全文获取类型
收费全文 | 409854篇 |
免费 | 4731篇 |
国内免费 | 1713篇 |
专业分类
电工技术 | 6834篇 |
综合类 | 2847篇 |
化学工业 | 57062篇 |
金属工艺 | 20451篇 |
机械仪表 | 16092篇 |
建筑科学 | 9527篇 |
矿业工程 | 2703篇 |
能源动力 | 8654篇 |
轻工业 | 26469篇 |
水利工程 | 4852篇 |
石油天然气 | 7365篇 |
武器工业 | 45篇 |
无线电 | 46968篇 |
一般工业技术 | 85470篇 |
冶金工业 | 58239篇 |
原子能技术 | 8606篇 |
自动化技术 | 54114篇 |
出版年
2021年 | 2269篇 |
2019年 | 2156篇 |
2018年 | 22679篇 |
2017年 | 22248篇 |
2016年 | 16095篇 |
2015年 | 3509篇 |
2014年 | 4749篇 |
2013年 | 12413篇 |
2012年 | 11864篇 |
2011年 | 24474篇 |
2010年 | 20995篇 |
2009年 | 19136篇 |
2008年 | 20154篇 |
2007年 | 22548篇 |
2006年 | 8161篇 |
2005年 | 11500篇 |
2004年 | 9817篇 |
2003年 | 9362篇 |
2002年 | 7813篇 |
2001年 | 7041篇 |
2000年 | 6793篇 |
1999年 | 6873篇 |
1998年 | 16396篇 |
1997年 | 11655篇 |
1996年 | 9019篇 |
1995年 | 6903篇 |
1994年 | 6092篇 |
1993年 | 6133篇 |
1992年 | 4449篇 |
1991年 | 4248篇 |
1990年 | 4110篇 |
1989年 | 4091篇 |
1988年 | 3789篇 |
1987年 | 3429篇 |
1986年 | 3427篇 |
1985年 | 3770篇 |
1984年 | 3483篇 |
1983年 | 3242篇 |
1982年 | 3048篇 |
1981年 | 3051篇 |
1980年 | 3042篇 |
1979年 | 2838篇 |
1978年 | 2881篇 |
1977年 | 3144篇 |
1976年 | 4103篇 |
1975年 | 2422篇 |
1974年 | 2383篇 |
1973年 | 2399篇 |
1972年 | 2018篇 |
1971年 | 1782篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Electrochemical impedance spectroscopy (EIS), anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI ... 相似文献
102.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms. 相似文献
103.
V. N. Oparin V. I. Vostrikov O. M. Usol’tseva P. A. Tsoi V. N. Semenov 《Journal of Mining Science》2015,51(3):624-633
The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids. 相似文献
104.
Quantitative UPLC‐MS/MS analysis of chlorogenic acid derivatives in antioxidant fractionates from dandelion (Taraxacum officinale) root 下载免费PDF全文
Owen Kenny Thomas J. Smyth Chandralal M. Hewage Nigel P. Brunton 《International Journal of Food Science & Technology》2015,50(3):766-773
While qualitative studies have identified chlorogenic acids in antioxidant extracts, particularly ethyl acetate‐derived extracts, of Taraxacum officinale, quantitative analysis of these phenolic compounds remains largely unreported for this species. In this study, bioactivity‐guided fractionation of an antioxidant crude ethyl acetate extract (DPPH = 295.481 ± 0.955 mg TE g?1 extract) from T. officinale root resulted in a number of reverse‐phase fractions that demonstrated high antioxidant activity (DPPH = 1058.733–1312.136 mg TE g?1 extract), stronger than that of the synthetic antioxidant Trolox®. UPLC‐MS/MS screening of these fractions for the presence of selected mono‐ and di‐caffeoylquinic acids revealed large quantities of 1,5‐dicaffeoylquinic acid present in several fractions (853.052–907.324 μg mg?1), respectively. Due to the antioxidant potency and high levels of 1,5‐dicaffeoylquinic acid observed in these fractions, it was concluded that specifically this chlorogenic acid derivative is a major contributor to the antioxidant efficacy of dandelion root. 相似文献
105.
106.
107.
108.
A. A. Babenko V. I. Zhuchkov L. A. Smirnov A. V. Sychev A. A. Akberdin A. S. Kim M. F. Vitushchenko A. A. Dobromilov 《Steel in Translation》2015,45(11):883-886
A technology for slag formation in the ladle–furnace unit is considered; the slag is based on the CaO–SiO2–MgO–Al2O3–B2O3 system. This technology permits both microalloying of the steel with boron (reduced from the oxide phase) and desulfurization of the steel. The resulting boron content in the steel is 0.001–0.008%; the sulfur content in low-alloy steel and pipe steel is low (0.004–0.010%); and the consumption of manganese ferroalloys is reduced to 0.5 kg/t for 08кп steel and 1.4 kg/t for 09Г2C steel. In addition, the proposed technology increases the strength of the rolled steel, without loss in its plasticity; and reduces the environmental impact thanks to the replacement of fluorspar by colemanite. 相似文献
109.
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
110.