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   18503篇
  免费   1760篇
  国内免费   66篇
耳鼻咽喉   238篇
儿科学   568篇
妇产科学   393篇
基础医学   2244篇
口腔科学   361篇
临床医学   2485篇
内科学   3570篇
皮肤病学   211篇
神经病学   1410篇
特种医学   843篇
外国民族医学   3篇
外科学   2425篇
综合类   483篇
一般理论   9篇
预防医学   1991篇
眼科学   601篇
药学   1535篇
中国医学   14篇
肿瘤学   945篇
  2021年   314篇
  2020年   206篇
  2019年   291篇
  2018年   325篇
  2017年   204篇
  2016年   283篇
  2015年   301篇
  2014年   409篇
  2013年   584篇
  2012年   800篇
  2011年   867篇
  2010年   496篇
  2009年   420篇
  2008年   735篇
  2007年   853篇
  2006年   847篇
  2005年   777篇
  2004年   765篇
  2003年   695篇
  2002年   649篇
  2001年   573篇
  2000年   607篇
  1999年   536篇
  1998年   253篇
  1997年   221篇
  1996年   223篇
  1995年   208篇
  1994年   178篇
  1993年   169篇
  1992年   420篇
  1991年   421篇
  1990年   395篇
  1989年   427篇
  1988年   376篇
  1987年   351篇
  1986年   348篇
  1985年   329篇
  1984年   270篇
  1983年   233篇
  1982年   159篇
  1981年   124篇
  1979年   195篇
  1978年   173篇
  1977年   152篇
  1976年   133篇
  1975年   113篇
  1974年   160篇
  1973年   144篇
  1972年   129篇
  1971年   116篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
An accurate prediction of birth weight during gestation can provide useful information for assessing fetal and newborn health status, enabling the clinician to better predict infant morbidity and mortality. Two previously reported standard methods for birth-weight estimation used data collected in utero to derive formulas by least-squares linear regression. The rationale for the inclusion of particular variables in these equations, however, has not been clearly defined. This study was undertaken to examine the efficacy of some previously used variables as well as some new variables in estimating fetal birth weight. The authors used measurements of femur length, biparietal diameter, and abdominal circumference from 107 fetuses (2500 to 4000 g) as variables to compare the two standard methods of birth-weight estimation. A new formula is presented that is derived from a simple model based on the known relationship between volume and weight. The head is represented as a sphere and the body as a cylinder. This study presents a more systematic approach to formula development in which statistical biases are minimized by examining the underlying distributions of the variables used to predict birth weight.  相似文献   
102.
The development of selective irreversible ligands has proven to be an invaluable technique for the isolation, purification and characterization of many receptor proteins. An isothiocyanato-derivative of the muscarinic antagonist aprophen was synthesized and evaluated as a potential irreversible ligand for muscarinic receptors. This compound (aprophit) displaced [3H]N-methylscopolamine binding from rat cerebral cortex with a Ki of 3.1 x 10(-7) M. The inhibition was concentration-dependent and could not be reversed by extensive washing. Aprophit inhibited the acetylcholine-stimulated release of catecholamines from isolated, perfused guinea pig adrenal glands in a concentration-dependent manner. This inhibition was not reversed by perfusing the tissue with Locke's solution and was not due to a non-selective acylation by the isothiocyanate function. The data suggest that aprophit is selectively acylating muscarinic receptor proteins and thus may be useful in their further characterization.  相似文献   
103.
Thirty-four social drinkers who had referred themselves to the Regional Brain Damage Unit for assessment of the effects of drinking alcohol were compared with 42 volunteer control subjects of equivalent age but with low alcohol intake, using two 'learning' tests — the Rey Auditory Verbal Learning Test (RAVLT) and the Austin Button Maze. The Maze Test gave no evidence of disorder, but the two groups were significantly different on the RAVLT. No abnormalities in standard cognitive tests were apparent. These results suggest that a deficit in learning ability may be an early feature of the brain dysfunction associated with excessive alcohol consumption.  相似文献   
104.
Geographical variations in the incidence of disease are of considerable theoretical and practical importance. It has been claimed that the distribution of acute lymphoblastic leukemia (ALL) phenotypes in Saudi Arabia is different from that recorded in the Western literature. One hundred and twelve (112) patients under 15 years of age, diagnosed as ALL between January 1992 and May 1994 had immunophenotypes performed on their blast cells. Common ALL (cALL) together with pre-B-ALL, formed 86.5% of the total; B-cell 3%, T-cell 6% and null cell 4.5%. These figures are not significantly different from the Western literature. A previous claim from this institution in 1990, that both null and B-cell ALL were significantly increased compared with elsewhere, is not supported by the present figures. Age and sex distribution, and FAB classification, L1 77%, L2 20% and L3 3%, were also of the same order as described elsewhere and, in particular, there was no increase in the frequency of L3 subtype.  相似文献   
105.
OBJECTIVES: To investigate common presentations and expected outcomes in patients with traumatically induced otologic dysfunction. STUDY DESIGN: Retrospective case review of patients who underwent otologic surgery for sequelae of otologic trauma over a 28-year period. Patients were stratified into major and minor trauma cohorts. Major trauma was designated as closed head injury with or without temporal bone fracture; lower-energy insults comprised the minor trauma group. Preoperative and postoperative audiograms were obtained and correlated with extent of injury. SETTING: Tertiary referral center. RESULTS: Major trauma accounted for 44.9 percent of all patients. The remaining 55.1 percent suffered minor trauma, of which simple traumatic tympanic membrane perforation was the most common insult (33.6%). Two hundred twenty-seven cases were performed on 214 patients. Pure tone averages improved a significant 20.8 dB to essentially normal levels postoperatively. CONCLUSION: Regardless of injury extent, surgical rehabilitation of conductive losses attains excellent hearing results that surpass those historically reported for the chronic ear population.  相似文献   
106.
107.
The aim was to study firstly, the motor effects of a new 5-HT1A antagonist, NDL-249 [(R)-3-(N-cyclopentyl-N-propylamino)-8-fluoro-3,4-dihydro-2H-1-benzopyran-5-carboxamide hydrochloride] and of the reference 5-HT1A antagonist WAY-100 635 [N-(2-(1-(4-(2-methoxyphenyl)piperazinyl))ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride], in comparison to the 5-HT1A agonist (±)-8-OH-DPAT [(8-hydroxy-2-(di-N-propylamino) tetralin, hereafter 8-OH-DPAT], in rats acclimatised to the automated activity cages; secondly, to study whether the behavioural effects of NDL-249 and 8-OH-DPAT are sensitive to the 5-HT depleting effects of p-chlorophenylalanine (PCPA); thirdly, to characterise the nature of the antagonist-induced activation seen in the automatic activity cages with the aid of a behavioural observation analysis; fourthly, to examine the interaction between the 5-HT1Areceptors mediating the behavioural effects and dopamine (DA) receptors. NDL-249 was found to bind in vitro to rat hippocampal 5-HT1A receptors with high affinity and selectivity. In second messenger studies, it was devoid of agonist-like effects. In the locomotor activity studies, each antagonist significantly increased the incidence of horizontal activity, peripheral activity and rearing. 8-OH-DPAT, while significantly increasing peripheral and horizontal activities, decreased the incidence of rearing. PCPA blocked the motor effects of NDL-249 but did not affect those of 8-OH-DPAT. Observational analyses indicated that NDL-249 induced significant increases at one or more doses in sniffing, rearing and locomotion together with a significant reduction in stillness. WAY-100 635 significantly increased the incidence of rearing, intense grooming and vacuous chewing. The significant increases in sniffing, grooming and intense grooming and the significant decrease in stillness induced by the DA D1 agonist, SK&F 38393 [(±)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride], were not altered by concomitant pre-treatment with NDL-249. Pre-treatment of rats with either the DA D1 antagonist SCH-23390 (2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol) or the DA D2 antagonist, raclopride, blocked the reduced stillness and increased sniffing and rearing induced by NDL-249. In conclusion, 5-HT1A antagonists including the new selective antagonist, NDL-249, induce mild behavioural activation in rats, which is mediated probably indirectly via DA systems. Received: 3 April 1997/Final version: 23 February 1998  相似文献   
108.
We examined the potential protective effect of pretreatment with corticosteroids or antioxidants (ascorbic acid or allopurinol) in rabbits with reper-fusion-induced damage to skeletal muscle after ischemia.

4 hours of limb ischemia induced by a pneumatic tourniquet, followed by reperfusion for 1 hour, caused a considerable amount of ultrastructural damage to the anterior tibialis muscles accompanied by a rise in circulating creatine kinase activity. Pretreatment of animals with depomedrone by a single 8 mg bolus injection led to a preservation of the anterior tibialis structure on both light and electron microscopy. High-dose continuous intravenous infusion with ascorbic acid (80 mg/hr) throughout the period of ischemia and reperfusion also preserved skeletal muscle structure, although allopurinol in various doses had no protective effect.

These data are fully compatible with a mechanism of ischemia/reperfusion-induced injury to skeletal muscle, involving generation of oxygen radicals and neutrophil sequestration and activation. They also indicate that damage to human skeletal muscle caused by prolonged use of a tourniquet is likely to be reduced by simple pharmacological interventions.  相似文献   
109.
Thirty-five patients who had been surgically treated for major symptomatic isolated chronic anterior cruciate ligament deficiency by lateral extra-articular reconstruction alone were reviewed at an average of five years after operation. Seventy-seven per cent of patients reviewed were improved subjectively, and 83% of patients who were examined had objective evidence of only minor instability or none at follow-up. However, only a few patients had "normal" knees and many continued to have minor symptoms of instability with some restriction of activity. Most of the unsatisfactory results were in patients with significant chondral pathology at the time of reconstruction. While an extra-articular pivot-shift repair did not correct all the symptoms and signs completely, most patients were improved subjectively and objectively, and there were few complications.  相似文献   
110.
Torque range of motion (TROM) measurements of the metatarsophalangeal joint (MTPJ) of the great toe were made to determine the relationship of joint stiffness and plantar ulceration. Subjects included 20 patients with a history of plantar ulceration of the great toe (GTU), 20 patients with a history of ulceration on the plantar surface of the foot excluding the great toe (NGTU), and 20 normal controls. Peak MTPJ extension was significantly reduced in the GTU group compared to NGTU and control groups (p < 0.0001). The slopes of the TROM and stiffness curves were significantly steeper (p < 0.0001) in the GTU group compared to the control group (p < 0.0001). Results support the hypothesis that stiffness is a factor in plantar ulceration of the great toe.J Orthop Sports Phys Ther 1988;10(5):172-176.  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