全文获取类型
收费全文 | 199494篇 |
免费 | 2502篇 |
国内免费 | 612篇 |
专业分类
电工技术 | 3468篇 |
综合类 | 149篇 |
化学工业 | 28961篇 |
金属工艺 | 8049篇 |
机械仪表 | 6068篇 |
建筑科学 | 4812篇 |
矿业工程 | 1303篇 |
能源动力 | 5127篇 |
轻工业 | 17118篇 |
水利工程 | 2297篇 |
石油天然气 | 4040篇 |
武器工业 | 8篇 |
无线电 | 23068篇 |
一般工业技术 | 40013篇 |
冶金工业 | 37231篇 |
原子能技术 | 5086篇 |
自动化技术 | 15810篇 |
出版年
2021年 | 1604篇 |
2019年 | 1569篇 |
2018年 | 2573篇 |
2017年 | 2646篇 |
2016年 | 2775篇 |
2015年 | 1794篇 |
2014年 | 3074篇 |
2013年 | 8939篇 |
2012年 | 5051篇 |
2011年 | 7021篇 |
2010年 | 5591篇 |
2009年 | 6351篇 |
2008年 | 6443篇 |
2007年 | 6512篇 |
2006年 | 5579篇 |
2005年 | 5230篇 |
2004年 | 5006篇 |
2003年 | 4887篇 |
2002年 | 4525篇 |
2001年 | 4657篇 |
2000年 | 4579篇 |
1999年 | 4726篇 |
1998年 | 11373篇 |
1997年 | 8122篇 |
1996年 | 6409篇 |
1995年 | 4673篇 |
1994年 | 4271篇 |
1993年 | 4074篇 |
1992年 | 3223篇 |
1991年 | 3076篇 |
1990年 | 2870篇 |
1989年 | 2951篇 |
1988年 | 2826篇 |
1987年 | 2398篇 |
1986年 | 2308篇 |
1985年 | 2715篇 |
1984年 | 2505篇 |
1983年 | 2345篇 |
1982年 | 2090篇 |
1981年 | 2203篇 |
1980年 | 2029篇 |
1979年 | 2126篇 |
1978年 | 2120篇 |
1977年 | 2366篇 |
1976年 | 3188篇 |
1975年 | 1833篇 |
1974年 | 1761篇 |
1973年 | 1772篇 |
1972年 | 1443篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
A conceptualization of intended learning outcomes supporting self‐regulated learners in indicating learning paths 下载免费PDF全文
P. Tangworakitthaworn L. Gilbert G.B. Wills 《Journal of Computer Assisted Learning》2015,31(5):393-404
Intended learning outcomes (ILOs) indicate what learners will be able to achieve after they are taught. Traditionally, ILOs are expressed as plain text or unstructured documents. What if all ILOs of a specific course of study can be conceptualized through a structured diagrammatic technique? It was hypothesized that learners can benefit from this conceptualization in learning, especially in self‐regulated learning. The aim of this study was to investigate whether the ILOs represented in unstructured or structured formats can facilitate learners to identify learning paths. The results revealed that the mean ratings of all learning paths were statistically significantly higher with structured ILOs. 相似文献
23.
24.
25.
Machine Learning - We propose a data-driven approach to quantify the uncertainty of models constructed by kernel methods. Our approach minimizes the needed distributional assumptions, hence,... 相似文献
26.
Kozhitov L. V. Kiselev B. G. Raykova T. B. Popkova A. V. Kostishin V. G. Muratov D. G. Yakushko E. V. Kosushkin V. G. Bebenin V. G. 《Russian Microelectronics》2019,48(8):599-612
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical... 相似文献
27.
28.
Lorena Rodríguez-López Myriam Rincón-Fontán Xanel Vecino Ana B. Moldes Jose M. Cruz 《Journal of surfactants and detergents》2020,23(1):79-90
Over the last few years, the global biosurfactant market has raised due to the increasing awareness among consumers, for the use of biological or bio-based products. Because of their composition, it can be speculated that these are more biocompatible and more biodegradable than their chemical homologous. However, at the moment, no studies exist in the literature about the biodegradability of biosurfactants. In this work, a biosurfactant contained in a crude extract, obtained from a corn wet-milling industry stream that ferments spontaneously in the presence of lactic acid bacteria, was subjected to a biodegradation study, without addition of external microbial biomass, under different conditions of temperature (5–45 °C), biodegradation time (15–55 days), and pH (5–7). For that, a Box–Behnken factorial design was applied, which allowed to predict the percentage of biodegradation for the biosurfactant contained in the crude extract, between the range of the independent variables selected in the study, obtaining biodegradation values between 3 and 80%. The percentage of biodegradation for the biosurfactant was calculated based on the increase in the surface tension of samples of the crude extract. Furthermore, it was also possible to predict the variation in t1/2 for the biosurfactant (time to achieve the 50% of biodegradation) under different conditions. 相似文献
29.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions. 相似文献
30.
Lecture capture with real‐time rearrangement of visual elements: impact on student performance 下载免费PDF全文
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance. 相似文献