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   11143篇
  免费   1170篇
  国内免费   123篇
耳鼻咽喉   71篇
儿科学   373篇
妇产科学   362篇
基础医学   1599篇
口腔科学   200篇
临床医学   1248篇
内科学   2326篇
皮肤病学   136篇
神经病学   816篇
特种医学   684篇
外国民族医学   1篇
外科学   1460篇
综合类   340篇
一般理论   7篇
预防医学   1128篇
眼科学   114篇
药学   927篇
中国医学   4篇
肿瘤学   640篇
  2021年   143篇
  2020年   99篇
  2019年   154篇
  2018年   159篇
  2017年   131篇
  2016年   137篇
  2015年   179篇
  2014年   257篇
  2013年   367篇
  2012年   476篇
  2011年   529篇
  2010年   306篇
  2009年   284篇
  2008年   436篇
  2007年   485篇
  2006年   453篇
  2005年   454篇
  2004年   404篇
  2003年   382篇
  2002年   382篇
  2001年   331篇
  2000年   355篇
  1999年   317篇
  1998年   212篇
  1997年   205篇
  1996年   230篇
  1995年   169篇
  1994年   159篇
  1993年   170篇
  1992年   236篇
  1991年   275篇
  1990年   241篇
  1989年   235篇
  1988年   249篇
  1987年   276篇
  1986年   227篇
  1985年   247篇
  1984年   173篇
  1983年   153篇
  1982年   117篇
  1981年   101篇
  1980年   95篇
  1979年   112篇
  1978年   96篇
  1977年   93篇
  1976年   97篇
  1975年   93篇
  1973年   89篇
  1972年   85篇
  1971年   77篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
BACKGROUND: Equilibration of hemoglobin concentration after transfusion has been estimated to take about 24 hours, but some studies have shown that earlier measurements reflect steady-state values in persons who have not bled recently. This study was aimed at assessing the changes over time in hemoglobin concentration after transfusion in acutely anemic patients because of recent bleeding. STUDY DESIGN AND METHODS: Thirty-two normovolemic patients recovering from an acute bleeding episode who were no longer thought to be bleeding and who received a 2- unit red cell transfusion were studied. At baseline and 15, 30, 60, and 120 minutes and 24 hours after transfusion, hemoglobin concentration and hematocrit values were measured. RESULTS: The administration of 2 units of packed red cells elicited a 24-hour increase of 22.4 +/− 6.8 g per L in hemoglobin concentration. Hemoglobin values were not different at any of the defined posttransfusion times. Hematocrit levels experienced similar changes over time. Agreement between 15-minute and 24-hour values was excellent, as only 6 percent of patients exhibited a clinically significant difference (> 6 g/L) between the hemoglobin measurements. CONCLUSION: Hemoglobin and hematocrit values rapidly equilibrate after transfusion in normovolemic patients who are recovering from an acute bleeding episode. This fact would allow a rapid assessment of the effects of transfusion and of the recurrence of bleeding in patients remaining at risk.  相似文献   
62.
Features of 111 mammary carcinomas derived from breast cancer screening were compared with those of 69 carcinomas presenting 'clinically'. Screen detected cancers were smaller, had less likelihood of nodal metastases, included a higher proportion of in situ tumours and if invasive, tended to be of lower grade. Using immunohistochemical methods, the expression of c-erbB-2 oncoprotein, epidermal growth factor receptor (EGFR) and cathepsin D were compared in the two groups. A similar proportion of screened and unscreened tumours expressed c-erbB-2 oncoprotein and EGFR but expression of the oestrogen regulated protein cathepsin D was significantly more frequent in the screened group (P less than 0.05). Although a relatively small series, the results suggest a biological difference between 'screened' and 'clinical' tumours.  相似文献   
63.
The reported prevalence of human papillomavirus (HPV) type 16 in the genital tracts of women with various gynaecological conditions is highly variable. In particular, some results with the polymerase chain reaction (PCR) technique have suggested that HPV-16 is a ubiquitous or very common virus. We undertook this study to help clarify the current confusion. PCR with HPV consensus L1 primers and specific E6 primers was used to study 89 women attending two gynaecology referral clinics, as well as 99 women attending a health maintenance organization (HMO) clinic; 70 of these latter women had no current or prior history of genital HPV disease. HPV-16 was detected in less than 5% of cytologically normal women from either group and in 17% (6/36) and 31% (9/29) of women with cervical intraepithelial neoplasia (CIN) from the referral clinic and the HMO, respectively. The other high-risk or intermediate-risk HPVs (types 18, 31, 33 or 35) were less prevalent than HPV 16 in all groups of women. A majority of the HPV types detected by the L1 primers in normal women were uncharacterized HPVs. Overall these uncharacterized HPVs were detected in 37% (46/123) of the normal women and in 48% (31/65) of the women with CIN. Using the most sensitive PCR product detection method employed in the study, HPV DNA was detected in 36% (4/11) of swab specimens obtained from the external abdomen.  相似文献   
64.
In acute quadriplegia we have noted that about one in five patients develops unexplained production of markedly excessive and tenacious bronchial mucus. Spontaneous recovery from mucus hypersecretion usually occurs within weeks to months. Mucus samples collected from 12 patients have been found to be abnormal. Macromolecular contents of single aspirates yielded as much as 500 mg. Analytical ultracentrifuge analysis showed the mucus to contain considerable epithelial glycoprotein (GP) of typical buoyant density; its amino acid and carbohydrate compositions were characteristic of the GP from hypersecretory bronchial mucus such as in chronic bronchitis and cystic fibrosis. In five patients studied after recovery from hypersecretion, there tended to be relatively less GP. The mucus samples contained a high density glycoconjugate (GC): this had sugars of GP but also reacted positively with a monoclonal antibody to keratan sulfate. Its amino acid composition was different from that of GP: threonine was lower and glycine was higher than in GP. In mucus from one patient who died, chondroitin sulfate ABC and hyaluronic acid were identified as well. This suggests proteoglycans are involved in the pathophysiology of mucus hypersecretion. The sudden onset and spontaneous recovery of hypersecretion suggests that it is not due to gland hypertrophy. We speculate that in acute quadriplegia it is due to disturbed neuronal control of bronchial mucus gland secretion, perhaps related to initial disappearance and later reappearance of peripheral sympathetic nervous system tone.  相似文献   
65.
BACKGROUND: Cyclosporin has been shown to facilitate renal vasoconstriction and to have an antinatriuretic effect. The existence of an interference of cyclosporin with the vasodilating properties of endothelium mediated by nitric oxide production could mediate these effects. On the other hand, the infusion of the nitric oxide precursor L-arginine has been shown to induce renal vasodilatation and to facilitate natriuresis in normal volunteers. We have investigated the renal effects of the administration of an infusion of L-arginine in renal transplant patients chronically treated with cyclosporin. To facilitate the analysis of the data the effects of the administration of a similar dose of cyclosporin on renal function during the infusion of a vehicle were also investigated during the administration of a vehicle of L-arginine. DESIGN: Ten male renal transplant patients, chronically treated with cyclosporin and with a stable renal function were studied during 2 consecutive days after the administration of the usual morning dose of cyclosporin. The first day they received an intravenous infusion of vehicle and the second the infusion of graded doses of L-arginine (50, 100, 150 mg/kg/h) during 3 consecutive h. RESULTS: The first day, after cyclosporin administration a significant fall (P < 0.01) was observed in natriuresis and kaliuresis in the absence of changes in renal plasma flow and glomerular filtration rate. After the administration of L-arginine significant (P < 0.01) increases of renal plasma flow, glomerular filtration rate, and natriuresis were seen. The increase in blood levels of cyclosporin after its administration did not differ between days 1 and 2. CONCLUSION: These results indicate that L-arginine facilitates renal vasodilatation and natriuresis in renal transplant patients. Furthermore, the observed increase in sodium excretion could indicate that L-arginine counteracts the antinatriuretic effect of cyclosporin.   相似文献   
66.
1. The alpha 2-adrenoceptor antagonist activity of L-659,066 has been investigated in studies of healthy normotensive males to whom doses of up to 8 mg were administered by short intravenous infusion. 2. L-659,066 had no effect on basal levels of glucose or insulin and no significant effect on the plasma glucose and plasma insulin time profiles following an intravenous glucose load. 3. There was a non-significant trend for plasma noradrenaline concentrations to be higher after L-659,066. 4. L-659,066 had no significant effects on mood changes or on physical symptom scores. 5. There were no significant effects on supine blood pressure but there were consistent increases in heart rate both supine (non-significant) and erect (P < 0.01). 6. Ex vivo platelet aggregation studies confirmed alpha 2-adrenoceptor antagonist activity with L-659,066 but with an approximately 9-fold lesser potency than yohimbine. 7. While L-659,066 has alpha 2-adrenoceptor antagonist activity these results suggest that it is unlikely to present a new therapeutic approach for improving insulin release.  相似文献   
67.
68.
Generic substitution of salbutamol lags behind that of other drugs in Scotland and a negative perception by both patients and doctors may explain this. The aim of this study was to assess whether, in clinical practice, there was any difference in efficacy between branded salbutamol (Ventolin) and a generic preparation. Asthmatic patients using a Ventolin metered-dose inhaler at least twice a day for symptom relief were entered into a double-blind cross-over study, comparing Ventolin, blinded Ventolin and a generic salbutamol in random order for two weeks each. Daily peak flows, inhaler use and bronchodilator response were recorded. At the end of each treatment period patients rated their inhaler against their usual Ventolin on a 5-point scale. Forty patients were entered into the study; 90% received 1000 micrograms or more of inhaled steroids per day. Eleven patients dropped out during the run-in phase. In the remaining 29 patients, no significant difference between treatments could be found in any of the objective parameters measured. Fifty-five per cent of patients said they could detect a difference between the inhalers, and 45% noted a difference between their usual Ventolin and the open or blinded Ventolin. This study showed clinical equivalence between a generic and branded salbutamol. Patients'' own assessment of their relief inhaler seems to be influenced by factors other than efficacy. The study highlights that careful encouragement is required when changing to a generic product and has particular implications for the forthcoming conversion to CFC-free products.  相似文献   
69.
70.
A previous paper in this series described experiments and observations which could have been produced by properties derived from the quality of laboratory space. In particular, action at a distance was of commonplace occurrence. It was argued that support for this idea was forthcoming from two recent developments in physics, that of non-linear thermodynamics and that of quantum mechanics followed by quantum electrodynamics. The first permitted the concept of a formative or structuring role for energy permeating matter the second the concept of a structure and function for space. One of these functions was to provide for the creation of subatomic particles and thus of matter. This creativity is achieved from an origin in a non-observable world where the equations have no terms for distance or time. The demonstration of the insignificance of distance in the experiments reported using both crystal and biological growth was used to infer that events in this growth process were similarly preceeded by events in the non-observable world. The implications of such an origin for growth and new growth are discussed.  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