating both holes transfer and oxidation process for high photo-stability and photo-activity. 相似文献
2.
旱灾具有出现频率高、持续时间长、波及范围广等特点,本文运用降水距平百分率、Z指数、SPI标准化降水指数,对朝阳地区50a(1969~2018)干旱特征进行分析。结果表明:Z指数与SPI标准化降水指标得到的朝阳地区干旱特征情况基本一致,能较好地反映出该地区的干旱特征,朝阳地区1969~2018年自然灾害频繁发生,严重干旱年份主要集中在1980、1981、1982 年,与实际相符。 相似文献
3.
《Soils and Foundations》2022,62(6):101246
This study analyzed the effect of different treatment methods in enzyme-induced carbonate precipitation (EICP) on the mechanical properties of soil. Soybean crude urease was used to catalyze the precipitation of calcium carbonate (CaCO3). A multiple-phase method was proposed and further compared with commonly practiced EICP treatment methods (including the one-phase method, two-phase method, and premix-and-compact method) from the aspects of chemical conversion efficiency, CaCO3 precipitation distribution, permeability, and unconfined compressive strength. Based on the findings, the characteristics of each method were further discussed and summarized. Although the enzymatic CaCO3 precipitation generated from all the treatment methods could potentiate the soil strength to a great or less degree, using the proposed multiple-phase method could bring about a high chemical conversion efficiency, uniform distribution of CaCO3 as well as preferable permeability retention. In addition, the multiple-phase method could significantly improve the efficiency of urease usage. 相似文献
4.
Pengyu Xu Hao Wang Wenjun Cui Qiangguo Chen Bingtian Tu Xiahan Sang Weimin Wang Zhengyi Fu 《Journal of the American Ceramic Society》2022,105(6):3735-3739
Here we report a transparent dual-phase ZnO·2.7Al2O3 ceramic. The composite is pore-free and consists of thin nanosheets with a spinel phase and a hexagonal phase, while the two phases match closely in both lattice and refractive index. Such features result in excellent optical transmittance (maximum value >80% in the visible spectrum) at comparable phase volume. This work may provide a new thought for the rational structural design of optical nanocomposites. 相似文献
5.
Borage oil [BO: 40.9% linoleic acid (LNA) and 24.0% γ-linolenic acid (GLA)] reverses disrupted epidermal lipid barrier in essential fatty acid deficiency (EFAD). We determined the effects of BO on lamellar body (LB) content and LNA and GLA incorporation into epidermal ceramide 1 (CER1) and epidermal ceramide 2 (CER2), major barrier lipids. EFAD was induced in guinea pigs by a diet of 6% hydrogenated coconut oil (HCO) for 10 weeks (group HCO) or 8 weeks followed by 6% BO for 2 weeks (group HCO + BO). LB content and LNA and GLA incorporation into CER1 were higher in group HCO + BO than in group HCO. Small but significant levels of LNA, GLA, and their C20-metabolized fatty acids [dihomo-γ-linolenic acid (DGLA) and arachidonic acid (ARA)] were incorporated into CER2, where ARA was detected at a level lower than LNA, but DGLA incorporation exceeded that for GLA in group HCO + BO. Dietary BO enhanced LB content and differential incorporation of GLA into CER1 and DGLA into CER2. 相似文献
6.
The combined effect of resistance spot welding and precipitation hardening on the localised corrosion of A286 superalloy is studied. The specimens tested by double loop electrochemical potentiokinetic reactivation were welded in the solution treated condition, and then subjected to different precipitation hardening treatments. For both base metal and weld nugget, the maximum localised corrosion is reached when η phase is clearly observable. The fact that the localised corrosion resistance of weld nugget is different from that shown by base metal may be explained by the segregation of Ni and Ti towards the interdendritic region of weld nugget (studied by using scanning electron microscope/energy dispersive X-ray analysis). 相似文献
7.
通过硬度测试、拉伸性能测试、透射电镜观察等分析手段研究了不同强变形工艺下2519A铝合金的力学性能与微观组织。结果表明,经50%的冷轧变形和165 ℃人工时效后,2519A合金的力学性能明显提高,其抗拉强度、屈服强度和伸长率分别为522 MPa、468 MPa和8.5%。而在冷变形前添加165 ℃×2 h预时效处理,合金的力学性能进一步提高,其抗拉强度、屈服强度和伸长率分别达到535 MPa、497 MPa和8%。预时效处理可以提高合金中θ′相的密度,使析出相分布更加均匀,有助于提高合金的力学性能。 相似文献
8.
本文以竹荪为原料提取多糖成分并以乙醇分级制备竹荪多糖(DPs)不同组分,通过青春双歧杆菌体外增殖试验初步评价竹荪多糖及其分级醇沉组分的益生元功效。结果显示在α-淀粉酶溶液中水解4 h后,20%、40%、50%、60%竹荪多糖醇沉组分水解度分别为9.10%、8.02%、8.88%、11.67%,与对照组菊粉(水解度13.15%)相比差异显著(P<0.05);80%竹荪多糖醇沉组分、未分级醇沉组分与菊粉对照组相比差异不显著(P>0.05)。在模拟胃液中水解6 h后,20%、40%、50%竹荪多糖醇沉组分水解度分别为17.30%、14.52%、9.61%,与对照组菊粉(水解度5.72%)相比差异显著(P<0.05);60%竹荪多糖醇沉组分、80%竹荪多糖醇沉组分、未分级醇沉组分水解度与对照组相比无显著差异(P>0.05)。随着竹荪多糖添加量的增加,青春双歧杆菌的菌体浓度呈现先增大而后不断减小的趋势。分级醇沉浓度达到80%的竹荪多糖组分和未分级的多糖组分,青春双歧杆菌体外增殖作用与pH下降显著且效果优于菊粉(P<0.05),并在20 h的发酵时间内两者表现出相似的效果。不同竹荪多糖醇沉组分对青春双歧杆菌均有增殖效果,且不同竹荪多糖醇沉组分的增殖效果和抗水解能力随乙醇浓度的增加而增强,未分级的多糖组分同样可以加强青春双歧杆菌增殖能力,具有益生元潜力。 相似文献
9.
10.