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   8701篇
  免费   918篇
  国内免费   18篇
耳鼻咽喉   85篇
儿科学   280篇
妇产科学   164篇
基础医学   1177篇
口腔科学   166篇
临床医学   936篇
内科学   1639篇
皮肤病学   157篇
神经病学   663篇
特种医学   253篇
外科学   1284篇
综合类   122篇
一般理论   11篇
预防医学   1171篇
眼科学   181篇
药学   625篇
中国医学   4篇
肿瘤学   719篇
  2023年   99篇
  2022年   178篇
  2021年   443篇
  2020年   252篇
  2019年   368篇
  2018年   430篇
  2017年   298篇
  2016年   297篇
  2015年   314篇
  2014年   441篇
  2013年   510篇
  2012年   764篇
  2011年   724篇
  2010年   387篇
  2009年   266篇
  2008年   483篇
  2007年   371篇
  2006年   369篇
  2005年   332篇
  2004年   346篇
  2003年   243篇
  2002年   268篇
  2001年   110篇
  2000年   82篇
  1999年   95篇
  1998年   50篇
  1997年   53篇
  1996年   49篇
  1995年   38篇
  1994年   42篇
  1992年   40篇
  1991年   47篇
  1990年   62篇
  1989年   59篇
  1988年   49篇
  1987年   38篇
  1986年   34篇
  1985年   50篇
  1984年   30篇
  1983年   26篇
  1979年   33篇
  1978年   37篇
  1977年   22篇
  1976年   36篇
  1975年   21篇
  1974年   23篇
  1973年   39篇
  1972年   32篇
  1970年   22篇
  1969年   30篇
排序方式: 共有9637条查询结果,搜索用时 15 毫秒
61.
At the time of implantation, the extracellular matrix proteinslaminin and fibronectin are abundant in the decidua and aredistributed pericellularly around each individual stromal cell.First trimester human trophoblast expresses both laminin andfibronectin receptors, specifically the 1ß1 5ß16ß1 and 6ß4 integrin heterodimers. In thisstudy we have demonstrated that in-vitro adhesion of first trimesterhuman trophoblast to purified extracellular matrix proteinsand to purified decidual stromal cell monolayers can be inhibitedby monoclonal antibodies directed against appropriate integrinsubunits and by synthetic peptides containing an arginine-glycine-asparticacid sequence. Monoclonal antibodies (mAbs) to the 5 and ß1integrin subunits and a synthetic peptide significantly inhibitedadhesion to fibronectin. Binding of trophoblast to laminin wasblocked with mAbs to the 6 and ß1 but not 1 and ß4integrinsubunits. Similarly, integrin-mediated adhesion to monolayersof decidual stromal cells could be blocked with mAbs to the5, 6, ß6 and ß4 integrin subunits. Integrin-mediatedsignal transduction in normal and malignant trophoblast wasinvestigated by Western blotting. A 115 kDa protein was themajor tyrosine phosphorylated protein detected in trophoblastafter binding to laminin or fibronectin. The profile of tyrosinephosphorylated proteins differed for malignant trophoblast. integrins/matrix/signal transduction/trophoblast  相似文献   
62.
BACKGROUND: Most persons who have serologic evidence of infection with herpes simplex virus (HSV) type 2 (HSV-2) are asymptomatic. Historically, it has been assumed that these persons have less frequent viral reactivation than those with symptomatic infection. METHODS: We conducted a prospective study to investigate genital shedding of HSV among 53 subjects who had antibodies to HSV-2 but who reported having no history of genital herpes, and we compared their patterns of viral shedding with those in a similar cohort of 90 subjects with symptomatic HSV-2 infection. Genital secretions of the subjects in both groups were sampled daily and cultured for HSV for a median of 94 days. RESULTS: HSV was isolated from the genital mucosa in 38 of the 53 HSV-2-seropositive subjects (72 percent) who reported no history of genital herpes, and HSV DNA was detected by the polymerase-chain-reaction assay in cultures prepared from genital mucosal swabs in 6 additional subjects. The rate of subclinical shedding of HSV in the subjects with no reported history of genital herpes was similar to that in the subjects with such a history (3.0 percent vs. 2.7 percent). Of the 53 subjects who had no reported history of genital herpes, 33 (62 percent) subsequently reported having typical herpetic lesions; the duration of their recurrences in these subjects was shorter (median, three days vs. five days; P<0.001) and the frequency lower (median, 3.0 per year vs. 8.2 per year; P<0.001) than in the 90 subjects with previously diagnosed symptomatic infection. Only 1 of these 53 subjects had no clinical or virologic evidence of HSV infection. CONCLUSIONS: Seropositivity for HSV-2 is associated with viral shedding in the genital tract, even in subjects with no reported history of genital herpes.  相似文献   
63.
BACKGROUND: Clinical correlates of HerpeSelect ELISA index values are poorly understood. OBJECTIVES: This study was designed to determine the effects of time of infection, test variability, and antibody avidity on index values. STUDY DESIGN: Sera (N=313) from 81 patients with new HSV-2 infections and 236 sera from 32 patients with long-standing (median 11.3 years) HSV-2 were tested by HerpeSelect HSV-2 ELISA. High positive, low positive and negative controls were run on 42 test plates to establish test variability. RESULTS: Index values tended to rise after infection, peaking a median of 9-10 weeks post-infection (range 8-323 days). Of 32 patients with established HSV-2 infections, 7 (22%) had at least one low index value (>1.1 to < or =3.5), and one had a transient seroreversion event. Test variability of index values was substantially lower than inter- or intra-patient variability. Median antibody avidity was higher in sera with high versus low index values in established infections, but unrelated to index value in patients with early infections. CONCLUSIONS: Index values or index value changes are not absolute indicators of early versus established HSV-2 infection or solely a function of test variability. Low antibody avidity may contribute to low index values once infection is established.  相似文献   
64.
Introduction: Ghrelin is an orexigenic hormone which favors food-seeking behavior and has been postulated to be a biomarker of stress. We conducted a systematic review and meta-analysis on the evolution of ghrelin levels following acute stress. Methods: The PubMed, Cochrane Library, Embase, and ScienceDirect databases were searched for studies reporting ghrelin levels before and after acute stress in humans. Results: We included ten studies for a total of 348 patients. Acute stress (intervention) was always in a laboratory. Acute stress was psychological (Trier Social Stress Test), physical, or mixed (cold pressure test). The overall meta-analysis demonstrated an increase in ghrelin after the stress intervention (ES = 0.21, 95CI 0.09 to 0.34) compared with baseline levels. Stratification by time demonstrated an acute increase in ghrelin levels in the five minutes immediately following the initiation of stress (0.29, 0.10 to 0.48) but without any difference after. Obese individuals had a more significant (ES = 0.51, 95CI 0.18 to 0.84) and prolonged increase in ghrelin levels for up to 45 min compared with non-obese individuals who had a significant increase only five minutes after stress. Moreover, the ghrelin levels increased in response to stress with BMI (coefficient 0.028, 0.01 to 0.49; p = 0.013) and decreased with the time after the stress intervention (coefficient -0.007, −0.014 to −0.001; p = 0.025). Conclusion: Ghrelin is a biomarker of stress, with a short-term increase following acute stress. Obese individuals have both a higher and prolonged response, emphasizing the link between obesity and stress.  相似文献   
65.
Time-restricted feeding (TRF) is becoming a popular way of eating in physically active populations, despite a lack of research on metabolic and performance outcomes as they relate to the timing of food consumption in relation to the time of exercise. The purpose of this study was to determine if the timing of feeding/fasting after exercise training differently affects muscle metabolic flexibility and response to an acute bout of exercise. Male C57BL/6 mice were randomized to one of three groups for 8 weeks. The control had ad libitum access to food before and after exercise training. TRF-immediate had immediate access to food for 6 h following exercise training and the TRF-delayed group had access to food 5-h post exercise for 6 h. The timing of fasting did not impact performance in a run to fatigue despite TRF groups having lower hindlimb muscle mass. TRF-delayed had lower levels of muscle HSL mRNA expression and lower levels of PGC-1α expression but displayed no changes in electron transport chain enzymes. These results suggest that in young populations consuming a healthy diet and exercising, the timing of fasting may not substantially impact metabolic flexibility and running performance.  相似文献   
66.
Birthing can be an empowering experience for women. Within many Indigenous cultures around the world, birth is a ceremony to celebrate new life, acknowledging the passing from the spiritual world into the physical world. While initiatives to “indigenize” health care have been made, this paper argues that the United Nations Declaration on the Rights of Indigenous Peoples and the United Nations Sustainable Development Goals contain frameworks for Indigenous rights that include the right to incorporate Indigenous childbirth ceremonies into clinical practice. Examining the importance of birthplace, this paper details a current movement in Manitoba, Canada, to “bring birth home,” which recognizes that the determinants of health experienced in the early stages of a child’s development can have health implications for an individual’s future.  相似文献   
67.
Context  Herpes simplex virus type 2 (HSV-2) is one of the most common sexually transmitted infections in the United States. No prospective study has shown the ability of condoms to reduce transmission of HSV-2. Objective  To evaluate risk factors for HSV-2 acquisition and efficacy of condoms in prevention of HSV-2 transmission. Design  Analysis of data from a randomized, double-blind, placebo-controlled trial conducted December 13, 1993, to June 28, 1996, of an ineffective candidate HSV-2 vaccine with 18 months of follow-up. Setting  Eighteen clinical trial centers in the United States. Participants  A total of 528 monogamous couples discordant for HSV-2 infection, including an HSV-2–susceptible population of 261 men and 267 women. Main Outcome Measure  Acquisition of HSV-2 infection by susceptible partners, compared with those remaining free of HSV-2 with regard to demographic characteristics, sexual activity, and condom use. Results  Twenty-six women (9.7%) vs 5 men (1.9%) acquired HSV-2, for a rate per 10 000 sex acts (episodes of sexual intercourse) of 8.9 vs 1.5, respectively (P<.001). In multivariable analysis, younger age (adjusted hazard ratio [HR] per 5 years, 1.57; 95% confidence interval [CI], 1.22-2.04), seropositivity for HSV-1 and HSV-2 vs HSV-2 alone in the source partner (adjusted HR, 2.34; 95% CI, 1.14-4.82), and more frequent sexual activity (adjusted HR per additional sex act per week, 1.10; 95% CI, 1.01-1.19) were associated with higher risk of HSV-2 acquisition. Condom use during more than 25% of sex acts was associated with protection against HSV-2 acquisition for women (adjusted HR, 0.085; 95% CI, 0.01-0.67) but not for men (adjusted HR, 2.02; 95% CI, 0.32-12.50). Risk of HSV-2 transmission declined from 8.5 per 100 person-years in the initial 150-day interval to 0.9 per 100 person-years in the final 150-day interval (P = .002 for trend), concurrent with a decrease in sexual activity and proportion of sex acts occurring when the source partner had genital lesions. Conclusions  Condom use offers significant protection against HSV-2 infection in susceptible women. Changes in sexual behavior, correlated with counseling about avoiding sex when a partner has lesions, were associated with reduction in HSV-2 acquisition over time. These data suggest that identification of discordant couples can reduce transmission of HSV-2, especially for heterosexual couples in which the male partner has HSV-2 infection.   相似文献   
68.
69.
BackgroundThe prevalence of total joint arthroplasty (TJA) in the United States has drawn the attention of health care stakeholders. The payers have also used a variety of strategies to regulate the medical necessity of these procedures. The purpose of this study was to examine the level of evidence of the coverage policies being used by commercial payers in the United States.MethodsThe references of the coverage policies of four commercial insurance companies were reviewed for type of document, level of evidence, applicability to a TJA population, and success of nonoperative treatment in patients with severe degenerative joint disease.Results282 documents were reviewed. 45.8% were primary journal articles, 14.2% were level I or II, 41.2% were applicable to patients who were candidates for TJA, and 9.9% discussed the success of nonoperative treatment in patients who would be candidates for TJA.ConclusionMost of the references cited by commercial payers are of a lower level of scientific evidence and not applicable to patients considered to be candidates for TJA. This is relatively uniform across the reviewed payers. The dearth of high-quality literature cited by commercial payers reflects the lack of evidence and difficulty in conducting high level studies on the outcomes of nonoperative versus operative treatment for patients with severe, symptomatic osteoarthritis. Patients, surgeons, and payers would all benefit from such studies and we encourage professional societies to strive toward that end through multicenter collaboration.  相似文献   
70.
BackgroundTo determine unicompartmental (UKR) and total knee replacement (TKR) revision rates, compare UKR revision rates with what they would have been had they received TKR instead, and assess subsequent re-revision and 90-day mortality rates.MethodsUsing National Joint Registry data, we estimated UKR and TKR revision and mortality rates. Flexible parametric survival modeling (FPM) was used to model failure in TKR and make estimates for UKR. Kaplan-Meier estimates were used to compare cumulative re-revision for revised UKRs and TKRs.ResultsTen-year UKR revision rates were 2.5 times higher than expected from TKR, equivalent to 70 excess revisions/1000 cases within 10 years (5861 excess revisions in this cohort). Revision rates were 2.5 times higher for the highest quartile volume UKR surgeons compared to the same quartile for TKR and 3.9 times higher for the lowest quartiles respectively. Re-revision rates of revised TKRs (10 years = 17.5%, 95% confidence interval [CI] 16.4-18.7) were similar to revised UKRs (15.2%, 95% CI 13.4-17.1) and higher than revision rates following primary TKR (3.3%, 95% CI 3.1-3.5). Ninety-day mortality rates were lower after UKR compared with TKR (0.08% vs 0.33%) and lower than predicted had UKR patients received a TKR (0.18%), equivalent to 1 fewer death per 1000 cases.ConclusionUKR revision rates were substantially higher than TKR even when demographics and caseload differences were accounted for; however, fewer deaths occur after UKR. This should be considered when forming treatment guidelines and commissioning services. Re-revision rates were similar between revised UKRs and TKRs, but considerably higher than for primary TKR, therefore UKR cannot be considered an intermediate procedure.  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