全文获取类型
收费全文 | 47864篇 |
免费 | 6689篇 |
国内免费 | 1559篇 |
专业分类
电工技术 | 2157篇 |
综合类 | 1952篇 |
化学工业 | 13369篇 |
金属工艺 | 2224篇 |
机械仪表 | 1781篇 |
建筑科学 | 4292篇 |
矿业工程 | 1556篇 |
能源动力 | 960篇 |
轻工业 | 6629篇 |
水利工程 | 982篇 |
石油天然气 | 1532篇 |
武器工业 | 223篇 |
无线电 | 4394篇 |
一般工业技术 | 5639篇 |
冶金工业 | 2576篇 |
原子能技术 | 532篇 |
自动化技术 | 5314篇 |
出版年
2024年 | 145篇 |
2023年 | 925篇 |
2022年 | 2260篇 |
2021年 | 3702篇 |
2020年 | 1648篇 |
2019年 | 1705篇 |
2018年 | 1876篇 |
2017年 | 2404篇 |
2016年 | 3526篇 |
2015年 | 3961篇 |
2014年 | 4054篇 |
2013年 | 3943篇 |
2012年 | 2764篇 |
2011年 | 2079篇 |
2010年 | 1768篇 |
2009年 | 1774篇 |
2008年 | 1664篇 |
2007年 | 2716篇 |
2006年 | 2937篇 |
2005年 | 2474篇 |
2004年 | 1518篇 |
2003年 | 1483篇 |
2002年 | 1074篇 |
2001年 | 678篇 |
2000年 | 621篇 |
1999年 | 351篇 |
1998年 | 197篇 |
1997年 | 174篇 |
1996年 | 185篇 |
1995年 | 134篇 |
1994年 | 148篇 |
1993年 | 98篇 |
1992年 | 85篇 |
1991年 | 85篇 |
1990年 | 105篇 |
1989年 | 84篇 |
1988年 | 49篇 |
1987年 | 53篇 |
1986年 | 53篇 |
1985年 | 55篇 |
1984年 | 63篇 |
1983年 | 39篇 |
1982年 | 34篇 |
1981年 | 34篇 |
1980年 | 45篇 |
1966年 | 25篇 |
1964年 | 34篇 |
1962年 | 65篇 |
1959年 | 21篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
131.
The results of a comprehensive experimental program, aimed at providing a fundamental understanding of the behavior of shear-critical exterior reinforced concrete (RC) joints strengthened with fiber reinforced polymers (FRP) under simulated seismic load, are presented in this study. The role of various parameters on the effectiveness of FRP is examined through 2/3-scale testing of 18 exterior RC joints. Conclusions are drawn on the basis of certain load versus imposed displacement response characteristics, comprising the strength (maximum lateral load), the stiffness, and the cumulative energy dissipation capacity. The results demonstrate the important role of mechanical anchorages in limiting premature debonding, and they provide important information on the role of various parameters, including: area fraction of FRP; distribution of FRP between the beam and the column; column axial load; internal joint (steel) reinforcement; initial damage; carbon versus glass fibers; sheets versus strips; and effect of transverse beams. 相似文献
132.
Photoluminescence features in a commercial grade cured DGEBA-based epoxy resin have been investigated with as objective to determine which of the material compounds are responsible for cured resin emissions. The origin of the bands has been approached by considering photoluminescence of base resin and hardener taken separately, of their mixture, and in the course of curing. Most of the bands observed in the cured resin could be interpreted based on those found in the components taken separately. Fluorescence of the cured resin appears dominated by two broad bands that are characteristic of the hardener and exhibits a blue shift by up to 30 nm in the course of curing which could be used for cure monitoring purpose of the investigated system. Fluorescence of the base resin is clearly detected in the resin cured with tertiary amine as catalyser. However, it is very weak if the catalyser is not added. Two phosphorescence processes have been isolated in the cured resin, one of them being related to the base resin. Finally, a chemiluminescence spectrum has been recorded in the course of curing, which has been related to either curing-related reactions or to an oxidation process. 相似文献
133.
134.
135.
R. Adam Rebeles A. Hermanne S. Takcs F. Trknyi S.F. Kovalev A. Ignatyuk 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,260(2):672-684
In the frame of a systematic study of light ion induced threshold reactions on natural tin (Sn) excitation functions for alpha particles induced reactions are presented in a 12–38 MeV energy domain. Using a stacked foil activation method the following radioisotopes were identified: 116Te, 117Te, 118Te, 119Te, 121Te, 123Te, 117Sb, 118Sb, 120Sb, 122Sb, 124Sb, 126Sb, 117Sn, 111In. The experimental cross sections for these isotopes are presented for the first time in this energy range and a direct comparison with values calculated with the ALICE-IPPE code is discussed. Possible use of these data for production of some isotopes relevant in nuclear medicine is suggested. 相似文献
136.
Bestehen ausreichende Anhaltspunkte für die Hochwassergef?hrdung, ist die Gemeinde verpflichtet, sich durch Nachforschungen
Gewissheit über das Vorliegen oder Nichtvorliegen eines Hochwasserabflussgebietes gem § 38 Abs 3 WRG zu verschaffen. Liegt
ein solches vor, hat sie gem § 12 Abs 1 Z 2 krnt GplG dieses im Fl?chenwidmungsplan ersichtlich zu machen. Erteilt die Gemeinde
eine Baubewilligung ohne diese von der Erteilung einer wasserrechtlichen Bewilligung abh?ngig zu machen, haftet sie für die
Kosten der Bauführung, die bei gesetzes-konformer Vorgangsweise unterlassen worden w?re. 相似文献
137.
138.
Ring‐opening polymerization of D,L ‐lactide (LA) has been successfully carried out by using rare earth 2,6‐dimethylaryloxide (Ln(ODMP)3) as single component catalyst or initiator for the first time. The effects of different rare earth elements, solvents, monomers and catalyst concentration as well as polymerization temperature and time on the polymerization were investigated. The results show that La(ODMP)3 exhibits higher activity to prepare poly(D,L ‐lactide) (PLA) with a viscosity molecular weight of 4.5 × 104 g mol?1 and the conversion of 97 % at 100 °C in 45 min. The catalytic activity of Ln(ODMP)3 has following sequence: La > Nd > Sm > Gd > Er > Y. A kinetic study has indicated that the polymerization is first order with respect to both monomer and catalyst concentration. The apparent activation energy of the polymerization of LA with La(ODMP)3 is 69.6 kJ mol?1. The analyses of polymer ends indicate that the LA polymerization proceeds according to ‘coordination–insertion’ mechanism with selective cleavage of the acyl–oxygen bond of the monomer. Copyright © 2004 Society of Chemical Industry 相似文献
139.
郯庐断裂带是中国东部一条巨型断裂构造带,该文从其基本构造特征入手,分析了它的几何学、运动学和动力学特征,并进一步研究其含油气特点,认为:a)郯庐断裂带对中国东部诸多中新生代含油气盆地的形成及演化有重要的控制作用,不同演化阶段产生并控制了不同的沉积盆地(如松辽盆地和渤海湾盆地);b)郯庐断裂带对油气藏的形成及演化有重要的控制作用,不仅控制盆地烃源岩的发育、基本的储集层和盖层条件,以及圈闭的形成等等,而且对油气的生成、运移及聚集成藏、大中型油气田的形成及分布等有重要的控制作用. 相似文献
140.
介绍了选针片式小提花横机常见选针故障的各种原因,并对不同原因导致的选针故障提出了针对性解决方法。 相似文献