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   1066篇
  免费   93篇
  国内免费   4篇
耳鼻咽喉   23篇
儿科学   52篇
妇产科学   55篇
基础医学   109篇
口腔科学   35篇
临床医学   75篇
内科学   198篇
皮肤病学   27篇
神经病学   48篇
特种医学   30篇
外国民族医学   1篇
外科学   211篇
综合类   51篇
一般理论   1篇
预防医学   99篇
眼科学   31篇
药学   74篇
中国医学   1篇
肿瘤学   42篇
  2023年   3篇
  2022年   13篇
  2021年   28篇
  2020年   22篇
  2019年   31篇
  2018年   35篇
  2017年   20篇
  2016年   36篇
  2015年   28篇
  2014年   33篇
  2013年   51篇
  2012年   63篇
  2011年   67篇
  2010年   40篇
  2009年   49篇
  2008年   70篇
  2007年   54篇
  2006年   45篇
  2005年   70篇
  2004年   61篇
  2003年   55篇
  2002年   41篇
  2001年   13篇
  2000年   21篇
  1999年   16篇
  1998年   4篇
  1997年   5篇
  1996年   4篇
  1995年   15篇
  1994年   8篇
  1993年   5篇
  1992年   25篇
  1991年   10篇
  1990年   18篇
  1989年   5篇
  1988年   8篇
  1987年   10篇
  1986年   9篇
  1985年   14篇
  1984年   4篇
  1980年   4篇
  1978年   4篇
  1977年   3篇
  1974年   8篇
  1973年   6篇
  1972年   7篇
  1971年   3篇
  1968年   3篇
  1967年   3篇
  1966年   3篇
排序方式: 共有1163条查询结果,搜索用时 14 毫秒
81.
82.
A comparative multicenter clinical trial of two combined oral contraceptives (OCs) was conducted at clinics located in the Sudan, Sri Lanka, Chile, the Dominican Republic and Ecuador. The trial was designed to determine if there were differences in efficacy, safety and acceptability between a triphasic and a low-dose monophasic OC. This report includes analysis of 1088 women. At each center, subjects were randomly allocated to one of the two OCs. Follow-up visits were scheduled at 1, 4, 8 and 12 months after admission. There were two accidental pregnancies attributed to user failure reported during the study period; one in the triphasic group and one in the monophasic group. Adverse experiences were mainly minor with headaches and dizziness being the most common complaints; frequency of reports was similar in both groups. Cycle control was good in both groups with women in the triphasic group reporting fewer complaints of intermenstrual bleeding. Both OCs were safe and effective.  相似文献   
83.
A new methodology for objective evaluation of discomfort in whole-body vibration (WBV) is introduced in this work. The proposed objective discomfort characterizes discomfort based on the relative motion between adjacent segments of the human body from neutral positions. It peaks when the joints reach their limits. The objective discomfort has been tested on five subjects in the fore-aft direction using discrete sinusoidal frequencies of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, 12, 14, and 16 Hz. Each frequency file runs for 15 s with a 3 s resting period as a reference for discomfort comparison. All files run at a constant acceleration of 0.7 m/s(2). The subjects were tested with back support and without back support, and their subjective discomfort was reported based on the Borg CR-10 scale. The proposed objective discomfort has shown significant correlation with the subjective discomfort. The objective discomfort has also been tested on five subjects under multiple-axis random WBV with three common industrial seating configurations (seat-mounted control, floor-mounted control, and steering wheel), and has shown promising results.  相似文献   
84.
This work proposes an alternative green and selective biocatalytic route for Glycerin Monostearate (α-monostearin) production. The conventional method of production uses an elevated temperature. Apart from the high energy consumption, such high temperatures darken the final product's color, lead to random reactions, and produce high orders of diglycerides and triglycerides instead of monoglycerides. The proposed production process was performed by esterifying stearic acid with glycerin in an organic medium using Candida antarctica lipase (Novozym 435) at a mild temperature. The reaction conditions were optimized using the response surface methodology (RSM): optimum conditions were a temperature of 60 °C, glycerin to stearic acid molar ratio of 8:1, and Novozym 435 amount of 6% w/w. The solvent addition remarkably improved the α-monostearin yield to nearly 80% without the need for the energy-intensive distillation step. The conventional autocatalytic esterification (AUT) process was also performed to investigate the comparative monoglyceride yield, and it was found to be 22.5%. Proton nuclear magnetic resonance and gas-chromatography confirmed that α-monostearin could be produced with the highest purity using the proposed enzymatic method (ENZ). Economic and environmental analyses were also conducted for the proposed ENZ process, and the results were compared with those of the AUT process. The total capital investment of α-monostearin production, considering a projected capacity of 4950 t year?1 and 11% interest for the proposed ENZ process, was favorably 2.5 times lower than that of the AUT process, suggesting a promising investment opportunity. However, the total production costs showed unfavorable negative net present value (NPV) and return on investment (ROI) for the ENZ process and favorable positive NPV and ROI for the AUT process, indicating that the proposed venture is not profitable for α-monostearin production. However, the process can be profitable at improved operational stability of Novozym 435 up to 1 kg per 3-ton product. The carbon footprint was calculated on the basis of the given capacity and conditions of 50 and 656 t CO2 eq./year for the ENZ and AUT processes, respectively. The synthesis of α-monostearin using the proposed route can be considered a building block toward a cleaner large-scale production of α-monoglycerides.  相似文献   
85.
Eighteen brick kilns of three brick-making technologies (Fixed Chimney Kiln (FCK), Zigzag, and Hoffmann) were selected to measure the concentrations of particulate matter (PM2.5) with Aerocet 531S (USA) sampler, black carbon (BC) with Magee Scientific, OT-21 Soot scan Transmissometer (USA), and gaseous pollutants (CO2, CO, SO2, NOx, and volatile organic carbon (VOC)) with Aeroqual 500 gas sampler (New Zealand) to understand the emission scenario from brick sector in Greater Dhaka region, Bangladesh. Emission factor (EF) of each pollutant was computed from their respective concentration for three brick kiln technologies. Ambient PM2.5 and PM10 were measured in brick kiln premises and 1 km far from the respective kilns to see the effect on the surrounding areas. The PM2.5 concentration was found on an average of 141?±?86, 128?±?72, and 110?±?53 mg/m3 in FCK, Zigzag, and Hoffmann kilns, respectively. The average BC concentration was found 16.6?±?7.1 (FCK), 11.8?±?4.2 (Zigzag), and 8.9?±?4.4 (Hoffmann) mg/m3. FCK has a greater emission of CO, whereas Zigzag has a higher CO2 emission. A comparatively higher value of CO2 and lower value of CO indicates effective combustion of coal, and this is found to be more efficient for Zigzag and Hoffmann compared to traditional FCK. SO2 and VOC emissions were depending not only on the kiln types but also on the fuel qualities. From EF calculation, approximately 4526 t of PM2.5, 340 t of BC, 209,776 t of CO2, 8700 t of CO, 19,441 t of SO2, and 835,450 t of VOC per year found to emit from 1000 brick kilns. The conversion of traditional FCK to improved one, i.e., Zigzag and/or Hoffman is not a straight forward solution, as CO2 emission was higher in Zigzag whereas BC and PM2.5 emissions were higher in FCK. Therefore, considering EF of various pollutants from these three types of kilns, conversion of FCK to Zigzag or Hoffmann could be a better choice.  相似文献   
86.
Trace element deficiency or excess is implicated in the development or progression in some cancers. Here we report the elevated level of copper and low level of zinc in the plasma of esophageal cancer patients in Kashmir India—a high incidence area. The average level of copper was significantly higher (P < 0.0001) for patients than for controls, with a mean concentration of 169 μg/dl and 149 μg/dl for patients and controls, respectively. The control group consisted of 55 healthy individuals matched for age, sex, and place of residence of the patients. In contrast, the average level of zinc in patients was significantly lower than in controls (P < 0.0001), with a mean concentration of 86.8 μg/dl and 96.1 μg/dl for patients and controls, respectively. The levels of both copper and zinc showed significant differences based on gender and age in patients as compared to controls. Similarly, smokers depicted a significant increase in serum copper (N = 39, P = 0.002) and a decrease in serum zinc approaching level of significance in the patient group as compared to controls. The copper and zinc levels were significantly altered in patients (N = 40) when compared to controls as a function of snuff consumption. The differences in the levels of copper and zinc showed significant association with the consumption of local salted tea up to 1,500 ml per day, but the changes were insignificant beyond that. Patients with poorly differentiated tumors (N = 7) had a higher copper concentration than those with moderately or well-differentiated tumors (P < 0.0001). To validate the general notion that imbalance in copper and zinc levels may lead to higher prevalence of TP53 mutations, we compared the 3 variables, and no association was found between copper concentration and TP53 mutation status; but patients with TP53 mutant tumor had lower zinc levels than those with no mutation. In conclusion, our results point toward a role of the trace element imbalance in the esophageal tumorigenesis in high-risk Kashmiri population exposed to a range of nitroso compounds or their precursors. Further prospective cohort studies are warranted to determine whether change in the plasma zinc and copper homeostasis may represent an independent risk factor for this malignancy as well as a possible target for preventive intervention.  相似文献   
87.
Cysteamine, a potent somatostatin depletor, was used in the present study to investigate the role of endogenous somatostatin in acute peripheral inflammation. The acute inflammation was induced by intraplantar injection of carrageenan (1%), histamine (5 micromol), or formalin (2.5%) in the rat hind paw. The induced inflammation and the formation of oedema were determined by measurement of the paw thickness. Given subcutaneously (s.c.) 1 h before carrageenan, cysteamine caused significant, dose-dependent and long-lasting inhibition of rat paw oedema induced by carrageenan. At doses of 12.5, 25, 50 or 100 mg kg (-1), cysteamine significantly inhibited the carrageenan-induced paw oedema at 4 h by 52.3, 40, 40.7 or 26.3%. Cysteamine given at 300 mg kg (-1), a dose well known to deplete tissue somatostatin, reduced oedema by only 16.2% vs control values. Significant inhibition of the carrageenan-induced rat paw oedema was still evident 24 h post-injection at cysteamine doses of 12.5, 25, 50 or 100 mg kg (-1). Given s.c. at 300 mg kg (-1), 4 h prior to carrageenan, cysteamine decreased rat paw oedema at 4 h by 14.9%. Cysteamine (300 mg kg (-1)), 4 h beforehand, had little modulatory effect on the oedema induced by formalin (2.5%) but reduced that caused by intraplantar histamine (5 micromol). The anti-oedematogenic effect of indomethacin, but not that of the selective COX-2 inhibitor celecoxib, was less marked in rats pre-treated with cysteamine at 300 mg kg (-1). Cysteamine (0.3 microg- 0.3 mg paw (-1)) co-administered with carrageenan was devoid of anti-inflammatory effect and even promoted inflammation at low concentrations. Cysteamine given locally alone induced slight paw oedema. These data indicate that systemic cysteamine possesses potent and long-lasting anti-inflammatory effects and modulates the anti-inflammatory effect of cyclooxygenase inhibitors in a model of peripheral inflammation in the rat. The effect of cysteamine is likely to be mediated via central action.  相似文献   
88.
Background: Acrolein is a ubiquitous environmental hazard to human health. Acrolein has been reported to activate the DNA damage response and induce apoptosis. However, little is known about the effects of acrolein on cellular senescence.Objectives: We examined whether acrolein induces cellular senescence in cultured normal human lung fibroblasts (NHLF).Methods: We cultured NHLF in the presence or absence of acrolein and determined the effects of acrolein on cell proliferative capacity, senescence-associated β-galactosidase activity, the known senescence-inducing pathways (e.g., p53, p21), and telomere length.Results: We found that acrolein induced cellular senescence by increasing both p53 and p21. The knockdown of p53 mediated by small interfering RNA (siRNA) attenuated acrolein-induced cellular senescence. Acrolein decreased Werner’s syndrome protein (WRN), a member of the RecQ helicase family involved in DNA repair and telomere maintenance. Acrolein-induced down-regulation of WRN protein was rescued by p53 knockdown or proteasome inhibition. Finally, we found that acrolein accelerated p53-mediated telomere shortening.Conclusions: These results suggest that acrolein induces p53-mediated cellular senescence accompanied by enhanced telomere attrition and WRN protein down-regulation.Citation: Jang JH, Bruse S, Huneidi S, Schrader RM, Monick MM, Lin Y, Carter AB, Klingelhutz AJ, Nyunoya T. 2014. Acrolein-exposed normal human lung fibroblasts in vitro: cellular senescence, enhanced telomere erosion, and degradation of Werner’s syndrome protein. Environ Health Perspect 122:955–962; http://dx.doi.org/10.1289/ehp.1306911  相似文献   
89.
Objectives: The purpose of this study was to report prevalence, clinical characteristics, precipitating factors, management and outcome of patients with coronary artery disease (CAD) among patients hospitalized with heart failure (HF) in seven Middle Eastern countries and compare them to non-CAD patients.

Methods: Data were derived from Gulf CARE (Gulf aCute heArt failuRe rEgistry), a prospective multicenter study of 5005 consecutive patients hospitalized with acute HF during February-November 2012 in 7 Middle Eastern countries.

Results: The prevalence of CAD among Acute Heart Failure (AHF) patients was 60.2% and varied significantly among the 7 countries (Qatar 65.7%, UAE 66.6%, Kuwait 68.0%, Oman 65.9%, Saudi Arabia 62.5%, Bahrain 52.7% and Yemen 49.1%) with lower values in the lower income countries. CAD patients were older and more likely to have diabetes, hypertension, dyslipidemia and chronic kidney disease. Moreover, CAD patients were more likely to have history of cerebrovascular and peripheral vascular disease when compared to non-CAD patients. In-hospital mortality rates were comparable although CAD patients had more frequent re-hospitalization and worse long-term outcome. However, CAD was not an independent predictor of poor outcome.

Conclusion: The prevalence of CAD amongst patients with HF in the Middle East is variable and may be related to healthcare sources. Regional and national studies are needed for assessing further the impact of various etiologies of HF and for developing appropriate strategies to combat this global concern.  相似文献   

90.
INTRODUCTION: Although treatment with statins reduces cardiovascular (CV) events in patients with dyslipidemia, a residual 60 - 70% CV risk remains. This CV risk may be inversely related to high-density lipoprotein-cholesterol (HDL-C). Interest in niacin has re-emerged because of its HDL-C raising effects. The flushing associated with niacin which has previously affected patient compliance can now be significantly blocked with laropiprant (LRPT). AREAS COVERED: This review aims to assess the efficacy, clinical effectiveness and safety of extended-release niacin (ERN) with LRPT. The authors searched PubMed and MEDLINE for literature published between January 2006 and November 2011, for efficacy, clinical effectiveness and safety reports of ERN with LRPT. EXPERT OPINION: Niacin has been shown to prevent CV events, reduce mortality and has beneficial effects on vascular endothelial function. Evidence suggests that this is due to its broad-spectrum lipid altering properties, including lowering lipoprotein (a) (Lp(a)), and its pleiotropic actions. While side effects associated with niacin have limited its use in the past, the extended-release formulations and co-administration of LRPT have increased its tolerability, particularly by reducing flushing. The authors advise that ERN should be used in patients with a high risk of cardiovascular disease, who have failed to reach conventional targets.  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