全文获取类型
收费全文 | 54511篇 |
免费 | 5281篇 |
国内免费 | 2352篇 |
专业分类
电工技术 | 2521篇 |
技术理论 | 2篇 |
综合类 | 2898篇 |
化学工业 | 11588篇 |
金属工艺 | 7284篇 |
机械仪表 | 2926篇 |
建筑科学 | 2303篇 |
矿业工程 | 1458篇 |
能源动力 | 8524篇 |
轻工业 | 3424篇 |
水利工程 | 476篇 |
石油天然气 | 1484篇 |
武器工业 | 447篇 |
无线电 | 4179篇 |
一般工业技术 | 6660篇 |
冶金工业 | 3071篇 |
原子能技术 | 496篇 |
自动化技术 | 2403篇 |
出版年
2024年 | 183篇 |
2023年 | 998篇 |
2022年 | 1819篇 |
2021年 | 2885篇 |
2020年 | 2204篇 |
2019年 | 1848篇 |
2018年 | 1602篇 |
2017年 | 2087篇 |
2016年 | 1960篇 |
2015年 | 1957篇 |
2014年 | 3161篇 |
2013年 | 3286篇 |
2012年 | 3802篇 |
2011年 | 4671篇 |
2010年 | 3388篇 |
2009年 | 3224篇 |
2008年 | 2943篇 |
2007年 | 3234篇 |
2006年 | 2964篇 |
2005年 | 2389篇 |
2004年 | 1976篇 |
2003年 | 1735篇 |
2002年 | 1567篇 |
2001年 | 1261篇 |
2000年 | 984篇 |
1999年 | 764篇 |
1998年 | 619篇 |
1997年 | 495篇 |
1996年 | 410篇 |
1995年 | 316篇 |
1994年 | 303篇 |
1993年 | 220篇 |
1992年 | 191篇 |
1991年 | 137篇 |
1990年 | 104篇 |
1989年 | 111篇 |
1988年 | 65篇 |
1987年 | 34篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 27篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
31.
《International Journal of Hydrogen Energy》2022,47(75):32303-32314
Membrane electrode assembly (MEA) is considered a key component of a proton exchange membrane fuel cell (PEMFC). However, developing a new MEA to meet desired properties, such as operation under low-humidity conditions without a humidifier, is a time- and cost-consuming process. This study employs a machine-learning-based approach using K-nearest neighbor (KNN) and neural networks (NN) in the MEA development process by identifying a suitable catalyst layer (CL) recipe in MEA. Minimum redundancy maximum relevance and principal component analysis were implemented to specify the most important predictor and reduce the data dimension. The number of predictors was found to play an essential role in the accuracy of the KNN and NN models although the predictors have self-correlations. The KNN model with a K of 7 was found to minimize the model loss with a loss of 11.9%. The NN model constructed by three corresponding hidden layers with nine, eight, and nine nodes can achieve the lowest error of 0.1293 for the Pt catalyst and 0.031 for PVA as a good additive blending in the CL of the MEA. However, even if the error is low, the prediction of PVA seems to be inaccurate, regardless of the model structure. Therefore, the KNN model is more appropriate for CL recipe prediction. 相似文献
32.
Xueru Chen Yin Zhang Dashui Yuan Wu Huang Jing Ding Hui Wan Wei-Lin Dai Guofeng Guan 《材料科学技术学报》2021,71(12):211-220
Porous g-C3N4 nanosheets (PCN) were prepared by the nickel-assisted one-step thermal polymerization method.Hydrogen (H2) which was produced by the reaction between nickel (Ni) foam and ammonia (NH3) defined the structure and properties of PCN.During the formation of PCN,the participation of H2 not only enhanced the spacing between layers but also boosted the specific surface area that more active sites were exposed.Additionally,H2 promoted pores formation in the nanosheets,which was beneficial to the transfer of photons through lamellar structure and improved the absorption efficiency of visible light.Remarkably,the obtained PCN possessed better Cr(Ⅵ) photocatalytic reduction efficiency than pure g-C3N4.The reaction rate constant (k) of PCN (0.013 min-1) was approximately twice that of bare g-C3N4 (0.007 min-1).Furthermore,the effects of original pH and concentration of Cr(Ⅵ)-containing solution on removal efficiency of Cr(Ⅵ) were explored.A possible photocatalytic mechanism was proposed based on the experiments of radical scavengers and photoelectrochemical characterizations. 相似文献
33.
34.
Lucía Beltrn-Camacho Marta Rojas-Torres M
Carmen Durn-Ruiz 《International journal of molecular sciences》2021,22(5)
Critical limb ischemia (CLI) constitutes the most severe form of peripheral arterial disease (PAD), it is characterized by progressive blockade of arterial vessels, commonly correlated to atherosclerosis. Currently, revascularization strategies (bypass grafting, angioplasty) remain the first option for CLI patients, although less than 45% of them are eligible for surgical intervention mainly due to associated comorbidities. Moreover, patients usually require amputation in the short-term. Angiogenic cell therapy has arisen as a promising alternative for these “no-option” patients, with many studies demonstrating the potential of stem cells to enhance revascularization by promoting vessel formation and blood flow recovery in ischemic tissues. Herein, we provide an overview of studies focused on the use of angiogenic cell therapies in CLI in the last years, from approaches testing different cell types in animal/pre-clinical models of CLI, to the clinical trials currently under evaluation. Furthermore, recent alternatives related to stem cell therapies such as the use of secretomes, exosomes, or even microRNA, will be also described. 相似文献
35.
Indoor surfaces may be adsorptive sinks with the potential to change Indoor Air Quality. To estimate this effect, the sorption parameters of formaldehyde and toluene were assessed on five floorings by an experimental method using solid-phase microextraction in an airtight emission cell. Adsorption rate constants ranged from 0.003 to 0.075 m·h−1, desorption rate constants from 0.019 to 0.51 h−1, and the partition coefficient from 0.005 to 3.9 m, and these parameters vary greatly from one volatile organic compound/material couple to another indicating contrasted sorption behaviors. A rubber was identified as a sink of formaldehyde characterized by a very low desorption constant close to 0. For these sorbent floorings identified, the adsorption rates of formaldehyde are from 2 to 4 times higher than those of toluene. Two models were used to evaluate the sink effects of floorings on indoor pollutant concentrations in one room from different realistic conditions. The scenarios tested came to the conclusion that the formaldehyde sorption on one rubber (identified as a sink) has a maximum contribution from 15% to 21% for the conditions of low air exchange rate. For other floorings, the sorption has a minor contribution less than or equal to 5%, regardless of the air exchange rate. 相似文献
36.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018)
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
37.
SPEEK/cSMM membrane for simultaneous electricity generation and wastewater treatment in microbial fuel cell
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
38.
Jie-Long He An-Te Chen Jyong-Huei Lee Shih-Kang Fan 《International journal of molecular sciences》2015,16(9):22319-22332
The basic structural and functional unit of a living organism is a single cell. To understand the variability and to improve the biomedical requirement of a single cell, its analysis has become a key technique in biological and biomedical research. With a physical boundary of microchannels and microstructures, single cells are efficiently captured and analyzed, whereas electric forces sort and position single cells. Various microfluidic techniques have been exploited to manipulate single cells through hydrodynamic and electric forces. Digital microfluidics (DMF), the manipulation of individual droplets holding minute reagents and cells of interest by electric forces, has received more attention recently. Because of ease of fabrication, compactness and prospective automation, DMF has become a powerful approach for biological application. We review recent developments of various microfluidic chips for analysis of a single cell and for efficient genetic screening. In addition, perspectives to develop analysis of single cells based on DMF and emerging functionality with high throughput are discussed. 相似文献
39.
40.
We report a simple processing method to simultaneously improve the efficiency and stability of organic solar cells (OSCs). Poly(4-styrene sulfonate)-doped poly(3,4-ethylenedioxy-thiophene (PEDOT:PSS), widely used as hole transport layer (HTL) in OSCs, tends to accelerate the degradation of devices because of its hygroscopic and acidic properties. In this regard, we have modified PEDOT:PSS to reduce its hygroscopic and acidic properties through a condensation reaction between PEDOT:PSS and poly(ethylene glycol) methyl ether (PEGME) in order to improve the efficiency and stability of OSCs. As a result, the power conversion efficiency (PCE) increased by 21%, from 2.57% up to 3.11%. A better energy level alignment by the reduced work function of the modified PEDOT:PSS with a highest occupied molecular orbital (HOMO) level of poly(3-hexylthiophene-2,5-diyl) (P3HT) is considered the origin of the improved the efficiency. The half-life of OSCs with PEDOT:PSS modified with PEGME buffer layer also increased up to 3.5 times compared to that of devices with pristine PEDOT:PSS buffer layer. 相似文献