全文获取类型
收费全文 | 777篇 |
免费 | 46篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 178篇 |
金属工艺 | 7篇 |
机械仪表 | 14篇 |
建筑科学 | 42篇 |
能源动力 | 35篇 |
轻工业 | 90篇 |
水利工程 | 8篇 |
石油天然气 | 1篇 |
无线电 | 69篇 |
一般工业技术 | 123篇 |
冶金工业 | 29篇 |
原子能技术 | 4篇 |
自动化技术 | 212篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 39篇 |
2021年 | 30篇 |
2020年 | 18篇 |
2019年 | 27篇 |
2018年 | 30篇 |
2017年 | 17篇 |
2016年 | 28篇 |
2015年 | 27篇 |
2014年 | 55篇 |
2013年 | 65篇 |
2012年 | 54篇 |
2011年 | 58篇 |
2010年 | 36篇 |
2009年 | 51篇 |
2008年 | 44篇 |
2007年 | 43篇 |
2006年 | 15篇 |
2005年 | 20篇 |
2004年 | 18篇 |
2003年 | 23篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有824条查询结果,搜索用时 0 毫秒
711.
Space communications with variable elevation angle faded by rain: Radio links to the Sun–Earth first Lagrangian point L1 下载免费PDF全文
Emilio Matricciani 《International Journal of Satellite Communications and Networking》2016,34(6):809-831
How rain attenuation affects space links with variable elevation angles is not yet fully researched. The aim of this paper is to investigate this topic by simulating rain attenuation at Ka Band, in slant paths with variable elevation angles, with the Synthetic Storm Technique (SST), in links connected with spacecrafts at the Sun–Earth first Lagrangian point L1, viewed from Spino d'Adda (Italy), Tampa (Florida), White Sands (New Mexico). The input to the SST is a large database of time series of 1‐min rain rate recorded on site, 10 years in Spino d'Adda, 4 years at Tampa and White Sands. After recalling known results on the elevation angle of the Sun (i.e. L1), θs (°), seen from latitude λ (°), I report what seems to be a new result: the mode of the probability density function of θs in a year, in the range 0 ≤ λ ≤ 90° ? ε (Earth axis tilt angle ε = 23.44°), coincides with the peak angle found at the day of the Winter solstice at the site, a result valid also for other planets, once their tilt angle is used. Compared to the complementary probability distribution function (pdf) of rain attenuation calculated for a geostationary (GEO) link (fixed elevation angle), the pdf to L1 depends on the rain‐rate pdf during the contact time with L1, according to the local climate. I show that, to obtain a good and easier estimate of the rain attenuation pdf in L1 links, we can consider a GEO link with elevation angle equal to the mean angle and rain rate pdf, both during the contact time, and that the mode angle gives an upper bound to the rain attenuation pdf in the sites considered. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
712.
Karla Alejandra Pérez-Vega Olga Castañer Albert Sanllorente Camille Lassale Emilio Ros Xavier Pintó Ramón Estruch Jordi Salas-Salvadó Dolores Corella Ángel M. Alonso-Gómez Lluis Serra-Majem Cristina Razquin Miquel Fiol José Lapetra Enrique Gómez-Gracia Francisco J. Tinahones Álvaro Hernáez Montserrat Fitó 《Molecular nutrition & food research》2023,67(1):2200338
713.
Emilio Sabia Matthias Gauly Fabio Napolitano Giulia Francesca Cifuni Salvatore Claps 《International Journal of Dairy Technology》2020,73(3):594-603
The objective of this study was to evaluate the effect of two dietary treatments, ryegrass hay (RH) and wrapped ryegrass silage (WRS) on the volatile organic compounds (VOCs) of buffalo Mozzarella cheese. The primary data were collected from 40 female buffaloes. Twenty animals were fed RH, and other twenty received WRS. Volatile organic compounds were identified using a mass selective detector after extraction with a ‘purge and trap’ system and a gas chromatographic analysis. Our results showed differences in the aromatic profile of Mozzarella cheese samples obtained from buffaloes receiving different feed. In particular, 5 VOCs allowed the discrimination between cheese samples. 相似文献
714.
715.
We consider the problem of a particle traveling from an initial configuration to a final configuration (given by a point in the plane along with a prescribed velocity vector) in minimum time with non-homogeneous velocity and with constraints on the minimum turning radius of the particle over multiple regions of the state space. Necessary conditions for optimality of these paths are derived to characterize the nature of optimal paths, both when the particle is inside a region and when it crosses boundaries between neighboring regions. These conditions are used to characterize families of optimal and nonoptimal paths. Among the optimality conditions, we derive a “refraction” law at the boundary of the regions that generalizes the so-called Snell’s law of refraction in optics to the case of paths with bounded curvature. Tools employed to deduce our results include recent principles of optimality for hybrid systems. A numerical example is given to demonstrate the derived results. 相似文献
716.
Poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) is a polymer or hydrogel that is both thermosensitive and pH sensitive, with a low critical solution temperature (LCST) around 38 °C and a pH critical point of 2.5. Poly(4‐vinylpyridine) (P4VP) shows pH sensitivity with a critical point of 5.1. Grafting of stimuli‐sensitive polymers onto mechanically durable poly(propylene) (PP) substrates was used in this study. We have focused on the influence of temperature and pH on the response of binary graft films produced by gamma irradiation in one and two steps. An LCST‐type hydration transition in the grafts was observed by measuring swelling of the films and water contact angle at different temperatures and pH. An upper critical solution temperature (UCST)‐type behavior was also observed by swelling PP‐g‐DMAEMA and DMAEMA/4VP binary grafting onto PP films at pH 2.2.
717.
In an urban site affected by fresh vehicle exhaust emissions, the ambient air number concentrations of particles coarser than 3 nm (N) was split into two components, N=N1+N2. This was done using a method based on the high correlation between black-carbon (BC) and number (N) concentrations which is typically observed in ambient air and is the result of vehicle exhaust emissions. The component N1 accounts for “those aerosol components directly emitted in the particle phase” and “those components nucleating immediately after emission”. The component N2 accounts for the new particle formation enhancements during the “dilution and cooling of the vehicle exhaust” and is also influenced by “in situ new particle formation in ambient air”. The contribution of N1 to N exhibits a maximum of 55% during the morning rush hours (07:00–08:00). The contribution of N2 to N exhibits a daily evolution with a broad maximum during daylight (as solar radiation intensity), while for about 7 h (11:00–17:00) the N2 contribution to N is about 70%. During some “afternoon N2 events”, N2 contributions exceeded 90%. Enhancements in the new particle formation processes may increase the N/BC concentrations ratio in one order of magnitude, from 4.82×106 particles/ng BC to 47×106 particles/ng BC and during some events up to 97×106 particles/ng BC. The results show evidence of the high potential of the vehicle exhausts and of the urban atmosphere to trigger new particle formation if the ambient air conditions are favourable. The method used in this study is useful in assessing future changes in the number to BC relationship due to forthcoming regulations in the vehicle exhaust emissions. 相似文献
718.
Nitrate stimulation of indigenous nitrate-reducing, sulfide-oxidising bacterial community in wastewater anaerobic biofilms 总被引:4,自引:0,他引:4
Garcia-de-Lomas J Corzo A Carmen Portillo M Gonzalez JM Andrades JA Saiz-Jimenez C Garcia-Robledo E 《Water research》2007,41(14):3121-3131
The role of the nitrate-reducing, sulfide-oxidising bacteria (NR-SOB) in the nitrate-mediated inhibition of sulfide net production by anaerobic wastewater biofilms was analyzed in two experimental bioreactors, continuously fed with the primary effluent of a wastewater treatment plant, one used as control (BRC) and the other one supplemented with nitrate (BRN). This study integrated information from H(2)S and pH microelectrodes, RNA-based molecular techniques, and the time course of biofilm growth and bioreactors water phase. Biofilms were a net source of sulfide for the water phase (2.01 micromol S(2-)(tot)m(-2)s(-1)) in the absence of nitrate dosing. Nitrate addition effectively led to the cessation of sulfide release from biofilms despite which a low rate of net sulfate reduction activity (0.26 micromol S(2-)(tot)m(-2)s(-1)) persisted at a deep layer within the biofilm. Indigenous NR-SOB including Thiomicrospira denitrificans, Arcobacter sp., and Thiobacillus denitrificans were stimulated by nitrate addition resulting in the elimination of most sulfide from the biofilms. Active sulfate reducing bacteria (SRB) represented comparable fractions of total metabolically active bacteria in the libraries obtained from BRN and BRC. However, we detected changes in the taxonomic composition of the SRB community suggesting its adaptation to a higher level of NR-SOB activity in the presence of nitrate. 相似文献
719.
Andreani G Santoro M Cottignoli S Fabbri M Carpenè E Isani G 《The Science of the total environment》2008,390(1):287-294
The first aim of our study was to determine the concentrations of selected trace elements (Zn, Cu, Fe, Mn, Cd and Pb) in tissues of green turtles from Tortuguero National Park on the North Caribbean coast of Costa Rica and of loggerheads from the Mediterranean Sea. Zn, Cu, Fe, Mn and Cd were present at detectable concentrations in all samples and showed clear organotropism, whereas Pb was not always over the detection limit and did not show any particular tissue distribution. The two species presented significant differences: Cu and Cd in liver and kidney of Chelonia mydas were significantly higher with respect to the concentrations found in Caretta caretta. The second and major goal of our study was to evaluate hepatic and renal metallothionein (MT) as a biomarker of environmental metal exposure. The present paper is the first to describe and quantify MT in kidney and liver of loggerhead turtles and in kidney of green turtles. MT concentrations were higher in green than in loggerhead turtles. In addition, positive correlations were found between Cu and Cd concentrations and Cu-MT and Cd-MT in liver and kidney in both species, suggesting a pivotal role of MT in metal storage and detoxification. The quantification of metals and MT in liver and kidney may be a valid biomarker of metal exposure in the aquatic environment to assess the health of marine sea turtles as long as accurate analytical methods are adopted. 相似文献
720.
Emilio Bucio 《Polymer》2005,46(12):3971-3974
A series of aromatic polyesters containing 1,6-diazaspiro[4,4]-nonane-2,7-dione were synthesized under phase-transfer conditions. The copolymers were obtained in essentially quantitative yield, theses were soluble in common organic solvents, and would readily form clear, colorless films from solution. The optimum conditions of polymerization, was obtained via polycondensation at room temperature and reaction time of 4 h in chloroform. All polymers were characterized by FTIR, GPC, viscosity, water contact angle, water absorption, TGA, DSC and TMA. The prepared polyesters showed excellent thermal stability, as measured by TGA (10 wt% loss), are only moderate due to the alicyclic component and range from 365 to 401 °C in air; however, glass transition temperatures are quite high (245-309 °C). The inherent viscosities of these solutions ranged from 0.77 to 1.40 dl g−1, depending on the polyester structure. The structures of the polyesters were confirmed by FTIR spectroscopy. 相似文献