全文获取类型
收费全文 | 785篇 |
免费 | 32篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 206篇 |
金属工艺 | 7篇 |
机械仪表 | 5篇 |
建筑科学 | 32篇 |
能源动力 | 26篇 |
轻工业 | 166篇 |
水利工程 | 1篇 |
石油天然气 | 2篇 |
无线电 | 43篇 |
一般工业技术 | 120篇 |
冶金工业 | 146篇 |
原子能技术 | 11篇 |
自动化技术 | 42篇 |
出版年
2022年 | 19篇 |
2021年 | 37篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 18篇 |
2015年 | 16篇 |
2014年 | 38篇 |
2013年 | 49篇 |
2012年 | 44篇 |
2011年 | 42篇 |
2010年 | 46篇 |
2009年 | 33篇 |
2008年 | 33篇 |
2007年 | 42篇 |
2006年 | 37篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 13篇 |
2001年 | 13篇 |
2000年 | 5篇 |
1999年 | 11篇 |
1998年 | 56篇 |
1997年 | 29篇 |
1996年 | 27篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 10篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 5篇 |
1970年 | 2篇 |
排序方式: 共有817条查询结果,搜索用时 15 毫秒
21.
22.
23.
Custodio E Descalzo MA Roche J Sánchez I Molina L Lwanga M Bernis C Villamor E Baylin A 《Food and nutrition bulletin》2008,29(1):49-58
BACKGROUND: In Equatorial Guinea, as a result of the recent growth of the oil industry, there is an opportunity to address important public health problems through public and private initiatives. To propose effective nutrition and public health strategies, it is important first to have reliable information on the nutritional status of the population and the underlying factors affecting it. OBJECTIVE: To assess the nutritional status and the prevalence of anemia among Equatoguinean children in a nationally representative sample and to identify the risk factors associated with the nutritional problems detected. METHODS: The study was a cross-sectional survey using a multistaged, stratified, cluster-selected sample. The survey included a sociodemographic, health, and dietary questionnaire and measurement of hematocrit and anthropometric features, from which nutritional indicators based on the National Center for Health Statistics (NCHS) reference and the World Health Organization (WHO) standards were calculated. Logistic regression models were used for the multivariate analysis. A total of 552 children aged 0 to 60 months were surveyed. RESULTS: The overall prevalence of stunting (< -2 height-for-age z-scores [HAZ]) was 29.7% based on the NCHS reference and 35.2% based on WHO standards; the risk factors associated with stunting were age (p < .0001), low socioeconomic status (p = .01), and fishing by a member of the household (p = .003) The prevalence of mild anemia (hemoglobin < 110 g/L) was 69.3%, and that of moderate or severe anemia (hemoglobin < 80 g/L) was 8.3%. The only significant risk factor associated with moderate to severe anemia was low household socioeducational level (p = .01). CONCLUSIONS: Stunting and anemia are public health problems in Equatorial Guinea. Integrated strategies, including fighting poverty and improving maternal education, should be undertaken. 相似文献
24.
The objective of this study was to quantify the effect of periparturient body condition score (BCS) and body weight (BW) related traits on the incidence of calving dystocia and stillbirths, and to determine any consequent effect of dystocia and stillbirths on BCS, BW, milk production, udder health, and fertility in grazing Holstein-Friesian dairy cows. Up to 2,384 lactation records with data on calving dystocia or stillbirths were available from one research herd across 15 yr. Mixed models and generalized estimating equations were used to quantify all effects. Body condition score or BW 8 wk precalving or at calving, or change precalving did not significantly affect the odds of a difficult calving or stillbirth. Cows that experienced dystocia lost, on average, more BCS and BW between calving and nadir and had significantly reduced nadir BCS and BW. Incidence of stillbirths did not affect BCS in early lactation, although BW loss postpartum was greater following a stillbirth. A dystocia or stillbirth event was associated with reduced 60-d milk yield (42 and 52 kg less milk produced following a difficult calving or a stillbirth, respectively). The effect of stillbirth on milk yield was independent of dystocia. Cows that experienced dystocia had reduced milk concentration of fat, protein, and lactose, whereas average somatic cell score (natural logarithm of somatic cell count) in the first 60-d postpartum was elevated. There was no significant effect of dystocia or stillbirth on clinical mastitis, but pregnancy rates to first service and throughout the 12-wk breeding season were compromised in cows that had experienced difficulty at calving. The significance of the effects of stillbirth on somatic cell score and reduced fertility were mediated through its association with dystocia. In conclusion, periparturient BCS and BW within the range observed in the current study did not significantly affect incidence of dystocia and stillbirth, but these events negatively affected cow performance in early lactation. 相似文献
25.
Data from 113 lactations across 76 cows between the years 2002 to 2004 were used to determine the effect of strain of Holstein-Friesian (HF) dairy cow and concentrate supplementation on milk production, body weight (BW), and body condition score (BCS; 1 to 5 scale) lactation profiles. New Zealand (NZ) and North American (NA) HF cows were randomly allocated to 1 of 3 levels of concentrate supplementation [0, 3, or 6 kg of dry matter (DM)/cow per d] on a basal pasture diet. The Wilmink exponential model was fitted within lactation (YDIM = a + b e(−0.05 × DIM) + c × DIM). The median variation explained by the function for milk yield was 86%, between 62 and 69% for milk composition, and 80 and 70% for BW and BCS, respectively. North American cows and cows supplemented with concentrates had greater peak and 270-d milk yield. Concentrate supplementation tended to accelerate the rate of incline to peak milk yield, but persistency of lactation was not affected by either strain of HF or concentrate supplementation. No significant strain by diet interaction was found for parameters reported. New Zealand cows reached nadir BCS 14 d earlier and lost less BW (22 kg) postcalving than NA cows. Concentrate supplementation reduced the postpartum interval to nadir BW and BCS, and incrementally increased nadir BCS. New Zealand cows gained significantly more BCS (i.e., 0.9 × 10−3 units/d more) postnadir than NA cows, and the rate of BCS replenishment increased linearly with concentrate supplementation from 0.5 × 10−3 at 0 kg of DM/d to 0.8 × 10−3 and 1.6 × 10−3 units/d at 3 and 6 kg of DM/d concentrates, respectively. Although there was no significant strain by diet interaction for parameters reported, there was a tendency for a strain by diet interaction in 270-d BCS, suggesting that the effect of concentrate supplementation on BCS gain was, at least partly, strain dependent. 相似文献
26.
Virginie Dulong Renauld Forbice Eric Condamine Didier Le Cerf Luc Picton 《Polymer Bulletin》2011,67(3):455-466
Rheological and swelling properties of hydrogels based on pullulan crosslinked with sodium trimetaphosphate (STMP) are explained according to various polymer and crosslinking agent concentrations using 31P-nuclear magnetic resonance study. This method has allowed determining the amount of all the species present in the medium when varying both pullulan and STMP concentrations. We have clearly demonstrated with a good agreement by both 31P-NMR and rheology that a critical STMP concentration occurs which is function of pullulan concentration. This typical crosslinking agent concentration delimitates the maximum of gel structure together with the minimum of swelling. 相似文献
27.
Jean-Luc Adam Laurent Calvez Johann Trolès Virginie Nazabal 《International Journal of Applied Glass Science》2015,6(3):287-294
The last advances in the synthesis and shaping techniques of chalcogenide glasses suitable for infrared photonics are reported. Ball milling combined with spark plasma sintering allows the preparation of bulk chalcogenide glasses at lower temperature and at lower cost. Microstructuring of optical fibers results in enhanced nonlinear properties leading to the demonstration of low-threshold Brillouin laser at 1.55 μm, all-optical wavelength conversion and time-domain demultiplexing with a 170 Gb/s rate, and supercontinuum between 1.5 and 2.8 μm. The potential of integrated waveguides for functions such as near-IR sensing, mid-IR injection, and (bio)-chemical functionalization is shown. 相似文献
28.
Virginie N. Kapchie Lili T. Towa Catherine C. Hauck Patricia A. Murphy 《Journal of the American Oil Chemists' Society》2012,89(5):947-956
The aim of this study was to investigate soy protein recovery feasibility after lab- and pilot-plant scale oleosome isolation.
The proteins were isolated by isoelectric precipitation and by ultrafiltration. The functional properties of the recovered
proteins were compared to soy protein isolate produced in our laboratory. The residual lipid content in the aqueous supernatant
affected the protein recovery yields and purities. Ethanol precipitation and ultrafiltration resulted in the best protein
yields, which were 25 and 26% greater than protein yield obtained by isoelectric precipitation with distilled water dilution.
The protein content of the isoelectric precipitated pilot-plant supernatant was higher (98%) than the protein content of ethanol-precipitated
proteins (80%). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed similar peptide profiles for laboratory and
pilot-plant supernatants. Protein solubility curves between pH 3 and 8 were typical for soy protein isolate with higher solubilities
for proteins obtained from pilot-plant supernatant. The soy protein isolate and ethanol-precipitated protein had the highest
emulsification capacity on a dry-weight basis. These desirable functional properties of proteins recovered as co-products
after oleosome isolation suggest they are highly suitable for industrial application as food ingredients and their recovery
would contribute to the economics of the overall oleosome fractionation process. 相似文献
29.
C. Renault J. Roche M. R. Ciumag T. Tzedakis S. Colin K. Serrano O. Reynes C. André-Barrès P. Winterton 《Journal of Applied Electrochemistry》2012,42(9):667-677
The study focuses on the design and construction, as well as the theoretical and experimental optimization of electrochemical filter press microreactors for the electrosynthesis of molecules with a high added value. The main characteristics of these devices are firstly a high-specific electrochemical area to increase conversion and selectivity, and secondly the shape and size of the microchannels designed for a uniform residence time distribution of the fluid. A heat exchanger is integrated into the microstructured electrode to rapidly remove (or supply) the heat required in exo- or endothermic reactions. The microreactors designed are used to perform-specific electrosynthesis reactions such as thermodynamically unfavorable reactions (continuous NADH regeneration), or reactions with high enthalpy changes. 相似文献
30.
Partial Sperm beta1 Integrin Subunit Deletion Proves Its Involvement in Mouse Gamete Adhesion/Fusion
Virginie Barraud-Lange Cme Ialy-Radio Cline Chalas Isabelle Holtzmann Jean-Philippe Wolf Sandrine Barbaux Ahmed Ziyyat 《International journal of molecular sciences》2020,21(22)
We have previously shown, using antibodies, that the sperm alpha6beta1 integrin is involved in mouse gamete fusion in vitro. Here we report the conditional knockdown of the sperm Itgb1 gene. It induced a drastic failure of sperm fusogenic ability with sperm accumulation in the perivitelline space of in vitro inseminated oocytes deleted or not for the Itgb1 gene. These data demonstrate that sperm, but not oocyte, beta1 integrin subunit is involved in gamete adhesion/fusion. Curiously, knockdown males were fertile in vivo probably because of the incomplete Cre-mediated deletion of the sperm Itgb1 floxed gene. Indeed, this was shown by Western blot analysis and confirmed by both the viability and litter size of pups obtained by mating partially sperm Itgb1 deleted males with females producing completely deleted Itgb1 oocytes. Because of the total peri-implantation lethality of Itgb1 deletion in mice, we assume that sperm that escaped the Itgb1 excision seemed to be preferentially used to fertilize in vivo. Here, we showed for the first time that the deletion, even partial, of the sperm Itgb1 gene makes the sperm unable to normally fertilize oocytes. However, to elucidate the question of the essentiality of its role during fertilization, further investigations using a mouse expressing a recombinase more effective in male germ cells are necessary. 相似文献