全文获取类型
收费全文 | 19323篇 |
免费 | 1477篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 133篇 |
综合类 | 13篇 |
化学工业 | 6825篇 |
金属工艺 | 203篇 |
机械仪表 | 483篇 |
建筑科学 | 717篇 |
矿业工程 | 31篇 |
能源动力 | 465篇 |
轻工业 | 4462篇 |
水利工程 | 176篇 |
石油天然气 | 85篇 |
无线电 | 907篇 |
一般工业技术 | 2770篇 |
冶金工业 | 842篇 |
原子能技术 | 50篇 |
自动化技术 | 2652篇 |
出版年
2024年 | 66篇 |
2023年 | 258篇 |
2022年 | 1007篇 |
2021年 | 1278篇 |
2020年 | 629篇 |
2019年 | 634篇 |
2018年 | 812篇 |
2017年 | 840篇 |
2016年 | 940篇 |
2015年 | 724篇 |
2014年 | 954篇 |
2013年 | 1549篇 |
2012年 | 1440篇 |
2011年 | 1494篇 |
2010年 | 1073篇 |
2009年 | 1024篇 |
2008年 | 940篇 |
2007年 | 902篇 |
2006年 | 671篇 |
2005年 | 506篇 |
2004年 | 438篇 |
2003年 | 385篇 |
2002年 | 363篇 |
2001年 | 208篇 |
2000年 | 144篇 |
1999年 | 165篇 |
1998年 | 149篇 |
1997年 | 146篇 |
1996年 | 127篇 |
1995年 | 105篇 |
1994年 | 79篇 |
1993年 | 84篇 |
1992年 | 82篇 |
1991年 | 59篇 |
1990年 | 45篇 |
1989年 | 45篇 |
1988年 | 43篇 |
1987年 | 37篇 |
1986年 | 49篇 |
1985年 | 48篇 |
1984年 | 36篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
Four molecular Pt-carbonyl clusters decorated by Cd-Br fragments, i.e., [Pt(13)(CO)(12){Cd(5)(μ-Br)(5)Br(2)(dmf)(3)}(2)](2-) (1), [Pt(19)(CO)(17){Cd(5)(μ-Br)(5)Br(3)(Me(2)CO)(2)}{Cd(5)(μ-Br)(5)Br(Me(2)CO)(4)}](2-) (2), [H(2)Pt(26)(CO)(20)(CdBr)(12)](8-) (3) and [H(4)Pt(26)(CO)(20)(CdBr)(12)(PtBr)(x)](6-) (4) (x = 0-2), have been obtained from the reactions between [Pt(3n)(CO)(6n)](2-) (n = 2-6) and CdBr(2)·H(2)O in dmf at 120 °C. The structures of these molecular clusters with diameters of 1.5-2 nm have been determined by X-ray crystallography. Both 1 and 2 are composed of icosahedral or bis-icosahedral Pt-CO cores decorated on the surface by Cd-Br motifs, whereas 3 and 4 display a cubic close packed Pt(26)Cd(12) metal frame decorated by CO and Br ligands. An oversimplified and unifying approach to interpret the electron count of these surface decorated platinum carbonyl clusters is suggested, and extended to other low-valent organometallic clusters and Au-thiolate nanoclusters. 相似文献
992.
Lux J Peña EJ Bolze F Heinlein M Nicoud JF 《Chembiochem : a European journal of chemical biology》2012,13(8):1206-1213
The design, preparation and characterisation of a library of malachite green (MG) derivatives for two-photon RNA labelling is described. Some of these MG derivatives exhibit an increased affinity for an MG-aptamer, as well as improved two-photon sensitivity when compared to the classical malachite green chloride. The underlying mechanisms and potential benefits for in vivo RNA visualisation are discussed. 相似文献
993.
Lizcano LJ Viloria-Bernal M Vicente F Berrueta LA Gallo B Martínez-Cañamero M Ruiz-Larrea MB Ruiz-Sanz JI 《International journal of molecular sciences》2012,13(5):5454-5467
Diverse plants of ethnobotanic interest in Amazonia are commonly used in traditional medicine. We determined the antioxidant potential against lipid peroxidation, the antimicrobial activity, and the polyphenol composition of several Amazonian plants (Brownea rosademonte, Piper glandulosissimum, Piper krukoffii, Piper putumayoense, Solanum grandiflorum, and Vismia baccifera). Extracts from the plant leaf, bark, and stem were prepared as aqueous infusions, as used in folk medicine, and added to rat liver microsomes exposed to iron. The polyphenolic composition was detected by reverse-phase HPLC coupled to diode-array detector and MS/MS analysis. The antimicrobial activity was tested by the spot-on-a-lawn method against several indicator microorganisms. All the extracts inhibited lipid oxidation, except the P. glandulosissimum stem. The plant extracts exhibiting high antioxidant potential (V. baccifera and B. rosademonte) contained high levels of flavanols (particularly, catechin and epicatechin). By contrast, S. grandiflorum leaf, which exhibited very low antioxidant activity, was rich in hydroxycinnamic acids. None of the extracts showed antimicrobial activity. This study demonstrates for the first time the presence of bioactive polyphenolic compounds in several Amazonian plants, and highlights the importance of flavanols as major phenolic contributors to antioxidant activity. 相似文献
994.
L Tamborini A Pinto TK Smith LL Major MC Iannuzzi S Cosconati L Marinelli E Novellino L Lo Presti PE Wong MP Barrett C De Micheli P Conti 《ChemMedChem》2012,7(9):1623-1634
Acivicin analogues with an increased affinity for CTP synthetase (CTPS) were designed as potential new trypanocidal agents. The inhibitory activity against CTPS can be improved by increasing molecular complexity, by inserting groups able to establish additional interactions with the binding pocket of the enzyme. This strategy has been pursued with the synthesis of α‐amino‐substituted analogues of Acivicin and N1‐substituted pyrazoline derivatives. In general, there is direct correlation between the enzymatic activity and the in vitro anti‐trypanosomal efficacy of the derivatives studied here. However, this cannot be taken as a general rule, as other important factors may play a role, notably the ability of uptake/diffusion of the molecules into the trypanosomes. 相似文献
995.
A Kuczyńska A Kosmala M Surma T Adamski 《International journal of molecular sciences》2012,13(8):10410-10423
Barley (Hordeum vulgare L.) is an important cereal crop grown for both the feed and malting industries. The allelic dwarfing gene sdw1/denso has been used throughout the world to develop commercial barley varieties. Proteomic analysis offers a new approach to identify a broad spectrum of genes that are expressed in the living system. Two-dimensional electrophoresis and mass spectrometry were applied to investigate changes in protein abundance associated with different juvenile growth habit as effect of the denso locus in barley homozygous lines derived from a Maresi × Pomo cross combination. A total of 31 protein spots were revealed that demonstrate quantitative differences in protein abundance between the analyzed plants with different juvenile growth habit, and these protein spots were selected to be identified by mass spectrometry. Identification was successful for 27 spots, and functional annotations of proteins revealed that most of them are involved in metabolism and disease/defense-related processes. Functions of the identified proteins and their probable influence on the growth habit in barley are discussed. 相似文献
996.
Edgar Uquiche Ximena Fica Katherine Salazar José M. del Valle 《Journal of the American Oil Chemists' Society》2012,89(6):1135-1144
This work explored the possibility of using supercritical carbon dioxide (SC-CO2) to achieve fractionation of pre-pressed rapeseed (Brassica napus) cake oil at 30–50 MPa, at 40 or 80 °C, and increase the concentration of minor lipids (sterols, tocopherols, carotenoids) in the oil. Minor lipids are partially responsible for desirable antioxidant effects that protect against degradation and impart functional value to the oil. The weight and concentration of minor lipids in oil fractions collected during the first 60 min were analyzed. Cumulative oil yield increased with pressure, and with temperature at ≥40 MPa, but was lower at 80 °C than at 40 °C when working at pressure ≤35 MPa. Differences in solubility between the oil and minor lipids explained fractionation effects that were small for tocopherols. Unlike tocopherols, which are more soluble in SC-CO2 than the oil, sterols and carotenoids are less soluble than the oil, and their concentration increased in the later stages of extraction, particularly at ≥40 MPa, when there was not enough oil to saturate the CO2 phase. Because of the fractionating effects on rapeseed oil composition, there was an increase in the antioxidant activity of the oil in the second half as compared to the first half of the extraction. Consequently, this study suggests that SC-CO2 extraction could be used to isolate vegetable oil fractions with increased functional value. 相似文献
997.
Joydeep?Ray William?MacNaughtan Peng?Siong?Chong Josélio?Vieira Bettina?WolfEmail author 《Journal of the American Oil Chemists' Society》2012,89(3):437-445
The formulation of reduced fat chocolate has been of interest to the confectionery industry for a considerable time. It presents
a challenge, as fat reduction strategies are often accompanied by poor quality of the formulated product due to an increased
viscosity of the molten chocolate. This causes difficulties during processing and poor sensory properties of the final product.
The addition of limonene to chocolates leads to fat reduced chocolates that are less hard and have a lower melt viscosity.
This study was undertaken to shed light on the changes produced by the addition of limonene on the crystallization and microstructure
of cocoa butter. Based on evidence obtained by X-ray diffraction, differential scanning calorimetry and polarized light microscopy,
it is proposed that the presence of limonene enhances the production of lower polymorphic forms on cooling but accelerates
the transformation to more stable polymorphic forms. This is demonstrated in the transformation of the α and β′IV forms in cocoa butter to form βV at early storage times (t = 0–1 week), and the transformation to form βVI at times >2–3 weeks at 20 °C. There is a complex but marked effect on crystal size, mainly at early storage times. 相似文献
998.
Characterization of a water-based paint for corrosion protection 总被引:1,自引:0,他引:1
Paula Dias Catarina Carneiro Luísa Andrade José Sousa João Machado Adélio Mendes 《Journal of Coatings Technology and Research》2012,9(3):365-374
Corrosion of steel rebars in reinforced concrete is one of the major problems in the construction industry. Carbonation reactions of concrete with carbon dioxide and, mainly, the chloride salts action are the main causes responsible for concrete degradation. Protective coatings help to improve the durability of concrete structures by acting as a physical barrier against the corrosion agents. Waterborne paints are usually used for concrete protection rather than solvent-based paints since they are less pollutant. The aim of this work is to investigate the influence of the pore size and porosity on the permeability of the paints films toward sodium chloride. Three characterization methods from membrane science were implemented to characterize paint coatings. The time-lag method was used to determine the permeability toward the sodium chloride and toward helium and argon, these for approximately 100% relative humidity. From the seven waterborne paints formulated, only one was found to be suitable for surface protection of reinforced concrete, since its permeability toward NaCl was smaller than 10−14 m2 s−1, the threshold value required by National Laboratory of Civil Engineering (LNEC) in Portugal. For the formulated paints, it was observed that the average pore size correlates well with the permeability toward sodium chloride. This is an important result since obtaining the permeability toward sodium chloride of corrosion protective paints is very time consuming, while the average pore size can be obtained in a much shorter time. 相似文献
999.
Luciano Hocevar Vitória R. B. Soares Fábio S. Oliveira Maria Graças A. Korn Leonardo S. G. Teixeira 《Journal of the American Oil Chemists' Society》2012,89(5):781-786
Mid-infrared spectroscopy, in association with multivariate chemometric techniques, was employed for pattern recognition and
the determination of the composition of waste frying oils (WFO); data are presented in terms of the percentage of soybean
oil, palm oil and hydrogenated vegetable fat in frying oil blends. Principal component analysis (PCA) was performed using
spectral data (3,000–600 cm−1) to discriminate between the samples containing 100% soybean oil, 100% palm oil, 100% hydrogenated vegetable fat groups and
their blends. Additionally, the results indicated that partial least squares (PLS) models based on mid-infrared spectra were
suitable as practical analytical methods for predicting the oil contents in WFO blends. PLS models were validated by a representative
prediction set, and the root mean square errors of prediction (RMSEP) were 2.8, 4.7 and 5.5% for palm oil, soybean oil and
hydrogenated vegetable fat, respectively. The proposed methodology can be very useful for the rapid and low cost determination
of waste frying oil composition while also aiding in decisions regarding the management of oil pretreatment and production
routes for biodiesel production. 相似文献
1000.
Crosslinking and grafting ethylene vinyl acetate copolymer with accelerated electrons in the presence of polyfunctional monomers 总被引:1,自引:2,他引:1
Maria Daniela Stelescu Elena Manaila Gabriela Craciun Niculina Zuga 《Polymer Bulletin》2012,68(1):263-285
In this study, we have studied the effects of polyfunctional monomers (PFMs) on physical properties of ethylene vinyl acetate (EVA) copolymer crosslinked with electron beam (EB) or peroxides. The PFMs used were triallylcyanurate, triallylisocyanurate, trimethylolpropane trimethacrylate, zinc diacrylate, and ethylene glycol dimethacrylate. Using PFMs has led to (1) optimum cure time t 90 decrease from 19′25″ to 17′30″–18′45″, (2) scorch time increase from 2′ to maximum 3′45″, (3) increasing the crosslink density of peroxide or EB-cured systems by increasing the efficiency of productive radical reactions. The most efficient PFM for EVA copolymer blends has been triallylisocyanurate. Tensile strength and tear strength of samples crosslinked with EB for all irradiation doses are significantly better than those obtained for samples crosslinked with peroxides (differences up to 190%). The results show that EB irradiation gave the best results 相似文献