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   2167篇
  免费   147篇
  国内免费   8篇
  2322篇
  2024年   11篇
  2023年   29篇
  2022年   91篇
  2021年   124篇
  2020年   75篇
  2019年   115篇
  2018年   133篇
  2017年   83篇
  2016年   96篇
  2015年   99篇
  2014年   104篇
  2013年   173篇
  2012年   138篇
  2011年   140篇
  2010年   88篇
  2009年   72篇
  2008年   78篇
  2007年   74篇
  2006年   62篇
  2005年   64篇
  2004年   72篇
  2003年   59篇
  2002年   40篇
  2001年   20篇
  2000年   15篇
  1999年   14篇
  1998年   9篇
  1996年   15篇
  1994年   8篇
  1992年   11篇
  1991年   5篇
  1990年   13篇
  1989年   7篇
  1988年   15篇
  1987年   11篇
  1986年   10篇
  1985年   15篇
  1984年   10篇
  1983年   8篇
  1981年   6篇
  1980年   8篇
  1979年   12篇
  1978年   8篇
  1977年   11篇
  1976年   5篇
  1974年   5篇
  1973年   6篇
  1971年   5篇
  1970年   6篇
  1969年   5篇
排序方式: 共有2322条查询结果,搜索用时 15 毫秒
51.
A series of 15 previously reported N4-substituted isatin-3-thiosemicarbazones 3a-o has been screened for cytotoxic, antibacterial, antifungal and urease inhibitory activities. Compounds 3b, 3e and 3n proved to be active in cytotoxicity assay; 3e exhibited a high degree of cytotoxic activity (LD50 = 1.10 × 10? 5 M). Compound 3h exhibited significant antibacterial activity against B. subtilis, whereas compounds 3a, 3k and 3l displayed significant antifungal activity against one or more fungal strains i.e. T. longifusus, A. flavus and M. canis. In human urease enzyme inhibition assay, compounds 3g, 3k and 3m proved to be the most potent inhibitors, exhibiting relatively pronounced inhibition of the enzyme. These compounds, being non-toxic, could be potential candidates for orally effective therapeutic agents to treat certain clinical conditions induced by bacterial ureases like H. pylori urease. This study presents the first example of inhibition of urease by isatin-thiosemicarbazones and as such provides a solid basis for further research on such compounds to develop more potent inhibitors.  相似文献   
52.
A validated simple and sensitive spectrofluorimetric method was developed for the determination of chlorpromazine hydrochloride, promethazine hydrochloride, trifluperazine hydrochloride, thioridazine hydrochloride, perazine maleate and oxomemazine. The method was based on condensation of malonic acid/acetic anhydride (MAA) under the catalytic effect of the tertiary amine moiety of the studied phenothiazines to provide a deep yellow to brown colour with green florescence. Relative fluorescence intensity of the products was measured at λexc 398 nm and λem 432 nm. Different variables affecting the reaction were studied and optimized. The method was successfully applied for the determination of the studied drugs in commercial dosage forms. The lower detection limits allowed the application of this method for the determination of the compounds in plasma as an example of a biological fluid. In addition, the method was considered specific for the determination of tertiary amines in the presence of primary and secondary amines; as a result, it was deemed suitable for the determination of the cited drugs in the presence of their degradation products resulting from N‐dealkylation or oxidation of the corresponding sulphoxides or sulphones. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
53.
A cDNA encoding farnesyl pyrophosphate synthase of Babesia bovis (BbFPPS) has been isolated, cloned and characterized as molecular drug target. Sequence analysis revealed that BbFPPS contains an open reading frame of 1011 bp with predicted 336 amino acids and molecular mass of 38 kDa. Antiserum raised in mice against recombinant BbFPPS expressed in Escherichia coli specifically reacted with native protein of B. bovis parasites by Western blot analysis and indirect immunofluorescent test. Enzymatic assay using recombinant BbFPPS revealed that the Km value of the enzyme for isopentenyl pyrophosphate and dimethylallyl pyrophosphate was 2.494 ± 1.536 μM. Risedronate inhibited the activity of BbFPPS yielding IC50 value of 8.4 ± 1.2 nM. Furthermore, the in vitro growth of B. bovis was significantly inhibited in the presence of a micromolar concentration of risedronate (IC50 = 4.02 ± 0.91 μM). No regrowth of B. bovis was observed at 10 μM of risedronate in the subsequent viability test. These results demonstrate that BbFPPS is the molecular target of risedronate, which could inhibit the in vitro growth of B. bovis.  相似文献   
54.
A new fungal endophyte, Scolecobasidium humicola, was identified as a common dark septate endophytic fungal (DSE) species under both natural and agricultural conditions. This fungus was found to grow endophylically in the roots of tomato seedlings. Light microscopy of cross-sections of colonized tomato roots showed that the intercellular, pigmented hyphae of the fungus were mostly limited to the epidermal layer and formed outer mantle-like structures. Two isolates of S. humicola, H2-2 and F1-3, have shown the ability to increase plant biomass with an organic nitrogen source. This finding is the first report of S. humicola as an endophyte and could help to improve plant growth with organic nitrogen sources.  相似文献   
55.
56.
Biological Trace Element Research - Heavy metal pollution of soils in industrial zones continues to attract attention because of its potential human health risks. The present research is an attempt...  相似文献   
57.
Effects on development, longevity, fecundity and predation of the predatory phytoseiid mite Typhlodromus mangiferus Zaher and El-Brolossy were studied in the laboratory at different temperatures and relative humidities using four prey mite species: the motile stages of the eriophyid mango bud mite Aceria mangiferae Sayed, the eriophyid leaf coating and webbing mite Cisaberoptus kenyae Keifer, the eriophyid mango rust mite Metaculus mangiferae (Attiah) and nymphs of the tetranychid mango red mite Oligonychus mangiferus (Rahman and Sabra). The increase of different temperatures and decrease of relative humidities from 25°C and 60% to 30°C and 55% and 35°C and 50% shortened development and increased reproduction and prey consumption. The developmental durations were almost similar when the predator was fed on eriophyids compared to that on tetranychid. The maximum reproduction (2.70, 2.08, 1.97 and 1.66 eggs/ ♀ /day) was recorded at the highest temperature and the lowest relative humidity, while the minimum reproduction (1.7, 1.54, 1.53, and 1.06 eggs/ ♀ /day) was noted at the lowest temperature and highest relative humidity with all mango prey species. Life table parameters indicated that feeding of T. mangiferus on A. mangiferae led to the highest reproduction rate (rm = 0.204 and 0.139 females/female/day), while feeding on O. mangiferus gave the lowest reproduction rate (rm = 0.137 and 0.116) at 35°C and 50% relative humidity and 25°C and 60% relative humidity, respectively. T. mangiferus seems to be a voracious predator of both mango eriophyid and tetranychid mites. The adult female daily consumed about 127 A. mangiferae, 97 C. kenyae, 86 M. mangiferae, and 18 O. mangiferus at 35°C and 50% relative humidity, while it devoured only 99.81, 86, 81, and 15 individuals, respectively at 25°C and 60% relative humidity. The present study revealed that each injurious mite is thought to be profitable prey species to T. mangiferus as a facultative predator.  相似文献   
58.
Abstract

The possible biological control of damping-off fungi, Fusarium oxysporum and Pythium ultimum by Pythium oligandrum or Trichoderma harzianum was in vitro investigated. Results of comparing the antagonistic activity of P. oligandrum and T. harzianum in dual plates against the tested phytopathogens indicated different degrees of antagonism. After 12 days of incubation colony of the phytopathogenic fungus was completely overgrown by the antagonist, except for the interaction between T. harzianum and F. oxysporum which showed no overgrowth or any hyphal penetration by the antagonist. However, growth and proliferation of F. oxysporum colony was repressed. T. harzianum and P. oligandrum produced chitinase and β-1,3-glucanase when they were grown on liquid culture medium supplemented with chitin or fungal dried mycelium as a sole carbon source, and enzyme production was higher by T. harzianum comparing with P. oligandrum under the same condition. Fungal dried mycelium of F. oxysporum was the most selective carbon source for enzyme production, on the other hand, chitinase production was significant locked when P. ultimum dried mycelium was used as a carbon source. Production of volatile compounds by P. oligandrum or T. harzianum against F. oxysporum and P. ultimum was examined using the inverted plates method. F. oxysporum was inhibited by the antagonist volatile compounds and it is inhibited 100% by increasing the amount of inoculum size. Production of potential biocontrol agents provided with economically features and working under field conditions are recommended.  相似文献   
59.
The combined effect of gamma radiation and both hot water and sodium carbonate on physiological decay and chemical constituents of stored mandarin fruits was investigated in this work. In this consideration, the studied fruits were gamma irradiated at doses of 0, 0.3, 0.6, 1.2 and 2.4 KGy. Then, the irradiated and non-irradiated fruits were treated either by hot water or sodium bicarbonate to examine their capacity to give a further maintenance and increasing shelf life or storage periods of mandarin. Treated and non-treated fruit samples were taken at intervals of 10 days and up to 60 days. Physiological decay, total acidity, vitamin C, total sugars and TSS were investigated during the different intervals. Gamma radiation treatments showed a promising effect for maintaining the studied fruits and retarding the development of decay. On the other hand, applying both hot water and sodium bicarbonate as a further combined treatments induced a powerful effect on delaying decay development, keeping the chemical constituents near to the normal level and in turn maximizing shelf life and storage periods of the fruits under investigation.  相似文献   
60.
Protein tyrosine kinases (PTKs) play an important role in T cell development and activation. In vitro and in vivo defects, resulting in variable deficiencies in thymic development and in T cell antigen receptor (TCR) signal transduction, in PTKs have been shown. ZAP70, one of those PTKs, is a 70-kDa tyrosine phosphoprotein and associates with the ζ chain and undergoes tyrosine phosphorylation following TCR stimulation. It is expressed in T and natural killer (NK) cells. Several mutations were shown to lead to an autosomal recessive form of severe combined immunodeficiency disease (SCID).  相似文献   
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