全文获取类型
收费全文 | 72543篇 |
免费 | 7494篇 |
国内免费 | 4102篇 |
专业分类
电工技术 | 6838篇 |
技术理论 | 4篇 |
综合类 | 6475篇 |
化学工业 | 5375篇 |
金属工艺 | 3907篇 |
机械仪表 | 5842篇 |
建筑科学 | 13784篇 |
矿业工程 | 2684篇 |
能源动力 | 2374篇 |
轻工业 | 4433篇 |
水利工程 | 3500篇 |
石油天然气 | 4372篇 |
武器工业 | 1554篇 |
无线电 | 4698篇 |
一般工业技术 | 7050篇 |
冶金工业 | 3498篇 |
原子能技术 | 732篇 |
自动化技术 | 7019篇 |
出版年
2024年 | 310篇 |
2023年 | 933篇 |
2022年 | 1847篇 |
2021年 | 2201篇 |
2020年 | 2503篇 |
2019年 | 1964篇 |
2018年 | 1930篇 |
2017年 | 2543篇 |
2016年 | 2804篇 |
2015年 | 2964篇 |
2014年 | 4717篇 |
2013年 | 4372篇 |
2012年 | 5372篇 |
2011年 | 5785篇 |
2010年 | 4362篇 |
2009年 | 4370篇 |
2008年 | 3938篇 |
2007年 | 4698篇 |
2006年 | 4305篇 |
2005年 | 3736篇 |
2004年 | 3136篇 |
2003年 | 2601篇 |
2002年 | 2268篇 |
2001年 | 1957篇 |
2000年 | 1532篇 |
1999年 | 1280篇 |
1998年 | 1023篇 |
1997年 | 819篇 |
1996年 | 789篇 |
1995年 | 632篇 |
1994年 | 489篇 |
1993年 | 349篇 |
1992年 | 283篇 |
1991年 | 182篇 |
1990年 | 182篇 |
1989年 | 139篇 |
1988年 | 89篇 |
1987年 | 63篇 |
1986年 | 54篇 |
1985年 | 34篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1981年 | 26篇 |
1980年 | 72篇 |
1979年 | 50篇 |
1965年 | 30篇 |
1964年 | 39篇 |
1959年 | 34篇 |
1956年 | 31篇 |
1955年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
为研究喷射混凝土套拱加固前后二次衬砌与混凝土套拱的受力状况,依托陕西汉中至留坝段八里关隧道,运用有限元软件建立隧道混凝土结构套拱加固分析模型,并通过现场监测获取二次衬砌与套拱间的接触压力、套拱格栅拱架钢筋应力、套拱混凝土应力,将数值模拟结果与现场测试结果相结合,得出套拱结构的一般受力变化规律。结果表明:套拱加固前衬砌结构的最不利荷载位置位于施工缝附近的拱顶、拱肩与拱脚处; 由于衬砌局部变形与温度应力的影响,套拱混凝土应力变化呈现反复“上升-下降-上升”最后趋于稳定的特点; 套拱的作用是控制二次衬砌的进一步变形,套拱施作后所承受荷载较小,套拱反作用力远小于围岩作用于衬砌的应力,在应力计算中不应将衬砌与套拱作为整体计算; 套拱结构数值模拟所得的结果与现场测试套拱结构内力(轴力、弯矩)的大小及分布相似度高,但在衬砌裂损严重部位,数值模拟所得结果误差较大,应以现场测试结果为准。 相似文献
22.
23.
Ramesh Shruthy Stephen Jancy Radhakrishnan Preetha 《International Journal of Food Science & Technology》2021,56(8):3991-3999
In this study, the cellulose nanoparticles (CNP) isolated from potato peel were used for reinforcement of polyvinyl alcohol (PVA)-based active packaging film. The above film was used to pack the raw prawns (Penaeus monodon) at −20 °C, and the colour change, protein content, TVB-N, TMA and microbial analysis were done at regular interval for prawns stored in CNP-PVA active packaging film. A significant difference was observed in the quality of prawns stored in potato CNP-PVA film compared with prawns packed and stored in polyethylene film. The newly designed active packaging with CNP and fennel seed oil enhanced the shelf life of prawns up to two months for both HOSO (head on shell on) prawn and PD (peeled and deveined) prawn. Hence, the study recommends the potato peel CNP-PVA film with fennel seed oil as better choice to extend the shelf life of the prawns during storage compared with polyethylene packaging. 相似文献
24.
Effect of chitosan on Bacillus cereus inhibition and quality of cooked rice during storage
下载免费PDF全文
![点击此处可从《International Journal of Food Science & Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Chitsiri Rachtanapun Juthamas Tantala Phatthranit Klinmalai Savitree Ratanasumawong 《International Journal of Food Science & Technology》2015,50(11):2419-2426
Improper cooling of cooked rice at an inappropriate temperature or leaving cooked rice at room temperature can cause food poisoning attributed to Bacillus cereus. Natural food preservative of either squid or crab polymer chitosan solution was added to examine their antibacterial properties against Bacillus cereus in cooked rice during storage at 37 and 4 °C. Both types of chitosan could retard the growth of B. cereus and total aerobic counts in cooked rice stored at 37 °C up to 1 day. In addition, the effect of chitosans on the physical and textural properties of cooked rice during storage was studied. Both chitosans slightly increased the moisture content of cooked rice. However, chitosans had no effect on the whiteness and hardness of cooked rice during storage (P > 0.05). Therefore, both chitosans have a potential to be used as food preservative for cooked rice with no negative effects on rice quality. 相似文献
25.
针对高可靠度机载多余度EWIS各组成部分寿命服从指数分布但参数未知的情况,提出采用无失效数据可靠度分析方法评估EWIS的可靠度水平。通过Monte-Carlo仿真方法对连接形式为“先并联、后串联”EWIS各组成部分寿命进行抽样,利用“最小最大值”方法获得系统寿命的抽样值,用概率纸检验法初步判断EWIS寿命是否服从威布尔分布,再用Pearson拟合优度检验法判断EWIS寿命是否服从威布尔分布。结合无故障飞行时间的样本值与EWIS寿命服从威布尔分布的假设,采用无失效数据分析方法评估EWIS的可靠度水平。研究方法对机载多余度EWIS无失效数据可靠度分析有一定的贡献。 相似文献
26.
对射频电缆幅相稳定性进行了介绍,阐述了射频测试电缆相位和幅度变化的因素,并详细分析了射频电缆相位性能以及幅度性能的不同测试方法,最后通过实测数据的展示,总结说明了在日常测试中该如何正确使用测试电缆。 相似文献
27.
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
28.
29.
《Geotextiles and Geomembranes》2021,49(5):1256-1269
This study investigates the seismic performance of geosynthetic-reinforced modular block retaining walls backfilled with cohesive, fine grained clay-sand soil mixture. Shaking table tests were performed for three ½ scaled (wall height 190 cm) and ¼ scaled model walls to investigate the effects of backfill type, the influence of reinforcement length and reinforcement stiffness effects. The El Centro and Kobe earthquake records of varying amplitudes were used as base acceleration. Displacement of the front wall, accelerations at different locations, strains on the reinforcements, and the visual observations of the facing and the backfill surface were used to evaluate the seismic performance of model walls. The model walls were subjected to rigorous shaking and the walls did not exhibit any stability problems or signs of impending failure. The maximum deformations observed on the models with cohesive backfill was less than half of the deformation of the sand model. The load transfers between the geogrid and cohesive soil was comparable to that of sand and hence the needed reinforcement length was similar as well. As a result; the model walls with cohesive backfills performed within acceptable limits under seismic loading conditions when compared with granular backfilled counterparts. 相似文献
30.
Zhuang CHENG Jianfeng WANG Matthew Richard COOP Guanlin YE 《Frontiers of Structural and Civil Engineering》2020,14(2):357
The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray micro-tomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of (diameter height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils. 相似文献