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   28141篇
  免费   1503篇
  国内免费   71篇
耳鼻咽喉   434篇
儿科学   1128篇
妇产科学   909篇
基础医学   4568篇
口腔科学   591篇
临床医学   2295篇
内科学   5570篇
皮肤病学   747篇
神经病学   2722篇
特种医学   1143篇
外国民族医学   14篇
外科学   4062篇
综合类   122篇
一般理论   4篇
预防医学   1468篇
眼科学   512篇
药学   1507篇
中国医学   25篇
肿瘤学   1894篇
  2022年   266篇
  2021年   433篇
  2020年   283篇
  2019年   390篇
  2018年   476篇
  2017年   384篇
  2016年   536篇
  2015年   522篇
  2014年   713篇
  2013年   895篇
  2012年   1320篇
  2011年   1391篇
  2010年   687篇
  2009年   736篇
  2008年   1252篇
  2007年   1346篇
  2006年   1256篇
  2005年   1271篇
  2004年   1062篇
  2003年   1062篇
  2002年   966篇
  2001年   907篇
  2000年   939篇
  1999年   796篇
  1998年   359篇
  1997年   275篇
  1996年   223篇
  1995年   212篇
  1994年   190篇
  1993年   188篇
  1992年   483篇
  1991年   510篇
  1990年   490篇
  1989年   406篇
  1988年   388篇
  1987年   403篇
  1986年   394篇
  1985年   392篇
  1984年   271篇
  1983年   214篇
  1982年   141篇
  1981年   147篇
  1979年   261篇
  1978年   185篇
  1977年   156篇
  1976年   153篇
  1975年   167篇
  1974年   197篇
  1973年   169篇
  1972年   155篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
OBJECTIVE: To examine fetal (FHR) and neonatal heart rate patterns following use of common oral antihypertensives in pregnancy. METHODS: A systematic review of randomized controlled trials (RCTs), observational studies (N >/= 6 women), and animal studies. Data were abstracted (two reviewers) to determine relative risk (RR) (or risk difference (RD) for low event rates) and 95% CI. RESULTS: Eighteen RCTs (1858 women), one controlled observational study (N = 22), and seven case series (N = 117) were reviewed. Most hypertension was pregnancy-induced (N = 14 studies). The FHR was assessed by cardiotocogram (CTG) (N = 17 studies (visual interpretation); 1 study (computerized CTG), or umbilical artery velocimetry (N = 4). Four studies examined neonatal heart rate. In placebo-controlled RCTs (N = 192 women), adverse FHR effects did not differ between groups [9/101 (drugs) vs. 7/91 (placebo); RD 0.02, 95% CI (- 0.06, 0.11); chi2 = 1.02]. In six drug vs. drug RCTs (295 women), adverse FHR effects did not differ between groups [29/144 (methyldopa) vs. 42/151 (other drugs); RR 0.72, 95% CI (0.49, 1.07); chi2 = 0.69]. In one labetalol vs. placebo trial, neonatal bradycardia did not differ between groups [4/70 (labetalol) vs. 4/74 (placebo); OR 1.06, 95% CI (0.26, 4.39)], while in three drug vs. drug RCTs, neonatal bradycardia was not observed (0/24 vs. 0/26). CONCLUSIONS: Available data are inadequate to conclude whether oral methyldopa, labetalol, nifedipine, or hydralazine adversely affect fetal or neonatal heart rate and pattern. Until definitive data are available, FHR changes cannot be reliably attributed to drug effect, but may be due to progression of the underlying maternal or placental disease.  相似文献   
82.
83.
This paper gives an overview of the diagnostics and therapy of specific developmental language disorders. In addition, the present understanding of etiology and in particular genetics is discussed. For the classification of a specific language impairment both the linguistic and the general cognitive abilities have to be evaluated.For this purpose, standardised tests should be used instead of informal methods. Hearing impairment has to be ruled out for each language retarded child. If a decrease or stagnation of the language ability is observed, it is necessary to initiate detailed cerebral diagnostics. In the therapy the language symptoms must be directly treated,whereas a training of basic, non-linguistic abilities does not appear to be effective.Additional symptoms, in particular hyperactivity, conduct and emotional disorders, should be considered sufficiently in the treatment.Parents should be included in the therapeutic process more strongly than has been the case in the past.  相似文献   
84.
We present a correspondence-based system for visual object recognition with invariance to position, orientation, scale and deformation. The system is intermediate between high- and low-dimensional representations of correspondences. The essence of the approach is based on higher-order links, called here maplets, which are specific to narrow ranges of mapping parameters (position, scale and orientation), which interact cooperatively with each other, and which are assumed to be formed by learning. While being based on dynamic links, the system overcomes previous problems with that formulation in terms of speed of convergence and range of allowed variation. We perform face recognition experiments, comparing ours to other published systems. We see our work as a step towards a reformulation of neural dynamics that includes rapid network self-organization as essential aspect of brain state organization.  相似文献   
85.
Accommodative convergence in hypermetropia   总被引:2,自引:0,他引:2  
We compared the clinical characteristics of esotropic, hypermetropic children whose strabismus was fully corrected with spectacles (refractive accommodative esotropia) with those who remained orthotropic (that is, had no manifest strabismus on the cover test) in the presence of uncorrected hypermetropia. In addition to a standard ophthalmologic and orthoptic examination, we determined the stimulus accommodative convergence/accommodation (AC/A) ratio by using the gradient method over a range of 6 diopters, the near point of accommodation, and random dot stereopsis. Hypermetropic patients without esotropia or significant esophoria were found to have a low AC/A ratio in contrast to those patients with refractive accommodative esotropia. This finding explains why esodeviations may be absent in some hypermetropic patients with uncorrected vision. We found a high prevalence of abnormally low near points of accommodation and defective or absent stereopsis in both groups of patients.  相似文献   
86.
In a prospective study we compared duplex-ultrasound characteristics of symptomatic internal carotid artery (ICA) stenoses with cranial computerized tomographic (CCT) findings in 82 patients suffering from completed or transient middle cerebral artery symptoms. The aim was to assess the pathogenic role of ICA plaque morphology and the potential embolic risk of ICA plaques. The degree of carotid stenosis was estimated by spectral analysis of the pulsed Doppler signal. The CCT findings were classified as being either normal, lacunar lesions, hemodynamically induced low-perfusion infarctions, or territorial embolic infarctions. According to their ultrasonic features we characterized the ICA plaque surface as smooth or irregular and their structure as homogeneous or heterogeneous. Plaques with an irregular surface and heterogeneous echogenicity dominated significantly in CCT-territorial infarctions (p < 0.01), whereas hemodynamically induced low-perfusion infarctions showed no relationship with any plaque characteristic. High degree ICA stenoses (> 50>%) dominated in both territorial infarctions and low-perfusion infarctions, as compared to ipsilateral normal CCT or lacunes (p < 0.05). Normal CCT and lacunar infarctions were associated with homogeneous and smooth plaques (both p < 0.05). We conclude that > 50% ICA stenoses can cause both hemodynamically induced low-perfusion infarctions as well as thromboembolic territorial infarctions, whereas ulcerated and heterogeneous plaques constitute a high risk factor for arterio-arterial embolic stroke. Furthermore, carotid ultrasound may help to estimate the clinical significance of carotid lesions.  相似文献   
87.
Ten patients with childhood optic neuritis (5 with a single attack of ON and 5 with later MS) were studied at various stages of the disease. Lymphocyte count and function were analysed in the peripheral blood of all patients, 3 repeatedly, and in one they were also analysed in the CSF. T-lymphocytes counts were normal in all but 2 MS cases who had high counts. In acute stages the T4/T8 ratio were high in 1/3 determinations, in recovery low in 2/2 determinations, and in stable stages normal in 6/8 determinations. Lymphocyte function, measured by PHA, ConA and PWM stimulation, was normal in all but one. One patient showed significantly higher T-cell percentages and a high number of stimulated lymphocytes in CSF but a lower count of suppressor cells than in the blood. We found no abnormalities specific to MS nor to childhood MS or to disease activity stage. Rather than peripheral blood, it would seem more worthwhile to study CSF to clarify the pathogenesis of ON and MS.  相似文献   
88.
Marked neovascularization is a hallmark of many neoplasms in the nervous system. Recent reports indicate that the endothelial mitogen vascular endothelial growth factor (VEGF) may play a critical role in the regulation of vascular endothelial proliferation in malignant gliomas. Using novel monoclonal antibodies to the VEGF polypeptide we have determined the expression and cellular distribution of VEGF protein in a representative series of 171 human central nervous system (CNS) tumors by immunohistochemistry and immunoblotting. In agreement with previous in situ hybridization data, 19 out of 20 glioblastomas (95%) showed immunoreactivity for VEGF, whereas both the percentage of immunoreactive tumors and the extent of immunoreactivity for VEGF were significantly lower in astrocytomas. Of the pilocytic astrocytomas (WHO grade I) 44% were immunoreactive for VEGF, but we observed several cases with pronounced vascular proliferates in the absence of VEGF. In ependymomas, meningiomas, hemangioblastomas, and primitive neuroectodermal tumors, there was no correlation between VEGF expression, vascular endothelial proliferation and the grade of malignancy. Oligodendrogliomas and the oligodendroglial component of mixed gliomas lacked immunoreactive VEGF, indicating that endothelial growth factors other than VEGF may regulate tumor angiogenesis in these neoplasms. Western blot analysis showed a predominant VEGF protein species of 23 kDa and confirmed the immunohistochemical data in all cases. Our findings demonstrate that VEGF is expressed in a wide spectrum of brain tumors in which it may induce neovascularization. However, other angiogenic factors also appear to contribute to the vascularization of CNS neoplasms. Received: 18 April 1996 / Revised, accepted: 20 August 1996  相似文献   
89.
From 1984 to 1992 153 children were treated at the pediatric surgical department of the University of Mainz, of whom 19 had fractures of the radius, 9 of the ulna and 125 had a combination of both in the diaphysis of the forearm. Factors like patient's age, type of fracture and therapeutic methods were analyzed. One hundred and forty-one children were treated conservatively, 12 by operation. One hundred and one of these patients were healthy, when discharged (about 8 weeks after accident). Follow-up was possible in 69 cases. We found that occasional a remaining dislocation angle does not impair function: in 65 cases the result was “good” and “very good”, but only “moderate” in 4 cases. These 4 children had been treated conservatively by reposition and plaster cast; 2 of these 4 children showed bone reconstruction without dislocation. Twenty-two of the 56 X-ray follow-up's showed persisting dislocation. To prevent functional problems (2 of our cases) it is essential to obtain a very exact reposition of diaphyseal forearm fractures. Therefore we would recommand a more generous indication for operation, preferably using elastic-stable Nancy pins.  相似文献   
90.
Uncemented total hip replacements have resulted in a higher incidence of postoperative complaints than cemented ones. The theoretical explanation of these not well defined discomforts is based on the differences of the stress and strain fields around the distal portions of the femoral components. While the noncemented stems are press-fitted and most of them tapered distally, thus creating hoop stresses and strains in the surrounding cortical bone, the shrinkage of the cement prevents these mechanical irritations. The relatively sudden disappearance of these discomforts within the first 2 postoperative years is attributed to the shift of the main zone of load transmission from the distal to the proximal portion of the stems following bone remodeling.  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