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   15949篇
  免费   1060篇
  国内免费   69篇
耳鼻咽喉   166篇
儿科学   427篇
妇产科学   205篇
基础医学   1933篇
口腔科学   371篇
临床医学   1529篇
内科学   3802篇
皮肤病学   287篇
神经病学   1665篇
特种医学   467篇
外科学   2186篇
综合类   188篇
一般理论   14篇
预防医学   1485篇
眼科学   439篇
药学   970篇
中国医学   11篇
肿瘤学   933篇
  2023年   92篇
  2022年   137篇
  2021年   355篇
  2020年   191篇
  2019年   329篇
  2018年   361篇
  2017年   293篇
  2016年   278篇
  2015年   326篇
  2014年   510篇
  2013年   681篇
  2012年   1162篇
  2011年   1168篇
  2010年   638篇
  2009年   597篇
  2008年   1070篇
  2007年   1206篇
  2006年   1149篇
  2005年   1109篇
  2004年   1078篇
  2003年   941篇
  2002年   909篇
  2001年   124篇
  2000年   129篇
  1999年   117篇
  1998年   187篇
  1997年   135篇
  1996年   109篇
  1995年   112篇
  1994年   93篇
  1993年   99篇
  1992年   84篇
  1991年   63篇
  1990年   64篇
  1989年   68篇
  1988年   52篇
  1987年   49篇
  1986年   65篇
  1985年   62篇
  1984年   85篇
  1983年   85篇
  1982年   93篇
  1981年   101篇
  1980年   92篇
  1979年   33篇
  1978年   52篇
  1977年   33篇
  1976年   40篇
  1975年   38篇
  1974年   34篇
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
61.
Participants in this study suffered from severe mental illness and were homeless at baseline. They were given their choice of five different treatment programs. The current study investigated two major questions: (1) what is the impact of positive expectancies about the efficacy of the chosen program on number of contacts with the chosen program and client outcomes; and (2) what is the impact of positive views about nonchosen programs (alternative choice variables) on contact with the chosen program and client outcomes. Client outcomes assessed were psychotic symptoms, days homeless, and client satisfaction. Positive expectancy variables were the number of reasons for choosing a program and confidence that the program would help. Alternative choice variables were the number of nonchosen programs visited and the attractiveness of a nonchosen program. Only the number of reasons for choosing the program was significantly related to program contact with the chosen program. Both of the positive expectancy variables and program contact were significantly correlated with consumer satisfaction. In general, neither the positive expectancy variables nor the alternative choice variables predicted changes in psychotic symptoms nor days homeless. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 339–348, 2003.  相似文献   
62.
CPEB is an mRNA-binding protein that stimulates polyadenylation-induced translation of maternal mRNA once it is phosphorylated on Ser 174 or Thr 171 (species-dependent). Disruption of the CPEB gene in mice causes an arrest of oogenesis at embryonic day 16.5 (E16.5), when most oocytes are in pachytene of prophase I. Here, we show that CPEB undergoes Thr 171 phosphorylation at E16.5, but dephosphorylation at the E18.5, when most oocytes are entering diplotene. Although phosphorylation is mediated by the kinase aurora, the dephosphorylation is due to the phosphatase PP1. The temporal control of CPEB phosphorylation suggests a mechanism in which CPE-containing mRNA translation is stimulated at pachytene and metaphase I.  相似文献   
63.
Previous studies of coping, hostility, and depressive symptoms have highlighted the significant relations between all possible pairs of these 3 variables. To more completely explore the nature of depressive symptoms, we link them all together in this study by testing a coping→hostility→depressive symptoms path model. One hundred forty participants completed psychological questionnaires measuring coping strategies, hostility, and depressive symptoms. While controlling age and social class as covariates, SPSS stepwise regression analyses were used to examine relations among these 3 constructs. Results suggest that coping has a direct relation with depressive symptoms as well as an indirect relation mediated by hostility. Passive coping may lead to increased hostility, resulting in depressive symptoms. Active coping may have the opposite effect. These findings suggest that the inclusion of measures of both coping strategies and hostility yields a more thorough understanding of concomitants of depressive symptoms. From a clinical perspective, knowing what coping strategies a person uses and how much anger they experience and express may be useful in guiding the management of depressive symptoms.  相似文献   
64.
The random amino acid copolymers FYAK and VWAK ameliorate EAE in a humanized mouse model expressing both a human transgenic myelin basic protein (MBP)85-99-specific T cell receptor and HLA-DR2. Here we show that microglia isolated from the central nervous system (CNS) of humanized mice with EAE induced by MBP85-99 and treated with these copolymers had reduced expression of HLA-DR, and thus reduced capacity to present MBP85-99 and activate transgenic T cells. In vitro microglia up-regulated empty HLA-DR2 upon activation with GM-CSF with or without LPS or IFN-gamma, but not with IL-4 or IL-10. Correspondingly, gene chip arrays showed that the CNS of untreated and YFAK-treated mice differentially expressed pro- and anti-inflammatory molecules during MBP85-99-induced EAE. Interestingly, microglia expressed the full-length gammabeta and alphabeta subunits of the tetrameric adaptor protein complexes AP-1 and AP-2 respectively, but after treatment with GM-CSF these complexes were cleaved, as had been found in immature dendritic cells derived from bone marrow. Strikingly, in vivo the perivascular lymphocyte infiltration seen in untreated mice immunized with MBP85-99 was composed of equal numbers of hVbeta2+ MPB85-99-specific transgenic and hVbeta2- endogenous T cells, while the much smaller infiltration seen after treatment with YFAK was composed predominantly of hVbeta2- endogenous T cells.  相似文献   
65.
The research evaluated an intervention strategy designed to prevent skin cancer in young adolescents. The intervention used parents as change agents to effectively communicate the risks of skin cancer and encourage their children to avoid high-risk sun-related behaviors while increasing positive sun-safe behaviors. Three hundred and forty parents in two regions of the United States were educated about the dangers of risky sun behaviors and how to convey information about skin cancer prevention to their children. Parents were then encouraged to talk with their children about these issues over a 1-month period prior to the onset of summer. Following this time period, children whose parents received and implemented the intervention materials were compared with a control sample of 129 children. These two groups were matched on age, gender, and school on number of sunburns and sunburn severity, attitudes and beliefs, and sunbathing behavior. Children in the treatment condition differed significantly from controls in the predicted directions on all outcome variables. The findings are discussed in terms of reducing skin cancer risk behaviors of children via parent-based intervention approaches.  相似文献   
66.
Infection of J774.1 murine macrophages by influenza A virus (IAV) induces two major responses, production of host defense molecules and death by apoptosis. We investigated whether induction of two cytotoxic compounds, tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO), directly caused IAV-induced apoptosis, and whether induction could be modulated by interferon-gamma (IFN-gamma) or the replication competence of the virus. Live IAV potently induced production of both TNF-alpha and NO, but UV inactivated virus was a poor inducer of both molecules. When cells were pre-treated with IFN-gamma, inactive IAV became as effective an inducer of NO, but not TNF-alpha, as live IAV. Amantadine, which antagonizes viral entry and replication, partly inhibited TNF-alpha and NO production in unprimed cells, but did not inhibit NO in IFN-gamma primed cells. IAV-induced cytotoxicity was not due to the induction of TNF-alpha or NO. Cells were insensitive to either TNF-alpha-containing supernatants or to recombinant TNF-alpha. Anti-TNF-alpha antibody did not protect cells from IAV-induced cell death, and anti-oxidants that inhibited TNF-alpha production also failed to increase cell survival. Inhibitors of NO production did not protect from IAV-induced cell death, either alone or in combination with superoxide dismutase (SOD). We conclude that, even though IAV was a potent inducer of TNF-alpha and NO in macrophages, IAV-induced apoptosis was not mediated directly by them. Importantly, viral replication was not required for the induction of TNF-alpha or NO, and the action of inactive IAV could be potentiated by IFN-gamma.  相似文献   
67.
The new 2017 diagnostic criteria for hypermobile Ehlers–Danlos Syndrome (hEDS) provide a framework for diagnosing hEDS but are more stringent than the previous Villefranche criteria. Our clinical experience at the GoodHope EDS clinic was that the 2017 criteria left many highly symptomatic patients without a diagnosis of hEDS. We conducted a retrospective cohort study to confirm our clinic experience and assess the accuracy of the 2017 diagnostic criteria for hEDS in patients who had a previous hEDS diagnosis based on the Villefranche criteria. Our study found that 15% (n = 20 of 131) of patients with a prior diagnosis of hEDS met the 2017 diagnostic criteria, and many of the traits used to distinguish hEDS were not significantly more frequent in patients who met 2017 criteria versus those who did not. In both groups objective systemic manifestations were found less frequently than subjective systemic manifestations. Beighton score (BS) as assessed by primary care practitioner was found to be higher than assessment by EDS practitioner in 81% (n = 74 of 91) of cases. Generalized joint hypermobility was confirmed in only 46% (n = 51 of 111) of patients who had a previous diagnosis of hEDS. Higher BS did not correlate with increased number of systemic manifestations in our cohort. Common comorbidities of hEDS were found with similar frequency in those who met 2017 criteria and those who did not. Based on our cohort, the 2017 hEDS diagnostic criteria require refinement to improve its diagnostic accuracy.  相似文献   
68.
Behavioral control of abnormal breathing in sleep was studied to determine if an intervention procedure could reduce apnea duration and also SaO 2 (blood oxygen) desaturation levels. Sleep apnea patients (n=11) were instructed while awake that tones would be presented in sleep whenever an apnea event occurred. They were told to breathe deeply to the tones and were given practice in doing so. Intervention and nonintervention hours alternated across 2 nights following 2 baseline nights. As expected, during the intervention hours, the duration but not the frequency of apneic events was reduced. The procedure also resulted in higher SaO 2 levels during the intervention hours. Daytime sleepiness was not greater following intervention but sleep staging effects were observed. The results are sufficiently promising to warrant additional research.This research was supported by NIH Grants 2 HL 27149-84 and HL 34125 entitled Behavioral Control of Respiration in Sleep.  相似文献   
69.
This study examines the effect of length on the dose-response (D-R) relationship and the effect of agonist concentration on the length-tension (L-T) relationship in vascular smooth muscle. The experiments used 2-mm rings from isolated segments of the dog anterior tibial artery. In D-R experiments the length (internal ring circumference) for maximum active force (Lmax) was determined first. D-R relationships were obtained from cumulative responses to increasing concentrations of norepinephrine (NE) or potassium (K+). L-T relationships were obtained from individual responses to a specific concentration of agonist as the ring was stretched in increments of L0 (the initial length for resting force). Dimensions of the arterial rings were measured with a video caliper. For NE and K+ stimulations at lengths equal to and less than Lmax: (a) The concentration for half maximal response (ED50) was lowest (most sensitive) at Lmax and increased significantly as length decreased from Lmax; (b) When the direction of length change was reversed, the direction of change in ED50 was reversed; and (c) The ED50 of repeated dose-response experiments at Lmax was not significantly different. For NE: (a) the ED50 decreased significantly when length was increased from Lmax; and (b) the ED50 increased significantly when length was decreased to Lmax. The results of L-T experiments show Lmax is significantly longer for a low concentration of NE (10−6 M) than for a high concentration (10−5 M). With force normalized to the maximum force, the L-T curve is significantly lower, and the initial length for an active response was 80% longer for 10−6 M than for 10−5 M NE. It may be concluded that vascular smooth muscle has a length-dependent dose-response relationship and a concentration-dependent length-tension relationship.  相似文献   
70.
Sunbathing and sunscreen use, as well as related intentions, attitudes, beliefs, and knowledge, were assessed in 90 Southern Appalachian undergraduates. A large majority (75%) reported sunbathing, with more than half reporting sun lamp use. A slight majority (56.7%) reported some use of sunscreen. Subjects reporting an intention to tan spent more time sunbathing, both outside and under a sun lamp. Individuals reporting a sun protection intention had lighter tans and spent less time sunbathing. Sunbathing was predicted by perceptions of sunbathing as relaxing, while sun lamp use was predicted by more positive views of suntatns. Sunscreen use was predicted by more positive sun protection attitudes and less negative sunscreen attitudes.  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