全文获取类型
收费全文 | 1704952篇 |
免费 | 43942篇 |
国内免费 | 15713篇 |
专业分类
电工技术 | 46095篇 |
技术理论 | 24篇 |
综合类 | 20697篇 |
化学工业 | 289494篇 |
金属工艺 | 76140篇 |
机械仪表 | 56195篇 |
建筑科学 | 60434篇 |
矿业工程 | 18886篇 |
能源动力 | 55843篇 |
轻工业 | 123471篇 |
水利工程 | 18981篇 |
石油天然气 | 51757篇 |
武器工业 | 1781篇 |
无线电 | 217300篇 |
一般工业技术 | 305238篇 |
冶金工业 | 191023篇 |
原子能技术 | 36104篇 |
自动化技术 | 195144篇 |
出版年
2021年 | 22665篇 |
2020年 | 18338篇 |
2019年 | 20000篇 |
2018年 | 21566篇 |
2017年 | 21776篇 |
2016年 | 27377篇 |
2015年 | 25735篇 |
2014年 | 39276篇 |
2013年 | 100024篇 |
2012年 | 49187篇 |
2011年 | 63524篇 |
2010年 | 55556篇 |
2009年 | 62689篇 |
2008年 | 56605篇 |
2007年 | 53425篇 |
2006年 | 56466篇 |
2005年 | 49816篇 |
2004年 | 49342篇 |
2003年 | 46894篇 |
2002年 | 43662篇 |
2001年 | 39915篇 |
2000年 | 38089篇 |
1999年 | 38969篇 |
1998年 | 51972篇 |
1997年 | 43865篇 |
1996年 | 38563篇 |
1995年 | 34500篇 |
1994年 | 31835篇 |
1993年 | 30776篇 |
1992年 | 27217篇 |
1991年 | 24252篇 |
1990年 | 24296篇 |
1989年 | 23064篇 |
1988年 | 21540篇 |
1987年 | 19613篇 |
1986年 | 19004篇 |
1985年 | 22226篇 |
1984年 | 22207篇 |
1983年 | 20121篇 |
1982年 | 19169篇 |
1981年 | 19260篇 |
1980年 | 17913篇 |
1979年 | 18401篇 |
1978年 | 17673篇 |
1977年 | 17812篇 |
1976年 | 19727篇 |
1975年 | 15929篇 |
1974年 | 15431篇 |
1973年 | 15511篇 |
1972年 | 13042篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
21.
We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms. 相似文献
22.
文章率先提出一种新型防屈曲高强钢腹板可更换钢连梁(简称“新型钢连梁”):腹板采用高强钢,可提高钢连梁的屈服抗剪强度,连梁变形减小,从而减小可更换结构整体变形,便于更换;加劲肋紧贴腹板(但不焊接)提供约束,仅与上下翼缘焊接,可减少60%以上的焊接量。其次,设计并开展了11个试件的拟静力试验,研究了加劲肋间距(规范限值dmax、0.85dmax)、腹板厚度(6mm、8mm)、腹板钢材强度(Q460、Q550)和构造形式(加劲肋与腹板贴紧或焊接)等参数对新型钢连梁抗震性能的影响。试验结果表明:试件均发生剪切破坏;满足加劲肋间距限值的新型钢连梁,滞回曲线饱满,峰值时腹板未发生鼓曲且极限转角均超过0.1rad,大于规范限值0.08rad,表现出良好的耗能和变形能力;缩小加劲肋间距、增加腹板厚度或提高腹板钢材强度,新型钢连梁刚度及承载力提高;新型钢连梁峰值承载力较传统构造试件低约5%。最后,基于试验结果建立了有限元模型并开展了分析,研究结果表明:对腹板采用Q460、Q550高强钢材的新型钢连梁,峰值承载力计算时超强系数建议取1.43(长度比为0.5~1.0)或1.39(长度比为1.0~1.6)、1.25,以期为实际工程设计提供依据。 相似文献
23.
24.
25.
Muhammad Yazid Samatra Nor Qhairul Izzreen Mohd Noor Umi Hartina Mohamad Razali Jamilah Bakar Sharifudin Md. Shaarani 《Comprehensive Reviews in Food Science and Food Safety》2022,21(4):3153-3176
Gelatin is one of the most important multifunctional biopolymers and is widely used as an essential ingredient in food, pharmaceutical, and cosmetics. Porcine gelatin is regarded as the leading source of gelatin globally then followed by bovine gelatin. Porcine sources are favored over other sources since they are less expensive. However, porcine gelatin is religiously prohibited to be consumed by Muslims and the Jewish community. It is predicted that the global demand for gelatin will increase significantly in the future. Therefore, a sustainable source of gelatin with efficient production and free of disease transmission must be developed. The highest quality of Bovidae-based gelatin (BG) was acquired through alkaline pretreatment, which displayed excellent physicochemical and rheological properties. The utilization of mammalian- and plant-based enzyme significantly increased the gelatin yield. The emulsifying and foaming properties of BG also showed good stability when incorporated into food and pharmaceutical products. Manipulation of extraction conditions has enabled the development of custom-made gelatin with desired properties. This review highlighted the various modifications of extraction and processing methods to improve the physicochemical and functional properties of Bovidae-based gelatin. An in-depth analysis of the crucial stage of collagen breakdown is also discussed, which involved acid, alkaline, and enzyme pretreatment, respectively. In addition, the unique characteristics and primary qualities of BG including protein content, amphoteric property, gel strength, emulsifying and viscosity properties, and foaming ability were presented. Finally, the applications and prospects of BG as the preferred gelatin source globally were outlined. 相似文献
26.
Liu Yang Pengfei Yu Wenyuan Li Fengliang Cao Xin Jin Sheng Xue Xianglong Zhang Tingwei Zhang Mingbo Wu Wenting Wu 《American Institute of Chemical Engineers》2022,68(9):e17760
Hydrogen peroxide (H2O2) has been listed as one of the 100 most important chemicals in the world. However, huge amount of residual H2O2 is hard to timely decomposed into O2 and H2O under acidic condition, easily resulting in explosion hazard. Here, we reported a core–shell structure catalyst, that is graphene with Co N structure encapsulated Co nanoparticles. Co N graphene shell serves as the active site for the H2O2 decomposition, and Co core further enhance this decomposition. Benefiting from it, the H2O2 decomposition were close to 100% after 6 cycles without pH adjustment, which increased 6 orders of magnitude compared with no catalyst. At the same time, the O2 generation reached 99.67% in 2 h with little metal leaching, and ·OH has been greatly inhibited to only 0.08%. This work can cleanly remove H2O2 with little deep oxidation and protect the process of H2O2 utilization to achieve a safer world. 相似文献
27.
Sk Tanbir Islam Sudip K. Samanta Santanu Das Himadri Chattopadhyay 《Journal of the American Ceramic Society》2022,105(7):4608-4620
The micro-powder injection molding (micro-PIM) process has the potential to bridge the gap between the design and manufacturing of micro-components that are often used in small and handy devices. Numerical modeling helps to analyze and overcome various difficulties of micro-PIM. In the present work, a numerical model is developed to predict the powder–binder separation (a common defect in PIM and especially severe in micro-PIM) during the injection of an alumina feedstock. A powder–binder separation criterion is proposed dealing with applied injection pressure and friction force between the powder and binder. An indirect comparison of feedstock travel time between two locations is used to validate the model. The predicted segregation from the simulated result is supported by a qualitative experimental measurement. The developed model can be used to optimize injection parameters to get a defect-free product. 相似文献
28.
Journal of Porous Materials - In this work, a trifluoromethanesulfonic acid (TFOH) modified clay (TFOH-Clay) was developed for the removal of trace olefins in heavy naphtha. 5%TFOH-Clay can... 相似文献
29.
Wireless Personal Communications - In a communication system, ultra-wideband (UWB) is the most promising solution because of its high speed, high data rate, and short-range communication. However,... 相似文献
30.
Journal of Computer and Systems Sciences International - A method for the synthesis of fast finite state machines on programmable logic integrated circuits such as field-programmable gate arrays is... 相似文献