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   1193篇
  免费   47篇
  国内免费   3篇
耳鼻咽喉   6篇
儿科学   28篇
妇产科学   30篇
基础医学   111篇
口腔科学   86篇
临床医学   141篇
内科学   287篇
皮肤病学   33篇
神经病学   75篇
特种医学   70篇
外科学   114篇
综合类   11篇
预防医学   71篇
眼科学   10篇
药学   68篇
中国医学   1篇
肿瘤学   101篇
  2022年   12篇
  2021年   29篇
  2020年   12篇
  2019年   15篇
  2018年   23篇
  2017年   13篇
  2016年   21篇
  2015年   17篇
  2014年   39篇
  2013年   34篇
  2012年   58篇
  2011年   64篇
  2010年   49篇
  2009年   43篇
  2008年   46篇
  2007年   69篇
  2006年   60篇
  2005年   59篇
  2004年   49篇
  2003年   42篇
  2002年   34篇
  2001年   35篇
  2000年   23篇
  1999年   27篇
  1998年   7篇
  1997年   7篇
  1996年   14篇
  1995年   15篇
  1992年   10篇
  1991年   13篇
  1990年   18篇
  1989年   18篇
  1988年   12篇
  1987年   17篇
  1986年   13篇
  1985年   24篇
  1984年   22篇
  1983年   13篇
  1981年   13篇
  1980年   7篇
  1979年   17篇
  1978年   5篇
  1977年   14篇
  1975年   9篇
  1974年   12篇
  1973年   10篇
  1972年   13篇
  1971年   8篇
  1969年   5篇
  1960年   6篇
排序方式: 共有1243条查询结果,搜索用时 78 毫秒
951.
CONTEXT: Androgens influence sexual differentiation and behavior, body composition, and physical functioning in men, but their role in women is less well understood. Because circulating androgens decline with age, the use of androgen supplementation for women to improve health and well-being has been increasing. OBJECTIVE: The aim of this study was to assess the association between androgens and a variety of end points thought to be affected by androgens. DESIGN: In a community-based baseline cohort of women aged 42-52 yr from the Study of Women's Health Across the Nation, we measured circulating testosterone (T), dehydroepiandrosterone sulfate, and SHBG, and calculated a free androgen index (FAI) in 2961 women. MAIN OUTCOME MEASURES: Correlations of androgen measures with each other and with body mass index, waist circumference, and waist-hip ratio were computed, and odds ratios (OR) were estimated for the categorical outcomes of functional limitations, functional status, self-reported health, scores indicative of depressed mood, quality of life, sexual desire and arousal, and the presence of the metabolic syndrome. RESULTS: Androgens, and particularly SHBG, were associated most strongly with body mass index, waist circumference, and waist-hip ratio. SHBG was associated prominently inversely with the metabolic syndrome (OR = 0.32; 95% confidence interval = 0.26-0.39), which was present in 17% of women at baseline. Dehydroepiandrosterone sulfate was associated modestly with functional status and self-reported health. T was associated minimally with increased sexual desire (OR = 1.09; 95% confidence interval = 1.00-1.18). The association of FAI with self-reported health and depressive symptomatology based on the Center for Epidemiologic Studies Depression Scale score was explained more by T than by SHBG, whereas the association of FAI with sexual arousal and metabolic syndrome was due more to SHBG than to T. CONCLUSIONS: Circulating SHBG and androgens are most strongly associated with physical characteristics and the metabolic syndrome in women in this community-based cohort. Androgens are related weakly to physical functioning and other symptoms to which they commonly are attributed, such as sexual desire, sexual arousal, and well-being.  相似文献   
952.
953.
954.
955.
956.
Human mesenchymal stem cells (MSCs), bone marrow-derived pluripotent adherent cells of mesenchymal origin can differentiate along the osteogenic, chondrogenic, adipogenic, and tendonogenic lineages. In this report we characterize cytokine and growth factor gene expression by MSCs and investigate the modulation of cytokine expression that occurs during osteogenic and stromal differentiation. MSCs constitutively expressed mRNA for interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF), macrophage colony-stimulating factor (M-CSF), and stem cell factor (SCF). MSCs treated with IL-1alpha upregulated mRNA levels of IL-6, IL-11, and LIF, and began to express detectable levels of granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF). mRNA levels of M-CSF and SCF did not change. MSCs cultured in osteogenic medium differentiated along the osteogenic lineage and downregulated mRNA levels of IL-6, IL-11 and LIF whereas, M-CSF and SCF expression were unchanged and G-CSF and GM-CSF remained undetectable. IL-3 was not detected in MSC culture under any conditions. MSCs precultured in control medium, IL-1alpha, or osteogenic medium maintained similar capacity to support long-term culture initiating cell (LT-CIC). Thus, primary and osteogenic differentiated MSCs produce important hematopoietic cytokines and support hematopoiesis in long-term cultures, suggesting that these cells may provide an excellent ex vivo environment for hematopoiesis during progenitor cell expansion and may be important for in vivo cell therapy.  相似文献   
957.
Davis BM  Koç ON  Gerson SL 《Blood》2000,95(10):3078-3084
The limited efficacy of hematopoietic gene therapy can be improved by in vivo selection for transduced long-term repopulating cells (LTRC). We selected for G156A MGMT (triangle upMGMT) transduced LTRC present in 5 x 10(4) to 100 x 10(4) marrow cells infused into nonmyeloablated mice by the administration of O(6)-benzylguanine (BG) and BCNU every 3 to 4 weeks. To facilitate engraftment, mice were given a nonablative dose of BG and BCNU before infusion. Without selection, triangle upMGMT was not detected in any hematopoietic colony-forming units (CFU) 24 to 30 weeks after infusion. After BG and BCNU, triangle upMGMT(+) CFU were frequently detected, and their proportions increased with each treatment cycle. After 2 to 3 cycles of BG and BCNU, many mice were stably reconstituted with 75% to 100% triangle upMGMT(+) CFU for at least 6 months, representing up to 940-fold enrichment. Thus, BG and BCNU stem cell toxicity allows triangle upMGMT-transduced LTRC to repopulate the bone marrow. This degree of selection pressure in nonmyeloablated mice is far greater than that observed in previous drug-resistance gene transfer studies. These data support our approved clinical trial to select for drug-resistant, transduced hematopoietic cells, potentially decreasing cumulative drug-induced myelosuppression in patients with cancer. These data also suggest that triangle upMGMT may be a potent, dominant, selectable marker for use in dual gene therapy.  相似文献   
958.
PURPOSE: Methoxyamine has been shown to potentiate the cytotoxic effect of temozolomide both in vitro and in human tumor xenograft models. We postulate that the enhanced cytotoxicity is mediated by methoxyamine-bound apurininc/pyrimidinic (MX-AP) site, a key lesion formed by the combination of temozolomide and methoxyamine. When located within topoisomerase IIalpha (topo II) cleavage sites in DNA, MX-AP sites act as dual lethal targets, not only functionally disrupting the base excision repair (BER) pathway but also potentially poisoning topo II. EXPERIMENTAL DESIGN: Using oligonucleotide substrates, in which a position-specific MX-AP site is located within topo II cleavage sites, we examined the effect of MX-AP site on both AP endonuclease- and topo II-mediated DNA cleavage in vitro. RESULTS: MX-AP sites were refractory to the catalytic activity of AP endonuclease, indicating their ability to block BER. However, they were cleaved by either purified topo II or nuclear extracts from tumor cells expressing high levels of topo II, suggesting that MX-AP sites stimulate topo II-mediated DNA cleavages. In cells, treatment with temozolomide and methoxyamine increased the expression of topo II and enriched the formation of gammaH2AX foci, which were colocalized with up-regulated topo II, confirming that DNA double-strand breaks marked by gammaH2AX foci are associated with topo II in cells. CONCLUSIONS: Our findings identify a molecular mechanism of cell death whereby MX-AP sites that cumulated in cells due to resistance to BER potentially convert topo II into biotoxins, resulting in enzyme-mediated DNA scission and cell death.  相似文献   
959.
BACKGROUND: Hysterectomy for a benign condition is common, particularly in the underserved. The objective was to determine if ethnic differences could be explained by known risk factors. METHODS: A phone survey was conducted at random on 15,160 women, ages 40-55, from seven US cities. Subjects were 49.9% Caucasian, 28.1% African American, 12.3% Hispanic, and 9.8% Asian American. RESULTS: Ethnicity was associated with past hysterectomy (odds ratio [OR]: Caucasian = 1.0, African American = 1.66; confidence interval [CI] = 1.46-1.88, Hispanic = 1.64, CI = 1.29-2.07; Asian American = 0.44, CI = 0.34-0.56), after adjustment for age, education, fibroids, body mass index, marital status, smoking, geographic site, and country of education. CONCLUSION: Because the highest rates occurred in the disadvantaged African American and Hispanic subgroups, and could not be explained by known risk factors, disparity in the form of overuse in these disadvantaged groups may exist.  相似文献   
960.
Contrary to common clinical perceptions, individuals with personality disorders attempt and commit suicide at nearly the same rate as individuals with major depression. In particular, those with borderline personality disorder are at high risk for suicidal behavior and nonsuicidal self-injury. Yet there is significant controversy surrounding the diagnosis of borderline personality disorder in terms of its existence, its definition and symptom structure, its Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) axis location, and its importance as a contributing factor to suicidality and nonsuicidal self-injury. Furthermore, both suicidal and nonsuicidal self-harm is prominent in borderline personality disorder. There is often confusion between suicidal and nonsuicidal self-injury with one sometimes mistaken for the other. Nonsuicidal self-injury is sometimes met with hospitalization, because it is viewed as life threatening. Alternately, the potential lethality of suicidal behavior is underestimated, because it occurs in the context of multiple low lethality self-harm behaviors. It is possible to view these behaviors as distinct yet on a spectrum in borderline personality-disordered patients. With respect to treatment of self-injury in personality disorders, some recent pharmacotherapy trials have been conducted, though efficacy is often unclear. Findings with respect to psychotherapy, particularly dialectical behavior therapy, a form of cognitive behavioral treatment, are promising.  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