全文获取类型
收费全文 | 286224篇 |
免费 | 4108篇 |
国内免费 | 1310篇 |
专业分类
电工技术 | 4945篇 |
综合类 | 545篇 |
化学工业 | 42032篇 |
金属工艺 | 11320篇 |
机械仪表 | 8579篇 |
建筑科学 | 6969篇 |
矿业工程 | 1609篇 |
能源动力 | 7155篇 |
轻工业 | 23734篇 |
水利工程 | 3086篇 |
石油天然气 | 5791篇 |
武器工业 | 43篇 |
无线电 | 34139篇 |
一般工业技术 | 58786篇 |
冶金工业 | 51091篇 |
原子能技术 | 7549篇 |
自动化技术 | 24269篇 |
出版年
2021年 | 2334篇 |
2019年 | 2215篇 |
2018年 | 3882篇 |
2017年 | 3974篇 |
2016年 | 4238篇 |
2015年 | 2773篇 |
2014年 | 4712篇 |
2013年 | 12607篇 |
2012年 | 7510篇 |
2011年 | 10270篇 |
2010年 | 7964篇 |
2009年 | 9178篇 |
2008年 | 9568篇 |
2007年 | 9592篇 |
2006年 | 8154篇 |
2005年 | 7528篇 |
2004年 | 7437篇 |
2003年 | 7198篇 |
2002年 | 6904篇 |
2001年 | 7011篇 |
2000年 | 6602篇 |
1999年 | 6870篇 |
1998年 | 16396篇 |
1997年 | 11683篇 |
1996年 | 9009篇 |
1995年 | 6909篇 |
1994年 | 6081篇 |
1993年 | 6112篇 |
1992年 | 4431篇 |
1991年 | 4228篇 |
1990年 | 4113篇 |
1989年 | 4093篇 |
1988年 | 3781篇 |
1987年 | 3421篇 |
1986年 | 3439篇 |
1985年 | 3829篇 |
1984年 | 3534篇 |
1983年 | 3262篇 |
1982年 | 3072篇 |
1981年 | 3076篇 |
1980年 | 3078篇 |
1979年 | 2861篇 |
1978年 | 2903篇 |
1977年 | 3162篇 |
1976年 | 4120篇 |
1975年 | 2437篇 |
1974年 | 2401篇 |
1973年 | 2423篇 |
1972年 | 2030篇 |
1971年 | 1793篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
D. Solís-Cortés E. Navarrete-Astorga J.L. Costa-Krämer J. Salguero-Fernandez R. Schrebler D. Leinen E.A. Dalchiele J.R. Ramos-Barrado F. Martín 《Ceramics International》2019,45(5):5577-5587
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films. 相似文献
104.
P.Y. Raval P.R. Pansara A.R. Makadiya N.H. Vasoya S.N. Dolia K.B. Modi 《Ceramics International》2018,44(15):17667-17674
The consequences of high energy mechanical milling, microwave-assisted heating and rapid thermal cooling on magnetic ordering in polycrystalline CaCu3Ti4O12 cubic perovskite have been investigated by means of X-ray powder diffractometry (300?K), dc magnetization in field – cooled and zero – field cooled modes (H = 100?Oe and 1000?Oe, T?=?5–300?K) (M – T curves) and M – H loop characteristics (T?=?5?K and 300?K, Hmax = 70?kOe). The M – T curves of unmilled and 16?h milled samples show pure antiferromagnetic and weak ferromagnetic ordering, respectively, 1?h and 6?h milled samples demonstrate the coexistence of both the phases while microwave-assisted and quenched samples exhibit classic antiferromagnetic transition and a low temperature paramagnetic–like contribution with different weights, well supported by the M – H loop characteristics. The observed transformations in the magnetic ordering are attributed to the ball-milling induced stress which curtails hybridization of empty Ti-3d orbitals with Cu-3d and O-2p orbitals and secondary phase formation. Oxygen vacancies associated with bound magnetic polarons originate ferromagnetism in the milled samples while unpaired electrons inhabited at the empty sites are the cause of paramagnetic centers. The low-temperature Curie – tail in M – T curve for quenched and microwave assisted samples is attributed to Ti3+ cations. 相似文献
105.
106.
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
107.
A. M. Mirzabaev V. P. Kanonerov T. A. Makhkamov O. R. Sytdykov Sh. M. Mirzabekov 《Applied Solar Energy》2018,54(3):224-226
The data on the use of solar photovoltaic plants (PVPs) for providing a reliable and guaranteed power supply to telecommunication systems and cellular communication systems in the conditions prevalent in Uzbekistan are given. The research-based structures developed by OOO MIR SOLAR and the selection of PVP elements ensuring their reliable operation are described. The main influencing factors are discussed, and the use of effective combinations of different types of panels (from monocrystalline and polycrystalline silicon) and a specially developed controller are considered. 相似文献
108.
109.
Sukharev S. V. Zabolotskii A. V. Kotrovskii P. V. Turchin M. Yu. 《Refractories and Industrial Ceramics》2020,60(6):539-542
Refractories and Industrial Ceramics - We study the problem of evaluation of the influence of design of the metal receiver of a large-capacity tundish of slab continuous-casting machine on the... 相似文献
110.
Abraham G. Alvarado Rosaura Hernández-Montelongo Martin Rabelero Lourdes A. Pérez-Carrillo Jorge E. Puig Francisco López-Serrano 《Polymer Engineering and Science》2020,60(2):223-232
A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0-1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers 相似文献