首页 | 官方网站   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   3571篇
  免费   175篇
  国内免费   67篇
医药卫生   3813篇
  2023年   27篇
  2022年   17篇
  2021年   92篇
  2020年   55篇
  2019年   68篇
  2018年   91篇
  2017年   83篇
  2016年   98篇
  2015年   143篇
  2014年   162篇
  2013年   165篇
  2012年   256篇
  2011年   265篇
  2010年   155篇
  2009年   113篇
  2008年   186篇
  2007年   197篇
  2006年   194篇
  2005年   166篇
  2004年   140篇
  2003年   119篇
  2002年   111篇
  2001年   101篇
  2000年   92篇
  1999年   85篇
  1998年   27篇
  1997年   21篇
  1996年   29篇
  1995年   21篇
  1994年   19篇
  1993年   14篇
  1992年   34篇
  1991年   39篇
  1990年   38篇
  1989年   34篇
  1988年   19篇
  1987年   22篇
  1986年   22篇
  1985年   30篇
  1984年   19篇
  1983年   13篇
  1979年   16篇
  1978年   21篇
  1977年   13篇
  1976年   13篇
  1975年   15篇
  1974年   17篇
  1973年   14篇
  1972年   18篇
  1966年   16篇
排序方式: 共有3813条查询结果,搜索用时 109 毫秒
71.
The levels of thymidine kinase (TK; EC 2.7.1.21) mRNA were determined in nine established cell lines derived from TK-ts13, a temperature-sensitive mutant cell line that arrests in late G1 phase of the cell cycle at the restrictive temperature. The derivative cell lines carried either a cDNA or a minigene of human TK under the control of TK promoters of different lengths. A tenth cell line carried a human TK cDNA under the control of a simian virus 40 promoter. Two different assays were used to determine the S-phase-specific regulation of human TK mRNA levels in quiescent cells stimulated to proliferate. Results from these two assays indicated that (i) the first two introns of the human TK gene had no effect on the S-phase-specific regulation of TK mRNA levels, although the presence of introns increased the amount of TK mRNA; (ii) similar amounts of TK mRNA were present in cells containing constructs with an 83-base-pair (bp) promoter as with other TK promoters comprising up to approximately 4000 bp of 5' flanking sequence; (iii) a 456-bp promoter was fully S-phase-regulated, whereas the 83-bp promoter was only partially regulated; (iv) a 63-bp promoter was much less regulated than an 83-bp promoter; and (v) the crucial element in the 20-bp fragment comprising bp -83 to -64 has been localized, by site-directed mutagenesis, to the CCAAT element at -70.  相似文献   
72.
73.
Somatic mosaicism for DNA copy‐number alterations (SMC‐CNAs) is defined as gain or loss of chromosomal segments in somatic cells within a single organism. As cells harboring SMC‐CNAs can undergo clonal expansion, it has been proposed that SMC‐CNAs may contribute to the predisposition of these cells to genetic disease including cancer. Herein, the gross genomic alterations (>500 kbp) were characterized in uninvolved mammary glandular tissue from 59 breast cancer patients and matched samples of primary tumors and lymph node metastases. Array‐based comparative genomic hybridization showed 10% (6/59) of patients harbored one to 359 large SMC‐CNAs (mean: 1,328 kbp; median: 961 kbp) in a substantial portion of glandular tissue cells, distal from the primary tumor site. SMC‐CNAs were partially recurrent in tumors, albeit with considerable contribution of stochastic SMC‐CNAs indicating genomic destabilization. Targeted resequencing of 301 known predisposition and somatic driver loci revealed mutations and rare variants in genes related to maintenance of genomic integrity: BRCA1 (p.Gln1756Profs*74, p.Arg504Cys), BRCA2 (p.Asn3124Ile), NCOR1 (p.Pro1570Glnfs*45), PALB2 (p.Ser500Pro), and TP53 (p.Arg306*). Co‐occurrence of gross SMC‐CNAs along with point mutations or rare variants in genes responsible for safeguarding genomic integrity highlights the temporal and spatial neoplastic potential of uninvolved glandular tissue in breast cancer patients.  相似文献   
74.
Background: Few studies have shown an association between prenatal phthalate exposure and adverse effects on neurodevelopment and behavior in young children.Objectives: We aimed to assess the relationship between prenatal exposure to phthalate esters and behavior syndromes in children at 8 years of age.Methods: A total of 122 mother–child pairs from the general population in central Taiwan were studied from 2000 to 2009. Mono-methyl phthalate (MMP), mono-ethyl phthalate (MEP), mono-butyl phthalate (MBP), mono-benzyl phthalate (MBzP), and three di-(2-ethylhexyl) phthalate (DEHP) metabolites—mono-2-ethylhexyl, mono-2-ethyl-5-hydroxyhexyl, and mono-2-ethyl-5-oxohexyl phthalates (MEHP, MEHHP, and MEOHP)—were measured in maternal urine collected during the third trimester of pregnancy using liquid chromatography–electrospray ionization–tandem mass spectrometry. Behavioral syndromes of children at 8 years of age were evaluated using the Child Behavior Checklist (CBCL). Associations between log10-transformed creatinine-corrected phthalate concentrations and standardized scores of the CBCL were estimated using linear regression models or multinomial logistic regressions with adjustments for potential confounders.Results: Externalizing problem scores were significantly higher in association with a 1-unit increase in log10-transformed creatinine-corrected concentrations of maternal MBP (β = 4.29; 95% CI: 0.59, 7.99), MEOHP (β = 3.74; 95% CI: 1.33, 6.15), and MEHP (β = 4.28 ; 95% CI: 0.03, 8.26) after adjusting for the child’s sex, intelligence, and family income. Meanwhile, MBP and MEOHP were significantly associated with Delinquent Behavior and Aggressive Behavior scores. The same pattern was found for borderline and/or clinical ranges.Conclusions: Our findings suggest positive associations between maternal DEHP and dibutyl phthalate (DBP) exposure and externalizing domain behavior problems in 8-year-old children.Citation: Lien YJ, Ku HY, Su PH, Chen SJ, Chen HY, Liao PC, Chen WJ, Wang SL. 2015. Prenatal exposure to phthalate esters and behavioral syndromes in children at 8 years of age: Taiwan Maternal and Infant Cohort Study. Environ Health Perspect 123:95–100; http://dx.doi.org/10.1289/ehp.1307154  相似文献   
75.
76.

Purpose

We report here a unique case of a sudden loss of vision as the first symptom of an advanced chronic nephropathy.

Methods and Results

A 25-year-old man was referred to the Department of Ophthalmology with sudden visual deterioration presumptively diagnosed as bilateral retinitis. The patient had never been under any medical care before and had never had any clinical signs of any chronic disease. He underwent an ophthalmic examination with optical coherence tomography (OCT). Based on the clinical features, OCT scans and systemic blood pressure (BP) assessment (225/145 mm Hg), the patient was definitely diagnosed with hypertensive retinopathy and choroidopathy due to hypertensive crisis. After urgent diagnostic procedures, the patient was diagnosed with a chronic kidney disease at stage 5 in the course of chronic glomerulonephritis. Immediately, a renal replacement therapy was started and the patient was qualified for renal transplantation.

Conclusion

Adolescents with an unclear picture of retinal lesions, who have neither a history nor clinical signs of a systemic disease, should undergo careful systemic screening with BP assessment. A sudden deterioration of vision may be the first symptom of a previously undiagnosed severe systemic disease (very rare chronic) that requires immediate treatment.Key Words: Hypertensive crisis, Hypertensive choroidopathy, Hypertensive retinopathy, Chronic renal failure  相似文献   
77.
We evaluated the concordance between visceral fat area (VFA) estimated by bioelectrical impedance analysis (BIA) or computed tomography (CT) in Korean subjects with a wide range in age and body mass index (BMI). In 1006 individuals (mean age 55.2 ± 11.8 (19–87) years, mean BMI 26.0 ± 3.5 (17–46) kg/m2, 48.9% men), VFA quantified by CT was compared with VFA using multifrequency BIA machines within 15 days. Concordance rates were compared by age or BMI using correlation analysis, Bland-Altman plots, and intraclass correlation coefficient (ICC). Using BIA data, we established a regression formula to reflect CT-VFA. The mean VFAs by CT and BIA were 131.9 ± 57.3 cm2 and 110.5 ± 33.9 cm2, respectively (r = 0.605, p < 0.001). The mean difference was 21.4 ± 45.6 cm2, tending to increase with BMI. In women with BMI <25 kg/m2 or age <50 years, the VFAs by BIA were similar to those by CT (ICC = 0.496 in BMI <25 kg/m2 and ICC = 0.638 in age <50 years). However, the difference was greater in men with BMI ≥25 kg/m2 or age ≥50 years. Applying our formula, the difference between estimations decreased to 0.2 ± 38.2cm2. VFA estimated by BIA correlated well with that by CT, but a more accurate formula is needed to match CT data, particularly in older men or subjects with a high BMI.  相似文献   
78.
In this study, the removal of acetic acid by supported liquid membrane (SLM) using hybrid polyethersulfone (PES)–graphene membrane prepared by vapor induced phase separation (VIPS) was investigated. The effects of graphene loading, coagulation bath temperature, air exposure time, and air humidity on the morphology, mechanical strength, porosity, and contact angle of the membrane were analyzed. The performance and stability of the hybrid membrane as a SLM support for acetic acid removal were studied. The best PES–graphene membrane support was produced at a coagulation bath temperature of 50 °C, an air exposure time of 30 s and air humidity of 80%. The fabricated membrane has a symmetrical micropore cellular structure, high porosity and high contact angle. Under specific SLM conditions, almost 95% of acetic acid was successfully removed from 10 g L−1 aqueous acetic acid solution. The hybrid membrane remains stable for more than 116 h without suffering any membrane breakage during the continuous SLM process.

In this study, the removal of acetic acid by supported liquid membrane (SLM) using hybrid polyethersulfone (PES)–graphene membrane prepared by vapor induced phase separation (VIPS) was investigated.  相似文献   
79.
The aim of the present study was to identify the effect of canavanine on the imidazoline receptor because canavanine is a guanidinium derivative that has a similar structure to imidazoline receptor ligands. Transfected Chinese hamster ovary‐K1 cells expressing imidazoline receptors (nischarin (NISCH)‐CHO‐K1 cells) were used to elucidate the direct effects of canavanine on imidazoline receptors. In addition, the imidazoline I3 receptor has been implicated in stimulation of insulin secretion from pancreatic β‐cells. Wistar rats were used to investigate the effects of canavanine (0.1, 1 and 2.5 mg/kg, i.v.) on insulin secretion. In addition the a specific I3 receptor antagonist KU14R (4 or 8 mg/kg, i.v.) was used to block I3 receptors. Canavanine decreased blood glucose by increasing plasma insulin in rats. In addition, canavanine increased calcium influx into NISCH‐CHO‐K1 cells in a manner similar to agmatine, the endogenous ligand of imidazoline receptors. Moreover, KU12R dose‐dependently attenuated canavanine‐induced insulin secretion in HIT‐T15 pancreatic β‐cells and in the plasma of rats. The data suggest that canavanine is an agonist of I3 receptors both in vivo and in vitro. Thus, canavanine would be a useful tool in imidazoline receptor research.  相似文献   
80.
The development of concise methods for the synthesis of small functionalised spirocyclic molecules is important in the search of new bioactive molecules. To contribute this, here we represent a diastereoselective oxa-hetero-Diels–Alder reaction for the synthesis of novel spiro indanone fused pyrano[3,2-c]chromene derivatives and studied their in vitro anticancer activities. Using previously less explored cyclic ketone i.e. indane-1,3-dione and 3-vinyl-2H-chromene derivatives, we obtained novel spiro-heterocyclic frameworks at the interphase between “drug-like” molecules and natural products. Various spiro indanone fused pyrano[3,2-c]chromene derivatives were synthesized regiospecifically bearing a quaternary stereocenter in high yields (up to 85%) with excellent diastereoselectivity in toluene using 4 Å MS as additive under reflux condition at 120 °C. In vitro cytotoxic studies of these compounds against MCF-7 (breast cancer), HCT-116 (colon cancer), H-357 (oral cancer), MD-MB-231(Breast cancer) cell lines were evaluated by MTT {3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide} assay in vitro. The screening results revealed that many of the compounds are showing moderate to high levels of anticancer activities against the tested cancer cell lines and some displayed potent inhibitory activities in comparison to the commercial anticancer drug 5-fluorouracil (5-FU). Among the series, compound 3′c showed most potent cytotoxicity (15.0–27.5 μM) in three cancer cell lines (MCF-7, HCT-116 and MD-MB-231).

Synthesis of novel spiro indanone fused pyrano[3,2-c]chromene derivatives following hetero-Diels–Alder reaction has been demonstrated and evaluated for their in vitro anticancer activity.  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-23

京公网安备 11010802026262号