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   4131篇
  免费   228篇
  国内免费   24篇
耳鼻咽喉   29篇
儿科学   116篇
妇产科学   68篇
基础医学   528篇
口腔科学   126篇
临床医学   301篇
内科学   937篇
皮肤病学   56篇
神经病学   330篇
特种医学   123篇
外科学   776篇
综合类   19篇
预防医学   366篇
眼科学   56篇
药学   217篇
中国医学   25篇
肿瘤学   310篇
  2023年   31篇
  2022年   75篇
  2021年   136篇
  2020年   82篇
  2019年   119篇
  2018年   142篇
  2017年   79篇
  2016年   92篇
  2015年   124篇
  2014年   150篇
  2013年   181篇
  2012年   331篇
  2011年   303篇
  2010年   191篇
  2009年   148篇
  2008年   269篇
  2007年   287篇
  2006年   266篇
  2005年   226篇
  2004年   212篇
  2003年   255篇
  2002年   228篇
  2001年   37篇
  2000年   22篇
  1999年   35篇
  1998年   31篇
  1997年   23篇
  1996年   24篇
  1995年   18篇
  1994年   16篇
  1993年   18篇
  1992年   24篇
  1991年   16篇
  1990年   23篇
  1989年   20篇
  1988年   18篇
  1987年   12篇
  1986年   20篇
  1985年   9篇
  1984年   10篇
  1983年   4篇
  1982年   15篇
  1981年   8篇
  1980年   5篇
  1978年   7篇
  1976年   3篇
  1975年   5篇
  1935年   6篇
  1933年   3篇
  1929年   2篇
排序方式: 共有4383条查询结果,搜索用时 15 毫秒
21.
22.
Journal of Public Health - Neighbourhood composition is considered a social determinant of mental health that can be addressed by policymakers to improve outcomes. Deprived neighbourhoods typically...  相似文献   
23.
Summary A comparative study of four skin graft donor site dressings was undertaken. This was a prospective and cross-over study of 25 consecutive patients with burns up to 40% TBSA treated with split skin grafts. Each donor site was divided into four sections and covered with different dressings in order to evaluate their effectiveness in healing, the time required for complete epithelialization, patient acceptance and any intolerance or local infection. The results showed that the occlusive hydrocolloid dressing significantly decreases (p<0.01) the mean time required for complete healing (7.45 days) compared with a semiocclusive hydrocolloid (10.29 days), a polyurethane sheet (9.4 days) and the conventional dressing (10.04 days).Presented at the IV European Burns Congress in Barcelona, Spain, September 25, 1991 (Abstract No. 117)  相似文献   
24.
25.
The specific mechanism underlying the genesis of vasogenic brain edema is still debated: the role of arachidonic acid is considered extremely important, as it is a possible activator of self-maintaining reactions enhancing the release of vasoactive and cytotoxic compounds. The relationship between arachidonic acid metabolism and brain edema has been studied primarily in brain tissue samples or in the extracellular fluid, whereas the residual capacity of perilesional tissue to synthesize and release eicosanoids has not been investigated. In the present study, perilesional samples of brain tissue were available from 4 patients operated on for brain metastasis, from 8 patients who had malignant neuroepithelial tumors, from 4 with meningiomas, and from 5 with subarachnoid hemorrhage. A brain edema index was calculated from the preoperative computed tomographic scan. The "ex vivo" method allowed determination of the residual capacity of endogenous arachidonic acid metabolism. The edema index is significantly higher in patients with brain metastasis (6.5 +/- 0.8) and neuroepithelial tumors (3.6 +/- 0.2) than in those with meningiomas (1.5 +/- 0.06), subarachnoid hemorrhage (1.7 +/- 0.18), and in controls. In patients with metastatic and neuroepithelial tumors there is a significant correlation between peritumoral brain edema and the capacity to synthesize leukotriene C4 (P less than 0.05); the capacity to synthesize leukotriene C4 is also significantly elevated after subarachnoid hemorrhage (13.91 +/- 2.6 ng/ml of incubation medium) when compared with control cases (5.56 +/- 0.91). The capacity to synthesize prostacyclin is significantly higher in patients with brain metastasis than in those with neuroepithelial tumors and meningiomas (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
26.
Summary The main dolichol diphosphate-bound oligosaccharides present in primary cultures of both normal and tumor mouse mammary epithelial cells had the same size, yielded the same pattern after acetolysis and paper chromatography, had the same number of mannose residues susceptible to-mannosidase degradation, and were composed of the same monosaccharide residues. This is the first demonstration that normal and tumor mammary cells have dolichol diphosphate-bound oligosaccharides with very similar, if not identical, structures. These compounds are intermediates in the synthesis of asparagine-linked oligosaccharides. On the other hand, normal and tumor cells showed differences in the specific activities of the enzymes involved in the transfer of the distal monosaccharides from the sugar nucleotides to glycoproteins. Sialyl- and fucosyl-transferases were elevated and galactosyl- and N-acetylglucosaminyltransferases were diminished in mammary tumor cells. The intact tumor cells showed an increased fucosylation of glycoproteins of the asparagine-linkage type. Address for reprints: Roberto L. Ceriani, M.D., Ph.D., Bruce Lyon Memorial Research Laboratory, Children's Hospital Medical Center, 51st and Grove Streets, Oakland, CA 94609, USA.  相似文献   
27.
28.
OBJECTIVE: To investigate the intraplatelet cyclic guanosine-3',5'-monophosphate (cGMP) levels during normal pregnancy and preeclampsia. STUDY DESIGN: Pregnant women (n = 15), women with preeclampsia (n = 15), and nonpregnant, normotensive women (n = 15) were included. Intraplatelet cyclic guanosine-3',5'-monophosphate levels were measured by an enzyme-linked immunosorbent assay. RESULTS: Intraplatelet cGMP levels were significantly different among all groups (p < 0.02). The values were higher in normal pregnant women (mean 19.8 SD 2.6 fmol/10(5) platelets) in comparison to nonpregnant women (mean 7.6 SD 0.3 fmol/10(5)platelets; p = 0.001) and women with preeclampsia (mean 11.3 SD 1.8 fmol/10(5) platelets; p = 0.05). Plasma nitric oxide levels did not reveal differences between all groups. CONCLUSIONS: The results of this study in a high-risk Andean population demonstrated that intraplatelet cyclic guanosine-3',5'-monophosphate levels are decreased during preeclampsia compared to normal pregnancy, suggesting a lack in action of nitric oxide.  相似文献   
29.
El uso de fármacos conlleva innegables beneficios en las personas mayores, pero no está exento de efectos indeseables. La deprescripción es el proceso de revisión sistemática de la medicación con el objetivo de lograr la mejor relación riesgo-beneficio en base a la mejor evidencia disponible. Este proceso es especialmente importante en mayores polimedicados, sobretratados, frágiles, con enfermedades terminales y en el final de la vida.La deprescripción debe hacerse de forma escalonada, estableciendo un seguimiento estrecho por si aparecen problemas tras la retirada. En la toma de decisiones es muy importante contar con la opinión del paciente y de los cuidadores, valorando los objetivos del tratamiento según la situación clínica, funcional y social del enfermo.Existen múltiples herramientas para facilitar a los clínicos la tarea de seleccionar qué fármacos deprescribir (criterios Beers, STOPP-START…). Los grupos farmacológicos más susceptibles de intervención son: antihipertensivos, antidiabéticos, estatinas, benzodiacepinas, antidepresivos, anticolinérgicos, anticolinesterásicos y neurolépticos.Palabras clave: Polifarmacia, Envejecimiento, Comorbilidad, Prescripción inadecuada, Efectos adversos, Deprescripción  相似文献   
30.
The present study evaluates the feasibility of partially dealuminated natural mordenite as a catalyst support by studying improvement in its textural properties. This is the first study that reports the dealumination of natural zeolite-based tuffs from Ecuador. For this purpose, mordenite-rich tuffs were obtained from deposits close to Guayaquil, Ecuador. The raw material was micronized in order to increase its surface, and treated with NH4Cl. NH4+ cation-exchanged samples were finally reacted with HCl(aq) to complete the dealumination process. The partially dealuminated samples were characterized using techniques such as XRD, FT-IR, SEM-EDS, and identification of their textural properties. Dealumination with HCl(aq) increased the Si/Al ratio up to 9 and kept the crystallographic structure of natural mordenite, as XRD results showed that the structure of mordenite was not altered after the dealumination process. On the other hand, textural properties such as surface area and microporosity were improved as compared to natural mordenite. In view of these results, the feasibility of using natural mordenite as a catalyst support is discussed in this study.  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