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   10434篇
  免费   674篇
  国内免费   23篇
耳鼻咽喉   81篇
儿科学   254篇
妇产科学   207篇
基础医学   1510篇
口腔科学   168篇
临床医学   1137篇
内科学   1996篇
皮肤病学   142篇
神经病学   1051篇
特种医学   387篇
外国民族医学   26篇
外科学   1527篇
综合类   85篇
一般理论   4篇
预防医学   827篇
眼科学   235篇
药学   712篇
中国医学   24篇
肿瘤学   758篇
  2023年   54篇
  2022年   137篇
  2021年   203篇
  2020年   134篇
  2019年   179篇
  2018年   240篇
  2017年   196篇
  2016年   231篇
  2015年   227篇
  2014年   308篇
  2013年   490篇
  2012年   553篇
  2011年   615篇
  2010年   327篇
  2009年   300篇
  2008年   490篇
  2007年   446篇
  2006年   424篇
  2005年   403篇
  2004年   393篇
  2003年   377篇
  2002年   406篇
  2001年   300篇
  2000年   298篇
  1999年   262篇
  1998年   123篇
  1997年   92篇
  1996年   68篇
  1995年   70篇
  1993年   52篇
  1992年   174篇
  1991年   167篇
  1990年   168篇
  1989年   146篇
  1988年   138篇
  1987年   125篇
  1986年   129篇
  1985年   130篇
  1984年   98篇
  1983年   76篇
  1982年   63篇
  1981年   58篇
  1979年   65篇
  1978年   64篇
  1977年   59篇
  1976年   53篇
  1974年   68篇
  1973年   55篇
  1972年   52篇
  1969年   52篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
61.
We developed a clinical neurologic and behavioral scoring system composed of 10 items to measure the post-operative pain levels in infants: (1) sleep during preceeding hour, (2) facial expression of pain, (3) quality of cry, (4) spontaneous motor activity, (5) Spontaneous excitability, (6) flexion of fingers and toes, (7) sucking, (8) global evaluation of tone, (9) consolability and (10) sociability. Using this system, a group of infants ranging from one to seven months in age and undergoing minor surgical procedures was studied. The infants were randomly assigned to two groups: Group I received Fentanyl intravenously (3 g/kg) prior to surgery, and Group II received a placebo. The infants then were studied post-operatively in the recovery room at 30, 60, 90 and 120 min intervals. Over the entire post-operative observation period, 54% of the infants in Group I had satisfactory analgesia compared to 18% in Group II. There were no significant differences in Group I and Group II in oxygenation, carbon dioxide elimination, blood pressure, heart rate or temperature.  相似文献   
62.
Brains were obtained at autopsy from 24 patients with Down's syndrome, ranging in age from 13 to 71 years. Neurofibrillary tangle containing neurones of the hippocampus were stained using a Palmgren silver method and immunocytochemically (PAP) using antisera to paired helical filament protein, human tau protein and ubiquitin, as primary antibody. Counts of cells stained by each method were compared. In patients under 50 years of age, in whom only a limited number of tangle bearing cells were present, the number of profiles visualized with silver, anti-paired helical filament and anti-tau methods were similar. However, in patients over 50 years of age (and in certain of those under 50), in whom numerous tangles were present, the number of cell profiles visualized with silver and anti-paired helical filament methods were still similar though anti-tau detected fewer positive cells. This was because of the increased presence, in such patients, of extracellular tangles which had "lost" anti-tau immunoreactivity. Such data suggest that although tau protein forms a major antigenic determinant of neurofibrillary tangles in Down's syndrome (as it does in Alzheimer's disease) this protein may only decorate the basic paired helical filament protein skeleton, and is removed by macrophagic activity upon neuronal death. In all patients, anti-ubiquitin revealed fewer tangles than any other method. It is possible that ubiquitin may be present only transiently, within tangles perhaps following initial formation and lasting only as long as the normal protein degradation processes remain viable within the diseased neurone.  相似文献   
63.
In order to test whether 4-aminopyridine (4-AP), a potassium channel blocker, may be of therapeutic value in demyelinating neuropathies, a focal tibial nerve conduction block with demyelination was produced in adult rats by an intraneural microinjection of potassium tellurite. Onset and recovery of the lesion were monitored by evoked compound muscle action potentials (CMAP) activated from the proximal and distal nerve one day before and 1, 4, 7, 14, 21 and 28 days after the injection. Intraperitoneal 4-AP (2 mg/kg) or buffered saline were injected prior to the potassium tellurite and 6 days per week for 28 days. The data show that 4-AP is tolerated, it does not prevent conduction block, and only has a modest effect on increasing its recovery from day 4 to 7 (91 % increase in CMAP ratio compared with control of 35%). Recovery is similar by day 28 in 4-AP treated or untreated animals. These results suggest that 4-AP will have limited use in the therapy of subacute demyelinating neuropathies.  相似文献   
64.
In a molecular epidemiological study of lung cancer cases (n = 81) and noncancer controls (n = 67), polycyclic aromatic hydrocarbon (PAH)-DNA adducts were evaluated in peripheral blood leukocytes from all subjects and in a smaller number of lung tissue specimens collected prior to or at surgery. Sister chromatid exchanges (SCE) in lymphocytes were also studied in a subset of cases and controls. Questionnaire, medical record, or tumor registry data provided a family history of cancer, as well as information on cigarette smoking, dietary and occupational exposure to PAHs, and other factors related to SCEs. In both cases and controls PAH-DNA adducts in leukocytes measured by an enzyme-linked immunosorbent assay were not significantly related to age, sex, ethnicity, amount of cigarette smoking, passive smoking, dietary charcoal, or caffeine consumption. Nor did family history of cancer or histological type of cancer significantly affect adduct levels. However, when subjects were stratified by smoking status (current, former, and nonsmoker), lung cancer cases who were current smokers had significantly higher levels of covalent adducts than current smoker controls. A seasonal variation was observed in PAH-DNA binding, with a peak in adduct levels during July-October. This peak corresponds to that seen in a prior study of aryl hydrocarbon hydroxylase inducibility by other investigators. The finding of significant levels of PAH-DNA adducts in former smokers and non-smokers supports an earlier observation that this marker is not smoking specific but reflects a pervasive and variable "background" exposure to PAH. These results are consistent with a genetically determined enhancement of PAH-DNA adduct formation in leukocytes of lung cancer cases which is evident in current smokers. The results in lung tissue are limited by the small number of samples. Adduct levels were not significantly increased in lung tissue of smokers compared with nonsmokers. An inverse linear correlation was seen between adduct values in lung tissue and age of the donors. SCEs were significantly related to pack years of smoking. However, there was no difference in the frequency of SCE between cases and controls; nor were SCE and DNA adducts significantly correlated in this small sample.  相似文献   
65.
Recently, divergent reports on the role of mast cells (MC) in different glomerular diseases have brought our attention to their role in an accelerated model of anti-glomerular basement membrane (GBM) glomerulonephritis (GN). Genetically MC-deficient Kit(W)/Kit(W-v) mice, MC-reconstituted Kit(W)/Kit(W-v) mice and Kit+/+ control mice were subjected to anti-GBM GN. Kit(+/+) mice developed moderate proteinuria and glomerular damage following the induction of anti-GBM nephritis. In contrast, proteinuria and glomerular damage were dramatically increased in MC-deficient Kit(W)/Kit(W-v) mice. MC-reconstituted Kit(W)/Kit(W-v) mice showed proteinuria and glomerular damage comparable to Kit+/+ mice. A significant increase in infiltrating T cells and macrophages was detected in MC-deficient Kit(W)/Kit(W-v) mice as compared to Kit+/+ control mice and MC-reconstituted Kit(W)/Kit(W-v) mice. Accordingly, we observed an increase of TGF-beta1 mRNA in kidneys from Kit(W)/Kit(W-v) mice. Interestingly, we did not detect MC in the kidney using either Giemsa staining or RT-real-time PCR, but MC were found in the regional lymph nodes. Finally, mortality of Kit(W)/Kit(W-v) mice was significantly increased after the induction of anti-GBM GN due to uremia. Our report provides the first direct evidence that MC are protective in anti-GBM GN, possibly by modulating the influx of effector T cells and macrophages to inflammatory sites in the kidney.  相似文献   
66.
67.
W Chen  M Teodorescu  I F McKenzie    E P Mayer 《Immunology》1981,42(2):285-295
Three T-cell subpopulations (T1, T2 and T3) can be identified by their binding of various bacteria (Mayer, Chen, Dray & Teodorescu, 1978). In this work we determined how the three subpopulations identified by their Ly-1, -2 and -3 alloantigens were distributed among the T1, T2 and T3 subpopulations. We found that the T1 subpopulation contained most of the Ly-1+2+3+ cells, that the T2 subpopulation contained some Ly-1+2-3- and some Ly-1-2+3+ cells and that the T3 subpopulation contained the remainder of the Ly-1+2+3+, Ly-1+2-3- and Ly-1-2+3+ cells. Thus the subpopulations identified by their bacterial adherence properties subdivided the three subpopulations identified by their Ly-1, -2 and -3 alloantigens. We also investigated whether the specific cytotoxic T lymphocytes were contained in the T1, T2 and/or T3 cells. We found that essentially all of the cytotoxic T lymphocytes were contained in the T3 subpopulation. Since the T3 cells contained a subpopulation of Ly-1-2+3+ cells the data indicated that essentially all of the cytotoxic T lymphocytes were contained in a subpopulation of Ly-1-2+3+ cells.  相似文献   
68.
The effects of two dermatophytes (Microsporum gypseum and Trichophyton mentagrophytes) and four moulds (Scopulariopsis brevicaulis, Alternaria alternata, Geotrichum candidum and Penicillium spp.) on living keratinocyte cultures were examined in vitro using primary human keratinocytes. Rates of apoptosis of infected cells were determined using a colorimetric TUNEL system which detects the characteristic nuclear DNA fragmentation of apoptotic cells. The cytotoxicity of the individual fungi was tested by quantitatively measuring cytosolic enzyme lactate dehydrogenase, released upon cell lysis, in culture supernatants. Additionally, the cell structures within the infected keratinocytes in cultures were examined by scanning electron microscopy. All of the fungi exhibited high cytotoxicity, whereas the development of only the two dermatophytes and the mould Scopulariopsis brevicaulis resulted in distinctly increased apoptosis. Electron microscopy showed that all fungi studied caused similar alterations in the cell structure, with Microsporum gypseum being the most harmful. Increasing loss of cell adhesion as a consequence of a decreasing number of reticulating cell appendices and a reduced cell plasticity were the most evident alterations.  相似文献   
69.
Octacalcium phosphate (OCP) and Mn(2+)-doped carbonate hydroxyapatite (Mn-CHA) thin films were deposited on pure, highly polished and chemically etched Ti substrates with pulsed laser deposition. The coatings exhibit different composition, crystallinity and morphology that might affect their osteoconductivity. Human osteoblasts were cultured on the surfaces of OCP and Mn-CHA thin films, and the cell attachment, proliferation and differentiation were evaluated up to 21 days. The cells showed a normal morphology and a very good rate of proliferation and viability in every experimental time. Alkaline phosphatase activity was always higher than the control and Ti groups. From days 7 to 21 collagen type I production was higher in comparison with control and Ti groups. The level of transforming growth factor beta 1 (TGF-beta1) was lower at 3 and 7 days, but reached the highest values during following experimental times (14 and 21 days). Our data demonstrate that both calcium phosphate coatings favour osteoblasts proliferation, activation of their metabolism and differentiation.  相似文献   
70.
Telomere length is a well established marker of cellular senescence and thus biological age. Quantitative PCR allows the determination even from very low amounts of tissue by using telomere specific and single copy gene primers. Comparing a directly processed tissue sample to a 4% formaldehyde fixed one showed a significantly reduced efficiency of PCR reactions (mainly in single copy gene experiments) in a storage time-dependent manner resulting in an artificial increase in reported relative telomere length. This effect was not seen when the tissue was stored in RNA later solution. In summary, telomere length determination from formaldehyde fixed material by quantitative PCR is not a reliable method. Unfortunately therefore, many easily accessible tissue samples from pathology laboratories are unsuitable for this technique.  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