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   14468篇
  免费   901篇
  国内免费   66篇
耳鼻咽喉   144篇
儿科学   324篇
妇产科学   251篇
基础医学   2231篇
口腔科学   184篇
临床医学   1418篇
内科学   3458篇
皮肤病学   362篇
神经病学   1446篇
特种医学   764篇
外科学   2307篇
综合类   109篇
一般理论   2篇
预防医学   569篇
眼科学   238篇
药学   879篇
中国医学   9篇
肿瘤学   740篇
  2023年   89篇
  2022年   110篇
  2021年   273篇
  2020年   177篇
  2019年   241篇
  2018年   282篇
  2017年   263篇
  2016年   339篇
  2015年   363篇
  2014年   440篇
  2013年   521篇
  2012年   818篇
  2011年   941篇
  2010年   559篇
  2009年   526篇
  2008年   821篇
  2007年   876篇
  2006年   764篇
  2005年   848篇
  2004年   806篇
  2003年   749篇
  2002年   776篇
  2001年   269篇
  2000年   266篇
  1999年   266篇
  1998年   204篇
  1997年   176篇
  1996年   140篇
  1995年   114篇
  1994年   89篇
  1993年   100篇
  1992年   150篇
  1991年   119篇
  1990年   100篇
  1989年   123篇
  1988年   104篇
  1987年   108篇
  1986年   92篇
  1985年   99篇
  1984年   79篇
  1983年   71篇
  1982年   63篇
  1981年   52篇
  1979年   47篇
  1978年   44篇
  1977年   48篇
  1976年   45篇
  1975年   47篇
  1974年   55篇
  1971年   51篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
62.
Patients after kidney, heart and lung transplantation differ in their immunosuppressive drug regimens and in susceptibility to infectious complications with cytomegalovirus (CMV). In this study, CMV-specific T-cell responses were characterized in long-term transplant recipients and associated with the frequency of infectious complications. CMV-reactive CD4 T cells from 50 healthy controls, 68 renal, 14 heart and 24 lung transplant recipients were flow cytometrically quantified by the induction of cytokines after specific stimulation. Moreover, the immunosuppressive effect of calcineurin inhibitors on specific T-cell reactivity was quantified in vitro and compared with responses in vivo. Median CMV-specific T-cell frequencies in long-term renal (1.48%; range 0.06-17.26%) and heart transplant recipients (0.90%; 0.13-12.49%) did not differ from controls (1.82%; 0.26-21.00%). In contrast, CMV-specific T-cell levels were significantly lower in lung transplant recipients (0.50%; <0.05-4.98%) and showed a significant correlation with the frequency of infectious episodes (r =-0.57, p = 0.005). The differences within the groups were associated with increasing dosages of immunosuppressive drugs, as exemplified for calcineurin inhibitors that dose dependently reduced specific T-cell reactivity in vitro. In conclusion, monitoring CMV-specific CD4 T cells may serve as a measure for long-term disease susceptibility and may contribute to an improved management of CMV complications after lung transplantation.  相似文献   
63.
Although breast milk is recommended as the optimal source of infant nutrition, breastfeeding initiation is below recommended levels, especially among teenage mothers. Breastfeeding initiation rates among Michigan (US) teenage mothers (12-19 y) were compared by demographics and health behaviors. Multivariate analyses determined which factors were significant independent predictors of breastfeeding initiation among teenage mothers enrolled prenatally in the Michigan Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) program in 1995. Significant predictors independently associated with breastfeeding initiation were race/ethnicity, education, marital status, postpartum anemia status, parity, prenatal trimester of WIC enrollment, and smoking. The strongest predictor of breastfeeding initiation differed for white mothers (positive predictor: education beyond high school [OR = 3.13]) and black mothers (negative predictor: multiparous [OR = 0.25]). Initiation rates for this population of teenage mothers fall below the national average for mothers of all ages and the US Healthy People 2010 goals. Research is needed concerning how breastfeeding support and education can be improved to reach the US national health goals.  相似文献   
64.
Ohne ZusammenfassungMit 10 Abbildungen im Text.Die Arbeit wurde ausgeführt mit Unterstützung der Lady Tata Memorial-Stiftung, der wir für die Ermöglichung unserer Arbeiten zu größtem Danke verpflichtet sind.  相似文献   
65.
Methods. To assess the occupational exposure of the anaesthetist to anaesthetic gases, a total of 1 German and 25 Swiss hospitals were investigated. A Brüel & Kjær Type 1302 multi-gas monitor was used to measure concentrations of nitrous oxide and halogenated anaesthetic agents in the anaesthetist's breathing zone. Measurements were performed during 114 general anaesthetic, 55 of which were in patients under 11 years of age. In these 55 patients, the influence of various factors on the exposure (time-weighted average concentrations) was estimated by comparing different data groups. The efficiency of the applied scavenging equipment was examined by surveying the exhalation valve with a leak detector (type TIF 5600, TIF Instruments, Miami). Results. Sessions with patients under 11 years of age revealed much higher anaesthetic gas exposures compared to older patients. The concentrations of nitrous oxide were on average threefold (Fig. 1), those of the halogenated anaesthetics fivefold higher (Fig. 2) for the younger patients. In 11- to 16-year-old patients the exposure level was the same as in adult patients. The measurements showed a reduction of 85% in exposure if an efficient scavenging system (i.e., no waste gas discharge to room air through the exhalation valve) or lower fresh gas flow were used (Fig. 4); 42% of the inspected scavengers were inefficient, and reduced the exposure on average by only 30%. In operating theatres with a ventilation rate of at least ten air changes per h, the measured concentrations of anaesthetic gases in the inhalation zone of the anaesthetists were reduced more than 50% compared to poorly ventilated rooms (Figs. 4 and 5). The use of tracheal intubation or laryngeal mask airway (LMA) anaesthesia resulted in a reduction of 80% in exposure compared to standard face masks if efficient scavenging was used. The exposures during sessions with inefficiently scavenged Bain coaxial systems or unscavenged semi-open delivery systems of the Jackson-Rees type were tenfold higher than with scavenged rebreathing circuit systems (Fig. 6). During anaesthesia with IV or double-mask induction, the average levels of inhalation anaesthetics were reduced by about 80% compared to inhalational induction with standard masks (Fig. 7). The anaesthetist's working technique is a very important factor that strongly influences the concentrations. Poor work practices, like lifting off the face mask with anaesthetic gas flow turned on, increased the exposure of the anaesthetist and other operating room personnel drastically, even if the other conditions (scavenger and room ventilation) were good. Discussion. The exposure levels of anaesthetic gases are generally higher during anaesthesia in children up to 10 years of age than in older patients. Nevertheless, the measurements showed that exposure during paediatric anaesthesia can be kept below the recommended limit (8-h TWA in Switzerland) of 100 ppm nitrous oxide and 5 ppm halothane or 10 ppm enflurane or isoflurane. Causes of high exposures were particularly high fresh gas flows often applied without scavenging or together with inefficient scavenging devices and the high part of mask anaesthesia and inhalation induction with a loosely held mask. To achieve an effective reduction of occupational exposure, well-adjusted and maintained scavenging systems and low-leakage work practices are of primary importance. As leakage can never be completely avoided, a ventilation rate of at least ten air changes per h should be maintained in operating rooms and rooms where anaesthesia is induced to keep down concentrations of waste anaesthetic gases. High exposure during mask anaesthesia and inhalation induction can be prevented by further measures. Using a LMA instead of a standard mask reduces the exposure to the same level as endotracheal intubation. The exposure during induction can be reduced remarkably by the use of the double-mask system or IV induction. Applying low fresh gas flows reduces not only the exposure concentrations in the theatres, but also the contribution to the environmental burden (`?greenhouse effect?' and ozone layer destruction).  相似文献   
66.
B Meier 《Herz》1992,17(1):27-39
A chronic coronary occlusion consists of an atherosclerotic plaque and one or several thrombi. It clinically imitates a tight stenosis but is exempt from the risk of truly unstable angina or myocardial infarction. Hence, quality of life is at stake and not longevity. This holds true for balloon angioplasty as well as for surgery. Indications for angioplasty are based on an estimate of technical difficulties and clinical risks balanced against potential subjective benefit and amount of viable myocardium concerned. An occlusion flush at the orifice of the vessel, tapering into a small sidebranch, with bridging collaterals, or devoid of collaterals is no target for angioplasty. Primary success is around 65% and complications are extremely rare. Abrupt vessel closure is common but harmless. No Q-wave infarctions have been reported in that context. The need for emergency bypass surgery may arise from acute closure of a vessel proximal to the occlusion in an exceptional case. Duration and length of occlusion are the most important predictors of success. Recurrence averages 62% (17% reocclusion and 45% restenosis). An important factor for the high recurrence rate is the competitive pressure exerted by the collaterals on standby. Recurrence happens almost exclusively within the first six months. It is innocuous but produces symptoms prompting further interventions (repeat angioplasty or bypass surgery). The conventional technique uses a stiff guidewire and advances the balloon catheter close to the tip of the guidewire for additional rigidity. New technologies are under investigation but no breakthrough has happened so far. They encompass blunt mechanical instruments (e.g., Magnum wire), drills of various velocities, laser energy applied directly to the tissue (some angioscopically guided, some triggered by on-line spectral tissue analysis), catheters dispersing laser energy through a sapphire or converting it into heat (hot tip), and electrical or radiofrequency heat applicators. As low-yield procedures had better be low-risk and low-cost, there are definite limits to how sophisticated, complicated, risky, and expensive tools and techniques for percutaneous coronary recanalization can become. Close relatives of conventional gear such as the Magnum system offer themselves as first choice equipment complemented, in case of need, by mechanical drills.  相似文献   
67.
4 patients with a mean age of 20 years and isolated congenital radial head dislocation (1 unilateral anterior, 1 unilateral posterior and 2 bilateral anterior dislocations) were all pain-free and had almost normal elbow function.  相似文献   
68.
Two recently discovered genes, the recombination activating genes 1 and 2 (RAG-1 and RAG-2), are necessary to perform variable (V), diversity (D), and joining (J) recombination. They synergistically activate VDJ recombination to generate immunocompetent lymphocytes. Disruption of either gene results in a maturation arrest at a very early B and T cell progenitor stage. Expression and downregulation of RAG's are closely associated with interleukin 7, sIgM and TCR-CD3 complex, respectively. Assessment of RAG mRNA expression is a valuable marker in identifying the genotypic maturation status of leukemias and lymphomas. Persistent RAG expression in otherwise mature lymphoid proliferations may explain puzzling biological and clinical observations such as multiple rearrangements in lymphomas with a mature phenotype. Lack of RAG expression in Hodgkin's disease with abundant Reed-Stern-berg cells is consistent with a mature phenotype of the latter. Availability of a anti-RAG-1 monoclonal antibody in the near future will facilitate RAG analysis of lymphomas.  相似文献   
69.
Zusammenfassung In der Zeit vom 01. Juli 1990 bis zum 30. Juni 1994 wurden 65 113 Untersuchungen au?erhalb der Regeldienstzeit durchgeführt. Die vorliegende Analyse schlüsselt die Leistungen auf nach Alter und Geschlecht im Vergleich zum Gesamtkollektiv dieser Vierjahresperiode, nach dem Zeitpunkt der Untersuchung, nach den untersuchten Organen und nach der eingesetzten Technik. Ca. 1/3 der Leistungen fallen in den Zeitraum zwischen 16.00 und 20.00 Uhr und k?nnten durch einen versetzten Tagdienst aufgefangen werden. Ein weiteres Drittel entf?llt auf den Zeitraum zwischen 20.00 und 8.00 Uhr am Folgetag. Der Rest entf?llt auf Feiertage und Wochenenden. Die h?ufigste Anforderung betrifft Thoraxaufnahmen auf den Intensivstationen. Etwa die H?lfte dieser Untersuchungen werden au?erhalb der Dienstzeit angefertigt; 17,2 % der Untersuchungen im Nacht- und Bereitschaftsdienst betreffen Computer- und Magnetresonanztomographie. Das am 01. 01. 93 in Kraft getretene Gesundheitsstrukturgesetz führte zu keinen nennenswerten Verschiebungen hinsichtlich Art, Umfang und H?ufigkeit der Untersuchungen im Nacht- und Bereitschaftsdienst. Eingegangen am 17. Juni 1996 Nach überarbeitung angenommen am 24. Juli 1996  相似文献   
70.
 This study aimed to examine the influence of acute tissue hypoxygenation on the expression of immediate early genes in different rat tissues. To this end male Sprague-Dawley rats were exposed to 0.1% carbon monoxide for 0.5, 1 and 6 h or to 9% oxygen for 6 h and mRNA levels for c-jun, c-fos, c-myc and EGR-1 were assayed by RNase protection in hearts, kidneys, livers and lungs. We found that hypoxia increased c-jun mRNA levels between twofold (lung) and eightfold (liver) in all organs examined; c-fos mRNA increased between threefold (lung) and 20-fold (heart); c-myc mRNA increased between twofold (lung) and sixfold (heart); and EGR-1 mRNA increased between twofold (lung) and sixfold (heart). Our findings suggest that acute tissue hypoxygenation is a general stimulus of the expression of immediate early genes in vivo. With regard to the sensitivity to hypoxia, organ differences appear to exist in that the lung is rather insensitive, whilst the heart is rather sensitive. Received: 25 February 1997 / Received after revision: 17 June 1997 / Accepted: 19 June 1997  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