全文获取类型
收费全文 | 854篇 |
免费 | 99篇 |
国内免费 | 1篇 |
专业分类
954篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 18篇 |
2020年 | 10篇 |
2019年 | 7篇 |
2018年 | 29篇 |
2017年 | 20篇 |
2016年 | 29篇 |
2015年 | 33篇 |
2014年 | 35篇 |
2013年 | 54篇 |
2012年 | 47篇 |
2011年 | 56篇 |
2010年 | 40篇 |
2009年 | 26篇 |
2008年 | 21篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 32篇 |
2004年 | 36篇 |
2003年 | 31篇 |
2002年 | 28篇 |
2001年 | 26篇 |
2000年 | 30篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 22篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 5篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1969年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有954条查询结果,搜索用时 15 毫秒
71.
Melatonin could act on immune system by regulating cytokine production of immunocompetent cells. The hormone enhances IL-2, IFN-gamma and IL-6 production by cultured human mononuclear cells. As enhancement of IL-6 production is related to monocyte activation by melatonin, the hormone acts on human lymphoid cells causing a Th1-type response. This paper shows that melatonin seems to promote a Th1-response by increasing IL-12 production. The hormone enhances IL-12 production by cultured monocytes under suboptimal stimulation in a dose-dependent way. The effect of the hormone increases when PBMCs are incubated with melatonin before monocyte isolation. Enhanced IL-12 production by melatonin can also be shown in cultured human mononuclear cells. 相似文献
72.
73.
Sita S. Withers Philip H. Kass Carlos O. Rodriguez Katherine A. Skorupski Danielle O’Brien Teri A. Guerrero Kristen D. Sein Robert B. Rebhun 《Translational oncology》2014,7(3):377-383
Fasting reduces gastrointestinal cellular proliferation rates through G1 cycle blockade and can promote cellular protection of normal but not cancer cells through altered cell signaling including down-regulation of insulin-like growth factor 1 (IGF-1). Consequently, the purpose of this study was to determine the effects of fasting on delayed-type chemotherapy-induced nausea and vomiting in dogs receiving doxorubicin. This prospective randomized crossover study involved intended administration of two doses of doxorubicin. Cancer-bearing dogs were randomized to be fasted for 24 hours beginning at 6 P.M. the night before the first or second doxorubicin administration, and all treatments were administered within an hour before or after 12 P.M. Dogs were fed normally before the alternate dose. Circulating IGF-1 concentrations were determined from serum samples obtained immediately before each doxorubicin treatment. Data from 35 doses were available from 20 dogs enrolled. Dogs that were fasted exhibited a significantly lower incidence of vomiting, when compared to fed dogs (10% compared to 67%, P = .020). Furthermore, among the 15 dogs that completed crossover dosing, vomiting was abrogated in four of five dogs that experienced doxorubicin-induced vomiting when fed normally (P = .050). No differences in other gastrointestinal, constitutional, or bone marrow toxicities or serum IGF-1 levels were observed. 相似文献
74.
Fed‐batch synthesis of galacto‐oligosaccharides with Aspergillus oryzae β‐galactosidase using optimal control strategy 下载免费PDF全文
Fed‐batch synthesis of galacto‐oligosaccharides (GOS) from lactose with β‐galactosidase from Aspergillus oryzae was evaluated experimentally and reaction yield was maximized via optimal control technique. The optimal lactose and enzyme feed flow rate profiles were determined using a model for GOS synthesis previously reported by the authors. Experimentally it was found that fed‐batch synthesis allowed an increase on the maximum total GOS concentration from 115 (batch synthesis) to 218 g L?1 as consequence of the increase in total sugars concentration from 40 to 58% w/w. Such high concentration of total sugars was not attainable in batch operation because of the low solubility of lactose at the reaction temperature (40°C). Simulations predicted a GOS yield of 32.5 g g?1 in fed‐batch synthesis under optimal conditions, while experimentally the same yield as in batch synthesis was obtained (28 g g?1). Besides, an enrichment of total oligosaccharides in GOS with a high polymerization degree (GOS‐5 and GOS‐6) was observed in the fed‐batch synthesis. Experimental profiles for all sugars were similar to the ones predicted by simulation, which supports the use of this methodology for the optimization of GOS synthesis. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:59–67, 2014 相似文献
75.
José Luis Reino Raul F. Guerrero Rosario Hernández-Galán Isidro G. Collado 《Phytochemistry Reviews》2008,7(1):89-123
Trichoderma species are free-living fungi that are highly interactive in root, soil and foliar environments and have been used successfully
in field trials to control many crop pathogens. Structural and biological studies of the metabolites isolated from Trichoderma species are reviewed. This review, encompassing all the literature in this field up to the present and in which 269 references
are cited, also includes a detailed study of the biological activity of the metabolites, especially the role of these metabolites
in biological control mechanisms. Some aspects of the biosynthesis of these metabolites and related compounds are likewise
discussed. 相似文献
76.
77.
Sabariego Ruiz S Díaz de la Guardia Guerrero C Alba Sánchez F 《Revista iberoamericana de micología》2004,21(3):121-127
This study analysed the seasonal and intradiurnal behaviour of fungal spores from Alternaria and Cladosporium on air samples collected in the city of Almeria (SE Spain), as well as the influence that meteorological parameters have on the concentration of these type of spores. Aerobiological sampling was made during four years (1998-2001) using a Hirst-type volumetric spore trap. Spores of Alternaria and Cladosporium were detected throughout the year, reaching the highest concentrations from May to October. The diurnal patterns of these taxons reflected a presence similar of spores during a 24 h period, with values horary close to 4% of total sampling daily. The correlations show a positive association with temperature, hours of sunshine and accumulate rainfall, but negative with daily rainfall. 相似文献
78.
Age at acquisition of Helicobacter pylori infection: comparison of two areas with contrasting risk of gastric cancer 总被引:2,自引:0,他引:2
Background. Helicobacter pylori infection is usually acquired during childhood and is a known risk factor for the development of gastric malignancies in adulthood. It has been reported that early age at first infection may determine a neoplastic outcome in adults. The purpose of this study was to determine the prevalence of Helicobacter pylori infection in children residing in areas with high (Pasto) and low risk (Tumaco) of gastric cancer in Colombia to evaluate whether differences in the age of acquisition of H. pylori infection were present in the two populations. Materials and Methods. The study sample was based on a census taken in 1999. Using the 13C‐urea breath test, we compared the prevalence of H. pylori infection among children aged 1–6 years. Results. Among 345 children in Pasto, 206 (59.7%) were H. pylori‐positive, compared with 188 (58.6%) among 321 children in Tumaco. The two populations share a common pattern of very early age at infection and marked increase in prevalence during the first 4 years of life. No differences in any one year were observed when comparing the two groups. Conclusions. The prevalence of infection was similarly high and increased with age in both populations. In these populations the age of acquisition of H. pylori after 1 year of age does not appear to be a primary factor responsible for the differences in the rates of gastric cancer incidence in adults. Previous findings in adults showed lower prevalence of the most virulent genotypes in Tumaco compared to Pasto, and bacterial virulence may play a key role in determining cancer outcome. 相似文献
79.
Systematic Parasitology - Four new species of Molinema (Filarioidea: Onchocercidae), parasites of echimyid rodents in South America, are described: M. algardneri n. sp. from Proechimys... 相似文献
80.
In both sexes, the Drosophila genital disc contains the female and male genital primordia. The sex determination gene doublesex controls which of these primordia will develop and which will be repressed. In females, the presence of Doublesex(F) product results in the development of the female genital primordium and repression of the male primordium. In males, the presence of Doublesex(M) product results in the development and repression of the male and female genital primordia, respectively. This report shows that Doublesex(F) prevents the induction of decapentaplegic by Hedgehog in the repressed male primordium of female genital discs, whereas Doublesex(M) blocks the Wingless pathway in the repressed female primordium of male genital discs. It is also shown that Doublesex(F) is continuously required during female larval development to prevent activation of decapentaplegic in the repressed male primordium, and during pupation for female genital cytodifferentiation. In males, however, it seems that Doublesex(M) is not continuously required during larval development for blocking the Wingless signaling pathway in the female genital primordium. Furthermore, Doublesex(M) does not appear to be needed during pupation for male genital cytodifferentiation. Using dachshund as a gene target for Decapentaplegic and Wingless signals, it was also found that Doublesex(M) and Doublesex(F) both positively and negatively control the response to these signals in male and female genitalia, respectively. A model is presented for the dimorphic sexual development of the genital primordium in which both Doublesex(M) and Doublesex(F) products play positive and negative roles. 相似文献