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   1278601篇
  免费   98049篇
  国内免费   1989篇
耳鼻咽喉   18423篇
儿科学   44351篇
妇产科学   35012篇
基础医学   182206篇
口腔科学   33585篇
临床医学   111256篇
内科学   258269篇
皮肤病学   28022篇
神经病学   100366篇
特种医学   51198篇
外国民族医学   660篇
外科学   196380篇
综合类   27048篇
现状与发展   1篇
一般理论   377篇
预防医学   95716篇
眼科学   27913篇
药学   94775篇
  2篇
中国医学   2422篇
肿瘤学   70657篇
  2018年   13132篇
  2017年   9963篇
  2016年   10897篇
  2015年   12370篇
  2014年   17164篇
  2013年   26212篇
  2012年   36024篇
  2011年   38064篇
  2010年   22800篇
  2009年   21811篇
  2008年   36643篇
  2007年   39250篇
  2006年   39511篇
  2005年   38452篇
  2004年   37603篇
  2003年   36457篇
  2002年   35808篇
  2001年   63994篇
  2000年   66498篇
  1999年   56409篇
  1998年   15129篇
  1997年   13753篇
  1996年   14195篇
  1995年   13456篇
  1994年   12767篇
  1993年   11793篇
  1992年   44557篇
  1991年   43465篇
  1990年   42217篇
  1989年   40114篇
  1988年   36894篇
  1987年   36236篇
  1986年   33622篇
  1985年   32279篇
  1984年   24136篇
  1983年   20268篇
  1982年   11724篇
  1981年   10691篇
  1980年   9517篇
  1979年   21343篇
  1978年   14821篇
  1977年   12532篇
  1976年   11693篇
  1975年   12623篇
  1974年   14661篇
  1973年   14117篇
  1972年   12946篇
  1971年   11729篇
  1970年   11051篇
  1969年   10024篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Corneal epithelial permeability for fluorescein was determined after provocation by a local anesthetic in 18 non-insulin-dependent diabetes mellitus (NIDDM) patients, 23 insulin-dependent diabetes mellitus (IDDM) patients, and 22 healthy controls to evaluate the corneal epithelial barrier function in diabetes. All volunteers had Oxybuprocaine instilled into one eye and saline into the other eye. The epithelial permeability values were determined by fluorophotometry, and the ratio between both eyes was calculated for each individual. The mean permeability values of the saline-instilled eyes in the diabetic patients did not differ significantly from those in the healthy controls (P greater than 0.2). The individual ratios between Oxybuprocaine- and saline-instilled eyes in the NIDDM and IDDM patients differed significantly from those in the healthy controls (mean ratios: 2.6, 1.9, and 1.0, respectively; P less than 0.002). The permeability ratios and the percentage glycosylated hemoglobin (HbAlc) were linearly correlated in the NIDDM patients but not in the IDDM patients (r = 0.73, P less than 0.001, and r = 0.09, P greater than 0.68, respectively). The results showed that the corneal epithelial barrier function in the diabetic patients was not impaired compared with that in the healthy controls. After provocation by a local anesthetic, the barrier function was impaired in the diabetic patients only.  相似文献   
992.
An open, multi-centre, general practice study was carried out in 1661 asthmatic patients to assess the efficacy, in terms of symptom relief and changes in lifestyle, of budesonide and to record objective lung function changes and any adverse events. After a 1-week run-in period on any pre-trial anti-asthma medication, patients received either 200 micrograms or 400 micrograms budesonide twice daily by metered dose inhaler for 4 weeks. Peak expiratory flow rate (PEFR) was measured by the doctor on entry, after the run-in, and at the end of the study and patients were asked to complete diary cards on a daily basis to record compliance, bronchodilator usage and the severity of cough, wheeze and sleep disturbance, and weekly to record 5 lifestyle assessments, e.g. physical activity. Analysis of data from the clinic visits and 1375 completed diary cards showed that PEFR increased significantly from 321 +/- 3 l/min at the end of the run-in to 368 +/- 3 l/min at the end of the trial; 77% of patients had an improved PEFR. Bronchodilator use decreased significantly from 4.2 +/- 0.1 times/day during the run-in period to 3.0 +/- 0.1 times/day at the end of the study; 65% of patients used less bronchodilator. Significant improvements were recorded in all the symptoms and lifestyle indices monitored; 76% of patients improved in at least 5 of the 11 assessments. Treatment-emergent adverse events occurred in 103 (6%) of patients: none was classified as serious or unexpected. No sub-group of patients was identified in which the results were at variance from the full sample. It is concluded that budesonide improves patients' lifestyle and ability to carry out normal activities, as well as improving PEFR and reducing bronchodilator use, in mild to moderately severe asthmatics treated in general practice.  相似文献   
993.
Desferrioxamine (DFO) metabolism and its pharmacokinetics were studied in a swine model using high-performance liquid chromatography. DFO and three iron-binding metabolites occurred in plasma. Interindividual differences in pharmacokinetics and metabolism were observed. Urine analysis in 4 pigs showed three iron-binding metabolites. The mean percent dose excreted in urine in the form of the parent drug was 45 +/- 10% and 10 +/- 2% (means +/- SD) in the form of metabolites. Of the total amount of the parent drug infused, 3 h after initiation, 87% was in the form of DFO, whereas 13% was present as the DFO-iron III complex which represented 45 mg of urinary iron elimination. The described DFO infusion protocol provides for sufficient DFO to chelate significant amounts of ferric iron in excess of normal levels, thus allowing experimental studies of iron chelation in a variety of disease states.  相似文献   
994.
995.
In the present study, chlorogenic acid (CGA) isolated from Anthocephalus cadamba was screened for hepatoprotective activity by in vitro and in vivo assay methods using carbon tetrachloride (CCl4) as a model of liver injury. Intraperitoneal administration of CGA to mice at a dose of 100 mg/kg body weight for 8 days caused significant reversal in lipid peroxidation, enzymatic leakage, cytochrome P450 (Cyt P450) inactivation and produced enhancement of cellular antioxidant defence in CCl4-intoxicated mice, revealing that the antioxidative action of CGA is responsible for its liver protective activity. CGA exhibited a better therapeutic protective action than silymarin (SM), in CCl4-administered mice.  相似文献   
996.
3β-hydroxysteroid dehydrogenase/Δ5−Δ4isomerase (3β-HSD) activity was measured in primary dissociated cell cultures prepared from telencephalons of developing zebra finches. 3β-HSD activity was confirmed after cultures were incubated with [7-3H]pregneno- lone (Preg) or (1,2,6,7-3H-) dehydroepiandrosterone (DHEA) and3H-progesterone (Prog) and3H-androstenedione (AE) were detected in the medium. Product identity was confirmed by recrystallizations and by HPLC analysis. When DHEA was used as substrate,3H-estradiol and3H-estrone were also detected in the culture medium, presumably derived from the aromatization of3H-AE or3H-T produced from3H-DHEA. To test this idea, cultures were incubated with3H-DHEA together with radioinert AE or with fadrozole HCl, a potent and specific aromatase inhibitor. In the presence of radioinert AE,3H-AE increased but metabolites of3H-AE decreased in the media; in the presence of fadrozole,3H-estrogens decreased but3H-AE and its androgenic metabolite3H-5β-androstanedione increased. These data demonstrate 3β-HSD activity in the songbird brain. The presence of Prog and estradiol in these cultures suggest that Preg and DHEA can potentially serve as substrates for the ultimate formation of active sex steroids in the songbird telencephalon.  相似文献   
997.
P. Abimelec  M.D.    M. Rybojad  M.D.    S. Cambiaghi  M.D.    I. Moraillon  M.D.    B. Cavelier-Balloy  M.D.    C. Marx  M.D.    P. Morel  M.D. 《Pediatric dermatology》1995,12(4):340-342
Abstract: The postpubertal appearance of subungual, painful keratotic tumors is a rare feature of incontinentia pigmenti. A patient affected by incontinentia pigmenti developed subungual, painful, nontumoral, hyperkeratotic lesions of the hands at 10 years of age. The mildness of the subungual lesions may be explained by the early stage of the disorder, but it is difficult to correlate the severity of the fingertip pain with the absence of true tumoral swelling. To our knowledge this is the youngest patient reported so far and the only one with a prepubertal expression of this puzzling disorder.  相似文献   
998.
Critical to the proper management of pyoderma gangrenosum are correct diagnosis, identification and treatment of any underlying disorder, and the proper choice of topical and systemic therapy. Many agents are available for the treatment of pyoderma gangrenosum. We review the current therapeutic options, their efficacy and side effects, and we offer some guidelines for their proper selection.  相似文献   
999.
PURPOSETo investigate the decrease in signal intensity on T1 - weighted MR images of some hemorrhagic intracranial lesions after administration of contrast material.METHODSPostprocessing digital image subtraction was performed in 16 MR studies (13 patients) of lesions that showed hyperintensity on noncontrast T1-weighted images. Repetition time and echo time were identical for all precontrast and postcontrast studies. Regions of interest were measured in each lesion, contralateral white matter, and background (before and after contrast enhancement).RESULTSIn six of 16 MR studies, a significant net decrease in signal intensity was seen within the hemorrhagic lesion after contrast enhancement (reverse enhancement). All the lesions were hematomas within residual or recurrent malignant tumors.CONCLUSIONSDigital image subtraction confirms the existence of reverse enhancement. This phenomenon is due to the combined T2-shortening effects of two paramagnetic substances, methemoglobin and gadolinium, which cause the signal reduction produced by the T2 effects to occur at lower concentrations of gadolinium.  相似文献   
1000.
We have described a method for the microtransplantation of a suspension of a few thousand cells from mid to late embryonic mouse hippocampi into the fimbria of immunosuppressed adult rat hosts. There was close graft-to-host contact, across a non-scarred interface. The transplanted cells included CA3 type pyramids, and were enclosed within the host myelinated fibre tract, whose glial framework was largely undisturbed. Immunohistochemistry of two species-specific markers (M6 and Thy-1.2) showed that the donor mouse neurons grew fine (<0.5 μm diameter) axons which extended singly or in fascicles through the rat host fimbria for a maximum distance of at least 10 mm. The donor axons were intimately integrated among and closely aligned to the host tract axons and to the interfascicular glial rows of the host tract. The axons travelled (i) laterally through the ipsilateral fimbria, (ii) medially across the midline in the ventral hippocampal commissure to reach the contralateral fimbria and alveus, and (iii) rostro-medially to the septum. On approaching the terminal fields appropriate to hippocampal CA3 pyramidal cell axons, the transplant axons gave rise to fine preterminal branches which were continuous with a reticular or amorphous immunoreactivity in the stratum oriens and stratum pyramidale of the ipsilateral hippocampus, and in the lateral and triangular septal nuclei. The donor axons extended along the host fimbria at a rate of ∼ 1 mm per day, reaching their terminal field destinations by ∼1–2 weeks. At 7 weeks the projections were maintained, but with little further extension. These observations indicate that the microenvironment of myelinated adult fibre tracts is permissive for an abundant and rapid growth of axons from transplanted embryonic cell suspensions. These axons can leave host tracts to invade appropriate terminal fields.  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