全文获取类型
收费全文 | 342854篇 |
免费 | 12856篇 |
国内免费 | 6485篇 |
专业分类
电工技术 | 11431篇 |
技术理论 | 6篇 |
综合类 | 7557篇 |
化学工业 | 54391篇 |
金属工艺 | 16195篇 |
机械仪表 | 13572篇 |
建筑科学 | 13449篇 |
矿业工程 | 4523篇 |
能源动力 | 7788篇 |
轻工业 | 31122篇 |
水利工程 | 4670篇 |
石油天然气 | 10282篇 |
武器工业 | 1111篇 |
无线电 | 37686篇 |
一般工业技术 | 58074篇 |
冶金工业 | 50558篇 |
原子能技术 | 6591篇 |
自动化技术 | 33189篇 |
出版年
2022年 | 3596篇 |
2021年 | 5830篇 |
2020年 | 4191篇 |
2019年 | 4143篇 |
2018年 | 5640篇 |
2017年 | 5916篇 |
2016年 | 6057篇 |
2015年 | 6462篇 |
2014年 | 8980篇 |
2013年 | 16611篇 |
2012年 | 13720篇 |
2011年 | 16640篇 |
2010年 | 14080篇 |
2009年 | 14601篇 |
2008年 | 15125篇 |
2007年 | 15083篇 |
2006年 | 13456篇 |
2005年 | 11704篇 |
2004年 | 9543篇 |
2003年 | 8619篇 |
2002年 | 8459篇 |
2001年 | 8291篇 |
2000年 | 7580篇 |
1999年 | 7470篇 |
1998年 | 13908篇 |
1997年 | 10480篇 |
1996年 | 8104篇 |
1995年 | 6206篇 |
1994年 | 5632篇 |
1993年 | 5353篇 |
1992年 | 4256篇 |
1991年 | 3989篇 |
1990年 | 4024篇 |
1989年 | 3933篇 |
1988年 | 3662篇 |
1987年 | 3098篇 |
1986年 | 3118篇 |
1985年 | 3437篇 |
1984年 | 3349篇 |
1983年 | 3085篇 |
1982年 | 2720篇 |
1981年 | 2915篇 |
1980年 | 2661篇 |
1979年 | 2847篇 |
1978年 | 2743篇 |
1977年 | 2846篇 |
1976年 | 3700篇 |
1975年 | 2460篇 |
1974年 | 2293篇 |
1973年 | 2322篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
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
112.
113.
Maria A. Ospina Monica Pizarro Thierry Tran Julien Ricci John Belalcazar Jorge L. Luna Luis F. Londoño Sandra Salazar Hernan Ceballos Dominique Dufour Luis A. Becerra Lopez-Lavalle 《International Journal of Food Science & Technology》2021,56(3):1343-1353
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes. 相似文献
114.
Mengting Ma Zijun Li Feng Yang Huaixiang Wu Wuyang Huang Zhongquan Sui Harold Corke 《International Journal of Food Science & Technology》2021,56(7):3607-3617
Waxy, normal and high-amylose maize starches were subjected to heat-moisture treatment (HMT) and then added to wheat flour (WF) in different ratios (1%, 5% and 10%). The properties of blends and their cooked noodles were studied to investigate the effects of HMT starches. The incorporation of HMT starch in WF led to an increase in swelling power, peak viscosity and breakdown and to a decrease in setback, thus inhibiting retrogradation, hence enhancing resultant noodle softness. Compared to the same addition ratio of native starch to WF, HMT starch led to higher tensile strength and extensibility in resultant noodles. WF with added HMT starch had higher resistant starch than with native starch. This study showed that addition of HMT maize starch has potential to bring nutritional benefits. However, it is necessary to select the proper blending ratio and amylose content of starch to add, in consideration of its effect on noodle quality. 相似文献
115.
The phase shift characteristics reflect the state change of electromagnetic wave in plasma sheath and can be used to reveal deeply the action mechanism between electromagnetic wave and plasma sheath. In this paper, the phase shift characteristics of electromagnetic wave propagation in plasma were investigated. Firstly, the impact factors of phase shift including electron density,collision frequency and incident frequency were discussed. Then, the plasma with different electron density distribution profiles were employed to investigate the influence on the phase shift characteristics. In a real case, the plasma sheath around the hypersonic vehicle will affect and even break down the communication. Based on the hypersonic vehicle model, we studied the electromagnetic wave phase shift under different flight altitude, speed, and attack angle. The results indicate that the phase shift is inversely proportional to the flight altitude and positively proportional to the flight speed and attack angle. Our work provides a theoretical guidance for the further research of phase shift characteristics and parameters inversion in plasma. 相似文献
116.
Chinh Ngo Radhika Mehta Kanchan Aggarwal Audrey G. Fikes Dr. Ines C. Santos Dr. Sylvester M. Greer Prof. Dr. Emily L. Que 《Chembiochem : a European journal of chemical biology》2019,20(8):1003-1007
One-third of all proteins are estimated to require metals for structural stability and/or catalytic activity. Desthiobiotin probes containing metal binding groups can be used to capture metalloproteins with exposed active-site metals under mild conditions so as to prevent changes in metallation state. The proof-of-concept was demonstrated with carbonic anhydrase (CA), an open active site, Zn2+-containing protein. CA was targeted by using sulfonamide derivatives. Linkers of various lengths and structures were screened to determine the optimal structure for capture of the native protein. The optimized probes could selectively pull down CA from red blood cell lysate and other protein mixtures. Pull-down of differently metallated CAs was also investigated. 相似文献
117.
Donghai Xu Peng Feng Yang Wang Wanpeng Yang Yu Wang Shaoyan Sun 《American Institute of Chemical Engineers》2022,68(2):e17472
Corrosion and salt deposition problems severely restrict the industrialization of supercritical water oxidation. Transpiring wall reactor can effectively weaken these two problems by a protective water film. In this work, methanol was selected as organic matter, and the influences of vital structural parameters on water film properties and organic matter removal were studied via numerical simulation. The results indicate that higher than 99% of methanol conversion could be obtained and hardly affected by transpiration water layer, transpiring wall porosity and inner diameter. Increasing layer and porosity reduced reactor center temperature, but inner diameter's influence was lower relatively. Water film temperature reduced but coverage rate raised as layer, porosity, and inner diameter increased. Notably, the whole reactor was in supercritical state and coverage rate was only approximately 85% in the case of one layer. Increasing reactor length affected slightly the volume of the upper supercritical zone but enlarged the subcritical zone. 相似文献
118.
Kozhitov L. V. Kiselev B. G. Raykova T. B. Popkova A. V. Kostishin V. G. Muratov D. G. Yakushko E. V. Kosushkin V. G. Bebenin V. G. 《Russian Microelectronics》2019,48(8):599-612
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical... 相似文献
119.
针对低速大转矩切向结构永磁同步电机中磁钢尺寸对性能的影响进行研究.提出一种"工"字形排布的磁钢径向并联组合优化方案.在保证电机磁钢轴向长度和体积不变前提下,分析磁钢磁化方向长度变化对电机性能的影响.分析表明:磁钢的磁化方向长度在一定范围内增加可降低磁钢漏磁、增大反电动势和降低转矩波动;但磁钢的磁化方向长度过度增加会大大降低电机磁通面积,使得电机反电动势不增反降.在此基础上,提出一种降低磁钢漏磁、增大反电动势和降低转矩波动的三块磁钢径向并联组合的"工"字形排布方案:近气隙侧和近隔磁槽侧磁钢槽内分别插入磁化方向长度短、径向宽度窄的磁钢以降低近气隙侧和近隔磁套侧磁钢漏磁;近气隙侧磁钢和近隔磁槽侧磁钢之间采用磁化方向长度较短的磁钢以保证磁钢磁通面积降低得不多.通过仿真实验验证所提方案的可行性. 相似文献
120.
Spiridonova E. A. Rotko V. O. Samonin V. V. Podvyaznikov M. L. 《Protection of Metals and Physical Chemistry of Surfaces》2021,57(1):45-51
Protection of Metals and Physical Chemistry of Surfaces - In this work, a universal sorbent has been obtained that works according to the mechanisms of chemisorption and adsorption by impregnating... 相似文献