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   3088篇
  免费   167篇
  国内免费   13篇
耳鼻咽喉   17篇
儿科学   68篇
妇产科学   94篇
基础医学   408篇
口腔科学   91篇
临床医学   262篇
内科学   762篇
皮肤病学   73篇
神经病学   275篇
特种医学   120篇
外科学   392篇
综合类   24篇
预防医学   133篇
眼科学   111篇
药学   180篇
中国医学   12篇
肿瘤学   246篇
  2023年   38篇
  2022年   53篇
  2021年   84篇
  2020年   48篇
  2019年   61篇
  2018年   92篇
  2017年   65篇
  2016年   79篇
  2015年   75篇
  2014年   98篇
  2013年   120篇
  2012年   185篇
  2011年   235篇
  2010年   126篇
  2009年   95篇
  2008年   164篇
  2007年   201篇
  2006年   190篇
  2005年   169篇
  2004年   159篇
  2003年   173篇
  2002年   135篇
  2001年   35篇
  2000年   49篇
  1999年   46篇
  1998年   25篇
  1997年   16篇
  1996年   17篇
  1995年   17篇
  1994年   12篇
  1993年   14篇
  1992年   26篇
  1991年   23篇
  1990年   32篇
  1989年   32篇
  1988年   35篇
  1987年   34篇
  1986年   21篇
  1985年   36篇
  1984年   24篇
  1983年   14篇
  1982年   9篇
  1981年   7篇
  1979年   15篇
  1978年   16篇
  1977年   9篇
  1975年   6篇
  1972年   5篇
  1969年   8篇
  1968年   6篇
排序方式: 共有3268条查询结果,搜索用时 15 毫秒
31.
We are using infectious disease test kits consisting of positive serum diluted with negative pooled serum (P-S) and positive control (P-C). In two anti-HIV antibody tests the results for both P-S and P-C fluctuated between positive and negative depending on the lot No. of the reagent. In Western blot tests carried out to confirm the tests, the P-C was found to be positive and the P-S tests were both inconclusive. We speculated that the P-S had very weak antibodies that reacted differently from patient samples. Manufacturers of such kits, however, must supply reagents with appropriate reactivity, so it is important that they be informed of inconsistencies that could invalidate cut-off values and lead to false-positives and false-negatives.  相似文献   
32.
KD is an acute febrile illness in children characterized by coronary arteritis accompanied by aneurysm and thrombotic occlusion. The etiology of KD is unknown. It has been recently reported that KD is associated with the selective expansion of V beta 2+ and V beta 8.1+ T cells in peripheral blood lymphocytes (PBL), by studying the T cell receptor (TCR) repertoire of in vitro activated T cells. KD may therefore be caused by a superantigen [1-3]. To understand better the immunopathology of KD, we investigated TCR V beta 2 and V beta 8.1 expression on both the T cells of freshly isolated PBL and T cell clones (TCC) from patients with KD. Cytokine production by TCC was also studied. Blood samples were obtained from patients with acute (n = 20) and convalescent (n = 20) KD, age-matched children with non-infectious diseases (n = 18), and healthy adults (n = 20). Among these four groups, there were no significant differences in the percentages of either V beta 2+ or V beta 8.1+ T cells of freshly isolated PBL. The same was true for the CD4+ or CD8+ T cell subsets. One hundred and five TCC (98 CD3+ CD4+ CD8- and seven CD3+ CD4- CD8+) established from the affected skin, lymph node or PBL of six patients with KD were also negative for either V beta 2 or V beta 8.1 TCR. Sixty-eight of 105 TCC (65%) produced detectable levels (> 5 pg/ml) of TNF-alpha (6-1016 pg/ml), in the absence of any stimuli. In contrast, only 11 (10%) of 105 TCC or 7 (7%) of 97 TCC produced detectable levels of IL-2 or IL-6, respectively, in the absence of any stimuli. Stimulation with phytohaemagglutinin (PHA) and phorbol myristate acetate (PMA) induced most TCC to produce higher amounts of TNF-alpha, IL-2 and IL-6. These results suggest that CD4+ T helper cells expressing TCR-beta other than V beta 2 or V beta 8 receptor, primarily through TNF-alpha production, are involved in the immunopathology of KD.  相似文献   
33.
A peptidoglycan layer of Treponema pallidum kazan was isolated by solubilization of whole cells with 1% warm sodium dodecyl sulfate and subsequent digestion of an insoluble residue with proteases. Electron microscopy revealed that the peptidoglycan was isolated as a single-layered sacculus of less than 5 nm in thickness, freed from axial filaments and an envelope sheath. An isolated peptidoglycan fraction was mainly composed of glucosamine, muramic acid, alanine, glutamic acid, ornithine, and glycine in molar ratios of 0.65:0.68:1.63:1.00:0.75:1.03. Amino (N)- and carboxyl (C)-terminal amino acid analyses suggested the involvement of at least a part of the glycine residue in cross-linking between the amino group of ornithine residue at one strand of the stem peptide subunit and the carboxyl group of alanine of the neighboring strand. The treponemal peptidoglycan lacked the immunoadjuvant activity both to stimulate antibody production and to induce delayed-type hypersensitivity against ovalbumin, as well as the properties necessary to stimulate guinea pig and mouse splenocytes and guinea pigs peritoneal macrophages, unlike the cell walls or peptidoglycans (group A type of Schleifer and Kandler's classification, Bacteriol. Rev. 36:407-477, 1972) isolated from many bacterial species parasitic to the mammal. However, the peptidoglycan activated the human complement system through the alternative pathway, as well as the classical one, and caused a liberation of 5-hydroxytryptamine in rabbit blood platelets in a similar manner to the cell wall peptidoglycans of both group A and B types.  相似文献   
34.
Leukemic cells from 32 cases of acute leukemia were cultured in vitro with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) to study their differentiative potential. Three cases of acute undifferentiated leukemia (AUL) were studied intensively. We found that culturing of leukemic cells with TPA can induce changes in cell surface antigens. In particular, MCS-2, a "pan" granulocyte/monocyte marker, was inducible in vitro in AUL and in acute myelogenous leukemia, while it was not inducible in acute lymphoblastic leukemia. BA-2 (recognizing the Mr 24,000 protein) and TA-1 (recognizing the Mr 170,000 and Mr 95,000 proteins) were also inducible in cases of AUL, acute myelocytic leukemia, and acute monoblastic leukemia, although these antigens are not limited only to leukemias of the myelomonocytic lineage. Our studies also indicate that undifferentiated cells could be induced to nonspecific esterase and sometimes to chloroacetate esterase reactivity while losing terminal deoxynucleotidyl transferase. Morphological studies in these cases revealed cytological maturation following TPA treatment. In most cases, these changes were also partially inducible by culturing cells in medium alone or with the addition of dimethyl sulfoxide but not to the extent that was demonstrated by TPA. Our studies showed that MCS-2 is a very good, specific marker of acute nonlymphocytic leukemia. A potential use for TPA to aid in the subclassification of patients with AUL is also suggested.  相似文献   
35.
A broad range of chronic conditions, including heart failure (HF), have been associated with vitamin D deficiency. Existing clinical trials involving vitamin D supplementation in chronic HF patients have been inconclusive. We sought to evaluate the outcomes of patients with vitamin D supplementation, compared with a matched cohort using real-world big data of HF hospitalization. This study was based on the Diagnosis Procedure Combination database in the Japanese Registry of All Cardiac and Vascular Datasets (JROAD-DPC). After exclusion criteria, we identified 93,692 patients who were first hospitalized with HF between April 2012 and March 2017 (mean age was 79 ± 12 years, and 52.2% were male). Propensity score (PS) was estimated with logistic regression model, with vitamin D supplementation as the dependent variable and clinically relevant covariates. On PS-matched analysis with 10,974 patients, patients with vitamin D supplementation had lower total in-hospital mortality (6.5 vs. 9.4%, odds ratio: 0.67, p < 0.001) and in-hospital mortality within 7 days and 30 days (0.9 vs. 2.5%, OR, 0.34, and 3.8 vs. 6.5%, OR: 0.56, both p < 0.001). In the sub-group analysis, mortalities in patients with age < 75, diabetes, dyslipidemia, atrial arrhythmia, cancer, renin-angiotensin system blocker, and β-blocker were not affected by vitamin D supplementation. Patients with vitamin D supplementation had a lower in-hospital mortality for HF than patients without vitamin D supplementation in the propensity matched cohort. The identification of specific clinical characteristics in patients benefitting from vitamin D may be useful for determining targets of future randomized control trials.  相似文献   
36.
Hereditary apolipoprotein A-1 (ApoA-1) amyloidosis is a rare disease characterized by progressive deposition of amyloid fibrils in the kidney, heart, and liver. We observed a 45-year-old male patient with liver failure. Liver dysfunction was detected at 30 years of age during an annual health check-up. At 35 years of age, renal dysfunction was also found. At 40 years of age, the pathologic findings of the liver revealed amyloid deposition. A testis biopsy specimen taken at 42 years of age to identify the cause of male infertility showed amyloid accumulation. At 43 years of age, the amyloid results and genetic profile led to a definitive diagnosis of hereditary ApoA-1 amyloidosis caused by Glu34Lys mutation. A family history was absent. Liver failure showed Budd-Chiari–like formation, including enlargement of the caudate lobe and liver congestion. Although the patient showed end-stage liver cirrhosis and renal failure, only liver transplant was performed considering the burden for a living donor. The enlarged liver (4.9 kg) showed amyloid deposition in parenchyma and the space of Disse. Amyloid also accumulated in the giant spleen. The APOA1 mutation Glu34Lys is extremely rare, and in this case hepatic failure was successfully treated by liver transplant to both replace organ function and reduce production of the amyloidogenic ApoA-1–variant protein. Careful observation for reaccumulation of amyloidosis in the organ is required.  相似文献   
37.
38.
Journal of Artificial Organs - Few reports have examined the association between changes in cerebral oxygenation and clinical factors, including blood pressure (BP), upon standing after...  相似文献   
39.
Is the Gauer-Henry reflex important for immersion diuresis in men?   总被引:4,自引:0,他引:4  
BACKGROUND: This study examines the relationship between the threshold for plasma vasopressin concentration [PVP] responses and diuresis (Gauer-Henry reflex), and tests the hypothesis that water intake would not influence diuresis. METHODS: Eight men (19-25 yr) underwent four treatments: euhydration in air (Eu-air), euhydration in water immersion (Eu-H2O), and with prior 3.6% hypohydration in air (Hypo-air), and hypohydration in immersion (Hypo-H2O). Ad libitum drinking was allowed during the 3-h experimental and 1-h recovery periods. RESULTS: Drinking was greatest during the first 10 min: 3.5 ml x kg(-1) with Hypo-air (450 ml x 3 h(-1)) and only 1.7 ml x kg(-1) (p < 0.05) with Hypo-H2O (235 ml x 3 h(-1)). At 1 h, concomitant [PVP] decreased from a control level of 6.6+/-1.5 to 4.0+/-1 .0 pg x ml(-1) (delta = 2.6 pg x ml(-1), p < 0.05) with Hypo-air, and from 5.9+/-0.6 to 2.3+/-0.2 pg x ml(-1) (delta = 3.6 pg x ml(-1), p < 0.05) with Hypo-H2O. Urine flow was unchanged from control level (<1.0 ml x min(-1)) with Hypo-air, Hypo-H2O, and Eu-air, but increased to 4-5 ml x min(-1) with Eu-H2O. Neither water intake volume nor urine flow was related to the magnitude of [PVP] depression. Regression of Uosm/Posm ratio on [PVP] and urine flow indicated that [PVP] above 2 pg x ml(-1) did not affect urine flow. Thus, ad libitum water intake in previously hypohydrated subjects did not affect urine flow or the decrease in [PVP]. The threshold [PVP] to initiate significant diuresis was about 2 pg x ml(-1), and significant diuresis can occur with no change in [PVP] maintained at about 1 pg x ml(-1) during immersion in euhydrated subjects. CONCLUSIONS: Thus, it appears that the Gauer-Henry reflex is not the major mechanism for immersion-induced diuresis. Clearly, other diuretic factors are also involved.  相似文献   
40.
A case of synchronous squamous cell carcinomas in the soft palate,larynx and esophagus is reported, along with findings of molecular-pathologicalanalysis. A biopsy sample from the aryngeal carcinoma revealedwell differentiated squamous cell carcinoma harboring two pointmutations at codons 144 and 148 of the p53 gene but not at codon299, and more than 50% of the cancer cells showed accumulationof p53 protein immunohistochemically. The esophageal tumor,which was moderately differentiated squamous cell carcinoma,showed immunoreactivity for p53 within the nuclei of 25–50%of cancer cells with a missense mutation at codon 299 but notat codon 144 or 148. This cancer also showed immunoreactivityfor transforming growth factor alpha. On the other hand, thepoorly differentiated squamous cell carcinoma in the soft palateshowed negative immunoreactivity for p53 and no point mutationin exons 5 to 8 of the gene. These results suggest that thethree synchronous squamous cell carcinomas arose as independentevents.  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