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   25660篇
  免费   1791篇
  国内免费   48篇
耳鼻咽喉   188篇
儿科学   868篇
妇产科学   594篇
基础医学   3412篇
口腔科学   256篇
临床医学   3858篇
内科学   4483篇
皮肤病学   497篇
神经病学   2598篇
特种医学   461篇
外科学   2634篇
综合类   211篇
一般理论   41篇
预防医学   3413篇
眼科学   402篇
药学   1576篇
中国医学   20篇
肿瘤学   1987篇
  2024年   31篇
  2023年   246篇
  2022年   352篇
  2021年   774篇
  2020年   572篇
  2019年   748篇
  2018年   889篇
  2017年   656篇
  2016年   692篇
  2015年   704篇
  2014年   1029篇
  2013年   1486篇
  2012年   2215篇
  2011年   2297篇
  2010年   1213篇
  2009年   1061篇
  2008年   1781篇
  2007年   1879篇
  2006年   1705篇
  2005年   1588篇
  2004年   1439篇
  2003年   1261篇
  2002年   1240篇
  2001年   122篇
  2000年   113篇
  1999年   138篇
  1998年   218篇
  1997年   176篇
  1996年   132篇
  1995年   110篇
  1994年   109篇
  1993年   95篇
  1992年   50篇
  1991年   40篇
  1990年   34篇
  1989年   28篇
  1988年   16篇
  1987年   19篇
  1986年   23篇
  1985年   22篇
  1984年   29篇
  1983年   15篇
  1982年   28篇
  1981年   21篇
  1980年   12篇
  1979年   17篇
  1977年   10篇
  1976年   13篇
  1975年   9篇
  1974年   8篇
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
991.
We report a patient with an unclassifiable myeloproliferative disorder and the rare t(X;20)(q13;q13.3) as the sole cytogenetic abnormality. The breakpoint on Xq is consistent with other reports of translocations involving the X chromosome with breakpoints that cluster to Xq13 and association with myeloid disorders. Late replication studies demonstrated the inactive X chromosome was involved in this translocation. The critical event in patients with myeloproliferative disease and deletion of 20q appears to be the loss of tumor suppressor genes. This may also be the mechanism in this patient with a potential cryptic deletion associated with the translocation. Alternatively, spreading of X inactivation into the derivative chromosome 20 provides a second mechanism for the loss of function of tumor suppressor genes on 20q. The finding in this patient of t(X;20) together with three others reported in the literature indicates that this may represent a primary non-random abnormality associated with myeloid malignancy, which may take on clinical significance with the accumulation of more cases.  相似文献   
992.
993.
Staphylococcal enterotoxins (SEs) belong to a large group of bacterial exotoxins that cause severe immunopathologies, especially when delivered as an aerosol. SEs elicit the release of lethal amounts of cytokines by binding to major histocompatibility complex (MHC) class II and cross-linking susceptible T-cell receptors. Efforts to develop effective therapeutic strategies to protect against SEs delivered as an aerosol have been hampered by the lack of small animal models that consistently emulate human responses to these toxins. Here, we report that human leukocyte antigen-DQ8 (HLA-DQ8) transgenic (Tg) mice, but not littermate controls, succumbed to lethal shock induced by SEB aerosols without potentiation. Substantial amounts of perivascular edema and inflammatory infiltrates were noted in the lungs of Tg mice, similar to the pathology observed in nonhuman primates exposed by aerosol to SEB. Furthermore, the observed pathologies and lethal shock correlated with an upsurge in proinflammatory cytokine mRNA gene expression in the lungs and spleens, as well as with marked increases in the levels of proinflammatory circulating cytokines in the Tg mice. Unlike the case for littermate controls, telemetric evaluation showed significant hypothermia in Tg mice exposed to lethal doses of SEB. Taken together, these results show that this murine model will allow for the examination of therapeutics and vaccines developed specifically against SEB aerosol exposure and possibly other bacterial superantigens in the context of human MHC class II receptors.  相似文献   
994.
BACKGROUND: Food allergies occur in 2% to 3% of the pediatric population. These reactions can vary from mild cutaneous manifestations to severe life-threatening reactions. Limited information is available on which specific factors may predict the severity of subsequent reactions. OBJECTIVE: To determine whether the organ system or the specific food involved in the initial allergic reaction predicts the outcome of subsequent food challenge. METHODS: Retrospective review of all food sensitive children who underwent food challenges at The Children's Hospital of Philadelphia, Philadelphia, PA, in a 5-year period (n = 998 challenges). The specific food, initial symptom on presentation, and reaction on open challenges were recorded. RESULTS: A total of 413 of 998 food challenges produced positive results. Milk, egg, and peanut were the most common foods to be associated with a positive challenge result. The most common presentation of food allergy was cutaneous followed by multiorgan reactions. Peanut, milk, and egg sensitivities were more likely to cause a multiple-organ system reaction on challenge than wheat or other foods. Patients with egg allergy were more likely to have a different reaction on rechallenge than other foods. CONCLUSIONS: Milk, egg, and peanut are the most common foods associated with food challenges. Patients will typically experience similar reaction on re-exposure to the initial reaction. However, multiple-organ system reactions can occur after any initial clinical presentation, with milk, egg, and peanut having more multiple-organ reactions than other foods.  相似文献   
995.
Cognitive factors in Postconcussion Syndrome symptom report.   总被引:3,自引:0,他引:3  
Past studies suggest a variety of factors that influence the report of Postconcussion Syndrome (PCS) symptoms, including head injury, depression, pain, and subjective expectation. Participants included 190 undergraduates across 8 groups chosen to examine the relative contribution of these factors, as well as treatment-seeking behavior, in the report of both current and past PCS symptoms. Depressed persons, depressed persons receiving treatment, and headache sufferers receiving treatment reported elevated rates of PCS symptoms when compared to controls. Five of the eight groups reported experiencing more current than past symptoms. Head-injured persons and headache sufferers underestimated premorbid symptom rates relative to the baseline of controls. These findings are consistent with the growing number of studies that suggest non-neurologic factors may be more closely related to PCS symptom report than head injury status and raise further concern regarding use of self-reported PCS symptoms in the diagnosis of head injury.  相似文献   
996.
BACKGROUND: The aim of this study was to examine the role of apoptosis and reactive oxygen species (ROS) in inducing DNA damage in ejaculated spermatozoa. METHODS: We examined ejaculated spermatozoa from 31 patients examined for infertility and 19 healthy donors for apoptosis, production of ROS and DNA damage using annexin V binding, chemiluminescence assay and sperm chromatin structure assay. RESULTS: The percentage of spermatozoa that underwent apoptosis in the whole ejaculate and mature fraction was higher in the patients than in the donors (P<0.001 and P=0.009, respectively). Levels of ROS in the whole ejaculate and immature fraction were higher in the patients than in the donors (P=0.002 and P=0.009). Apoptosis was significantly correlated with ROS within patients in the whole ejaculate [r (95% confidence interval)=0.53 (0.19-0.86)] and in the mature [0.71 (0.39-1.00)] and immature spermatozoa [0.75 (0.45-1.00)]. Only apoptosis and the DNA fragmentation index (DFI) were significantly correlated within patients in the whole ejaculate [0.57 (0.18-0.97)]. CONCLUSIONS: DNA damage may be induced by oxidative assault. Apoptosis may not contribute significantly to the DNA damage.  相似文献   
997.
Fluorescent amplified fragment length polymorphism (FAFLP) analysis was applied to 276 Campylobacter jejuni strains and 87 Campylobacter coli strains isolated from humans, pigs, cattle, poultry, and retail meats to investigate whether certain FAFLP genotypes of C. jejuni and C. coli are associated with a particular host and to determine the degree of association between FAFLP-defined genotypes and heat-stable serotypes and/or phage types. Within C. coli, the poultry strains clustered separately from those of porcine origin. In contrast, no evidence of host specificity was detected among C. jejuni strains. While C. coli strains show host specificity by FAFLP genotyping, C. jejuni strains that are genotypically similar appear to colonize a range of hosts, rather than being host adapted. Some serotypes and/or phage types (C. jejuni serotype HS18, phage type PT6, and serophage type HS19/PT2 and C. coli HS66, PT2, and HS56/PT2) were the most homogeneous by FAFLP genotyping, while others were more heterogeneous (C. jejuni HS5 and PT39, and C. coli HS24 and PT44) and therefore poor indicators of genetic relatedness between strains. The lack of host specificity in C. jejuni suggests that tracing the source of infection during epidemiological investigations will continue to be difficult. The lack of congruence between some serotypes and/or phage types and FAFLP genotype underlines the need for phenotypic testing to be supplemented by genotyping. This study also demonstrates how, in general, FAFLP generates "anonymous" genetic markers for strain characterization and epidemiological investigation of Campylobacter in the food chain.  相似文献   
998.
Effects of breastfeeding chemosignals on the human menstrual cycle   总被引:4,自引:0,他引:4  
BACKGROUND: To date, there has not been an investigation to determine whether lactating women and their infants influence the ovarian function of other women with whom they interact. METHODS: In a randomized, double-blind, placebo-controlled study of 47 nulliparous women, we utilized both within- and between-subjects controls to assess the effects of sustained exposure to breastfeeding compounds on menstrual cycle length, as well as characteristics of each phase of the ovarian cycle. RESULTS: Breastfeeding compounds modulated ovarian cycle length in comparison with the carrier control (0.01 < or = all P values < or = 0.05), disrupting the normal homeostatic regulation of cycle length and tripling its variance. Hence, women with long cycles stayed long and did not regress to the mode of 29 days and women with short cycles maintained short cycles. This effect was driven by changes in both the follicular and luteal phases of the cycle (0.01 < or = all P values < or = 0.04) and changed the timing of the pre-ovulatory surge of LH. CONCLUSIONS: Because compounds from lactating women and their infants modulated the ovarian cycles of women, as is seen in other mammals, they have the potential to function as pheromones, regulating fertility within groups of women.  相似文献   
999.
Arsenic (As) contamination in ground water has affected more than 19 countries. Approximately 36 million people in the Bengal delta alone are exposed to this toxicant via drinking water (>50 microg/l) and are at potential health risk. Chronic ingestion of As via drinking water is associated with occurrence of skin lesions, cancer and other arsenic-induced diseases in West Bengal, India. An in vitro cytogenetic study was performed utilizing chromosomal aberrations (CA) in lymphocytes treated with sodium arsenite (0-5 microM) in six symptomatic (having arsenic-related skin lesions) individuals, six age- and sex-matched As-exposed asymptomatic (no arsenic-related skin lesions) individuals and six control individuals with similar socio-economic status residing in non-affected districts of West Bengal with no evidence of As exposure. The mean As content in nails and hair was 9.61 and 5.23 microg/g in symptomatic, 3.48 and 2.17 microg/g in asymptomatic and 0.42 and 0.33 microg/g in the control individuals, respectively. The main aim of our study was to determine whether genotoxic effects differed in the lymphocytes of the control (no exposure to arsenic), asymptomatic and symptomatic individuals after in vitro treatment with sodium arsenite. Although both the exposed groups had chronic exposure to As through the drinking water, individuals with skin lesions accumulated more As in their nails and hair and excreted less in urine (127.80 versus 164.15 microg/l). The results show that sodium arsenite induced a significantly higher percentage of aberrant cells in the lymphocytes of control individuals than in the lymphocytes of both the exposed groups. Within the two exposed groups As induced higher incidences of CA in the symptomatic than the asymptomatic individuals. These results suggest that asymptomatic individuals have relatively lower sensitivity and susceptibility to induction of genetic damage by As compared with the symptomatic individuals.  相似文献   
1000.
In the Saguenay-Lac-Saint-Jean region (Quebec, Canada), a predictive DNA-testing program for myotonic dystrophy type 1 (DM1) has been available as a clinical service since 1988. From 1 to 12 years (median, 5 years) after receiving predictive testing, a total of 308 participants (44 carriers and 264 non-carriers) answered a questionnaire to determine the psychosocial impact of this genetic testing. The main reasons for wanting to be tested were to learn if children are at risk for DM1 or for reproductive decision making (75%) and to relieve the uncertainty for themselves (17%). The majority of participants (96.1%) remembered correctly their test result. At the time of the survey, the perception of the general well-being, the psychological distress (Psychiatric Symptom Index), and the self-esteem (Rosenberg Self-Esteem Scale) were similar in carriers, in non-carriers, and in the reference (Quebec) population. When participants indicated a change in different aspects of their lives following predictive testing, it was perceived as a change for the better by non-carriers and as a change for the worse by carriers. Nevertheless, for a majority of carriers and of non-carriers, the test result did not bring changes in their lives. All respondents believed that predictive testing should be available for the at-risk population and the vast majority of carrier and of non-carriers would recommend the use of predictive testing to their family members. Predictive testing for individuals at-risk of DM1 can be offered safely within a well-organized clinical and genetic counseling program that includes careful pre-test counseling, pre-test clinical assessment, post-test psychological support, and follow-up for those identified as carriers.  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