全文获取类型
收费全文 | 213689篇 |
免费 | 28409篇 |
国内免费 | 19389篇 |
专业分类
电工技术 | 18881篇 |
技术理论 | 11篇 |
综合类 | 26195篇 |
化学工业 | 18817篇 |
金属工艺 | 11699篇 |
机械仪表 | 18361篇 |
建筑科学 | 18737篇 |
矿业工程 | 9653篇 |
能源动力 | 11132篇 |
轻工业 | 5495篇 |
水利工程 | 11624篇 |
石油天然气 | 11878篇 |
武器工业 | 4917篇 |
无线电 | 17622篇 |
一般工业技术 | 19173篇 |
冶金工业 | 7227篇 |
原子能技术 | 2604篇 |
自动化技术 | 47461篇 |
出版年
2024年 | 1150篇 |
2023年 | 3339篇 |
2022年 | 6517篇 |
2021年 | 7321篇 |
2020年 | 7889篇 |
2019年 | 6465篇 |
2018年 | 6345篇 |
2017年 | 7990篇 |
2016年 | 9374篇 |
2015年 | 9954篇 |
2014年 | 13789篇 |
2013年 | 14094篇 |
2012年 | 16458篇 |
2011年 | 17808篇 |
2010年 | 13486篇 |
2009年 | 13773篇 |
2008年 | 13425篇 |
2007年 | 15647篇 |
2006年 | 13459篇 |
2005年 | 11448篇 |
2004年 | 9407篇 |
2003年 | 7838篇 |
2002年 | 6255篇 |
2001年 | 5157篇 |
2000年 | 4328篇 |
1999年 | 3387篇 |
1998年 | 2795篇 |
1997年 | 2295篇 |
1996年 | 2117篇 |
1995年 | 1793篇 |
1994年 | 1481篇 |
1993年 | 1024篇 |
1992年 | 835篇 |
1991年 | 677篇 |
1990年 | 538篇 |
1989年 | 443篇 |
1988年 | 293篇 |
1987年 | 176篇 |
1986年 | 159篇 |
1985年 | 124篇 |
1984年 | 133篇 |
1983年 | 74篇 |
1982年 | 89篇 |
1981年 | 46篇 |
1980年 | 65篇 |
1979年 | 62篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1959年 | 37篇 |
1951年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation. 相似文献
62.
为了提高非稳定渗流计算的计算精度 ,通过数学分析得到了水位传导系数随时间变化时 ,一类非稳定渗流井流模型的半解析解 ,并进行了计算比较 相似文献
63.
通信性能评估的仿真实验研究 总被引:1,自引:0,他引:1
研究了流量控制和差错控制对通信性能的综合影响,着重分析了停止-等待协议和连续ARQ协议的优缺点,讨论了信道利用率和帧长的关系。介绍了几种多点接人技术的基本原理,如CSMA和CSMA/CD,并给出了各自相应的性能仿真曲线。所设计的通信性能评估实验,仿真界面形象丰富,与实验知识点紧密结合,可以大大提高实验教学的效率和质量。 相似文献
64.
Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry 相似文献
65.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
66.
The Intellectual Development of Science and Engineering Students. Part 2: Teaching to Promote Growth
As college students experience the challenges of their classes and extracurricular activities, they undergo a developmental progression in which they gradually relinquish their belief in the certainty of knowledge and the omniscience of authorities and take increasing responsibility for their own learning. At the highest developmental level normally seen in college students (which few attain before graduation), they display attitudes and thinking patterns resembling those of expert scientists and engineers, including habitually and skillfully gathering and analyzing evidence to support their judgments. This paper proposes an instructional model designed to provide a suitable balance of challenge and support to advance students to that level. The model components are (1) variety and choice of learning tasks; (2) explicit communication and explanation of expectations; (3) modeling, practice, and constructive feedback on high‐level tasks; (4) a student‐centered instructional environment; and (5) respect for students at all levels of development. 相似文献
67.
68.
69.
Models that link ecological responses to hydrologic changes are important for assessing the effects of flow regulation on aquatic and riparian ecosystems. Based on the Recruitment Box Model, a graphical model used to prescribe environmental flows for cottonwood (Populus spp.) recruitment, we designed a simulation model to represent the influence of river flow dynamics on seedling recruitment of riparian pioneer woody plants. The model simulates the influence of temporal patterns of river stage on dispersal, germination, initial recruitment and over‐winter survival of first‐year seedlings of riparian pioneer shrubs and trees. We used the model to simulate seedling recruitment patterns for five species (Acer saccharinum, Betula nigra, Populus deltoides, Salix nigra and Salix exigua) on the Wisconsin River (Wisconsin, USA) under three flow scenarios: historic (1935–2002), simulated natural (1915–1975) and simulated regulated flows (1915–1975). Simulation results agreed well with field‐observed relative differences among years (1997–2000) in seedling densities for the five focal species. Simulated successful recruitment years were highly synchronous among species, but species differed in their sensitivity to flows at different times during the growing season, consistent with among‐species differences in seed dispersal timing. Comparison of simulated natural and regulated flows for 1915–1975 showed that flow regulation decreased monthly flow variability, increased late summer to winter baseflow and reduced the magnitude of spring peaks. Simulated recruitment and over‐winter survival of tree seedlings of all species was enhanced under the regulated flow scenario, likely due to increased summer baseflow and reductions in peak flood magnitude. Our analyses show the utility of extending the Recruitment Box Model to include multiple species of riparian shrubs and trees, and the effects of post‐colonization flows on their recruitment success. However, some key functional relationships between flow patterns and woody seedling demography (e.g. shear stress thresholds for seedling mortality) have not been adequately quantified and merit further study. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
70.
A stochastic model for local disturbances, particularly for a temporal harmonic with random modulations in amplitude and/or phase, is proposed in this paper. Results for the second moment responses of a linear single-degree-of-freedom system to this type of stochastic loading demonstrate a significant change in response characteristics due to a small uncertainty. A local phenomenon may last much longer and resonance may be smeared to a broad range. Integrated with wavelet transform, the proposed approach may be used to model a random process with non-stationary frequency content. Especially, it can be effectively used for Monte Carlo simulation to generate large size of samples that have similar characteristics in time and frequency domains as a pre-selected mother sample has. The technique has a great potential for the case where uncertainty study is warranted but the available samples are limited. 相似文献