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   8941篇
  免费   580篇
  国内免费   58篇
耳鼻咽喉   53篇
儿科学   224篇
妇产科学   257篇
基础医学   1381篇
口腔科学   278篇
临床医学   806篇
内科学   1836篇
皮肤病学   139篇
神经病学   869篇
特种医学   349篇
外国民族医学   1篇
外科学   1267篇
综合类   85篇
一般理论   12篇
预防医学   646篇
眼科学   175篇
药学   607篇
中国医学   4篇
肿瘤学   590篇
  2023年   51篇
  2022年   79篇
  2021年   165篇
  2020年   93篇
  2019年   176篇
  2018年   224篇
  2017年   137篇
  2016年   162篇
  2015年   203篇
  2014年   306篇
  2013年   402篇
  2012年   516篇
  2011年   567篇
  2010年   317篇
  2009年   262篇
  2008年   511篇
  2007年   530篇
  2006年   491篇
  2005年   451篇
  2004年   509篇
  2003年   446篇
  2002年   416篇
  2001年   144篇
  2000年   155篇
  1999年   163篇
  1998年   107篇
  1997年   65篇
  1996年   72篇
  1995年   72篇
  1994年   60篇
  1993年   42篇
  1992年   69篇
  1991年   53篇
  1990年   56篇
  1989年   57篇
  1988年   58篇
  1987年   47篇
  1986年   72篇
  1985年   59篇
  1984年   62篇
  1983年   55篇
  1982年   49篇
  1981年   42篇
  1980年   38篇
  1979年   33篇
  1978年   40篇
  1977年   38篇
  1975年   29篇
  1973年   37篇
  1971年   25篇
排序方式: 共有9579条查询结果,搜索用时 156 毫秒
71.
Anti-Müllerian hormone concentrations in maternal serum during pregnancy   总被引:1,自引:0,他引:1  
BACKGROUND: In females, anti-Müllerian hormone (AMH) is expressed only by the ovary. AMH is secreted by the granulosa cells of ovarian follicles and appears to regulate early follicle development. AMH is detected in serum from women of reproductive age and its levels vary slightly with the menstrual cycle, reaching the peak value in the late follicular phase. This study investigated serum AMH levels throughout gestation and after delivery in healthy pregnant women. METHODS: This cross-sectional study recruited pregnant women and healthy non-pregnant women, 84 in total. AMH, FSH and E2 were measured in the follicular phase, in the three trimesters of pregnancy and in early puerperium. RESULTS: Estradiol and FSH levels followed the expected patterns during gestation. During the follicular phase of the menstrual cycle AMH levels were 1.9 +/- 0.5 ng/ml. In the three trimesters of pregnancy and in early puerperium AMH levels were: 2.1 +/- 0.56, 2.4 +/- 0.64, 1.95 +/- 0.6 and 2.05 +/- 0.55 ng/ml respectively. No significant modifications were found in AMH levels during pregnancy and in the early puerperium. CONCLUSIONS: This study has obtained information on AMH and on the possible relationship with FSH. We hypothesize that the profile of the new marker of ovarian activity AMH may indicate that initial non-cyclic ovarian follicular activity during pregnancy is not abolished. Moreover FSH, does not seem to play a direct role on AMH synthesis and secretion.  相似文献   
72.
AIMS: To describe a new fixation and embedding method for tissue samples, immunohistowax processing, which preserves both morphology and antigen immunoreactivity, and to use this technique to investigate the role of dendritic cells in the immune response in peripheral tissues. METHODS: This technique was used to stain a population of specialised antigen presenting cells (dendritic cells) that have the unique capacity to sensitise naive T cells, and therefore to induce primary immune responses. The numbers of dendritic cells in peripheral organs of mice either untreated or injected with live Escherichia coli were compared. RESULTS: Numbers of dendritic cells were greatly decreased in heart, kidney, and intestine after the inoculation of bacteria. The numbers of dendritic cells in the lung did not seem to be affected by the injection of E coli. However, staining of lung sections revealed that some monocyte like cells acquired morphological and phenotypic features of dendritic cells, and migrated into blood vessles. CONCLUSIONS: These observations suggest that the injection of bacteria induces the activation of dendritic cells in peripheral organs, where they play the role of sentinels, and/or their movement into lymphoid organs, where T cell priming is likely to occur.  相似文献   
73.
Cells bearing the form of the TCR make up only 1–3% ofT cells in the adult murine thymus and peripheral lymphold organs.Evidence from studies of nude mice suggests that the developmentof at least some T cells is thymus dependent; however, untilnow it has not been directly demonstrated that cells are exportedfrom the thymus. In this paper we have used the technique oflabelling thymocytes in vivo with FITC, followed by flow cytometrlcanalysis to trace cells emigrating from the thymus to the spleen.Using this approach we have been able to demonstrate for thefirst time that T cells are exported from the adult murinethymus to the spleen. We also demonstrate that the cells emigratingto the spleen are a selected subset of thymocytes being heatstable antigen positive, Thy-1+, and expressing low levels ofCD44 (Pgp-1). In addition, investigation of TCR V; gene usageamong adult + thymocytes, recent emigrants, and spleen cells,indicated a selective emigration of cells expressing certainVgenes.  相似文献   
74.
In Saccharomyces cerevisiae cells a number of genes are required for progression through, or else to pass beyond, the G1 phase. We characterized a novel gene, RPG1, which is also involved in this phase. RPG1 is an essential gene encoding a 110-kDa evolutionarily conserved protein. Elutriated or α-factor-synchronized cells of the rpg1-1 temperature-sensitive mutant were arrested in the first cell cycle when shifted to a non-permissive temperature. The cells remained unbudded and neither grew nor duplicated DNA. rpg1-1 cells synchronized in S phase completed mitosis and arrested as unseparated G1 cells after a shift to a non-permissive temperature. Similarly, the asynchronous rpg1-1 cells accumulated in G1 at the non-permissive temperature, but mother and daughter cells did not separate. A bulk of Calcofluor-stained material was localized in the region adjacent to the cell septum. Our data show that Rpg1p is required for passage through the G1 phase and may be involved in growth control. Data published recently indicate that Rpg1p exhibits significant sequence similarity to a subunit of the mammalian translation initiation factor 3. Received: 6 October 1997 / 8 November 1997  相似文献   
75.
Three patients are described who demonstrate the "target-sign" of optic nerve atrophy on CT scanning. This sign is produced by the centrally located atrophic optic nerve surrounded by a patulous perioptic subarachnoid space. An explanation for this phenomenon is proposed.  相似文献   
76.
The utility of scintigraphic views obtained after administration of sodium bicarbonate-citric acid-simethicone crystals (E-Z-GAS) for the determination of gastric extrahepatic perfusion was evaluated in 20 technetium-99m macroaggregated albumin hepatic arterial perfusion studies performed in 19 patients. These crystals produce carbon dioxide gas, distend the stomach, and allow better delineation of gastric activity (extrahepatic perfusion to the stomach). Conversely, a lack of change in activity in the left upper quadrant after the effervescent crystals have been ingested suggests no gastric activity (and no extrahepatic perfusion to the stomach). These "air-contrast" views added useful information in 16 of 20 studies. In three cases prior hepatic arterial perfusion studies without air contrast were misinterpreted as lacking extrahepatic perfusion, which was only recognized on subsequent studies through the use of the air-contrast views. In another case extrahepatic perfusion was erroneously diagnosed on a hepatic arterial perfusion study without air contrast, with a follow-up air-contrast hepatic arterial perfusion study showing this to have been a false-positive diagnosis. Air-contrast views of the stomach can be extremely helpful in verifying or excluding the diagnosis of gastric extrahepatic perfusion on technetium-99m macroaggregated albumin hepatic arterial perfusion studies.  相似文献   
77.
The extent of first-pass elimination of racemic propranolol and dextropropranolol in doses of 0.25 or 0.50 mg was investigated in relation to the site of drug administration in the rectum of rats. The compounds were given orally, i.v., and rectally at distances of 2 and 1 cm from and directly at the anus by low volume zero-order 30 min infusion. Unchanged propranolol was determined in blood, and propranolol and three metabolites were measured in urine. The systemic availability of propranolol after oral administration was approximately 6 %. Rectal administration at 2 cm, at 1 cm and directly at the anus (0.2 cm) gave two, three and six times higher values, respectively. The more distal application site produced urinary metabolite profiles that were comparable to those observed after oral administration, while application directly at the anus was similar to i.v. dosing. In all experiments log-linear elimination phases with comparable elimination half-lives (range 12–18 min) were found, except with the 0.50 mg dose after i.v. and rectal administration close to the anus which showed a non-linear profile. The mean systemic availability after rectal administration of 0.25 mg dextro-propranolol close to the anus was 50 and 64 % as compared to a 0.25 and 0.125 mg i.v. dose, respectively. The rectal route may be used for propranolol to partially prevent hepatic first-pass metabolism. However, avoidance of presys-temic elimination is maximal only in the immediate vicinity of the anus as the venous blood supply of the upper part of the rectum of rats appears to be connected to the portal system and the lower part to the general circulation.  相似文献   
78.
Dengue virus (DENV) and Zika virus (ZIKV) belong to the Flaviviridae family of viruses spread by Aedes aegypti mosquitoes in tropical and subtropical areas. Accurate diagnostic tests to differentiate the 2 infections are necessary for patient management and disease control. Using characterized ZIKV and DENV patient plasma in a blind manner, we validated an ELISA and a rapid immunochromatographic test for ZIKV detection. We engineered the ZIKV nonstructural protein 1 (NS1) for sensitive serologic detection with low cross reactivity against dengue and developed monoclonal antibodies specific for the ZIKV NS1 antigen. As expected, the serologic assays performed better with convalescent than acute plasma samples; the sensitivity ranged from 71% to 88%, depending on the performance of individual tests (IgM/IgG/NS1). Although serologic tests were generally less sensitive with acute samples, our ZIKV NS1 antibodies were able to complement the serologic tests to achieve greater sensitivity for detecting early infections.  相似文献   
79.
PurposePrevious reports in the literature demonstrate racial and ethnic disparities for children diagnosed with acute appendicitis, with minorities experiencing worse outcomes. At our institution, we have developed an evidence based patient driven protocol for children following laparoscopic appendectomy. However, the influence of such protocol on mitigating racial and ethnic disparities in outcomes remains unknown. The purpose of our study is to assess the impact of our protocol by evaluating the influence of race and ethnicity on surgical outcomes among children treated for acute appendicitis.Material and methodsA retrospective review of prospectively collected data was conducted. Children undergoing a laparoscopic appendectomy at our freestanding children's hospital between December 2015 and July 2017 were included. Demographic data, post-operative length of stay, same day discharge rates and hospital readmission rates were abstracted from patient medical records. Patients were classified by their race and ethnic background. Comparative analysis was performed in STATA with a p value < .05 determined as significant.ResultsA total of 786 children were included, with the majority being either White (70%, n = 547), Black (8%, n = 62) or Hispanic (17%, n = 133); 569 patients (72%) were found to have non-perforated appendicitis. There was no statistically significant difference in the rates of same day discharge among White, Black or Hispanic children respectively (88% vs. 77% vs. 86%, p = .126). Of the 217 children with perforated appendicitis, Hispanic children had increased rates of perforation (41%, n = 55) compared to White and Black children respectively (23%, n = 128 and 29%, n = 18, p = .001). However, average post-operative length of stay were similar among White, Black and Hispanic children (96 h vs. 95 h vs. 98 h, p = .015). On multivariate analysis, the only significant risk factor for an elevated post-operative length of stay was the presence of a perforation.ConclusionOur evidence based patient driven protocol effectively mitigates racial and ethnic disparities found in children with acute appendicitis. Further prospective investigation into the role of such patient-driven protocols to mitigate healthcare disparities is warranted.Levels of EvidenceTherapeutic study; Level 3.  相似文献   
80.
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