全文获取类型
收费全文 | 269772篇 |
免费 | 32974篇 |
国内免费 | 14127篇 |
专业分类
电工技术 | 58708篇 |
技术理论 | 14篇 |
综合类 | 21859篇 |
化学工业 | 35039篇 |
金属工艺 | 12980篇 |
机械仪表 | 14798篇 |
建筑科学 | 17568篇 |
矿业工程 | 8462篇 |
能源动力 | 13163篇 |
轻工业 | 15404篇 |
水利工程 | 6753篇 |
石油天然气 | 9627篇 |
武器工业 | 2528篇 |
无线电 | 27177篇 |
一般工业技术 | 20459篇 |
冶金工业 | 12185篇 |
原子能技术 | 3452篇 |
自动化技术 | 36697篇 |
出版年
2024年 | 577篇 |
2023年 | 3998篇 |
2022年 | 7909篇 |
2021年 | 10235篇 |
2020年 | 9402篇 |
2019年 | 8001篇 |
2018年 | 7319篇 |
2017年 | 9858篇 |
2016年 | 11961篇 |
2015年 | 13003篇 |
2014年 | 19351篇 |
2013年 | 17760篇 |
2012年 | 20327篇 |
2011年 | 21066篇 |
2010年 | 15578篇 |
2009年 | 15796篇 |
2008年 | 14732篇 |
2007年 | 18428篇 |
2006年 | 16976篇 |
2005年 | 14224篇 |
2004年 | 11338篇 |
2003年 | 9789篇 |
2002年 | 7657篇 |
2001年 | 6243篇 |
2000年 | 4969篇 |
1999年 | 3982篇 |
1998年 | 2832篇 |
1997年 | 2280篇 |
1996年 | 2203篇 |
1995年 | 1747篇 |
1994年 | 1547篇 |
1993年 | 966篇 |
1992年 | 890篇 |
1991年 | 682篇 |
1990年 | 546篇 |
1989年 | 471篇 |
1988年 | 330篇 |
1987年 | 223篇 |
1986年 | 175篇 |
1985年 | 163篇 |
1984年 | 195篇 |
1983年 | 149篇 |
1982年 | 132篇 |
1981年 | 106篇 |
1980年 | 103篇 |
1979年 | 58篇 |
1977年 | 39篇 |
1964年 | 46篇 |
1962年 | 76篇 |
1959年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
《International Journal of Hydrogen Energy》2022,47(49):21231-21240
To explore the feasibility and related mechanism of MFC biosensor for wastewater detection under the action of combined heavy metals. Cyclic voltammetry (CV) and scanning electrochemical impedance spectroscopy (EIS) were used to explore the related bioelectrochemical process. The response of the reactor to single/combined heavy metals, low/high heavy metal concentrations, and the differences in ohmic resistance (Rs) and charge transfer resistance (Rct) were investigated using Ni as the core heavy metal and the combined action of Cd, Cu and Zn. The results indicated that there was a linear relationship between the concentration and output voltage of the MFC biosensor under the action of combined heavy metals (R2 = 0.8803–0.973). However, the internal resistance (Rint) of the MFC biosensor under the action of single heavy metal was far less than that of the combined heavy metal group, and the power density (19.849 W m?3) was 4 times that of the combined heavy metal group (3.109–4.589 W m?3). The Rs of the biosensors in the combined heavy metal group were 0.868Ω and 0.860, which were higher than 0.768Ω of the single heavy metal sensor. With the increase of the concentration of heavy metals in the influent, the increase of Rct was more obvious in the combined group, while the Rs in the single group significantly increased (P < 0.05). The results imply that it is possible for MFC biosensors to be used in the detection of actual water polluted by various heavy metals, but the biosensor performance is mainly limited by Rct, which needs to be further improved. 相似文献
4.
Efficient electricity price forecasting plays a significant role in our society. In this paper, a novel influencer-defaulter mutation (IDM) mutation operator has been proposed. The IDM operator has been combined with six well-known optimization algorithms to create mutated optimization algorithms whose performance has been tested on twenty-four standard benchmark functions. Further, the artificial neural network is integrated with mutated optimization algorithms to solve the electricity price prediction problem. The policymakers can identify appropriate variables based on the predicted prices to help future market planning. The statistical results prove the efficacy of the IDM operator on the recent optimization algorithms. 相似文献
5.
Liu Yang Pengfei Yu Wenyuan Li Fengliang Cao Xin Jin Sheng Xue Xianglong Zhang Tingwei Zhang Mingbo Wu Wenting Wu 《American Institute of Chemical Engineers》2022,68(9):e17760
Hydrogen peroxide (H2O2) has been listed as one of the 100 most important chemicals in the world. However, huge amount of residual H2O2 is hard to timely decomposed into O2 and H2O under acidic condition, easily resulting in explosion hazard. Here, we reported a core–shell structure catalyst, that is graphene with Co N structure encapsulated Co nanoparticles. Co N graphene shell serves as the active site for the H2O2 decomposition, and Co core further enhance this decomposition. Benefiting from it, the H2O2 decomposition were close to 100% after 6 cycles without pH adjustment, which increased 6 orders of magnitude compared with no catalyst. At the same time, the O2 generation reached 99.67% in 2 h with little metal leaching, and ·OH has been greatly inhibited to only 0.08%. This work can cleanly remove H2O2 with little deep oxidation and protect the process of H2O2 utilization to achieve a safer world. 相似文献
6.
甫沙4井位于塔里木盆地塔西南坳陷昆仑山前冲断带的柯东构造带上,北部和东部分别发育有柯克亚和柯东1井油气田。为研究甫沙4井原油来源与充注过程,对原油样品和连续抽提后的含油砂样各组分(游离态、束缚态、包裹体)进行GC、GC?MS和 GC?IRMS分析,与柯克亚凝析油气田油样进行油—油对比。结果表明:甫沙4井晚期充注原油组分具有C29?32重排藿烷、重排甾烷和Ts相对含量高,C27?29甾烷ααα 20R分布呈反“L”型,以及正构烷烃单体碳同位素值较低等特征,与柯克亚凝析油气田来源于二叠系普司格组(P2?3p)烃源岩的主体原油(I类)地球化学特征一致。而早期充注的原油组分具有重排藿烷、重排甾烷和Ts相对含量较低,C27?29甾烷ααα 20R分布呈“V”型,以及正构烷烃单体碳同位素值较高等特征,与柯克亚凝析油气田来源于中—下侏罗统湖相泥岩的II类原油地球化学特征一致。甫沙4井经历3个阶段成藏过程:①在上新世,二叠系烃源岩于生油晚期阶段生成的I类原油运移至柯克亚构造带或柯东构造带深部形成油藏;②在更新世早期,侏罗系烃源岩于生油早—中期生成的II类原油运移至甫沙4井白垩系储层;③在第四纪,强烈的构造作用使深部I类原油沿断裂调整进入甫沙4井白垩系储层。最终造成甫沙4井白垩系储层II类原油先充注,I类原油后充注的特殊现象。 相似文献
7.
电力线是一类形状细长、特征稀疏、随着视角的变化容易混淆在大量背景信息中的特殊障碍物,常规电力线检测识别算法得到的目标框对电力线所在位置的估计不够准确。为此,提出了一种相对角度估计方法,基于常规电力线目标检测与识别算法,并结合电力线相对角度估计,从而提高电力线的检测识别过程中所在位置的精度。相比电力线绝对角度回归的方法,提出的相对角度估计方法容易训练易收敛,计算量小,适用于实时性要求较高的应用场合。 相似文献
8.
9.
《Journal of the European Ceramic Society》2022,42(3):1014-1022
In this work we have investigated the effect of the solvent during the processing of SrFe12O19 platelet-based permanent magnets by cold sintering process (CSP) plus a post-thermal treatment. Several organic solvents: glacial acetic acid, oleic acid and oleylamine have been analyzed, optimizing the CSP temperatures at 190?270 °C, under pressures of 375?670 MPa and 6?50 wt% of solvent. Modifications in the morphological and structural properties are identified depending on the solvent, which impacts on the magnetic response. Independently of the solvent, the mechanical integrity of ferrite magnets obtained by CSP is improved by a post-annealing at 1100 °C for 2 h, resulting in relative densities around 92 % with an average grain size of 1 μm and a fraction of SrFe12O19 phase >91 %. HC ≥ 2.1 kOe and MS of 73 emu/g are obtained in the final sintered ceramic magnets, exhibiting the highest HC value of 2.8 kOe for the magnet sintered using glacial acetic acid. 相似文献
10.
大规模多输入多输出(Multiple-Input Multiple-Output, MIMO)可以有效提升5G SA网络的上行链路数据传输速率以及可靠性。针对5G SA网络上行链路速率和覆盖不均衡的情况,提出了基于大规模MIMO的分组算法,将发送信号矢量进行分组,组内采用最大似然检测,组外采用基于正交三角分解(QR分解)的干扰消除检测,并且结合5G频谱的叠加策略,在降低算法复杂度的同时,有效提升网络覆盖和速率。通过5G SA现网实测,通过MIMO降低分组数量能够提升分组检测性能,结合上行低频段频谱叠加策略能够有效提升5G SA网络上行覆盖30%,提升5G SA网络上行平均速率40%~80%,特别是弱覆盖边缘的网络速率,最高可达600%。 相似文献