全文获取类型
收费全文 | 182239篇 |
免费 | 69768篇 |
国内免费 | 46597篇 |
专业分类
电工技术 | 27966篇 |
技术理论 | 3篇 |
综合类 | 21318篇 |
化学工业 | 23421篇 |
金属工艺 | 24992篇 |
机械仪表 | 6198篇 |
建筑科学 | 12111篇 |
矿业工程 | 13054篇 |
能源动力 | 8320篇 |
轻工业 | 20213篇 |
水利工程 | 7240篇 |
石油天然气 | 12596篇 |
武器工业 | 3608篇 |
无线电 | 29801篇 |
一般工业技术 | 29744篇 |
冶金工业 | 6491篇 |
原子能技术 | 1260篇 |
自动化技术 | 50268篇 |
出版年
2024年 | 2700篇 |
2023年 | 4363篇 |
2022年 | 4751篇 |
2021年 | 5404篇 |
2020年 | 8530篇 |
2019年 | 18098篇 |
2018年 | 19515篇 |
2017年 | 20781篇 |
2016年 | 20514篇 |
2015年 | 19364篇 |
2014年 | 18029篇 |
2013年 | 17089篇 |
2012年 | 16347篇 |
2011年 | 12633篇 |
2010年 | 11505篇 |
2009年 | 8545篇 |
2008年 | 6569篇 |
2007年 | 6024篇 |
2006年 | 5132篇 |
2005年 | 4824篇 |
2004年 | 7628篇 |
2003年 | 6311篇 |
2002年 | 5969篇 |
2001年 | 5214篇 |
2000年 | 4856篇 |
1999年 | 4632篇 |
1998年 | 4213篇 |
1997年 | 3790篇 |
1996年 | 3638篇 |
1995年 | 3679篇 |
1994年 | 3004篇 |
1993年 | 2768篇 |
1992年 | 2670篇 |
1991年 | 1912篇 |
1990年 | 1530篇 |
1989年 | 1444篇 |
1988年 | 1085篇 |
1987年 | 325篇 |
1986年 | 283篇 |
1985年 | 214篇 |
1984年 | 142篇 |
1983年 | 101篇 |
1982年 | 154篇 |
1981年 | 150篇 |
1980年 | 100篇 |
1976年 | 227篇 |
1975年 | 203篇 |
1972年 | 235篇 |
1971年 | 127篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Valerie Shute Seyedahmad Rahimi Ginny Smith Fengfeng Ke Russell Almond Chih-Pu Dai Renata Kuba Zhichun Liu Xiaotong Yang Chen Sun 《Journal of Computer Assisted Learning》2021,37(1):127-141
In this study, we investigated the validity of a stealth assessment of physics understanding in an educational game, as well as the effectiveness of different game-level delivery methods and various in-game supports on learning. Using a game called Physics Playground, we randomly assigned 263 ninth- to eleventh-grade students into four groups: adaptive, linear, free choice and no-treatment control. Each condition had access to the same in-game learning supports during gameplay. Results showed that: (a) the stealth assessment estimates of physics understanding were valid—significantly correlating with the external physics test scores; (b) there was no significant effect of game-level delivery method on students' learning; and (c) physics animations were the most effective (among eight supports tested) in predicting both learning outcome and in-game performance (e.g. number of game levels solved). We included student enjoyment, gender and ethnicity in our analyses as moderators to further investigate the research questions. 相似文献
992.
王代 《网络安全技术与应用》2012,(6):62-63
随着当今网络技术的迅猛发展,人们的行为和生活越来越受到其影响,发生着改变,故调整其行为规范的网络相关法律法规也越来越受到人们的关注。从法理学角度出发对网络法律进行构建与研究,在此基础上规范其基本理念和适用原则,对于建立完善网络法律体系尤为重要。本文从法理学角度出发,对网络法律的基本理念和原则进行了简要探析。 相似文献
993.
A Houjin is an n by n square lattice with each cell containing a symbol (such as a number or a letter). Further, these numbers or letters are designed
to exhibit symmetry. For example, a magic square is a Houjin where the embedded symmetry is that the numbers in each row,
column, and a center diagonal have an equal sum. This article reports a new Houjin: a dynamic Houjin. A dynamic Houjin changes
its numbers at each time step while satisfying the symmetry as a Houjin (a magic square). The dynamic Houjin has a further
symmetry in a time dimension, i.e., the sums of the numbers in each cell are identical. 相似文献
994.
Most face recognition systems employ 2-D color or gray-scale images. However, face recognition based on 2-D images is adversely
affected by 3-D movement, variable lighting, and the use of cosmetics. 3-D image measurement technology has the potential
to overcome these limitations of face recognition based on 2-D images since it can perform geometric analysis. We propose
a method that is capable of recognizing a person from a 3-D facial image obtained using a 3-D shape measurement system by
employing a technique that optimizes the intensity-modulation pattern projection. This face recognition method is based on
the iterative closest point algorithm. It is robust to changes in reflectivity and color. Since the 3-D facial information
can be registered, this method can estimate rotations and translations to compensate for different positions or directions.
In order to prove the validity of the proposed technique, a verification experiment was conducted which used 105 sample 3-D
images obtained from 15 subjects. It achieved a detection rate of 96% when heads were turned at an angle of 20° or less relative
to the camera. 相似文献
995.
996.
本文用数值模拟方法,按照大庆油田的油层条件,系统研究了水驱特征曲线的一般特征、出现直线段的时间及直线最小适用范围,同时重新评价了小井距试验区的水驱特征曲线,从而为在本油田正确使用水驱特征曲线提供了依据。文中用中期采油量倍增法估算的可采储量也可为开发决策提供参考数据。 相似文献
997.
U. Schfißler Franz Ledl 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1989,189(2):138-140
Summary The title compound has been synthesized by a novel route fromN
-trifluoroacetyl lysine methyl ester and 2,9-dimethyldeca-2,8-diene-4,7-dione. Transformation of the pyrrole substituents and easy cleavage of protecting groups yields the compound in samples of high purity.
Synthese der 2-Amino-6-(2-formyl-5-hydroxymethyl-l-pyrrolyl)-hexansäure
Zusammenfassung Die Titelverbindung wird auf einem neuen Weg ausN -Trifluoracetyllysinmethylester und 2,9-Dimethyldeca-2,8-dien-4,7-dion synthetisiert. Nach Umwandlung der Pyrrolsubstituenten und Abspaltung der Schutzgruppen unter milden Bedingungen erhält man die Titelverbindung in hoher Reinheit.相似文献
998.
Corrigendum
Prediction of mode I fracture toughness of unidirectional fibre composites with arbitrary crack fibre orientation from its lowest or matrix fracture tougnessby P.K. Sarkar and S.K. Maiti 相似文献999.
1000.
In this paper we analyze the average-case performance of the Modified Harmonic algorithm for on-line bin packing. We first analyze the average-case performance for arbitrary distribution of item sizes over (0,1]. This analysis is based on the following result. Letf
1 andf
2 be two linear combinations of random variables {N
i
}
i=1
k
where theN
i
's have a joint multinomial distribution for eachn=
i=1
k
,N
i
. LetE(f
1) O andE(f
2) 0. Then limn
E(max(f
1,f
2
))/n = lim
n
max(E(f
1),E(f
2))/n. We then consider the special case when the item sizes are uniformly distributed over (0,1]. For specific values of the parameters, the Modified Harmonic algorithm turns out to be better than the other two linear-time on-line algorithms—Next Fit and Harmonic—in both the worst case as well as the average case. We also obtain optimal values for the parameters of the algorithm from the average-case standpoint. For these values of the parameters, the average-case performance ratio is less than 1.19. This compares well with the performance ratios 1.333. and 1.2865. of the Next Fit algorithm and the Harmonic algorithm, respectively. 相似文献