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   4609篇
  免费   155篇
  国内免费   35篇
耳鼻咽喉   23篇
儿科学   95篇
妇产科学   63篇
基础医学   573篇
口腔科学   61篇
临床医学   259篇
内科学   1133篇
皮肤病学   47篇
神经病学   356篇
特种医学   197篇
外科学   957篇
综合类   23篇
预防医学   91篇
眼科学   189篇
药学   248篇
中国医学   8篇
肿瘤学   476篇
  2023年   19篇
  2022年   43篇
  2021年   95篇
  2020年   44篇
  2019年   63篇
  2018年   72篇
  2017年   59篇
  2016年   95篇
  2015年   99篇
  2014年   134篇
  2013年   176篇
  2012年   282篇
  2011年   300篇
  2010年   138篇
  2009年   129篇
  2008年   254篇
  2007年   300篇
  2006年   258篇
  2005年   290篇
  2004年   296篇
  2003年   293篇
  2002年   293篇
  2001年   62篇
  2000年   65篇
  1999年   76篇
  1998年   62篇
  1997年   65篇
  1996年   55篇
  1995年   58篇
  1994年   54篇
  1993年   60篇
  1992年   37篇
  1991年   41篇
  1990年   32篇
  1989年   36篇
  1988年   27篇
  1987年   22篇
  1986年   23篇
  1985年   23篇
  1984年   23篇
  1983年   25篇
  1982年   21篇
  1981年   21篇
  1980年   18篇
  1979年   23篇
  1978年   16篇
  1976年   13篇
  1975年   10篇
  1974年   15篇
  1970年   11篇
排序方式: 共有4799条查询结果,搜索用时 15 毫秒
11.
To find antiviral agents, various sulfonamidobenzophenone oximes (II) were synthesized from the appropriate m-sulfonamidobenzophenones by hydroxylamine reaction. The reaction products were generally obtained as syn/anti mixtures which were separable by fractional crystallization. The anti isomer had more potent antipoliovirus activity than the syn isomer. Various sulfonamidobenzamides (III) which were structurally related to II were synthesized by the reactions of amino-substituted benzamides with sulfuryl chloride or amines with (aminosulfonyl)benzoyl chloride. Antiviral activity was examined by the plaque-inhibition test. Compounds 5, 36, and 69 exhibited strong antipicornavirus activity. The structure-activity relationships are discussed.  相似文献   
12.
Chemical shift MRI is widely used for identifying adenomas, but it is not a perfect method. We determined whether combined dynamic MRI methods can lead to improved diagnostic accuracy. Fifty-seven adrenal masses were examined by chemical shift and dynamic MR imaging using 2 MR systems. The masses included 38 adenomas and 19 non-adenomas. In chemical shift MRI studies, the signal intensity index (SI) was calculated, and the lesions classified into 5 types in the dynamic MRI studies. Of the 38 adenomas studied, 37 had an SI greater than 0. In the dynamic MRI, 34 of 38 adenomas showed a benign pattern (type 1). If the SI for the adenomas in the chemical shift MRI was considered to be greater than 0, the positive predictive value was 0.9, and the negative predictive value was 0.94 and kappa = 0.79. If type 1 was considered to indicate adenomas in the dynamic MRI, the corresponding values were 0.94, 0.81 and kappa = 0.77 respectively. The results obtained when the 2 methods were combined were 1, 0.95 and kappa = 0.96 respectively. The chemical shift MRI was found to be useful for identifying adenomas in most cases. If the adrenal mass had a low SI (0 < SI < 5), dynamic MRI was also found to be helpful for making a differential diagnosis.  相似文献   
13.
We report a case of primary pulmonary low-grade marginal zone B-cell lymphoma of the mucosa-associated lymphoid tissue (MALT)-type with prominent sclerosis, which morphologically resembled pulmonary hyalinizing granuloma (PHG) or inflammatory pseudotumor (IPT) of the lung. The patient, a 66-year-old Japanese female with a history of Sj?gren's syndrome and primary biliary cirrhosis, presented with a lower left lobe mass 6.8 cm in diameter. Histologically, the lesion is characterized by dense bundles of collagen with scattered plasma cells, mature small lymphocytes, and histiocytes among the collagen bundles. Only the peripheral area of the nodule contained dense lymphoplasmacytoid and histiocytoid infiltrates. A few centrocyte-like cells were obscured by the numerous plasma cells and plasmacytoid cells. In addition, lymphoepithelial lesions and colonalized lymphoid follicles were identified by immunohistochemistry alone. Although PHG and IPT are unlikely to be confused with pulmonary MALT-type lymphomas, the present case suggests that MALT-type lymphoma should be added to the list of differential diagnoses for PHG and IPT.  相似文献   
14.
Imaging by scanning electron microscopy (SEM) can provide insight into viral egress. At a low magnification level, varicella zoster virions (VZV) emerge from an infected cell surface in a distinctive pattern previously described as "viral highways." Viral highways consist of thousands of particles arranged in linear pathways across the syncytial surface. This egress pattern has not been described with other herpesviruses, but a systematic analysis has not been performed. Therefore, the characteristic arrangement of VZV egress was compared with that of six other members of the herpes virus family, including herpes simplex virus (HSV) types 1 and 2, human cytomegalovirus (CMV), pseudorabies virus (PRV), and human herpesvirus types 6 and 7 (HHV-6 and HHV-7). Only VZV-infected cells exhibited viral highways. Subsequent SEM examination of VZ virions at an ultra high-resolution revealed that more than 70% were aberrant. Further imaging of the other herpesviruses demonstrated that VZV structure was more closely related to PRV than HSV-1 or HSV-2. Finally, it is noted that the individual members of the herpesvirus family have distinguishable SEM profiles.  相似文献   
15.
By light and electron microscopy, we observed foamy cells in the spleens from a patient with hemolytic anemia due to red cell adenosine deaminase (ADA) overproduction, a patient with rheumatoid arthritis (RA) treated with gold, and patients with idiopathic thrombocytopenic purpura (ITP)

The foamy cells associated with red cell ADA overproduction were essentially similar to Gaucher-like cells described in patients with thalassemia, and it was suggested that the accelerated destruction of red cells was one of the factors responsible for the development of foamy cells. Foamy cells in ITP and RA were closely associated with an increased destruction of platelets in the spleen. Morphologic transitions between phagocytosed platelets and myelinlike materials were traced in these disorders. In RA, however, foamy cells were heterogeneous from an ultrastructural standpoint, with different cytoplasmic inclusions. In addition to myelinlike materials, dense bodies, vacuoles with flocculent materials, and gold were noted in most of foamy cells. As gold compounds are known to inhibit lysosomal enzymes, we surmise that an acquired disturbance in lysosomal digestion is partially responsible for the accumulation of intermediate metabolites.

In the pathogenesis of foamy cells associated with blood cell dyscrasia, the accelerated destruction of blood cells and/or acquired disorders in catabolic pathways within the macrophages are suggested to be the underlying mechanism of an intralysosomal accumulation of incompletely degraded cellular debris.  相似文献   
16.
Ohta H  Makita K  Komukai S  Nozawa S 《Maturitas》2002,43(1):27-33
OBJECTIVES: To investigate if menopause and oophorectomy may represent different risk factors for bone resorption/loss. METHODS: The urinary levels of pyridinoline (Pyr) and deoxypyridinoline (D-pyr), the serum levels of type I carboxy-terminal pyridinoline cross-linked telopeptide (ICTP), and lumbar bone mineral density (BMD), were compared in 80 Japanese women after menopause or oophorectomy. These women were divided into four groups of 20 women each as follows: early postmenopausal stage (early physiologic menopause < 3 years before study entry); late postmenopausal stage (physiologic menopause > or = 3 years before study entry); early postoophorectomy stage (oophorectomy < or = 03 years before study entry); or late oophorectomy stage (oophorectomy > 3 years before study entry). RESULTS: Lumbar BMD was significantly lower in the late groups compared to their respective early groups and was lowest in the late postoophorectomy group. The ratio of D-pyr/creatinine (Cr) was not significantly different among the four groups. The ratio of Pyr/Cr was significantly higher in the early postoophorectomy subjects compared with either late group. The serum level of ICTP was significantly higher in the early postoophorectomy group compared to all other groups. CONCLUSIONS: These findings suggest that serum ICTP may be useful in detecting changes in bone resorption after oophorectomy and that women are at greater risk for bone resorption after oophorectomy than after physiologic menopause, although this difference appears to diminish with time.  相似文献   
17.
Isopropoxyethyne (1a) and tert-butoxyethyne (1b) were polymerized using group 5 and 6 transition metal catalysts to give poly(isopropoxyethyne) (2a) and poly(tert-butoxyethyne) (2b) , respectively. The weight-average molecular weight (M?w) of the resulting poly(alkoxyethyne)s was up to 1.0 × 104. Among the transition metal catalysts, a tungsten alkoxide or a molybdenum alkoxide having low Lewis acidity were found to effectively promote the polymerization without causing side reactions. Poly(tert-butoxyethyne) was successfully converted to poly(β-ketone) 3 by acid hydrolysis of the tert-butyl vinyl moiety.  相似文献   
18.
2-(Hydroxyphenyl)-2oxazolines(p- and n-isomers 1a and 1b ) were used for the synthesis of various polymers. Cationic polymerization of 2-methyl-2-oxazoline initiated with the N-methyl 2 -oxazolinium species 3 , Derived from 1 , Gave telechelic poly(N-acetylethylenimine) ( 5 ) having a hydroxyl group of different reactivity at both ends. Anionic polymerization of ethylene oxide induced by the lithium salt of 1, 7 , produced a poly(ethylene oxide) macromer, 9 , having a ringopening polymerizable 2-oxazoline group. The copolymer from 9 and 2-phenyl-2oxazoline, 10 , has been shown to have good properties as a nonionic polymeric surfactant in which the N-benzoylethylenimine main-chain behaves as a lipophilic group whereas the oxyethylene graftchains act as a hydrophilic group. Di-salt 11 derived from 1 was polymerized to give polymide 13 (“amphi-ionic polymerization”).  相似文献   
19.
Formalin-fixed paraffin-embedded hippocampal sections of brains with early-onset and late-onset Alzheimer's disease were studied immunohistochemically with antisera against cathepsin D and cathepsin B. In addition to the staining of neuronal perikarya, some of the senile plaques visualized by Bielshowsky silver staining and some of reactive astrocytes were positively stained with the antisera against cathepsin D and cathepsin B in brains with Alzheimer's disease. Abnormal localization of cathepsin D and cathepsin B immunoreactivity in neuronal perikarya was observed in brains with early-onset Alzheimer's disease. These findings demonstrate that the distribution of lysosomal proteases was altered in brains with Alzheimer's disease, suggesting the primary and/or secondary involvement of the lysosomal proteases in the pathological process of Alzheimer's disease.  相似文献   
20.
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