全文获取类型
收费全文 | 563023篇 |
免费 | 7249篇 |
国内免费 | 1008篇 |
学科分类
工业技术 | 571280篇 |
出版年
2021年 | 5346篇 |
2020年 | 4151篇 |
2019年 | 5398篇 |
2018年 | 9406篇 |
2017年 | 9577篇 |
2016年 | 9999篇 |
2015年 | 6115篇 |
2014年 | 10409篇 |
2013年 | 26401篇 |
2012年 | 15951篇 |
2011年 | 21333篇 |
2010年 | 17161篇 |
2009年 | 19043篇 |
2008年 | 19259篇 |
2007年 | 18919篇 |
2006年 | 16445篇 |
2005年 | 14856篇 |
2004年 | 14105篇 |
2003年 | 13678篇 |
2002年 | 12780篇 |
2001年 | 12320篇 |
2000年 | 11560篇 |
1999年 | 11352篇 |
1998年 | 27155篇 |
1997年 | 19595篇 |
1996年 | 15067篇 |
1995年 | 12009篇 |
1994年 | 10821篇 |
1993年 | 10608篇 |
1992年 | 8309篇 |
1991年 | 8077篇 |
1990年 | 7998篇 |
1989年 | 7718篇 |
1988年 | 7437篇 |
1987年 | 6722篇 |
1986年 | 6526篇 |
1985年 | 7412篇 |
1984年 | 6712篇 |
1983年 | 6424篇 |
1982年 | 5773篇 |
1981年 | 5890篇 |
1980年 | 5620篇 |
1979年 | 5722篇 |
1978年 | 5673篇 |
1977年 | 6198篇 |
1976年 | 7721篇 |
1975年 | 5102篇 |
1974年 | 4894篇 |
1973年 | 4974篇 |
1972年 | 4271篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Dolmatov O. Yu. Kuznetsov M. S. Semenov A. O. Shamanin I. V. Verkhoturova V. V. 《Atomic Energy》2021,130(1):1-5
Atomic Energy - An implementation assessment of PSKD-600 type power reactors was made. It was established that the readiness level of all PSKD-600 nuclear fuel cycle technologies is no lower than... 相似文献
102.
Atomic Energy - An economic and mathematical model has been developed to determine the competitiveness of REMIX-A and -C uranium-plutonium fuel obtained by reprocessing spent fuel from thermal... 相似文献
103.
L.L. Oliveira J.A. Cortés B.S. Caldeira T. Strusch U. Wiedwald A.Z. Simoes 《Ceramics International》2021,47(15):20768-20780
In this work, praseodymium (Pr) doped cerium oxide (CeO2) was prepared using the microwave-assisted hydrothermal method (MAH) and the properties were investigated by X-ray diffraction analysis (XRD), Raman spectroscopy, Field Emission Gun Scanning Electron Microscope (FEG-SEM), BET method, Photoluminescence spectroscopy (PL), Fourier-transform infrared spectroscopy (FTIR), Ultraviolet–visible spectroscopy (UV–Vis), Electron paramagnetic resonance spectroscopy (EPR) and Magnetometry. The results showed that increasing the Pr-doping promotes a structural disorder due to increased oxygen vacancies. XRD confirmed a cubic structure without deleterious phases with modifications in the structure caused by alteration in the cerium oxidation state as well as changes in the crystallite size and strain obtained by Wellinson-Hall method. Raman spectroscopy shows that changing the Pr content results in samples with different defect densities at short range. FEG-SEM showed that the nanocrystals are agglomerated with small particles tend to aggregate spontaneously to decrease the surface energy. BET method showed that the Pr doping results in a gain of specific surface area. PL indicated that Pr3+ leads to distinct emissions; red emission associated to oxygen vacancies located near the conduction band (shallow defects), green emission associated to electron-hole recombination and orange emission associated to shallow defects and electron-hole recombination. FTIR indicated the complete process of nucleation with no other phase. UV–Vis showed the transitions between oxygen 2p, cerium 4f and praseodymium 4f states. The EPR signal shows events occurring around 344 mT. These events can be related due the presence of paramagnetic elements containing unpaired electrons, such as Ce (III), which is indicative of cerium reduction caused by Pr ions, as evidenced by Rietveld data. Regardless of the Pr concentration used in this research, the magnetic measurements show a superparamagnetic system below the blocking temperature of ~20 K and a paramagnetic system above this temperature, which indicates no significant changes in the average size of the nanoparticles. Surface area, crystallite size and the temperature are important parameters, which control the magnetic properties of such N-type semiconductors. 相似文献
104.
Delf-Magnus Kummerfeld Carsten A. Raabe Juergen Brosius Dingding Mo Boris V. Skryabin Timofey S. Rozhdestvensky 《International journal of molecular sciences》2021,22(7)
Prader-Willi syndrome (PWS) is a neurogenetic multifactorial disorder caused by the deletion or inactivation of paternally imprinted genes on human chromosome 15q11-q13. The affected homologous locus is on mouse chromosome 7C. The positional conservation and organization of genes including the imprinting pattern between mice and men implies similar physiological functions of this locus. Therefore, considerable efforts to recreate the pathogenesis of PWS have been accomplished in mouse models. We provide a summary of different mouse models that were generated for the analysis of PWS and discuss their impact on our current understanding of corresponding genes, their putative functions and the pathogenesis of PWS. Murine models of PWS unveiled the contribution of each affected gene to this multi-facetted disease, and also enabled the establishment of the minimal critical genomic region (PWScr) responsible for core symptoms, highlighting the importance of non-protein coding genes in the PWS locus. Although the underlying disease-causing mechanisms of PWS remain widely unresolved and existing mouse models do not fully capture the entire spectrum of the human PWS disorder, continuous improvements of genetically engineered mouse models have proven to be very powerful and valuable tools in PWS research. 相似文献
105.
Agata Campisi Giuseppina Raciti Giovanni Sposito Rosaria Grasso Maria A. Chiacchio Michela Spatuzza Alessandro Attanzio Ugo Chiacchio Luisa Tesoriere Mario Allegra Rosalia Pellitteri 《International journal of molecular sciences》2021,22(7)
Herein, we assessed the effect of full native peptide of amyloid-beta (Aβ) (1-42) and its fragments (25-35 and 35-25) on tissue transglutaminase (TG2) and its isoforms (TG2-Long and TG2-Short) expression levels on olfactory ensheathing cells (OECs). Vimentin and glial fibrillary acid protein (GFAP) were also studied. The effect of the pre-treatment with indicaxanthin from Opuntia ficus-indica fruit on TG2 expression levels and its isoforms, cell viability, total reactive oxygen species (ROS), superoxide anion (O2−), and apoptotic pathway activation was assessed. The levels of Nestin and cyclin D1 were also evaluated. Our findings highlight that OECs exposure to Aβ(1-42) and its fragments induced an increase in TG2 expression levels and a different expression pattern of its isoforms. Indicaxanthin pre-treatment reduced TG2 overexpression, modulating the expression of TG2 isoforms. It reduced total ROS and O2− production, GFAP and Vimentin levels, inhibiting apoptotic pathway activation. It also induced an increase in the Nestin and cyclin D1 expression levels. Our data demonstrated that indicaxanthin pre-treatment stimulated OECs self-renewal through the reparative activity played by TG2. They also suggest that Aβ might modify TG2 conformation in OECs and that indicaxanthin pre-treatment might modulate TG2 conformation, stimulating neural regeneration in Alzheimer’s disease. 相似文献
106.
Alekseeva O. V. Rodionova A. N. Syrbu S. A. Bagrovskaya N. A. Noskov A. V. 《Protection of Metals and Physical Chemistry of Surfaces》2021,57(1):30-36
Protection of Metals and Physical Chemistry of Surfaces - Modification of polystyrene (PS) with bentonite was carried out, and film materials with improved sorption properties toward... 相似文献
107.
Drinberg A. S. Ivakhnyuk G. K. Mametnabiev T. E. Nedvedskii G. R. 《Glass Physics and Chemistry》2022,48(1):50-53
Glass Physics and Chemistry - It is found that the chemical composition of the surface cannot fully provide superhydrophobicity, as a combination of a hydrophobic material with an appropriate... 相似文献
108.
Kul’ga K. S. Siluyanova M. V. Krivosheev I. A. Kuritsyna V. V. Kuritsyn D. N. Valiev A. A. 《Russian Engineering Research》2022,42(10):1101-1101
Russian Engineering Research - An Erratum to this paper has been published: https://doi.org/10.3103/S1068798X22100355 相似文献
109.
Programming and Computer Software - In this paper, we propose an algorithm for solving the Cauchy problem for a two-dimensional difference equation with constant coefficients at a point, based on... 相似文献
110.
Aleksandrova L. Yu. Moshinskii A. I. 《Theoretical Foundations of Chemical Engineering》2022,56(3):271-278
Theoretical Foundations of Chemical Engineering - The operation of an unsteady-state well-stirred flow-through biochemical reactor is studied. Nonlinear boundary-value problems describing the... 相似文献