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   2697801篇
  免费   194115篇
  国内免费   7825篇
耳鼻咽喉   35827篇
儿科学   88229篇
妇产科学   74298篇
基础医学   380164篇
口腔科学   73672篇
临床医学   241362篇
内科学   539247篇
皮肤病学   65593篇
神经病学   223246篇
特种医学   102641篇
外国民族医学   737篇
外科学   399725篇
综合类   50971篇
现状与发展   5篇
一般理论   991篇
预防医学   210633篇
眼科学   59881篇
药学   196749篇
  8篇
中国医学   5774篇
肿瘤学   149988篇
  2021年   21996篇
  2019年   22957篇
  2018年   33322篇
  2017年   25086篇
  2016年   28625篇
  2015年   32061篇
  2014年   43285篇
  2013年   64800篇
  2012年   87961篇
  2011年   92864篇
  2010年   55071篇
  2009年   51964篇
  2008年   85640篇
  2007年   90873篇
  2006年   92148篇
  2005年   88023篇
  2004年   84599篇
  2003年   81452篇
  2002年   78379篇
  2001年   130685篇
  2000年   133939篇
  1999年   112449篇
  1998年   31684篇
  1997年   28172篇
  1996年   28494篇
  1995年   27619篇
  1994年   25257篇
  1993年   23587篇
  1992年   86293篇
  1991年   82633篇
  1990年   79865篇
  1989年   76970篇
  1988年   70396篇
  1987年   68874篇
  1986年   64456篇
  1985年   61374篇
  1984年   45606篇
  1983年   38485篇
  1982年   22784篇
  1981年   20268篇
  1979年   39745篇
  1978年   27997篇
  1977年   23823篇
  1976年   22021篇
  1975年   23404篇
  1974年   27585篇
  1973年   26223篇
  1972年   24548篇
  1971年   22716篇
  1970年   20913篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Gonadotropins have been implicated in the development of epithelial ovarian cancers. These tumors are derived from ovarian surface epithelium (OSE). The purpose of this study was to determine the effects of these hormones on DNA synthesis and spontaneous cell death in primary cultures of OSE and three immortalized OSE cultures. Primary cultures of OSE cells were generated from the ovaries of women with benign disease. The effects of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) on DNA synthesis and cell death were determined using [(3)H]thymidine incorporation and JAM assays. Significant inductions of DNA synthesis were demonstrated with LH in 4/12 (33%) primary cultures of OSE and 2/3 OSE cell lines and with FSH in 4/11 (36%) primary cultures of OSE and 2/3 OSE cell lines. A significant protection from cell death was also observed in the presence of FSH in 2/4 primary cultures of OSE and 1/3 OSE cell lines and in the presence of LH in 1/4 primary cultures of OSE and 2/3 OSE cell lines. The results indicate that while gonadotropins have the potential to induce cell proliferation and protect from cell death in OSE cells in vitro, their effects are variable in OSE cells from different women.  相似文献   
992.
993.
BACKGROUND: Arterial hypertension and postmenopausal reduction of estrogen levels may be involved in modifications of the stiffness of large arteries. OBJECTIVES: To evaluate the pulse-wave velocity (PWV) and indirectly the arterial stiffness in hypertensive postmenopausal women submitted to hormone therapy with estradiol alone or combined with norethisterone acetate. SUBJECTS: Forty-five hypertensive postmenopausal women were double-blindly, randomly assigned to three arms of treatment: placebo (group I); estradiol 2 mg/day (group II); or estradiol 2 mg/day and norethisterone acetate 1 mg/day (group III). METHODS: Arterial stiffness was assessed from PWV measurements of the common carotid and femoral arteries (CF-PWV) and the common carotid and radial arteries (CR-PWV) obtained using the automatic Complior(R) device, taken at baseline and after 12 weeks of treatment. RESULTS: After the 12-week treatment, values of CF-PWV and CR-PWV were not significantly different (p = 0.910 and p = 0.736, respectively) among the groups. Systolic blood pressure showed a positive correlation with CF-PWV in groups II and III (p = 0.02 and p < 0.001, respectively). CONCLUSIONS: PWV and arterial stiffness in postmenopausal hypertensive women did not reduce over a 12-week treatment with estradiol alone compared with the same period of treatment with estradiol combined with norethisterone acetate.  相似文献   
994.
Female urinary incontinence is a common but underreported condition. Initial investigation and treatment can in most cases be undertaken without urodynamic or other detailed tests. History by the use of validated symptom and quality of life questionnaires is key to the initial investigation. Initial treatment includes pelvic floor muscle training (PFMT) regardless of the type of incontinence; lifestyle interventions and bladder retraining, anticholinergics and serotonin/noradrenaline reuptake inhibitors (e.g. duloxetine) are also included depending on the type of symptoms. In mixed incontinence the predominant symptom should be treated first. When this initial treatment is ineffective, further investigation should be offered prior to specialised treatment. Urodynamics should be considered for all patients prior to surgery. Imaging and cystoscopy to exclude pathology, for example in elderly patients with an overactive bladder, are also necessary. Newer surgical interventions should be offered after careful consideration of the risk:benefit ratio for each individual woman and the amount of evidence that is currently available to support their use.  相似文献   
995.
996.
OBJECTIVE: Visual symptoms are common in patients with preeclampsia, and are caused by various underlying pathological changes in the retina. Blurred vision may be one of these symptoms. We describe three cases in which the underlying retinal pathology of blurred vision was clarified using optical coherence tomography (OCT), a novel, non-invasive ophthalmic imaging technique that provides micrometer-scale resolution images of the human retina. METHODS: Three patients with preeclampsia complained of blurred vision postpartum. In all cases, ophthalmoscopy was performed at the bedside, followed by the assessment of best corrected visual acuity, slit-lamp biomicroscopy, fluorescein angiography (FLA), and OCT. In all cases, the presence of central visual defects was examined by an Amsler-grid. RESULTS: In one case, the symptoms were bilateral. In all affected eyes, the patients complained of a relative central scotoma. Ophthalmoscopy showed edema in the affected maculae, while OCT examination clarified a serous neurosensory detachment of the macula. In one case, a neurosensory detachment was also detected in the papillomacular region of a fellow eye with no symptoms. In two cases, FLA was performed, but only in one case could we detect late leakage and subretinal exudates. The serous detachments observed showed total resolution in all cases within 5 to 10 weeks, with restoration of visual acuity. CONCLUSION: In patients with preeclampsia, OCT may provide a useful method for the precise assessment of retinal changes, distinguishing retinal edema from serous neurosensory detachments. This finding may help to clarify the pathophysiological circulatory changes seen in preeclampsia.  相似文献   
997.
INTRODUCTION: Transesophageal echocardiography (TEE) has become increasingly useful in the study of patients with suspected pulmonary thromboembolism. OBJECTIVE: The aim of this study was to prospectively evaluate the usefulness of TEE in the study of the distal part of the left pulmonary artery (LPA) as well as the influence of this procedure on total echocardiographic exam duration. METHODOLOGY: A prospective study in two groups of consecutive patients referred for TEE with a one- year interval between evaluation of Group A: 33 patients, 17 male, mean age 54 +/- 24 years, and Group B: 42 patients, 20 male, mean age 48 +/- 27 years (p = NS). The procedure was considered long when it took more than 3 min to evaluate the distal part of the LPA. RESULTS: In group A we were able to visualize the distal part of the LPA in 24 patients (73%) without significant prolongation of total exam duration in 16 patients (48% of group A). In one of the patients with suspected pulmonary thromboembolism thrombi were only observed in the distal part of the LPA. In group B we were able to visualize the distal part of the LPA in 36 patients (86%) without significant prolongation of total exam duration in 26 patients (61% of group B). CONCLUSIONS: 1. Visualization of the distal part of the LPA was possible in more patients, and with TEE time prolongation in less patients, in group B. These differences can be accounted for by the training of the operator in this technique. 2. The importance of visualization of this part of the LPA in guiding treatment in the subset of patients with pulmonary thromboembolism confirms the usefulness of this specific procedure.  相似文献   
998.
999.
1000.
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