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   19014篇
  免费   1273篇
  国内免费   74篇
耳鼻咽喉   217篇
儿科学   449篇
妇产科学   355篇
基础医学   2617篇
口腔科学   339篇
临床医学   1655篇
内科学   4900篇
皮肤病学   422篇
神经病学   1635篇
特种医学   616篇
外科学   2688篇
综合类   260篇
一般理论   8篇
预防医学   1407篇
眼科学   412篇
药学   1129篇
中国医学   77篇
肿瘤学   1175篇
  2023年   133篇
  2022年   329篇
  2021年   545篇
  2020年   306篇
  2019年   447篇
  2018年   515篇
  2017年   342篇
  2016年   364篇
  2015年   449篇
  2014年   621篇
  2013年   838篇
  2012年   1333篇
  2011年   1348篇
  2010年   774篇
  2009年   666篇
  2008年   1127篇
  2007年   1195篇
  2006年   1175篇
  2005年   1106篇
  2004年   1008篇
  2003年   959篇
  2002年   952篇
  2001年   132篇
  2000年   117篇
  1999年   163篇
  1998年   201篇
  1997年   168篇
  1996年   175篇
  1995年   131篇
  1994年   125篇
  1993年   105篇
  1992年   108篇
  1991年   108篇
  1990年   93篇
  1989年   72篇
  1988年   85篇
  1987年   85篇
  1986年   71篇
  1985年   92篇
  1984年   101篇
  1983年   99篇
  1982年   115篇
  1981年   125篇
  1980年   110篇
  1979年   70篇
  1978年   75篇
  1977年   89篇
  1976年   62篇
  1975年   51篇
  1974年   52篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
A consecutive series of six adult patients ranging in age from 29 to 53 years is presented. The clinical and radiological features in each patient are described. Attention is drawn to the features demonstrated on computed axial tomography. In only one patient, the first encountered, was surgical excision undertaken and histological verification obtained. One patient died before any form of treatment could be instituted. The remaining four patients were treated with antituberculous chemotherapy alone and their progress monitored by sequential computed tomography. The excellent response and good outcome in this conservatively treated group are documented.  相似文献   
72.
Eight patients with parkinsonism who developed severe orthostatic sypotension, were treated with oral ergotamine/caffeine. Significant long-term improvement in standing systolic blood pressure and symptoms of syncope and light-headedness were observed in four of these patients. One patient in whom the drug was effective discontinued it because of nausea. Another lost benefit after 2 weeks of sucessful therapy. Significant supine systolic hypertension occureed in only one patient, which was easily managed by nifedipine given at night. Symptoms or signs of ergotism were not observed. Oral ergotamine/caffeine should be considered as a cost-effective teratment for refactory orthostatic hypotension in carefully selected patients with parkinsonism.  相似文献   
73.
74.
PURPOSE: A pseudo forward ray-tracing (PFRT) algorithm is developed to evaluate surface reconstruction in corneal topography. The method can be applied to topographers where one-to-one correspondence between mire and image points can be established. METHODS: The PFRT algorithm was applied on a corneal topographer designed and constructed at the VU University Medical Center, Amsterdam, The Netherlands. Performance of the algorithm was evaluated using artificial test surfaces and two sample eyes. The residual output of the PFRT algorithm is displayed as pixel displacements of actual feature points on the corneal image. Displacement of 1 pixel indicates submicrometer corneal height accuracy. RESULTS: PFRT residual increases with complexity of the measured surface. Using Zernike radial order 6, the mean residual for the artificial surfaces is subpixel. The mean residual for the regular cornea and the irregular cornea is 1.16 and 2.94 respectively. To some extent, increasing the Zernike radial order improves the accuracy. The improvement from order 6 to 20 is factor 2.3 for the irregular cornea. Using the residuals to further improve the accuracy brought local changes as high as 0.28 D in some areas of the reconstructed corneal power map. CONCLUSION: PFRT can be used to evaluate how close a reconstructed corneal surface is to the actual one. The residue information obtained from this algorithm can be displayed simultaneously with the corneal image. This provides accurate information about the corneal shape that is useful for application in laser refractive surgery.  相似文献   
75.
The number of cryopreserved human spermatozoa which penetrated zona-free hamster oocytes afier stimulation with 2μmol A23187 per litre was increased by the hrther addition of 0.6 or 3.6 mmol pentoxifjrlline per litre. With spermatozoa prepared by washing by repeated centrifugation, the median numbers of sperm headd/egg were 1.9, 7.9 and 10.8 in the presence of 0, 0.6 or 3.6 mmol pentoxifylline per litre, respectively. A similar effect was observed with spermatozoa prepared on a Percoll gradient. As A23187 inhibited sperm motility, and this was exacerbated by pentoxifylline, the increased penetration rate of hamster oocytes cannot be explained by improved sperm motility. The number of spermatozoa stimulated to acrosome react by 2 μmol A23187 per litre was increased 3-fold by 3.6 mmol pentoxifylline per litre and 4-fold by 5 mmol caffeine per litre. These data suggest that CAMP may act synergistically with Ca2+ to stimulate the acrosome reaction. Pentoxifjrlline may improve the fertility of poor-quality human spermatozoa by enhancing their ability to respond to the Ca2+ signal produced by binding to the zona pellucida.  相似文献   
76.
77.
Microneurographic measurements of muscle sympathetic nerve activity (SNA) have suggested that, during static exercise, central command is much less important than skeletal muscle afferents in causing sympathetic neural activation. The possibility remains, however, that the sympathetic discharge produced by central command is targeted mainly to tissues other than skeletal muscle. To examine this possibility, we recorded SNA with microelectrodes placed selectively in skin, as well as in muscle, nerve fascicles of the peroneal nerve during static handgrip maneuvers designed to separate the effects of central command from those of muscle afferents. To study the relative effects of cutaneous sympathetic activation on sudomotor versus vasomotor function, we simultaneously estimated changes in skin blood flow (laser Doppler velocimetry) and in sudomotor (electrodermal) activation in the region of skin innervated by the impaled nerve fascicle. Two minutes of static handgrip at 10%, 20%, and 30% of maximal voluntary contraction caused large and intensity-dependent increases in skin SNA. These increases in SNA immediately preceded the onset of muscle tension, accelerated progressively during sustained handgrip, and resolved promptly with the cessation of motor effort. The handgrip-induced increases in skin SNA were not maintained when handgrip was followed by arrest of the forearm circulation, a maneuver that maintains the stimulation of chemically sensitive muscle afferents while eliminating the influences of central command and mechanically sensitive muscle afferents. During normothermia, static handgrip at 30% maximal voluntary contraction caused sustained increases in skin SNA (+400 +/- 83%, mean +/- SEM, p less than 0.05) and in electrodermal activity (+276 +/- 56%, p less than 0.05) but only transient increases in estimated skin vascular resistance (+11 +/- 2%, p less than 0.05). When skin temperature was increased or decreased to a new stable baseline level, subsequent increases in skin SNA during handgrip were accompanied by sustained but directionally opposite changes in estimated skin vascular resistance, with exercise-induced vasodilation during hyperthermia but exercise-induced vasoconstriction during hypothermia. From these observations, we conclude the following: 1) static exercise markedly increases sympathetic outflow to skin as well as to skeletal muscle; 2) the increases in skin SNA, unlike muscle SNA, appear to be caused mainly by central command rather than by muscle afferent reflexes; and 3) this cutaneous sympathetic activation appears to be targeted both to sweat glands and to vascular smooth muscle, with the relative targeting being temperature dependent.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
78.
Abstract: Coagulation leading to fibrosis of mammo-graphically detected breast cancers by interstitial laser therapy was tested as an alternative to surgical removal. Availability of computerized stereotaxic digital imaging allows the precise placement of laser and thermal needles into the target tumor and its controlled ablation by heat. The methodology of interstitial laser therapy (ILT), evolution of the subsequently removed tumors, and their histologic appearance are outlined.
Eight patients with mammographically well-defined tumors were selected. Definitive diagnosis and receptor evaluation were made on core biopsies. Under local anesthesia, stereotaxically guided diode laser energy at 5–10 w was delivered via a 400 xm fiber in a 19-gauge needle placed into the center of the tumor until the peripheral temperature exceeded 60°C. Patients experienced transient pain and pyrexia. Subsequent to ILT, seven invasive carcinomas were excised while one case of multiple papillomas was kept under surveillance. Histologic study revealed central necrosis but some peripheral residual tumor in the first five cases. In the last two, central necrosis surrounded by concentrically arranged, recognizable but severely injured, focally "windswept" and "ghostlike" tumor and granulation tissue were noted. The multiple papillomas showed radiologic shrinkage at 5 months and extensive fibrosis on needle biopsy.
ILT is an attractive new method of treating small, well-defined breast tumors and offers a potentially significant alternative to surgical removal; further exploration is warranted.  相似文献   
79.
OBJECTIVE: Our aim was to evaluate the clinical course and management of congenital cervical atresia. STUDY DESIGN: This retrospective analysis included 7 patients referred to our clinic and a review of the medical literature. RESULTS: Including this case series, 58 cases of congenital cervical atresia have been reported in the literature. Forty-eight percent of patients had isolated congenital cervical atresia with a normal vagina whereas the remainder had either complete or partial vaginal atresia (“shortened blind vaginal pouches”). Surgical management has included abdominal hysterectomy or uterovaginal cannulation with or without vaginoplasty. In 59% of patients who underwent uterovaginal canalization procedures (23/39), normal menstrual bleeding was achieved. Four of these patients subsequently became pregnant and were delivered at term. CONCLUSION: Surgical canalization in selected patients with congenital cervical atresia can be successfully performed to provide patients an opportunity for conservative management, resulting in normal menstrual bleeding, resolution of cyclic pelvic pain, and some potential (albeit limited) for fertility.(Am J Obstet Gynecol 1997;177:25)  相似文献   
80.
We conducted a case-control study based on computer-recorded information accrued in the United Kingdom General Practice Research Database to assess and compare the relation between different antihypertensive drug therapies and myocardial infarction in patients with no known clinical or laboratory risk factors for myocardial infarction other than hypertension. Cases were treated hypertensive patients with no other known risk factors who developed a first acute myocardial infarction between January 1, 1993, and October 31, 1994. They were ascertained from a review of the clinical record together with a questionnaire filled out by the attending general practitioner. Controls were matched to each case for age, sex, general practice, and index date. Antihypertensive therapy was derived from the computerized patient record. The study consisted of 210 cases and 793 controls. Compared with users of β-blockers alone, the adjusted relative risk (RR) estimates for all other treatment regimens were close to 1.0. A comparison of users of calcium channel blockers alone with users of β-blockers alone yielded a RR estimate of 0.9 (95% CI 0.5, 1.7). We conclude that the risk of acute myocardial infarction in otherwise healthy, treated hypertensive patients is not materially associated with the particular drug they receive.  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