全文获取类型
收费全文 | 497981篇 |
免费 | 44007篇 |
国内免费 | 24570篇 |
专业分类
电工技术 | 33396篇 |
技术理论 | 24篇 |
综合类 | 36068篇 |
化学工业 | 78626篇 |
金属工艺 | 27488篇 |
机械仪表 | 30961篇 |
建筑科学 | 40568篇 |
矿业工程 | 13670篇 |
能源动力 | 14134篇 |
轻工业 | 37705篇 |
水利工程 | 10086篇 |
石油天然气 | 24105篇 |
武器工业 | 4462篇 |
无线电 | 60188篇 |
一般工业技术 | 56667篇 |
冶金工业 | 23115篇 |
原子能技术 | 5415篇 |
自动化技术 | 69880篇 |
出版年
2024年 | 2232篇 |
2023年 | 7579篇 |
2022年 | 14879篇 |
2021年 | 20105篇 |
2020年 | 14838篇 |
2019年 | 12109篇 |
2018年 | 13321篇 |
2017年 | 15572篇 |
2016年 | 14199篇 |
2015年 | 19677篇 |
2014年 | 25286篇 |
2013年 | 30983篇 |
2012年 | 33612篇 |
2011年 | 36813篇 |
2010年 | 32865篇 |
2009年 | 31444篇 |
2008年 | 30826篇 |
2007年 | 29220篇 |
2006年 | 28333篇 |
2005年 | 23755篇 |
2004年 | 16645篇 |
2003年 | 14451篇 |
2002年 | 13962篇 |
2001年 | 12311篇 |
2000年 | 10950篇 |
1999年 | 10609篇 |
1998年 | 8951篇 |
1997年 | 7290篇 |
1996年 | 6783篇 |
1995年 | 5706篇 |
1994年 | 4689篇 |
1993年 | 3544篇 |
1992年 | 2737篇 |
1991年 | 2109篇 |
1990年 | 1646篇 |
1989年 | 1410篇 |
1988年 | 1103篇 |
1987年 | 779篇 |
1986年 | 614篇 |
1985年 | 476篇 |
1984年 | 325篇 |
1983年 | 267篇 |
1982年 | 240篇 |
1981年 | 227篇 |
1980年 | 223篇 |
1979年 | 158篇 |
1978年 | 85篇 |
1977年 | 81篇 |
1976年 | 117篇 |
1975年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
针对目前单螺杆泵使用中存在的转速低、振动大和离心力大等局限性,研制了一种实用的新型双转动单螺杆泵。这种泵结构简单,省掉了减速机构和万向装置,实现了内、外转子同方向高速平稳转动。该泵有4大特点:(1)把现有螺杆泵转子的滚动+绕偏心距摆动的复杂运动简化成绕其中心的纯转动,故噪声小,振动小,离心力小;(2)内、外转子是纯转动,无摆动现象,故动力轴和螺杆之间无需万向装置,内、外转子可制成全金属型,耐温达200℃以上;(3)无需减速机构,电动机可直接与内、外转子对接,使螺杆泵转速由400r/min提高到3500r/min;(4)外转子可以模块化加工。 相似文献
983.
产品数据管理系统数据库设计 总被引:1,自引:0,他引:1
工程数据库EDB(Engineering Database),是工程设计及制造领域中相互有关的数据所组成的集合,本文在详细分析工程数据库的特点及其实现方式的基础上,结合SF-PDM数据库设计,深入讨论了使用UML进行数据库概念设计和逻辑设计的方法与步骤,总结介绍了SF-PDM数据库物理设计的思路与相关实现过程。 相似文献
984.
Shyi-Ming Chen Chung-Ming Huang 《Fuzzy Systems, IEEE Transactions on》2003,11(4):495-506
In recent years, some methods have been proposed to estimate values in relational database systems. However, the estimated accuracy of the existing methods are not good enough. In this paper, we present a new method to generate weighted fuzzy rules from relational database systems for estimating values using genetic algorithms (GAs), where the attributes appearing in the antecedent part of generated fuzzy rules have different weights. After a predefined number of evolutions of the GA, the best chromosome contains the optimal weights of the attributes, and they can be translated into a set of rules to be used for estimating values. The proposed method can get a higher average estimated accuracy rate than the methods we presented in two previous papers. 相似文献
985.
The modulation characteristics of first-order backscatter-induced crosstalk noise in a 2-D frequency-division-multiplexed fiber gyro system are analyzed and experimental results presented. The noise can be reduced from 5°/h to 0.2°/h (0.25 NEB) by proper choice of modulation depth and/or frequency 相似文献
986.
指出施工监理是一项细致而又责任重大的工作。把握好污水处理厂关键工序的施工及检查,才能对污水处理工程进行有效地控制和管理,使之发挥最大的经济和社会效益。 相似文献
987.
988.
989.
The purpose of this study was to evaluate the relationship between the number of yolk sacs and amnionicity in monochorionic twin pregnancies scanned early in the first trimester. We retrospectively reviewed images of all monochorionic twins scanned between 6 and 9.5 weeks' gestation and with pathologic or sonographic confirmation of chorionicity-amnionicity. Each film was reviewed for the number of yolk sacs present, as well as for the gestational age at which the amniotic membrane was first visualized. Twenty monochorionic-diamniotic pregnancies and two monochorionic-monoamniotic pregnancies met the criteria for inclusion in the study. In diamniotic pregnancies scanned at less than 8 weeks' gestation, only the yolk sacs were identified; none of the dividing amniotic membranes were detected. Two yolk sacs were identified in all but one case. In this case, although one yolk sac was seen at 6 weeks, follow-up scanning at 8 weeks revealed two yolk sacs. In each of the monochorionic-monoamniotic twin pregnancies, one yolk sac was seen at 9 weeks and a single amnion encircled both embryos. We conclude that the sonographic identification of two yolk scas in monochorionic twins enables us to make the diagnosis of diamniotic twins early in the first trimester, before the amniotic membrane can be imaged. The presence of one yolk sac should prompt a follow-up ultrasonogram to assign amnionicity definitively. 相似文献
990.
Bor -Yir Chen Wei -Hsiung Wu Jiann -Ruey Chen Chum -Sam Hong 《Journal of Materials Science》1995,30(9):2254-2256
The temperature dependence characteristics of hydrogenated amorphous silicon thin-film transistors were investigated. The results indicate that as the temperature was increased, the threshold voltage and the field-effect mobility were first increased, and then decreased, which may be controlled by different mechanisms at low and high temperatures. In addition, if the temperature was higher than 420 K, the Fermi level was promoted to the degenerate-like states, the current channel always existed due to the temperature effect, and the threshold voltage became negative. 相似文献