首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   32923篇
  免费   3037篇
  国内免费   1498篇
电工技术   2569篇
综合类   3511篇
化学工业   2421篇
金属工艺   2172篇
机械仪表   6021篇
建筑科学   6646篇
矿业工程   1645篇
能源动力   1000篇
轻工业   1062篇
水利工程   1204篇
石油天然气   1059篇
武器工业   270篇
无线电   1819篇
一般工业技术   2210篇
冶金工业   1932篇
原子能技术   160篇
自动化技术   1757篇
  2024年   161篇
  2023年   427篇
  2022年   877篇
  2021年   1008篇
  2020年   1085篇
  2019年   822篇
  2018年   747篇
  2017年   988篇
  2016年   1168篇
  2015年   1274篇
  2014年   2157篇
  2013年   1620篇
  2012年   2458篇
  2011年   2596篇
  2010年   1874篇
  2009年   1930篇
  2008年   1684篇
  2007年   2314篇
  2006年   2087篇
  2005年   1759篇
  2004年   1391篇
  2003年   1244篇
  2002年   1154篇
  2001年   954篇
  2000年   801篇
  1999年   622篇
  1998年   520篇
  1997年   365篇
  1996年   372篇
  1995年   254篇
  1994年   216篇
  1993年   125篇
  1992年   96篇
  1991年   65篇
  1990年   51篇
  1989年   50篇
  1988年   22篇
  1987年   33篇
  1986年   18篇
  1985年   9篇
  1984年   7篇
  1983年   6篇
  1982年   16篇
  1980年   11篇
  1979年   10篇
  1967年   1篇
  1966年   1篇
  1964年   1篇
  1959年   1篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Mangiferin (MGF) is a phenolic compound isolated from mango, but its poor solubility significantly limits its use. In this study, MGF was embedded into the inner aqueous phase of W1/O/W2 emulsions. Firstly, the dissolution method of MGF was determined. MGF remained stable in solution with pH 13 at 30 min, and its solubility reached 10 mg mL−1. When the pH of MGF solutions was adjusted from pH 13 to pH 6, MGF did not immediately crystallise, providing sufficient time to construct the MGF-loaded W1/O/W2 emulsions. Subsequently, the MGF-loaded W1/O/W2 emulsions were constructed using polyglycerol polyricinoleate (PGPR) and calcium caseinate (CAS). The formation and stability of the W1/O/W2 emulsions were investigated. The MGF-loaded W1/O/W2 emulsions stabilised with 1% PGPR and 1% – 3% CAS exhibited a low viscosity, limited loading capacity, and poor stability. Conversely, the MGF-loaded W1/O/W2 emulsions stabilised by 3%PGPR–3%CAS exhibited optimal loading capacity (encapsulation efficiency = 95.31% and loading efficiency = 0.91%) and stability, which was attributed to the fact that high viscosity and gel state retarded the migration of inner aqueous phase. These results indicated that the W1/O/W2 emulsions stabilised by PGPR and CAS may be a potential alternative for encapsulating mangiferin.  相似文献   
2.
In actual engineering scenarios, limited fault data leads to insufficient model training and over-fitting, which negatively affects the diagnostic performance of intelligent diagnostic models. To solve the problem, this paper proposes a variational information constrained generative adversarial network (VICGAN) for effective machine fault diagnosis. Firstly, by incorporating the encoder into the discriminator to map the deep features, an improved generative adversarial network with stronger data synthesis capability is established. Secondly, to promote the stable training of the model and guarantee better convergence, a variational information constraint technique is utilized, which constrains the input signals and deep features of the discriminator using the information bottleneck method. In addition, a representation matching module is added to impose restrictions on the generator, avoiding the mode collapse problem and boosting the sample diversity. Two rolling bearing datasets are utilized to verify the effectiveness and stability of the presented network, which demonstrates that the presented network has an admirable ability in processing fault diagnosis with few samples, and performs better than state-of-the-art approaches.  相似文献   
3.
《云南化工》2019,(9):59-60
扩展有限元法是近年经过大量运用的,在传统有限元的范围中求解不连续问题一种有效计算方法,它是基于单位分解的思想,在计算不连续问题时加入跳跃函数。以ABAQUS为平台,基于扩展有限元方法 (XFEM),以含双穿透型裂纹的有限宽板受横向拉伸载荷为力学模型,建立相应的裂纹尖端应力的有限元模型,研究焊接接头区域不同间距双裂纹相互作用对裂纹扩展速率的影响。结果表明:双裂纹间距的的大小并没有对裂纹的扩展速率产生影响。  相似文献   
4.
Two electron oxygen reduction reaction to produce hydrogen peroxide (H2O2) is a promising alternative technique to the multistep and high energy consumption anthraquinone process. Herein, Ni–Fe layered double hydroxide (NiFe-LDH) has been firstly demonstrated as an efficient bifunctional catalyst to prepare H2O2 by electrochemical oxygen reduction (2e? ORR) and oxygen evolution reaction (OER). Significantly, the NiFe-LDH catalyst possesses a high faraday efficiency of 88.75% for H2O2 preparation in alkaline media. Moreover, the NiFe-LDH catalyst exhibits excellent OER electrocatalytic property with small overpotential of 210 mV at 10 mA cm?2 and high stability in 1 M KOH solution. On this basis, a new reactor has been designed to electrolyze oxygen and generate hydrogen peroxide. Under the ultra-low cell voltage of 1 V, the H2O2 yield reaches to 47.62 mmol gcat?1 h?1. In order to evaluate the application potential of the bifunctional NiFe-LDH catalyst for H2O2 preparation, a 1.5 V dry battery has been used as the power supply, and the output of H2O2 reaches to 83.90 mmol gcat?1 h?1. The excellent electrocatalytic properties of 2e? ORR and OER make NiFe-LDH a promising bifunctional electrocatalyst for future commercialization. Moreover, the well-designed 2e? ORR-OER reactor provides a new strategy for portable production of H2O2.  相似文献   
5.
This paper introduces the potential feasibility that ELID (electrolytic in-process dressing) grinding replaces superfinishing in bearing manufacturing, but ELID grinding will bring new challenges. Different regions present distinguish surface profile due to the non-uniform contact in ELID groove grinding. However, few reports explaining the non-uniform contact are available. This article explores the mechanisms of the non-uniform contact during ELID groove grinding. Experiments on the non-uniform contact between bearing raceway and grinding wheel have been carried out under different conditions. The results show that non-uniform contact exists in ELID groove grinding process and it exerts influence on the profile of the raceway surface. Non-uniform contact influences the Rsk and Rku value all the time, but it influences the Ra value occasionally. Improvement strategies of eliminating the non-uniform contact are also discussed based on the experimental study.  相似文献   
6.
烧结机导料箱、单辊破碎机和卸料漏斗承载着烧结热矿的导料、破碎与输送,是烧结生产的重要组成部分。高温、重载的工况环境决定着机尾卸料装置必须具有抗磨损、耐高温的特性。针对邯钢1^#435m^2烧结机机尾关键部件耐磨工作面寿命短,更换不方便等问题,分析磨损机理与失效原因,提出改进抗磨工作面结构,升级耐磨材料,优化焊接工艺等措施。通过技术方案的实施,使烧结机导料箱、单辊破碎机和卸料漏斗等卸料装置维持了较高的抗磨损性能,达到了预期的改造效果。  相似文献   
7.
In this research, the three‐dimensional structural and colorimetric modeling of three‐dimensional woven fabrics was conducted for accurate color predictions. One‐hundred forty single‐ and double‐layered woven samples in a wide range of colors were produced. With the consideration of their three‐dimensional structural parameters, three‐dimensional color prediction models, K/S‐, R‐, and L*a*b*‐based models, were developed through the optimization of previous two‐dimensional models which have been reported to be the three most accurate models for single‐layered woven structures. The accuracy of the new three‐dimensional models was evaluated by calculating the color differences ΔL*, ΔC*, Δh°, and ΔECMC(2:1) between the measured and the predicted colors of the samples, and then the error values were compared to those of the two‐dimensional models. As a result, there has been an overall improvement in color predictions of all models with a decrease in ΔECMC(2:1) from 10.30 to 5.25 units on average after the three‐dimensional modeling.  相似文献   
8.
压裂是低孔、低渗油层改造的主要增产措施。根据常规测井资料、岩石物理实验分析数据及试油成果。研究储层四性关系,确定区块的低孔、低渗储层评价标准。进一步对油层进行分类,有针对性地为油层压裂提供施工层位和准确的储层参数。通过商543区块实例,阐述了选择压裂层位的方法。  相似文献   
9.
Reports an error in "Tradeoffs and Theory: The Double-Mediation Model" by Marc Scholten and Steven J. Sherman (Journal of Experimental Psychology: General, 2006 May, Vol 135[2], 237-261). This article was inadvertently printed with the incorrect title. The original title was "Tradeoffs and Conflict: The Double-Mediation Model." This title highlights the relation between tradeoffs and conflict as investigated by the authors and accounted for by their model. However, readers are asked to refer to the article by the title with which it was printed to facilitate its retrieval.. (The following abstract of the original article appeared in record 2006-06642-006.) Most theories of decision making suggest that, when options imply tradeoffs between their attributes, conflict increases as tradeoff size increases, because greater sacrifices are to be incurred in choosing one option instead of another. An alternative view is that conflict decreases as tradeoff size increases, because stronger arguments can be made for any decision. The authors propose a unified model, the double-mediation model, which combines the mediating effects of sacrifice and argumentation. Our model generally predicts an inverse U-shaped relation between tradeoff size and conflict. Results support this prediction. Also, when the decision situation increases the mediating effect of sacrifice relative to that of argumentation, the relation between tradeoff size and conflict changes in an upward direction; conversely, when the decision situation increases the mediating effect of argumentation relative to that of sacrifice, the relation changes in a downward direction. Results support these predictions as well. Commonalities and differences between our model and other formulations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
10.
文中分析了大同市水资源开发利用的状况,并对水资源承载能力的有关问题进行了讨论。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号