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   2387篇
  免费   121篇
  国内免费   3篇
  2023年   20篇
  2022年   35篇
  2021年   65篇
  2020年   47篇
  2019年   58篇
  2018年   53篇
  2017年   39篇
  2016年   74篇
  2015年   106篇
  2014年   119篇
  2013年   163篇
  2012年   165篇
  2011年   201篇
  2010年   100篇
  2009年   91篇
  2008年   124篇
  2007年   118篇
  2006年   112篇
  2005年   106篇
  2004年   88篇
  2003年   80篇
  2002年   74篇
  2001年   37篇
  2000年   31篇
  1999年   35篇
  1998年   19篇
  1997年   14篇
  1996年   12篇
  1995年   17篇
  1994年   11篇
  1993年   15篇
  1992年   27篇
  1991年   20篇
  1990年   17篇
  1989年   20篇
  1988年   23篇
  1987年   15篇
  1986年   14篇
  1985年   17篇
  1984年   11篇
  1983年   11篇
  1982年   11篇
  1981年   10篇
  1980年   10篇
  1979年   9篇
  1978年   11篇
  1977年   8篇
  1976年   6篇
  1975年   6篇
  1974年   12篇
排序方式: 共有2511条查询结果,搜索用时 0 毫秒
51.
The structural and spectroscopic properties of novel five-coordinated dimeric-Cu(II) system have been investigated. The biocidal activities of all eight compounds, ligands, cupric nitrate and standard drugs against six bacteria and three fungi were determined. The DNA interaction activity of complexes was studied using spectrophotometry and electrophoresis. The superoxide dismutase (SOD)-like activity of the complexes was compared with previously reported monomeric- and dimeric copper complexes. The results support the five-coordinated dimeric square pyramidal geometry for the quinolone-Cu(II) system.  相似文献   
52.
Patients with chronic alcoholism and/or Alzheimer's disease show degenerative changes in the cerebral cortex and hippocampus. To investigate possible changes in insulin-like growth factor I receptor binding sites in brain tissue of patients with these pathological conditions, the number of 125I-insulin-like growth factor I binding sites was determined in tissues obtained from control patients and those with Alzheimer's and/or with a history of alcoholism. The four experimental groups examined consisted of patients from similar age groups. Postmortem histology and a clinical history were used for the diagnosis of Alzheimer's disease and alcoholism, respectively. Careful clinical records were kept concerning other variables such as immediate cause of death and medications administered before death. Specific binding of 125I-insulin-like growth factor I to homogenates prepared from cerebral cortex of Alzheimer's, alcoholic, alcoholic Alzheimer's, and age-matched control patients was similar, although Alzheimer's patients tended to have slightly higher binding values. No significant differences in insulin-like growth factor I binding in cerebral cortex were found with regard to age of patients, the interval between death and autopsy, and CNS-active medications. No statistical differences in 125I-insulin-like growth factor I binding were noted in hippocampal tissue from the four patient groups. Thus, human insulin-like growth factor I binding sites in cerebral cortex and hippocampus appear unaffected by several variables.  相似文献   
53.
Screening of fifteen nutrients belonging to four categories, viz., carbon, nitrogen, salt and complex organic sources was carried out using Plackett-Burman design for the production of thermostable #-amylase and pullulanase by Clostridium thermosulfurogenes SV2 in solid-state fermentation (SSF). This design involves screening of up to `nу' variables in just `n' number of experiments. Regression co-efficients and t-values were calculated by subjecting the experimental data to statistical analysis. Lactose, diammonium hydrogen phosphate, calcium chloride and casein hydrolysate showed higher regression co-efficients in the biomass formation. Among the fifteen nutrients screened, based on their performance in terms of product promoting ability, availability and cost, magnesium chloride, potato starch, ferrous sulphate, pearl millet flour and corn steep liquor were identified as most effective and, therefore, selected for inclusion in further optimization studies.  相似文献   
54.
Artonin E is a prenylated flavonoid isolated from the stem bark of Artocarpus elasticus Reinw.(Moraceae). This study aimed to investigate the apoptotic mechanisms induced by artonin E in a metastatic human ovarian cancer cell line SKOV-3 in vitro. MTT assay, clonogenic assay, acridine orange and propidium iodide double staining, cell cycle and annexin V analyses were performed to explore the mode of artonin E-induced cell death at different time points. DNA laddering, activation of caspases-3, -8, and -9, multi-parametric cytotoxicity-3analysis by high-content screening, measurement of reactive oxygen species generation, and Western blot were employed to study the pathways involved in the apoptosis. MTT results showed that artonin E inhibited the growth of SKOV-3 cells, with IC50 values of 6.5±0.5μg/mL after 72 h treatment, and showed less toxicity toward a normal human ovarian cell lineT1074, with IC50 value of 32.5±0.5μg/mL. Results showed that artonin E induced apoptosis and cell cycle arrest at the S phase. This compound also promoted the activation of caspases-3, -8, and -9. Further investigation into the depletion of mitochondrial membrane potential and release of cytochrome c revealed that artonin E treatment induced apoptosis via regulation of the expression of pro-survival and pro-apoptotic Bcl-2 family members. The expression levels of survivin and HSP70 proteins were also down regulated in SKOV-3 cells treated with artonin E. We propose that artonin E induced an antiproliferative effect that led to S phase cell cycle arrest and apoptosis through dysregulation of mitochondrial pathways, particularly the pro- and anti-apoptosis signaling pathways.  相似文献   
55.
The diversity of natural enemies harboured by flowering forbs on rice field bunds was recorded. Ageratum conozoides with a maximum Shannon diversity index of 1.8 followed by Acmella uliginosa, Eclipta alba and Tridax procumbens are amenable for ecological engineering, providing nectar, pollen and alternate prey to natural enemies.  相似文献   
56.
57.

Finite element method (FEM) simulations have been carried out on free-standing and finite dielectric substrate-supported eccentric (i) silica core-gold nanoshell dimers and (ii) gold core-silica nanoshell dimers for understanding their near- and far-field plasmonic properties. In the case of eccentric silica core-gold nanoshell dimers, multiple peaks are observed in the near- and far-field spectra due to the plasmon hybridization. The number of peaks is found to be sensitive to the core offset parameters of the nanoshells forming nanodimer. The wavelength locations of the peaks due to the constructive coupling of the lower order modes found relatively more sensitive to the dielectric substrate. The number of peaks in the near- and far-field spectra found the same presence and absence of the dielectric substrate. The values of full width at half maximum (FWHM) of the peaks observed in the near-field spectra are found larger as compared to those observed in the far-field spectra. In contrast, in the case of eccentric gold core-silica nanoshell dimers, multiple peaks have not been observed. The FWHM of the observed peak is found sensitive to the core offset parameters of the nanoshells, and the number of peaks in the near field- and far-field spectra found not same in the presence and absence of the dielectric substrate. Moreover, the differences in near- and far-field spectra of plasmonically coupled (i) concentric nanoshells, (ii) eccentric nanoshells, and (iii) concentric and eccentric nanoshells also investigated numerically.

  相似文献   
58.
Purinergic Signalling - Bone marrow (BM) as an active hematopoietic organ is highly sensitive to changes in body microenvironments and responds to external physical stimuli from the surrounding...  相似文献   
59.
Breast Cancer (BCa) is the most often diagnosed cancer among women who were in the late 1940’s. Breast cancer growth is largely dependent on the expression of estrogen and progesterone receptor. Breast cancer cells may have one, both, or none of these receptors. The treatment for breast cancer may involve surgery, hormonal therapy (Tamoxifen, an aromatase inhibitor, etc.) and oral chemotherapeutic drugs. The molecular docking technique reported the findings on the potential binding modes of the 2‐(2‐bromo‐3‐nitrophenyl)‐5‐phenyl‐1,3,4‐oxadiazole derivatives with the estrogen receptor (PDB ID: 3ERT). The 1,3,4‐oxadiazole derivatives 4a – 4j have been synthesized and described by spectroscopic method. 2‐(2‐Bromo‐6‐nitrophenyl)‐5‐(4‐bromophenyl)‐1,3,4‐oxadiazole ( 4c ) was reconfirmed by single‐crystal XRD. All the compounds have been tested in combination with generic Imatinib pharmaceutical drug against breast cancer cell lines isolated from Caucasian woman MCF‐7, MDA‐MB‐453 and MCF‐10A non‐cancer cell lines. The compounds with the methoxy (in 4c ) and methyl (in 4j ) substitution were shown to have significant cytotoxicity, with 4c showing dose‐dependent activation and decreased cell viability. The mechanism of action was reported by induced apoptosis and tested by a DNA enzyme inhibitor experiment (ELISA) for Methyl Transferase. Molecular dynamics simulations were made for hit molecule 4c to study the stability and interaction of the protein?ligand complex. The toxicity properties of ADME were calculated for all the compounds. All these results provide essential information for further clinical trials.  相似文献   
60.
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