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   4673篇
  免费   162篇
  国内免费   36篇
耳鼻咽喉   23篇
儿科学   86篇
妇产科学   69篇
基础医学   610篇
口腔科学   72篇
临床医学   265篇
内科学   1165篇
皮肤病学   54篇
神经病学   361篇
特种医学   202篇
外科学   900篇
综合类   34篇
预防医学   101篇
眼科学   185篇
药学   239篇
中国医学   8篇
肿瘤学   497篇
  2023年   19篇
  2022年   48篇
  2021年   96篇
  2020年   46篇
  2019年   68篇
  2018年   76篇
  2017年   65篇
  2016年   98篇
  2015年   103篇
  2014年   139篇
  2013年   182篇
  2012年   291篇
  2011年   305篇
  2010年   144篇
  2009年   136篇
  2008年   267篇
  2007年   297篇
  2006年   261篇
  2005年   292篇
  2004年   293篇
  2003年   286篇
  2002年   296篇
  2001年   56篇
  2000年   65篇
  1999年   95篇
  1998年   64篇
  1997年   68篇
  1996年   59篇
  1995年   61篇
  1994年   57篇
  1993年   62篇
  1992年   43篇
  1991年   42篇
  1990年   29篇
  1989年   33篇
  1988年   24篇
  1987年   24篇
  1986年   25篇
  1985年   20篇
  1984年   17篇
  1983年   26篇
  1982年   19篇
  1981年   20篇
  1980年   17篇
  1979年   10篇
  1978年   17篇
  1977年   11篇
  1976年   12篇
  1974年   13篇
  1971年   8篇
排序方式: 共有4871条查询结果,搜索用时 31 毫秒
51.
52.
Carcinosarcoma of the uterine corpus containing endolymphatic stromal myosis (ESM) is extremely rare. This report describes the light- and electron-microscopic findings of ESM coexisting with adenocarcinoma of the uterus in a 58-year-old female. The polypoid tumor originated from the fundus uteri and filled the uterine cavity. In addition to papillary and medullary acinous adenocarcinoma at the apex of the polypoid mass, the major portion of the tumor specimen was composed of cells resembling endometrial stromal cells that infiltrated the myometrium and lymphatic channels, and a diagnosis of ESM was made due to the relative cell uniformity, rare mitoses, and the presence of invasive growth. There have been few reports on the ultra-structure of ESM and endometrial stromal sarcoma, and there are no reports on the ultrastructural difference between these tumors. In addition to the ultrastructural observations of our case, the electron-microscopic findings of previous reports are discussed.  相似文献   
53.
An electron microscopic immunohistochemical localization of thyroglobulin (TG) using PAP methods has been made in 15 cases of cold follicular adenoma. All cases of follicular adenoma showed organ specific functions such as synthesis, storage, reabsorption, and hydrolysis of thyroglobulin except for an area composed of follicular cells with trabecular arrangement. Immuno-reaction product for TG was precisely demonstrated in follicular lumina, subapical vesicles and reabsorbed colloid droplets. The reaction product observed in the follicular lumen was clearly demarcated from the cytoplasm of the follicular cells by the apical plasma membrane. The subapical vesicles ranging approximately from 50 mμ to 300 mμ in diameter were rarely observed in follicular adenoma and some of them fused with the reabsorbed colloid droplets. The reabsorbed colloid droplets usually had the intense reaction product and hydrolyzed colloid droplets had a vacuole containing floccular low electron dense materials. There is no reaction product in rough endoplasmic reticulum and Golgi complexes.  相似文献   
54.
We evaluated the respiratory functions of patients with pulmonary emphysema who underwent lung volume reduction surgery (LVRS) by the mean transit time (MTT) with Xe-133 lung ventilation scintigraphy, forced expiration volume in 1 sec (FEV1.0), residual volume (RV), distance walked in 6 min (6-min walk), and the Hugh-Jones classification (H-J classification) before and after LVRS. In 69 patients with pulmonary emphysema (62 men, 7 women; age range, 47-75 years; mean age, 65.4 years +/- 6.1, preoperative H-J classification, III (two were II)-V) who underwent LVRS, all preoperative and postoperative parameters (MTT 3 weeks after LVRS and the others 3 months after LVRS) were judged statistically by the Wilcoxon signed-ranks test and Odds ratio. Every postoperative parameter was improved with a significant difference (P < 0.05) compared to preoperative parameters. MTT at 3 weeks after LVRS was not associated with %FEV1.0 and the H-J classification at 3 months after LVRS, but was associated with RV and a 6-min walk at 3 months after LVRS. MTT was useful for the clinical evalution of aerobic capability after LVRS.  相似文献   
55.
This paper describes a new ring-opening-closing alternating copolymerization (ROCAC) of 2-methyl-2-oxazoline (five-membered cyclic imino ether, 1 ) with N-methyldiacrylamide ( 2 ). The reaction of a 1 : 1 monomer feed ratio proceeded without any added catalyst to give an alternating copolymer 3 having two structural units formed by ring-opening and ring-closing (cyclization). The structure of copolymer 3 was determined by 1H, 13C NMR, and IR spectroscopies. The extent of cyclization was at most 65%. The copolymerization was reasonably explained by a mechanism of propagation via zwitterion intermediates.  相似文献   
56.
BACKGROUND: We have previously shown that fisetin, a flavonol, inhibits IL-4 and IL-13 synthesis by allergen- or anti-IgE-antibody-stimulated basophils. This time, we investigated the inhibition of IL-4 and IL-13 production by basophils by other flavonoids and attempted to determine the fundamental structure of flavonoids related to inhibition. We additionally investigated whether flavonoids suppress leukotriene C4 synthesis by basophils and IL-4 synthesis by T cells in response to anti-CD3 antibody. METHODS: Highly purified peripheral basophils were stimulated for 12 h with anti-IgE antibody alone or anti-IgE antibody plus IL-3 in the presence of various concentrations of 18 different kinds of flavones and flavonols. IL-4 and IL-13 concentrations in the supernatants were then measured. Leukotriene C4 synthesis was also measured after basophils were stimulated for 1 h in the presence of flavonoids. Regarding the inhibitory activity of flavonoids on IL-4 synthesis by T cells, peripheral blood mononuclear cells were cultured with flavonoids in anti-CD3-antibody-bound plates for 2 days. RESULTS: Luteolin, fisetin and apigenin were found to be the strongest inhibitors of both IL-4 and IL-13 production by basophils but did not affect leukotriene C4 synthesis. At higher concentrations, these flavonoids suppressed IL-4 production by T cells. Based on a hierarchy of inhibitory activity, the basic structure for IL-4 inhibition by basophils was determined. CONCLUSIONS: Due to the inhibitory activity of flavonoids on IL-4 and IL-13 synthesis, it can be expected that the intake of flavonoids, depending on the quantity and quality, may ameliorate allergic symptoms or prevent the onset of allergic diseases.  相似文献   
57.
The expression of -GlcNAcβ1–6Man-(β1–6) branched oligosaccharides In carcinoma cells has been considered to influence their metastatic potentials. In the present paper, the lectin histochemistry of oral squamous cell carcinomas obtained in biopsy from 34 patients with Phaseolus vulgaris leukoagglutinin (L-PHA), which potentially binds to N-glycosidic carbohydrates with β1–6 linked lactosamin antennae, was studied in order to analyze the relationship between their staining patterns and metastases. The L-PHA-binding oligosaccharides of the carcinomas were expressed on the cell surface in the following patterns: (i) all cells were positive for the staining ('positive'); (ii) some cells were positive but the rest of the carcinoma cells were negative ('weakly positive'); and (iii) all were negative ('negative'). Statistical analysis revealed that the incidence of the metastasis to regional lymph nodes in the 'positive' cases was significantly higher than that in the 'negative' cases. Moreover, the number of the CD14 positive cells including macrophages in the Stroma adjacent to the cardnomas in the 'positive' cases was less than that in the 'negative' or 'weakly positive' cases. The expression of L-PHA-binding oligosaccharides in oral squamous cell carcinoma may be responsible for their metastatic potential to regional lymph nodes, possibly Including their ability to escape macrophage recognition.  相似文献   
58.
In analyzing repeated measurements from randomized controlled trials with mixed‐effects models, it is important to carefully examine the conventional normality assumption regarding the random‐effects distribution and its dependence on treatment allocation in order to avoid biased estimation and correctly interpret the estimated random‐effects distribution. In this article, we propose the use of a gradient function method in modeling with the different random‐effects distributions depending on the treatment allocation. This method can be effective for considering in advance whether a proper fit requires a model that allows dependence of the random‐effects distribution on covariates, or for finding the subpopulations in the random effects.  相似文献   
59.
Akt/protein kinase B (PKB) plays an important role in cell survival. However, the role of Akt in the biology of gastric cancer has not been well studied. We sought to investigate the expression of Akt or phosphorylated Akt (pAkt) in human gastric carcinomas and to analyze the relationship between Akt or pAkt and the clinicopathologic parameters. The expressions of Akt and pAkt were evaluated immunohistochemically in 311 gastric carcinomas using the tissue array method. Akt expression was detected in 74% of the tumors and pAkt expression in 78%. pAkt was highly expressed in the early stage of pTNM (p=0.011). We also found an inverse association between pAkt and lymphatic invasion (p=0.01) or lymph node metastasis (p=0.008). pAkt expression was significantly correlated with a higher survival in patients with stage I carcinomas (p=0.0003). Interestingly, combined evaluation revealed that the group with pAkt-positive and lymph node-negative carcinomas showed a better prognosis than the other groups (p<0.0001). In addition, pAkt was shown to correlate positively with APC (p=0.002) and Smad4 (p<0.0001) expression. These findings suggest that pAkt expression may help to predict the clinical outcome of gastric cancer patients.  相似文献   
60.
The localization of apolipoprotein E (ApoE) has been examined immunohistochemically in the autopsied brains of middle-aged and old-aged control subjects, with and without amyloid protein (A) deposits, and of Alzheimer's disease patients. Senile plaques were consistently labeled with ApoE antiserum even in the very early stage of senile plaque formation seen in the fifth decade. In the cerebellar molecular layer, small dots of ApoE immunoreactivity, which were prominent in the Alzheimer's disease subjects, were observed in addition to immunoreactivity in diffuse plaques. ApoE antisera labeled all of the extracellular neurofibrillary tangles (NFT), whereas only a small minority of extracellular NFT were positive for A. A punctate pattern of ApoE immunoreactivity was seen at the media of the meningeal vessels lacking amyloid, when senile plaques were present in the nearby cortex. In the early stage of amyloid angiopathy, the distribution of ApoE immunoreactivity was much more extensive than that of A positivity. These findings suggest that ApoE accumulates in the early stage of senile plaque formation and, furthermore, that ApoE accumulation precedes A deposition in extracellular NFT and amyloid angiopathy.  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