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   220206篇
  免费   20264篇
  国内免费   15479篇
耳鼻咽喉   1903篇
儿科学   2197篇
妇产科学   2980篇
基础医学   26582篇
口腔科学   3689篇
临床医学   30844篇
内科学   33012篇
皮肤病学   2230篇
神经病学   12397篇
特种医学   8298篇
外国民族医学   138篇
外科学   21739篇
综合类   35405篇
现状与发展   55篇
一般理论   19篇
预防医学   13162篇
眼科学   6704篇
药学   22735篇
  196篇
中国医学   12388篇
肿瘤学   19276篇
  2024年   698篇
  2023年   3559篇
  2022年   9198篇
  2021年   11570篇
  2020年   8606篇
  2019年   7596篇
  2018年   8038篇
  2017年   7087篇
  2016年   6658篇
  2015年   10257篇
  2014年   12557篇
  2013年   10698篇
  2012年   16008篇
  2011年   17953篇
  2010年   10524篇
  2009年   8190篇
  2008年   11115篇
  2007年   11093篇
  2006年   11234篇
  2005年   11331篇
  2004年   7005篇
  2003年   6616篇
  2002年   5501篇
  2001年   4938篇
  2000年   5347篇
  1999年   5688篇
  1998年   3542篇
  1997年   3513篇
  1996年   2828篇
  1995年   2617篇
  1994年   2156篇
  1993年   1386篇
  1992年   1895篇
  1991年   1595篇
  1990年   1290篇
  1989年   1103篇
  1988年   1023篇
  1987年   895篇
  1986年   732篇
  1985年   530篇
  1984年   340篇
  1983年   247篇
  1982年   156篇
  1981年   151篇
  1980年   117篇
  1979年   143篇
  1978年   51篇
  1977年   55篇
  1975年   62篇
  1974年   56篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
BackgroundA growing number of studies have found a close association between thyroid hormones and thyrotrophin (TSH), and they also have prognostic significance in some cancer types; this study aimed to investigate the prognostic value of free triiodothyronine (fT3), free thyroxine (fT4), fT3/fT4, TSH, and their combination in patients with papillary thyroid carcinoma (PTC).MethodsThis study retrospectively analyzed the relevant data of 726 newly diagnosed PTC patients. Both univariate and multivariate analyses were used to predict the recurrence rate, and a risk score was established. In addition, with the use of a random survival forest, a random forest (RF) score was constructed. After calculating the area under the curve (AUC), the diagnostic efficacy of risk score, RF score, and four indicators was compared.ResultsfT3, fT4, fT3/fT4, and TSH were strongly associated with some invasive clinicopathological features and postoperative recurrence. Patients with high expression of fT4 and TSH have a high risk of recurrence. By contrast, patients with high expression of fT3 and fT3/fT4 have a low risk of recurrence. At the same time, the combined use of various indicators is more helpful for establishing an accurate diagnosis. By comparison, we found that the RF score was better than the risk score in terms of predicting the recurrence of PTC.ConclusionThe diagnostic accuracy of a combination of fT3, fT4, fT3/fT4, and TSH can help improve our clinical estimate of the risk of recurrent PTC, thus allowing the development of a more effective treatment plan for patients.  相似文献   
992.
BackgroundHepatocellular carcinoma (HCC) is the sixth most common cancer and the fourth leading cause of cancer‐related death in the world. A number of challenges remain for the early detection and effective treatment of HCC. In recent years, microbiota have been proven to be associated with the development of HCC. Many studies have explored the pathogenesis, diagnostic marker, and therapeutic target potential of microbiota in hepatocellular carcinoma. Therefore, we aimed to introduce the research methods and achievements of gut microbiota in hepatocellular carcinoma and discuss the value of gut microbiota in the pathogenesis, diagnosis, and treatment of hepatocellular carcinoma.MethodsKeywords are used to search relevant articles which were mainly published from 2010 to 2021, and we further selected targeted articles and read the full text.ResultsGut microbiota involved in promoting the formation and development of hepatocellular carcinoma, and differential gut microbiota and microbial metabolites have the potential to be the biomarkers of hepatocellular carcinoma. Purposefully regulated gut microbiota can improve the prognosis of patients, which is expected to be used in hepatocellular carcinoma.ConclusionThe study of gut microbiota in hepatocellular carcinoma is definitely worthy of study. In‐depth and elaborate research design is crucial for the study of the mechanism of gut microbiota involved in hepatocellular carcinoma, which can provide new directions and targets for the diagnosis, treatment, and prognosis of hepatocellular carcinoma.  相似文献   
993.
BackgroundThe selective pressure imposed by chemotherapy creates a barrier to tumor eradication and an opportunity for metastasis and recurrence. As a newly discovered stemness marker of pancreatic ductal adenocarcinoma (PDAC), the impact of CD9 on tumor progression and patient''s prognosis remain controversial.MethodsA total of 179 and 211 PDAC patients who underwent surgical resection with or without neoadjuvant chemotherapy, respectively, were recruited for immunohistochemical analyses of CD9 expression in both tumor and stromal areas prior to statistical analyses to determine the prognostic impact and predictive accuracy of CD9.ResultsThe relationship between CD9 and prognostic indicators was not significant in the non‐neoadjuvant group. Nevertheless, CD9 expression in both tumor (T‐CD9) and stromal areas (S‐CD9) was significantly correlated with the clinicopathological features in the neoadjuvant group. High levels of T‐CD9 were significantly associated with worse OS (p = 0.005) and RFS (p = 0.007), while positive S‐CD9 showed the opposite results (OS: p = 0.024; RFS: p = 0.008). Cox regression analyses identified CD9 in both areas as an independent prognostic factor. The T&S‐CD9 risk‐level system was used to stratify patients with different survival levels. The combination of T&S‐CD9 risk level and TNM stage were accurate predictors of OS (C‐index: 0.676; AIC: 512.51) and RFS (C‐index: 0.680; AIC: 519.53). The calibration curve of the nomogram composed of the combined parameters showed excellent predictive consistency for 1‐year RFS. These results were verified using a validation cohort.ConclusionNeoadjuvant chemotherapy endows CD9 with a significant prognostic value that differs between tumor and stromal areas in patients with pancreatic cancer.  相似文献   
994.
ObjectivesThis study aimed to investigate the effect of hemoglobin (Hb) fluctuation after dialysis on the prognosis of cardiovascular‐related and all‐cause deaths in peritoneal dialysis (PD).MethodsAccording to the Hb fluctuation, patients were divided into low fluctuation group, moderate fluctuation group, and high fluctuation group, and then, the effects of Hb fluctuation after dialysis on the prognosis of cardiovascular‐related and all‐cause death in PD were analyzed by regression analysis.ResultsA total of 232 patients were selected in this study. Compared with the low Hb fluctuation group, the moderate and high fluctuation groups had lower body mass index (BMI), estimated glomerular filtration rate (eGFR), and baseline Hb, and the moderate fluctuation group had less erythropoietin (EPO) and dialysis dose. Compared with survivors, patients with cardiovascular‐related and all‐cause deaths had lower mean Hb and Hb fluctuation (all p < 0.05). Cox regression analysis showed that before and after adjusting for confounding factors, Hb fluctuation was still independently correlated with cardiovascular prognosis, and higher Hb fluctuation was still a protective factor for cardiovascular‐related death in the Hb‐substandard group, but there was no significant correlation between Hb fluctuation and all‐cause death. Multivariate linear regression analysis revealed that Hb fluctuation was positively correlated with Kt/V and EPO dosage, but negatively correlated with the baseline Hb.ConclusionHigh Hb fluctuation was a protective factor for cardiovascular‐related death in PD with substandard Hb. Compared with Hb fluctuation, correction of anemia timely and making Hb reaches the standard level had a greater impact on reducing cardiovascular‐related death in PD.  相似文献   
995.
In this paper, we report self-assembled sonogels formed from 1,4-naphthalenedicarbonyldinicotinic acid hydrazide (NDC-NN3) in some liquids including ethanol, tetrahydrofuran (THF), 1,4-dioxane, n-propanol, n-butanol and n-pentanol. When the clear solution of NDC-NN3 in the selected liquids mentioned above at a suitable concentration was irradiated with ultrasound waves at room temperature, a sonogel was formed. Upon heating, the sonogel dissolved gradually and finally became a clear solution again. Upon cooling the hot solution to room temperature, the solution state did not change even after standing for a few days. Nevertheless, if the solution underwent sonication for a certain time, a stable gel was obtained again. The critical gelation concentrations (CGCs) of NDC-NN3 in ethanol, THF, 1,4-dioxane, n-propanol, n-butanol and n-pentanol are 10, 8, 6, 8, 6 and 8 mg mL−1, respectively. The obtained sonogels display excellent mechanical properties. The crystal structure of NDC-NN3 suggests that the naphthalene ring, hydrazide group and the position of N in the pyridine ring mediate the self-assembly process. Upon sonication, the formation of suitable π–π stacking and intermolecular hydrogen bonding drives the gelator molecules to self-assemble into fibers, spheres and micro-burdock-shaped balls in various solvents, which ultimately confine the liquids.

Ultrasound-induced gelation of a novel type of gelator, 1,4-naphthalenedicarbonyl- dinicotinic acid hydrazide, is reported. The gelator self-assembled into various architectures in different solvents.  相似文献   
996.
By using glycidol as a catalyst, high porosity, low-density resorcinol (R) and formaldehyde (F) aerogels and carbon aerogels (CAs) were synthesized via a sol-gel method. The effect of glycidol and water on the color, density, morphology, textual characteristics and adsorption properties of the resultant RF aerogels and CAs were investigated in detail. The results revealed that the properties of RF aerogels and CAs can be controlled by adjusting the amount of glycidol and water. The resultant RF aerogels and CAs were porous materials, the minimum densities of RF aerogels and CAs were 96 and 110 mg cm−3 respectively while the maximum specific surface areas of RF aerogels and CAs were 290 and 597 m2 g−1. The maximum adsorption capacity of CAs was about 125 mg g−1 on Rhodamine B, which was higher than that of some reported CAs catalyzed by base and acid catalysts. The sol-gel mechanisms of RF aerogels and CAs can be attributed to the opening of the epoxy group of glycidol in the mixture of R and F.

The sol-gel mechanism of glycidol-catalyzed RF aerogels is the opening of the epoxy ring rather than the preservation the of epoxy ring.  相似文献   
997.
目的 探索骨膜蛋白水平2型糖尿病男性患者骨质疏松的关系.方法 收集了2016年3月至2017年3月在我院门诊诊断为2型糖尿病男性病人90例,体检中心健康男性人群中随机选取30例作为正常对照组,记录患者的年龄、腹围、身高、体重,计算BMI,测定甘油三酯、总胆固醇、高密度脂蛋白、低密度脂蛋白、糖化血红蛋白,血清骨膜蛋白水平...  相似文献   
998.
In this study, the effect of pH shock during the treatment of sulfate-containing organic wastewater was investigated using an anaerobic fermentation system reinforced with graphene oxide (GO)/iron series systems. The results show that the anaerobic system with the GO/iron series systems exhibited enhanced resistance to pH shock. Among them, the GO/Fe0 system had the strongest resistance to pH shock, the systems of GO/Fe3O4 and GO/Fe2O3 followed close behind, while the blank system performed the worst. After pH shock, the CODCr removal rate, SO42− removal rate, and gas production of the GO/Fe0 group were significantly improved compared with those of the control group by 51.0%, 65.3%, and 34.6%, respectively, while the accumulation of propionic acid was the lowest. Further, detailed microbial characterization revealed that the introduction of the GO/iron series systems was beneficial to the formation of more stable anaerobic co-metabolic flora in the system, and the relative abundance of Geobacter, Clostridium, Desulfobulbus and Desulfovibrio increased after acidic and alkaline shock.

In this paper, we studied the pH shock resistance mechanism of GO/iron series from the perspectives of the treatment effect, changes in effluent pH and VFA, and microbial co-metabolic stability, providing a reference for the practical application.  相似文献   
999.
Heteroatom-doped carbon materials used in supercapacitors are low in cost and demonstrate extraordinary performance. Here, ethylenediamine tetraacetic acid (EDTA) with intrinsic N and O elements is selected as a raw material for the preparation of heteroatom self-doped porous carbon. Furthermore, N/O self-doped porous carbon with a large surface area has been successfully prepared using K2CO3 as the activator. The derived sample with a 1 : 2 molar ratio of EDTA to K2CO3 (EK-2) demonstrates a porous structure, rich defects, a large surface area of 2057 m2 g−1 and a micropore volume of 0.25 cm3 g−1. Benefiting from high N content (2.89 at%) and O content (10.75 at%), EK-2 exhibits superior performance, including high capacitance of 325 F g−1 at 1 A g−1 and outstanding cycling stability with 96.8% retention after 8000 cycles at 10 A g−1, which strongly confirms its immense potential toward many applications. Additionally, the maximum energy density of EK-2 reaches was 17.01 W h kg−1 at a power density of 350 W kg−1 in a two-electrode system. This facile and versatile strategy provides a scalable approach for the batch synthesis of N/O co-doped carbonaceous electrode materials for energy storage.

Heteroatom-doped carbon materials used in supercapacitors are low in cost and demonstrate extraordinary performance.  相似文献   
1000.
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