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   1717篇
  免费   193篇
  国内免费   2篇
电工技术   24篇
综合类   1篇
化学工业   551篇
金属工艺   16篇
机械仪表   50篇
建筑科学   66篇
矿业工程   3篇
能源动力   50篇
轻工业   347篇
水利工程   12篇
石油天然气   9篇
无线电   119篇
一般工业技术   266篇
冶金工业   118篇
原子能技术   8篇
自动化技术   272篇
  2024年   5篇
  2023年   42篇
  2022年   106篇
  2021年   133篇
  2020年   70篇
  2019年   79篇
  2018年   90篇
  2017年   80篇
  2016年   95篇
  2015年   77篇
  2014年   110篇
  2013年   137篇
  2012年   138篇
  2011年   137篇
  2010年   94篇
  2009年   53篇
  2008年   74篇
  2007年   64篇
  2006年   57篇
  2005年   45篇
  2004年   26篇
  2003年   24篇
  2002年   22篇
  2001年   10篇
  2000年   8篇
  1999年   9篇
  1998年   30篇
  1997年   22篇
  1996年   15篇
  1995年   10篇
  1994年   5篇
  1993年   11篇
  1992年   4篇
  1991年   4篇
  1990年   4篇
  1988年   1篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1981年   3篇
  1980年   2篇
  1978年   2篇
  1977年   2篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1968年   1篇
  1959年   1篇
排序方式: 共有1912条查询结果,搜索用时 31 毫秒
991.
992.
Though the process of composting features a high microbiological activity, its potential to methylate metals and metalloids has been little investigated so far in spite of the high impact of this process on metal(loid) toxicity and mobility. Here, we studied the biotransformation of arsenic, tellurium, antimony, tin and germanium during composting. Time resolved investigation revealed a highly dynamic process during self-heated composting with markedly differing time patterns for arsenic and tellurium species. Extraordinary high concentrations of up to 150 mg kg(-1) methylated arsenic species as well as conversion rates up to 50% for arsenic and 5% for tellurium were observed. In contrast, little to no conversion was observed for antimony, tin and germanium. In addition to experiments with metal(loid) salts, composting of arsenic hyperaccumulating ferns Pteris vittata and P. cretica grown on As-amended soils was studied. Arsenic accumulated in the fronds was efficiently methylated resulting in up to 8 mg kg(-1) methylated arsenic species. Overall, these studies indicate that metal(loid)s can undergo intensive biomethylation during composting. Due to the high mobility of methylated species this process needs to be considered in organic waste treatment of metal(loid) contaminated waste materials.  相似文献   
993.
DNA-based single-molecule studies, nanoelectronics and nanocargos require a precise placement of DNA in an orientation-defined manner. Until now, there is a lack of orientation-defined alignment and immobilization of DNA over distances smaller than several micrometers. However, this can be realized by designing bifunctionalized DNA with thiol at one end and (3-aminopropyl) tri-ethoxy silane at the other end, which specifically binds to a gold and SiO? layer after and during alignment, respectively. The electrode assembly consists of platinum as the electrode material for applying the AC voltage and islands of gold and silicon dioxide fabricated at a distance of about 500-800 nm by electron-beam lithography. The orientation-defined alignment and covalent binding of pUC19 DNA to specific surfaces are carried out in frequency ranges of 50 Hz-1 kHz and 100 kHz-1 MHz and observed after metallization of DNA by palladium ions by field emission scanning electron microscopy (FESEM). The bifunctionalized 890 nm long DNA was effectively aligned and immobilized between a gap of 500 to 600 nm width.  相似文献   
994.
In industry as well as many areas of scientific research, data collected often contain a number of responses of interest for a chosen set of exploratory variables. Optimization of such multivariable multiresponse systems is a challenge well suited to genetic algorithms as global optimization tools. One such example is the optimization of coating surfaces with the required absolute and relative sensitivity for detecting analytes using devices such as sensor arrays. High-throughput synthesis and screening methods can be used to accelerate materials discovery and optimization; however, an important practical consideration for successful optimization of materials for arrays and other applications is the ability to generate adequate information from a minimum number of experiments. Here we present a case study to evaluate the efficiency of a novel evolutionary model-based multiresponse approach (EMMA) that enables the optimization of a coating while minimizing the number of experiments. EMMA plans the experiments and simultaneously models the material properties. We illustrate this novel procedure for materials optimization by testing the algorithm on a sol-gel synthetic route for production and optimization of a well studied amino-methyl-silane coating. The response variables of the coating have been optimized based on application criteria for micro- and macro-array surfaces. Spotting performance has been monitored using a fluorescent dye molecule for demonstration purposes and measured using a laser scanner. Optimization is achieved by exploring less than 2% of the possible experiments, resulting in identification of the most influential compositional variables. Use of EMMA to optimize control factors of a product or process is illustrated, and the proposed approach is shown to be a promising tool for simultaneously optimizing and modeling multivariable multiresponse systems.  相似文献   
995.
In recent years, a lot of scientific effort has been put into reusing the energy potential of sugarcane vinasse by dark fermentation. However, the findings so far indicate that new pathways need to be followed. In this context, this study assessed the effect of hydraulic retention time (HRT, from 24 to 1 h) on vinasse fermentation (10, 20, and 30 g COD L?1) in three mesophilic expanded granular sludge bed reactors (EGSB). The carbohydrate conversion remained above 60% at all organic loading rates applied. The maximum hydrogen production rate (8.77 L day?1 L?1) was obtained for 720 kg COD m?3 day?1 and associated to the lactate-acetate pathway. The highest productivities of propionic, acetic, and butyric acids were 3.11, 1.68, and 2.45 g L?1 h?1, respectively, at a HRT of 1 h. At this HRT, the degrees of acidification remained between 54% and 76% in all EGSB reactors. This research provides insights for carboxylate production from sugarcane vinasse and suggests applying the EGSB setup in the acidogenic stage of two-stage processes.  相似文献   
996.
Probiotic properties of Lactobacillus amylovorus DSM 16698 were previously demonstrated in piglets. Here, its potential as a human probiotic was studied in vitro, using the TIM-1 system, which is fully validated to simulate the human upper gastrointestinal tract. To evaluate the effect of the food matrix composition on the survival of L. amylovorus DSM 16698 in TIM-1, the microorganism was inoculated alone or with prebiotic galactooligosaccharides (GOS), partially skimmed milk (PSM) and/or commercial probiotic Bifidobacterium animalis subsp. lactis Bb-12 (Bb-12). Samples were collected from TIM-1 for six hours, at one-hour intervals and L. amylovorus populations were enumerated on MRS agar plates with confirmation of identity of selected isolates by randomly amplified polymorphic DNA (RAPD) fingerprinting. The cumulative survival for L. amylovorus alone (control) was 30% at the end of the experiment (t = 6 h). Co-administration of L. amylovorus with GOS, PSM and/or Bb-12 increased its survival in comparison with the control significantly from the 4th hour after ingestion onwards (P < 0.05). Furthermore, by the use of High Performance Anion Exchange Chromatography, both L. amylovorus and Bb-12 were observed to promptly degrade GOS compounds in samples collected from TIM-1, as assessed at t = 2 h. Hence, food matrix composition interfered with survival and growth of L. amylovorus during passage through TIM-1, providing leads towards optimization of probiotic properties in vivo.  相似文献   
997.
Conjugated linoleic acid (CLA) has a range of biological properties, including effects on lipid metabolism, milk and body composition in animals. This study investigated the effects of dietary CLA on lactating rats and development of the suckling pups. Dams were fed either a control diet or the same diet supplemented with 25 g/kg of a fat supplement containing 540 g CLA/kg (final concentration of 13.5 g CLA/kg diet) from parturition to the 15th day post-partum. The CLA mixture used in this study contained the following isomers (per 100 g): cis-9, trans-11 (24 g); cis-10, trans-12 (35 g); cis-8, trans-10 (15 g); cis-11, trans-13 (17 g) and others (9 g). On d 15 post partum, CLA supplementation reduced milk fat content by 33% and pup growth by 21%. The milk fatty acid profile, with decreased content of short and medium chain acids, suggests CLA inhibition was more pronounced for de novo lipid synthesis. Consistent with these results, activities of fatty acid synthase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were reduced by CLA treatment in the mammary gland and liver. In contrast, the activity of NADP-malate dehydrogenase was unchanged.  相似文献   
998.
The female prostate is a differentiated organ found in several mammal species, including humans and rodents. This gland has been related to important functions on female reproductive biology. Although the factors, which regulate prostate's development and activity are not well known, its functionality has been related to steroid hormones. It is well established that cyclic changes of estradiol and progesterone levels promote histophysiological adaptations of the whole female body. In contrast, only a few is found about those adaptations in female prostate. Thus, this study aimed to evaluate the effect of estradiol and estradiol + testosterone association on gerbil female prostate in order to verify, which hormonal associations are necessary to its homeostasis. For this, adult females had the ovaries surgically removed. After recovering, they received estradiol and estradiol + testosterone doses through 30 days, each 48 h. The prostatic tissue underwent morphological and morphometric‐estereological analysis. Hormonal restriction caused great gland involution and decreased secretory activity, aspects that were reverted by exposure to estradiol and estradiol + testosterone. However, these hormones were not able to re‐establish the normal prostate histoarchitecture. The immunoreaction of steroid receptors (ER‐α, ER‐β, and AR) responded differently among the experimental and control groups, and PCNA assay showed a decrease in epithelial cell proliferation within groups that had hormone privation. Therefore, we conclude that estradiol and testosterone are able to influence prostate morphophysiology and the maintenance of gland homeostasis depends on a balance among these and other hormones. Microsc. Res. Tech. 76:486–495, 2013. © 2013 Wiley Periodicals, Inc.  相似文献   
999.
Curcumin, a yellow polyphenol extracted from the turmeric root is used as a diet supplement. It exhibits anti-inflammatory, antioxidant, and antitumor properties by modulating different intracellular mechanisms. Due to their low solubility in water, the curcumin molecules must be encapsulated into liposomes to improve the bioavailability and biomedical potential. For the periodontal tissue and systemic health, it is essential to regulate the local inflammatory response. In this study, the possible beneficial effect of liposomes loaded with curcumin (CurLIP) in neural crest-derived human periodontal ligament stem cells (hPDLSCs) and in endothelial-differentiated hPDLSCs (e-hPDLSCs) induced with an inflammatory stimulus (lipopolysaccharide obtained from Porphyromonas gingivalis, LPS-G) was evaluated. The CurLIP formulation exhibited a significant anti-inflammatory effect by the downregulation of Toll-like receptor-4 (TLR4)/Myeloid differentiation primary response 88 (MyD88)/nuclear factor kappa light chain enhancer of activated B cells (NFkB)/NLR Family Pyrin Domain Containing 3 (NLRP3)/Caspase-1/Interleukin (IL)-1β inflammation cascade and reactive oxygen species (ROS) formation. Moreover, the exposure to LPS-G caused significant alterations in the expression of epigenetic modifiers, such as DNA Methyltransferase 1 (DNMT1) and P300, while the CurLIP treatment showed physiological expression. Overall, our in vitro study provides novel mechanistic insights into the intracellular pathway exert by CurLIP in the regulation of inflammation and epigenetic modifications.  相似文献   
1000.

Aims

The relationship between variants in SLCO1B1 and SLCO2B1 genes and lipid-lowering response to atorvastatin was investigated.

Material and Methods

One-hundred-thirty-six unrelated individuals with hypercholesterolemia were selected and treated with atorvastatin (10 mg/day/4 weeks). They were genotyped with a panel of ancestry informative markers for individual African component of ancestry (ACA) estimation by SNaPshot® and SLCO1B1 (c.388A>G, c.463C>A and c.521T>C) and SLCO2B1 (−71T>C) gene polymorphisms were identified by TaqMan® Real-time PCR.

Results

Subjects carrying SLCO1B1 c.388GG genotype exhibited significantly high low-density lipoprotein (LDL) cholesterol reduction relative to c.388AA+c.388AG carriers (41 vs. 37%, p = 0.034). Haplotype analysis revealed that homozygous of SLCO1B1*15 (c.521C and c.388G) variant had similar response to statin relative to heterozygous and non-carriers. A multivariate logistic regression analysis confirmed that c.388GG genotype was associated with higher LDL cholesterol reduction in the study population (OR: 3.2, CI95%:1.3–8.0, p < 0.05).

Conclusion

SLCO1B1 c.388A>G polymorphism causes significant increase in atorvastatin response and may be an important marker for predicting efficacy of lipid-lowering therapy.  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