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   1094篇
  免费   62篇
  国内免费   2篇
  2023年   10篇
  2022年   34篇
  2021年   78篇
  2020年   61篇
  2019年   76篇
  2018年   51篇
  2017年   34篇
  2016年   35篇
  2015年   64篇
  2014年   68篇
  2013年   87篇
  2012年   79篇
  2011年   81篇
  2010年   36篇
  2009年   36篇
  2008年   38篇
  2007年   31篇
  2006年   27篇
  2005年   23篇
  2004年   22篇
  2003年   19篇
  2002年   14篇
  2001年   6篇
  2000年   7篇
  1999年   7篇
  1998年   9篇
  1997年   6篇
  1995年   2篇
  1994年   7篇
  1993年   4篇
  1992年   4篇
  1991年   9篇
  1990年   8篇
  1989年   3篇
  1988年   4篇
  1987年   6篇
  1986年   6篇
  1985年   2篇
  1984年   4篇
  1983年   3篇
  1982年   7篇
  1981年   4篇
  1980年   9篇
  1979年   10篇
  1978年   3篇
  1977年   6篇
  1976年   3篇
  1975年   3篇
  1974年   6篇
  1972年   4篇
排序方式: 共有1158条查询结果,搜索用时 265 毫秒
201.
202.
Background:The available evidence has increasingly demonstrated that a combination of genetic and epigenetic factors, such as DNA methylation, could be considered as causing leukemia. Epigenetic changes and methylation of the suppressor of the cytokine signaling 1 promoter (SOCS1) CpG region silence SOCS1 expression in cancer. In the current study, we evaluated the impact of epigallocatechin gallate (EGCG) and RG108 on SOCS1 promoter methylation and expression in U937 cells.Methods:In the current study, U937 leukemic cells were treated with EGCG and RG108 for 12, 24, 48, and 72 h and SOCS1 promoter methylation and its expression were measured by methylation-specific PCR (MSP) and quantitative real-time PCR, respectively.Results:The outcomes indicated that the SOCS1 promoter is methylated in U937 cells, and treatment of these cells with either EGCG or RG108 reduced its methylation. Moreover, we observed that SOCS1 expression was significantly upregulated in a time-dependent manner by both EGCG and RG108 in U937 cells compared with control cells. In the RG108-treated group at 12, 24, 48, and 72 h, SOCS1 expression was upregulated by 1, 4.2, 16.6, and 32.6 -fold respectively, and in the EGCG-treated group, by 0.5, 3.2, 10.8, and 22.3 -fold, respectively. Conclusion:Treatment with either EGCG or RG108 reduced SOCS1 promoter methylation and increased SOCS1 expression in U937 cells in a time-dependent manner, which may play a role in leukemia therapy.Key Words: DNA Methylation, EGCG, Leukemia, RG108, SOCS1  相似文献   
203.
The prevalence of self-medication (SM) has increased in health professionals due to awareness of disease and symptoms. Incorrect use of medication caused harmful effects. To assess the knowledge, attitude and practice of health professionals, this survey was conducted. A cross-sectional study was carried out among health professionals of different specialities. Knowledge, attitude and practice-based questions were asked through an electronically distributed questionnaire. Data were statistically tested using the Chi-square test with SPSS. Most of the health professionals were aware with the term of self-medication; however the knowledge about related questions was not satisfactory. Almost half of the participants practiced self-medication. The prevalence of self-medication among participants was high. They need to be trained and educate about the incorrect use of self-medication.  相似文献   
204.
Ajuga bracteosa is a medicinally important plant globally used in the folk medicine against many serious ailments. In the present study, effects of two significant elicitors, methyl jasmonate (Me-J) and phenyl acetic acid (PAA) were studied on growth parameters, secondary metabolites production, and antioxidant potential in adventitious root suspension cultures of A. bracteosa. The results showed a substantial increase in biomass accumulation, exhibiting longer log phases of cultures growth in response to elicitor treatments, in comparison to control. Maximum dry biomass formation (8.88 DW g/L) was recorded on 32nd day in log phase of culture when  0.6 mg/L Me-J was applied; however, PAA at 1.2 mg/L produced maximum biomass (8.24 DW g/L) on day 40 of culture.  Furthermore, we observed the elicitors-induced enhancement in phenolic content (total phenolic content), flavonoid content (total flavonoid content) and antioxidant activity (free radical scavenging activity) in root suspension cultures of A. bracteosa. Application of 0.6 mg/L and 1.2 mg/L of Me-J, root cultures accumulated higher TPC levels (3.6 mg GAE/g DW) and (3.7 mg GAE/g DW) in the log phase and stationary phase, respectively, while 2.5 mg/L Me-J produced lower levels (1.4 mg GAE/g DW) in stationary phase of growth stages. Moreover, TFC and FRSA values were found in correspondence to TPC values in the respective growth phases at the similar elicitor treatment. Thus, a feasible protocol for establishment of adventitious roots in A. bracteosa was developed and enhancement in biomass and metabolite content in adventitious root was promoted through elicitation.  相似文献   
205.
The behavior of a single Aβ40 molecule within a dipalmitoylphosphatidylcholine (DPPC) bilayer was studied by all‐atom molecular dynamics simulations. The effect of membrane structure was investigated on Aβ40 behavior, secondary structure, and insertion depth. Simulations were performed at three temperatures (323, 310, and 300 K) to probe three different bilayer fluidities. Results show that at all above temperatures, the peptide contains two short helices, coil, bend, and turn structures. At 300 K, the peptide contains a region with β structure in C‐terminal region. Our results also show that Aβ decreases the bilayer thickness and the order of lipids in its vicinity which leads to water insertion into the bilayer and concomitant increase in the local fluidity. The peptide remains embedded in the bilayer at all temperatures, and become inserted into the bilayer up to several residues at 323 and 310 K. At 310 and 300 K, the dominant interaction energy between Aβ and bilayer changes from electrostatic to van der Waals. It can be proposed that at higher temperatures (e.g., 323 K), Lys28 and the C‐terminal region of the peptide play the role of two anchors that keep Aβ inside the top leaflet. This study demonstrates that Aβ molecule can perturb the integrity of cellular membranes. Proteins 2017; 85:1298–1310. © 2017 Wiley Periodicals, Inc.  相似文献   
206.
Cibotium barometz is an endangered tree fern, used both as ornamental plant and traditional Chinese medicinal plant. In this study, an effective in vitro propagation protocol was obtained through formation of green globular bodies (GGBs) from in vitro juvenile sporophytes. The effect of plant growth regulators (PGRs) on GGB induction and multiplication, as well as mineral salt concentration and active charcoal (AC) on plantlet regeneration from GGBs was evaluated. Thidiazuron (TDZ; 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea) had a significant effect on GGB induction and multiplication (P?<?0.001), while a-naphthaleneacetic acid (NAA) did not (P?>?0.05). GGB induction rate was above 80?% on 1/2 Murashige and Skoog (MS) media supplemented with TDZ (1.0 mg L??1) and NAA (0.1, 0.3 or 0.5 mg L??1). The same media were also optimal for GGB multiplication. GGBs cultured on 1/4 MS media supplemented with 0.1 or 0.2?% (w/v) AC showed a high rate of GGB development into plantlets above 90?%. 1/2 MS media supplemented with 0.1 or 0.2?% AC were the most effective for plantlet growth. Regenerated plantlets were successfully acclimatized (80?%) in greenhouse conditions. Morphological and histological analysis revealed that C. barometz GGBs was a yellow-green globular structure composed of the single GGB with meristems and hair-like structures, and new single GGBs were initiated from the epidermal cells of meristem zone.  相似文献   
207.
The main objective was to determine the elemental profile of the lung lining fluid of rats which are used as model animals in various experiments. Lung lining fluid elemental constitution obtained after bronchoalveolar lavage fluid (BALF) was analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine the biological trace elements along with calcium and magnesium. BALF was collected from healthy rats using a tracheal cannula. However, cells in BALF were counted to monitor any underlying inflammatory lung condition. Cell free BALF samples were processed and analyzed for the elements including magnesium (Mg), calcium (Ca), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), selenium (Se), bromine (Br), and iodine (I). In view of this, calcium concentration was the highest (6318.08 ± 3094.3 μg/L) and copper concentration was the lowest (0.89 ± 0.21 μg/L). The detected elements, from high to low concentration, include Ca > Mg > Fe > Br > I > Cr > Ni > Zn > Mn > Se > Cu. Pearson’s correlation analysis revealed no significant correlation between cell count and concentration of any of the element detected in BALF. Correlation analysis also revealed significant positive correlation among Fe, I, Cr, Ni, and Mn. Ca was found to be correlated negatively with Cu and positively with Se. Br and Mg found to be positively correlated with each other. Zn remained the only element that was not found to be correlated with any of the elements in the rat BALF.  相似文献   
208.
The role of insecticidal application and host plant resistance in managing Spodoptera exigua has been well documented, but the effect of different host plants, on which the pest cycles its population in the field, has seldom been investigated. Therefore, we have studied the vulnerability of S. exigua against commonly used insecticides (cypermethrin, chlorpyrifos, lufenuron, and emamectin benzoate) with different mode of actions when it switches its generations from natal to auxiliary hosts and vice versa. Different field populations being established on different host plants including castor, cauliflower, cotton, okra, and spinach were collected and reared in the laboratory before insecticidal bioassays. The role of larval diet and host plant switching on their response to tolerate applied insecticides was studied using leaf‐dip bioassay methods. Host switching demonstrated a significant role in altering the vulnerability of S. exigua populations to tested insecticides. Spodoptera exigua sourced from castor, when switched host to okra and spinach, exhibited 50% higher mortality when treated with emamectin benzoate. This trend in mortality was consistent upon complete host switch cycle (natal—auxiliary—natal host). However, the highest increase (92%) in vulnerability was recorded when the larvae were shifted to spinach from cotton. In general, chlorpyrifos and lufenuron had highest efficacies in terms of larval mortality. The findings of present studies provide insights to a better understanding the behavior of polyphagous pests and the role of different host plants in altering the susceptibility of these pests against applied insecticides. Ultimately the results warrant that due consideration should be given to cropping patterns and time of host switching by pest population during planning and executing chemical control.  相似文献   
209.
2-Hydroxyphenacyl azole and 2-hydroxyphenacyl azolium compounds have been described as a new class of azole antifungals. Most target compounds showed significant in vitro antifungal activities against tested fungi (Candida albicans, Saccharomyces cerevisiae, Aspergillus niger, and Microsporum gypseum) with low MICs values included in the range of 0.25-32 microg/mL comparable to reference drug fluconazole. The most active compounds were also assessed for their cytotoxicity using MTT colorimetric assay on normal mouse fibroblast (NIH/3T3) cells. The results of antifungal activity and toxicity tests indicated that these compounds display antifungal activity at non-cytotoxic concentrations.  相似文献   
210.
Novel isosteric analogs of the ceramidase inhibitors (1S,2R)-N-myristoylamino-phenylpropanol-1 (d-e-MAPP) and (1R,2R)-N-myristoylamino-4'-nitro-phenylpropandiol-1,3 (B13) with modified targeting and physicochemical properties were developed and evaluated for their effects on endogenous bioactive sphingolipids: ceramide, sphingosine, and sphingosine 1-phosphate (Cer, Sph, and S1P) in MCF7 cells as determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). Time- and dose-response studies on the effects of these compounds on Cer species and Sph levels, combined with structure-activity relationship (SAR) data, revealed 4 distinct classes of analogs which were predominantly defined by modifications of the N-acyl-hydrophobic interfaces: N-acyl-analogs (class A), urea-analogs (class B), N-alkyl-analogs (class C), and omega-cationic-N-acyl analogs (class D). Signature patterns recognized for two of the classes correspond to the cellular compartment of action of the new analogs, with class D acting as mitochondriotropic agents and class C compounds acting as lysosomotropic agents. The neutral agents, classes A and B, do not have this compartmental preference. Moreover, we observed a close correlation between the selective increase of C(16)-, C(14)-, and C(18)-Cers and inhibitory effects on MCF7 cell growth. The results are discussed in the context of compartmentally targeted regulators of Sph, Cer species, and S1P in cancer cell death, emphasizing the role of C(16)-Cer. These novel analogs should be useful in cell-based studies as specific regulators of Cer-Sph-S1P inter-metabolism, in vitro enzymatic studies, and for therapeutic development.  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