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   7856篇
  免费   339篇
  国内免费   63篇
耳鼻咽喉   56篇
儿科学   139篇
妇产科学   137篇
基础医学   1160篇
口腔科学   184篇
临床医学   531篇
内科学   2135篇
皮肤病学   38篇
神经病学   798篇
特种医学   248篇
外科学   1028篇
综合类   64篇
预防医学   151篇
眼科学   134篇
药学   623篇
中国医学   31篇
肿瘤学   801篇
  2023年   44篇
  2022年   73篇
  2021年   179篇
  2020年   79篇
  2019年   126篇
  2018年   162篇
  2017年   119篇
  2016年   158篇
  2015年   169篇
  2014年   216篇
  2013年   327篇
  2012年   461篇
  2011年   527篇
  2010年   322篇
  2009年   260篇
  2008年   480篇
  2007年   532篇
  2006年   555篇
  2005年   485篇
  2004年   477篇
  2003年   472篇
  2002年   494篇
  2001年   91篇
  2000年   96篇
  1999年   116篇
  1998年   118篇
  1997年   98篇
  1996年   89篇
  1995年   72篇
  1994年   102篇
  1993年   75篇
  1992年   78篇
  1991年   68篇
  1990年   52篇
  1989年   54篇
  1988年   52篇
  1987年   27篇
  1986年   42篇
  1985年   48篇
  1984年   43篇
  1983年   24篇
  1982年   18篇
  1981年   18篇
  1980年   21篇
  1979年   18篇
  1978年   17篇
  1977年   14篇
  1974年   10篇
  1971年   11篇
  1970年   11篇
排序方式: 共有8258条查询结果,搜索用时 15 毫秒
81.
AIM: This study aims to investigate the existence of any relationship between homocysteine levels and insulin resistance in Turkish women with polycystic ovary syndrome. METHODS: A case-controlled, cross-sectional, observational study was undertaken in a total of 94 infertile Turkish women who required professional help in the Department of Infertility of Dr Zekai Tahir Burak Women's Health Research and Education Hospital. The correlation between serum homocysteine with age, body mass index, hormone profile, fasting insulin and glucose concentrations and insulin resistance were examined in patients with polycystic ovary syndrome and the results were compared to those of women with normal ovaries, who served as a control group. RESULTS: The mean serum fasting glucose and insulin levels, thus insulin resistance index of women with polycystic ovary syndrome, were significantly higher than those of the control subjects. The mean serum homocysteine levels were significantly higher in women with polycystic ovary syndrome than those in the control group. A positive correlation was detected between the mean homocysteine, the insulin resistance index determined by homeostasis model assessment and the fasting insulin levels in polycystic ovary syndrome patients. CONCLUSIONS: Serum homocysteine levels are elevated in women with polycystic ovary syndrome, and this elevation is associated with the serum insulin level rather than androgen excess. The intense treatment of hyperhomocysteinemia in women with polycystic ovary syndrome might improve reproductive outcome and contribute to protection from cardiovascular risks.  相似文献   
82.
Although placental proteins play multiple roles in fetal and placental development and in the maintenance of pregnancy, many remain inadequately characterized. In the present study, we comprehensively analyzed these proteins by using a proteomic approach. Samples were denatured with guanidine hydrochloride, which was found to be superior to the commonly used urea for the present purpose, and subjected to 2-dimensional (2D) electrophoresis (2-DE) to obtain placental proteome maps. The identified protein spots (ca. 60% of the total) on the proteome maps included several pregnancy-related proteins (PRPs). Furthermore, a novel 2D immunoblotting (2-DI) analysis of molecules related to pre-eclampsia revealed three immunopositive spots that appeared to correspond to dynactin p-50, a protein related to cell turn-over. The rate of positivity for dynactin p-50-reactive antibodies was significantly (P=0.0024) higher in 26 pre-eclamptic women than in 58 normally pregnant women. These results indicate that dynactin p-50 may be involved in the pathophysiology of pre-eclampsia.  相似文献   
83.
A design for an octahedrally ligated phthalocyanine complex with high-spin manganese(iii) (S = 2) and MnIII(Pc)Cl2 (Pc = phthalocyanine) is presented. The presence of high-spin state MnIII in the fabricated Ph4P[MnIII(Pc)Cl2]2 (Ph4P = tetraphenylphosphonium) semiconducting molecular crystal is indicated by the Mn–Cl distance, which suggests an electronic configuration of (dyz, dzx)2(dxy)1(dz2)1. This was confirmed by the Curie constant (C = 5.69 emu K mol−1), which was found to be significantly larger than that of the isostructural Ph4P[MnIII(Pc)(CN)2]2, where MnIII adopts a low-spin state (S = 1). The magnetoresistance (MR) effects of Ph4P[MnIII(Pc)Cl2]2 at 26.5 K under 9 T static magnetic fields perpendicular and parallel to the c-axis were determined to be −30% and −20%, respectively, which are significantly larger values than those of Ph4P[MnIII(Pc)(CN)2]2. Furthermore, the negative MR effect is comparable to that of Ph4P[FeIII(Pc)(CN)2]2 (S = 1/2), which exhibits the largest negative MR effect reported for [MIII(Mc)L2]-based systems (Mc = macrocyclic ligand, L = axial ligand). This suggests that the spin state of the metal ion is the key to tuning the MR effect.

A Ph4P[MnIII(Pc)Cl2]2 molecular crystal where MnIII adopts a high-spin state (S = 2) was designed. The large magnetoresistance effect of fabricated Ph4P[MnIII(Pc)Cl2]2 suggests that the spin state of the metal ion is the key to tuning the MR effect.  相似文献   
84.
Background: The importance of maintaining good mental health with overall well-being has recently drawn attention from various spheres of academics and the working population. Amino acid intake has been reported to reduce depression symptoms and other mental health problems. However, the effectiveness of amino acid intake (i.e., single or combined) remains unknown. In this study, we assessed a combination of five amino acids (serine, alanine, glutamate, aspartate, and tyrosine; SAGAT) reported to regulate mental health. Methods: A randomized, double-blind, placebo-controlled exploratory trial was conducted. Participants, aged between 20 and 65 years with fatigue sensation, were randomized to receive either SAGAT or the placebo and ingested them for four weeks. A transient mental work was loaded at day 0 and after four weeks of intervention. As the primary outcomes, the fatigue sensation was assessed. The mood status, cognitive function, work efficiency, and blood marker were also measured as secondary outcomes. Results: The number of participants analyzed for the efficacy evaluation were 20 in SAGAT and 22 in the placebo. There were no significant differences in the primary outcomes. However, as the secondary outcomes, the SAGAT group showed a significant improvement in motivation and cognitive function in the recovery period after mental work loaded in a four-week intervention compared to the placebo. Conclusion: The current findings suggest that SAGAT contributes to maintaining proper motivation and cognitive function. Clinical Trial Registration: University Hospital Medical Information Network Clinical Trial Registry (ID: UMIN 000041221).  相似文献   
85.
Genetic analyses of highly pathogenic avian influenza H5 subtype viruses isolated from the Izumi Plain, Japan, revealed cocirculation of 2 genetic groups of clade 2.3.4.4b viruses among migratory waterfowl. Our findings demonstrate that both continuous surveillance and timely information sharing of avian influenza viruses are valuable for rapid risk assessment.  相似文献   
86.
The effects of tolbutamide and glibenclamide on hepatic glycogenolysis in perfused rat liver were investigated. Tolbutamide per se did not influence glucose output from the liver, but at therapeutic concentrations (about 350 microM) it significantly inhibited the glycogenolysis induced by phenylephrine, vasopressin and angiotensin II, while glibenclamide did not. Neither tolbutamide nor glibenclamide inhibited the glycogenolysis induced by glucagon. Tolbutamide potentiated the inhibitory effect of submaximal concentrations of insulin on glycogenolysis induced by phenylephrine. This effect of tolbutamide was elicitable even in the absence of calcium in the perfusate, and was additive to that of trifluoperazine. However, tolbutamide did not potentiate the inhibitory effect of insulin on glucagon-induced glycogenolysis. Tolbutamide inhibited the glycogenolysis induced by A23187, a calcium ionophore. These results indicate that, in addition to its known effect on insulin secretion, tolbutamide has a direct effect on the liver to inhibit glycogenolysis induced by Ca2+-dependent hormones (catecholamines, vasopressin and angiotensin II) and A23187. Thus, it is likely that tolbutamide inhibits the effect of Ca2+ mobilized by Ca2+-dependent hormones to stimulate glycogenolysis.  相似文献   
87.
88.
We conducted a questionnaire survey about radiation-safety management condition in Japanese nuclear medicine facilities to make materials of proposition for more reasonable management of medical radioactive waste. We distributed a questionnaire to institutions equipped with Nuclear Medicine facilities. Of 1,125 institutions, 642 institutes (52.8%) returned effective answers. The questionnaire covered the following areas: 1) scale of an institution, 2) presence of enforcement of radiotherapy, 3) system of a tank, 4) size and number of each tank, 5) a form of draining-water system, 6) a displacement in a radioactive rays management area, 7) a measurement method of the concentration of medical radioactive waste in draining water system, 8) planned and used quantity of radioisotopes for medical examination and treatment, 9) an average displacement of hospital for one month. In most institutions, a ratio of dose limitation of radioisotope in draining-water system was less than 1.0, defined as an upper limitation in ordinance. In 499 hospitals without facilities of hospitalization for unsealed radioisotope therapy, 473 hospitals reported that sum of ratios of dose limits in a draining-water system was less than 1.0. It was calculated by used dose of radioisotope and monthly displacement from hospital, on the premise that all used radioisotope entered in the general draining-water system. When a drainage including radioactivity from a controlled area join with that from other area before it flows out of a institution, it may be diluted and its radioactive concentration should be less than its upper limitation defined in the rule. Especially, in all institutions with a monthly displacement of more than 25,000 m3, the sum of ratio of the concentration of each radionuclide to the concentration limit dose calculated by used dose of radioisotope, indicated less than 1.0.  相似文献   
89.
BACKGROUND: The molecular mechanisms in malignant transformation of laryngeal mucosa are unknown; many clinical and pathological factors affect prognosis. We investigated a possible correlation between overexpression of p53, proliferating cell nuclear antigen (PCNA), and c-erbB-2, and the clinicopathologic features of laryngeal squamous cell carcinoma (SCC) and clarify their prognostic value. MATERIAL/METHODS: Thirty-three men with laryngeal SCC participated; all underwent primary surgery or surgery plus radiotherapy between 1999 and 2004 at our department. Paraffin sections of laryngeal SCC were immunohistochemically stained for p53, PCNA, and c-erbB-2. RESULTS: Overall, p53 overexpression was found in 16 patients. There was no relation between p53 immunohistochemical staining and tumor region. PCNA immunostaining was significantly stronger in supraglottic tumors compared with glottic tumors. Immunostaining of c-erbB-2 was not different in either location. There was no relation between the T stage of the tumor and p53 and c-erbB-2 immunostaining. However, there was a statistically significant positive correlation between the PCNA staining and T stage (stronger staining was present in T3 and T4 stages than in T1 and T2 stages). CONCLUSIONS: We could not find a statistically significant correlation between p53, PCNA, and c-erbB-2 and lymph node status, histologic differentiation, and survival rate. We demonstrated only a statistically significant positive correlation between PCNA staining and T stage. These data suggest that overexpression of p53, PCNA, and c-erbB-2 is not prognostic in laryngeal SCC.  相似文献   
90.
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