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   790篇
  免费   36篇
  2023年   8篇
  2022年   5篇
  2021年   27篇
  2020年   17篇
  2019年   21篇
  2018年   24篇
  2017年   21篇
  2016年   25篇
  2015年   28篇
  2014年   42篇
  2013年   51篇
  2012年   54篇
  2011年   74篇
  2010年   37篇
  2009年   35篇
  2008年   54篇
  2007年   54篇
  2006年   48篇
  2005年   44篇
  2004年   42篇
  2003年   31篇
  2002年   25篇
  2001年   19篇
  2000年   8篇
  1999年   10篇
  1998年   1篇
  1997年   5篇
  1996年   3篇
  1993年   2篇
  1992年   1篇
  1990年   2篇
  1988年   1篇
  1984年   1篇
  1980年   1篇
  1972年   1篇
  1968年   1篇
  1967年   1篇
  1964年   1篇
  1962年   1篇
排序方式: 共有826条查询结果,搜索用时 218 毫秒
91.
We report a newborn with Fryns syndrome and atypical findings like a large midline cleft on forehead. Abnormal findings included congenital left diaphragmatic hernia, prominent forehead, hypertelorism, broad nasal bridge, anteverted nostrils, cleft palate, low set ears, tapered fingers, macrocephaly, congenital heart defect, midline defects and renal anomalies. This is the first case that has a midline cleft on forehead with normal cranial MRI findings.  相似文献   
92.
Nano-structure of a new Pb(II) two-dimensional coordination polymer, {[Pb(2-pyc)(N3)(H2O)]n (1), 2-Hpyc = 2-pyridinecarboxylic acid} was synthesized by a sonochemical method. The new nano-structure was characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Compound 1 was structurally characterized by single crystal X-ray diffraction and consists of two-dimensional polymeric units. The thermal stability of compound 1 was studied by thermal gravimetric and differential thermal analyses and compared. PbO nano-powder was obtained by calcination of the nano-structure of compound 1 at 400 °C. This study demonstrates the coordination polymers may be suitable precursors for the preparation of nano-scale materials and dependent on their packing they may produce different and interesting morphologies.  相似文献   
93.
The antimicrobial activity and the MIC values of the ethanol, chloroform, diethyl ether, and acetone extracts of the chemical races of Pseudevernia furfuracea (var. furfuracea and var. ceratea) and their physodic acid, chloroatranorin, atranorin, and olivetoric acid constituents have been investigated against some microorganisms. Nearly all extracts of both chemical races showed antimicrobial activity against Aeromonas hydrophila, Bacillus cereus, Bacillus subtilis, Listeria monocytogenes, Proteus vulgaris, Staphylococcus aureus, Streptococcus faecalis, Yersinia enterocolitica, Candida albicans, Candida glabrata, Alternaria alternata, Ascochyta rabiei, Aspergillus niger, Fusarium culmorum, Fusarium moniliforme, Fusarium oxysporum, Fusarium solani, and Penicillium notatum. There was no antimicrobial activity of the extracts against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Pseudomonas syringae, Salmonella typhimurium, Alternaria citri, Alternaria tenuissima, and Gaeumannomyces graminis. Chloroatranorin and olivetoric acid were active against the same microorganisms with few exceptions. Physodic acid was active against about the same bacteria and yeasts and inactive against all of the filamentous fungi tested. Also no activity of atranorin against the filamentous fungi was observed.  相似文献   
94.
Postoperative intraperitoneal adhesion formation is a major cause of intestinal obstruction, pain and infertility. This experimental study was designed to evaluate the degree of adhesion formation and peritoneal tissue levels of malondialdehyde (MDA), reduced glutathione (GSH) and total nitrite and nitrate (NO) and the effect of aminoguanidine (AG) on these metabolite values after postoperative intraperitoneal adhesion formation in rats. A total of 21 adult male Wistar albino rats were randomly divided into three groups. Control rats were untreated; the AG group received AG 200 mg kg(-1) i.p. for 10 consecutive days intraperitoneally after surgery. The sham group was given 0.9% NaCl. The rats were killed on postoperative day 10. The peritoneal tissues were harvested to determine the tissue levels of MDA, GSH, and NO activity. For light microscopic evaluation, the cecum was removed. Adhesion formation scores in the AG group were significantly lower than those of the control and sham groups (p < 0.017, p < 0.026 respectively). In the AG-treated rats, tissue levels of MDA and NO were significantly lower than in the control group (p < 0.017). The levels of GSH in aminoguanidine-treated rats were significantly higher than those of the control group (p < 0.01). The severity of the inflammation was more prominent in the control group compared with the AG-injected rats. The results demonstrate that in this experimental model, intraperitoneal administration of aminoguanidine decreases the incidence and extent of peritoneal adhesions and causes a decrease in MDA and NO and an increase in GSH values.  相似文献   
95.
Isoniazid (INH) still remains a first-line drug both for treatment and prophylaxis of tuberculosis, but various organs toxicity frequently develops in patients receiving this drug. We aimed to investigate possible toxic effects of INH on rat red blood cells (RBCs), and to elucidate whether Caffeic acid phenethyl ester (CAPE) prevents a possible toxic effect of INH. Experimental groups were designed as follows: control group, INH group, INH + CAPE group. Compared with the control, the INH caused a significant increase in superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels, and a decrease in glutathione peroxidase (GSH-Px) and catalase (CAT), which are recently used to monitor the development and extent of damage due to oxidative stresses. CAPE administration to INH group ameliorated above changes due to INH.  相似文献   
96.
Drug-induced liver toxicity is a common cause of liver injury. This study was designed to elucidate whether high dose vancomycin (VCM) induces oxidative stress in liver and to investigate the protective effects of erdosteine, an expectorant agent. Twenty-two young Wistar rats were divided into three groups as follows: control group, VCM, and VCM plus erdosteine. VCM was administered intraperitoneally in the dosage of 200 mg/kg twice daily for 7 days. Erdosteine was administered orally administered once a day at a dose of 10 mg/kg body weight. The activities of antioxidant enzymes such as superoxide dismutase and catalase as well as the concentration of malondialdehyde, as an indicator of lipid peroxidation, were measured to evaluate oxidative stress in homogenates of the liver. VCM administration increased malondialdehyde levels (p < 0.001), superoxide dismutase (p < 0.01) and catalase (p < 0.001) activities. Erdosteine co-administration with VCM injections caused significantly decreased malondialdehyde levels (p < 0.001), superoxide dismutase (p < 0.01) and catalase (p < 0.001) activities in liver tissue when compared with VCM alone. It can be concluded that erdosteine may prevent VCM-induced oxidative changes in liver by reducing reactive oxygen species.  相似文献   
97.
Doxorubicin (DOX) is a broad-spectrum anthracycline antibiotic that has cardiotoxicity as a major side effect. One mechanism of this toxicity is believed to involve the reactive oxygen radical species (ROS); these agents likely account for the pathophysiology of DOX-induced cardiomyopathy. Aminoguanidine (AG) is an effective antioxidant and free radical scavenger which has long been known to protect against ROS formation. We investigated the effects of AG on DOX-induced changes in thiobarbituric acid reactive substances (TBARS) and reduced glutathione (GSH) content. The rats were divided into four groups:1) Control; 2) DOX group; injected intraperitoneally (i.p.) with DOX 20 mg/kg in a single dose 3) AG-treated group; injected i.p. in single dose of 20 mg/kg DOX plus 100 mg/kg AG 1 h before the DOX for 3 days, 4) AG group; injected i.p. with AG 100 mg/kg for 3 days. DOX administration to control rats increased TBARS and decreased GSH levels. AG administration before DOX injection caused significant decrease in TBARS and increase in GSH levels in the heart tissue when compared with DOX only. Morphological changes, including severe myocardial fibrosis and inflammatory cell infiltration were clearly observed in the DOX-treated heart. AG reversed the DOX-induced heart damage. Therefore AG could protect the heart tissue against free radical injury. The application of AG during cancer chemotherapy may attenuate tissue damage and improve the therapeutic index of DOX.  相似文献   
98.
The genotoxic effects of the fungicide afugan were analysed by measuring chromosomal aberrations (CAs), sister chromatid exchange (SCE) and micronuclei (MN) in cultured human peripheral lymphocytes. Concentrations of 2.5, 5, 10 and 20 microg/ml of afugan were used during 24 and 48 h. Afugan significantly increased the frequency of CAs at 5, 10 and 20 microg/ml concentrations during a 48 h treatment period. A significant increase was observed for induction of SCE and MN at all treatments compared with the negative control. A significant dose-response correlation was found in all tests. Afugan did not affect the replicative index (RI), however it significantly decreased the mitotic index (MI) at all treatment concentrations except 2.5 microg/ml, and at both treatment times. The present results indicate that afugan is clastogenic and cytotoxic to cultured human lymphocytes.  相似文献   
99.
1. One of the fundamental insights of behavioural ecology is that resources influence breeding systems. For instance, when food resources are plenty, one parent is able to care for the young on its own, so that the other parent can desert and became polygamous. We investigated this hypothesis in the context of classical polyandry when females may have several mates within a single breeding season, and parental duties are carried out largely by the male. 2. We studied a precocial wader, the Kentish plover Charadrius alexandrinus, that exhibits variable brood care such that the chicks may be raised by both parents, only by the female or, more often, only by the male. The timing of female desertion varies: some females desert their brood at hatching of the eggs and lay a clutch for a new mate, whereas other females stay with their brood until the chicks fledge. Kentish plovers are excellent organisms with which to study breeding system evolution, as some of their close relatives exhibit classical polyandry (Eurasian dotterel Eudromias morinellus, mountain plover Charadrius montanus), whereas others are polygynous (northern lapwing Vanellus vanellus). 3. Kentish plovers raised their broods in two habitats in our study site in southern Turkey: saltmarsh and lakeshore. Food intake was higher on the lakeshore than in the saltmarsh as judged from feeding behaviour of chicks and adults. As the season proceeded and the saltmarsh dried out, the broods moved toward the lakeshore. 4. As the density of plovers increased on lakeshore, the parents spent more time defending their young, and female parents stayed with their brood longer on the lakeshore. 5. We conclude that the influence of food abundance on breeding systems is more complex than currently anticipated. Abundant food resources appear to have profound implications on spatial distribution of broods, and the social interactions between broods constrain female desertion and polyandry.  相似文献   
100.
The aromatase gene encodes the key enzyme for estrogen formation. Aromatase enzyme inhibitors eliminate total body estrogen production and are highly effective therapeutics for postmenopausal breast cancer. A distal promoter (I.4) regulates low levels of aromatase expression in tumor-free breast adipose tissue. Two proximal promoters (I.3/II) strikingly induce in vivo aromatase expression in breast fibroblasts surrounding malignant cells. Treatment of breast fibroblasts with medium conditioned with malignant breast epithelial cells (MCM) or a surrogate hormonal mixture (dibutyryl (Bt2)cAMP plus phorbol diacetate (PDA)) induces promoters I.3/II. The mechanism of promoter-selective expression, however, is not clear. Here we reported that sodium butyrate profoundly decreased MCM- or Bt2cAMP + PDA-induced promoter I.3/II-specific aromatase mRNA. MCM, Bt2cAMP + PDA, or sodium butyrate regulated aromatase mRNA or activity only via promoters I.3/II but not promoters I.1 or I.4 in breast, ovarian, placental, and hepatic cells. Mechanistically, recruitment of phosphorylated ATF-2 by a CRE (-211/-199, promoter I.3/II) conferred inductions by MCM or Bt2cAMP + PDA. Chromatin immunoprecipitation-PCR and immunoprecipitation-immunoblotting assays indicated that MCM or Bt2cAMP + PDA stabilized a complex composed of phosphorylated ATF-2, C/EBPbeta, and cAMP-response element-binding protein (CREB)-binding protein in the common regulatory region of promoters I.3/II. Overall, histone acetylation patterns of promoters I.3/II did not correlate with sodium butyrate-dependent silencing of promoters I.3/II. Sodium butyrate, however, consistently disrupted the activating complex composed of phosphorylated ATF-2, C/EBPbeta, and CREB-binding protein. This was mediated, in part, by decreased ATF-2 phosphorylation. Together, these findings represent a novel mechanism of sodium butyrate action and provide evidence that aromatase activity can be ablated in a signaling pathway- and cell-specific fashion.  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