全文获取类型
收费全文 | 2628篇 |
免费 | 147篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 34篇 |
综合类 | 5篇 |
化学工业 | 713篇 |
金属工艺 | 37篇 |
机械仪表 | 43篇 |
建筑科学 | 114篇 |
矿业工程 | 10篇 |
能源动力 | 110篇 |
轻工业 | 188篇 |
水利工程 | 28篇 |
石油天然气 | 5篇 |
无线电 | 236篇 |
一般工业技术 | 467篇 |
冶金工业 | 169篇 |
原子能技术 | 9篇 |
自动化技术 | 610篇 |
出版年
2024年 | 4篇 |
2023年 | 43篇 |
2022年 | 143篇 |
2021年 | 138篇 |
2020年 | 80篇 |
2019年 | 82篇 |
2018年 | 100篇 |
2017年 | 84篇 |
2016年 | 105篇 |
2015年 | 89篇 |
2014年 | 117篇 |
2013年 | 189篇 |
2012年 | 145篇 |
2011年 | 227篇 |
2010年 | 144篇 |
2009年 | 137篇 |
2008年 | 175篇 |
2007年 | 119篇 |
2006年 | 109篇 |
2005年 | 71篇 |
2004年 | 50篇 |
2003年 | 56篇 |
2002年 | 38篇 |
2001年 | 29篇 |
2000年 | 31篇 |
1999年 | 23篇 |
1998年 | 56篇 |
1997年 | 48篇 |
1996年 | 32篇 |
1995年 | 18篇 |
1994年 | 20篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有2778条查询结果,搜索用时 15 毫秒
71.
Nanoindentation Characterization of Submicro- and Nano-Sized Liquid-Phase-Sintered SiC Ceramics 总被引:1,自引:0,他引:1
Stefano Guicciardi Diletta Sciti Cesare Melandri Alida Bellosi 《Journal of the American Ceramic Society》2004,87(11):2101-2107
Submicro- and nano-sized liquid-phase-sintered SiC ceramics were mechanically tested by nanoindentation in the peak load range 5–400 mN. The submicro-sized sample showed a marked indentation size effect which the nano-sized samples did not exhibit. The relevance of indentation depth with respect to the microstructural scale has been outlined. In the investigated grain-size range, the hardness dependence on the grain size could be described by a load-dependent inverse Hall–Petch relation. Young's modulus was less microstructure- and load-dependent. Because of the very fine microstructure, the nano-sized SiC materials gave lower elastic values than the submicro-sized SiC ceramic. 相似文献
72.
Maria?Antonietta BresciaEmail author Vincenzo?Mazzilli Angela?Sgaramella Stefano?Ghelli Francesco?Paolo Fanizzi Antonio?Sacco 《Journal of the American Oil Chemists' Society》2004,81(5):431-436
Characterization of the lipid fraction of raw cow and buffalo milk samples, collected in different breeding areas in Apulia,
a region of southern Italy, were performed by means of 1H NMR. The aim of this work was to establish whether FA composition data obtained by 1H NMR can be used in the differentiation of buffalo and cow milk samples according to species. A complete assignment of the
signals present in the spectrum was attempted by COSY, heteronuclear coherence spectra. Quantification of FA was carried out
by inserting the integrals of particular peaks in suitable calculations. Multivariate statistical analysis, conducted on the
results of the quantification, permitted buffalo and cow milks to be distinguished. 相似文献
73.
Gianluca Galimberti Stefania Pagliara Stefano Ponzoni Stefano Dal Conte Federico Cilento Gabriele Ferrini Stephan Hofmann Muhammad Arshad Cinzia Cepek Fulvio Parmigiani 《Carbon》2011,49(15):5246-5252
Using time-resolved reflectivity measurements on unaligned and aligned bundled single-wall carbon nanotubes with a pump energy of 1.55 eV, quasi-resonant with the second Van Hove singularity of semiconducting tubes, a positive sign of the transient reflectivity is detected in unaligned nanotubes. In contrast a negative sign is detected in aligned nanotubes. This discovery addresses a long-standing question showing that in unaligned nanotubes the stronger intertube interactions favor the formation of short-lived free charge carriers in semiconducting tubes. A detailed analysis of the transient reflectivity spectral response shows that the free carriers in the photo-excited state of semiconducting tubes move towards metallic tubes in about 400 fs. 相似文献
74.
Polymer-based solar cells (PSC) represent a promising technology in the field of photovoltaics, although they still suffer from poor environmental stability. Poly(3-hexylthiophene) (P3HT) is one of the most commonly employed electron-donor materials for the preparation of the photo-active layer of PSC and it is known to undergo degradation when exposed to light. In this work, the degradation of P3HT was studied by irradiating polymer films by means of simulated sunlight. The results of this study highlighted a remarkable instability of P3HT. Substantial modifications of the infrared as well as of the UV–Vis spectra of the polymer were reported and a degradation pathway was suggested, in agreement with recent literature results. In order to stabilize the structure, two additives were evaluated namely a standard Hindered Amine Light Stabilizer (HALS) and Multi-Walled Carbon Nanotubes (MWCNT). The addition of MWCNT appeared to significantly reduce the rate of degradation. 相似文献
75.
76.
Biava M Porretta GC Poce G Battilocchio C Alfonso S de Logu A Manetti F Botta M 《ChemMedChem》2011,6(4):593-599
Tuberculosis (TB) represents a never-ending challenge toward which research efforts are needed. Drug resistance is the key problem that scientists in the field need to fight. The development of new drugs endowed with novel modes of action against different biological targets is of extreme importance; these new agents should also exhibit lower toxicity compared with the anti-TB drugs currently available. Furthermore, new drugs should be inexpensive since most of the TB-infected population lives in developing nations. In the last few years, numerous researchers have focused their attention on TB, leading to the discovery of some interesting compounds. Among these, the pyrrole-derived compounds we developed can be considered very promising antimycobacterial agents. Aided by molecular modeling studies, we synthesized numerous compounds characterized by the same 1,5-diarylpyrrole scaffold and elucidated very interesting antitubercular/antimycobacterial properties. Some compounds identified are extremely promising and represent a step towards the design of novel lead structures in the fight against TB. Our efforts to this end are reviewed here. 相似文献
77.
Sanjaya D. Senanayake Jaime Evans Stefano Agnoli Laura Barrio Tsung-Liang Chen Jan Hrbek Jos�� A. Rodriguez 《Topics in Catalysis》2011,54(1-4):34-41
X-ray and ultraviolet photoelectron spectroscopies were used to study the interaction of Ni atoms with CeO2(111) surfaces. Upon adsorption on CeO2(111) at 300 K, nickel remains in a metallic state. Heating to elevated temperatures (500?C800 K) leads to partial reduction of the ceria substrate with the formation of Ni2+ species that exists as NiO and/or Ce1?xNixO2?y. Interactions of nickel with the oxide substrate significantly reduce the density of occupied Ni 3d states near the Fermi level. The results of core-level photoemission and near-edge X-ray absorption fine structure point to weakly bound CO species on CeO2(111) which are clearly distinguishable from the formation of chemisorbed carbonates. In the presence of Ni, a stronger interaction is observed with chemisorption of CO on the admetal. When the Ni is in contact with Ce+3 cations, CO dissociates on the surface at 300 K forming NiCx compounds that may be involved in the formation of CH4 at higher temperatures. At medium and large Ni coverages (>0.3 ML), the Ni/CeO2(111) surfaces are able to catalyze the production of methane from CO and H2, with an activity slightly higher than that of Ni(100) or Ni(111). On the other hand, at small coverages of Ni (<0.3 ML), the Ni/CeO2(111) surfaces exhibit a very low activity for CO methanation but are very good catalysts for the water?Cgas shift reaction. 相似文献
78.
Maga G Falchi F Radi M Botta L Casaluce G Bernardini M Irannejad H Manetti F Garbelli A Samuele A Zanoli S Esté JA Gonzalez E Zucca E Paolucci S Baldanti F De Rijck J Debyser Z Botta M 《ChemMedChem》2011,6(8):1371-1389
A hit optimization protocol applied to the first nonnucleoside inhibitor of the ATPase activity of human DEAD-box RNA helicase DDX3 led to the design and synthesis of second-generation rhodanine derivatives with better inhibitory activity toward cellular DDX3 and HIV-1 replication. Additional DDX3 inhibitors were identified among triazine compounds. Biological data were rationalized in terms of structure-activity relationships and docking simulations. Antiviral activity and cytotoxicity of selected DDX3 inhibitors are reported and discussed. A thorough analysis confirmed human DDX3 as a valid anti-HIV target. The compounds described herein represent a significant advance in the pursuit of novel drugs that target HIV-1 host cofactors. 相似文献
79.
The quantification of Methyldibenzothiophene isomers (MDBTs) is used in the geochemical characterization of crude oils. The relative ratio of these isomers can give useful information about the nature and the maturity of the source rock. This paper describes a novel analytical technique for the quantitative determination of MDBTs through triple quadrupole tandem mass spectrometry (GC-MS/MS). Through the multiple reaction monitoring (MRM) scan mode, it was possible to reach high selectivity for the MDBTs and their quantification was obtained without preliminary fractionation of the crude oil. In order to reduce the carryover of high boiling components, a recently developed backflush system in the GC program was applied. This novel protocol has been tested on sixteen samples of crude oil from different oil fields around the world. It was concluded to be more reliable than previously reported analytical methods based on selected ion monitoring (SIM) scan mode. 相似文献
80.
Cozza G Gianoncelli A Bonvini P Zorzi E Pasquale R Rosolen A Pinna LA Meggio F Zagotto G Moro S 《ChemMedChem》2011,6(12):2273-2286
Casein kinase 2 (CK2) is a ubiquitous, essential, and highly pleiotropic protein kinase; its abnormally high constitutive activity is suspected to underlie its pathogenic potential in neoplasia and other relevant diseases. Previously, using different in silico screening approaches, two potent and selective CK2 inhibitors were identified by our group: ellagic acid, a naturally occurring tannic acid derivative (K(i)=20 nM) and 3,8-dibromo-7-hydroxy-4-methylchromen-2-one (DBC, K(i)=60 nM). Comparing the crystallographic binding modes of both ellagic acid and DBC, an X-ray structure-driven merging approach was taken to design novel CK2 inhibitors with improved target affinity. A urolithin moiety is proposed as a possible bridging scaffold between the two known CK2 inhibitors, ellagic acid and DBC. Optimization of urolithin A as the bridging moiety led to the identification of 4-bromo-3,8-dihydroxy-benzo[c]chromen-6-one as a novel, potent and selective CK2 inhibitor, which shows a K(i) value of 7 nM against the protein kinase, representing a significant improvement in affinity for the target compared with the two parent fragments. 相似文献