全文获取类型
收费全文 | 594559篇 |
免费 | 9163篇 |
国内免费 | 2469篇 |
专业分类
电工技术 | 12162篇 |
技术理论 | 5篇 |
综合类 | 1797篇 |
化学工业 | 91279篇 |
金属工艺 | 25211篇 |
机械仪表 | 20199篇 |
建筑科学 | 14919篇 |
矿业工程 | 3087篇 |
能源动力 | 13774篇 |
轻工业 | 53212篇 |
水利工程 | 6057篇 |
石油天然气 | 10083篇 |
武器工业 | 252篇 |
无线电 | 67397篇 |
一般工业技术 | 116017篇 |
冶金工业 | 103669篇 |
原子能技术 | 10864篇 |
自动化技术 | 56207篇 |
出版年
2021年 | 4700篇 |
2019年 | 4249篇 |
2018年 | 13870篇 |
2017年 | 14168篇 |
2016年 | 11059篇 |
2015年 | 5828篇 |
2014年 | 8861篇 |
2013年 | 24798篇 |
2012年 | 16727篇 |
2011年 | 26177篇 |
2010年 | 21977篇 |
2009年 | 22490篇 |
2008年 | 23375篇 |
2007年 | 25000篇 |
2006年 | 15897篇 |
2005年 | 17244篇 |
2004年 | 14964篇 |
2003年 | 14131篇 |
2002年 | 13058篇 |
2001年 | 12752篇 |
2000年 | 12114篇 |
1999年 | 12399篇 |
1998年 | 28782篇 |
1997年 | 21058篇 |
1996年 | 16341篇 |
1995年 | 12445篇 |
1994年 | 11435篇 |
1993年 | 11033篇 |
1992年 | 8464篇 |
1991年 | 8049篇 |
1990年 | 8022篇 |
1989年 | 7842篇 |
1988年 | 7534篇 |
1987年 | 6337篇 |
1986年 | 6536篇 |
1985年 | 7429篇 |
1984年 | 6968篇 |
1983年 | 6503篇 |
1982年 | 5827篇 |
1981年 | 6159篇 |
1980年 | 5665篇 |
1979年 | 5763篇 |
1978年 | 5481篇 |
1977年 | 6218篇 |
1976年 | 8102篇 |
1975年 | 4809篇 |
1974年 | 4545篇 |
1973年 | 4633篇 |
1972年 | 3892篇 |
1971年 | 3456篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
171.
Journal of Computer and Systems Sciences International - We consider a controlled mechanical system with one degree of freedom described by an angular coordinate. The system is under the action of... 相似文献
172.
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
173.
174.
175.
The current study establishes the unprecedented involvement in the evolution and production of novel core–shell nanocomposites composed of nanosized titanium dioxide and aniline‐o‐phenylenediamine copolymer. TiO2@copoly(aniline and o‐phenylenediamine) (TiO2@PANI‐o‐PDA) core–shell nanocomposites were chemically synthesized in a molar ratio of 5:1 of the particular monomers and several weights of nano‐TiO2 via oxidative copolymerization. The construction of the TiO2@PANI‐o‐PDA core–shell nanocomposites was ascertained from Fourier transform IR spectroscopy, UV–visible spectroscopy and XRD. A reasonable thermal behavior for the original copolymer and the TiO2@PANI‐o‐PDA core–shell nanocomposites was investigated. The bare PANI‐o‐PDA copolymer was thermally less stable than the TiO2@PANI‐o‐PDA nanocomposites. The core–shell feature of the nanocomposites was found to have core and shell sizes of 17 nm and 19–26 nm, respectively. In addition, it was found that the addition of a high ratio of TiO2 nanoparticles increases the electrical conductivity and consequently lowers the electrical resistivity of the TiO2@PANI‐o‐PDA core–shell nanocomposites. The hybrid photocatalysts exhibit a dramatic photocatalytic efficacy of methylene blue degradation under solar light irradiation. A plausible interpretation of the photocatalytic degradation results of methylene blue is also demonstrated. Our setup introduces a facile, inexpensive, unique and efficient technique for developing new core–shell nanomaterials with various required functionalities and colloidal stabilities. © 2018 Society of Chemical Industry 相似文献
176.
177.
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
178.
C. G. Prosgolitis S. G. Lambrakos A. D. Zervaki 《Journal of Materials Engineering and Performance》2018,27(10):5102-5113
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size. 相似文献
179.
180.
László Lőrincz Máté Zsemberi György Bánsághi Tamás Sohajda Edit Székely 《化学工程与技术》2018,41(7):1466-1472
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts. 相似文献