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   25899篇
  免费   1648篇
  国内免费   80篇
耳鼻咽喉   232篇
儿科学   871篇
妇产科学   481篇
基础医学   3570篇
口腔科学   676篇
临床医学   2878篇
内科学   5437篇
皮肤病学   579篇
神经病学   2686篇
特种医学   742篇
外国民族医学   5篇
外科学   2930篇
综合类   206篇
一般理论   22篇
预防医学   2292篇
眼科学   357篇
药学   1820篇
中国医学   65篇
肿瘤学   1778篇
  2023年   144篇
  2022年   227篇
  2021年   639篇
  2020年   356篇
  2019年   517篇
  2018年   653篇
  2017年   475篇
  2016年   512篇
  2015年   582篇
  2014年   813篇
  2013年   1110篇
  2012年   1675篇
  2011年   1870篇
  2010年   1047篇
  2009年   840篇
  2008年   1607篇
  2007年   1564篇
  2006年   1546篇
  2005年   1512篇
  2004年   1366篇
  2003年   1194篇
  2002年   1126篇
  2001年   592篇
  2000年   570篇
  1999年   510篇
  1998年   264篇
  1997年   200篇
  1996年   206篇
  1995年   175篇
  1994年   184篇
  1993年   153篇
  1992年   377篇
  1991年   304篇
  1990年   288篇
  1989年   251篇
  1988年   204篇
  1987年   191篇
  1986年   187篇
  1985年   179篇
  1984年   138篇
  1983年   111篇
  1982年   90篇
  1981年   94篇
  1980年   78篇
  1979年   119篇
  1978年   79篇
  1977年   59篇
  1974年   61篇
  1973年   63篇
  1972年   80篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
One hundred sixty consecutive patients with histologically confirmed colorectal cancer (advanced disease) without prior chemotherapy were entered in a randomized trial comparing 5-fluorouracil (5-FU) 1,000 mg/m2 intravenously per day for 5 consecutive days in continuous infusion versus cisplatin (CP) 100 mg/m2 on day 1 plus 5-FU as described on days 2 to 6. In both arms, treatment was recycled every 4 weeks. Both groups were well balanced for age, sex, colon or rectal origin, median time between diagnosis to advanced disease, performance status at entry, and visceral involvement. The overall response rate in the combination and in the single arm were 18 and 23%, respectively. There were no differences in time to progression (a median of 17.8 and 14.9 weeks for CP-5-FU and 5-FU, respectively) and in overall survival (a median of 71.2 and 59.6 weeks, respectively). The incidence of grade 3-4 emesis was significantly higher in the CP-containing chemotherapy (p = .00001). Our study has failed to demonstrate any clinical benefit from adding cisplatin to 5-FU in patients with cancer of the colon and rectum.  相似文献   
102.
Between 1982 and 1988, 111 elderly women with breast cancer but without clinical involvement of the axillary lymph nodes underwent wide lumpectomy in a Day Hospital regimen at the National Cancer Institute of Milan. The patients ranged in age from 70 to 92 years (median, 79). An adjuvant treatment was carried out in all but 9 cases: tamoxifen only in 84 cases, tamoxifen plus radiotherapy in 6 cases, radiotherapy alone in 12 cases. The median duration of follow-up was 44 months (range, 30-109 months). Four patients (3.6%) were lost to follow-up. In the remaining 107 patients, 10 local-regional relapses (9.1%) and 7 distant metastases (6.5%) occurred. Six patients died from the disease, 14 from unrelated conditions. This retrospective study showed that selected elderly patients with breast cancers can be treated successfully under local anesthesia on an outpatient basis. The treatment guarantees local control of the disease, meets the favor of elderly women and consequently improves their quality of life.  相似文献   
103.
Five hundred six consecutive cases of ductal infiltrating carcinoma of the breast (T1-T2,N0,M0) were evaluated to define the frequency of peritumoral lymphatic invasion (PLI) and verify its possible prognostic significance. Histologically, PLI was characterized by the presence of neoplastic emboli within vascular lumina lined by recognizable endothelial cells, adjacent to but outside the margins of the carcinoma. In routine histopathologic assessment the frequency of PLI was 68% whereas in a randomly selected group of 234 reviewed cases the frequency rose to 20%. Patients with routinely evaluated PLI had a worse prognosis than those without PLI with reference both to disease-free survival (P = 0.0001) and total survival rates (P = 0.0001). The difference for local recurrences was prognostically highly significant (P = 0.0001) and also significant for the development of metastases (P = 0.0576). In the reviewed material the difference in prognosis between PLI-positive and PLI-negative cases was not confirmed for total survival whereas the significance for the disease-free interval persisted. The assessment of PLI, carried out following strict histopathologic criteria, appears to select a group of node-negative breast cancer patients who have an increased risk of recurrences and might benefit from a treatment different from that reserved for node-negative and PLI-negative patients.  相似文献   
104.
This work describes the design and construction of a device that facilitates the loading of DNA samples onto polyacrylamide gels for detection in the Perkin Elmer/Applied Biosystems (PE/ABI) 373 and 377 DNA sequencing instruments. The device is mounted onto the existing gel cassettes and makes the process of loading high-density gels less cumbersome while the associated time and errors are reduced. The principle of operation includes the simultaneous transfer of the entire batch of samples, in which a spring-loaded air cylinder generates positive pressure and flexible silica capillaries transfer the samples. A retractable capillary array carrier allows the delivery ends of the capillaries to be held up clear of the gel during loader attachment on the gel plates, while enabling their insertion in the gel wells once the device is securely mounted. Gel-loading devices capable of simultaneously transferring 72 samples onto the PE/ABI 373 and 377 are currently being used in our production sequencing groups while a 96-sample transfer prototype undergoes testing.  相似文献   
105.
Summary Neoplastic invasion of the brain parenchyma results in a disruption of the ultrastructure of the blood vessel walls such that serum proteins extravasate into the surrounding tissue, resulting in cerebral edema. The structural changes involved are not well understood, since the pores through which serum constituents pass (permeability routes) in normal barrier vessels and in tumor vessels where the barrier is compromised, have not been extensively explored. In this study we investigate the ultrastructure of human brain microvessels in biopsied samples of control brain tissue and five glioblastoma multiforme tumors. Electron micrographs of a total of 78 vessels were analysed with computer assisted morphometry for ultrastructural evidence of permeability routes. Fenestrations in the endothelium were not seen. Pinocytotic vesicle number and arrangement did not differ significantly from that seen in control brain vessels. Interendothelial junctions with enlarged distensions (which may represent sections through transendothelial channels) were seen in some vessels from most tumors but not in control barrier vessels. In addition, large gaps in the endothelial layer were seen in less than two percent of tumor vessels. In conclusion, glioblastoma multiforme vessels in this study show subtle alterations in vessel morphology from that seen in controls. We suggest that the high vascular permeability and resultant brain edema seen in glioblastoma multiforme tumors is likely due to the presence of channels through interendothelial junctions, and rare but large breaks in the endothelial wall.  相似文献   
106.
The purpose of the studies was to determine how gross physical characteristics of cerebrospinal fluid (CSF) shunts and the cellular proliferative response to shunts contribute to shunt obstruction. Ventricular catheters with round holes, slots, and flanges were implanted into the lateral ventricles of rabbits for 4 weeks. All shunt designs were subject to ingrowth of tissue from the ventricle wall or choroid plexus. There were no qualitative or quantitative differences between normal and hydrocephalic rabbits. Astroglial cells from newborn mice were cultured on shunt catheters for 2 or 4 weeks. The growth of these cells was poor, probably because the cells cannot attach well to the silicone rubber substrate. Contact between the shunt catheter and vascularized brain tissue is the most important factor in the genesis of shunt obstruction.  相似文献   
107.
108.
This study was performed to see whether or not protection of the endothelial cells contributes to the antithrombotic effects of heparin. New Zealand albino rabbits were subjected to jugular vein stasis by single caudal ligation for 2 h. Three treatments were given: saline (control group), heparin (0.2 mg/kg) 5 or 45 min before ligature of the vein. Groups of 6-8 animals were killed at 0, 5, 15, 30 and 120 min. The following parameters were determined: (1) involution and damage of the endothelial cells by scanning and transmission electron microscopy; (2) incidence and weight of thrombi in the lumens of the veins after 2 h stasis, and (3) effects of heparin on APTT and anti-Xa activity. In the control group, stasis caused a considerable involution of the endothelial cells in the first 30 min, followed by fibrin deposition and thrombus generation. Heparin strongly reduced the damage to the endothelial cells, with very evident protection of the cell membranes, and prevented thrombus generation: there were significant decreases in both incidence and weight of thrombi. These effects of heparin were evident both shortly after (maximal anticoagulant effect) and long after (no anticoagulant effect) pretreatment. We think that, under the experimental conditions we used, heparin prevented venous thrombosis at least partially by protection of the endothelial cells, through unknown mechanisms.  相似文献   
109.
The immunohistochemical occurrence of the neurotrophin (NT) proteins nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4), and neurotrophin-3 (NT-3) is shown in the pre-term newborn, infant, and adult human post-mortem cerebellum. The NT-like immunoreactive structures were unevenly distributed and showed regional differences among cerebellar lobules and folia. NGF-, NT-4-, and NT-3-positive neuronal perikarya were observed in all specimens examined. At variance with the other neurotrophins, the BDNF antiserum labelled neuronal cell bodies only in newborn life and infancy, as well as extensive nerve fibre systems, whose density increased with age. The NT-antibodies, tested by Western blot on human cerebellum homogenates, revealed immunoreactive bands corresponding to proteins of heterogenous molecular weight. The results obtained provide a first demonstration of the tissue localization of the NTs in the human cerebellum from perinatal to adult age, thus suggesting their involvement in the development, differentiation and maintenance of the cerebellar connectivity. Codistribution of the four NTs or sets of them was observed in cortical and deep nuclei neurons. Multiple trophic roles for NTs, encompassing the classic target-derived and local mechanisms of support, are envisaged as significant in development, differentiation, and maintenance of the human cerebellar connectivity.  相似文献   
110.
To investigate the influence of glucocorticosteroid therapy on the neonatal blood count, the haematologic data of 68 preterm and term infants, who had received a single dose of 1 mg dexamethasone i.v., were reviewed. White blood cell (WBC) count and platelet count increased after steroid therapy. The increase in WBCs was associated with an increase in the number of neutrophilic granulocytes, whereas the number of eosinophils decreased. We conclude that glucocorticosteroids after the neonatal blood count and influence its value as a diagnostic marker for bacterial infections.  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