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   3618篇
  免费   259篇
  国内免费   27篇
耳鼻咽喉   25篇
儿科学   96篇
妇产科学   77篇
基础医学   685篇
口腔科学   92篇
临床医学   224篇
内科学   893篇
皮肤病学   98篇
神经病学   303篇
特种医学   73篇
外科学   438篇
综合类   21篇
一般理论   3篇
预防医学   212篇
眼科学   88篇
药学   283篇
中国医学   9篇
肿瘤学   284篇
  2024年   6篇
  2023年   45篇
  2022年   124篇
  2021年   174篇
  2020年   102篇
  2019年   119篇
  2018年   143篇
  2017年   103篇
  2016年   104篇
  2015年   141篇
  2014年   150篇
  2013年   170篇
  2012年   265篇
  2011年   254篇
  2010年   160篇
  2009年   126篇
  2008年   243篇
  2007年   214篇
  2006年   214篇
  2005年   223篇
  2004年   190篇
  2003年   174篇
  2002年   139篇
  2001年   26篇
  2000年   22篇
  1999年   33篇
  1998年   34篇
  1997年   29篇
  1996年   17篇
  1995年   16篇
  1994年   11篇
  1993年   7篇
  1992年   8篇
  1991年   10篇
  1990年   10篇
  1989年   14篇
  1988年   6篇
  1987年   10篇
  1986年   8篇
  1985年   6篇
  1984年   9篇
  1983年   5篇
  1982年   3篇
  1981年   4篇
  1980年   4篇
  1979年   3篇
  1978年   4篇
  1971年   4篇
  1970年   6篇
  1967年   3篇
排序方式: 共有3904条查询结果,搜索用时 15 毫秒
71.
72.
Solid basaloid adenoid cystic carcinoma (SB‐AdCC) is a subtype of breast AdCC which shows more aggressive clinical behavior than other subtypes. Fine‐needle aspiration (FNA) cytology is a useful diagnostic tool for breast malignancies. However, most of the diagnostic cytological characteristics of AdCC are not present in SB‐AdCC and cytomorphological studies of this subtype are limited. Here, we evaluated the utility of FNA in the diagnosis of SB‐AdCC of the breast. A search of the pathology archives of our institutions for FNA specimens of histologically confirmed SB‐AdCC between 2012 and 2019 identified four patients with SB‐AdCC of the breast. All patients were female and the average age was 60 years. Cytologically, one case was classified as malignant, two as indeterminate, and one as unsatisfactory. Smears had low to moderate cellularity. All smears showed ribbon‐like material surrounding the clusters and a vertical nuclear arrangement toward the peripheral rim. Hyaline globules appeared only in one case. Cells in all cases showed an oval, angular, and spindle shape hyperchromatic nuclei with mild to severe atypia, and also dispersed naked nuclei similar to the cells of the clusters were detected in one case. In histological sections, these cytological findings were compatible with the histological findings and divergent histological differentiation was detected. Diagnosing of few cellular smears of SB‐AdCC is difficult whereas the features of peripheral rim of the clusters, naked nuclei, and the divergent differentiation may be important for diagnosing SB‐AdCC of the breast.  相似文献   
73.
Abdominal uterine electromyograms (uEMG) studies have focused on uterine contractions to describe the evolution of uterine activity and preterm birth (PTB) prediction. Stationary, non-contracting uEMG has not been studied. The aim of the study was to investigate the recurring patterns in stationary uEMG, their relationship with gestation age and PTB, and PTB predictivity. A public database of 300 (38 PTB) three-channel (S1–S3) uEMG recordings of 30 min, collected between 22 and 35 weeks’ gestation, was used. Motion and labour contraction-free intervals in uEMG were identified as 5-min weak-sense stationarity intervals in 268 (34 PTB) recordings. Sample entropy (SampEn), percentage recurrence (PR), percentage determinism (PD), entropy (ER), and maximum length (L MAX) of recurrence were calculated and analysed according to the time to delivery and PTB. Random time series were generated by random shuffle (RS) of actual data. Recurrence was present in actual data (p < 0.001) but not RS. In S3, PR (p < 0.005), PD (p < 0.01), ER (p < 0.005), and L MAX (p < 0.05) were higher, and SampEn lower (p < 0.005) in PTB. Recurrence indices increased (all p < 0.001) and SampEn decreased (p < 0.01) with decreasing time to delivery, suggesting increasingly regular and recurring patterns with gestation progression. All indices predicted PTB with AUC ≥0.62 (p < 0.05). Recurring patterns in stationary non-contracting uEMG were associated with time to delivery but were relatively poor predictors of PTB.  相似文献   
74.
75.
The nature of active acid sites of zeolite H-BEA with different Si/Al ratios (15–407) in liquid phase etherification of isobutylene with ethanol in a continuous flow reactor in the temperature range 80–180 °C has been explored. We describe and discuss data concerning the strength and concentration of acid sites of H-BEA obtained by techniques of stepwise (quasi-equilibrium) thermal desorption of ammonia, X-ray diffraction, low-temperature adsorption of nitrogen, FTIR spectroscopy of adsorbed pyridine and solid-state 27Al MAS NMR. The average values of the adsorption energy of NH3 on H-BEA were experimentally determined as 63.7; 91.3 and 121.9 mmol g−1 (weak, medium, and strong, respectively). In agreement with this, a correlation between the rate of ethyl-tert-butyl ether synthesis and the concentration of weak acid sites (ENH3 = 61.6–68.9 kJ mol−1) has been observed. It was concluded that the active sites of H-BEA for this reaction are Brønsted hydroxyls representing internal silanol groups associated with octahedrally coordinated aluminum in the second coordination sphere.

The active sites of H-BEA zeolites for ETBE synthesis are the weak Brønsted acid sites representing internal silanol groups.  相似文献   
76.

Purpose

In the recent years in Japan, an increasing number of patients with neuroblastoma (NB) are being treated by the “delayed local treatment (DL)” policy, undergoing surgery after the completion of high-dose chemotherapy with hematopoietic stem cell rescue (HDC). We reviewed the histopathological findings of second-look operations, including those of patients treated with DL.

Patients

From 1998 to 2013, 26 patients with high-risk NB underwent radical operation following chemotherapy. Surgery was performed after induction chemotherapy in 17 cases (standard; STD), whereas 9 cases completed induction chemotherapy and HDC before undergoing tumor resection (DL). The amount of necrosis and the degree of differentiation within the post-treatment tumor were assessed.

Results

Eighty-eight percent of the tumors showed necrosis in more than 1/3 of the specimen. Two DL cases showed complete disappearance of viable tumor cells. Amount of necrosis did not affect the prognosis of the patient. Tumors with immature, poorly differentiated phenotypes showed an extremely aggressive thereafter. Though not statistically proven, 123I-MIBG (metaiodobenzylguanidine) uptake may be correlated with the amount of viable cells remaining within the tumor, but not with the degree of differentiation.

Conclusions

Our results support the previous reports advocating that tumors that sustain unfavorable histology after chemotherapy behave aggressively thereafter.  相似文献   
77.
HPS is a significant complication of portal hypertension in children with chronic liver disease and is an established indication for LT. It is characterized clinically by the triad of pulmonary vascular dilatation causing hypoxemia in the setting of advanced liver disease. NRH, a cause of non‐cirrhotic portal hypertension, is characterized by diffuse benign transformation of the hepatic parenchyma into small regenerative nodules with minimal or no fibrosis. Development of NRH and HPS in pediatric LT recipients has not been reported, although occasional cases have been reported in adult LT recipients. In this report, we discuss a case of a three‐yr‐old male who developed HPS, two yr after LT. Pulmonary and cardiac causes for hypoxemia were ruled out by appropriate investigations including a chest X ray, echocardiogram, cardiac catheterization, and a CT angiographic study. The diagnosis of HPS was confirmed via bubble echocardiogram that demonstrated intrapulmonary shunting. Open liver biopsy revealed marked NRH. The patient underwent liver retransplantation that resulted in complete reversal of his pulmonary symptoms and normal oxygen saturations within three months after LT.  相似文献   
78.
79.
Synapses in the middle molecular layer of the rat dentate gyrus were analyzed by electron microscopy during the maintenance phase of long-term potentiation (LTP). LTP was induced by high-frequency stimulation of the medial perforant path carried out on each of 4 consecutive days. The dentate gyrus was examined electron microscopically 13 days following the fourth stimulation. At this time point, synaptic responses were still significantly enhanced relative to baseline, although the extent of their potentiation was lower than 1 hour after the last high-frequency stimulation. Stimulated, but not potentiated, rats served as controls. Using the stereological double disector method, estimates of the number of different morphological types of synapses per postsynaptic neuron were obtained. The number of asymmetrical axodendritic synapses increased (by 28%) during LTP maintenance, whereas the number of other synaptic types was not significantly altered. Our previous work demonstrated that the induction of LTP is followed by a selective increase in the number of axospinous perforated synapses with multiple, completely partitioned, transmission zones. Thus, the induction and maintenance phases of LTP are characterized by different structural synaptic alterations. These alterations may be related to each other as indicated by another finding of the present study regarding the existence of perforated synapses that appear to be transitional between axospinous and axodendritic junctions. This suggests a model of structural synaptic plasticity associated with LTP in which some axospinous perforated synapses increase in numbers shortly after the induction of LTP and are then converted into axodendritic ones during LTP maintenance. © 1996 Wiley-Liss, Inc.  相似文献   
80.
The ability of cells to adhere to substrates is an important factor for the effectiveness of biotechnologies and bioimplants. This research demonstrates that the statistical distribution of the sizes of the cells (Saccharomyces cerevisiae) attached to the substrate surface correlates with the statistical distribution of electrical potential on the substrate’s surface. Hypothetically, this behavior should be taken into consideration during the processing of surfaces when cell adhesion based on cell size is required.  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