全文获取类型
收费全文 | 135508篇 |
免费 | 3806篇 |
国内免费 | 2409篇 |
专业分类
电工技术 | 3428篇 |
综合类 | 2069篇 |
化学工业 | 16392篇 |
金属工艺 | 6945篇 |
机械仪表 | 5064篇 |
建筑科学 | 5038篇 |
矿业工程 | 776篇 |
能源动力 | 3978篇 |
轻工业 | 8093篇 |
水利工程 | 1186篇 |
石油天然气 | 2497篇 |
武器工业 | 225篇 |
无线电 | 19880篇 |
一般工业技术 | 25867篇 |
冶金工业 | 26948篇 |
原子能技术 | 1806篇 |
自动化技术 | 11531篇 |
出版年
2023年 | 690篇 |
2022年 | 1255篇 |
2021年 | 1810篇 |
2020年 | 1380篇 |
2019年 | 1401篇 |
2018年 | 1922篇 |
2017年 | 2041篇 |
2016年 | 2027篇 |
2015年 | 2026篇 |
2014年 | 2928篇 |
2013年 | 6488篇 |
2012年 | 4491篇 |
2011年 | 5915篇 |
2010年 | 4836篇 |
2009年 | 5467篇 |
2008年 | 5591篇 |
2007年 | 5750篇 |
2006年 | 5423篇 |
2005年 | 4883篇 |
2004年 | 4252篇 |
2003年 | 3984篇 |
2002年 | 3619篇 |
2001年 | 3760篇 |
2000年 | 3605篇 |
1999年 | 4040篇 |
1998年 | 10353篇 |
1997年 | 6904篇 |
1996年 | 5516篇 |
1995年 | 3785篇 |
1994年 | 3277篇 |
1993年 | 3163篇 |
1992年 | 1931篇 |
1991年 | 1818篇 |
1990年 | 1747篇 |
1989年 | 1478篇 |
1988年 | 1300篇 |
1987年 | 951篇 |
1986年 | 963篇 |
1985年 | 971篇 |
1984年 | 847篇 |
1983年 | 729篇 |
1982年 | 729篇 |
1981年 | 700篇 |
1980年 | 585篇 |
1979年 | 486篇 |
1978年 | 419篇 |
1977年 | 543篇 |
1976年 | 970篇 |
1975年 | 303篇 |
1974年 | 282篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Lecture capture with real‐time rearrangement of visual elements: impact on student performance
下载免费PDF全文
![点击此处可从《Journal of Computer Assisted Learning》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
42.
Dr. Yahu A. Liu Dr. Qihui Jin Qiang Ding Dr. Xueshi Hao Tingting Mo Shanshan Yan Dr. Yefen Zou Dr. Zhihong Huang Xiaoyue Zhang Wenqi Gao Dr. Tom Y.-H. Wu Chun Li Dr. Badry Bursalaya Dr. Michael Di Donato Dr. You-Qing Zhang Lisa Deaton Dr. Weijun Shen Dr. Brandon Taylor Anwesh Kamireddy Dr. George Harb Dr. Jing Li Dr. Yong Jia Dr. Andrew M. Schumacher Dr. Bryan Laffitte Dr. Richard Glynne Dr. Shifeng Pan Dr. Peter McNamara Dr. Valentina Molteni Dr. Jon Loren 《ChemMedChem》2020,15(16):1562-1570
Loss of β-cell mass and function can lead to insufficient insulin levels and ultimately to hyperglycemia and diabetes mellitus. The mainstream treatment approach involves regulation of insulin levels; however, approaches intended to increase β-cell mass are less developed. Promoting β-cell proliferation with low-molecular-weight inhibitors of dual-specificity tyrosine-regulated kinase 1A (DYRK1A) offers the potential to treat diabetes with oral therapies by restoring β-cell mass, insulin content and glycemic control. GNF4877, a potent dual inhibitor of DYRK1A and glycogen synthase kinase 3β (GSK3β) was previously reported to induce primary human β-cell proliferation in vitro and in vivo. Herein, we describe the lead optimization that lead to the identification of GNF4877 from an aminopyrazine hit identified in a phenotypic high-throughput screening campaign measuring β-cell proliferation. 相似文献
43.
Dr. Emilianne M. Limbrick Audrey E. Yñigez-Gutierrez Callie C. Dulin Dagmara K. Derewacz Dr. Jeffrey M. Spraggins Dr. Kathryn M. McCulloch Prof. T. M. Iverson Prof. Brian O. Bachmann 《Chembiochem : a European journal of chemical biology》2020,21(23):3349-3358
Everninomicins are orthoester oligosaccharide antibiotics with potent activity against multidrug-resistant bacterial pathogens. Everninomicins act by disrupting ribosomal assembly in a distinct region in comparison to clinically prescribed drugs. We employed microporous intergeneric conjugation with Escherichia coli to manipulate Micromonospora for targeted gene-replacement studies of multiple putative methyltransferases across the octasaccharide scaffold of everninomicin effecting the A1, C, F, and H rings. Analyses of gene-replacement and genetic complementation mutants established the mutability of the everninomicin scaffold through the generation of 12 previously unreported analogues and, together with previous results, permitted assignment of the ten methyltransferases required for everninomicin biosynthesis. The in vitro activity of A1- and H-ring-modifying methyltransferases demonstrated the ability to catalyze late-stage modification of the scaffold on an A1-ring phenol and H-ring C-4’ hydroxy moiety. Together these results establish the potential of the everninomicin scaffold for modification through mutagenesis and in vitro modification of advanced biosynthetic intermediates. 相似文献
44.
45.
46.
47.
48.
49.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
50.
This paper considers a novel distributed iterative learning consensus control algorithm based on neural networks for the control of heterogeneous nonlinear multiagent systems. The system's unknown nonlinear function is approximated by suitable neural networks; the approximation error is countered by a robust term in the control. Two types of control algorithms, both of which utilize distributed learning laws, are provided to achieve consensus. In the provided control algorithms, the desired reference is considered to be an unknown factor and then estimated using the associated learning laws. The consensus convergence is proven by the composite energy function method. A numerical simulation is ultimately presented to demonstrate the efficacy of the proposed control schemes. 相似文献