全文获取类型
收费全文 | 2002篇 |
免费 | 81篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 23篇 |
综合类 | 5篇 |
化学工业 | 513篇 |
金属工艺 | 29篇 |
机械仪表 | 39篇 |
建筑科学 | 120篇 |
矿业工程 | 32篇 |
能源动力 | 37篇 |
轻工业 | 155篇 |
水利工程 | 29篇 |
石油天然气 | 4篇 |
无线电 | 135篇 |
一般工业技术 | 310篇 |
冶金工业 | 148篇 |
原子能技术 | 5篇 |
自动化技术 | 505篇 |
出版年
2023年 | 23篇 |
2022年 | 43篇 |
2021年 | 60篇 |
2020年 | 29篇 |
2019年 | 26篇 |
2018年 | 59篇 |
2017年 | 51篇 |
2016年 | 79篇 |
2015年 | 69篇 |
2014年 | 80篇 |
2013年 | 94篇 |
2012年 | 110篇 |
2011年 | 134篇 |
2010年 | 78篇 |
2009年 | 116篇 |
2008年 | 103篇 |
2007年 | 89篇 |
2006年 | 99篇 |
2005年 | 69篇 |
2004年 | 63篇 |
2003年 | 46篇 |
2002年 | 53篇 |
2001年 | 31篇 |
2000年 | 29篇 |
1999年 | 35篇 |
1998年 | 33篇 |
1997年 | 36篇 |
1996年 | 37篇 |
1995年 | 38篇 |
1994年 | 30篇 |
1993年 | 20篇 |
1992年 | 15篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 14篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1973年 | 4篇 |
1971年 | 6篇 |
排序方式: 共有2089条查询结果,搜索用时 15 毫秒
991.
992.
993.
Rahmer J Weizenecker J Gleich B Borgert J 《IEEE transactions on medical imaging》2012,31(6):1289-1299
Magnetic particle imaging (MPI) is a new tomographic imaging approach that can quantitatively map magnetic nanoparticle distributions in vivo. It is capable of volumetric real-time imaging at particle concentrations low enough to enable clinical applications. For image reconstruction in 3-D MPI, a system function (SF) is used, which describes the relation between the acquired MPI signal and the spatial origin of the signal. The SF depends on the instrumental configuration, the applied field sequence, and the magnetic particle characteristics. Its properties reflect the quality of the spatial encoding process. This work presents a detailed analysis of a measured SF to give experimental evidence that 3-D MPI encodes information using a set of 3-D spatial patterns or basis functions that is stored in the SF. This resembles filling 3-D k-space in magnetic resonance imaging, but is faster since all information is gathered simultaneously over a broad acquisition bandwidth. A frequency domain analysis shows that the finest structures that can be encoded with the presented SF are as small as 0.6 mm. SF simulations are performed to demonstrate that larger particle cores extend the set of basis functions towards higher resolution and that the experimentally observed spatial patterns require the existence of particles with core sizes of about 30 nm in the calibration sample. A simple formula is presented that qualitatively describes the basis functions to be expected at a certain frequency. 相似文献
994.
Exposure of an adult population to perfluorinated substances using duplicate diet portions and biomonitoring data 总被引:4,自引:0,他引:4
Fromme H Schlummer M Möller A Gruber L Wolz G Ungewiss J Böhmer S Dekant W Mayer R Liebl B Twardella D 《Environmental science & technology》2007,41(22):7928-7933
Because dietary intake is supposed to be an important route of human exposure we quantified the dietary intake of perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorohexane sulfonate (PFHxS), perfluorohexanoate (PFHxA), and perfluorooctane sulfonamide (PFOSA) using 214 duplicate diet samples. The study was carried out with a study population of 15 female and 16 male healthy subjects aged 16-45 years. The participants collected daily duplicate diet samples over seven consecutive days in 2005. Duplicate samples were homogenized and their ultrasonic extracts were cleaned up by SPE and subjected to HPLC-ESI-MS/MS. In addition, individual intakes were estimated based on blood levels of PFOS and PFOA using a pharmacokinetic model. Blood samples were collected once during the sampling period. The median (90th percentile) daily dietary intake of PFOS and PFOA was 1.4 ng/kg b.w. (3.8 ng/kg b.w.) and 2.9 ng/kg b.w. (8.4 ng/kg b.w.), respectively. PFHxS and PFHxA could be detected only in some samples above detection limit with median (maximum) daily intakes of 2.0 ng/kg b.w. (4.0 ng/kg b.w.) and 4.3 ng/kg b.w. (9.2 ng/kg b.w.), respectively. Because PFOSA could not be detected above the limit of detection of 0.2 ng/g f.w. this indirect route of exposure seems to be of less significance. Overall, the results of this study demonstrate that the German population is exposed to PFOS and PFOA, but the median dietary intake did not reach the recommended tolerable daily intake by far. Biomonitoring data predict an exposure in a comparable range. We suppose that, normally, food intake is the main source of exposure of the general population to PFOS and PFOA. 相似文献
995.
996.
Bastian Tewes Dr. Bastian Frehland Dirk Schepmann Dr. Kai‐Uwe Schmidtke Thomas Winckler Prof. Dr. Bernhard Wünsch Prof. Dr. 《ChemMedChem》2010,5(5):687-695
Cleavage and reconstitution of a bond in the piperidine ring of ifenprodil ( 1 ) leads to 7‐methoxy‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepin‐1‐ols, a novel class of NR2B‐selective NMDA receptor antagonists. The secondary amine 7‐methoxy‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepin‐1‐ol ( 12 ), which was synthesized in six steps starting from 2‐phenylethylamine 3 , represents the central building block for the introduction of several N‐linked residues. A distance of four methylene units between the basic nitrogen atom and the phenyl residue in the side chain results in high NR2B affinity. The 4‐phenylbutyl derivative 13 (WMS‐1405, Ki=5.4 nM ) and the conformationally restricted 4‐phenylcyclohexyl derivative 31 (Ki=10 nM ) represent the most potent NR2B ligands of this series. Whereas 13 shows excellent selectivity, the 4‐phenylcyclohexyl derivative 31 also interacts with σ1 (Ki=33 nM ) and σ2 receptors (Ki=82 nM ). In the excitotoxicity assay the phenylbutyl derivative 13 inhibits the glutamate‐induced cytotoxicity with an IC50 value of 360 nM , indicating that 13 is an NMDA antagonist. 相似文献
997.
Elvira Ruppel Dr. Bernhard Aÿ Dr. Prisca Boisguerin Sabine Dölle Prof. Dr. Margitta Worm Dr. Rudolf Volkmer 《Chembiochem : a European journal of chemical biology》2010,11(16):2283-2293
Celery is a frequent cause of food allergy in pollen‐sensitized patients and can induce severe allergic reactions. Clinical symptoms cannot be predicted by skin prick tests (SPTs) or by determining allergen‐specific immunoglobulin E (IgE). Our aim was to identify specific IgE binding peptides by using an array technique. For our study, the sera of 21 patients with positive double‐blind, placebo‐controlled food challenge (DBPCFC) to celery, as well as the sera of 17 healthy patients were used. Additionally, all patients underwent skin tests along with determinations of specific IgE binding. The major allergen of celery Api g 1.0101 (Apium graveolens) was synthesized as an array of overlapping peptides and probed with the patients' sera. We developed an improved immunoassay protocol by investigating peptide lengths, peptide densities, incubation parameters, and readout systems, which could influence IgE binding. Sera of celery‐allergic patients showed binding to three distinct regions of Api g 1.0101. The region including amino acids 100 to 126 of Api g 1.0101 is the most important region for IgE binding. This region caused a fivefold higher binding of IgE from the sera of celery‐allergic patients compared to those of healthy individuals. In particular, one peptide (VLVPTADGGSIC) was recognized by all sera of celery‐allergic patients. In contrast, no binding to this peptide was detected in sera of the healthy controls. Our improved assay strategy allows us to distinguish between celery‐allergic and healthy individuals, but needs to be explored in a larger cohort of well‐defined patients. 相似文献
998.
Jakob Svehla Silvia Pabisch Bernhard Feichtenschlager Dietmar Holzmann Herwig Peterlik Guido Kickelbick 《大分子材料与工程》2012,297(3):219-227
A novel zirconia polyester nanocomposite is prepared using an in situ approach. Surface‐functionalized zirconia nanoparticles are obtained by attaching 3‐phosphonopropionic acid to the metal oxide. Neat and surface‐covered metal oxide particles are incorporated at the beginning of the polyesterification reaction of isophthalic acid and neopentyl glycol resulting in zirconia/poly(neopentyl isophthalate) (PNI) nanocomposites. TEM shows that the dispersibility of the inorganic filler is improved by covering the zirconia surface with carboxylic acid groups. These results are verified by SAXS. Rheological measurements reveal that the viscosities are increasing compared to pristine PNI at particle loads of 10 wt% (neat zirconia) and 5 wt% (phosphonic‐acid‐capped zirconia), respectively.
999.
Concentrations and stable isotope compositions of nitrate from 11 karst springs in the Franconian Alb (southern Germany) were determined during low flow and high flow conditions to assess sources and processes affecting groundwater nitrate. During low flow, nitrate concentrations in groundwater were around 0.10 mM in springs draining forested catchments, whereas in agricultural areas nitrate concentrations were typically higher reaching up to 0.93 mM. The isotopic composition of groundwater nitrate during low flow (delta15N values of -3.1 to 6.7% per hundred, delta180 values of +2.1 to 4.0% per hundred) in concert with concentration data suggests that nitrate is formed by nitrification in forest and agricultural soils. In addition, synthetic fertilizer N that has undergone immobilization and subsequent remineralization likely constitutes an additional nitrate source in agriculturally used catchments. During recharge conditions, concentrations and delta15N values of groundwater nitrate changed little, but delta18O values were significantly elevated (up to 24.5%o per hundred suggesting that around 25% of the nitrate was directly derived from atmospheric deposition. Groundwater dating revealed that low nitrate concentrations in groundwater (_> or =0 years) are consistent with a mixture of old low nitrate-containing and young water, the latter being affected by anthropogenic N inputs predominantly in the agriculturally used catchment areas during the last few decades. Thermodynamic and hydrogeological evidence also suggests that denitrification may have occurred in the porous rock matrix of the karst aquifer. This study demonstrates that a combination of hydrodynamic, chemical, and isotopic approaches provides unique insights into the sources and the biogeochemical history of nitrate in karst aquifers, and therefore constitutes a valuable tool for assessing the vulnerability of karst aquifers to nitrate pollution in dependence on land use and assessing their self-purification capacity. 相似文献
1000.
Benton HP Want E Keun HC Amberg A Plumb RS Goldfain-Blanc F Walther B Reily MD Lindon JC Holmes E Nicholson JK Ebbels TM 《Analytical chemistry》2012,84(5):2424-2432
Liquid chromatography coupled to mass spectrometry (LC-MS) is a major platform in metabolic profiling but has not yet been comprehensively assessed as to its repeatability and reproducibility across multiple spectrometers and laboratories. Here we report results of a large interlaboratory reproducibility study of ultra performance (UP) LC-MS of human urine. A total of 14 stable isotope labeled standard compounds were spiked into a pooled human urine sample, which was subject to a 2- to 16-fold dilution series and run by UPLC coupled to time-of-flight MS at three different laboratories all using the same platform. In each lab, identical samples were run in two phases, separated by at least 1 week, to assess between-day reproducibility. Overall, platform reproducibility was good with median mass accuracies below 12 ppm, median retention time drifts of less than 0.73 s and coefficients of variation of intensity of less than 18% across laboratories and ionization modes. We found that the intensity response was highly linear within each run, with a median R(2) of 0.95 and 0.93 in positive and negative ionization modes. Between-day reproducibility was also high with a mean R(2) of 0.93 for a linear relationship between the intensities of ions recorded in the two phases across the laboratories and modes. Most importantly, between-lab reproducibility was excellent with median R(2) values of 0.96 and 0.98 for positive and negative ionization modes, respectively, across all pairs of laboratories. Interestingly, the three laboratories observed different amounts of adduct formation, but this did not appear to be related to reproducibility observed in each laboratory. These studies show that UPLC-MS is fit for the purpose of targeted urinary metabolite analysis but that care must be taken to optimize laboratory systems for quantitative detection due to variable adduct formation over many compound classes. 相似文献