全文获取类型
收费全文 | 47903篇 |
免费 | 6371篇 |
国内免费 | 3775篇 |
专业分类
电工技术 | 2383篇 |
技术理论 | 6篇 |
综合类 | 3918篇 |
化学工业 | 12301篇 |
金属工艺 | 1436篇 |
机械仪表 | 3601篇 |
建筑科学 | 4804篇 |
矿业工程 | 1148篇 |
能源动力 | 5107篇 |
轻工业 | 5206篇 |
水利工程 | 1314篇 |
石油天然气 | 1532篇 |
武器工业 | 346篇 |
无线电 | 2908篇 |
一般工业技术 | 5502篇 |
冶金工业 | 1943篇 |
原子能技术 | 1150篇 |
自动化技术 | 3444篇 |
出版年
2024年 | 259篇 |
2023年 | 902篇 |
2022年 | 1682篇 |
2021年 | 2113篇 |
2020年 | 1992篇 |
2019年 | 1945篇 |
2018年 | 1755篇 |
2017年 | 1755篇 |
2016年 | 1925篇 |
2015年 | 1866篇 |
2014年 | 2752篇 |
2013年 | 3359篇 |
2012年 | 3044篇 |
2011年 | 3513篇 |
2010年 | 2577篇 |
2009年 | 2561篇 |
2008年 | 2441篇 |
2007年 | 2957篇 |
2006年 | 2681篇 |
2005年 | 2503篇 |
2004年 | 2012篇 |
2003年 | 1898篇 |
2002年 | 1524篇 |
2001年 | 1224篇 |
2000年 | 1014篇 |
1999年 | 840篇 |
1998年 | 797篇 |
1997年 | 688篇 |
1996年 | 580篇 |
1995年 | 512篇 |
1994年 | 402篇 |
1993年 | 343篇 |
1992年 | 306篇 |
1991年 | 215篇 |
1990年 | 201篇 |
1989年 | 172篇 |
1988年 | 125篇 |
1987年 | 96篇 |
1986年 | 88篇 |
1985年 | 64篇 |
1984年 | 85篇 |
1983年 | 52篇 |
1982年 | 37篇 |
1981年 | 60篇 |
1980年 | 27篇 |
1979年 | 12篇 |
1975年 | 4篇 |
1966年 | 7篇 |
1959年 | 16篇 |
1951年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Xi Chen Zhengkun Yu Chen Yang Yao Chen Chao Jin Yuejiao Ding Wenbin Li Zhongmin Wan 《International Journal of Hydrogen Energy》2021,46(19):11127-11139
Flow field structure can largely determine the output performance of Polymer electrolyte membrane fuel cell. Excellent channel configuration accelerates electrochemical reactions in the catalytic layer, effectively avoiding flooding on the cathode side. In present study, a three-dimensional, multi-phase model of PEMFC with a 3D wave flow channel is established. CFD method is applied to optimize the geometry constructions of three-dimensional wave flow channels. The results reveal that 3D wave flow channel is overall better than straight channel in promoting reactant gases transport, removing liquid water accumulated in microporous layer and avoiding thermal stress concentration in the membrane. Moreover, results show the optimal flow channel minimum depth and wave length of the 3D wave flow channel are 0.45 mm and 2 mm, respectively. Due to the periodic geometric characteristics of the wave channel, the convective mass transfer is introduced, improving gas flow rate in through-plane direction. Furthermore, when the cell output voltage is 0.4 V, the current density in the novel channel is 23.8% higher than that of conventional channel. 相似文献
32.
Do T. Hue Rebel Skirving Tong Chen John L. Williams Cynthia D.K. Bottema Kiro Petrovski 《Journal of dairy science》2021,104(7):8164-8176
Colostrum is essential for good neonate health; however, it is not known whether different calves absorb the nutrients from colostrum equally well. In this study, the absorption of protein, IgG, and γ-glutamyl transferase was compared in newborn dairy bull calves for 1 wk after feeding colostrum from different sources. Thirty-five Holstein-Friesian bull calves were randomly allocated into 3 groups and fed colostrum within 4 h after birth. Group A calves (n = 12) were bottle fed colostrum from their own dam for 3 d. Colostrum from these group A cows was also used as foster cow colostrum for the group B calves (n = 12), such that each group A and B calf pair received identical colostrum from each milking of the respective group A dam (10% of birth weight per day). The group C calves (n = 11) were fed 1 bottle (2 L) of pooled colostrum and transition milk (referred to as pooled colostrum), as was the standard practice on the dairy farm. The pooled colostrum was collected from the other dairy cows on the farm 0 to 4 d postpartum and stored at 4°C for less than 12 h. Blood was sampled from calves before the first feeding and at 1, 2, 3, and 7 d after birth. Levels of total solids, total protein, and IgG were higher in the dam colostrum than in the pooled colostrum. At birth, there were no differences between the calf groups for any measurements, and all calves had very low IgG levels. After receiving colostrum, the glucose, plasma γ-glutamyl transferase, serum total protein, and IgG concentrations increased significantly in all calves. There were no differences in any blood measurements at any time point between the pairs of group A and group B calves that received colostrum from the same cow except for the IgG concentration 2 d after birth. However, the group A calves had a higher total serum protein level and IgG concentration than the group C calves for all the time points after the first feeding. The group B calves had a higher IgG concentration than the group C calves on d 1, 2, and 7 after birth. Compared with groups A and B, there was no difference in the proportion of calves in group C that failed to have passive immunity transferred adequately based on the IgG threshold (<10 g/L). Thus, the calves receiving identical colostrum from the same cow had the same levels of IgG, and even the pooled colostrum provided sufficient transfer of IgG as the calves were fed within 4 h after birth. 相似文献
33.
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
34.
Vaidhegi Kugarajah Moogambigai Sugumar Elamathi Swaminathan Nagaraj Balasubramani Sangeetha Dharmalingam 《International Journal of Hydrogen Energy》2021,46(42):22134-22148
Hydrothermally prepared zinc oxide nanorods are sulphonated (S–ZnO NR) and incorporated into 15% Sulphonated Poly (1,4-Phenylene Ether Ether Sulfone) (SPEES) to improve the hydrophilicity, water uptake and ion transfer capacity. Water uptake and ion transfer capacity increased to 34.6 ± 0.6% and 2.0 ± 0.05 meq g?1 from 29.8 ± 0.3% and 1.4 ± 0.04 meq g?1 by adding 7.5 wt% S–ZnO NR to SPEES. Morphological studies show the prepared S–ZnO NR is well dispersed in the polymer matrix. SPEES +7.5 wt% S–ZnO NR membrane exhibits optimum performance after three-weeks of continual operation in a fabricated microbial fuel cell (MFC) to produce a maximum power density of 142 ± 1.2 mW m?2 with a reduced biofilm compared to plain SPEES (59 ± 0.8 mW m?2), unsulphonated filler incorporated SPEES (SPEES + 7.5 wt% ZnO, 68 ± 1.1 mW m?2) and Nafion (130 ± 1.5 mW m?2) thereby suggesting its suitability as a sustainable and improved cation exchange membrane (CEM) for MFCs. 相似文献
35.
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
36.
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
37.
A microchannel heat exchanger with a triangular wave and symmetrical triangular wave structure was proposed in this paper. In addition, a new N-type microchannel heat exchanger was developed to balance the heat transfer performance and pressure drop. The relationship between different configurations of the N structure of the microchannel and the heat transfer performance was analyzed. The results showed that, at a high inlet flow rate, the symmetrical triangular wave microchannel had the best heat transfer performance, followed by the triangular wave microchannel and the straight channel. At the same flow rate, the degree of disturbance of the fluid was highest in the symmetrical N-structure microchannel, and an excellent heat transfer effect was observed. 相似文献
38.
39.
Abdul Rahman Mohtasebzadeh Longfei Ye Thomas M. Crawford 《International journal of molecular sciences》2015,16(8):19769-19779
We study magnetic-field directed self-assembly of magnetic nanoparticles onto templates recorded on perpendicular magnetic recording media, and quantify feature width and height as a function of assembly time. Feature widths are determined from Scanning Electron Microscope (SEM) images, while heights are obtained with Atomic Force Microscopy (AFM). For short assembly times, widths were ~150 nm, while heights were ~14 nm, a single nanoparticle on average with a 10:1 aspect ratio. For long assembly times, widths approach 550 nm, while the average height grows to 3 nanoparticles, ~35 nm; a 16:1 aspect ratio. We perform magnetometry on these self-assembled structures and observe the slope of the magnetic moment vs. field curve increases with time. This increase suggests magnetic nanoparticle interactions evolve from nanoparticle–nanoparticle interactions to cluster–cluster interactions as opposed to feature–feature interactions. We suggest the aspect ratio increase occurs because the magnetic field gradients are strongest near the transitions between recorded regions in perpendicular media. If these gradients can be optimized for assembly, strong potential exists for using perpendicular recording templates to assemble complex heterogeneous materials. 相似文献
40.
In this present work, Ca-alginate-biochar adsorbent has been synthesized, characterized and tested its effectiveness in the removal of aqueous phase Zn2+ metal. The removal efficiency was studied under various physicochemical process parameters. External mass transfer model, intraparticle diffusion model and pseudo-first-order and pseudo-second-order models were used to fit the experimental Zn2+ adoption kinetic results and to identify the mechanism of adsorption. The desorption studies indicate the possibilities of ion-exchange and physical–chemical adsorption of Zn2+. The adsorption was best described by Langmuir isotherm model. Thermodynamic parameters suggested that the adsorption process becomes spontaneous, endothermic and irreversible in nature. 相似文献