全文获取类型
收费全文 | 48017篇 |
免费 | 3337篇 |
国内免费 | 68篇 |
专业分类
电工技术 | 446篇 |
综合类 | 33篇 |
化学工业 | 10116篇 |
金属工艺 | 1054篇 |
机械仪表 | 1200篇 |
建筑科学 | 1444篇 |
矿业工程 | 115篇 |
能源动力 | 1140篇 |
轻工业 | 6969篇 |
水利工程 | 378篇 |
石油天然气 | 146篇 |
武器工业 | 5篇 |
无线电 | 3384篇 |
一般工业技术 | 8723篇 |
冶金工业 | 9192篇 |
原子能技术 | 326篇 |
自动化技术 | 6751篇 |
出版年
2023年 | 430篇 |
2022年 | 499篇 |
2021年 | 1201篇 |
2020年 | 997篇 |
2019年 | 1157篇 |
2018年 | 1872篇 |
2017年 | 1780篇 |
2016年 | 1990篇 |
2015年 | 1537篇 |
2014年 | 1870篇 |
2013年 | 3752篇 |
2012年 | 2738篇 |
2011年 | 2780篇 |
2010年 | 2251篇 |
2009年 | 2099篇 |
2008年 | 2027篇 |
2007年 | 1805篇 |
2006年 | 1354篇 |
2005年 | 1147篇 |
2004年 | 1074篇 |
2003年 | 949篇 |
2002年 | 935篇 |
2001年 | 708篇 |
2000年 | 653篇 |
1999年 | 705篇 |
1998年 | 2760篇 |
1997年 | 1925篇 |
1996年 | 1281篇 |
1995年 | 807篇 |
1994年 | 651篇 |
1993年 | 695篇 |
1992年 | 315篇 |
1991年 | 300篇 |
1990年 | 249篇 |
1989年 | 246篇 |
1988年 | 222篇 |
1987年 | 223篇 |
1986年 | 206篇 |
1985年 | 224篇 |
1984年 | 208篇 |
1983年 | 169篇 |
1982年 | 183篇 |
1981年 | 200篇 |
1980年 | 217篇 |
1979年 | 137篇 |
1978年 | 126篇 |
1977年 | 333篇 |
1976年 | 682篇 |
1975年 | 98篇 |
1973年 | 111篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
81.
Mohammad Reza Gaeeni Morteza Sasani Ghamsari Abbas Majd Abadi Mohammad Hossein Majles Ara Wooje Han Hyung‐Ho Park 《Journal of the American Ceramic Society》2015,98(6):1818-1822
A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before. 相似文献
82.
83.
84.
Yang Yang Yibei Zhou Juan Ren Qiaoji Zheng Kwok Ho Lam Dunmin Lin 《Journal of the European Ceramic Society》2018,38(2):557-566
Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO3-xCaHfO3 was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO3 (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d33~400 pC/N), inverse piezoelectric coefficient (d33*~547 pm/V) and planar electromechanical coupling factor (kp~58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response. 相似文献
85.
86.
Meza-Espinoza Libier de los Ángeles Vivar-Vera María de Lourdes García-Magaña María Sáyago-Ayerdi Sonia G. Chacón-López Alejandra Becerrea-Verdín Eduardo M. Montalvo-González Efigenia 《Food science and biotechnology》2018,27(2):509-517
Food Science and Biotechnology - The enzymatic activity and partial characterization of proteases from Bromelia karatas fruits were evaluated and compared with Bromelia pinguin proteases. The... 相似文献
87.
88.
Honour Index (HoI), a method to evaluate research performance within different research fields, was derived from the impact
factor (IF). It can be used to rate and compare different categories of journals. HoI was used in this study to determine
the scientific productivity of stem cell research in the Asian Four Dragons (Hong Kong, Singapore, South Korea and Taiwan)
from 1981 to 2001. The methodology applied in this study represents a synthesis of universal indicator studies and bibliometric
analyses of subfields at the micro-level. We discuss several comparisons, and conclude the developmental trend in stem cell
research for two decades.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
89.
Real-time multimedia applications have to use forward error correction (FEC) anderror concealment techniques to cope with
losses in today’s best-effort Internet. The efficiency of these solutions is known however to depend on the correlation between
losses in the media stream. In this paper we investigate how the packet size distribution affects the packet loss process,
that is, the distribution of the number of lost packets in a block, the related FEC performance and the average loss run length.
We present mathematical models for the loss process of the MMPP+M/D/1/K and the MMPP+M/M/1/K queues; we validate the models
via simulations, and compare the results to simulation results with an MPEG-4 coded video trace. We conclude that the deterministic
packet size distribution (PSD) not only results in lower stationary loss probability than the exponential one, but also gives
a less correlated loss process, both at a particular average link load and at a particular stationary loss probability as
seen by the media stream.Our results show that for applications that can only measure the packet loss probability, the effects
of the PSD on FEC performance are higher in access networks, where a single multimedia stream might affect the multiplexing
behavior. Our results show that the effects of the PSD on FEC performance are higher in access networks, where a single multimedia
stream might affect the multiplexing behavior and thus can improve the queuing performance by decreasing the variance of its
PSD. 相似文献
90.
Kruk Menno R.; Halász József; Meelis Wout; Haller József 《Canadian Metallurgical Quarterly》2004,118(5):1062
Aggressive behavior induces an adrenocortical stress response, and sudden stressors often precipitate violent behavior. Experiments in rats revealed a fast, mutual, positive feedback between the adrenocortical stress response and a brain mechanism controlling aggression. Stimulation of the aggressive area in the hypothalamus rapidly activated the adrenocortical response, even in the absence of an opponent and fighting. Hypothalamic aggression, in turn, was rapidly facilitated by a corticosterone injection in rats in which the natural adrenocortical stress response was prevented by adrenalectomy. The rapidity of both effects points to a fast, mutual, positive feedback of the controlling mechanisms within the time frame of a single conflict. Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献