全文获取类型
收费全文 | 54274篇 |
免费 | 4248篇 |
国内免费 | 2001篇 |
专业分类
电工技术 | 2690篇 |
技术理论 | 5篇 |
综合类 | 3422篇 |
化学工业 | 9751篇 |
金属工艺 | 2972篇 |
机械仪表 | 3200篇 |
建筑科学 | 4154篇 |
矿业工程 | 1455篇 |
能源动力 | 1394篇 |
轻工业 | 3322篇 |
水利工程 | 842篇 |
石油天然气 | 3588篇 |
武器工业 | 381篇 |
无线电 | 6122篇 |
一般工业技术 | 7094篇 |
冶金工业 | 2688篇 |
原子能技术 | 666篇 |
自动化技术 | 6777篇 |
出版年
2024年 | 234篇 |
2023年 | 839篇 |
2022年 | 1402篇 |
2021年 | 1930篇 |
2020年 | 1522篇 |
2019年 | 1304篇 |
2018年 | 1489篇 |
2017年 | 1719篇 |
2016年 | 1470篇 |
2015年 | 1936篇 |
2014年 | 2437篇 |
2013年 | 3070篇 |
2012年 | 3215篇 |
2011年 | 3546篇 |
2010年 | 3007篇 |
2009年 | 2805篇 |
2008年 | 2810篇 |
2007年 | 2653篇 |
2006年 | 2892篇 |
2005年 | 2705篇 |
2004年 | 1782篇 |
2003年 | 1576篇 |
2002年 | 1463篇 |
2001年 | 1262篇 |
2000年 | 1524篇 |
1999年 | 1725篇 |
1998年 | 1402篇 |
1997年 | 1251篇 |
1996年 | 1166篇 |
1995年 | 1006篇 |
1994年 | 784篇 |
1993年 | 590篇 |
1992年 | 464篇 |
1991年 | 361篇 |
1990年 | 279篇 |
1989年 | 241篇 |
1988年 | 200篇 |
1987年 | 111篇 |
1986年 | 98篇 |
1985年 | 65篇 |
1984年 | 36篇 |
1983年 | 23篇 |
1982年 | 43篇 |
1981年 | 27篇 |
1980年 | 22篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1970年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
This article proposes an active balancer, which features bidirectional charge shuttling and adaptive equalization current control, to fast counterbalance the state of charge (SOC) of cells in a lithium-ion battery (LIB) string. The power circuit consists of certain bidirectional buck-boost converters to transfer energy among the different cells back and forth. Owing to the characterization of the open-circuit voltage (OCV) vs SOC in LIB being relatively smooth near the SOC middle range, the SOC-inspected balance strategy can achieve more precise and efficient equilibrium than the voltage-based control. Accordingly, a compensated OCV-based SOC estimation is put forward to take into account the discrepancy of SOC estimation. Besides, the varied-duty-cycle (VDC) and curve-fitting modulation (CFM) methods are devised herein to tackle the problems of slow equalization rate and low balance efficacy, which arise from the diminution in balancing current as the SOC difference between the cells decreases in the later duration of equalization especially. The proposed strategies have taken the battery nonlinear characteristic and circuit parameter nonideality into account and can adaptively modulate the duty cycle with the SOC difference to keep balancing current constant throughout the balancing cycle. Simulated and experimental results are given to demonstrate the feasibility and effectiveness of the same prototype constructed. Compared with the fixed duty cycle and the VDC methods, the proposed CFM has the best balancing efficiency of 81.4%, and the balance time is shortened by 27.1% and 18.6%, respectively. 相似文献
12.
13.
AbstractBreast cancer is a common malignancy with poor prognosis. Cancer cells are heterogeneous and cancer stem cells (CSCs) are primarily responsible for tumor relapse, treatment-resistance and metastasis, so for breast cancer stem cells (BCSCs). Diets are known to be associated with carcinogenesis. Food-derived polyphenols are able to attenuate the formation and virulence of BCSCs, implying that these compounds and their analogs might be promising agents for preventing breast cancer. In the present review, we summarized the origin and surface markers of BCSCs and possible mechanisms responsible for the inhibitory effects of polyphenols on BCSCs. The suppressive effects of common dietary polyphenols against BCSCs, such as curcumin, epigallocatechin gallate (EGCG) and related polyphenolic compounds were further discussed. 相似文献
14.
15.
Traditionally, in supervised machine learning, (a significant) part of the available data (usually 50%-80%) is used for training and the rest—for validation. In many problems, however, the data are highly imbalanced in regard to different classes or does not have good coverage of the feasible data space which, in turn, creates problems in validation and usage phase. In this paper, we propose a technique for synthesizing feasible and likely data to help balance the classes as well as to boost the performance in terms of confusion matrix as well as overall. The idea, in a nutshell, is to synthesize data samples in close vicinity to the actual data samples specifically for the less represented (minority) classes. This has also implications to the so-called fairness of machine learning. In this paper, we propose a specific method for synthesizing data in a way to balance the classes and boost the performance, especially of the minority classes. It is generic and can be applied to different base algorithms, for example, support vector machines, k-nearest neighbour classifiers deep neural, rule-based classifiers, decision trees, and so forth. The results demonstrated that (a) a significantly more balanced (and fair) classification results can be achieved and (b) that the overall performance as well as the performance per class measured by confusion matrix can be boosted. In addition, this approach can be very valuable for the cases when the number of actual available labelled data is small which itself is one of the problems of the contemporary machine learning. 相似文献
16.
17.
聚乙二醇-三聚氰胺甲醛和聚乙烯醇半互穿网络的构建及表征 总被引:1,自引:0,他引:1
为提高三聚氰胺甲醛(MF)树脂制品的柔韧性,以聚乙二醇接枝三聚氰胺(M-PEG)替代部分三聚氰胺,并与甲醛、聚乙烯醇(PVA)在碱性条件下合成了聚乙二醇-三聚氰胺甲醛(PEG-MF)与PVA的半互穿聚合物网络体系(SemiIPN)。采用红外光谱、拉曼光谱、热重分析、差示扫描量热法等手段对Semi-IPN的微观结构进行了剖析,并分析了PEG、PVA等柔性链段对Semi-IPN黏度、游离甲醛含量、柔韧性等性能的影响。结果表明,PVA作为线型结构贯穿于聚乙二醇-三聚氰胺甲醛树脂交联网络体系结构中,形成了半互穿网络结构;所形成的Semi-IPN的热分解温度比MF树脂降低了60℃左右;Semi-IPN的韧性比纯MF树脂提高了800%,最高可达到19.700kJ/m2。 相似文献
18.
19.
Qi Yang Qilong Wu Yang Liu Shuiping Luo Xiaotong Wu Xixia Zhao Haiyuan Zou Baihua Long Wen Chen Yujia Liao Lanxi Li Pei Kang Shen Lele Duan Zewei Quan 《Advanced materials (Deerfield Beach, Fla.)》2020,32(36):2002822
Engineering novel Sn-based bimetallic materials could provide intriguing catalytic properties to boost the electrochemical CO2 reduction. Herein, the first synthesis of homogeneous Sn1−xBix alloy nanoparticles (x up to 0.20) with native Bi-doped amorphous SnOx shells for efficient CO2 reduction is reported. The Bi-SnOx nanoshells boost the production of formate with high Faradaic efficiencies (>90%) over a wide potential window (−0.67 to −0.92 V vs RHE) with low overpotentials, outperforming current tin oxide catalysts. The state-of-the-art Bi-SnOx nanoshells derived from Sn0.80Bi0.20 alloy nanoparticles exhibit a great partial current density of 74.6 mA cm−2 and high Faradaic efficiency of 95.8%. The detailed electrocatalytic analyses and corresponding density functional theory calculations simultaneously reveal that the incorporation of Bi atoms into Sn species facilitates formate production by suppressing the formation of H2 and CO. 相似文献
20.
Wenshu Chen Jiajun Gu Yongping Du Fang Song Fanxing Bu Jinghan Li Yang Yuan Ruichun Luo Qinglei Liu Di Zhang 《Advanced functional materials》2020,30(25)
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active / heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich / sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm?2, respectively, and has a low Tafel slope of 30 mV dec?1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions. 相似文献