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   27216篇
  免费   6089篇
  国内免费   74篇
耳鼻咽喉   179篇
儿科学   689篇
妇产科学   1777篇
基础医学   1289篇
口腔科学   351篇
临床医学   16114篇
内科学   4399篇
皮肤病学   257篇
神经病学   1163篇
特种医学   442篇
外科学   1840篇
综合类   322篇
一般理论   4篇
预防医学   2580篇
眼科学   129篇
药学   807篇
中国医学   13篇
肿瘤学   1024篇
  2023年   808篇
  2022年   132篇
  2021年   323篇
  2020年   686篇
  2019年   329篇
  2018年   1199篇
  2017年   1446篇
  2016年   1535篇
  2015年   1623篇
  2014年   1699篇
  2013年   1993篇
  2012年   776篇
  2011年   1096篇
  2010年   1253篇
  2009年   1527篇
  2008年   951篇
  2007年   894篇
  2006年   938篇
  2005年   836篇
  2004年   754篇
  2003年   667篇
  2002年   611篇
  2001年   767篇
  2000年   560篇
  1999年   650篇
  1998年   688篇
  1997年   766篇
  1996年   717篇
  1995年   665篇
  1994年   493篇
  1993年   421篇
  1992年   444篇
  1991年   434篇
  1990年   405篇
  1989年   355篇
  1988年   310篇
  1987年   300篇
  1986年   307篇
  1985年   312篇
  1984年   243篇
  1983年   198篇
  1982年   173篇
  1981年   170篇
  1980年   124篇
  1979年   198篇
  1978年   138篇
  1977年   139篇
  1976年   136篇
  1973年   117篇
  1972年   147篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
Seventy-four 8th- and 10th-grade students attending a private girls' school in Hawaii were queried about their perceptions of and preparation for menstruation using a questionnaire administered in a health education class. Eighty percent had already started menstruating. The most frequently cited perceptions by the respondents referred to both the inconveniences and the normalcy of menstruation. Many were first informed about menstruation by their mothers and stated that they also first informed their mothers when they started menstruating. Surprise, fear, and embarrassment were common initial reactions, while strong negative or positive emotions were more rare. Only 35% wanted boys and girls together during class discussion, but 89% stated that boys needed to be informed about menstruation. The most frequent reasons cited for noncoed settings were the girls' concern about their comfort in openly discussing menstruation. Thirty-eight percent thought parents should inform other siblings when they started menstruation, although almost half gave specific conditions the parents should consider. The majority thought the fifth to sixth grades were the best times to introduce menstruation content.  相似文献   
75.
76.
77.
78.
INTRODUCTION: Tooth movement has been studied largely with respect to the force required for tipping when pressure distribution varies along the length of the periodontal ligament. But important factors for effective canine translation include the nature and magnitude of applied stress and the patient's cell biology. The purpose of this research was to test 3 hypotheses: (1) the velocity of tooth translation (v(t)) is related to applied stress and growth status, (2) a threshold of stress accounts for the lag phase, and (3) v(t) is correlated with the ratio (AI) of 2 cytokines (IL-1beta, IL-1RA) measured in gingival crevicular fluid (GCF) and stimulated whole blood (SWB). METHODS: Continuous maxillary canine retraction stresses of 13 kPa and 4, 26, or 52 kPa were applied bilaterally in 6 growing and 4 adult subjects for 84 days. Dental models and GCF samples were collected at 1- to 14-day intervals. Cytokines were measured in GCF and SWB cell cultures. RESULTS: V(t) was positively related to stress and was higher in growing subjects (P = .001). It was also related to AI(GCF) in growers (R2= 0.56) and nongrowers (R2= 0.72). Canines moved with 52 kPa showed a lag phase, and postlag phase AI(GCF) was twice that of lag phase AI(GCF). Mean v(t) and associated AI(GCF) during the postlag phase were nearly double the values for canines moved with 13 and 26 kPa. SWB production of cytokines was dose-dependent. For growing subjects, SWB IL-1RA was correlated with v(t) (R = 0.70-0.72), and AI(SWB) and IL-1beta concentrations were correlated with AI(GCF) (R = 0.73-0.78). CONCLUSIONS: V(t) varied with growth status and stresses < or = 52 kPa; stresses of < 52 kPa showed no lag phase; and equivalent stresses yielded subject-dependent differences in v(t), which correlated with cytokines in GCF and SWB.  相似文献   
79.
OBJECTIVE: To assess the incidence and spectrum of complications associated with central venous catheter (CVC) placement in the critically ill infant. DESIGN: A prospective study of all babies hospitalized in a neonatal intensive care unit (NICU) from January 1989 to December 1989. Potential risk factors associated with infection were evaluated by a case-control comparison. SETTING: Conducted at a university-affiliated, tertiary care community hospital. PATIENTS: Neonates requiring intensive care and a central venous catheter. Controls consisted of noninfected babies. RESULTS: Of 263 critically ill neonates, only 13 (4.9%) required a CVC insertion. Seventeen CVCs were placed in these 13 neonates for a total duration of 600 days (median, 32 days/cannula). Fifteen (88%) of these cannulas had one or more complications during its catheter life including dislodgement or leakage (53%), occlusion or thrombosis (47%), infections (29%), or minor bleeding (12%). Five babies (29%) developed 6 episodes of bloodstream infection including 3 sporadic cases due to Staphylococcus epidermidis and a cluster of fungemia due to Malassezia furfur associated with lipid emulsion therapy. Infants with a CVC-associated infection were a younger gestational age (24 weeks versus 32 weeks, p = .04) and weighed less at birth (580 g versus 1285 g, p = .02). The overall rate of bloodstream infection was one episode per 100 days of catheter use. CONCLUSIONS: CVCs may be lifesaving to a critically ill neonate, but complications occur frequently. Use must be restricted to infants in whom alternate delivery routes of intravenous therapy or support are otherwise unavailable.  相似文献   
80.
Intubating conditions have been assessed at 60 s following administration of vecuronium 0.1 mg kg-1 or atracurium 0.5 mg kg-1 given either as a single dose after induction of anaesthesia with thiopentone or in divided doses; vecuronium 0.015 mg kg-1 followed 4 or 6 min later by 0.085 mg kg-1, or atracurium 0.075 mg kg-1 followed 4 or 6 min later by 0.425 mg kg-1. In the divided dose groups the smaller initial (priming) dose was given prior to induction of anaesthesia. Onset and duration of clinical relaxation were assessed using a peripheral nerve stimulator. The intubating conditions at 60 s improved significantly, with the use of relaxants in divided doses being acceptable in 80 and 70% of patients, respectively, with vecuronium and atracurium, but the conditions are not as good as those commonly found using suxamethonium. Priming at 6 min has no advantage over priming at 4 min. The onset of complete block was accelerated with priming, but the difference was not significant. The duration of clinical relaxation of vecuronium was significantly prolonged by giving it in divided doses. Unpleasant awareness of muscle weakness was observed in 15 patients, requiring early induction of anaesthesia in five of them.  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