全文获取类型
收费全文 | 39850篇 |
免费 | 4236篇 |
国内免费 | 2812篇 |
专业分类
电工技术 | 2841篇 |
技术理论 | 8篇 |
综合类 | 6006篇 |
化学工业 | 3042篇 |
金属工艺 | 1012篇 |
机械仪表 | 2745篇 |
建筑科学 | 4299篇 |
矿业工程 | 1397篇 |
能源动力 | 1338篇 |
轻工业 | 552篇 |
水利工程 | 1124篇 |
石油天然气 | 977篇 |
武器工业 | 706篇 |
无线电 | 3710篇 |
一般工业技术 | 4692篇 |
冶金工业 | 2295篇 |
原子能技术 | 356篇 |
自动化技术 | 9798篇 |
出版年
2024年 | 154篇 |
2023年 | 622篇 |
2022年 | 811篇 |
2021年 | 1039篇 |
2020年 | 1204篇 |
2019年 | 1116篇 |
2018年 | 1170篇 |
2017年 | 1329篇 |
2016年 | 1441篇 |
2015年 | 1478篇 |
2014年 | 2267篇 |
2013年 | 2757篇 |
2012年 | 2559篇 |
2011年 | 2916篇 |
2010年 | 2287篇 |
2009年 | 2420篇 |
2008年 | 2477篇 |
2007年 | 2659篇 |
2006年 | 2464篇 |
2005年 | 2165篇 |
2004年 | 1741篇 |
2003年 | 1445篇 |
2002年 | 1250篇 |
2001年 | 1009篇 |
2000年 | 884篇 |
1999年 | 760篇 |
1998年 | 610篇 |
1997年 | 545篇 |
1996年 | 451篇 |
1995年 | 427篇 |
1994年 | 355篇 |
1993年 | 300篇 |
1992年 | 280篇 |
1991年 | 206篇 |
1990年 | 165篇 |
1989年 | 180篇 |
1988年 | 142篇 |
1987年 | 74篇 |
1986年 | 97篇 |
1985年 | 69篇 |
1984年 | 68篇 |
1983年 | 51篇 |
1982年 | 53篇 |
1981年 | 42篇 |
1980年 | 31篇 |
1979年 | 32篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1964年 | 26篇 |
1955年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
The mirror effect for word frequency refers to the finding that low-frequency words have higher hit rates and lower false alarm rates than high-frequency words. This result is typically interpreted in terms of conventional signal detection theory (SDT), in which case it indicates that the order of the underlying old item distributions mirrors the order of the new item distributions. However, when viewed in terms of a mixture version of SDT, the order of hits and false alarms does not necessarily imply the same order in the underlying distributions because of possible effects of mixing. A reversal in underlying distributions did not appear for fits of mixture SDT models to data from 4 experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
43.
Gregory S. Ho Chen Huang Emily A. Carter 《Current Opinion in Solid State & Materials Science》2007,11(5-6):57-61
Orbital-free density functional theory (OF-DFT) can be made to scale linearly with sample size, allowing thousands of atoms to be treated explicitly with quantum mechanics. State-of-the-art kinetic energy density functionals and ion–electron pseudopotentials are used to obtain accurate structural property predictions for nanoparticles, nanowires, extended surfaces, and nanoindentation of simple metals. 相似文献
44.
阐述了时空效应规律在软土深基坑工程中的运用情况,实践证明,运用时空效应规律,能可靠而合理地利用土体自身在基坑开挖过程中控制土体位移的潜力而达到保护环境的目的。 相似文献
45.
新经济增长理论对我国人力资本发展的借鉴 总被引:3,自引:0,他引:3
新经济增长理论为人力资本理论注入了新的内容,为各国如何利用人力资本发展经济提供了理论指导。分析了新经济增长理论中有关人力资本的理论,以此对我国经济和人力资本的发展提出了一些借鉴;收益递增模型。 相似文献
46.
A motivational model of rural students' intentions to persist in, versus drop out of, high school. 总被引:1,自引:0,他引:1
Using self-determination theory, the authors tested a motivational model to explain the conditions under which rural students formulate their intentions to persist in, versus drop out of, high school. The model argues that motivational variables underlie students' intentions to drop out and that students' motivation can be either supported in the classroom by autonomy-supportive teachers or frustrated by controlling teachers. LISREL analyses of questionnaire data from 483 rural high school students showed that the provision of autonomy support within classrooms predicted students' self-determined motivation and perceived competence. These motivational resources, in turn, predicted students' intentions to persist, versus drop out, and they did so even after controlling for the effect of achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
47.
Academically selective schools are intended to affect academic self-concept positively, but theoretical and empirical research demonstrates that the effects are negative. The big-fish--little-pond effect (BFLPE), an application of social comparison theory to educational settings, posits that a student will have a lower academic self-concept in an academically selective school than in a nonselective school. This study, the largest cross-cultural study of the BFLPE ever undertaken, tested theoretical predictions for nationally representative samples of approximately 4,000 15-year-olds from each of 26 countries (N=103,558) who completed the same self-concept instrument and achievement tests. Consistent with the BFLPE, the effects of school-average achievement were negative in all 26 countries (M beta=-.20, SD=.08), demonstrating the BFLPE's cross-cultural generalizability. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
48.
In the past few years many systems for learning decision rules from examples were developed. As different systems allow different types of answers when classifying new instances, it is difficult to appropriately evaluate the systems' classification power in comparison with other classification systems or in comparison with human experts. Classification accuracy is usually used as a measure of classification performance. This measure is, however, known to have several defects. A fair evaluation criterion should exclude the influence of the class probabilities which may enable a completely uninformed classifier to trivially achieve high classification accuracy. In this paper a method for evaluating the information score of a classifier's answers is proposed. It excludes the influence of prior probabilities, deals with various types of imperfect or probabilistic answers and can be used also for comparing the performance in different domains. 相似文献
49.
Memory loss in retrograde amnesia has long been held to be larger for recent periods than for remote periods, a pattern usually referred to as the Ribot gradient. One explanation for this gradient is consolidation of long-term memories. Several computational models of such a process have shown how consolidation can explain characteristics of amnesia, but they have not elucidated how consolidation must be envisaged. Here findings are reviewed that shed light on how consolidation may be implemented in the brain. Moreover, consolidation is contrasted with alternative theories of the Ribot gradient. Consolidation theory, multiple trace theory, and semantization can all handle some findings well but not others. Conclusive evidence for or against consolidation thus remains to be found. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
50.
Stress State of Bent Buried Pipelines 总被引:1,自引:0,他引:1
The authors consider edge effects in buried pipelines that occur in the region of joining of a straight buried pipe and a bent insert (factory bend, elbow, or an elastically bent segment). The action of those effects results in the appearance of additional bending moments, which are proportional to the difference between the axial force in an infinite straight pipeline and that in a closed-end pipe, and depend on the geometrical parameters of the pipeline and physical-mechanical characteristics of the soil. Specific examples of analysis of elastic interaction of a pipeline with the soil for pipe bends with various radii of the bend arc are offered. It is shown that additional bending stresses may exceed appreciably the stresses from the axial force, and therefore, they should be taken into account when designing and building pipelines. The solution for an elastically bent segment has been obtained and analyzed. 相似文献