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   6790篇
  免费   217篇
  国内免费   38篇
耳鼻咽喉   240篇
儿科学   136篇
妇产科学   294篇
基础医学   831篇
口腔科学   49篇
临床医学   439篇
内科学   1810篇
皮肤病学   128篇
神经病学   605篇
特种医学   113篇
外科学   739篇
综合类   59篇
一般理论   10篇
预防医学   322篇
眼科学   199篇
药学   674篇
中国医学   4篇
肿瘤学   393篇
  2023年   20篇
  2022年   141篇
  2021年   261篇
  2020年   72篇
  2019年   135篇
  2018年   151篇
  2017年   113篇
  2016年   124篇
  2015年   164篇
  2014年   210篇
  2013年   321篇
  2012年   446篇
  2011年   566篇
  2010年   277篇
  2009年   185篇
  2008年   447篇
  2007年   540篇
  2006年   495篇
  2005年   532篇
  2004年   520篇
  2003年   452篇
  2002年   394篇
  2001年   18篇
  2000年   23篇
  1999年   28篇
  1998年   29篇
  1997年   18篇
  1996年   24篇
  1995年   33篇
  1994年   21篇
  1993年   18篇
  1992年   14篇
  1991年   21篇
  1990年   9篇
  1989年   12篇
  1988年   7篇
  1987年   16篇
  1986年   9篇
  1985年   14篇
  1984年   22篇
  1983年   16篇
  1982年   22篇
  1981年   12篇
  1980年   10篇
  1979年   15篇
  1978年   12篇
  1977年   7篇
  1976年   5篇
  1974年   7篇
  1973年   6篇
排序方式: 共有7045条查询结果,搜索用时 178 毫秒
31.
The clinical implications of increased cytokine levels after major surgery remain unclear. In this study, systemic concentration of a spectrum of cytokines, including interleukins IL-6, IL-8, IL-10, IL-1ra, and soluble tumor necrosis factor receptor-I (sTNF-RI) was examined in patients with and without postoperative septic complications following colorectal surgery. Although there were no significant changes in IL-1, TNF-, and IL-8 serum levels during the observation period, there was a significant rise in IL-6, IL-1ra, and sTNF-RI concentrations in the entire group of patients between postoperative day 1 and 14. There were no differences between the group without and with local complications when IL-6, IL-1ra, and IL-10 were examined. The serum levels of sTNF-RI, IL-1ra, and IL-6 were found to be sensitive indicators of the pro- and anti-inflammatory response to the surgical trauma, but only sTNF-RI turned out to be a sensitive early marker of local septic postoperative complications in patients with colorectal carcinoma.  相似文献   
32.
33.
Dilated cardiomyopathy (DCM) is one of the most common causes of heart failure with a prevalence of 1:2500. There are several primary and secondary etiologic factors, including gene mutations, infection agents, particularly viruses, toxins, autoimmune, and systemic disorders, and pheochromocytoma, neuromuscular, metabolic, mitochondrial, and nutritional disorders. However, a precise diagnosis can be reached only in no more than 50% of all cases. Herein, we report a rare case of hepatic damage and severe DCM as a consequence of relatively popular socially used narcotic-Ecstasy (3,4-methylenedioxy-N-methylamphetamine [MDMA]).  相似文献   
34.
We examined the acute stress response associated with having to deliver either bad or good medical news using a simulated physician–patient scenario. Twenty-five healthy medical students were randomly assigned to a bad medical news (BN), a good medical news (GN), or a control group that read magazines during the session. Self-report measures were obtained before and after the task. Blood pressure and heart rate were measured throughout the task period. Four blood samples were obtained across the task period. The BN and GN tasks produced significant increases in self-reported distress and cardiovascular responses compared with the control group. There was also a significant increase in natural killer cell function 10 min into the task in the BN group compared with the control group. The BN task was also somewhat more stressful than the GN task, as shown by the self-report and cardiovascular data. These findings suggest that a simulated physician–patient scenario produces an acute stress response in the physician, with the delivery of bad medical news more stressful than the delivery of good medical news.  相似文献   
35.
Melanin pigmentation in mammalian skin and its hormonal regulation   总被引:37,自引:0,他引:37  
Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.  相似文献   
36.
The paper investigates the conformational stability of bovine serum albumin (BSA) and fibrinogen during 24-h incubation in turn with a linear silicone polymer (polydimethylsiloxane (PDMS)), with linear silicone oligomers (hexamethyldisiloxane and octamethyltrisiloxane) and with cyclic silicone oligomers (octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5)). Ten-fold and 100-fold excesses of siloxanes with respect to the proteins were used. Using fluorescence spectroscopy of tryptophan located in the domain of proteins and fluorescence of 8-anilino-1-naphthalenesulfonic acid (1,8-ANS), which interacts with hydrophobic domains of proteins, changes in the tertiary structure of the protein were recorded. The results demonstrated that BSA does not change its native form during 24-h incubation with siloxanes. In contrast, the tertiary structure of fibrinogen was found to be altered by both short-chain linear siloxanes: (hexamethyldisiloxane and octamethyltrisiloxane) and long-chain PDMS. The changes can be observed only at a 100-fold excess of siloxanes with respect to the protein. No conformational changes in fibrinogen exposed to cyclic siloxanes were observed.  相似文献   
37.
The reaction of pyromellitic dianhydride (1,2 : 4,5-benzenetetracarboxylic dianhydride) ( 1 ) with L - and D -alanine ( 2 L ) and ( 2 D ) leads to new monomers which were used to synthesize new copolymers. These copolymers were obtained as a product of the condensation of optical isomers of bis[N-(1-chloroformylethyl)]pyromellitimides (CFEP) with poly(ethylene glycol) PEG-2000 ( 5 ). The effect of monomer structure on the structure and thermal properties of the polymers was studied using X-ray diffraction, differential scanning calorimetry and thermogravimetry. The copolymers were compared with similar copolyimides obtained previously from bis(N-chloroformylmethyl)pyromellitimide and poly(ethylene glycol), PEG 2000. The dominating effect of poly(ethylene glycol) comonomer on the crystallinity, structure and thermal stability of these new copolymers is proven.  相似文献   
38.
39.
40.
Bronchoalveolar lavage (BAL) or induced sputum (IS) techniques may provide leukocytes for the evaluation of airway inflammatory response in bronchial asthma. The aim of the present study was to compare features of leukocyte populations obtained by the two different methods regarding the cell types and their activity in patients with bronchial asthma. The nitric oxide (NO) level released from the cells was measured as a marker of their activity. Pulmonary leukocytes were obtained from the BAL and IS of 11 asthmatic patients in stable condition at the time of the study. The BAL and IS leukocyte populations varied in cell count and NO production. Macrophages were the predominant leukocyte population in BAL (median (Me) = 83.0%, range 67.9-88.4%), whereas sputum sediments were found to consist mainly of neutrophils (Me = 55.7%, range 29.0-64.9%). The IS leukocytes released much more NO (p = 0.0022) than the BAL leukocytes. In spite of these quantitative differences, a similar pattern of NO production was observed in BAL and in IS cells. Both BAL and IS leukocyte populations produced almost the same amounts of NO before and after lipopolysaccharide stimulation (p = 0.9063, p = 0.4801, respectively). Furthermore, a slight positive correlation Spearman's rank (RS) = 0.5578, p = 0.0594) was noticed between the neutrophil percentages and NO levels produced by BAL cells, whereas in IS a statistically significant correlation between the percentage of neutrophils and the levels of NO (RS = 0.6643, p = 0.0184) was observed. In conclusion, the BAL and IS leukocyte populations are different in cell type, their size and activity. Depending on the asthma severity and the type of cells needed in a study, either BAL or IS specimens may be chosen as a source of pulmonary leukocytes. The use of IS as a noninvasive technique is supposed to be potential value particularly in the study of the airway inflammatory response mediated mainly by neutrophils, i.e. during and/or after exacerbation of the disease. Based on our results, a possible contribution of neutrophils in the production of NO in the airways of asthmatic patients can be proposed apart from other cells such as macrophages.  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