首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1265篇
  免费   203篇
  国内免费   27篇
  2023年   23篇
  2022年   26篇
  2021年   39篇
  2020年   40篇
  2019年   34篇
  2018年   33篇
  2017年   81篇
  2016年   66篇
  2015年   55篇
  2014年   85篇
  2013年   132篇
  2012年   46篇
  2011年   75篇
  2010年   79篇
  2009年   77篇
  2008年   83篇
  2007年   55篇
  2006年   45篇
  2005年   30篇
  2004年   35篇
  2003年   28篇
  2002年   24篇
  2001年   17篇
  2000年   10篇
  1999年   11篇
  1998年   21篇
  1997年   8篇
  1996年   7篇
  1995年   18篇
  1994年   16篇
  1993年   11篇
  1992年   17篇
  1991年   15篇
  1990年   16篇
  1989年   16篇
  1988年   14篇
  1987年   12篇
  1986年   8篇
  1985年   11篇
  1984年   13篇
  1983年   4篇
  1982年   11篇
  1981年   4篇
  1980年   4篇
  1979年   4篇
  1978年   4篇
  1977年   5篇
  1976年   8篇
  1975年   6篇
  1973年   8篇
排序方式: 共有1495条查询结果,搜索用时 626 毫秒
991.
Traditional Tar Production from Cedrus libani A. Rich on the Taurus Mountains in Southern Turkey. Cedrus libani A. Rich is a magnificent and sacred tree species native to the eastern Mediterranean region. Today, traditional people in southern Turkey produce wood extract, called katran, from C. libani, and use it to protect wooden structures against insects and fungi, to fight parasites and bacteria, and to heal wounds and cure various diseases in humans and domestic animals, both internally and externally. Here we illustrate traditional methods of producing katran, its use by local people, and its chemical composition.  相似文献   
992.
During screening of some essential oils against Penicillium italicum, the oils of Mentha arvensis, Ocimum canum and Zingiber officinale were found to exhibit absolute fungitoxic activity against the test fungus. The oils were subsequently standardized through physico-chemical and fungitoxic properties. Practical applicability of the essential oils was observed in control of blue mould rot of oranges and lime fruits caused by P. italicum during storage. The Mentha oil-treated oranges and lime fruits showed enhancement of storage life of 6 and 8 days, respectively. The storage life of Ocimum oil-treated oranges and lime fruits was found to be enhanced by 6 days while in the case of Zingiber oil, it was 4 and 8 days enhancement of shelf life of oranges and lime fruits, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
993.
During screening of twenty six essential oils against Botrytis cinerea, the essential oils of the ten plants viz. Chenopodium ambrosioides, Eucalyptus citriodora, Eupatorium cannabinum, Lawsonia inermis, Ocimum canum, O. gratissimum, O. sanctum, Prunus persica, Zingiber cassumunar and Z. officinale were found to exhibit absolute fungitoxic activity (100% growth inhibition). The essential oils of O. sanctum, P. persica and Z. officinale were selected for further investigation because these oils showed lower Minimum Inhibitory Concentration (MIC) as compared to the other fungitoxic oils. The selected oils were subsequently standardized through physico-chemical and fungitoxic properties. The MIC values of O. sanctum, P. persica and Z. officinale were found to be 200, 100 and 100 ppm (mg/l) respectively. The oils showed fungistatic nature at their respective MIC. The oils were thermostable, and exhibited a wide range of fungitoxicity against 15 other post-harvest fungal pathogens. The oils had the potency to withstand high inoculum density. The antifungal potency of oils was found to be greater in comparison to some prevalent synthetic fungicides. Practical applicability of the essential oils was observed in control of grey mould of grapes caused by B. cinerea during storage. The O. sanctum- and P. persica-oil-treated grapes showed enhancement of storage life up to 5 and 4 days respectively. The storage life of Z. officinale-oil-treated grapes was found to be enhanced up to 6 days. The oils did not exhibit any phytotoxic effect on the fruit peel. Therefore, the oils could be recommended as a potential source of ecofriendly botanical fungicide, after long term and wide ranging trials.  相似文献   
994.
An insertion/deletion (I/D) polymorphism of Alpha2B-Adrenoceptor (ADRA2B) gene located on chromosome 2 has been studied extensively in related to cardiovascular diseases. The main aim of the present study was to examine the potential association of D allele frequency of I/D polymorphism of ADRA2B gene in Malaysian essential hypertensive subjects with or without type 2 diabetes mellitus (T2DM). This study includes 70 hypertensive subjects without T2DM, 65 hypertensive subjects with T2DM and 75 healthy volunteers as control subjects. Genotyping of I/D polymorphism was performed by conventional PCR method. There was significant difference found in age, body mass index, systolic/diastolic blood pressure and high density lipoprotein cholesterol level between the case and control subjects. DD genotypic frequency of I/D polymorphism was significantly higher in hypertensive subjects (42.84% vs. 29.33%; P-=0.029) and in hypertensive with T2DM subjects (46.15% vs. 29.33%; P=0.046) than control group. D allele frequency was higher in hypertensive group (67.41%) than control subjects (52.67%). However, no significant difference was found between the three genotypes of I/D polymorphism of ADRA2B gene and the clinical characteristics of the subjects. The result obtained in this study show D allele of ADRA2B gene was associated with essential hypertension with or without T2DM in Malaysian subjects.  相似文献   
995.
996.
There is accumulating evidence that the metabolism of several trace elements is altered in diabetes mellitus and that these nutrients might have specific roles in the pathogenesis and progress of this disease. The aim of present study was to compare the level of essential trace elements, chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), and zinc (Zn) in biological samples (whole blood, urine, and scalp hair) of patients who have diabetes mellitus type 2 (n = 257), with those of nondiabetic control subjects (n = 166), age ranged (45–75) of both genders. The element concentrations were measured by means of an atomic absorption spectrophotometer after microwave-induced acid digestion. The validity and accuracy was checked by conventional wet-acid-digestion method and using certified reference materials. The overall recoveries of all elements were found in the range of (97.60–99.49%) of certified values. The results of this study showed that the mean values of Zn, Mn, and Cr were significantly reduced in blood and scalp-hair samples of diabetic patients as compared to control subjects of both genders (p < 0.001). The urinary levels of these elements were found to be higher in the diabetic patients than in the age-matched healthy controls. In contrast, high mean values of Cu and Fe were detected in scalp hair and blood from patients versus the nondiabetic subjects, but the differences found in blood samples was not significant (p < 0.05). These results are consistent with those obtained in other studies, confirming that deficiency and efficiency of some essential trace metals may play a role in the development of diabetes mellitus.  相似文献   
997.
High-value oils from plants   总被引:8,自引:3,他引:5  
The seed oils of domesticated oilseed crops are major agricultural commodities that are used primarily for nutritional applications, but in recent years there has been increasing use of these oils for production of biofuels and chemical feedstocks. This is being driven in part by the rapidly rising costs of petroleum, increased concern about the environmental impact of using fossil oil, and the need to develop renewable domestic sources of fuel and industrial raw materials. There is also a need to develop sustainable sources of nutritionally important fatty acids such as those that are typically derived from fish oil. Plant oils can provide renewable sources of high-value fatty acids for both the chemical and health-related industries. The value and application of an oil are determined largely by its fatty acid composition, and while most vegetable oils contain just five basic fatty acid structures, there is a rich diversity of fatty acids present in nature, many of which have potential usage in industry. In this review, we describe several areas where plant oils can have a significant impact on the emerging bioeconomy and the types of fatty acids that are required in these various applications. We also outline the current understanding of the underlying biochemical and molecular mechanisms of seed oil production, and the challenges and potential in translating this knowledge into the rational design and engineering of crop plants to produce high-value oils in plant seeds.  相似文献   
998.
The calanoid copepod Temora longicornis and its food (seston of size < 200 μm) was sampled during three successive seasons (2002-04) in the Trondheimsfjord, Central Norway. Egg production (24 h) and hatching success (72 h) was determined by incubation experiments, and the essential fatty acid (EFA) content of their in situ food was analysed. The dominant EFA in the seston were DHA (22:6n-3) and EPA (20:5n-3), whereas ARA (20:4n-6) were present in low quantities. Egg production and hatching success was relatively low during early spring and late autumn (~ 10 eggs female- 1 day- 1 and ~ 30%), and relatively high during summer. Spring phytoplankton, dominated by diatoms, contained low amounts of DHA. Dinoflagellates, small flagellates, and ciliates dominated during summer, when a high content of DHA was recorded.The rate of egg production of T. longicornis did not show any relationship with food concentration (r2 = 0.003), but was positively correlated to temperature, although not statistically significantly (r2 = 0.48, p = 0.05). The quantitative and percent DHA contents of the food was significantly related to the rate of egg production (r2 = 0.96 and 0.95, respectively, p < 0.001), but no such relationship were observed for the quantitative or percent content of EPA and ARA in the seston. The egg production of T. longicornis during May-August was 43-47 eggs female- 1 day- 1, with dietary DHA contents higher than 7-8 mg DHA g- 1 DW. Also the hatching success of T. longicornis was positively correlated to the quantitative content of DHA in the diet (r2 = 0.88), but hatching was also inversely related to the percentage ARA (r2 = 0.84). The maximum hatching success was found when the ARA content was < 0.15% of total fatty acids and the DHA:ARA ratio was > 50. The conclusion that DHA most strongly affected egg production whereas ARA affected hatching, fit well with earlier findings for fish. Our results do not exclude that toxic aldehydes interact with reproduction of calanoid copepods when diatoms are present, but we observed a consistent pattern where dietary DHA and ARA alone explained a majority of the variability in egg production and hatching of T. longicornis.  相似文献   
999.
The essential oils of Guatteriopsis blepharophylla, Guatteriopsis friesiana and Guatteriopsis hispida were obtained by hydrodistillation and analysed by GC and GC/MS. The main compound found in the leaf oil of G. blepharophylla was caryophyllene oxide (1) (69.25%). The leaf oil of G. friesiana contained predominantly beta-eudesmol (2) (51.60%), gamma-eudesmol (3) (23.70%), and alpha-eudesmol (4) (14.56%). The major constituents identified in the leaf of G. hispida were beta-pinene (38.18%), alpha-pinene (30.77%) and (E)-caryophyllene (20.59%). The antimicrobial activity of the essential oils was evaluated against 11 species of microorganisms. The oil of G. friesiana exhibited significant antimicrobial activity for all microorganisms tested, whereas that of G. hispida and G. blepharophyla had potent activity against Rhodococcus equi with MIC of 50 microg mL(-1). The major constituents of each oil were also tested separately, and showed lower activity compared to the oils. Moreover, mixtures of the main constituents, in the same proportions found in G. friesiana and G. hispida oils, did not show the same activity as the original oils.  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号