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   2182455篇
  免费   153301篇
  国内免费   4788篇
耳鼻咽喉   30653篇
儿科学   70331篇
妇产科学   61585篇
基础医学   311660篇
口腔科学   59448篇
临床医学   189946篇
内科学   430287篇
皮肤病学   44667篇
神经病学   175844篇
特种医学   86720篇
外国民族医学   685篇
外科学   338508篇
综合类   44721篇
现状与发展   2篇
一般理论   696篇
预防医学   160788篇
眼科学   50456篇
药学   161111篇
  2篇
中国医学   4178篇
肿瘤学   118256篇
  2019年   17496篇
  2018年   24168篇
  2017年   18405篇
  2016年   20311篇
  2015年   23293篇
  2014年   33074篇
  2013年   49557篇
  2012年   68513篇
  2011年   72955篇
  2010年   43144篇
  2009年   40645篇
  2008年   69093篇
  2007年   74002篇
  2006年   74497篇
  2005年   73073篇
  2004年   70066篇
  2003年   67191篇
  2002年   65751篇
  2001年   90088篇
  2000年   92150篇
  1999年   79344篇
  1998年   24320篇
  1997年   21729篇
  1996年   21637篇
  1995年   20237篇
  1994年   19187篇
  1993年   17981篇
  1992年   62924篇
  1991年   61461篇
  1990年   60351篇
  1989年   58347篇
  1988年   54461篇
  1987年   53424篇
  1986年   51148篇
  1985年   48939篇
  1984年   36969篇
  1983年   31887篇
  1982年   19633篇
  1979年   34594篇
  1978年   24490篇
  1977年   20980篇
  1976年   19836篇
  1975年   21678篇
  1974年   25624篇
  1973年   24598篇
  1972年   23347篇
  1971年   21713篇
  1970年   20384篇
  1969年   19342篇
  1968年   18345篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
BACKGROUND: The MR and pathologic features of hippocampal sclerosis (HS) are well described and include volume decrease and T2-weighted signal increase for MRI, and neuron cell loss and gliosis for pathology. OBJECTIVE: To confirm the established correlation between hippocampal volumes and neuron cell counts, and to study the still controversial association between signal change and gliosis. METHODS: The authors studied 44 patients (22 men and 22 women; mean age at surgery, 37 years) with refractory temporal lobe epilepsy. Quantitative assessment of hippocampal volumes and T2 relaxometry, and neuron and glial cell count in the region CA1 and molecular layer of the dentate gyrus was performed. The proportion of glial fibrillary acidic protein (GFAP)-positive glial cells (reactive astrocytes) was indicated. RESULTS: In a stepwise regression, the ipsilateral hippocampal volume was predicted best by the neuron cell count in the dentate gyrus (p = 0.005, r = 0.4). Hippocampal T2 time, however, was predicted best by the glial cell count in the dentate gyrus (p = 0.01, r = 0.4). None of the other cell counts contributed to either model. In the dentate, 31% of the glial cells were reactive astrocytes, whereas in CA1, 5% were reactive. CONCLUSION: The results confirmed the correlation between hippocampal volumes and neuron cell counts. T2-weighted signal increase in the hippocampus was mainly influenced by gliosis in the dentate gyrus, where a high proportion of glial cells show abnormal activity. This activity may reflect changes important in the development of hippocampal epileptogenicity.  相似文献   
992.
INTRODUCTION: Intravascular brachytherapy (IVBT) utilises the percutaneous insertion of a radioactive source to inhibit myointimal hyperplasia in arteries treated by balloon angioplasty or stenting. A systematic review was performed of trials of IVBT in patients with Peripheral Arterial Disease (PAD). METHODS: Search strategy - the reviewers searched Medline, Embase, the Cochrane Peripheral Vascular Diseases Group trials register, DARE, CCT and NHS EED for clinical studies and trials of adjuvant IVBT in PAD. Two reviewers assessed trial quality independently. RESULTS: Fourteen clinical trials were identified by the search, representing five clinical studies (all allocated D for not randomised) and one randomised controlled trial (allocated A). The randomised trial showed a benefit for IVBT compared with placebo (OR 0.35, 95% CI 0.24-0.53). In the non-randomised studies, 12 month cumulative patency rates ranged from 60-87%. There were few technical complications. In the only report involving IVBT and routine concurrent stent insertion acute thrombosis occurred in 7 (21%) of patients. CONCLUSION: Early reports have confirmed the safety and technical feasibility of IVBT. However, follow-up is too short at present to assess the durability and long-term complications of this new therapeutic option.  相似文献   
993.
Since the introduction of in vitro fertilization in 1978, reproductive medicine and its associated scientific fields have developed rapidly. In Germany, progress in this field is impeded by the German Embryo Protection Act. Exemplary are the prohibition of embryo selection and the ban on genetic testing of the pre-implantation embryo. Nevertheless, infertility treatment outcome has to be optimized within the framework of this law, with the aim of making treatment more efficient, lowering the incidence of multiple gestations, making ovarian hyperstimulation safer, as well as reducing the financial costs for the couple.  相似文献   
994.
Mammalian fatty acid synthase (FASE) overexpression has been shown in a number of human malignancies including colonic adenocarcinoma. Since FASE synthesizes only saturated fatty acids, we hypothesized that cancer cells have a greater proportion of long-chain saturated fatty acids. We studied and found an unequivocal increase in saturated C18 fatty acid (stearic acid) in colonic adenocarcinoma compared to adjacent normal colonic mucosa. The increase is even more striking when measured as a ratio of stearic acid to the unsaturated C18 fatty acids (oleic acid and linoleic acid). This change in fatty acid composition of the cancer cells should significantly alter their physical and biological properties. The increase in relative proportion of saturated fatty acids should make the cancer cells more susceptible to cryodamage and measurement of fatty acid composition of cancer cells may help individualize the temperature for cryotherapy. Also, the lipid alterations may affect the structure and functions of lipid rafts, which may enable the cancer cells to affect signaling mechanisms such as those involved in cell growth and apoptosis. Dietary or therapeutic interventions targeting lipid rafts may thus be an option for cancer treatment.  相似文献   
995.
Scurvy is a nondiscriminatory disease process resulting from a nutritional deficiency of ascorbic acid (vitamin C). The severe vitamin deficiency produces a breakdown in the cellular structure of the body. This case report describes a middle-age woman with a history of edema, bruising of the lower extremities, anemia, and severe periodontal disease. Her presentation and medical history are classic for the signs of scurvy. Scurvy is now only uncommonly seen in developed countries, but there are still vulnerable populations whose nutritional status can lead to scurvy. The aim of this report is to help the clinician identify and treat scurvy, a disease that was once feared for its high mortality but is now easily treatable, even in cases that have progressed to multiple organ dysfunction and failure.  相似文献   
996.
997.
The atomic rearrangement cascade that follows the electron-capture decay process in low-Z radionuclides involves X-rays which have high photoelectric interaction probabilities. When the K-shell binding energy of the ionized atom (e.g., hydrogen) is significantly lower than the energy of the X-ray photon, the detector response to a photon-equivalent energy electron and the whole photoionization process are very similar. This is not the case when the scintillator cocktail contains larger atoms (e.g., oxygen and phosphorus in Ultima Gold). For larger Z atoms, the reduced energy of the whole photoionization process is less than the reduced energy of the interacting photon due to the nonlinear effects of ionization quenching. This paper shows the convenience of including a more detailed simulation of the photoionization process in the atomic rearrangement detection model for electron-capture nuclides such as (55)Fe, (51)Cr and (54)Mn. The need for more elaborate atomic rearrangement models is a consequence of the analysis of (125)I data.  相似文献   
998.
999.
Intracranial pathology is a common and important complication in extremely low birth weight babies. Lenticulostriate vasculopathy (LSV) is an abnormal finding on cranial ultrasounds of sick babies and has been associated with congenital infection, chromosomal aberration and twin-to-twin transfusion. We describe a previously unreported situation of LSV being detected in both donor and recipient twin. This pair of monochorionic, diamniotic twins was admitted to the Neonatal Intensive Care Unit at 28 weeks of gestation. The mother underwent an emergency caesarean section because ultrasound and Doppler studies showed stage III twin-to-twin transfusion syndrome. The first twin weighed 998 g and second twin weighed 600 g. The first twin had an uneventful stay, whereas the second twin needed prolonged continuous positive airway pressure and indomethacin for patent ductus arteriosus. Both of them developed LSV. The clinical significance of this condition on the neuro-developmental outcome of a neonate has not yet been fully determined.  相似文献   
1000.
Static analysis with finite element of a realistic femur nail bone-implant system in a typical proximal femoral fracture under physiological load bearing situations provides results for stress, displacement and strain. The question to be answered is, if simulation with the finite element analysis is able to explain biomechanically clinical observed patterns of failure. Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. Next steps were to unite the bone structure with the Proximal Femoral Nail and to model two relevant fractures (31-A2.2 and A2.3 according AO). After modelling of geometry, isotropic material behaviour and load application numeric calculation of the femur-nail system with FE-software was performed. FE simulation mainly shows an axial dislocation of the femoral head screw with nearly no dislocation of the antirotation screw. This so-called z-effect therefore means: (1) Tilting of the proximal main fragment around the sagittal axis between the screws and (2) relative movement of both screws in the frontal plane. Relative movement of the two screws against each other could be the reason for implant failure, the so called cut out. Furthermore simulation shows different gliding of the screws explaining the so called z-telescoping. The analyzed stress patterns have to be relativized, because isotropic material behaviour of cancellous bone was assumed. Further examinations for this issue are necessary.  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