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   13492篇
  免费   697篇
  国内免费   101篇
耳鼻咽喉   143篇
儿科学   317篇
妇产科学   236篇
基础医学   1878篇
口腔科学   356篇
临床医学   1185篇
内科学   3680篇
皮肤病学   223篇
神经病学   1253篇
特种医学   409篇
外科学   1915篇
综合类   41篇
一般理论   4篇
预防医学   650篇
眼科学   192篇
药学   776篇
中国医学   28篇
肿瘤学   1004篇
  2023年   96篇
  2022年   219篇
  2021年   362篇
  2020年   262篇
  2019年   304篇
  2018年   393篇
  2017年   292篇
  2016年   336篇
  2015年   399篇
  2014年   540篇
  2013年   698篇
  2012年   1106篇
  2011年   1104篇
  2010年   632篇
  2009年   556篇
  2008年   922篇
  2007年   933篇
  2006年   885篇
  2005年   855篇
  2004年   793篇
  2003年   652篇
  2002年   622篇
  2001年   105篇
  2000年   94篇
  1999年   119篇
  1998年   120篇
  1997年   101篇
  1996年   108篇
  1995年   72篇
  1994年   71篇
  1993年   51篇
  1992年   52篇
  1991年   52篇
  1990年   34篇
  1989年   33篇
  1988年   29篇
  1987年   25篇
  1986年   21篇
  1985年   19篇
  1984年   34篇
  1983年   29篇
  1982年   24篇
  1981年   23篇
  1980年   12篇
  1979年   11篇
  1978年   10篇
  1977年   9篇
  1976年   12篇
  1975年   10篇
  1974年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.

Ethnopharmacology relevance

Different plant species from Cordia genera are used in folk medicine as anti-inflammatory medication throughout the tropical and subtropical regions of the world. In Brazil, Cordia verbenacea is a medicinal plant known as “erva-baleeira”. The alcoholic extracts, decoctions and infusions with leaves of C. verbenacea are used in Brazilian traditional medicine for treatment of cough, pneumonia, parasitic diseases and, especially, the inflammatory processes. Anti-inflammatory activity was already demonstrated; however, molecular mechanisms of action are not completely understood. Considering the importance of histamine in early events of inflammation and in allergic diseases, we evaluated the effect of ethanol extract of leaves of C. verbenacea on histamine release (in vitro and in vivo studies) from different types of mast cells induced by chemical agents using several species of rodents.

Materials and Methods

The extraction and quantification of histamine were performed by using an automatic fluorometric continuous flow system.

Results

The extract of C. verbenacea (30 μg/ml) reduced the in vitro secretion of histamine from rat mast cells induced by ionophore A23187, concanavalin A and compound 48/80, respectively, to 22.1 ± 2.2%, 24.3 ± 2.5% and 21.4 ± 2.1%. At the same concentration, the extract also inhibited the secretion of histamine from mast cells of guinea pig induced by ionophore A23187 to 33.3 ± 2.2%, and mast cells of hamster induced by ionophore A23187 and concanavalin A to 15.8 ± 2.5% and 10.8 ± 2.6%, respectively. The oral treatment with the extract (300 mg/kg) also inhibited the secretion of histamine induced by A23187 about to 36.3 ± 3.2% in rats.

Conclusions

C. verbenacea inhibits the in vitro secretion of histamine from mast cells of different animal species, as well as the secretion of mast cells from animals treated with the extract, which gives not only the proven anti-inflammatory effect of the plant, but also anti-allergic effect, opening new possibilities for future anti-allergic herbal medicine.  相似文献   
992.
The diesters of benzene-1,2-dicarboxylic (phthalic) acid, commonly known as phthalates, are a family of industrial compounds, primarily used as plasticizers in enormous quantities for a variety of industrial uses in the formulation of plastics. Di-(2-ethylhexyl) phthalate (DEHP) is the most commonly used plasticizer. These plasticizers are not covalently bound to the polymer and leach out into the environment, thus becoming ubiquitous environmental contaminants. Cumulating evidence points out on the adverse effects of phthalate exposure during intrauterine life. Recently, it has been documented that in utero phthalate exposure is associated with a shorter duration of pregnancy. Phthalates induce and activate a subset of peroxisome proliferator-activated receptors (PPARs) and have an intrinsic pro-inflammatory activity, while some natural PPAR agonists induce cyclooxygenase (COX)-2 expression. To this regard, COX-2 is thought to be overexpressed in chorioamnionitis (CA), a fetal systemic inflammatory response syndrome and a leading cause of preterm birth. An adequate maternal dietary intake of essential fatty acids, well known anti-inflammatory agents, is indispensable to fetal development. Recently, it has been shown that phthalates alter the placental essential fatty acids (EFAs) homeostasis so potentially leading to abnormal fetal development. Likewise, a possible down-regulation of COX-2 by omega-3 fatty acids has been suggested. As a consequence, maternal supplementation with omega 3 during pregnancy could counteract the adverse effects of phthalates exposure in the human fetus. Here, we analyze the existing evidence on the link between antenatal phthalate exposure and abnormal fetal development, as well as on possible therapeutic tools to fight the adverse effect of this exposure.  相似文献   
993.
Although a number of compounds are currently used to treat Type 2 diabetes mellitus, achieving a sustained glycaemic control over time is often not possible using oral antidiabetics. Endogenous incretins exhibit beneficial effects that could be useful for Type 2 diabetes mellitus treatment, such as stimulating insulin secretion during hyperglycaemia, improving beta-cell mass and function, reducing glucagon secretion, delaying gastric emptying, reducing postprandial hyperglycaemia and diminishing body weight; however, their short half-life makes them unsuitable for treatment. Incretin mimetics such as liraglutide and exenatide were developed to overcome this limitation. This review discusses the effects of these compounds and their potential as a new class of antidiabetic agents.  相似文献   
994.

Background

Phthalates are ubiquitous industrial chemicals used as plasticizers in plastics made of polyvinyl chloride (PVC) to confer flexibility and durability. They are also present in products used for personal-care, industry and in medical devices. Phthalates have been associated with several adverse health effects, and recently it has been proposed that exposure to phthalates, could have an effect on metabolic homeostasis. This exploratory cross-sectional study evaluated the possible association between phthalate exposure and self-reported diabetes among adult Mexican women.

Methods

As part of an on-going case-control study for breast cancer, only controls were selected, which constituted 221 healthy women matched by age (±5 years) and place of residence with the cases. Women with diabetes were identified by self-report. Urinary concentrations of nine phthalate metabolites were measured by online solid phase extraction coupled to high performance liquid chromatography-isotope-dilution tandem mass spectrometry.

Results

Participants with diabetes had significantly higher concentrations of di(2-ethylhexyl) pththalate (DEHP) metabolites: mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP) and mono(2-ethyl-5-carboxypentyl) phthalate (MECPP) but lower levels of monobenzyl phthalate (MBzP) a metabolite of benzylbutyl phthalate, compared to participants without diabetes. A marginally significant positive associations with diabetes status were observed over tertiles with MEHHP (ORT3 vs. T1=2.66; 95% CI: 0.97–7.33; p for trend=0.063) and MEOHP (ORT3 vs. T1=2.27; 95% CI; 0.90–5.75; P for trend=0.079) even after adjusting for important confounders.

Conclusions

The results suggest that levels of some phthalates may play a role in the genesis of diabetes.  相似文献   
995.
996.
INTRODUCTION: The anterior cingulate region has been implicated in the pathophysiology of mood disorders. Studies have reported anatomical and functional abnormalities in this region in bipolar disorder patients. Few neurochemical studies have evaluated this region, especially on medicated bipolar patients. Lithium has been reported to increase NAA levels but not by all studies. We used proton magnetic spectroscopy ((1)HMRS) to measure the levels of N-acetyl-L-aspartate (NAA) and choline (Cho) relative to creatine (Cr) in the anterior cingulate of euthymic medicated bipolar subjects. METHODS: (1)HMRS was performed using a GE Signa 1.5 Tesla scanner in 13 euthymic bipolar patients who were taking lithium for at least four weeks before the scan and in 15 normal controls. The (1)HMRS signal was collected from an 8 cm(3) voxel placed in the anterior cingulate. Data analysis was performed with the automated PROBE/SV quantification tool. RESULTS: NAA/Cr and Cho/Cr ratios were not significantly different between patients and controls (NAA/Cr: 1.60 +/- 0.34 in patients, 1.68 +/- 0.34 in controls; Cho/Cr: 1.13 +/- 0.13 in patients, 1.11 +/- 0.20 in controls). CONCLUSIONS: We did not find a significant difference in the NAA/Cr and Cho/Cr ratio between bipolar patients and healthy controls. Chronic administration of psychotropic drugs could have had an effect on NAA/Cr levels of bipolar patients.  相似文献   
997.
Persistence on treatment affects the efficacy of antihypertensive treatment. We prospectively investigated the persistence on therapy and the extent of blood pressure (BP) control in 347 hypertensive patients (age 59.4 +/- 6 years) randomly allocated to a first-line treatment with: angiotensin-converting enzyme (ACE) inhibitors, calcium-channel blockers (CCBs), beta-blockers, angiotensin-II receptor blockers (ARBs), or diuretics and followed-up for 24-months. Persistence on treatment was higher in patients treated with ARBs (68.5%) and ACE inhibitors (64.5%) vs CCBs (51.6%; p < 0.05), beta-blockers (44.8%, p < 0.05), and diuretics (34.4%, p < 0.01). No ARB, ACE inhibitor, beta-blocker, or diuretic was associated with a higher persistence in therapy compared with the other molecules used in each therapeutic class. The rate of persistence was significantly higher in patients treated with lercanidipine vs others CCBs (59.3% vs 46.6%, p < 0.05). Systolic and diastolic BP was decreased more successfully in patients treated with ARBs (-11.2/-5.8 mmHg), ACE inhibitors (-10.5/-5.1 mmHg), and CCBs (-8.5/-4.6 mmHg) compared with beta-blockers (-4.0/-2.3 mmHg p < 0.05) and diuretics (-2.3/-2.1 mmHg, p < 0.05). No ARB, ACE inhibitor, beta-blocker, or diuretic was associated with a higher BP control compared with the other molecules used in each therapeutic class. A trend toward a better BP control was observed in response to lercanidipine vs other CCBs (p = 0.059). The present results confirm the importance of persistence on treatment for the management of hypertension in clinical practice.  相似文献   
998.
Brachytherapy dose distributions are calculated for 15 mm ROPES eye plaque loaded with model Theragenics200 and IR06-103Pd seeds. The effects of stainless steel backing and Acrylic insert on dose distribution along the central axis of the eye plaque and at critical ocular structure are investigated. Monte Carlo simulation was carried out with the Version 5 of the MCNP. The dose at critical ocular structure by considering the eye composition was calculated. Results are compared with the calculated data for COMS eye plaque loaded with Theragenics200 palladium-103 seeds and model 6711 iodine-125 seed. The air kerma strength of the IR06-103Pd seed to deliver 85 Gy in apex of tumor in water medium was calculated to be 4.10 U/seed. Along the central axis of stainless steel plaque loaded with new 103Pd seeds in Acrylic insert, the dose reduction relative to water is 6.9% at 5 mm (apex). Removal of the Acrylic insert from the plaque (replacing with water) did not make significantly difference in dose reduction results (~0.2%). The presence of the stainless steel backing results in dose enhancement near the plaque relative to water. Doses at points of interest are higher for ROPES eye plaque when compared to COMS eye plaque. The dosimetric parameters calculated in this work for the new palladium seed, showed that in dosimetry point of view, the IR06-103Pd seed is suitable for use in brachytherapy. The effect of Acrylic insert on dose distribution is negligible and the main effect on dose reduction is due to the presence of stainless steel plaque backing.  相似文献   
999.

Background

The contraceptive efficacy of emergency contraceptive pills containing levonorgestrel (LNG-EC) has been estimated in most previous studies by judging the day of ovulation from presumptive menstrual cycle data, thus providing poorly reliable estimates.

Methods

In the present study, the efficacy of LNG-EC was determined in 393 cycles by dating ovulation on the basis of reliable hormonal and ovarian parameters validated by a database constructed in a separate study. In addition, the efficacy was determined separately for cycles in which LNG-EC was given before or after ovulation.

Results

For the 148 women who had sexual intercourse during the fertile days, the overall accumulated probability of pregnancy was 24.7, while altogether 8 pregnancies were observed. Thus, the overall contraceptive efficacy of LNG-EC was 68%. Among the 103 women who took LNG-EC before ovulation (days −5 to −1), 16 pregnancies were expected and no pregnancy occurred (p<.0001). Among the 45 women who took LNG-EC on the day of ovulation (day 0) or thereafter, 8 pregnancies occurred and 8.7 were expected (p=1.00). These findings are incompatible with the inhibition of implantation by LNG-EC in women. The same cases were also analyzed using the presumptive menstrual cycle data, and important discrepancies were detected between the two methods.

Conclusion

The efficacy of LNG-EC has been overestimated in studies using presumptive menstrual cycle data. Our results confirm previous similar studies and demonstrate that LNG-EC does not prevent embryo implantation and therefore cannot be labeled as abortifacient.  相似文献   
1000.
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