首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1315篇
  免费   80篇
  国内免费   2篇
电工技术   38篇
综合类   2篇
化学工业   398篇
金属工艺   10篇
机械仪表   30篇
建筑科学   45篇
能源动力   44篇
轻工业   160篇
水利工程   10篇
石油天然气   5篇
无线电   143篇
一般工业技术   205篇
冶金工业   62篇
原子能技术   8篇
自动化技术   237篇
  2024年   4篇
  2023年   23篇
  2022年   35篇
  2021年   95篇
  2020年   46篇
  2019年   48篇
  2018年   51篇
  2017年   37篇
  2016年   52篇
  2015年   34篇
  2014年   83篇
  2013年   82篇
  2012年   88篇
  2011年   102篇
  2010年   81篇
  2009年   58篇
  2008年   51篇
  2007年   60篇
  2006年   59篇
  2005年   34篇
  2004年   30篇
  2003年   30篇
  2002年   20篇
  2001年   21篇
  2000年   10篇
  1999年   13篇
  1998年   17篇
  1997年   21篇
  1996年   15篇
  1995年   14篇
  1994年   6篇
  1993年   11篇
  1992年   4篇
  1991年   6篇
  1990年   9篇
  1989年   6篇
  1988年   6篇
  1985年   7篇
  1983年   4篇
  1982年   1篇
  1981年   2篇
  1980年   4篇
  1979年   2篇
  1978年   2篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1974年   2篇
  1970年   1篇
  1969年   1篇
排序方式: 共有1397条查询结果,搜索用时 828 毫秒
251.
In this study, poly(dl ‐lactide‐co‐glycolide)/porous silicon (PLGA/pSi) composite microspheres, synthesized by a solid‐in‐oil‐in‐water (S/O/W) emulsion method, are developed for the long‐term controlled delivery of biomolecules for orthopedic tissue engineering applications. Confocal and fluorescent microscopy, together with material analysis, show that each composite microsphere contained multiple pSi particles embedded within the PLGA matrix. The release profiles of fluorescein isothiocyanate (FITC)‐labeled bovine serum albumin (FITC‐BSA), loaded inside the pSi within the PLGA matrix, indicate that both PLGA and pSi contribute to the control of the release rate of the payload. Protein stability studies show that PLGA/pSi composite can protect BSA from degradation during the long term release. We find that during the degradation of the composite material, the presence of the pSi particles neutralizes the acidic pH due to the PLGA degradation by‐products, thus minimizing the risk of inducing inflammatory responses in the exposed cells while stimulating the mineralization in osteogenic growth media. Confocal studies show that the cellular uptake of the composite microspheres is avoided, while the fluorescent payload is detectable intracellularly after 7 days of co‐incubation. In conclusion, the PLGA/pSi composite microspheres offer an additional level of controlled release and could be ideal candidates as drug delivery vehicles for orthopedic tissue engineering applications.  相似文献   
252.
253.
In this work, the crossflow microfiltration (CFMF) performance of different lots of lager beer, produced in a pilot scale at the Italian Brewing Research Centre (CERB, Perugia, Italy), was assessed in a bench-top plant, equipped with a 0.8-μm ceramic tubular membrane module, under constant crossflow velocity of 6 m s?1, transmembrane pressure difference of 3.74 bar, temperature of ~10 °C, and periodic CO2 backflushing. By feeding different beer samples (i.e., as such, precentrifuged (C), or pretreated with a commercial enzyme preparation to degrade the original arabinoxylans and β-glucans and then centrifuged (EC) to minimize the fouling contribution of yeast cells, aggregates, and polysaccharides), it was possible to increase the average permeation flux (expressed as mean value?±?standard deviation) from 112?±?13 to 199?±?17 or 330?±?22 L m?2 h?1, respectively. Only when using the EC-pretreated beer specimens, the permeate turbidity at 20 °C approached the limiting one (<0.6 EBC unit) recommended by the European Brewery Convention standards. As expected, the permeate chill haze at 0 °C was generally higher than the above haze target. By submitting EC-pretreated beer seeded with 0.5 g L?1 of regenerable polyvinylpolypyrrolidone (PVPP) to CFMF, it was possible to reduce the initial total polyphenol content by 30 % and permeate chill haze to 0.60?±?0.01 EBC unit, but the average permeation flux fell to 84?±?4 L m?2 h?1. By performing sequentially EC pretreatments, PVPP stabilization, cartridge filtration, and CFMF, it was possible not only to re-enhance the average permeation flux at about 230 L m?2 h?1 near to those achievable with DE filters, but also to obtain a chill haze-free permeate ready for aseptic packaging.  相似文献   
254.
F2-isoprostanes are a biomarker of lipid peroxidation, and their measurement has emerged as a reliable approach to assess oxidative stress. However, dietary intervention studies in humans have provided contrasting results following supplementation with antioxidant-rich foods or supplements. In this paper, we have systematically reviewed the evidence about the effect of supplementation with antioxidant-rich foods and galenic antioxidants on isoprostanes levels in humans. Moreover, the association with nonenzymatic antioxidant capacity (NEAC), a biomarker of endogenous antioxidant status, has also been investigated.

MEDLINE database was searched using the terms “(isoprostane* OR isoP OR iso-PGF OR epi-PGF) AND (intervention* OR consumption* OR administration* OR supplementation*),” with limits activated “humans” and “English.” Abstracts and full texts were screened, from which were selected human intervention studies reporting isoprostanes measurement in biological fluids. The total of the studies carried out with antioxidant-rich foods and antioxidant galenic supplements was 113, reporting 154 interventions. Results suggest that dietary antioxidants modulate successfully the levels of isoprostanes in less than 45% of the interventions. A correspondence between the effect on isoprostane and NEAC has been evidenced, and this correspondence suggests the importance of measuring different biomarkers to obtain a better outline of the redox events following supplementation.  相似文献   

255.
The objective of this on-farm study was to determine the effect of corn planting density on the nutritional quality of whole-plant corn for silage. This study was performed in a commercial 1,900-cow dairy farm located in Piedritas (Buenos Aires, Argentina). Two commercial hybrids (A and B) were planted in experimental plots within a cornfield destined for corn silage. Hybrids were sown at a theoretical seeding rate of 60,000, 70,000, 80,000, and 90,000 seeds/ha in 4 replicates per hybrid. Plots were eight 50-m-long rows separated by 52 cm. Corn was planted with a no-till seeder equipped with a pneumatic dosing machine. Ten plants within each plot were cut by hand at 15 cm above ground. Whole plants were chopped, weighed, mixed thoroughly, and frozen until analysis. Nutritional composition was determined by near-infrared reflectance spectroscopy. Harvesting occurred at one-quarter milk-line [31.4% dry matter (DM)] and one-half milk-line (34.5% DM) stages of maturity for hybrids B and A, respectively. No interactions between hybrid and planting density were observed for any of the variables of interest. Planting density did not affect either plant DM weight or DM, crude protein, neutral detergent fiber, acid detergent fiber, or starch concentrations of whole-plant corn. Dry matter yield was significantly increased at higher planting densities. The similar per-plant biomass and nutritional quality among different densities can be explained by the abundant precipitation observed during this growing season (719 mm since the beginning of fallow until harvest). In conclusion, greater yields of silage can be obtained by increasing corn planting density without affecting its nutritional composition, although the effect of planting density with limiting resources (e.g., precipitation) still needs to be elucidated.  相似文献   
256.
Microporous organic polymers (MOPs) are of potential significance for gas storage, gas separation and low-dielectric applications. Among many approaches for obtaining such materials, solution-processable MOPs derived from rigid and contorted macromolecular structures are promising because of their excellent mass transport and mass exchange capability. Here we show a class of amorphous MOP, prepared by [2+3] cycloaddition modification of a polymer containing an aromatic nitrile group with an azide compound, showing super-permeable characteristics and outstanding CO(2) separation performance, even under polymer plasticization conditions such as CO(2)/light gas mixtures. This unprecedented result arises from the introduction of tetrazole groups into highly microporous polymeric frameworks, leading to more favourable CO(2) sorption with superior affinity in gas mixtures, and selective CO(2) transport by presorbed CO(2) molecules that limit access by other light gas molecules. This strategy provides a direction in the design of MOP membrane materials for economic CO(2) capture processes.  相似文献   
257.
Scanning electron microscopy is still the technique of choice for imaging and for in-line measurement of critical dimensions and overlay accuracy in most of the core technology processes. In particular, critical dimension microscopy provides information about design template matching and edge placement errors through links with design having proven beneficial effects on process yield and product reliability. In this paper, the use of high performance computing is demonstrated to simulate linescans and 2D secondary electron images to be used in optical proximity error correction strategies for nanometer scale technologies.  相似文献   
258.
A study was carried out on the presence of Anisakis and Hysterothylacium larvae in fish and cephalopods caught in Sardinian waters. A total of 369 specimens of 24 different species of teleosts and 5 species of cephalopods were collected from different fishing areas of Sardinia. Larvae were detected and isolated by both visual inspection and enzymatic digestion. These methods allowed Anisakis type I and type II third-stage larvae and Hysterothylacium third- and fourth-stage larvae to be detected. The prevalence, mean intensity, and mean abundance were calculated. The results obtained showed the highest prevalence of Anisakidae in Zeus faber (100%) and of Anisakis in Micromesistius poutassou (87.5%). The highest prevalence of Anisakis type I larvae was in M. poutassou (81.2%), and that of Anisakis type II larvae was in Todarodes sagittatus (20%). The highest values for prevalence, mean intensity, and mean abundance for Hysterothylacium were found in Z. faber. These prevalences and the mean intensity and abundance were higher than those reported by different authors in other Mediterranean areas. This may be because the enzymatic digestive method used in this research resulted in higher recovery levels. The data suggest that Sardinia may be a high-risk area for zoonotic diseases and that measures such as information campaigns, aimed at both sanitary service personnel and consumers, should be employed to limit the spread of such zoonosis.  相似文献   
259.
Growth of Listeria monocytogenes in low-acid fruits (melon, watermelon and papaya) at different times of incubation and at temperatures of 10, 20 and 30 degrees C was studied. Fruit pulp portions with an average pH of 5.87, 5.50 and 4.87 for melon, watermelon and papaya, respectively, were obtained aseptically, homogenized, weighed and inoculated with suspensions (approximately 10(2) CFU/g) of L. monocytogenes. Generation times of 7.12, 13.03 and 15.05 h at 10 degrees C, 1.74, 2.17 and 6.42 h at 20 degrees C and 0.84, 1.00 and 1.16 h at 30 degrees C were obtained, respectively, for melon, watermelon and papaya. The results showed that L. monocytogenes grew in low-acid fruits at all tested temperatures, although growth was diminished, but not inhibited at 10 degrees C.  相似文献   
260.
Key features of chronic lymphocytic leukemia (CLL) are defects in the immune system and the ability of leukemic cells to evade immune defenses and induce immunosuppression, resulting in increased susceptibility to infections and disease progression. Several immune effectors are impaired in CLL, including T and natural killer (NK) cells. The role of T cells in defense against CLL and in CLL progression and immunotherapy has been extensively studied. Less is known about the role of NK cells in this leukemia, and data on NK cell alterations in CLL are contrasting. Besides studies showing that NK cells have intrinsic defects in CLL, there is a large body of evidence indicating that NK cell dysfunctions in CLL mainly depend on the escape mechanisms employed by leukemic cells. In keeping, it has been shown that NK cell functions, including antibody-dependent cellular cytotoxicity (ADCC), can be retained and/or restored after adequate stimulation. Therefore, due to their preserved ADCC function and the reversibility of CLL-related dysfunctions, NK cells are an attractive source for novel immunotherapeutic strategies in this disease, including chimeric antigen receptor (CAR) therapy. Recently, satisfying clinical responses have been obtained in CLL patients using cord blood-derived CAR-NK cells, opening new possibilities for further exploring NK cells in the immunotherapy of CLL. However, notwithstanding the promising results of this clinical trial, more evidence is needed to fully understand whether and in which CLL cases NK cell-based immunotherapy may represent a valid, alternative/additional therapeutic option for this leukemia. In this review, we provide an overview of the current knowledge about phenotypic and functional alterations of NK cells in CLL and the mechanisms by which CLL cells circumvent NK cell-mediated immunosurveillance. Additionally, we discuss the potential relevance of using NK cells in CLL immunotherapy.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号