全文获取类型
收费全文 | 3639篇 |
免费 | 27篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 29篇 |
综合类 | 1篇 |
化学工业 | 241篇 |
金属工艺 | 22篇 |
机械仪表 | 22篇 |
建筑科学 | 51篇 |
矿业工程 | 3篇 |
能源动力 | 11篇 |
轻工业 | 181篇 |
水利工程 | 8篇 |
无线电 | 80篇 |
一般工业技术 | 124篇 |
冶金工业 | 2784篇 |
原子能技术 | 9篇 |
自动化技术 | 101篇 |
出版年
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 19篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 31篇 |
2015年 | 13篇 |
2014年 | 34篇 |
2013年 | 31篇 |
2012年 | 34篇 |
2011年 | 43篇 |
2010年 | 29篇 |
2009年 | 30篇 |
2008年 | 22篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 21篇 |
2004年 | 17篇 |
2003年 | 25篇 |
2002年 | 23篇 |
2001年 | 20篇 |
2000年 | 32篇 |
1999年 | 78篇 |
1998年 | 867篇 |
1997年 | 515篇 |
1996年 | 327篇 |
1995年 | 227篇 |
1994年 | 117篇 |
1993年 | 177篇 |
1992年 | 39篇 |
1991年 | 42篇 |
1990年 | 28篇 |
1989年 | 29篇 |
1988年 | 43篇 |
1987年 | 38篇 |
1986年 | 32篇 |
1985年 | 35篇 |
1984年 | 16篇 |
1983年 | 20篇 |
1982年 | 20篇 |
1981年 | 35篇 |
1980年 | 24篇 |
1979年 | 10篇 |
1978年 | 22篇 |
1977年 | 99篇 |
1976年 | 174篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1969年 | 7篇 |
排序方式: 共有3667条查询结果,搜索用时 15 毫秒
41.
The removal by centrifugation of epididymal contents from mouse spermatozoa had no deleterious effect on fertilization in vitro, and, depending on the genotype of the gametes, was frequently associated with increased levels of fertility. Washing of the spermatozoa significantly improved the fertilization rate of F1 eggs with TO spermatozoa and of BALB/c eggs with BALB/c spermatozoa, but had no significant effect of F1 spermatozoa with F1 eggs. 相似文献
42.
43.
The authors present clinical and case material on two male triplets with aberrant gender identity. Their findings coincide with those of the few family studies reported in which there were two or more transsexual members; they also reveal patterns generally in keeping with the psychological determinants of transsexualism suggested by Stoller. 相似文献
44.
45.
D.G.G. Schwarz M.C. Lima M. Barros F.L. Valente T.M. Scatamburlo N. Rosado C.T.S.A.M. Oliveira L.L. Oliveira M.A.S. Moreira 《Journal of dairy science》2017,100(10):8426-8429
Goat farming is a low-cost alternative to dairy production in developing countries. In Brazil, goat production has increased in recent years due in part to the implementation of programs encouraging this activity. Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of paratuberculosis, a disease that causes chronic granulomatous enteritis in ruminants, but MAP transmission dynamics are still poorly understood in goats. In a previously published study of our research group, 10 dairy goat farms (467 animals) from Minas Gerais state were analyzed for MAP detection; 2 fecal cultures and 11 milk samples tested positive for MAP by conventional PCR and were confirmed by sequencing. Because no clinical signs were observed over 1 yr of monitoring, we hypothesized that these MAP-positive goats could be passive shedders. Thus, in the present study, 4 positive goats (4/13) from the previous study were purchased and feces and milk samples were collected for evaluation (twice, with an interval of 3 mo between tests) by culture of MAP, IS900 PCR, or both. All analyses were negative for MAP. At the last time point, blood samples were collected for ELISA, the animals were killed, and tissues collected for tissue culture and histopathology. At necropsy, no macroscopic lesions related to paratuberculosis were observed. Similarly, no histological changes were observed and MAP in samples stained by Ziehl–Neelsen was not detected. These animals were characterized as potential passive shedders with upward contamination of the teat canal by MAP. This is the first report of the passive shedding phenomenon in goats in Brazil and it highlights the importance of identifying these animals for control programs and to ensure the quality of dairy products. 相似文献
46.
Waldemar Ternes Melanie Gronemeyer Karin Schwarz 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1995,201(6):544-547
p-Cymene-2,3-diol, carvacrol and thymol are components of thyme that exhibit antioxidant activities. The concentration of each substance was determined in different foodstuffs containing thyme extract. The stabilities ofp-cymene-2,3-diol, carvacrol and thymol were examined by heating lard containing thyme extract at temperatures from 80 °C to 160 °C. 相似文献
47.
Due to the complexity of biological tissue and man-made materials, the limits of light microscopy in quantitative image analysis are often reached. The scanning electron microscope provides a much higher resolution in such situations, especially when using the low noise secondary electrons signal. However, secondary electrons are sensitive to topography rather than to the elements constituting the specimen. This effect usually makes discrimination of distinct phases or objects by simple grey value thresholding difficult or even impossible. The additional information given by an energy dispersive X-ray system is the step to overcome this problem. The combination of both signals—grey level and energy dispersive information—leads to a masking procedure which eliminates image sections, not belonging to the phase under investigation, from the evaluation. 相似文献
48.
Milk fatty acid (FA) profile is a dynamic pattern influenced by lactational stage, energy balance and dietary composition. In the first part of this study, effects of the energy balance during the proceeding lactation [weeks 1-21 post partum (pp)] on milk FA profile of 30 dairy cows were evaluated under a constant feeding regimen. In the second part, effects of a negative energy balance (NEB) induced by feed restriction on milk FA profile were studied in 40 multiparous dairy cows (20 feed-restricted and 20 control). Feed restriction (energy balance of -63 MJ NEL/d, restriction of 49 % of energy requirements) lasted 3 weeks starting at around 100 days in milk. Milk FA profile changed markedly from week 1 pp up to week 12 pp and remained unchanged thereafter. The proportion of saturated FA (predominantly 10:0, 12:0, 14:0 and 16:0) increased from week 1 pp up to week 12 pp, whereas monounsaturated FA, predominantly the proportion of 18:1,9c decreased as NEB in early lactation became less severe. During the induced NEB, milk FA profile showed a similarly directed pattern as during the NEB in early lactation, although changes were less marked for most FA. Milk FA composition changed rapidly within one week after initiation of feed restriction and tended to adjust to the initial composition despite maintenance of a high NEB. C18:1,9c was increased significantly during the induced NEB indicating mobilization of a considerable amount of adipose tissue. Besides 18:1,9c, changes in saturated FA, monounsaturated FA, de-novo synthesized and preformed FA (sum of FA >C16) reflected energy status in dairy cows and indicated the NEB in early lactation as well as the induced NEB by feed restriction. 相似文献
49.
I.A. Carvalho P.A.G. PietralongaD.G.G. Schwarz A.C.S. FariaM.A.S. Moreira 《Journal of dairy science》2012
Mycobacterium avium ssp. paratuberculosis (MAP) is the etiological agent of paratuberculosis, a chronic granulomatous enteritis that affects all ruminants worldwide. Some researchers have indicated a possible role of MAP in Crohn's disease. Despite extensive research and large and important advances in the past few decades, the etiology of Crohn's disease remains indefinite. The most probable transmission route of MAP from animals to humans is milk and dairy products. Mycobacterium avium ssp. paratuberculosis has already been detected in milk samples worldwide, and some studies have reported that MAP is resistant to pasteurization. In Brazil, MAP has been reported in raw milk samples; however, Brazilian retail pasteurized milk has not yet been tested for viable MAP. The aim of this study was to investigate MAP in pasteurized milk in the region of Viçosa (Minas Gerais, Brazil). Thirty-seven samples were collected and processed for culture of MAP. One colony similar to MAP was observed and confirmed by IS900-nested PCR and sequencing. Analysis revealed 97 to 99% identity with the MAP K-10 strain. This study is the first report of the presence of MAP in retail pasteurized whole milk in Brazil. 相似文献
50.
Dodd JG Vegi A Vashisht A Tobias D Schwarz P Wolf-Hall CE 《Journal of food protection》2011,74(12):2134-2141
Molds and their mycotoxins are an expensive problem for the malting and brewing industries. Deoxynivalenol (DON) is a mycotoxin that is associated with Fusarium spp. These fungi frequently cause Fusarium head blight in wheat and barley in the midwestern region of the United States; Manitoba, Canada; Europe; and China. Barley growers and malt producers would benefit from a postharvest control method for mold growth and DON production. We evaluated the use of gaseous ozone (O(3)) for preventing Fusarium growth and mycotoxin production while maintaining malt quality characteristics. Micromalting was performed in three replications under standard conditions. Ozone treatment was applied to malting barley during steeping via a submerged gas sparger. Ozone treatment conditions were 26 mg/cm(3) for 120 min after 2 and 6 h of steeping. The effects of gaseous ozone on DON, aerobic plate counts, Fusarium infection, and mold and yeast counts of barley throughout the malting process were measured. Various quality parameters of the malt were measured after kilning. Statistical tools were used to determine the significance of all results. Ozonation of malting barley during steeping did not lead to significant reductions in aerobic plate counts but did lead to a 1.5-log reduction in mold and yeast counts in the final malt. The influence of gaseous ozone on DON concentration was inconclusive because of the low initial concentrations of DON in the barley. Ozone significantly reduced Fusarium infection in germinated barley. Gaseous ozone did not negatively influence any aspect of malt quality and may have subtle beneficial effects on diastatic power and β-glucan concentrations. 相似文献