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   28667篇
  免费   2496篇
  国内免费   782篇
耳鼻咽喉   125篇
儿科学   583篇
妇产科学   206篇
基础医学   1638篇
口腔科学   199篇
临床医学   2599篇
内科学   4312篇
皮肤病学   505篇
神经病学   2447篇
特种医学   432篇
外国民族医学   1篇
外科学   1425篇
综合类   3544篇
一般理论   3篇
预防医学   1768篇
眼科学   201篇
药学   9418篇
  15篇
中国医学   1408篇
肿瘤学   1116篇
  2023年   480篇
  2022年   622篇
  2021年   1009篇
  2020年   1054篇
  2019年   1111篇
  2018年   1126篇
  2017年   1229篇
  2016年   1107篇
  2015年   1059篇
  2014年   2089篇
  2013年   2878篇
  2012年   1854篇
  2011年   1928篇
  2010年   1521篇
  2009年   1323篇
  2008年   1296篇
  2007年   1343篇
  2006年   1049篇
  2005年   930篇
  2004年   746篇
  2003年   698篇
  2002年   489篇
  2001年   488篇
  2000年   379篇
  1999年   336篇
  1998年   278篇
  1997年   258篇
  1996年   254篇
  1995年   259篇
  1994年   215篇
  1993年   241篇
  1992年   239篇
  1991年   200篇
  1990年   186篇
  1989年   145篇
  1988年   162篇
  1987年   115篇
  1986年   115篇
  1985年   164篇
  1984年   133篇
  1983年   101篇
  1982年   119篇
  1981年   81篇
  1980年   87篇
  1979年   70篇
  1978年   73篇
  1977年   70篇
  1976年   57篇
  1975年   52篇
  1974年   30篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
我国奶牛养殖规模不断扩大,奶业产值比重逐步提高,给奶牛疫病防治带来巨大压力。奶牛乳房炎及细菌性肺炎等呼吸系统疾病和细菌性肠炎等消化系统疾病最为常见,抗菌药物的使用成为主要防治手段。但抗菌药物的不当使用易使细菌产生耐药性,增加临床治疗的成本和难度,危害我国奶牛产业发展。本文对截至2021年7月我国和美国、英国、日本、欧盟批准用于奶牛的抗菌药物产品进行整理、统计与分析,包括抗菌药物的分类、剂型以及适应证等,旨在为我国奶牛用抗菌药物管理、合理用药和新兽药开发提供参考。  相似文献   
2.
With a 5.3% of the global population involved, hepatitis B virus (HBV) is a major public health challenge requiring an urgent response. After a possible acute phase, the natural history of HBV infection can progress in chronicity. Patients with overt or occult HBV infection can undergo HBV reactivation (HBVr) in course of immunosuppressive treatments that, apart from oncological and hem-atological diseases, are also used in rheumatologic, gastrointestinal, neurological and dermatological settings, as well as to treat severe acute respiratory syndrome coronavirus 2 infection. The risk of HBV reactivation is related to the immune status of the patient and the baseline HBV infection condition. The aim of the present paper is to investigate the risk of HBVr in those not oncological settings in order to suggest strategies for preventing and treating this occurrence. The main studies about HBVr for patients with occult hepatitis B infection and chronic HBV infection affected by non-oncologic diseases eligible for immunosuppressive treatment have been analyzed. The occurrence of this challenging event can be reduced screening the population eligible for immunosuppressant to assess the best strategies according to any virological status. Further prospective studies are needed to increase data on the risk of HBVr related to newer immunomodulant agents employed in non-oncological setting.  相似文献   
3.
《Drug discovery today》2022,27(6):1724-1732
The enactment of orphan drug-specific legislation pioneered by the USA was subsequently followed by many regions, including the European Union (EU), Australia, Japan, and Taiwan. Here, we discuss the associated regulations established and their impacts in the aforementioned regions, which are among the first with frameworks specific for orphan drugs. Varied scopes of rare diseases or orphan drugs, diverse incentives, and heterogeneous types of reimbursement systems imply the prioritization of the agencies concerned. The numbers of designated and approved drugs reflect the impact of the regulatory and reimbursement frameworks. A comparison of the frameworks and their impact in the respective regions could provide valuable information for developing and improving related frameworks for countries worldwide.  相似文献   
4.
In the field of drug development, technology for producing human metabolites at a low cost is required. In this study, we explored the possibility of using prokaryotic water-soluble cytochrome P450 (CYP) to produce human metabolites. Streptomyces griseolus CYP105A1 metabolizes various non-steroidal anti-inflammatory drugs (NSAIDs), including diclofenac, mefenamic acid, flufenamic acid, tolfenamic acid, meclofenamic acid, and ibuprofen. CYP105A1 showed 4′-hydroxylation activity towards diclofenac, mefenamic acid, flufenamic acid, tolfenamic acid, and meclofenamic acid. It should be noted that this reaction specificity was similar to that of human CYP2C9. In the case of mefenamic acid, another metabolite, 3′-hydroxymethyl mefenamic acid, was detected as a major metabolite. Substitution of Arg at position 73 with Ala in CYP105A1 dramatically reduced the hydroxylation activity toward diclofenac, flufenamic acid, and ibuprofen, indicating that Arg73 is essential for the hydroxylation of these substrates. In contrast, substitution of Arg84 with Ala remarkably increased the hydroxylation activity towards diclofenac, mefenamic acid, and flufenamic acid. Recombinant Rhodococcus erythrocyte cells expressing the CYP105A1 variant R84A/M239A showed complete conversion of diclofenac into 4′-hydroxydiclofenac. These results suggest the usefulness of recombinant R. erythropolis cells expressing actinomycete CYP, such as CYP105A1, for the production of human drug metabolites.  相似文献   
5.
《Value in health》2022,25(12):1958-1966
ObjectivesNational health technology assessments (HTAs) across Europe show differences in evidentiary requirements from assessments by the European Medicines Agency (EMA), affecting time to patient access for drugs after marketing authorization. This article analyzes the differences between EMA and HTA bodies’ evidentiary requirements for oncology drugs and provides recommendations on potential further alignment to minimize and optimally manage the remaining differences.MethodsInterviews were performed with representatives and drug assessment experts from EMA and HTA bodies to identify evidentiary requirements for several subdomains and collect recommendations for potentially more efficiently addressing differences. A comparative analysis of acceptability of the evidence by EMA and the HTA bodies and for potential further alignment between both authorities was conducted.ResultsAcceptability of available evidence was higher for EMA than HTA bodies. HTA bodies and EMA were aligned on evidentiary requirements in most cases. The subdomains showing notable differences concerned the acceptance of limitation of the target population and extrapolation of target populations, progression-free survival and (other) surrogate endpoints as outcomes, cross-over designs, short trial duration, and clinical relevance of the effect size. Recommendations for reducing or optimally managing differences included joint early dialogues, joint relative effectiveness assessments, and the use of managed entry agreements.ConclusionsDifferences between assessments of EMA and HTA bodies were identified in important areas of evidentiary requirements. Increased alignment between EMA and HTA bodies is suggested and recommendations for realization are discussed.  相似文献   
6.

目的:观察青年人群近距离用眼后眼部生理及功能性参数的变化及恢复时间。

方法:前瞻性研究。随机选取2019-12/2020-06在我院进行医学验光的患者69例138眼,根据主觉验光结果分为正视组(+0.75D≤等效球镜度≤-0.50D,18例36眼)、低度近视组(-0.75D≤等效球镜度≤-3.00D,25例50眼)和中度近视组(-3.25D≤等效球镜度≤-6.00D,26例52眼)。所有受试者近距离阅读20min后远眺放松20min,分别于近距离用眼前、近距离用眼20min后、远眺5、10、15、20min时测量受试者眼部生理性参数\〖前房深度(ACD)、眼轴长度(AL)\〗和功能性参数\〖正相对调节(PRA)、调节反应(BCC)\〗,分析各参数的达极时间和恢复时间。

结果:近距离用眼后眼轴变长,前房变浅,PRA绝对值变大,BCC无明显变化,75%(52/69)的受试者AL在近距离用眼20min后达极,87%(60/69)的受试者ACD在远眺5min时达极,96%(66/69)的受试者PRA在近距离用眼20min后达极,且以上参数均在远眺10min后逐渐恢复至初始状态。

结论:近距离用眼后眼部参数发生改变,眼轴变长,前房变浅,PRA绝对值增大,但均在远眺放松过程中逐渐回退,且均需要10min以上才能恢复至初始状态。  相似文献   

7.
ObjectiveTo investigate the feasibility of transnasal heated humidified high flow nasal cannula oxygen therapy (HFNC) in the treatment of acute exacerbation of chronic obstructive pulmonary disease (AECOPD) with respiratory failure in elderly patients. MethodsA total of 176 elderly patients with AECOPD complicated with respiratory failure who were hospitalized at Peking University Shougang Hospital from December 2016 to January 2022 were enrolled, including 82 patients in an HFNC group and 94 patients in an NPPV group. After treatment, pulse oxygen saturation (SPO2), arterial partial pressure of carbon dioxide (PaCO2), oxygenation index (OI), respiratory rate (RR), heart rate (HR), mean arterial pressure (MAP), comfort score, discharge rate, rate of endotracheal intubation, rate of transfer to intensive care unit (ICU), and mortality were compared between the two groups. The independent sample t-test was used for comparison between the two groups. Statistical data are expressed in percentage or number of cases and the χ2 test was used for their comparisons. ResultsThe SPO2 values at 30 min, 1 h, and 6 h were significantly higher in the HFNC group than in the NPPV group (t=-2.049,-2.618, and -3.314, P=0.043, 0.010, and 0.001, respectively). SPO2 before discharge was significantly lower than that of the NPPV group (t=2.162, P=0.033), but OI at each time point and before discharge had no statistical significance (P>0.05). MAP at 6 h was significantly higher in the HFNC group than in the NPPV group (t=-2.209, P=0.029), but within the normal range. HRs at 2 h and 3 h in the HFNC group were significantly higher than those of the NPPV group (t=-2.199 and -2.336, P=0.030 and 0.021, respectively). There were no significant differences in RR, HR, or MAP between the two groups at other time points and before discharge (P>0.05). There was no significant difference in PaCO2 between the two groups (P>0.05). Comfort score in the HFNC group was significantly higher than that of the NPPV group (t=-46.807, P<0.001). There were no significant differences in discharge rate, ICU transfer rate, endotracheal intubation rate, and mortality between the two groups (P>0.05). ConclusionHFNC is as effective as NPPV in treating elderly patients with AECOPD complicated with type Ⅰ or mild type Ⅱ respiratory failure, and HFNC is more comfortable than NPPV.  相似文献   
8.
ObjectivesDonor-specific cell-free DNA shows promise as a noninvasive marker for allograft rejection, but as yet has not been validated in both adult and pediatric recipients. The study objective was to validate donor fraction cell-free DNA as a noninvasive test to assess for risk of acute cellular rejection and antibody-mediated rejection after heart transplantation in pediatric and adult recipients.MethodsPediatric and adult heart transplant recipients were enrolled from 7 participating sites and followed for 12 months or more with plasma samples collected immediately before all endomyocardial biopsies. Donor fraction cell-free DNA was extracted, and quantitative genotyping was performed. Blinded donor fraction cell-free DNA and clinical data were analyzed and compared with a previously determined threshold of 0.14%. Sensitivity, specificity, negative predictive value, positive predictive value, and receiver operating characteristic curves were calculated.ResultsA total of 987 samples from 144 subjects were collected. After applying predefined clinical and technical exclusions, 745 samples from 130 subjects produced 54 rejection samples associated with the composite outcome of acute cellular rejection grade 2R or greater and pathologic antibody-mediated rejection 2 or greater and 323 healthy samples. For all participants, donor fraction cell-free DNA at a threshold of 0.14% had a sensitivity of 67%, a specificity of 79%, a positive predictive value of 34%, and a negative predictive value of 94% with an area under the curve of 0.78 for detecting rejection. When analyzed independently, these results held true for both pediatric and adult cohorts at the same threshold of 0.14% (negative predictive value 92% and 95%, respectively).ConclusionsDonor fraction cell-free DNA at a threshold of 0.14% can be used to assess for risk of rejection after heart transplantation in both pediatric and adult patients with excellent negative predictive value.  相似文献   
9.
目的 分析双水平气道正压双水平气道正压通气(bi-level positive airway pressure,BiPAP)对阻塞性睡眠呼吸暂停低通气综合征(obstructive sleep apnea hypopnea syndrome,OSAHS)患者血管内皮功能及预后的影响。 方法 将100例OSAHS患者纳入研究,随机分为观察及对照组,各50例。观察组行BiPAP ,对照组行常规治疗,比较两组多导睡眠监测(polysomnography,PSG)检查指标(低通气指数、呼吸暂停指数、呼吸暂停及低通气时间、90%以下血氧饱和度次数、90%以下血氧饱和度时间)、心肺功能[脑钠肽(brainnatriureticpeptide,BNP)、右心室Tei指数、左心室Tei指数、一秒用力呼气容积占用力肺活量的百分比(forced expiratory volume in one second/forced vital capacity,FEV1/FVC)、一秒用力呼气容积占预计值的百分比(FEV1占预计值%)]、血管内皮功能[内皮素1(endothelin-1,ET-1)、一氧化氮(nitric oxide,NO)、凝血酶Ⅲ(antithrombin Ⅲ,AT-Ⅲ)]及生活质量。 结果 观察组低通气指数、呼吸暂停指数、呼吸暂停及低通气时间、90%以下血氧饱和度次数及时间指标均显著低于对照组(P<0.05)。观察组治疗后BNP以及Tei指数显著低于治疗前及对照组治疗后,FEV1/FVC、FEV1占预计值%显著高于治疗前及对照组治疗后(P<0.05)。观察组治疗后ET-1、AT-Ⅲ低于治疗前及对照组治疗后,NO高于治疗前及对照组治疗后(P<0.05)。观察组治疗后生活质量各项目评分高于对照组(P<0.05)。 结论 BiPAP治疗能够改善OSAHS患者的预后情况及血管内皮功能,效果确切。  相似文献   
10.
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