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   31357篇
  免费   1930篇
  国内免费   158篇
耳鼻咽喉   349篇
儿科学   447篇
妇产科学   307篇
基础医学   4634篇
口腔科学   933篇
临床医学   3026篇
内科学   7526篇
皮肤病学   459篇
神经病学   3529篇
特种医学   1875篇
外科学   4223篇
综合类   180篇
一般理论   11篇
预防医学   1288篇
眼科学   620篇
药学   1736篇
中国医学   52篇
肿瘤学   2250篇
  2024年   28篇
  2023年   267篇
  2022年   440篇
  2021年   821篇
  2020年   509篇
  2019年   712篇
  2018年   795篇
  2017年   619篇
  2016年   897篇
  2015年   1006篇
  2014年   1260篇
  2013年   1551篇
  2012年   2524篇
  2011年   2528篇
  2010年   1519篇
  2009年   1361篇
  2008年   2243篇
  2007年   2251篇
  2006年   2157篇
  2005年   2030篇
  2004年   1773篇
  2003年   1662篇
  2002年   1558篇
  2001年   272篇
  2000年   202篇
  1999年   289篇
  1998年   308篇
  1997年   231篇
  1996年   166篇
  1995年   152篇
  1994年   124篇
  1993年   93篇
  1992年   71篇
  1991年   73篇
  1990年   46篇
  1989年   73篇
  1988年   44篇
  1987年   39篇
  1986年   41篇
  1985年   42篇
  1984年   32篇
  1983年   41篇
  1982年   38篇
  1981年   32篇
  1980年   27篇
  1975年   24篇
  1938年   24篇
  1937年   30篇
  1936年   25篇
  1935年   35篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Vitiligo is a skin disease with a worldwide prevalence ranging from 0.5% to 4%. Conservative therapies include photochemotherapy, phototherapy with UVB radiation (broadband UVB 290–320 nm, narrow band UVB 311 nm), systemic steroids and pseudocatalase. Modern therapeutic options include treatment with topical immunomodulators (tacrolimus, pimecrolimus), analogues of vitamin D3, excimer laser and surgery/transplantation. Our analysis compares these therapies for vitiligo and the evidence levels supporting their effectiveness. Conclusions: The face and neck respond best to all therapeutic approaches, while the acral areas are least responsive. For generalized vitiligo, phototherapy with UVB radiation is most effective with the fewest side effects; PUVA is the second best choice.Topical corticosteroids are the preferred drugs for localized vitiligo. They may be replaced by topical immunomodulators which display comparable effectiveness and fewer side effects.The effectiveness of vitamin D analogues is controversial with limited data. Surgical therapy can be very successful, but requires an experienced surgeon and is very demanding of time and facilities, thus limiting its widespread use. L-phenylalanine therapy appears effective on the face but enjoys neither widespread use nor extensive data support. No single therapy for vitiligo can be regarded as the most effective as the success of each treatment modality depends on the type and location of vitiligo.  相似文献   
52.
Despite decreasing mortality rates, morbidity is still high after pancreatic head resection. Comparative data in the United States and Europe show a relationship between hospital volume and mortality. Treatment strategies vary frequently, partially because of the lack of evidence-based data. We performed a multi-institutional analysis in Germany evaluating current numbers, indications, techniques, and complication rates of pancreatic head resection. Questionnaires were completed by seven high-volume surgical departments regarding quantitative and qualitative aspects of pancreatic head resections in the period from 1999 to 2004 (five prospective and two retrospective institutional databases). A total of 1454 pancreatic head resections (944 for malignancy) were reported. Mean annual hospital volume ranged from 14 to 52 (10 to 43 in malignancy). Mortality was between 1.1% and 4.8%, morbidity was between 24% and 46%, and pancreatic leakage was between 9% and 20%. In malignant disease, all centers perform standard lymphadenectomy and regard arterial infiltration as a contraindication for resection. However, the rate of portal vein resection varied from 0% to 28%. No consensus is seen on the type of surgery for malignancy and chronic pancreatitis. After resection for pancreatic cancer less than one fourth of the patients receive adjuvant therapy. The results of our analysis in Germany confirm that pancreatic head resection can be performed with low mortality in specialized units. Variations in indications, operative technique, and perioperative care may demonstrate the lack of evidence-based data and/or personal and institutional experience. The low number of patients receiving adjuvant therapy after resection of pancreatic cancer suggests that more efforts must be made to establish novel adjuvant therapies under randomized study conditions. Presented at the Forty-Sixth Annual Meeting of The Society for Surgery of the Alimentary Tract, Chicago, Illinois, May 14–18, 2005 (oral presentation).  相似文献   
53.
The aim of this study was to estimate costs accrued by the health care of children with asthma in comparison to children with atopic eczema and seasonal rhinitis and to investigate cost determinants. From the multicenter cohort study (MAS-90), we selected children with an asthma, atopic eczema and/or seasonal rhinitis diagnosis during the first 8 years of life, and overall 8-year health care utilization was estimated retrospectively by reviewing medical records. Asthma treatment (n = 76) incurs an average cost of US$ 627 per year, 44% due to hospital stays. Atopic eczema treatment (n = 91) cost on average US$ 219 and seasonal rhinitis (n = 69) US$ 57 per year. In asthma and atopic eczema, costs increase significantly with disease severity. Allergy diagnostics use accounts for only 1% of total costs. Costs for asthma and atopic eczema treatment are highest in those years when topical steroids are used for the first time, but decrease with every further year of steroid use. A remarkable 25% of asthmatic children with severe symptoms were not treated according to national guidelines, so that most steroid treatment was initiated during the first hospital stay. In the case of asthma, total direct costs increased until the 3rd year of the disease, and then decreased with further years of diagnosis, while steroid use continued to increase. These results indicate a 'learning effect' in the treatment of asthma and atopic eczema for each patient as well as considerable cost-saving potential by preventing severe asthma. Moreover, the importance of considering cost-driving factors and using cohort or longitudinal designs in cost-of-illness approaches is emphasized.  相似文献   
54.
CASE REPORT: The reported female patient underwent sub-total resection of an intra-medullary cervicothoracic astrocytoma classified as WHO grade II in 1984 at the age of 18 months and received local irradiation. In 1989, a local recurrence was diagnosed and a partial resection was performed. Sixteen years later, a small recurrent cervicothoracic tumour was found and spinal seeding to the equine nerve roots and the left cerebellar cortex was apparent on MRI. The patient was implanted with a ventriculoperitoneal shunt for a pseudo-tumour cerebri producing papilloedema, which eventually lead to amaurosis. After an extended biopsy, the invasive lumbosacral tumour was classified as glioblastoma multiforme. Two months later, the patient died after rapid progression of the caudal cranial nerve dysfunction. DISCUSSION AND CONCLUSION: Anaplastic progression and dissemination of spinal astrocytomas even two decades after initial diagnosis and treatment are rare. Therapies and diagnostic follow-up strategies are discussed.  相似文献   
55.
OBJECTIVE: To assess the impact of the scalp site on the biological effects of TMS. METHODS: We performed high-resolution, three-dimensional whole head magnetic resonance imaging (MRI) in a healthy subject, systematically measured the scalp-to-cortex distance across the head and calculated the resulting electric field in the superficial cortex. RESULTS: The variability in scalp-to-cortex distance led to differences in calculated cortical electric field strengths of a factor of two. A major portion of this variability was explained by a lateral to medial gradient with scalp-to-cortex distances being greatest close to the midline and smallest towards the temporal coordinates. CONCLUSIONS: Because of the medio-lateral gradient in scalp-to-cortex distance interventions tailored on the basis of effects of TMS in the motor system will systematically induce stronger than expected electric currents when performed laterally to the motor spot. SIGNIFICANCE: The biological effects of TMS outside the motor spot may be markedly different from those observed in the motor system and this should be taken into account to optimize TMS for the evaluation or treatment of neuropsychiatric disorders.  相似文献   
56.
To determine if transforming growth factor alpha (TGFα) pretreatment protects hair cells from aminoglycoside induced injury by modifying their intracellular calcium concentration, we assayed hair cell calcium levels in organ of Corti explants both before and after aminoglycoside (i.e. neomycin, 10−3M) exposure either with or without growth factor pretreatment. After TGFα (500ng/ml) treatment, the intracellular calcium level of hair cells showed a five-fold increase as compared to the levels observed in the hair cells of control cultures. After ototoxin exposure, calcium levels in hair cells of control explants showed an increase relative to their baseline levels, while in the presence of growth factors pretreatment, hair cells showed a relative reduction in calcium levels. Pretreatment of organ of Corti explants afforded significant protection of hair cell stereocilia bundle morphology from ototoxic damage when compared to explants exposed to ototoxin alone. This study correlates a rise in hair cell calcium levels with the otoprotection of hair cells by TGFα in organ of Corti explants.  相似文献   
57.
Two recently discovered genes, the recombination activating genes 1 and 2 (RAG-1 and RAG-2), are necessary to perform variable (V), diversity (D), and joining (J) recombination. They synergistically activate VDJ recombination to generate immunocompetent lymphocytes. Disruption of either gene results in a maturation arrest at a very early B and T cell progenitor stage. Expression and downregulation of RAG's are closely associated with interleukin 7, sIgM and TCR-CD3 complex, respectively. Assessment of RAG mRNA expression is a valuable marker in identifying the genotypic maturation status of leukemias and lymphomas. Persistent RAG expression in otherwise mature lymphoid proliferations may explain puzzling biological and clinical observations such as multiple rearrangements in lymphomas with a mature phenotype. Lack of RAG expression in Hodgkin's disease with abundant Reed-Stern-berg cells is consistent with a mature phenotype of the latter. Availability of a anti-RAG-1 monoclonal antibody in the near future will facilitate RAG analysis of lymphomas.  相似文献   
58.
The pharmacokinetic behaviour of the 131-iodine-labelled title compound 3 * and its metabolites in mice was investigated. A two phase, 1st order elimination profile was observed. The second phase is very slow leaving about 35% of radioactivity in the mice even 100h after i.v. injection, because of high affinity to liver and spleen, caused by strong binding of oligoamines to phospholipids of liver and blood cell membranes. The blood-brain-barrier is not passed. No deep compartments were observed. The doses necessary for antithrombotic effects in vivo were calculated from the blood levels to be 20.5–39.7 μmol/kg for a time interval of 1–6 h after administration.  相似文献   
59.
The metabolic fate of the benzodiazepine antagonist RO 15-1788 labelled with 11C was studied in plasma from human subjects after intravenous administration in connection with positron emission tomography. Ro 15–1788 and its metabolites were separated by thin-layer chromatography and the radioactivity in the different compounds was determined. 11C-Ro 15–1788 was extensively and rapidly metabolised to the corresponding free acid. At 36 minutes after administration only 50% of the radioactivity in plasma represented unchanged compound.  相似文献   
60.
Purpose. The present investigation was done to study the intestinal absorption of three oxytocin peptide analogues and to elucidate the role of pancreatic juice on their absorption. Methods. In conscious chronically catheterized pigs (6–8 weeks of age) plasma concentration of the peptides, [Mpa1, D-Tyr(Ethyl)2, Thr4, Orn8]-oxytocin (F314), [Mpa1, D-Tyr(Ethyl)2, Val4, D-Arg8]-oxytocin (CAT), and [Mpa1, D-Tyr(Ethyl)2, Thr4, Orn8, desGly9, carba6]-oxytocin (F327) after intraduodenal administration, during presence or diversion of the pancreatic juice via a pancreatic duct catheter, were determined by radioimmunoassay. The stability of the peptides to degradation was determined in vitro by incubation with activated pancreatic juice, chymotrypsin or trypsin, followed by reversed phase HPLC analyses. Results. All peptides were absorbed with a bioavailability of about 0.5% in the presence of pancreatic juice, but increased to 1.0%, 2.1%, and 13.5% for F314, CAT, and F327, respectively, when the pancreatic juice was diverted from the intestine. After incubation with pancreatic juice 95% of F314, 98% of F327, and 100% of CAT was found intact. When incubated with trypsin CAT remained intact while F314 and F327 were degraded by 54% and 46%, respectively. Incubation with purified chymotrypsin did not degrade the test peptides. Conclusions. The results indicate that the increased absorption of peptides observed under conditions of diverted pancreatic juice cannot only be explained by the absence of pancreatic enzymes, but also by changed absorptive properties in the gastrointestinal tract.  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