全文获取类型
收费全文 | 8192篇 |
免费 | 639篇 |
国内免费 | 448篇 |
专业分类
电工技术 | 100篇 |
技术理论 | 1篇 |
综合类 | 637篇 |
化学工业 | 1497篇 |
金属工艺 | 436篇 |
机械仪表 | 202篇 |
建筑科学 | 734篇 |
矿业工程 | 418篇 |
能源动力 | 354篇 |
轻工业 | 1825篇 |
水利工程 | 413篇 |
石油天然气 | 712篇 |
武器工业 | 28篇 |
无线电 | 232篇 |
一般工业技术 | 702篇 |
冶金工业 | 540篇 |
原子能技术 | 211篇 |
自动化技术 | 237篇 |
出版年
2024年 | 27篇 |
2023年 | 106篇 |
2022年 | 191篇 |
2021年 | 234篇 |
2020年 | 260篇 |
2019年 | 236篇 |
2018年 | 234篇 |
2017年 | 271篇 |
2016年 | 335篇 |
2015年 | 264篇 |
2014年 | 477篇 |
2013年 | 501篇 |
2012年 | 590篇 |
2011年 | 606篇 |
2010年 | 406篇 |
2009年 | 454篇 |
2008年 | 392篇 |
2007年 | 518篇 |
2006年 | 423篇 |
2005年 | 405篇 |
2004年 | 333篇 |
2003年 | 284篇 |
2002年 | 279篇 |
2001年 | 226篇 |
2000年 | 192篇 |
1999年 | 180篇 |
1998年 | 136篇 |
1997年 | 111篇 |
1996年 | 93篇 |
1995年 | 107篇 |
1994年 | 53篇 |
1993年 | 60篇 |
1992年 | 58篇 |
1991年 | 39篇 |
1990年 | 39篇 |
1989年 | 32篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有9279条查询结果,搜索用时 0 毫秒
991.
盛荣 《核化学与放射化学》1998,20(2):109-113
以酸性氧化铝为吸附剂,制备了一个118MBq的188W-188Re发生器,并对发生器性能进行了为期4个月的检测。结果表明,188Re的淋洗产额在80%—90%之间,188W的穿透率约为1.0×10-4%。由于采用了较大高径比的交换柱,使188Re的放射性比活度较高,能满足用于放射免疫治疗研究的抗肿瘤单克隆抗体标记的要求。 相似文献
992.
本文系统介绍了武钢第一炼钢厂利用引进的溶铝、喷射设备,成功地开发出外沸内镇钢下注工艺,几年来在提高成坯率、扩大品种和设备国产化诸方面进行了多种工作并解剖了钢锭,目前该钢种已用于镀锌、镀锡板的生产,在用于汽车部件、旋开盖和易拉罐等试验中,已取得良好效果。 相似文献
993.
994.
995.
996.
In order to study the influence of microalloying elements in bainitic high strength steels, seven steels with different contents of V, Ti, Nb and N were investigated. The steel 35 CrMo 4 (C=0.38; Mn=0.82; Si= 0.25; Cr=0.83; Mo=0.17, all in wt.%) was used as reference steel. CCT diagrams were determined by dilatometric tests at different cooling rates, and the maximum and minimum cooling rates for bainite formation were determined. With regard to tensile tests, the presence of precipitates in the bainitic microstructure contributed to raising their yield strength, as was found by comparing the results for all the steels with the reference steel which did not contain microalloying elements. The yield strength can be predicted by an Orowan expression. 相似文献
997.
Michael Z. F. Li Anming Zhang Yimin Zhang 《International Transactions in Operational Research》2008,15(4):439-459
This paper examines the classical seat allocation problem under competition between two airlines with different cost structure. The cost asymmetry that has been ignored in the yield management literature can be caused by either operations or distributions. We investigate the decision problem of two airlines offering two identical fare classes under both the simultaneous and sequential allocations. For both allocation cases, we show the existence, uniqueness and stability of pure‐strategy Nash equilibrium under a reasonable condition on the ratios of relative profit margins of the two fare classes. We find that there will be fewer seats protected for the full‐fare class if the discount seats can be booked first. We found that the asymmetry in costs has two effects on the equilibrium solutions: (a) an airline behaves aggressively for the fare class where it enjoys a cost advantage; (b) an airline tends to balance the trade‐offs internally when it has absolute cost advantage in both fare classes. In deriving the collusive solution for both cases for comparative purposes, we discover new insights by solving the two‐flight, two‐fare seat allocation problem with different cost structures on the two flights. In particular, we show that rivalry in full‐fare seat protection leads to a Prisoners' Dilemma for the carriers. Finally, a numerical example is used to illustrate various analytical results. 相似文献
998.
E. Rius-Vilarrasa L. Bünger S. Brotherstone K.R. Matthews W. Haresign J.M. Macfarlane M. Davies R. Roehe 《Meat science》2009,81(4):619-625
A total of 7074 crossbred lambs, produced by mating crossbred Mule ewes with terminal sire rams were used in this study. Of these, 630 were scanned using a Video Image Analysis (VIA) to estimate carcass quality traits. Genetic parameters for average daily gain (ADG), scanning live weight (SW), ultrasonic measures of muscle (UMD) and fat (UFD) depths, cold carcass weight (CCW) and VIA measurements of primal carcass joint weights (LEG, CHUMP, LOIN, BREAST and SHOULDER) were estimated using multivariate animal models. Additionally, VIA traits were evaluated under a repeatability model, considering the primal joints as repeated measures of the same trait. Direct heritability estimates were low to moderate (0.08–0.26) for VIA measurements of primal joints. Repeatability estimates for VIA traits were high (>0.90). Moderate to high heritability estimates (0.25–0.55) were found for performance traits (ADG, SW, UMD and UFD) and CCW. Genetic correlations between VIA traits and ADG were strong (0.75–0.93). Most of the VIA traits were highly correlated to SW (0.60–0.97). UFD was significantly negatively correlated with UMD (−0.22), ADG (−0.18) and CCW (−0.18). The results of this study suggest that selection on performance and carcass traits, measured by VIA, could possibly improve primal meat yield of carcass cuts without increasing the overall carcass fatness. High repeatability estimates of VIA traits and moderate heritabilities of the most valuable carcass joints suggests that including VIA information in breeding programs would be useful in order to improve carcass quality. 相似文献
999.
1000.