全文获取类型
收费全文 | 6198篇 |
免费 | 175篇 |
国内免费 | 6篇 |
学科分类
工业技术 | 6379篇 |
出版年
2023年 | 33篇 |
2022年 | 104篇 |
2021年 | 112篇 |
2020年 | 65篇 |
2019年 | 90篇 |
2018年 | 101篇 |
2017年 | 106篇 |
2016年 | 103篇 |
2015年 | 88篇 |
2014年 | 138篇 |
2013年 | 338篇 |
2012年 | 244篇 |
2011年 | 378篇 |
2010年 | 251篇 |
2009年 | 271篇 |
2008年 | 261篇 |
2007年 | 276篇 |
2006年 | 265篇 |
2005年 | 224篇 |
2004年 | 191篇 |
2003年 | 182篇 |
2002年 | 182篇 |
2001年 | 113篇 |
2000年 | 113篇 |
1999年 | 123篇 |
1998年 | 129篇 |
1997年 | 128篇 |
1996年 | 135篇 |
1995年 | 102篇 |
1994年 | 109篇 |
1993年 | 116篇 |
1992年 | 110篇 |
1991年 | 51篇 |
1990年 | 84篇 |
1989年 | 93篇 |
1988年 | 79篇 |
1987年 | 90篇 |
1986年 | 77篇 |
1985年 | 95篇 |
1984年 | 63篇 |
1983年 | 66篇 |
1982年 | 43篇 |
1981年 | 55篇 |
1980年 | 45篇 |
1979年 | 44篇 |
1977年 | 35篇 |
1976年 | 23篇 |
1975年 | 30篇 |
1974年 | 23篇 |
1973年 | 23篇 |
排序方式: 共有6379条查询结果,搜索用时 15 毫秒
151.
In vitro antioxidant activity of anthocyanins of black soybean seed coat in human low density lipoprotein (LDL) 总被引:3,自引:0,他引:3
The objectives of this study were to determine the phenolic and anthocyanin contents in black soybean Mallika and Cikuray variety seed coat extract and to examine antioxidant activity of extract against DPPH radical and LDL oxidation. Black soybean seed coat of Mallika (M) and Cikuray (C) was extracted using methanol-1%HCl. The phenolic and anthocyanin contents were determined with Folin–Ciocalteu and pH differential methods, respectively. Individual anthocyanidins were identified with HPLCdiode array detector, and antioxidant activity was examined, using DPPH and TBARS assay with LDL as the oxidation substrate. BHT and rutin were used as antioxidant references. The phenolic content in M and C were 8.15 ± 0.23 and 6.46 ± 0.11 g GAE/100 g, respectively. The anthocyanin contents were 11.36 ± 0.12 and 1.45 ± 0.13 g/100 g, respectively. Cyanidin, delphinidin, and pelargonidin were found as individual anthocyanidins. The optimum DPPH radical scavenging capacity (%) of M and C were 92.78% and 91.50%, respectively, BHT and rutin were 77.0% and 91.94%, respectively. The optimum inhibition of TBARS formation from M and C were 37.10 and 30.37 nmol MDA equivalents/g LDL protein, respectively, and rutin were 30.10 nmol MDA equivalents/g LDL protein, respectively. These results suggest that black soybean seed coat has high levels of phenolic and anthocyanin, and also demonstrated considerable antioxidant activity of black soybean seed coat. 相似文献
152.
Effect of recombinant cytokines on leucocytes and physiological changes in bovine mammary glands during early involution 总被引:2,自引:0,他引:2
Wedlock DN McCarthy AR Doolin EE Lacy-Hulbert SJ Woolford MW Buddle BM 《The Journal of dairy research》2004,71(2):154-161
We examined the effects of administering recombinant bovine cytokines to non-lactating dairy cows and measured mammary gland leucocytes and the involution process. After the final milking, groups of cows were given an intramammary infusion of cytokine in two quarters. These cytokines were recombinant bovine interleukin-2 (rbolL-2) (2 x 10(5) units, n = 6), recombinant bovine granulocyte-macrophage colony stimulating factor (rboGM-CSF) (500 microg, n = 4) and recombinant bovine interleukin-1beta (rbolL-1beta) (10 microg, n = 10). Each animal also received an infusion of phosphate-buffered saline (PBS) in the other two quarters as controls. The rbolL-2 and rboGM-CSF were produced in a yeast expression system, while rbolL-1beta was produced in Escherichia coli. Leucocyte numbers, bactericidal activity of leucocytes, and concentrations of citrate and lactoferrin in quarter secretion samples were monitored after infusion of cytokine or PBS. Infusion of rbolL-2 had minimal effect on leucocyte numbers and concentrations of citrate and lactoferrin. Both rboGM-CSF and rbolL-1beta induced a rapid increase in the number of neutrophils and macrophages compared with control PBS quarters. Concentrations of lactoferrin in secretions were increased by rboGM-CSF and rbolL-1beta compared with control PBS quarters. In addition, infusion of glands with rbolL-1beta lowered the citrate:lactoferrin molar ratio compared with PBS control quarters. The results indicate that intramammary infusion of either rboGM-CSF or rbolL-1beta at cessation of milking immediately increased the number of phagocytic cells in the gland. These cytokines, in particular rbolL-1beta, also increased the rate of mammary gland involution during the early dry period. 相似文献
153.
Assessment of organometal pollution requires an understanding of the various processes that influence the bioavailability and toxicity of the contaminant. Organotins may exist as both cationic species and neutral hydroxides in aqueous solution, with the formation of chloride species in the presence of Cl-. Although these species have different chemical properties, there is very little information on the influence of speciation on organotin and microbial cell interactions. Tributyltin (TBT) and triphenyltin (TPT) interactions with the yeast Candida maltosa were investigated between pH 3.5 and 7.5 and in up to 0.5 M NaCl at pH 5.5. Toxicity increased with both pH and NaCl concentration and the mechanisms of interaction depended on the species present in solution. TBT and TPT interacted by different mechanisms, as evidenced by action on membrane fluidity. Furthermore, there was a strong correlation between toxicity and overall octanol-water distribution ratio (D(OW)) of organotin compounds. Triorganotin cations are less toxic than triorganotin hydroxides, which are in turn less toxic than triorganotin chlorides. These findings underline the importance of speciation effects on organotin interactions in the environment. 相似文献
154.
Tristan F. Burns Kraft Barbara M. Schmidt G.G. Yousef Christopher T.G. Knight Muriel Cuendet Young-Hwa Kang John M. Pezzuto David S. Seigler Mary Ann Lila 《Journal of food science》2005,70(3):S159-S166
ABSTRACT: Wild lowbush blueberry fruit extract was fractionated using vacuum chromatography and analyzed for chemopreventive potential using bioassays that test the ability of compounds to inhibit the initiation, promotion, and progression stages of carcinogenesis. A fraction containing phytosterols was active against the initiation stage (quinone reductase assay). However, more polar compounds were inhibitors of later stages of carcinogenesis; a fraction containing flavan-3-ols and fractions containing mainly anthocyanins, phenolic acids, flavan-3-ols, and some proanthocyanidin dimers demonstrated activity against the promotion stage (cyclooxygenase and ornithine decarboxylase assays, respectively), and a proanthocyanidin-rich fraction demonstrated antiproliferation activity (inhibition of cancerous murine hepatocyte proliferation is associated with the progression stage). These results indicate that lowbush blueberries contain a range of compounds that have bioactivity against multiple stages of carcinogenesis, and different types of phenolic compounds are active at different stages. 相似文献
155.
Josefina Reyes-Carmona Gad G. Yousef Ramon A. Martínez-Peniche Mary Ann Lila 《Journal of food science》2005,70(7):s497-s503
A range of blackberry genotypes harvested in different seasons and regions in Mexico (Michoacan) and in the United States (Pacific Northwest) were collected to determine their antioxidant capacity using oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) assays. Total acidity, ascorbic acid, soluble solids, total phenols, and total anthocyanins, as well as the correlation between all these parameters, were determined for all treatments. Total acidity ranged from 4.22% in wild blackberry from Patzcuaro, Mexico, to 1.02% in ‘Evergreen’ from Woodburn, Oreg. These treatments were also the outliers in terms of ascorbic acid content. Cultivar ‘Brazos’ did not exhibit any significant differences in acidity or ascorbic acid as a consequence of the geographic origin or harvest season. The highest concentration of soluble solids was recorded for ‘Evergreen’ from Woodburn and relatively low soluble solids levels were recorded for all the Mexican treatments. Wild blackberry from Patzcuaro exhibited the highest values for ORAC, FRAP, total phenolic and anthocyanin content. Other relatively high antioxidant capacity values were detected for ‘Marion’ and ‘Evergreen’, both produced in Oregon. Different cultivars grown in the same region/season consistently showed differences in antioxidant capacity. There was little effect of harvest season on phenolic levels. We conclude that levels of total acidity, ascorbic acid, soluble solids, antioxidant capacity, and polyphenols mainly depended on the genotype and not on the climate or the season. ORAC and FRAP values were both highly correlated with each other, and with total phenols and anthocyanin content. 相似文献
156.
G. X. Wang Y. Chen K. Konstantinov Jane Yao Jung-ho Ahn H. K. Liu S. X. Dou 《Journal of Alloys and Compounds》2002,340(1-2):L5-L10
Nanosize cobalt oxides (Co3O4) were synthesised by chemical decomposition of cobalt octacarbonyl in toluene at low temperature. Electrochemical properties of as-prepared Co3O4 as anodes in Li-ion cells were tested. The nanosized Co3O4 electrode demonstrate a stable reversible lithium storage capacity of 360 mAh/g within 30 cycles. The reactivity of as-prepared Co3O4 in Li-ion cells could be attributed to nanosize particles of Co3O4 and its lithiation products. 相似文献
157.
William M. Pitts Martin Werrel Marco Fernandez Mary A. Long Evan A. Eisenberg James Filliben Cory D. Runyon 《火与材料》2021,45(1):127-154
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF. 相似文献
158.
159.
Jane Turner John E. Snawder Alina Handorean Kevin M. McCabe 《Aerosol science and technology》2013,47(8):599-610
Epidemiological studies have shown that exposure to airborne particulate matter (PM) can be an important risk factor for some common respiratory diseases. While many studies have shown that PM exposures are associated with inflammatory reactions, the role of specific cellular responses in the manifestation of primary hypersensitivities and the progression of respiratory diseases remains unclear. In order to better understand mechanisms by which PM can exert adverse health effects, more robust approaches to support in vitro studies are warranted. In response to this need, a group of accepted toxicology assays was adapted to create an analytical suite for screening and evaluating the effects of important, ubiquitous atmospheric pollutants on two model human lung cell lines (epithelial and immature macrophage). To demonstrate the utility of this suite, responses to intact diesel exhaust particles (DEP) and mass-based equivalent doses of their organic extracts were examined. Results suggest that extracts have the potential to induce greater biological responses than those associated with their colloidal counterpart. Additionally, macrophage cells appear to be more susceptible to the cytotoxic effects of both intact DEP and their organic extract, than epithelial cells tested in parallel. As designed, the suite provided a more robust basis for characterizing toxicity mechanisms than the analysis of any individual assay. Findings suggest that cellular responses to PM are cell line dependent, and show that the collection and preparation of PM and/or their extracts have the potential to impact cellular responses relevant to screening fundamental elements of respiratory toxicity.Copyright 2015 American Association for Aerosol Research 相似文献
160.
Mary Sumner 《Information Systems Management》2013,30(2):28-34
Experience indicates that a change in technology must be accompanied by user education. It is not the technology alone, but the way in which the technology is planned, designed, and implemented that determines the success of change. Employees must not only understand the applications of office technologies but also deal with the organizational impact of change. Successful development of office automation systems must involve users, management, and systems professionals in the planning, design, and implementation of change. 相似文献