全文获取类型
收费全文 | 20269篇 |
免费 | 1807篇 |
国内免费 | 451篇 |
专业分类
耳鼻咽喉 | 162篇 |
儿科学 | 561篇 |
妇产科学 | 363篇 |
基础医学 | 2529篇 |
口腔科学 | 641篇 |
临床医学 | 1827篇 |
内科学 | 3560篇 |
皮肤病学 | 376篇 |
神经病学 | 848篇 |
特种医学 | 618篇 |
外国民族医学 | 2篇 |
外科学 | 2264篇 |
综合类 | 1966篇 |
现状与发展 | 5篇 |
一般理论 | 8篇 |
预防医学 | 2701篇 |
眼科学 | 247篇 |
药学 | 1880篇 |
13篇 | |
中国医学 | 1040篇 |
肿瘤学 | 916篇 |
出版年
2024年 | 72篇 |
2023年 | 587篇 |
2022年 | 909篇 |
2021年 | 1294篇 |
2020年 | 1066篇 |
2019年 | 1484篇 |
2018年 | 1303篇 |
2017年 | 1045篇 |
2016年 | 703篇 |
2015年 | 801篇 |
2014年 | 1185篇 |
2013年 | 1638篇 |
2012年 | 890篇 |
2011年 | 982篇 |
2010年 | 830篇 |
2009年 | 725篇 |
2008年 | 765篇 |
2007年 | 669篇 |
2006年 | 552篇 |
2005年 | 507篇 |
2004年 | 433篇 |
2003年 | 357篇 |
2002年 | 307篇 |
2001年 | 241篇 |
2000年 | 225篇 |
1999年 | 202篇 |
1998年 | 202篇 |
1997年 | 129篇 |
1996年 | 158篇 |
1995年 | 163篇 |
1994年 | 151篇 |
1993年 | 94篇 |
1992年 | 79篇 |
1991年 | 90篇 |
1990年 | 65篇 |
1989年 | 75篇 |
1988年 | 56篇 |
1987年 | 53篇 |
1986年 | 45篇 |
1985年 | 174篇 |
1984年 | 178篇 |
1983年 | 147篇 |
1982年 | 154篇 |
1981年 | 140篇 |
1980年 | 126篇 |
1979年 | 106篇 |
1978年 | 85篇 |
1977年 | 72篇 |
1976年 | 57篇 |
1975年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
It has been recently reported that neutrophils are involved in the regulation of NK cell activity. However, the mechanism of such regulation is unclear. The present study was designed to investigate the mechanisms involved in the regulation of NK cytotoxicity by human neutrophils. The role of indomethacin, an anti-inflammatory drug, in this interaction was studied. NK cells were purified from peripheral blood obtained from normal individuals. NK cell cytotoxicity was tested on K 562 cell line by Cr release assay. Autologous neutrophils obtained from peripheral blood were stimulated by opsonized zymosan either in the presence or absence of indomethacin. The role of neutrophil supernatant containing oxygen radicals and prostaglandins on NK cytotoxicity was examined. It was shown that supernatants from stimulated neutrophils significantly inhibited (P less than 0.05) the autologous NK cell cytotoxicity. The presence of indomethacin in the in vitro reaction mixture, or given orally to donors, partially or completely abolished the inhibitory effect of neutrophil supernatant. Indomethacin inhibited prostaglandin E2 release, and luminol-enhanced, myeloperoxidase-mediated chemiluminescence of activated PMN. Diafiltration of neutrophil supernatant showed that the inhibitory activity was present in the fraction containing molecules lower than 5,000 daltons. In conclusion, our findings indicate that down-regulation of NK cytotoxicity is mediated by prostaglandins produced by stimulated neutrophils and possibly by oxygen radicals. 相似文献
62.
63.
64.
A monoclonal antibody (RH1-38) which blocks multiple systems of cell-mediated cytotoxicity was functionally characterized. RH1-38 specifically blocks, in the absence of complement, natural killer (NK) activity (K562 targets) without any effect on NK-K562 conjugate formation. Kinetic studies suggested that the antibody blocks a step that occurs 30-120 min after effector populations are mixed with target cells. Single-cell cytotoxicity assays in agarose, combined with standard 51Cr release assays and Michaelis-Menten analysis revealed that RH1-38 markedly decreases Vmax and the number of active NK cells, again without any effect on the number of target-binding cells. The maximum recycling capacity was usually decreased, but in some experiments unchanged, in the presence of the monoclonal antibody. RH1-38 inhibited equally well whole peripheral blood mononuclear leukocytes (PBML), Percoll-fractionated lymphocytes enriched for NK activity, and interferon (IFN)-boosted NK activity. PBML exposed to RH1-38 and then washed mediated depressed NK activity which was partially reversed by subsequent treatment with IFN. These studies are most consistent with the hypothesis that RH1-38 inhibits a step late in the NK cytolytic mechanism rather than through an effect on conjugate formation. The primary effect is probably not on the IFN-generating or boosting mechanism, but a secondary effect on IFN-related mechanisms cannot be ruled out. Inhibition through an effect on a small lymphocyte modulator of NK activity is also unlikely but not rigorously excluded. Thus, RH1-38 appears to inhibit NK activity through a direct effect on NK effector cells, probably by interfering with a cell-surface molecule which is important in the expression of NK activity. The companion paper demonstrates that this monoclonal antibody immunoprecipitates a molecule which is very similar or identical to the LFA-1 antigen. Thus, RH1-38 recognizes either a novel epitope on the LFA-1 molecule or alternatively a distinct, functional killer cell surface molecule. The epitope appears to be involved in a late step in the cytolytic mechanism, possibly part of the effector cell lytic machinery. 相似文献
65.
G Hagner 《Immunobiology》1984,167(4):389-397
The erythroleukemic K562 cell line was induced to erythroid differentiation by a variety of agents, including hemin, bleomycin, and cytosine arabinoside. The sensitivity of induced cells to binding and lysis by non-sensitized peripheral blood mononuclear cells (MNC) in agarose was studied in relation to the target cell division rate. Differentiated K562 cells formed a lower proportion of conjugates with MNC, when compared with non-induced controls. The reduction correlated significantly with the level of differentiation, irrespective of the inducer and the proliferative status. The differentiation-induced alterations of lysis, however, were strongly influenced by the modification of target cell growth rate which was caused by the differentiating agent. These data suggest that target cell differentiation has distinct effects upon the steps of recognition and lysis by natural killer cells. 相似文献
66.
Transient aphasia with lithium toxicity 总被引:1,自引:0,他引:1
J M Krakower 《Psychosomatics》1978,19(1):25-26
A case of transient aphasia in a 48-year-old woman is described. The aphasia occurred when progressive renal insufficiency led to accumulation of lithium to toxic levels, and was associated with well-known clinical findings of lithium toxicity. 相似文献
67.
Yewande E. Odeyemi ODene Lewis Julius Ngwa Kristen Dodd Richard F. Gillum Alem Mehari 《Journal of the National Medical Association》2019,111(1):94-100
Purpose
There is presently an ongoing debate on the relative merits of suggested criteria for spirometric airway obstruction. This study tests the null hypothesis that no superiority exists with the use of fixed ratio (FR) of forced expiratory volume in the first second (FEV1)/forced vital capacity (FVC) < 0.7 versus less than lower limit predicted (LLN) criteria with or without FEV1 <80% predicted in regards to future mortality.Methods
In 1988–1994 the Third National Health and Nutrition Examination Survey (NHANES III) measured FEV1 and FVC with mortality follow-up data through December 31, 2011. For this survival analysis 7472 persons aged 40 and over with complete data formed the analytic sample.Results
There were a total of 3554 deaths. Weighted Cox proportional hazards regression revealed an increased hazard ratio in persons with both fixed ratio and lower limit of normal with a low FEV1 (1.79, p < 0.0001), in those with fixed ratio only with a low FEV1 (1.77, p < 0.0001), in those with abnormal fixed ratio only with a normal FEV1 (1.28, p < 0.0001) compared with persons with no airflow obstruction (reference group). These remained significant after adjusting for demographic variables and other confounding variables.Conclusions
The addition of FEV1 < 80% of predicted increased the prognostic power of the fixed ratio <0.7 and/or below the lower limit of predicted criteria for airway obstruction. 相似文献68.
69.
M ULANOVA M HAHN-ZORIC Y L LAU A LUCAS L HANSON 《Clinical and experimental immunology》1996,105(3):422-428
The Chinese population in Hong Kong has a low incidence of invasive Haemophilus influenzae type b (Hib) disease, as well as carriage of the microorganism. Likely stimuli for the natural antibodies to Hib, which might protect against Hib infection, are cross-reactive antigens of bacteria like Escherichia coli K100. Our aim was to determine the isotype and idiotype distribution and cross-reactivity of natural antibodies against Hib capsular polysaccharide (CP) in healthy Hong Kong Chinese. Titration of 20 sera by ELISA showed IgG antibodies reacting with Hib CP in all individuals. The antibodies were mainly IgG2, and their avidity index ranged widely. Isoelectric focusing (IEF) combined with immunoblotting showed patterns of IgG2 antibody clones against the CP of Hib and E. coli K100 which were similar in 10 cases. Absorption with Hib CP only eliminated some bands in two sera. Absorption with K100 CP did not remove any anti-Hib CP bands. In three sera additional clones of antibodies reacting to K100 CP only, disappeared after absorption with this CP. Spectrotypic analyses of IgG antibodies reacting with anti-Hib idiotype 1 (Id-1) revealed stronger IEF patterns with bands in differing locations compared with anti-Hib CP antibodies. The strong reactivity of serum IgG, IgA and IgM antibodies with monoclonal anti-Hib Id-1 was confirmed by ELISA. This reactivity was not abolished after absorption of the sera with either Hib CP, or K100 CP. The data indicate a high prevalence of Id-1 among Hong Kong Chinese. However, only one individual had Id-1 antibodies specific for Hib CP, judging from absorption experiments. Others had much lower activity of Id-1 anti-Hib CP antibodies compared with the total IgG Id-1, suggesting that Hong Kong subjects have Id-1-positive antibodies in their serum which are not specific for Hib CP. This is consistent with the nature of Id-1, which is a marker of A2VL region usage rather than a marker of a Hib CP paratope. We suggest that natural antibodies reacting with Hib CP in healthy Hong Kong Chinese are the product of exposure to some cross-reactive antigen(s), different from both Hib and E. coli K100 CP. 相似文献
70.
O. V. Bukharin Yu. A. Brudastov V. A. Gritsenko D. G. Deryabin 《Bulletin of experimental biology and medicine》1996,121(2):160-162
A relationship is found between the resistance ofEscherichia coli, Staphylococcus aureus, andStaphylococcus epidermidis to human serum and whole blood and their ability to inactivate the factors of natural antiinfectious resistance (lysozyme,
complement, immunoglobulins, and a bactericidal fraction of leukocytic interferon).
Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, N
o
2, pp. 174–176, February, 1996 相似文献