全文获取类型
收费全文 | 46594篇 |
免费 | 636篇 |
国内免费 | 1401篇 |
专业分类
电工技术 | 958篇 |
综合类 | 534篇 |
化学工业 | 4727篇 |
金属工艺 | 1636篇 |
机械仪表 | 2385篇 |
建筑科学 | 3160篇 |
矿业工程 | 1473篇 |
能源动力 | 333篇 |
轻工业 | 8525篇 |
水利工程 | 895篇 |
石油天然气 | 1128篇 |
武器工业 | 228篇 |
无线电 | 2958篇 |
一般工业技术 | 14938篇 |
冶金工业 | 979篇 |
原子能技术 | 474篇 |
自动化技术 | 3300篇 |
出版年
2024年 | 79篇 |
2023年 | 261篇 |
2022年 | 325篇 |
2021年 | 340篇 |
2020年 | 216篇 |
2019年 | 257篇 |
2018年 | 303篇 |
2017年 | 120篇 |
2016年 | 159篇 |
2015年 | 195篇 |
2014年 | 443篇 |
2013年 | 425篇 |
2012年 | 4482篇 |
2011年 | 5672篇 |
2010年 | 1313篇 |
2009年 | 773篇 |
2008年 | 3618篇 |
2007年 | 3476篇 |
2006年 | 2903篇 |
2005年 | 2413篇 |
2004年 | 2194篇 |
2003年 | 1859篇 |
2002年 | 1774篇 |
2001年 | 1647篇 |
2000年 | 1486篇 |
1999年 | 1036篇 |
1998年 | 572篇 |
1997年 | 723篇 |
1996年 | 664篇 |
1995年 | 617篇 |
1994年 | 595篇 |
1993年 | 392篇 |
1992年 | 477篇 |
1991年 | 523篇 |
1990年 | 491篇 |
1989年 | 530篇 |
1988年 | 411篇 |
1987年 | 487篇 |
1986年 | 483篇 |
1985年 | 549篇 |
1984年 | 508篇 |
1983年 | 450篇 |
1982年 | 462篇 |
1981年 | 356篇 |
1980年 | 320篇 |
1979年 | 238篇 |
1978年 | 140篇 |
1975年 | 86篇 |
1974年 | 85篇 |
1965年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Photoassisted degradation of azodyes over FeOxH2x-3/Fe0 in the presence of H2O2 at neutral pH values
Fe0 was calcined in air at 200 degrees C and showed enhanced activity in three cycling runs for the degradation of acid red B (ARB) in the presence of H2O2 under UVA irradiation. Subsequently, the catalyst's activity was maintained effectively after 10 successive cycling experiments. Moreover, the catalyst was found to be highly effective for the degradation of nonbiodegradable azodyes ARB, reactive brilliant red X-3B, reactive red K-2G, cationic red X-GRL, and cationic blue X-GRL at neutral pH values. On the basis of characterization by X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectra, the surface layer of the catalyst was mainly composed of alpha-FeOOH and gamma-Fe2O3, and the core was Fe0 (FeOxH2x-3/ Fe0). Fe,OxH2x3/Fe0 was very easily recovered from the reaction system by magnetic separation. The degradation of azodyes came from the synergistic effect of the catalysis of galvanic cells and the oxidation of heterogeneous photo-Fenton reaction on the basis of all information obtained under different experimental conditions. By the total organic carbon and GC-MS analysis, the degradation process of ARB was shown to proceed with decolorization and naphthalene ring openings into CO2 and small organic acid. 相似文献
992.
993.
994.
T Hu YY Guo QF Zhou XK Zhong L Zhu JH Piao J Chen JG Jiang 《Journal of food science》2012,77(9):C975-C982
Eclipta prostrasta L. is a traditional Chinese medicine herb, which is rich in saponins and has strong antiviral and antitumor activities. An ultrasonic-assisted extraction (UAE) technique was developed for the fast extraction of saponins from E. prostrasta. The content of total saponins in E. prostrasta was determined using UV/vis spectrophotometric methods. Several influential parameters like ethanol concentration, extraction time, temperature, and liquid/solid ratio were investigated for the optimization of the extraction using single factor and Box-Behnken experimental designs. Extraction conditions were optimized for maximum yield of total saponins in E. prostrasta using response surface methodology (RSM) with 4 independent variables at 3 levels of each variable. Results showed that the optimization conditions for saponins extraction were: ethanol concentration 70%, extraction time 3 h, temperature 70 °C, and liquid/solid ratio 14:1. Corresponding saponins content was 2.096%. The mathematical model developed was found to fit well with the experimental data. Practical Application: Although there are wider applications of Eclipta prostrasta L. as a functional food or traditional medicine due to its various bioactivities, these properties are limited by its crude extracts. Total saponins are the main active ingredient of E. prostrasta. This research has optimized the extraction conditions of total saponins from E. prostrasta, which will provide useful reference information for further studies, and offer related industries with helpful guidance in practice. 相似文献
995.
996.
2017年,国内绝大多数综艺节目仍充斥着大量娱乐化元素,盲目借鉴外来综艺模式致使创新动力不足、同质化现象普遍,令观众审美疲劳日益严重。此时,《国家宝藏》这一档由我国自主创作且品质极高的文化类节目犹如一匹综艺黑马成功闯入观众视线,俘获大批粉丝,并产生积极的社会影响力。本文在叙事学相关理论的基础上,通过从叙事者、叙事内容、叙事模式这三个方面对《国家宝藏》这一节目进行分析,希望能为未来中国综艺节目健康发展积累宝贵经验。 相似文献
997.
998.
999.
The effect of zeolite A supplementation in the dry period on periparturient calcium,phosphorus, and magnesium homeostasis 总被引:2,自引:0,他引:2
One potential way of preventing parturient hypocalcemia in the dairy cow is to feed dry cow rations very low in calcium (<20 g/d); but, because it is difficult to formulate rations sufficiently low in calcium, this principle has been almost abandoned. Recent studies have shown, however, that it is possible to prevent milk fever, as well as subclinical hypocalcemia, by supplementing the dry cow ration with sodium aluminium silicate (zeolite A), which has the capacity to bind calcium. The aim of this study was to further evaluate the effect, if any, of such supplementation on other blood constituents, feed intake, and milk production in the subsequent lactation. A total of 31 pregnant dry cows about to enter their third or later lactation were assigned as experimental or control cows according to parity and expected date of calving. The experimental cows received 1.4 kg of zeolite pellets per d (0.7 kg of pure zeolite A) for the last 2 wk of pregnancy. Blood samples were drawn from all cows 1 wk before the expected date of calving, at calving, at d 1 and 2 after calving, and 1 wk after calving. Additionally, a urine sample was drawn 1 wk before the expected date of calving. Zeolite supplementation significantly increased the plasma calcium level on the day of calving, whereas plasma magnesium as well as inorganic phosphate was suppressed. Serum 1,25(OH)2D was significantly increased 1 wk before the expected date of calving among the experimental cows, whereas there was no difference in the urinary excretion of the bone metabolite deoxypyridinoline between the two groups. Feed intake was decreased among the zeolite-treated cows during the last 2 wk of pregnancy. No effect was observed on milk yield, milk fat, and milk protein in the subsequent lactation. The mechanisms and interactions involved in zeolite supplementation are discussed in relation to the observed improvement in parturient calcium homeostasis and to the observed depression in blood magnesium and inorganic phosphate. 相似文献
1000.
Ongeng D Ryckeboer J Vermeulen A Devlieghere F 《International journal of food microbiology》2007,119(3):291-299
The effect of micro-architectural structure of cabbage (Brassica oleracea var. capitata L.) substratum and or background bacterial flora on the growth of Listeria monocytogenes as a function of incubation temperature was investigated. A cocktail mixture of Pseudomonas fluorescens, Pantoea agglomerans and Lactobacillus plantarum was constituted to a population density of approximately 5 log CFU/ml in order to pseudo-simulate background bacterial flora of fresh-cut cabbage. This mixture was co-inoculated with L. monocytogenes (approximately 3 log CFU/ml) on fresh-cut cabbage or in autoclaved cabbage juice followed by incubation at different temperatures (4-30 degrees C). Data on growth of L. monocytogenes were fitted to the primary growth model of Baranyi in order to generate the growth kinetic parameters of the pathogen. During storage, microbial ecology was dominated by P. fluorescens and L. plantarum at refrigeration and abuse temperature, respectively. At all temperatures investigated, lag duration (lambda, h), maximum specific growth rate (micro(max), h(-1)) and maximum population density (MPD, log CFU/ml) of L. monocytogenes were only affected by medium micro-architectural structure, except at 4 degrees C where it had no effect on the micro(max) of the pathogen. Comparison of observed values of micro(max) with those obtained from the Pathogen Modelling Program (PMP), showed that PMP overestimated the growth rate of L. monocytogenes on fresh-cut cabbage and in cabbage juice, respectively. Temperature dependency of micro(max) of L. monocytogenes, according to the models of Ratkowsky and Arrhenius, showed linearity for temperature range of 4-15 degrees C, discontinuities and linearity again for temperature range of 20-30 degrees C. The results of this experiment have shown that the constituted background bacterial flora had no effect on the growth of L. monocytogenes and that micro-architectural structure of the vegetable was the primary factor that limited the applicability of PMP model for predicting the growth of L. monocytogenes on fresh-cut cabbage. A major limitation of this study however is that nutrient profile of the autoclaved cabbage juice may be different from that of the raw juice thus compromising realistic comparison of the behaviour of L. monocytogenes as affected by micro-architectural structure. 相似文献