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排序方式: 共有3972条查询结果,搜索用时 31 毫秒
271.
Marianne Wittrup Larsen Dr. Dorota F. Zielinska Mats Martinelle Dr. Aurelio Hidalgo Dr. Lars Juhl Jensen Prof. Uwe T. Bornscheuer Prof. Karl Hult Prof. 《Chembiochem : a European journal of chemical biology》2010,11(6):796-801
A water tunnel in Candida antarctica lipase B that provides the active site with substrate water is hypothesized. A small, focused library created in order to prevent water from entering the active site through the tunnel was screened for increased transacylation over hydrolysis activity. A single mutant, S47L, in which the inner part of the tunnel was blocked, catalysed the transacylation of vinyl butyrate to 20 mM butanol 14 times faster than hydrolysis. The single mutant Q46A, which has a more open outer end of the tunnel, showed an increased hydrolysis rate and a decreased hydrolysis to transacylation ratio compared to the wild‐type lipase. Mutants with a blocked tunnel could be very useful in applications in which hydrolysis is unwanted, such as the acylation of highly hydrophilic compounds in the presence of water. 相似文献
272.
273.
Poljanc K Steinhauser G Sterba JH Buchtela K Bichler M 《The Science of the total environment》2007,374(1):36-42
Gas mantles for camping gas lanterns sometimes contain thorium compounds. During the last years, the use of thorium-free gas mantles has become more and more popular due to the avoidance of a radioactive heavy metal. We investigated a gas mantle type that is declared to be "non-radioactive" and that can be bought in Austria at the moment. Methods used were Instrumental Neutron Activation Analysis (INAA), gamma-spectroscopy, and Liquid Scintillation Counting (LSC). We found massive thorium contents of up to 259 mg per gas mantle. Leaching experiments showed that only 0.4% of the Th but approximately 90% of the decay products of (232)Th can be leached under conditions simulating sucking and chewing with human saliva. In this paper, the investigation of these gas mantles including the consideration of the environmental hazard caused by disposed mantles and the health hazard for unsuspecting consumers is presented and legal consequences are discussed for this fraud. 相似文献
274.
Chen PJ Rosenfeldt EJ Kullman SW Hinton DE Linden KG 《The Science of the total environment》2007,376(1-3):18-26
Numerous studies have investigated degradation of individual endocrine disrupting compounds (EDCs) in lab or natural waters. However, natural variations in water matrices and mixtures of EDCs in the environment may confound analysis of the treatment efficiency. Because chemical based analytical methods cannot represent the combined or synergistic activities between water quality parameters and/or the EDC mixtures at environmentally relevant concentrations (microg L(-1)-ng L(-1)), bioanalytical assessments of residual estrogenic activity in treated water were used to evaluate the performance of the UV based advanced oxidation process for estrogenic contaminants in water. Four EDCs including estradiol (E(2)), ethinyl estradiol (EE(2)), bisphenol-A (BPA) and nonylphenol (NP) were spiked individually or as a mixture at mug L(-1)-ng L(-1) in laboratory or natural river water. The removal rates of estrogenic activity were quantitatively evaluated by in vitro yeast estrogen screen (YES) and in vivo Vitellogenin (VTG) assays with Japanese medaka fish (Oryzias latipes). UV in combination with 10 ppm H(2)O(2) as an oxidation process was capable of decreasing in vitro and in vivo estrogenic activity, however, in vivo estrogenic activity of the EDC mixture in natural water was not completely removed at UV fluence up to 2000 mJ cm(-2). The removal rates of in vitro estrogenic activity of the EDC mixtures were lower than those observed for single compounds, and slower in natural waters, likely due to lower steady-state concentrations of hydroxyl radicals (*OH) in the presence of *OH scavengers from the water matrix and EDC mixture. 相似文献
275.
Gundacker C Komarnicki G Jagiello P Gencikova A Dahmen N Wittmann KJ Gencik M 《The Science of the total environment》2007,385(1-3):37-47
BACKGROUND: Detoxification is an essential process in all living organisms. Humans accumulate heavy metals primarily as a result of lifestyle and environmental contamination. However, not all humans experience the estimated individual exposure. This suggests the presence of genetic regulatory mechanisms. OBJECTIVE: In order to identify genetic factors underlying the inter-individual variance in detoxification capacity for the heavy metal mercury, 192 students were investigated. We focused on the relationship between polymorphisms in glutathione-S-transferase (GST) genes and mercury concentrations in blood, urine, and hair. The correlation between blood mercury levels, GSTT1 and GSTM1 polymorphism, and gene expression of certain metallothionein subgroups (MT1, MT3) was evaluated in a further group of students (N=30). METHODS: Mercury levels in acid digested samples were measured by cold vapor AAS. Genotyping of the GSTT1 and GSTM1-gene deletion polymorphism was performed by means of PCR. Gene expression of several MT genes was analyzed in lymphocytes from fresh peripheral blood by semiquantitative RT-PCR. RESULTS: The following was noted: a) hair mercury concentrations are significantly increased in persons with the double deleted genotype (GSTT1-/- and GSTM1-/-) as compared to persons with the intact genotype, and b) MT1X expression is higher in persons with the intact genotype (GSTT1+/+ and GSTM1+/+). CONCLUSIONS: We conclude that the epistatic effect of the GSTT1 and the GSTM1 deletion polymorphism is a risk factor for increased susceptibility to mercury exposure. The relationship between MT gene expression and GST gene polymorphisms needs further investigation. If MT expression depends on GST polymorphisms it would have important implications on the overall metal detoxification capability of the human organism. 相似文献
276.
Evaluation of UV irradiation for photolytic and oxidative degradation of pharmaceutical compounds in water 总被引:3,自引:0,他引:3
A medium-pressure (MP) ultraviolet (UV) system was used to investigate the UV photolysis and UV/H(2)O(2) oxidation of pharmaceutically active compounds (PhACs) that belong to different therapeutic classes and were found to occur in the aquatic environment. The results obtained in laboratory-grade water (LGW) and surface water (SW) were compared with low-pressure (LP) results reported previously. Overall, MP lamps proved to be more efficient to maximize the bench-scale degradation of the selected group of compounds (ketoprofen, naproxen, carbamazepine, ciprofloxacin, clofibric acid, and iohexol) by both UV photolysis and UV/H(2)O(2) oxidation. Fundamental direct and indirect photolysis parameters obtained in LGW are reported and used to model the MP-UV photolysis and MP-UV/H(2)O(2) oxidation of the pharmaceuticals in SW, predicting the experimental results very well. 相似文献
277.
Fredi Schwägele Carmen Haschke Gerhard Krauss Karl O. Honikel 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,203(1):14-20
A fast breakdown of glycogen is observed in muscles of stress-susceptible pigs leading to pale, soft and exudative (PSE) meat. We report a comparative study of pyruvate kinase from muscles of normal and PSE-prone pigs. Compared with the enzyme from normal muscle, pyruvate kinase isolated from PSE muscle shows a five times lower Michaelis constant,K
m, for phosphoenol pyruvate and a more than ten times higherk
cat/K
m value. The pH dependency of the enzymatic activity is shifted to more acidic values for pyruvate kinase from PSE muscles. According to isoelectric focusing, pyruvate kinase from PSE muscle consists of three isoforms, while only two isoforms are detectable in pyruvate kinase preparations from normal pigs. The various isoforms were isolated by preparative isoelectric focusing and their steady-state properties were compared. Isoform 3, which is found only in PSE muscle, shows a 10-fold higher specific activity, a 30-fold lowerK
m value and a 100-fold increasedk
cat/K
m value for phosphoenol pyruvate as compared to isoform 1. The presence of isoform 3 in PSE muscle appears to be responsible for the high activity of this enzyme under the more acidic conditions prevailing in PSE muscle. In vitro phosphorylation and dephosphorylation experiments using total enzyme and purified isoenzyme 1 suggest that isoforms 2 and 3 arise from isoform 1 by phosphorylation. Thus protein phosphorylation seems to be responsible for the shift in activity of pyruvate kinase, a key enzyme of glycolysis, under the acidic conditions of PSE muscles. 相似文献
278.
Karl Kaack Lene Pedersen Helle Nygaard Laerke Anne Meyer 《European Food Research and Technology》2006,224(2):199-207
The aim of this project was to compare the functional properties of five fibre fractions by baking of wheat bread by substitution 0, 4, 8 and 12 w/w% of wheat flour using dry potato pulp (Fibre 1), a commercial potato fibre (Fibre 2), two fibre prepared from potato pulp by enzymatic hydrolysis (Fibre 3 and 4), and one solubilised fibre (Fibre 5). The effect of chemical composition of fibre on texture, colour, specific weight and volume of wheat bread was studied using objective methods for measurement of texture characteristics, colour (L, a, b) and sensory analysis. Dry potato pulp, Potex (Fibre 2) and two enzymatically prepared fibre powders (Fibre 3 and 4) with a high concentration of lignin and insoluble non-starch polysaccharides (INCP) had a detrimental effect on bread quality by substitution of more than 8% of the wheat flour by fibre. The detrimental effect was mainly due to increased hardness, deformation energy, modulus and gumminess. Multiple linear regression analysis with forward selection was used for determination of the relationship between quality characteristics and of soluble non-starch polysaccharides (SNSP), insoluble non-starch polysaccharides (INCP), cellulose and lignin. The enzymatic solubilised fibre (Fibre 5) with a high concentration of soluble fibre and a low concentration of cellulose and lignin could be used for substitution of at least 12% wheat flour for baking of bread with an attractive colour, delicious texture and flavour. 相似文献
279.
280.
Xi-Chun Zhong Zhong-Wu Liu De-Chang Zeng Karl A. Gschneidner Jr. Vitalij K. Pecharsky 《稀有金属(英文版)》2014,33(5):552-555
Polycrystalline Pr2Fe17-xMnx(x = 0, 1, and 2)alloys were studied by X-ray diffraction(XRD), heat capacity, ac susceptibility, and isothermal magnetization measurements. All the alloys adopt the rhombohedral Th2Zn17-type structure. The Curie temperature increases from 283 K at x = 0 to 294 K at x = 1, and then decreases to 285 K at x = 2. The magnetic phase transition at the Curie temperature is a typical second-order paramagnetic–ferromagnetic transition. For an applied field change from0 to 5 T, the maximum-△SM for Pr2Fe17-xMnxalloys with x = 0, 1, and 2 are 5.66, 5.07, and 4.31 J·kg^-1·K^-1,respectively. The refrigerant capacity(RC) values range from 458 to 364 J·kg^-1, which is about 70 %–89 % that of Gd. The large, near room temperature △SM and RC values,chemical stability, and a high performance-to-cost ratio make Pr2Fe17-xMnxalloys be selectable materials for room temperature magnetic refrigeration applications. 相似文献