全文获取类型
收费全文 | 94781篇 |
免费 | 10408篇 |
国内免费 | 5662篇 |
专业分类
电工技术 | 4834篇 |
技术理论 | 7篇 |
综合类 | 6517篇 |
化学工业 | 18998篇 |
金属工艺 | 2504篇 |
机械仪表 | 5167篇 |
建筑科学 | 7932篇 |
矿业工程 | 7719篇 |
能源动力 | 6787篇 |
轻工业 | 9725篇 |
水利工程 | 2070篇 |
石油天然气 | 18798篇 |
武器工业 | 588篇 |
无线电 | 2449篇 |
一般工业技术 | 5610篇 |
冶金工业 | 6085篇 |
原子能技术 | 1248篇 |
自动化技术 | 3813篇 |
出版年
2024年 | 276篇 |
2023年 | 1267篇 |
2022年 | 2760篇 |
2021年 | 3802篇 |
2020年 | 3686篇 |
2019年 | 3219篇 |
2018年 | 2848篇 |
2017年 | 3041篇 |
2016年 | 3641篇 |
2015年 | 3539篇 |
2014年 | 6203篇 |
2013年 | 6071篇 |
2012年 | 7480篇 |
2011年 | 7701篇 |
2010年 | 5242篇 |
2009年 | 5065篇 |
2008年 | 4437篇 |
2007年 | 5624篇 |
2006年 | 5649篇 |
2005年 | 4692篇 |
2004年 | 3952篇 |
2003年 | 3532篇 |
2002年 | 2923篇 |
2001年 | 2564篇 |
2000年 | 2206篇 |
1999年 | 1778篇 |
1998年 | 1425篇 |
1997年 | 1227篇 |
1996年 | 980篇 |
1995年 | 837篇 |
1994年 | 679篇 |
1993年 | 504篇 |
1992年 | 403篇 |
1991年 | 319篇 |
1990年 | 264篇 |
1989年 | 233篇 |
1988年 | 110篇 |
1987年 | 88篇 |
1986年 | 74篇 |
1985年 | 66篇 |
1984年 | 64篇 |
1983年 | 42篇 |
1982年 | 59篇 |
1981年 | 130篇 |
1980年 | 56篇 |
1979年 | 16篇 |
1977年 | 6篇 |
1973年 | 6篇 |
1959年 | 7篇 |
1951年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Tatsuro Tanaka Yoshifumi Maeda Shinji Yamamoto Toru Iwao 《Electrical Engineering in Japan》2019,207(1):15-23
The arc welding has been used in various welding methods because it is inexpensive and high in strength after welding. However, it is a problem that accidents such as collapse of the bridge occur because of the welding defects. The welding of low cost and high productivity is required without the welding defects. The pulsed TIG welding is inexpensive and capable of high‐quality welding. The electromagnetic force contributing to penetration changes because the transient response of arc temperature and iron vapor generated from anode occurs. However, the analysis of pulsed TIG welding with metal vapor has been elucidated only metal vapor concentration near anode with transient phenomenon and heat flux. Thus, the theoretical elucidation of penetration depth with control factor has not been researched. In this paper, the contribution of metal vapor mass at the periphery part of pulsed arc to the electromagnetic force in the weld pool is elucidated. As a result, the iron vapor mass at periphery part decreased with increasing the frequency. The iron vapor was stagnated at axial center within one cycle. The electromagnetic force to the penetration depth direction in weld pool increased at axial center. Therefore, the metal vapor mass at periphery part plays an important role for the electromagnetic force increment at axial center. 相似文献
32.
Junyu Chen Yuze Li Yuming Jiang Liucheng Mao Mi Lai Lixia Jiang Huihui Liu Zongxiu Nie 《Advanced functional materials》2021,31(52):2106743
Cancer remains an intractable medical problem. Rapid diagnosis and identification of cancer are critical to differentiate it from nonmalignant diseases. High-throughput biofluid metabolic analysis has potential for cancer diagnosis. Nevertheless, the present metabolite analysis method does not meet the demand for high-throughput screening of diseases. Herein, a high-throughput, cost-effective, and noninvasive urine metabolic profiling method based on TiO2/MXene-assisted laser desorption/ionization mass spectrometry (LDI-MS) is presented for the efficient screening of bladder cancer (BC) and nonmalignant urinary disease. Combined with machine learning, TiO2/MXene-assisted LDI-MS enables high diagnostic accuracy (96.8%) for the classification of patient groups (including 47 BC and 46 ureteral calculus (UC) patients) from healthy controls (113 cases). In addition, BC patients can also be identified from noncancerous UC individuals with an accuracy of 88.3% in the independent test cohort. Furthermore, metabolite variations between BC and UC individuals are investigated based on relative quantification, and related pathways are also discussed. These results suggest that this method, based on urine metabolic patterns, provides a potential tool for rapidly distinguishing urinary diseases and it may pave the way for precision medicine. 相似文献
33.
Dr. Alejandra A. Carriles Alberto Mills Dr. María-José Muñoz-Alonso Dr. Dolores Gutiérrez Dr. Juan M. Domínguez Prof. Dr. Juan A. Hermoso Prof. Dr. Federico Gago 《Chembiochem : a European journal of chemical biology》2021,22(2):374-391
Spontaneous mutations in the EEF1A2 gene cause epilepsy and severe neurological disabilities in children. The crystal structure of eEF1A2 protein purified from rabbit skeletal muscle reveals a post-translationally modified dimer that provides information about the sites of interaction with numerous binding partners, including itself, and maps these mutations onto the dimer and tetramer interfaces. The spatial locations of the side chain carboxylates of Glu301 and Glu374, to which phosphatidylethanolamine is uniquely attached via an amide bond, define the anchoring points of eEF1A2 to cellular membranes and interorganellar membrane contact sites. Additional bioinformatic and molecular modeling results provide novel structural insight into the demonstrated binding of eEF1A2 to SH3 domains, the common MAPK docking groove, filamentous actin, and phosphatidylinositol-4 kinase IIIβ. In this new light, the role of eEF1A2 as an ancient, multifaceted, and articulated G protein at the crossroads of autophagy, oncogenesis and viral replication appears very distant from the “canonical” one of delivering aminoacyl-tRNAs to the ribosome that has dominated the scene and much of the thinking for many decades. 相似文献
34.
仪器仪表产品的脉冲耐压试验是产品型式试验、例行试验中的基本内容。通过对GB4793.1标准的整理,归纳了仪器仪表产品的脉冲耐压试验要求。通过对试验方法和设备特性的梳理,总结了特性参数,并介绍了应对脉冲耐压试验可采取的保护器件的类别及选用方法。 相似文献
35.
《Oil and Energy Trends》2019,44(1):26-28
Current data on natural gas production, as well as a breakdown of production by country. Updated on a monthly basis. 相似文献
36.
37.
The increase in the production of acid gas consisting of H2S, CO2, and associated impurities such as ammonia and hydrocarbons from oil and gas plants and gasification facilities has stimulated the interest in the development of alternative means of acid gas utilization to produce hydrogen and sulfur, simultaneously. The present literature lacks a detailed reaction mechanism that can reliably predict the thermal destruction of NH3 and its blend with H2S and CO2 to facilitate process optimization and commercialization. In this paper, a detailed mechanism of NH3 pyrolysis is developed and is merged with the reactions of NH3 oxidation and H2S/CO2 thermal decomposition from our previous works. The mechanism is validated successfully using different sets of experimental data on the pyrolysis and oxidation of NH3, H2S, and CO2. The proposed mechanism predicts the experimental data on NH3 pyrolysis remarkably better than the existing mechanisms in the literature. The mechanism is used to investigate the effects of NH3 concentration (0–20%) and reactor temperature (1000–1800 K) on the thermal decomposition of H2S and CO2. A synergistic effect is observed in the simultaneous decomposition of NH3 and CO2, i.e., NH3 conversion is improved in the presence of CO2 and the decomposition CO2 to CO is enhanced in the presence of NH3. The presence of H2S suppressed NH3 conversion, while the conversion of H2S remained unchanged with increasing NH3 concentration at temperature below 1400 K due to the low conversion of NH3 (up to 18%). At temperature above 1400 K, NH3 conversion increased rapidly and it triggered a decrease in H2S conversion as well as the yields of H2 and S2. The major reactions involved in the decomposition of H2S, CO2, and NH3 and the production of major products such as H2, S2, and CO are identified. The detailed reaction mechanism can facilitate the design and optimization of acid gas thermal decomposition to produce hydrogen and sulfur, simultaneously. 相似文献
38.
39.
随着我国石油需求量不断增加,致密油藏的开发也愈发重要。如何高效开发致密油藏是一项重点难点,其中致密油藏注天然气提高采收率是一个极具潜力的研究方向。因此,本文着重介绍以天然气作为能量补充介质在国内外的研究现状和应用现状,并且从两相特征等方面总结了理论研究中的一些机理,对致密油藏注天然气提高采收率的发展前景进行了一定的展望。 相似文献
40.
Abiodun B. Ogbesejana Zhong Ningning Oluwadayo O. Sonibare 《Petroleum Science and Technology》2019,37(18):1969-1977
The occurrence and distributions of dibenzofurans (DBFs) and benzo[b]naphthofurans were investigated in crude oils from Niger Delta, Nigeria, by gas chromatography-mass spectrometry-mass spectrometry. The distribution of DBFs was characterized by the predominance of C2-dibenzofurans. 4-Methyldibenzofuran was the most abundant among the methyldibenzofurans isomers while dimethyldibenzofuran-2 (DMDBF-2), ethyldibenzofuran-1, DMDBF-3, and DMDBF-6 occurred in higher amounts when compared with other DMDBFs. Among the benzonaphthofurans, the abundance of benzo[b]naphtho[2,1-d]furan was higher than other isomers. The DBFs distributions in the oils were not affected by source facies and depositional environments. However, the DBFs concentrations increased with increasing maturity in oils from ADL and MJO oilfields. 相似文献