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   1106篇
  免费   60篇
  2023年   10篇
  2022年   8篇
  2021年   21篇
  2020年   23篇
  2019年   25篇
  2018年   35篇
  2017年   26篇
  2016年   35篇
  2015年   49篇
  2014年   64篇
  2013年   72篇
  2012年   99篇
  2011年   84篇
  2010年   55篇
  2009年   53篇
  2008年   71篇
  2007年   65篇
  2006年   51篇
  2005年   40篇
  2004年   48篇
  2003年   45篇
  2002年   47篇
  2001年   9篇
  2000年   7篇
  1999年   4篇
  1998年   6篇
  1996年   6篇
  1994年   8篇
  1993年   5篇
  1992年   9篇
  1991年   7篇
  1990年   4篇
  1989年   9篇
  1988年   6篇
  1987年   2篇
  1986年   4篇
  1985年   4篇
  1984年   4篇
  1983年   6篇
  1981年   6篇
  1979年   3篇
  1974年   4篇
  1973年   6篇
  1967年   1篇
  1966年   4篇
  1965年   1篇
  1963年   2篇
  1959年   3篇
  1954年   1篇
  1951年   1篇
排序方式: 共有1166条查询结果,搜索用时 46 毫秒
1.
Groups of photosensitive, unstimulated or stimulated, male blackheaded buntings were subjected to photoregimes of 15 hr of green light of three intensities and 9 hr of dark per day. In some groups green light was interrupted with 90 min of bright fluorescent light at different times in the subjective day. While gonads did not develop or regressed in some groups, birds in others behaved as if exposed to long daylengths. The results besides suggesting the involvement of endogenous circadian rhythm during initiation and maintenance of gonadal growth indicate that the reproductive rhythms are entrained and induced by environmental photoperiod.  相似文献   
2.
The production of d-aminoacylase by Alcaligenes denitrificans and Alcaligenes faecalis has been studied. The enzyme was inducibly produced and N-acetyl-d-leucine and N-acetyl-d-valine were the most effective inducers. d-methionine, d-valine, d-phenylalamine and d-leucine were produced by the enzymic hydrolysis of the appropriate N-acetyl-d-amino-acids with whole cell biomass. The hydrolysis of N-acetyl-d-methionine by A. denitrificans and N-acetyl-d-valine by A. faecalis was preferential. Maximum yields of d-methionine and d-valine were 94.3 and 84.7% at a specific product formation rate of 20.10 and 19.19 μmol min−1 mg−1 of wet cells at 20 mM substrate concentration and 5 mg ml−1 of cell density.  相似文献   
3.
Candida species are opportunistic human fungal pathogens that cause acute and chronic infections against which only few antifungal agents are available. Here we have elucidated the antifungal effect of Syzygium samarangense leaf extracts (SSLE). Antifungal activity of SSLE was studied against Candida albicans, C. krusei, C. parapsilosis, C. glabrata, C. auris and C. tropicalis. Following experiments were performed: minimum fungicidal concentration (MFC) determination, agar well disc diffusion assays, fungal morphology analysis using scanning electron microscope (SEM), ex vivo fungal survival assays on porcine tongue and skin and in vivo fungal survival assays using Drosophila melanogaster fly model. Results demonstrated MFC of SSLE ranges between 100 and 125 mg ml−1. SEM images showed cell wall degradation of C. albicans when treated with SSLE. Around 75% decrease in C. albicans viability was observed when infected porcine tongue and skin were treated using SSLE. The C. albicans infected D. melanogaster when fed with SSLE showed significant decrease (around 80%) of fungal count than the infected control. Furthermore, agar plate disc diffusion assays demonstrated that the antifungal activity of SSLE could be due to chalcone, which is one of the active constituents in SSLE. Our study demonstrated that SSLE could be used for the topical treatment of Candida infections.  相似文献   
4.
The role of abscisic acid in the ripening of grapes   总被引:1,自引:0,他引:1  
Ripening in grapes ( Vitis vinifera L. cv. Thompson seedless) was accompanied by an increase in the levels of sucrose, glucose and fructose and a decrease in the levels of acids. The activity of glucose-6-phosphatase and fructose-l–6-bisphospbatase was lower in sweet grapes as compared to sour ones. Abscisic acid (10−6 M) stimulated the gluconeogenic process in sour grapes. The levels of some gluconeogenic enzymes were also elevated in its presence. Cyclohexitnide (0.036–1.8 mM) nullified the abscisic acid effect, suggesting that this effect involves de novo protein synthesis. The incorporation of [14C]-leucine into proteins was enhanced about 80% by abscisic acid, confirming that abscisic acid promoted protein synthesis. Again, cycloheximide blocked the hormone mediated increase in the incorporation of radioactivity into proteins. The results indicate that one of the factors for sourness in certain mature ripe grapes may be that abscisic acid is not available.  相似文献   
5.
6.
The flowering stage of African marigold Tagetes erecta (L.) was the most preferred for oviposition by Helicoverpa armigera (Hübner). The lower sides of leaf margins received more eggs compared to buds, stem tip and flowers. Olfactometer studies revealed that more female moths were attracted towards the flower extracts, followed by leaf, bud and stem tip extracts of African marigold. The thin layer chromatography analysis of these extracts showed a blend of compounds including careen, ocimene, methyl benzoate, phenyl acetaldehyde and phenyl ethanol. Attempts have been made to correlate insect behavior with the presence of these compounds.  相似文献   
7.
Observations on phenology of some representative trees, shrubs, under-shrubs and herbs in a subalpine forest of Uttarakhand, western Himalaya were recorded. With the commencement of favorable growth season in April, occurrence of leaf fall was indicatory growth phenomenon in Quercus semecarpifolia, Q. floribunda and Abies spectabilis. However, active vegetative growth in herbaceous species starts onward April and fruit maturation and seed dehiscence are completed from mid of September to October. In general, vegetative growth and reproductive stages in majority of the studied species seems to be dependent on adequate moisture content and also flowering and fruiting in subalpine plants correlate ambient temperature.  相似文献   
8.
Quantitative computed tomography-based finite element models of proximal femora must be validated with cadaveric experiments before using them to assess fracture risk in osteoporotic patients. During validation, it is essential to carefully assess whether the boundary condition (BC) modeling matches the experimental conditions. This study evaluated proximal femur stiffness results predicted by six different BC methods on a sample of 30 cadaveric femora and compared the predictions with experimental data. The average stiffness varied by 280% among the six BCs. Compared with experimental data, the predictions ranged from overestimating the average stiffness by 65% to underestimating it by 41%. In addition, we found that the BC that distributed the load to the contact surfaces similar to the expected contact mechanics predictions had the best agreement with experimental stiffness. We concluded that BC modeling introduced large variations in proximal femora stiffness predictions.  相似文献   
9.
10.
Gallbladder cancer (GBC) is an aggressive malignancy of gastrointestinal tract. Due to uncontrolled growth, GBC cells rapidly synthesize biomolecules including lipids. The lipids are integral component of cell membrane with a wide range of cellular functions. In this study, we measured the clinicopathological features in 40 cases of histologically confirmed GBC and 16 cases of chronic cholecystitis (CC). The female to male ratio in the GBC and CC groups were 3.44:1 and 2.2:1, respectively. The GBC patients exhibited well to poorly differentiated tumor. In the CC group, all patients showed cholecystitis with no evidence of dysplasia or malignancy. The majority of GBC and CC patients reported pain. Using 1H NMR spectroscopy, we observed 4-folds increase in the level of choline containing phospholipids (CCPLs) in the gallbladder of GBC patients as compared to CC patients. Other lipid metabolites such as cholesterol ester, C18-cholesterol and saturated fatty acids were insignificantly changed between GBC and CC patients. Moreover, the level of CCPLs in the GBC patients with BMI <25 kg/m2 was significantly higher as compared to CC patients. Further, a significant increase in the CCPLs level was observed in GBC female patients in comparison to CC patients. From the computational analyses, we observed that the genes involved in the biosynthesis of phosphatidylcholine (PtdCho) indirectly interact with the RELA, which encodes the NF-κB p65 subunit. The genes involved in the PtdCho biosynthesis were also correlated with the overall and disease-free survival of cholangiocarcinoma patients. The study opens new window for exploring the diagnostic and therapeutic potential of CCPLs in GBC patients.  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