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   4406篇
  免费   404篇
  国内免费   5篇
耳鼻咽喉   31篇
儿科学   100篇
妇产科学   63篇
基础医学   536篇
口腔科学   110篇
临床医学   396篇
内科学   1050篇
皮肤病学   56篇
神经病学   517篇
特种医学   457篇
外科学   456篇
综合类   60篇
一般理论   3篇
预防医学   392篇
眼科学   31篇
药学   209篇
中国医学   5篇
肿瘤学   343篇
  2022年   31篇
  2021年   67篇
  2020年   36篇
  2019年   72篇
  2018年   83篇
  2017年   77篇
  2016年   68篇
  2015年   85篇
  2014年   126篇
  2013年   166篇
  2012年   181篇
  2011年   207篇
  2010年   171篇
  2009年   146篇
  2008年   213篇
  2007年   206篇
  2006年   173篇
  2005年   174篇
  2004年   159篇
  2003年   135篇
  2002年   158篇
  2001年   146篇
  2000年   132篇
  1999年   147篇
  1998年   80篇
  1997年   69篇
  1996年   75篇
  1995年   66篇
  1994年   56篇
  1993年   53篇
  1992年   110篇
  1991年   94篇
  1990年   112篇
  1989年   89篇
  1988年   80篇
  1987年   69篇
  1986年   66篇
  1985年   65篇
  1984年   51篇
  1983年   39篇
  1982年   37篇
  1981年   46篇
  1980年   39篇
  1979年   38篇
  1978年   31篇
  1977年   27篇
  1975年   29篇
  1974年   31篇
  1973年   26篇
  1971年   23篇
排序方式: 共有4815条查询结果,搜索用时 31 毫秒
71.
Compromising alterations in villus-crypt structure are common in pigs postweaning. Possible contributions of local inflammatory reactions to villus-crypt alterations during the weaning transition have not been described. This study evaluated local inflammatory responses and their relationship with morphological changes in the intestine in 21-d-old pigs (n = 112) killed either at weaning (Day 0) or 0.5, 1, 2, 4 or 7 d after weaning to either milk- or soy-based pelleted diets. Cumulative intake averaged <100 g during the first 2 d postweaning, regardless of diet. During this period of weaning anorexia, inflammatory T-cell numbers and local expression of the matrix metalloproteinase stromelysin increased while jejunal villus height, crypt depth and major histocompatibility complex (MHC) class I RNA expression decreased. Upon resumption of feed intake by the fourth d postweaning, villus height and crypt depth, CD8(+) T cell numbers, MHC class I RNA expression and local expression of stromelysin returned to Day 0 values. Together the results indicate that inadequate feed intake during the immediate postweaning period may contribute to intestinal inflammation and thereby compromise villus-crypt structure and function.  相似文献   
72.
Levodopa is still the mainstay of the treatment of Parkinson's disease. Limitations of levodopa therapy have led to development of numerous therapeutic approaches at the level of levodopa/dopamine metabolism, dopamine receptors, dopamine transporter, and other neurotransmitter systems. New insights into the pathophysiology of Parkinson's disease have led to the promising concepts of neuroprotection and neurorestoration. In daily practice therapeutic management of Parkinson's disease is still symptomatic.  相似文献   
73.
Retrieval from long-term memory in patients with brain injuries was investigated with a memory scanning paradigm (Conway & Engle, 1994), that allows dissociation of scanning processes within short-term memory and memory retrieval processes from long-term memory. The study focused on the influence of brain injury on memory retrieval processes that are assumed to be automatic. Thirteen patients with memory impairment and 13 healthy matched control subjects were tested. In general, patients showed increased reaction times, but they showed set size independent retrieval from long-term memory indicating preserved automatic retrieval processes. In a subgroup of patients with more severe memory deficits, however, automatic retrieval processes appeared not to be intact. Learning profiles of the patients were characterized by smaller item chunks, indicating differences in the process of information acquisition.  相似文献   
74.
BACKGROUND: Local recurrence and death from metastases are occasional, but consistent, themes in reports of patients with phyllodes tumours. Factors that might contribute to these outcomes were sought. METHODS: Data from 38 patients with a phyllodes breast tumour were reviewed retrospectively, reclassifying the pathological material using the Pietruszka and Barnes criteria. RESULTS: At a median of 12 months, nine patients had developed a local recurrence and four had died from metastases. Following local excision in 24 patients (for diagnosis in 13, for 'fibroadenoma' in nine and for phyllodes tumour in two patients), 13 had no further surgery and five had local recurrence (three of eight benign tumours, two of two malignant tumours). Wide local excision or mastectomy in 18 patients was followed by four recurrences (one of eight borderline tumours, three of ten malignant tumours). All patients with recurrence had margin involvement on histological examination, but not all patients with margin involvement developed recurrence. Lack of statistical correlation between local recurrence and age, delay, size, grade or type of surgery was confounded by selection bias for more extensive surgery for malignant tumours. Death correlated with size (P = 0.05) and grade (P = 0.03) of tumour. CONCLUSION: Inadequate preoperative diagnosis ('fibroadenoma' or failure of triple assessment) frequently led to local excision with positive margins. Without revision this often resulted in local recurrence. Local recurrence of any grade was usually followed by further recurrence. Death was related to tumour size and histological grade, confirming these as prognostic factors.  相似文献   
75.
Shortly after birth, an otherwise healthy infant developed eye deviation and ptosis due to a hamartomatous lesion of the interpeduncular segment of the right oculomotor nerve. The left nerve became similarly involved when the child was 1.5 years of age. Direct nerve repair was not possible. Instead, the trochlear nerve was divided and its proximal end was attached to the distal end of the third nerve. Elevation of the upper eyelid and partial adduction of the eye developed gradually over the ensuing 3 to 5 months. Both functions were lost after an additional 2 months, presumably as a result of tumor recurrence or neuroma formation. This case report shows that surgically created fourth-third cranial nerve communication is feasible and may merit consideration under similar circumstances.  相似文献   
76.
OBJECTIVE: To compare the sensitivity of WOMAC and the two added dimensions Sport and Recreation Function and Knee Related Quality of Life in subjects with radiographic knee OA to that in controls. To study the influence of age on the reported outcomes. DESIGN: Outcomes were compared between subjects having had meniscectomy 21 years ago and which at time of follow-up had definite radiographic OA (N=41, mean age 57), and age- and sex-matched controls without radiographic OA (N=50, mean age 53). For the purpose of studying the impact of age, the groups were divided in two age groups, younger and older than 50 years, respectively. Close to 50% of both groups reported current physical activity levels of at least recreational golf, dancing, hiking, etc. Symptoms and function were assessed by WOMAC Osteoarthritis Index and the added dimensions Sport and Recreational Function (Sport/Rec) and Knee Related Quality of Life (QOL). A percentage score was calculated, 0 indicating extreme knee problems and 100 indicating no knee problems. RESULTS: The control group had mean scores of 88-98 for the different dimensions. The OA group scored significantly lower in all dimensions (P< 0.0001). The most discriminative dimensions in both age groups were Sport/Rec and QOL with mean scores of 52 and 59 (ranges 0-100). CONCLUSION: The dimensions Sport and Recreation Function, and Knee Related QOL were highly sensitive and discriminant outcomes in both age groups and should be assessed in addition to WOMAC in subjects with post-traumatic osteoarthritis of the knee.  相似文献   
77.
OBJECTIVE: To investigate whether intake of Lactobacillus acidophilus strain L-1 lowers serum cholesterol in healthy men and women. DESIGN: Randomised, placebo-controlled parallel trial. SETTING: Subjects were free-living. Blood sampling and distribution of yoghurts were administered at a local hospital. SUBJECTS: Seventy-eight adult men and women with cholesterol levels of 3.9-7.8 mmol/L (mean +/- s.d., 5.4+/-0.7). INTERVENTIONS: Subjects consumed 500 mL of control yoghurt daily for two weeks. They were then randomly allocated to receive 500 mL per day of control yoghurt or of yoghurt enriched with Lactobacillus acidophilus L-1 for another six weeks. The yoghurts were spiked with a trace of lithium; compliance as assessed by plasma lithium was excellent. RESULTS: Energy and nutrient intake was constant, and identical for the two groups. Mean body weight was stable. Baseline blood lipid concentrations in the control and treatment groups were highly similar. The effect of consumption of Lactobacillus acidophilus L-1 vs. control on total cholesterol was -0.02 mmol/L (95% CI, -0.18-0.15) after three weeks and 0.04 mmol/L (95% CI, -0.12-0.20) after six weeks. Serum LDL and HDL-cholesterol and triacylglycerol levels were also unaffected. CONCLUSIONS: Yoghurt enriched with Lactobacillus acidophilus L-1 does not lower serum cholesterol in men and women with normal to borderline high cholesterol levels.  相似文献   
78.
Adhesion molecules in lymphoma metastasis   总被引:4,自引:0,他引:4  
Summary Recently, many surface proteins of lymphoid cells that mediate adhesion to other cells and extracellular matrix have been identified. Several of these cellular adhesion molecules (CAM) are also expressed by metastatic lymphoma cells and may mediate adhesion to tissue components during the metastatic process. Correlations observed between expression of certain CAM, like MEL-14 and CD44, and particular patterns of spread, support this notion, but conclusive evidence is scarce.We have used T-cell hybridomas to study the mechanisms of wide-spread lymphoid metastasis. The results obtained with this model are reviewed here. The advantages are that a large number of genetically similar cell lines can be generated, which can be grouped in large panels of highly invasive and non-invasive cells. Invasiveness of these cells in hepatocyte and fibroblast monolayers correlates with exprimental metastasis.Lymphoid CAM that are potentially involved in metastasis are reviewed. Several of these CAM are not, or not consistently, expressed by the invasive T-cell hybridomas, indicating that they are not indispensable. Notably, some of the CAM involved in the onset of an immune response or in migration into inflamed tissues, like ICAM-1 and VLA-4, and the homing receptors MEL-14 and LPAM-1 do not seem to be involved. CAM that are consistently expressed by the T-cell hybrids include LFA-1, the beta-1 integrin subunit CD29, CD31 (PECAM-1) and CD44 (Hermes homing receptor).We have generated considerable evidence that LFA-1 is required for efficient metastasis of T-cell hybrids, based on the behavior of LFA-1-deficient mutants and revertants. High levels of LFA-1 are required. The relevant counterstructure is probably ICAM-2 rather than ICAM-1. Preliminary results suggest that also a beta-1 integrin, possibly VLA-5, plays a role. Finally, we summarize evidence indicating that CD31 and CD44 are primary candidates for involvement in metastatic spread of T-cell hybridomas.  相似文献   
79.
To clarify where and how beta-amyloid begins to deposit in senile plaques, we examined the ultrastructural localization of amyloid beta protein (Abeta) in diffuse plaques of brains with hereditary cerebral hemorrhage with amyloidosis-Dutch type. Alzheimer disease (AD), and from nondemented aged subjects. Serial ultrathin sections of osmium-plastic blocks were immunogold-labeled for Abetax-42 (Abeta42), and sections on grids were observed under the electron microscope (EM) after observing the exact localization of the diffuse plaques in sections on glass slides by the reflection contrast microscope. Abeta42 deposition, which was decollated with gold particles, appeared in 3 forms in all subjects under the EM: 1) Scattered small bundles of amyloid fibrils between cell processes, frequently seen in the densely stained area of diffuse plaques. 2) Scattered small foci of nonfibrillar materials between cell processes as a relatively minor form. 3) Abeta42 on a part of the cell surface plasma membrane of normal appearing cell processes, a major form in weakly immunostained areas. The last form was not associated with degenerative neurites or reactive glia. Abeta42 deposition on the cell surface plasma membrane appears to be an initial event in diffuse plaques, and then it develops into amorphous/fibrillar amyloid between cell processes.  相似文献   
80.
Choriocarcinoma was diagnosed in a 77-year-old woman with an acute massive, painless hematuria. One year after anterior pelvic exenteration and ileal conduit, the beta-human chorionic gonadotropin level increased to 934 mIU/mL without any sign of tumor progression. After six courses of chemotherapy (vincristine, actinomycin, and cyclophosphamide), the beta-human chorionic gonadotropin levels returned to normal. To our knowledge, this is the fourth case of pure choriocarcinoma in the bladder, with the longest survival time of 33 months so far.  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