全文获取类型
收费全文 | 3360篇 |
免费 | 144篇 |
专业分类
电工技术 | 26篇 |
综合类 | 1篇 |
化学工业 | 677篇 |
金属工艺 | 31篇 |
机械仪表 | 27篇 |
建筑科学 | 168篇 |
矿业工程 | 4篇 |
能源动力 | 48篇 |
轻工业 | 502篇 |
水利工程 | 42篇 |
石油天然气 | 12篇 |
无线电 | 126篇 |
一般工业技术 | 408篇 |
冶金工业 | 1120篇 |
原子能技术 | 7篇 |
自动化技术 | 305篇 |
出版年
2023年 | 23篇 |
2022年 | 66篇 |
2021年 | 112篇 |
2020年 | 57篇 |
2019年 | 68篇 |
2018年 | 87篇 |
2017年 | 72篇 |
2016年 | 97篇 |
2015年 | 53篇 |
2014年 | 95篇 |
2013年 | 205篇 |
2012年 | 158篇 |
2011年 | 219篇 |
2010年 | 166篇 |
2009年 | 166篇 |
2008年 | 173篇 |
2007年 | 175篇 |
2006年 | 147篇 |
2005年 | 140篇 |
2004年 | 92篇 |
2003年 | 89篇 |
2002年 | 98篇 |
2001年 | 65篇 |
2000年 | 59篇 |
1999年 | 64篇 |
1998年 | 48篇 |
1997年 | 41篇 |
1996年 | 58篇 |
1995年 | 44篇 |
1994年 | 49篇 |
1993年 | 46篇 |
1992年 | 40篇 |
1991年 | 16篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 36篇 |
1987年 | 24篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 20篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 10篇 |
1969年 | 8篇 |
排序方式: 共有3504条查询结果,搜索用时 31 毫秒
31.
LeAnn Southward Hogan Elizabeth Marschall Carol Folt Roy A. Stein 《Journal of Great Lakes research》2007,33(1):46-61
Lake Erie's food web has been dramatically modified by exotic species. Both exotic dreissenid mussels and the round goby Neogobius melanastomus have shifted the food web from a pelagicbased to a benthic-based one, potentially creating a new pathway for contaminant transfer to top predators. Before the invasion of round gobies, few predators of dreissenids occurred in Lake Erie, allowing contaminants to be confined to these benthic organisms. The invasion of the round goby has produced a new pathway through which these contaminants can enter the food web. To characterize heavy-metal transfer through this new food web and to assess risk to humans, water, surficial sediment, dreissenid, round goby, and smallmouth bass Micropterus dolomieui samples were collected at three sites during summers, 2002 and 2003, and analyzed for total lead (Pb), total mercury (Hg), and methyl mercury (MeHg). In addition, we compared smallmouth bass Pb and Hg concentrations to those measured in 1993/1994, before round gobies were prevalent. Pb biodiminished and MeHg biomagnified through the food web to smallmouth bass; patterns were similar among our three sites. Total Pb concentrations in smallmouth bass were higher before the incorporation of round gobies into their diet. We attributed this decline to changes in food web structure, changes in contaminant burdens in prey, or declines in sediment Pb concentrations in Lake Erie. By comparison, Hg concentrations in smallmouth bass changed little, before and after the round goby invasion, possibly due to a shift in diet that increased growth. Despite a decline in sediment Hg concentrations in Lake Erie, smallmouth bass continued to accumulate Hg at historical rates possibly because of their high consumption rates of benthivorous round gobies. As smallmouth bass continue to consume round gobies during their lives, their Hg concentrations may well continue to increase, potentially increasing the risk of Hg contamination to humans. 相似文献
32.
Elizabeth Bradley Robert H. Halstead Jr. 《International journal of parallel programming》1987,16(4):305-338
Circuits, especially logic circuits, are highly concurrent structures: signals flow along many parallel paths at once. This native concurrency, a function of both circuit size and topology, can be exploited in simulating these circuits on parallel machines. Simulation efficiency is affected by machine, language, and simulator implementation parameters like cycle speed, parallelism overhead, and partitioning of the circuit within the simulator, as well as by the amount of native concurrency. The experimental logic simulatorconsim, written in Multilisp and implemented on a 34 element shared-memory multiprocessor, was used to investigate these issues. 相似文献
33.
34.
Michael H. Guerra Thangal Yumnamcha Abdul-Shukkur Ebrahim Elizabeth A. Berger Lalit Pukhrambam Singh Ahmed S. Ibrahim 《International journal of molecular sciences》2021,22(9)
Disruption of retinal pigment epithelial (RPE barrier integrity is a hallmark feature of various retinal blinding diseases, including diabetic macular edema and age-related macular degeneration, but the underlying causes and pathophysiology are not completely well-defined. One of the most conserved phenomena in biology is the progressive decline in mitochondrial function with aging leading to cytopathic hypoxia, where cells are unable to use oxygen for energy production. Therefore, this study aimed to thoroughly investigate the role of cytopathic hypoxia in compromising the barrier functionality of RPE cells. We used Electric Cell-Substrate Impedance Sensing (ECIS) system to monitor precisely in real time the barrier integrity of RPE cell line (ARPE-19) after treatment with various concentrations of cytopathic hypoxia-inducing agent, Cobalt(II) chloride (CoCl2). We further investigated how the resistance across ARPE-19 cells changes across three separate parameters: Rb (the electrical resistance between ARPE-19 cells), α (the resistance between the ARPE-19 and its substrate), and Cm (the capacitance of the ARPE-19 cell membrane). The viability of the ARPE-19 cells and mitochondrial bioenergetics were quantified with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and seahorse technology, respectively. ECIS measurement showed that CoCl2 reduced the total impedance of ARPE-19 cells in a dose dependent manner across all tested frequencies. Specifically, the ECIS program’s modelling demonstrated that CoCl2 affected Rb as it begins to drastically decrease earlier than α or Cm, although ARPE-19 cells’ viability was not compromised. Using seahorse technology, all three concentrations of CoCl2 significantly impaired basal, maximal, and ATP-linked respirations of ARPE-19 cells but did not affect proton leak and non-mitochondrial bioenergetic. Concordantly, the expression of a major paracellular tight junction protein (ZO-1) was reduced significantly with CoCl2-treatment in a dose-dependent manner. Our data demonstrate that the ARPE-19 cells have distinct dielectric properties in response to cytopathic hypoxia in which disruption of barrier integrity between ARPE-19 cells precedes any changes in cells’ viability, cell-substrate contacts, and cell membrane permeability. Such differences can be used in screening of selective agents that improve the assembly of RPE tight junction without compromising other RPE barrier parameters. 相似文献
35.
Alfredo Jurez-Saldivar Elizabeth Barbosa-Cabrera Edgar E. Lara-Ramírez Alma D. Paz-Gonzlez Ana V. Martínez-Vzquez Virgilio Bocanegra-García Isidro Palos Nuria E. Campillo Gildardo Rivera 《International journal of molecular sciences》2021,22(11)
Infectious diseases caused by intestinal protozoan, such as Entamoeba histolytica (E. histolytica) and Giardia lamblia (G. lamblia) are a worldwide public health issue. They affect more than 70 million people every year. They colonize intestines causing primarily diarrhea; nevertheless, these infections can lead to more serious complications. The treatment of choice, metronidazole, is in doubt due to adverse effects and resistance. Therefore, there is a need for new compounds against these parasites. In this work, a structure-based virtual screening of FDA-approved drugs was performed to identify compounds with antiprotozoal activity. The glycolytic enzyme triosephosphate isomerase, present in both E. histolytica and G. lamblia, was used as the drug target. The compounds with the best average docking score on both structures were selected for the in vitro evaluation. Three compounds, chlorhexidine, tolcapone, and imatinib, were capable of inhibit growth on G. lamblia trophozoites (0.05–4.935 μg/mL), while folic acid showed activity against E. histolytica (0.186 μg/mL) and G. lamblia (5.342 μg/mL). 相似文献
36.
Annarita Falanga Valentina Del Genio Elizabeth A. Kaufman Carla Zannella Gianluigi Franci Marcus Weck Stefania Galdiero 《International journal of molecular sciences》2021,22(12)
Novel antiviral nanotherapeutics, which may inactivate the virus and block it from entering host cells, represent an important challenge to face viral global health emergencies around the world. Using a combination of bioorthogonal copper-catalyzed 1,3-dipolar alkyne/azide cycloaddition (CuAAC) and photoinitiated thiol–ene coupling, monofunctional and bifunctional peptidodendrimer conjugates were obtained. The conjugates are biocompatible and demonstrate no toxicity to cells at biologically relevant concentrations. Furthermore, the orthogonal addition of multiple copies of two different antiviral peptides on the surface of a single dendrimer allowed the resulting bioconjugates to inhibit Herpes simplex virus type 1 at both the early and the late stages of the infection process. The presented work builds on further improving this attractive design to obtain a new class of therapeutics. 相似文献
37.
Maria Elizabeth Afonso de Magalhães M.Sc. Ph.D. student Matthieu Tubino Ph.D. 《JOM Journal of the Minerals, Metals and Materials Society》1991,43(6):37-39
Gallium is normally obtained by direct electrolysis as a by-product from Bayer process residual liquor at an aluminum processing plant. However, to permit any net accumulation of the metal, the gallium concentration must be at least about 0.3 g/l in the liquor. This article describes a continuous process of extraction with organic solvents and rhodamine-B, followed by a re-extraction step into aqueous media. The final product is a solid containing up to 18 wt.% Ga in a solid mixture of hydroxides and oxides of gallium and aluminum. This final product can then be electrolyzed to recover the gallium more efficiently. 相似文献
38.
Elizabeth?Gutierrez Tong?WangEmail author 《Journal of the American Oil Chemists' Society》2004,81(10):971-977
Soybeans are believed to be a rich source of sphingolipids, a class of polar lipids that has received attention for their
possible cancer-inhibiting activities. The effect of processing on the sphingolipid content of various soybean products has
not been determined. Glucosylceramide (GlcCer), the major sphingolipid type in soybeans, was measured in several processed
soybean products to illustrate which product(s) GlcCer is partitioned into during processing and where it is lost. Whole soybeans
were processed into full-fat flakes, from which crude oil was extracted. Crude oil was refined by conventional methods, and
defatted soy flakes were further processed into alcohol-washed and acid-washed soy protein concentrates (SPC) and soy protein
isolates (SPI) by laboratory-scale methods that simulated industrial practices. GlcCer was isolated from the samples by solvent
extraction, solvent partition, and TLC and was quantified by HPLC. GlcCer remained mostly within the defatted soy flakes (91%)
rather than in the oil (9%) after oil extraction. Only 52, 42, and 26% of GlcCer from defatted soy flakes was recovered in
the acid-washed SPC, alcohol-washed SPC, and SPI products, respectively. All protein products had a similar GlcCer concentration
of about 281 nmol/g (dry wt basis). The minor quantity of GlcCer in the crude oil was almost completely removed by water degumming. 相似文献
39.
The fatty acids of seed oils of the Flacourtiaceae,Hydnocarpus anthelmintica, Caloncoba echinata andTaraktogenus kurzii, have been examined by a combination of capillary gas chromatography, silver ion high performance liquid chromatography and
gas chromatography-mass spectrometry. In addition to the common range of cyclopentenyl fatty acids found in such oils, 13-cyclopent-2-enyltridec-4-enoic
acid was a major component ofH. anthelmintica and was identified by mass spectrometry as its picolinyl ester and dimethyldisulphide adduct. It has not previously been
found in nature. In the other seed oils, the isolated double bond in the corresponding fatty acid was in position 6, as expected.
Similarly,cis-4-hexadecenoic acid and C16 and C18 cyclopentyl fatty acids were identified for the first time inH. anthelmintica. Iso- andanteiso-methylbranched fatty acids were present in trace amounts. 相似文献
40.
A computer model that treats ceramic-powder matrix–ceramic whisker composites as a percolative network of whiskers has been developed. The model calculates the critical fraction of whiskers at the percolation threshold for a two-dimensional random network of whiskers. The computed critical fraction was found to display an inverse dependence on whisker aspect ratio. In addition, the computed critical fraction (27 vol% for a whisker aspect ratio of 7) agreed well with the zero-shrinkage whisker fraction of 30 vol% in the densification of a colloid-pressed alumina–silicon carbide composite that exhibited a two-dimensional orientation of such whiskers. 相似文献