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   1006篇
  免费   89篇
  国内免费   1篇
  2023年   4篇
  2022年   17篇
  2021年   44篇
  2020年   12篇
  2019年   22篇
  2018年   19篇
  2017年   14篇
  2016年   28篇
  2015年   44篇
  2014年   51篇
  2013年   71篇
  2012年   69篇
  2011年   60篇
  2010年   57篇
  2009年   35篇
  2008年   52篇
  2007年   57篇
  2006年   40篇
  2005年   38篇
  2004年   48篇
  2003年   33篇
  2002年   31篇
  2001年   17篇
  2000年   22篇
  1999年   14篇
  1998年   12篇
  1995年   4篇
  1994年   4篇
  1993年   3篇
  1992年   9篇
  1991年   12篇
  1990年   10篇
  1989年   13篇
  1988年   7篇
  1987年   4篇
  1986年   5篇
  1985年   6篇
  1984年   9篇
  1983年   4篇
  1982年   5篇
  1979年   5篇
  1978年   7篇
  1977年   5篇
  1976年   8篇
  1975年   7篇
  1974年   5篇
  1972年   7篇
  1971年   4篇
  1968年   3篇
  1965年   3篇
排序方式: 共有1096条查询结果,搜索用时 15 毫秒
31.
International Journal of Peptide Research and Therapeutics - The original version of the article unfortunately contained a typo in co-author name.  相似文献   
32.
Lepidoptera is the second most diverse insect order outnumbered only by the Coeleptera. Acetylcholinesterase (AChE) is the major target site for insecticides. Extensive use of insecticides, to inhibit the function of this enzyme, have resulted in the development of insecticide resistance. Complete knowledge of the target proteins is very important to know the cause of resistance. Computational annotation of insect acetylcholinesterase can be helpful for the characterization of this important protein. Acetylcholinesterase of fourteen lepidopteran insect pest species was annotated by using different bioinformatics tools. AChE in all the species was hydrophilic and thermostable. All the species showed lower values for instability index except L. orbonalis, S. exigua and T. absoluta. Highest percentage of Arg, Asp, Asn, Gln and Cys were recorded in P. rapae. High percentage of Cys and Gln might be reason for insecticide resistance development in P. rapae. Phylogenetic analysis revealed the AChE in T. absoluta, L. orbonalis and S. exigua are closely related and emerged from same primary branch. Three functional motifs were predicted in eleven species while only two were found in L. orbonalis, S. exigua and T. absoluta. AChE in eleven species followed secretory pathway and have signal peptides. No signal peptides were predicted for S. exigua, L. orbonalis and T. absoluta and follow non secretory pathway. Arginine methylation and cysteine palmotylation was found in all species except S. exigua, L. orbonalis and T. absoluta. Glycosylphosphatidylinositol (GPI) anchor was predicted in only nine species.  相似文献   
33.
Barley (Hordeum vulgare L.) is a major cereal grain and is known as a halophyte (a halophyte is a salt-tolerant plant that grows in soil or waters of high salinity). We therefore conducted a pot experiment to explore plant growth and biomass, photosynthetic pigments, gas exchange attributes, stomatal properties, oxidative stress and antioxidant response and their associated gene expression and absorption of ions in H. Vulgare. The soil used for this analysis was artificially spiked at different salinity concentrations (0, 50, 100 and 150 mM) and different levels of ascorbic acid (AsA) were supplied to plants (0, 30 and 60 mM) shortly after germination of the seed. The results of the present study showed that plant growth and biomass, photosynthetic pigments, gas exchange parameters, stomatal properties and ion uptake were significantly (p < 0.05) reduced by salinity stress, whereas oxidative stress was induced in plants by generating the concentration of reactive oxygen species (ROS) in plant cells/tissues compared to plants grown in the control treatment. Initially, the activity of antioxidant enzymes and relative gene expression increased to a saline level of 100 mM, and then decreased significantly (P < 0.05) by increasing the saline level (150 mM) in the soil compared to plants grown at 0 mM of salinity. We also elucidated that negative impact of salt stress in H. vulgare plants can overcome by the exogenous application of AsA, which not only increased morpho-physiological traits but decreased oxidative stress in the plants by increasing activities of enzymatic antioxidants. We have also explained the negative effect of salt stress on H. vulgare can decrease by exogenous application of AsA, which not only improved morpho-physiological characteristics, ions accumulation in the roots and shoots of the plants, but decreased oxidative stress in plants by increasing antioxidant compounds (enzymatic and non-enzymatic). Taken together, recognizing AsA's role in nutrient uptake introduces new possibilities for agricultural use of this compound and provides a valuable basis for improving plant tolerance and adaptability to potential salinity stress adjustment.  相似文献   
34.
Recent imaging studies have reported directional motion biases in human visual cortex when perceiving moving random dot patterns. It has been hypothesized that these biases occur as a result of the integration of motion detector activation along the path of motion in visual cortex. In this study we investigate the nature of such motion integration with functional MRI (fMRI) using different motion stimuli. Three types of moving random dot stimuli were presented, showing either coherent motion, motion with spatial decorrelations or motion with temporal decorrelations. The results from the coherent motion stimulus reproduced the centripetal and centrifugal directional motion biases in V1, V2 and V3 as previously reported. The temporally decorrelated motion stimulus resulted in both centripetal and centrifugal biases similar to coherent motion. In contrast, the spatially decorrelated motion stimulus resulted in small directional motion biases that were only present in parts of visual cortex coding for higher eccentricities of the visual field. In combination with previous results, these findings indicate that biased motion responses in early visual cortical areas most likely depend on the spatial integration of a simultaneously activated motion detector chain.  相似文献   
35.
Kocide 101 (77% cupric hydroxide) and Ridomil plus (15% metalaxyl and 35% copper oxychloride) were used in the treatment of tomato plants in the field. Generally, the two fungicides exhibited an inhibitive effect on the total and individual counts of glucophilic fungi after different periods of treatment except in some cases, the counts were not affected or promoted compared with the control. Fungal genera and species associated with roots and shoots of tomato plants were isolated from untreated plants as control and then compared with those isolated from plants treated with different doses of fungicides. The most common fungal species recovered from soil and different parts of plants were Alternaria alternata, Aspergillus flavus, A. fumigatus, A. niger, A. terreus, Cochliobolus spicifer, Emericella nidulans, E. nidulans var. lata, Fusarium oxysporum, Gibberella fujikuroi, Mycosphaerella tassiana, Nectria haematococca, Penicillium chrysogenum, P. funiculosum, P. oxalicum, Stachybotrys chartarum and Rhizopus stolonifer.  相似文献   
36.
Ten tomato genotypes were screened for their resistance against cucumber mosaic virus (CMV) and its vector Myzus persicae under natural infection in field, using aphids M. persicae under net-house and mechanical inoculation under greenhouse. Large differences were observed among genotypes for infection percentage (IP) and severity index (SI) among the testing methods used. All genotypes showing tolerance to CMV in the field or through aphid inoculation, however, become susceptible and highly susceptible after mechanical inoculation. All the test genotypes also showed susceptibility to the aphid M. persicae population. Plants inoculated with CMV showed substantial decrease in yield and yield-contributing parameters which varied with cultivars that probably depended upon its genetic make up. All the test genotypes exhibited 0.97–30.19% decrease in plant height, 11.47–52.65% decrease in root length, 46.56–95.56% decrease in fresh plant weight, 65.78–92.84% decrease in root fresh weight, 19.97–87.65% decrease in the dry weight of plants, 75.63–95.43% decrease in dry root weight, 69.51–95.65% reduction in the number of fruits and 89.04–99.89% decrease in yield per plants. After 15 days of inoculation, the quantitative analysis using double beam spectrophotometer showed an increase in total phenolics in CMV-inoculated plants as compared to un-inoculated plants among genotypes. Similarly the thin layer chromatography (TLC) on silica gel G indicated that the number of phenolic compounds was increased in most of the inoculated genotypes while in others they were either decreased or remained same.  相似文献   
37.

Background:

Leaving hospital against medical advice may have adverse consequences. Previous studies have been limited by evaluating specific types of patients, small sample sizes and incomplete determination of outcomes. We hypothesized that leaving hospital against medical advice would be associated with increases in subsequent readmission and death.

Methods:

In a population-based analysis involving all adults admitted to hospital and discharged alive in Manitoba from Apr. 1, 1990, to Feb. 28, 2009, we evaluated all-cause 90-day mortality and 30-day hospital readmission. We used multivariable regression, adjusted for age, sex, socioeconomic status, year of hospital admission, patient comorbidities, hospital diagnosis, past frequency of admission to hospital, having previously left hospital against medical advice and data clustering (patients with multiple admissions). For readmission, we assessed both between-person and within-person effects of leaving hospital against medical advice.

Results:

Leaving against medical advice occurred in 21 417 of 1 916 104 index hospital admissions (1.1%), and was associated with higher adjusted rates of 90-day mortality (odds ratio [OR] 2.51, 95% confidence interval [CI] 2.18–2.89), and 30-day hospital readmission (within-person OR 2.10, CI 1.99–2.21; between-person OR 3.04, CI 2.79–3.30). In our additional analyses, elevated rates of readmission and death associated with leaving against medical advice were manifest within 1 week and persisted for at least 180 days after discharge.

Interpretation:

Adults who left the hospital against medical advice had higher rates of hospital readmission and death. The persistence of these effects suggests that they are not solely a result of incomplete treatment of acute illness. Interventions aimed at reducing these effects may need to include longitudinal interventions extending beyond admission to hospital.Patients leaving hospital against medical advice have been discussed in the medical literature for more than 50 years.1 Reported to occur in 1%–2% of patients in general hospitals,2,3 the numbers are large; in the United States, 368 000 patients left against medical advice in 2007,3 and rates higher than 10% have been documented in certain subgroups, including Canadian patients with HIV and predominantly poor residents of inner city areas.4,5 The main concern over leaving hospital against medical advice is that it may increase morbidity or mortality. Previous studies attempting to assess this effect2,413 have all been restricted to specific types of patients, and most studies were limited by small sample sizes and incomplete determination of outcomes. In this study, we used data that avoided these limitations to test the hypothesis that patients who leave hospital against medical advice have higher rates of hospital readmission and death.  相似文献   
38.
Described is the antibiotic activity of a marine natural product. Psammaplysin F (1) inhibited the growth of four Gram-positive strains by >80% at 50 μM, and the amine at position C-20 is responsible for the observed antibacterial activity. When tested against two strains of methicillin resistant Staphylococcus aureus (MRSA), the minimum inhibitory concentrations (MICs) for psammaplysin F (40–80 μM) were similar to the structurally-related alkaloid psammaplysin H (2). Psammaplysin F (1) increased membrane permeability by two to four-fold compared to psammaplysin H (2) or control-treated bacteria, respectively. Unlike psammaplysin H (2), we show that psammaplysin F (1) inhibits equal partitioning of DNA into each daughter cell, suggesting that this natural product is a unique prokaryotic cell division inhibitor.  相似文献   
39.
Predation influences prey diversity and productivity while it effectuates the flux and reallocation of organic nutrients into biomass at higher trophic levels. However, it is unknown how bacterivorous protists are influenced by the diversity of their bacterial prey. Using 456 microcosms, in which different bacterial mixtures with equal initial cell numbers were exposed to single or multiple predators (Tetrahymena sp., Poterioochromonas sp. and Acanthamoeba sp.), we showed that increasing prey richness enhanced production of single predators. The extent of the response depended, however, on predator identity. Bacterial prey richness had a stabilizing effect on predator performance in that it reduced variability in predator production. Further, prey richness tended to enhance predator evenness in the predation experiment including all three protists predators (multiple predation experiment). However, we also observed a negative relationship between prey richness and predator production in multiple predation experiments. Mathematical analysis of potential ecological mechanisms of positive predator diversity—functioning relationships revealed predator complementarity as a factor responsible for both enhanced predator production and prey reduction. We suggest that the diversity at both trophic levels interactively determines protistan performance and might have implications in microbial ecosystem processes and services.  相似文献   
40.

Background

Lack of reliable predictive biomarkers is a stumbling block in the management of prostate cancer (CaP). Prostate-specific antigen (PSA) widely used in clinics has several caveats as a CaP biomarker. African-American CaP patients have poor prognosis than Caucasians, and notably the serum-PSA does not perform well in this group. Further, some men with low serum-PSA remain unnoticed for CaP until they develop disease. Thus, there is a need to identify a reliable diagnostic and predictive biomarker of CaP. Here, we show that BMI1 stem-cell protein is secretory and could be explored for biomarker use in CaP patients.

Methodology/Principal Findings

Semi-quantitative analysis of BMI1 was performed in prostatic tissues of TRAMP (autochthonous transgenic mouse model), human CaP patients, and in cell-based models representing normal and different CaP phenotypes in African-American and Caucasian men, by employing immunohistochemistry, immunoblotting and Slot-blotting. Quantitative analysis of BMI1 and PSA were performed in blood and culture-media of siRNA-transfected and non-transfected cells by employing ELISA. BMI1 protein is (i) secreted by CaP cells, (ii) increased in the apical region of epithelial cells and stromal region in prostatic tumors, and (iii) detected in human blood. BMI1 is detectable in blood of CaP patients in an order of increasing tumor stage, exhibit a positive correlation with serum-PSA and importantly is detectable in patients which exhibit low serum-PSA. The clinical significance of BMI1 as a biomarker could be ascertained from observation that CaP cells secrete this protein in higher levels than cells representative of benign prostatic hyperplasia (BPH).

Conclusions/Significance

BMI1 could be developed as a dual bio-marker (serum and biopsy) for the diagnosis and prognosis of CaP in Caucasian and African-American men. Though compelling these data warrant further investigation in a cohort of African-American 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