全文获取类型
收费全文 | 63331篇 |
免费 | 3922篇 |
国内免费 | 59篇 |
学科分类
工业技术 | 67312篇 |
出版年
2023年 | 565篇 |
2022年 | 567篇 |
2021年 | 1448篇 |
2020年 | 1252篇 |
2019年 | 1201篇 |
2018年 | 2484篇 |
2017年 | 2462篇 |
2016年 | 2527篇 |
2015年 | 1863篇 |
2014年 | 2315篇 |
2013年 | 4703篇 |
2012年 | 3809篇 |
2011年 | 3498篇 |
2010年 | 2853篇 |
2009年 | 2533篇 |
2008年 | 2767篇 |
2007年 | 2477篇 |
2006年 | 1818篇 |
2005年 | 1496篇 |
2004年 | 1374篇 |
2003年 | 1233篇 |
2002年 | 1106篇 |
2001年 | 759篇 |
2000年 | 724篇 |
1999年 | 906篇 |
1998年 | 4929篇 |
1997年 | 3061篇 |
1996年 | 1939篇 |
1995年 | 1118篇 |
1994年 | 937篇 |
1993年 | 939篇 |
1992年 | 315篇 |
1991年 | 303篇 |
1990年 | 301篇 |
1989年 | 278篇 |
1988年 | 278篇 |
1987年 | 240篇 |
1986年 | 247篇 |
1985年 | 290篇 |
1984年 | 257篇 |
1983年 | 174篇 |
1982年 | 207篇 |
1981年 | 245篇 |
1980年 | 219篇 |
1979年 | 167篇 |
1978年 | 156篇 |
1977年 | 320篇 |
1976年 | 639篇 |
1975年 | 125篇 |
1973年 | 129篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this paper, we present an invariant‐set‐based method for actuator and sensor fault detection and isolation in Lure systems. The Lure plant is controlled by an observer‐based feedback tracking controller, designed for the nominal (fault‐free) system. Suitable residual signals are constructed from measurable system outputs and estimates associated with the nominal observer. Faults are diagnosed by online contrasting the residual signal trajectories against sets of values that the residuals are shown to attain under healthy or faulty operation. These values are obtained via set‐invariance analysis of the system closed‐loop trajectories. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
992.
Iván Jachmanián Lucía Margenat Ana I. Torres Maria A. Grompone 《Journal of the American Oil Chemists' Society》2007,84(6):597-601
The solubility of different ethyl esters derivatized from hake liver oil in supercritical carbon dioxide was studied. A selectivity
factor was used to determine optimal conditions to fractionate the ethyl ester mixture. A strong influence of solvent pressure
and temperature was observed within 8.63–18.04 MPa and 40–70 °C. The lowest total solubility of the ethyl ester mixture was
obtained when using supercritical carbon dioxide at the lowest density (the lowest pressure and the highest temperatures value
tested). The highest discrimination against long-chain polyunsaturated fatty acids (e.g. EPA and DHA) was also obtained at
these above conditions. Conversely, higher solubility and lower selectivity were obtained when solvent density increased.
Considering this inverse correlation between selectivity and solubility, a single-step batch-fractionation process was designed
to increase the 22:6 ethyl ester content from an initial value of 17.5% in the starting material to 55% in the final extract. 相似文献
993.
Jhon Harley Muñoz Romero Cindy Alejandra Sepúlveda Cadavid Natalie Cortés Julián Esteban López Correa 《臭氧:科学与工程》2020,42(1):36-42
ABSTRACTIn this study, the efficiency of gaseous ozone (O3) injected in the soil as an oxidizing agent for the inactivation of F. oxysporum was evaluated under laboratory conditions. The results show the treatment reached an inactivation efficiency of 76% after an applied dose of 0.40 g O3 kg ?1 soil. This shows that the injection of O3 can be a viable alternative to control pathogenic organisms in the soils. Nevertheless, it is clear that more studies on determining the effects of this treatment on soil quality are needed. 相似文献
994.
Small-angle X-ray and small-angle neutron scattering studies have been carried out on poly(vinyl chloride) (PVC), and blends of PVC with solution-chlorinated polyethylene (SCPE) and poly(butyl acrylate) (PBA). The PVC used was commercial (suspension-polymerized) or bulk-polymerized. The blends of PVC with PBA were prepared by solvent-casting and those with SCPE by in situ polymerization. PVC samples show shoulders in the scattering spectra, presumably due to crystallites, which persist even in samples which have been solvent cast. Blends of PVC with PBA also show a peak but at a higher ‘d’ spacing. The blends with SCPE which were prepared by in situ polymerization show no such peak. This suggests that the method of preparation prevents the formation of crystallites. An increase in scattering of the PBA blends was observed when the samples were heated to the temperature of phase separation. Neutron scattering studies were also carried out using 2% deuterium labelled PVC in PVC and in the blends. In the PVC this showed chain dimensions in good agreement with predicted values. In the blends, dimensions of the same order were obtained, confirming a molecular dispersion of chains in the single phase, but there was an apparent reduction in the chain dimensions. This could be explained by a true reduction in dimensions or a non-zero A2 value in the blends. 相似文献
995.
Chamorro G Salazar M Araújo KG dos Santos CP Ceballos G Castillo LF 《Archivos latinoamericanos de nutrición》2002,52(3):232-240
Spirulina (Arthrospira), a filamentous, unicellular alga, is a cyanobacterium grown in certain countries as food for human and animal consumption. It is also used to derive additives in pharmaceuticals and foods. This alga is a rich source of proteins, vitamins, amino acids, minerals, and other nutrients. Its main use, therefore, is as a food supplement. Over the last few years, however, it has been found to have many additional pharmacological properties. Thus, it has been experimentally proven, in vivo and in vitro that it is effective to treat certain allergies, anemia, cancer, hepatotoxicity, viral and cardiovascular diseases, hyperglycemia, hyperlipidemia, immunodeficiency, and inflammatory processes, among others. Several of these activities are attributed to Spirulina itself or to some of its components including fatty acids omega-3 or omega-6, beta-carotene, alpha-tocopherol, phycocyanin, phenol compounds, and a recently isolated complex, Ca-Spirulan (Ca-SP). This paper aims to update and critically review the results published over the last few years with regards to these properties. The conclusion is that even if this cyanobacterium has been one of the most extensively studied from the chemical, pharmacological and toxicological points of view, it is still necessary to expand the research in order to have more consistent data for its possible use in human beings. 相似文献
996.
F. Gutiérrez Rosales S. Perdiguero R. Gutiérrez J. M. Olias 《Journal of the American Oil Chemists' Society》1992,69(4):394-395
An analytical method has been developed to evaluate the intensity of the bitter taste in virgin olive oil. Results from the
proposed method, based on extraction of the bitter constituents of virgin olive oil with methanol/water and measurement of
the absorbance at 225 nm, show a significant correlation with the intensity of bitterness that had been evaluated in a sensorial
manner by a panel. The developed method, therefore, offers a real alternative to the panel test for the evaluation of this
attribute. 相似文献
997.
J. Hrivňák L. Soják J. Krupčík Y. P. Duchesne 《Journal of the American Oil Chemists' Society》1973,50(3):68-71
The influence of temperature on the gas chromatographic separation ofcis-trans isomers of the methyl esters of some monounsaturated fatty acids was studied on capillary columns coated with Apiezon L,
BDS and DEGS. As far as methyl oleate and methyl elaidate are concerned, the separation is better at lower temperatures on
Apiezon L (180–210 C) and at higher temperatures on polyester phases (BDS, DEGS; 150–180 C). The influence of temperature
on the separation ofcis-trans isomers on the three stationary phases under study is explained by the higher values of δECL/δt forcis isomers. The variation of the equivalent carbon chain length with temperature can be used for the identification ofcis-trans isomers in natural mixtures. 相似文献
998.
Daniel Escolar María R. Haro Jesús Ayuso 《Journal of the American Oil Chemists' Society》2002,79(8):769-774
Four polynomial expressions are obtained that provide a good approximation and an easy, rapid calculation of the chromatic
coordinates and the chroma—L
*, a
*, b
*, and C—for the illuminant C and the standard observer, for a virgin or extra virgin olive oil; absorbance is measured at only 480
and 670 nm. These are as follows: L
*=0.556458(A480)2−2.51145A480+0.55504(A670)2−8.53016A670+98.4089; a
*=0.177372(A480)2+2.1363A480+1.43254(A670)2−0.789231A670−13.9246; b
*=−16.0277(A480)2+79.8932A480−5.06558(A670)2+3.36169A670+31.9405; C=−15.8439(A480)2+78.9312A480−5.26784(A670)2+3.56917A670+33.3927. These give acceptable results, making the method a practical alternative to the extremely laborious Commission Internationale
d’Eclairage (CIE) L
*
a
*
b
*
system, by which 391 absorbance values must be measured individually, nanometer by nanometer, before applying more complex
equations. The validity of the proposed method has been confirmed by comparison, using a set of 20 sample oils different from
the set of 25 oils used to generate the order of the equations. The variations between the values provided by the proposed
and standard methods, respectively, had a mean of 0.00 for each of the chromatic variables—L
*
, a
*
, b
*
, and C; SD were moderate (0.71, 0.52, 1.22, and 1.22, respectively); the root mean square and the R
2-terms also confirmed the validity of the method. 相似文献
999.
Carbon dioxide has been previously identified as a critical volatile factor that stimulates hyphal growth ofGigaspora margarita, a vesiculararbuscular mycorrhizal fungus, and we determined the optimal concentration at 2.0%. The beneficial effect of CO2 on fungal development is also visible in the presence of stimulatory (quercetin, myricetin) or inhibitory (naringenin) flavonoids. Sterile root exudates from carrot seedlings stimulate the hyphal development ofG. margarita in the presence of optimal CO2 enrichment. Three flavonols (quercetin, kaempferol, rutin or quercetin 3-rutinoside) and two flavones (apigenin, luteolin) were identified in carrot root exudates by means of HPLC retention time. Flavonols like quercetin and kaempferol are known to have stimulatory effects on hyphal growth ofG. margarita. 相似文献
1000.
Polyamide 6 (PA6) isotropic films and oriented cables were prepared by compression molding or by consecutive extrusion and cold‐drawing. These samples were isothermally annealed in the 120–200°C range and were then subjected to tensile tests at room temperature. Synchrotron wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) patterns were obtained before and after mechanical failure. These data were related with the mechanical properties of the respective PA6 samples. The annealing of isotropic PA6 resulted in an increase in the Young's modulus (E) and yield stress (σy) values, which was attributed to the observed proportional reduction of the d‐spacings of the intersheet distances in both the α‐PA6 and γ‐PA6 polymorphs. Analysis of the WAXS and SAXS patterns of isotropic PA6 after break allowed the supposition of structural changes in the amorphous phase, with these being better pronounced with increasing annealing temperature; this made the samples less ductile. In oriented PA6 samples, annealing resulted in a drastic increase in the E and σy values accompanied by a phase transition from γ‐PA6 to α‐PA6 and a well‐pronounced reduction in the intersheet distances of both polymorphs. The stretching of the oriented samples led to an additional γ‐to‐α transition, whose extent was also related to structural changes in the amorphous phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2242–2252, 2007 相似文献