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   214857篇
  免费   19764篇
  国内免费   7995篇
耳鼻咽喉   1273篇
儿科学   4787篇
妇产科学   3031篇
基础医学   41581篇
口腔科学   4079篇
临床医学   13590篇
内科学   35318篇
皮肤病学   3612篇
神经病学   16757篇
特种医学   3917篇
外国民族医学   66篇
外科学   14982篇
综合类   27628篇
现状与发展   31篇
预防医学   9497篇
眼科学   2501篇
药学   29699篇
  30篇
中国医学   8276篇
肿瘤学   21961篇
  2024年   189篇
  2023年   3153篇
  2022年   4101篇
  2021年   8516篇
  2020年   7524篇
  2019年   8277篇
  2018年   7820篇
  2017年   7996篇
  2016年   7935篇
  2015年   9196篇
  2014年   13399篇
  2013年   15775篇
  2012年   13986篇
  2011年   16307篇
  2010年   13767篇
  2009年   13112篇
  2008年   12217篇
  2007年   10778篇
  2006年   9742篇
  2005年   8231篇
  2004年   7219篇
  2003年   6107篇
  2002年   4722篇
  2001年   3983篇
  2000年   3355篇
  1999年   3013篇
  1998年   2656篇
  1997年   2357篇
  1996年   1757篇
  1995年   1780篇
  1994年   1559篇
  1993年   1297篇
  1992年   1082篇
  1991年   949篇
  1990年   770篇
  1989年   643篇
  1988年   539篇
  1987年   431篇
  1986年   436篇
  1985年   897篇
  1984年   955篇
  1983年   656篇
  1982年   747篇
  1981年   561篇
  1980年   480篇
  1979年   408篇
  1978年   306篇
  1977年   251篇
  1976年   232篇
  1975年   168篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
91.
目的:了解循环张应力对小鼠颅底蝶枕软骨联合细胞(SOSCs)增殖及低氧诱导因子-1α表达的影响。方法:采集1 d龄小鼠的SOSCs进行体外培养,对第三代细胞加载牵张形变率分别为3%、6%、9%,频率为1 Hz,持续时间为1 h的循环张应力;用流式细胞术测算细胞增殖指数,用蛋白免疫印迹技术分析Hif-1α的表达水平。用按相同条件培养但不加力的细胞作为对照。结果:各实验组细胞的增殖指数和Hif-1α相对表达量都高于对照组(P<0.05);其中,6%牵张形变率组的细胞增殖指数和Hif-1α相对表达量较对照组增加最多。结论:适宜强度的循环张应力对体外培养小鼠SOSCs的增殖和Hif-1α表达具有促进作用。  相似文献   
92.
Background: Intraductal carcinoma and cribriform (IDC/C) tumor features are well-established prognosticators of biochemical recurrence (BCR), metastasis, and prostate cancer (PCa)-specific mortality. However, approximately 70% of PCa patients undergoing a radical prostatectomy are IDC/C negative, yet up-to 20% of these patients progress and experience BCR. Thus, tumor histopathologic characteristics such as IDC/C alone are limited in their ability to predict disease progression. Conversely, several nomograms such as Cancer of the Prostate Risk Assessment-Surgery (CAPRA-S) have been developed to aid in the prognostication of BCR, but not yet widely applied in clinical settings. Materials and methods: In this study, we assessed the combined prognostic utility of IDC/C, and CAPRA-S for BCR in 3 PCa patient cohorts. Results: CAPRA-S+IDC/C improved the predictive accuracy of BCR in all 3 cohorts (P < .001). Specifically, among IDC/C negative cases, CAPRA-S improved the prognostication of BCR in low-risk (Cohort 1; P < .001, Cohort 2; P < .001, Cohort 3; P = .003), intermediate (Cohort 1; P < .001, Cohort 2; P = .006, Cohort 3; P = .03) and high-risk (Cohort 1-3; P < .001) patients. Conversely, IDC/C improved the prognostication of BCR among CAPRA-S low-risk (Cohorts 1; P < .001 and Cohort 3; P = .003) patients. Conclusion: Our results suggest the investigation of histopathological IDC/C features in CAPRA-S low-risk patients and conversely, nomogram CAPRA-S among IDC/C negative patients improves the identification of patients likely to experience BCR, which would otherwise be missed through current assessment regimens. These patients can be offered more intensive monitoring and adjuvant therapies upfront to circumvent the development of recurrent cancer or overtreatment at the time of surgery.  相似文献   
93.
Most vaccines approved by regulatory bodies are administered via intramuscular or subcutaneous injections and have shortcomings, such as the risk of needle-associated blood infections, pain and swelling at the injection site. Orally administered vaccines are of interest, as they elicit both systemic and mucosal immunities, in which mucosal immunity would neutralize the mucosa invading pathogen before the onset of an infection. Hence, oral vaccination can eliminate the injection associated adverse effects and enhance the person's compliance. Conventional approaches to manufacturing oral vaccines, such as coacervation, spray drying, and membrane emulsification, tend to alter the structural proteins in vaccines that result from high temperature, organic and toxic solvents during production. Electrohydrodynamic processes, specifically electrospraying, could solve these challenges, as it also modulates antigen release and has a high loading efficiency. This review will highlight the mucosal immunity and biological basis of the gastrointestinal immune system, different oral vaccine delivery approaches, and the application of electrospraying in vaccines development.  相似文献   
94.
ObjectiveIdentify factors associated with healthcare providers' frequency of depot medroxyprogesterone acetate (DMPA) provision to adolescents.Study designWe analyzed data from surveys mailed to a nationally representative sample of public-sector providers and office-based physicians (n=1984). We estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs) of factors associated with frequent DMPA provision to adolescents in the past year.ResultsAlthough most providers (>95%) considered DMPA safe for adolescents, fewer reported frequent provision (89% of public-sector providers; 64% of office-based physicians). Among public-sector providers, factors associated with lower odds of frequent provision included working in settings without Title X funding (aOR 0.44, 95% CI 0.30–0.64), reporting primary care as their primary clinical focus versus reproductive or adolescent health (aOR 0.42, 95% CI 0.28–0.61), and providing fewer patients with family planning services. Among office-based physicians, factors associated with lower odds of frequent provision included specializing in obstetrics/gynecology (aOR 0.50, 95% CI 0.27–0.91) and family medicine (aOR 0.21, 95% CI 0.09–0.47) versus adolescent medicine, completing training ≥15 versus <5 years ago (aOR 0.27, 95% CI 0.09–0.83), and reporting that 0–24% of patients pay with Medicaid or other government healthcare assistance versus ≥50% (aOR 0.23, 95% CI 0.09–0.61). The reason most commonly reported by providers for infrequent DMPA provision was patient preference for another method.ConclusionsWhile most providers reported frequently providing DMPA to adolescents, training on evidence-based recommendations for contraception, focused on subgroups of providers with lower odds of frequent DMPA provision, may increase adolescents' access to contraception.ImplicationsAlthough >95% of providers considered depot medroxyprogesterone (DMPA) a safe contraceptive for adolescents, only 89% of public-sector providers and 64% of office-based physicians reported frequently providing DMPA to adolescents. Provider training on evidence-based recommendations for contraception counseling and provision may increase adolescents' access to DMPA and all methods of contraception.  相似文献   
95.

Background

The purpose of the study was to evaluate the association between fetal echocardiographic measurements and the need for intervention (primary coarctation repair, staged coarctation repair, or catheter intervention) in prenatally diagnosed coarctation of the aorta.

Methods

A single-centre retrospective cohort study (2005-2015) of 107 fetuses diagnosed with suspected coarctation of the aorta in the setting of an apex-forming left ventricle and antegrade flow across the mitral and aortic valves.

Results

Median gestational age at diagnosis was 32 weeks (interquartile range, 23-35 weeks). Fifty-six (52%) did not require any neonatal intervention, 51 patients (48%) underwent a biventricular repair. In univariable analysis, an increase in ascending aorta (AAo) peak Doppler flow velocity (odds ratio [OR], 1.40 [95% confidence interval [CI], 1.05-1.91] per 20 cm/s; P = 0.03) was associated with intervention. No intervention was associated with larger isthmus size (OR, 0.23; P < 0.001), transverse arch diameter (OR, 0.23; P < 0.001), and aortic (OR, 0.72; P = 0.02), mitral (OR, 0.58; P = 0.001), and AAo (OR, 0.53; P < 0.001) z-scores. In multivariable analysis, higher peak AAo Doppler (OR, 2.51 [95% CI, 1.54-4.58] per 20 cm/s; P = 0.001) and younger gestational age at diagnosis (OR, 0.81 [95% CI, 0.70-0.93] per week; P = 0.005) were associated with intervention, whereas a higher AAo z-score (OR, 0.65 [95% CI, 0.43-0.94] per z; P = 0.029) and transverse arch dimension (OR, 0.44 [95% CI, 0.18-0.97]; P = 0.05) decreased the risk of intervention.

Conclusions

In prenatally suspected coarctation, the variables associated with intervention comprised smaller AAo and transverse arch size, earlier gestational age at diagnosis, and the additional finding of a higher peak AAo Doppler.  相似文献   
96.
Signaling by the transforming growth factor-β (TGF-β) superfamily is important in the regulation of hematopoiesis and is dysregulated in myelodysplastic syndromes (MDS), contributing to ineffective hematopoiesis and clinical cytopenias. TGF-β, activins and growth differentiation factors exert inhibitory effects on red cell formation by activating canonical SMAD2/3 pathway signaling. SMAD2/3 overactivation is seen in numerous subtypes of MDS. Furthermore, reduced levels of inhibitory SMAD7 are

References

  • 1.Valcarcel D, Verma A, Platzbecker U, et al. Phase 2 Study of Monotherapy Galunisertib (LY2157299 Monohydrate) in Very Low-, Low-, and Intermediate-Risk Patients with Myelodysplastic Syndromes. Blood. 2015;126:1669.
  • 2.Suragani RN, Cawley SM, Li R, Wallner S, et al. Modified activin receptor IIB ligand trap mitigates ineffective erythropoiesis and disease complications in murine β-thalassemia. Blood. 2014 Jun 19;123(25):3864-72.
  • 3.Dussiot M, Maciel TT, Fricot A, et al. Nat Med. 2014 Apr;20(4):398-407.
  • 4.
  相似文献   
97.

Aim

Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is an immune inhibitory receptor which is expressed within most types of hematopoietic cells and negatively regulates immune responses. Recently, we found LAIR-1 expression to be present within tumors of nonhematopoietic lineages. However, the roles of LAIR-1 in hepatocellular carcinoma (HCC) have yet to be examined. The purpose of this study was to investigate the expression of LAIR-1 in HCC tissue and assess its clinical significance at this site.

Materials and methods

Expression levels of LAIR-1 within HCC samples collected from 90 patients and compared with that of slides of normal liver tissue collected from 9 non-HCC patients were measured by immunohistochemistry using tissue microarrays. A semiquantitative score was assigned, as was based on staining intensity and percent of positive cells and a Spearman Rank correlation test was used to assess any potential significant correlations between LAIR-1 expression and clinicopathological factors. Overall survival analysis was performed using the Kaplan-Meier and Log Rank statistical test.

Results

LAIR-1 expression was detected in cancer tissue and adjacent tumor tissue, but not in normal liver tissue. The percent of LAIR-1-positive expression in cancer tissue of HCC samples was 97.78% (88/90) while that in adjacent tumor tissue was 96.67% (87/90). Significantly greater expression levels of LAIR-1 were obtained from cancer tissue (Mean?±?SD?=?5.722?±?2.145) than that in adjacent tumor tissue (4.141?±?1.486). In addition, LAIR-1 expression was found to be significantly correlated with pathological grade of HCC, T stage, and age. Expression levels of LAIR-1 were related with worse overall survival rates of HCC patients, especially in HCC patients with hepatic cirrhosis.

Conclusion

Results of this study show that LAIR-1 is expressed in HCC tissues and that high levels of LAIR-1 expression are associated with the poor cancer differentiation. In addition, overexpression of LAIR-1 was significantly associated with worse overall survival in the patients with HCC. These data suggest that LAIR-1 may be an independent predictor for clinical outcomes in patients with HCC.  相似文献   
98.
《Vaccine》2019,37(31):4302-4309
Influenza A virus (IAV) vaccines in pigs generally provide homosubtypic protection but fail to prevent heterologous infections. In this pilot study, the efficacy of an intradermal pDNA vaccine composed of conserved SLA class I and class II T cell epitopes (EPITOPE) against a homosubtypic challenge was compared to an intramuscular commercial inactivated whole virus vaccine (INACT) and a heterologous prime boost approach using both vaccines. Thirty-nine IAV-free, 3-week-old pigs were randomly assigned to one of five groups including NEG-CONTROL (unvaccinated, sham-challenged), INACT-INACT-IAV (vaccinated with FluSure XP® at 4 and 7 weeks, pH1N1 challenged), EPITOPE-INACT-IAV (vaccinated with PigMatrix EDV at 4 and FluSure XP® at 7 weeks, pH1N1 challenged), EPITOPE-EPITOPE-IAV (vaccinated with PigMatrix EDV at 4 and 7 weeks, pH1N1 challenged), and a POS-CONTROL group (unvaccinated, pH1N1 challenged). The challenge was done at 9 weeks of age and pigs were necropsied at day post challenge (dpc) 5. At the time of challenge, all INACT-INACT-IAV pigs, and by dpc 5 all EPITOPE-INACT-IAV pigs were IAV seropositive. IFNγ secreting cells, recognizing vaccine epitope-specific peptides and pH1N1 challenge virus were highest in the EPITOPE-INACT-IAV pigs at challenge. Macroscopic lung lesion scores were reduced in all EPITOPE-INACT-IAV pigs while INACT-INACT-IAV pigs exhibited a bimodal distribution of low and high scores akin to naïve challenged animals. No IAV antigen in lung tissues was detected at necropsy in the EPITOPE-INACT-IAV group, which was similar to naïve unchallenged pigs and different from all other challenged groups. Results suggest that the heterologous prime boost approach using an epitope-driven DNA vaccine followed by an inactivated vaccine was effective against a homosubtypic challenge, and further exploration of this vaccine approach as a practical control measure against heterosubtypic IAV infections is warranted.  相似文献   
99.

Introduction/Hypothesis

Recruitment of participants into phase 1 vaccine clinical trials can be challenging since these vaccines have not been used in humans and there is no perceived benefit to the participant. Occasionally, as was the case with a phase 1 clinical trial of an Ebola vaccine in Halifax, Canada, during the 2014–2016 West African Ebola virus outbreak, recruitment is less difficult. In this study, we explored the motivations of participants in two phase 1 vaccine trials that were concurrently enrolling at the same centre and compared the motivations of participants in a high-profile phase 1 Ebola vaccine trial to those in a less high-profile phase 1 adjuvanted seasonal influenza vaccine study.

Methods

An online survey which included participants’ prior experience with clinical trials, motivations to participate (including financial incentives), and demographic information was developed to examine the motivations of healthy participants in two phase 1 clinical vaccine trials conducted at the Canadian Center for Vaccinology in Halifax, Nova Scotia. Participants were invited via email to complete the online survey. Readability and clarity were assessed through pilot testing.

Results

A total of 49 (55.7%) of 88 participants of the two studies completed the survey (22 [55%] of 40 participants from the Ebola vaccine study and 27 [56.3%] of 48 from the adjuvanted influenza vaccine study). Motivations that were most frequently ranked among participants' top three in both trials were (1) wanting to contribute to the health of others, (2) wanting to participate in something important, (3) wanting to contribute to the advancement of science, and (4) wanting to receive an incentive such as money or a tablet.

Conclusions/Recommendations

Although media attention and financial compensation were more often cited by Ebola vaccine trial participants as a reason to participate, both altruistic and self-interested factors were important motivations for participants in their decision to participate in a phase 1 vaccine clinical trial.  相似文献   
100.
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