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   26002篇
  免费   1764篇
  国内免费   1004篇
耳鼻咽喉   114篇
儿科学   311篇
妇产科学   582篇
基础医学   5128篇
口腔科学   322篇
临床医学   2548篇
内科学   4240篇
皮肤病学   439篇
神经病学   614篇
特种医学   742篇
外国民族医学   12篇
外科学   2737篇
综合类   4258篇
现状与发展   8篇
预防医学   1316篇
眼科学   187篇
药学   1439篇
  3篇
中国医学   275篇
肿瘤学   3495篇
  2024年   20篇
  2023年   306篇
  2022年   468篇
  2021年   820篇
  2020年   649篇
  2019年   678篇
  2018年   685篇
  2017年   690篇
  2016年   702篇
  2015年   766篇
  2014年   1255篇
  2013年   1302篇
  2012年   1193篇
  2011年   1506篇
  2010年   1249篇
  2009年   1237篇
  2008年   1247篇
  2007年   1432篇
  2006年   1285篇
  2005年   1205篇
  2004年   1023篇
  2003年   885篇
  2002年   925篇
  2001年   795篇
  2000年   702篇
  1999年   614篇
  1998年   572篇
  1997年   558篇
  1996年   474篇
  1995年   363篇
  1994年   414篇
  1993年   361篇
  1992年   285篇
  1991年   240篇
  1990年   283篇
  1989年   180篇
  1988年   184篇
  1987年   133篇
  1986年   117篇
  1985年   205篇
  1984年   154篇
  1983年   99篇
  1982年   102篇
  1981年   86篇
  1980年   78篇
  1979年   62篇
  1978年   49篇
  1977年   34篇
  1976年   35篇
  1974年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The subcellular distribution of the blood group antigen A in the transitional epithelium of the urinary tract and its neoplastic growths was studied using transmission immuno-electronmicroscopy. Sixty-five tissue specimens from 50 blood group A1 patients were processed according to an immunogold procedure which was optimized for preservation of both antigen and ultrastructure. The reactions were stronger in the glycocalyx of the luminal surfaces and at the interdigitating cytoplasmic processes of the cells. In the intracellular compartment the reactions were associated with tubulovesicular membrane-bound structures and with the Golgi complexes. Secretory products, intra- or extra-cellular, were also positive. The greatest variability was noted in the cell surface reactions, which were positive in 88% of normal but only 41% of neoplastic urothelial specimens. An inverse correlation was found between malignant behaviour and cell surface, but not intracellular, reactions. We conclude that, in transitional cell carcinomas, there is a quantitative defect in the processing of substance A which affects predominantly the cell surface component and may involve either the transport-insertion steps, the plasma membrane-associated glycosyltransferases or internalization of blood group antigen A.  相似文献   
92.
Genotyping of platelet alloantigens with the possibility of using any type of cellular material as a source of DNA has become a preferred procedure, particularly in thrombocytopenic patients when platelet counts are too low for phenotyping. Recently human platelet antigen 1 (HPA-1) has been identified as an inherited risk factor for coronary thrombosis. The different detection methods currently used have disadvantages for large-scale DNA diagnosis, including the need for electrophoresis (allele-specific restriction enzyme analysis, amplification with sequence-specific primers) or the potential risk of reduced specificity (allele-specific oligonucleotide hybridization). In this report we describe the adaptation of an automated oligonucleotide ligation assay to genotype HPA-1 in polymerase chain reaction (PCR)-amplified DNA samples. HPA-1a and HPA-1b phenotypes corresponded to the results of the different genotyping assays. The genotypes determined with the ELISA-based PCR-oligonucleotide ligation assay were in 100% concordance with the results obtained by conventional allele-specific restriction enzyme site analysis and PCR amplification with sequence-specific primers. The automated oligonucleotide ligation assay provides a rapid, reliable, nonisotopic method to genotype human platelet antigens that can rapidly be applied to large population screening.  相似文献   
93.
: A rising prostate specific antigen (PSA) following treatment for adenocarcinoma of the prostate indicates eventual clinical failure, but the rate of rise can be quite different from patient to patient, as can the pattern of clinical failure. We sought to determine whether the rate of PSA rise could differentiate future local versus metastatistic failure.

: Two thousand six hundred sixty-seven PSA values from 400 patients treated with radiotherapy for localized adenocarcinoma of the prostate were analyzed with respect to PSA patterns and clinical outcome. Patients had received no hormonal therapy or prostate surgey and had ?4 PSA values post-treatment PSA rate of rise, determined by the slope of the natural log, was classified as gradual (< 0.69 log (ng/ml)/year, or doubling time (DT) > 1 year), moderate (0.69-1.4 log (ng/ml)/year, or DT 6 months-1 year), or rapid [>1.4 log (ng/ml)/year, or DT < 6 months].

: SIxty-one percent of patients had non-rising PSA following treatment; 25% of patients with rising PSA developed clinical failure, and 93% of patients with clinical failure had rising PSA. The rate of rise discerned different clinical failure patterns. Local failure occurred in 23% of patients with moderate rate of rise versus 7% with gradual rise (p = 0.0001). Metastatic disease developed in 46% of those with rapid versus 8% with moderate rise (p < 0.0001). By multivariate analysis, in addition to rate of rise, PSA nadir and rate of decline predicted local failure; those with post-treatment nadir of 1–4 ng/ml were five times more likely to experience local failure than nadir < 1 ng/ml (p = 0.0002). Rapid rate of rise was the most significant independent predictor of metastastic failure.

: The rate of PSA rise following definitive radiotherapy can predict clinical failure patterns, with a rapidly rising PSA indicating metastatic recurrence and moderately rising PSA local recurrence. This information could potentially dirent therapy; if the rise predicts metastatic failure hormonal therapy could be cosidereed, while aggressive salvage therapy may benefit subclinical local recurrence identified by a moderate rate of PSA rise.  相似文献   

94.
We reported a new monoclonal antibody, designated FUB-1, reacting with normal and neoplastic large lymphoid cells. FUB-1 was produced using a Burkitt's lymphoma cell line (HBL-5) as an immunogen. Its immunoglobulin subtype was IgM. The determinant was not on the surface but in the cytoplasm. Western blotting analysis revealed that the molecular weight of the antigen was 52,000 dalton. In the normal lymphoid tissue, FUB-1 reacted with large lymphoid cells, but not with small or medium-sized lymphoid cells or plasma cells. In addition, the FUB-1 antigen was not found in resting cells in the peripheral blood (PB), but it was induced on mononuclear cells of PB by addition of PWM or PMA. In the B-cell lymphomas tested, FUB-1 reacted with small cleaved cell lymphomas (3/12), large cell lymphomas (7/10), Burkitt's lymphomas (4/4) and immunoblastic lymphomas (2/2), but not with small cell lymphomas (0/3) or intermediate lymphocytic lymphomas (0/8). These findings indicate that the FUB-1 antigen appears to be expressed on normal lymphoid cells during blastoid transformation and on neoplastic large lymphoid cells. FUB-1 also reacted with normal glandular epithelium and various adenocarcinomas. FUB-1 may be useful to investigate the mechanism of in vitro blastoid transformation or activation of lymphoid cells.  相似文献   
95.
Background :
The BTA test is a latex agglutination assay for the qualitative detection in the urine of analytes that are associated with bladder tumor. We compared the results of the BTA test with those of voided urine cytology (VUC) in patients with bladder cancer.
Methods :
A multicenter trial was performed at 6 institutions. A total of 132 patients with histologically diagnosed bladder cancer were enrolled. Urine samples were split for BTA and VUC testing.
Results :
The sensitivities of the BTA test and VUC were 57.6% and 37.9%, respectively; this difference was significant ( P < 0.001). The BTA test had much higher sensitivity for small, solitary, superficial tumors than did VUC.
Conclusion :
The BTA test is simple to perform, gives rapid results, and is far more sensitive than VUC for detection of bladder cancer. The BTA test has the potential to become an additional tool for detecting bladder cancer.  相似文献   
96.
BACKGROUND: We hypothesise that the density of proliferating cells at the invasive tumour front (ITF) has a positive relationship with prognostic and risk factors in human oral squamous cell carcinoma (SCC). METHODS: Tissues from 47 human oral SCC specimens were collected and stained with a monoclonal antibody directed against the Ki-67 antigen using a horseradish peroxidase based two-step immunostaining method. Counting was performed on two parallel sections at the ITF using an image analyser. The Ki-67 labelling index (LI) was determined by measuring the number of nuclei/mm(2) of epithelium. RESULTS: Our results show that the density of proliferating cells is related to clinical staging, with advanced stage of disease having a significantly higher Ki-67 LI compared with early stage of disease (2111 +/- 905 vs. 1908 +/- 913; P = 0.03). Importantly, this study shows that tumours that have metastasised have a significantly higher Ki-67 LI than tumours where distant metastasis was not detected (3257 +/- 650 vs. 1966 +/- 881; P < 0.0001). CONCLUSIONS: Cell proliferation, as measured by the Ki-67 LI at the ITF, has a positive relationship with clinical staging, tumour thickness, smoking status of the patient and alcohol consumption. Further, we suggest that a multicenter study with a large cohort of patients is indicated to fully elucidate whether cell proliferation at the ITF is directly related to patient survival.  相似文献   
97.
Localization of bone marrow-originated cells in the central nervous system (CNS) of the rat was investigated by using bone marrow chimeras. In order to do this, Lewis rats which carry major histocompatibility complex (MHC) class I antigens haplotype 1 (RT1.Al) were reconstituted with (Lew X PVG)F1 (RT1.Al/c) bone marrow cells after lethal irradiation. Transferred bone marrow cells were detected by immunohistochemical staining using a monoclonal antibody, OX27, specific for haplotype c of rat MHC class I antigens (RT1.Ac). The spleen and thymus of chimeric rats were fully reconstituted with transferred F1 cells 4 weeks after bone marrow transplantation. At this stage, mononuclear cells in the subarachnoid space of the CNS expressed OX27 antigen indicating that they were of bone marrow origin. A few OX27-positive blood cells were scattered in the CNS parenchyma 4-12 weeks after reconstitution. Ramified microglia, however, remained OX27-negative. Bone marrow-derived microglia were not observed throughout the period of examination until 24 weeks. In addition, experimental allergic encephalomyelitis (EAE) was induced in chimeric rats in order to augment the expression of MHC class I antigens on microglia. Even under this condition, no OX27-positive microglia were observed. Taken together, ramified microglia might be of neuroectodermal origin and there is little possibility that the microglia are derived from the bone marrow. However, if the ramified microglia are derived from blood cells, the microglia may be expected to have characteristic cell kinetics from the following points: (1) the precursor cells of the microglia may enter the CNS only at the perinatal stage; and (2) even under the condition in which lymphocytes and macrophages enter the CNS as observed in EAE, the precursor cells of the microglia are not supplied from the blood.  相似文献   
98.
The protective effect of affinity purified antigen has been investigated in an experimental model for malaria which shows a well marked recrudescence of parasitaemia, a feature of the disease in man. A monoclonal antibody (MoAb) recognizing an epitope common to two genetically distinct cloned lines of Plasmodium chabaudi (AS and CB), was used to purify a Mr250,000 polymorphic schizont antigen (PSA) from these parasites. The purified preparations were then examined for the presence of specific and cross-reactive epitopes by immunoprecipitation with a panel of MoAb raised against P. chabaudi AS. When tested previously on smears of parasitized blood by immunofluorescence, or against lysates of parasitized erythrocytes by immunoprecipitation, most of these MoAb had been found to be AS specific. When either AS or CB affinity purified Mr250,000 PSA was used as the target, these same MoAb immunoprecipitated both antigens, and in some cases, a number of associated polypeptides (AP) which copurify with the Mr250,000 PSA. Subsequently, mice were immunized with either the purified AS or CB antigens in Freund's complete adjuvant (FCA). Prechallenge sera were compared by indirect immunofluorescence and immunoprecipitation. Sera from mice immunized with AS antigen reacted strongly with AS and cross-reacted with CB parasite preparations. Pre-challenge serum from CB antigen immunized mice reacted well with CB, but only faintly with AS preparations. In mice immunized with the AS antigen and then challenged with either AS or CB parasites, the initial parasitaemias were delayed in appearance and the height of the peak parasitaemia reduced, an effect which was most pronounced after challenge with homologous parasites. Only homologous challenge of the mice immunized with CB antigen produced statistically significant modification of the initial parasitaemia. In the immunized mice challenged with homologous parasites, the delayed appearance and slightly reduced peak of the primary parasitaemia was associated with delayed resolution of the patent parasitaemia and significant enhancement of the recrudescence.  相似文献   
99.
The pattern of pre- and postnatal appearance of 5-HT1D receptors throughout the different areas of the human brain was studied by quantitative in vitro autoradiography, using [125I]GTI (serotonin O -carboxymethyl-glycyl-[125I]tyrosinamide) as a ligand. The anatomical distribution of 5-HT1D receptors in neonatal, infant and children's brain was in good agreement with that observed in the adult, the basal ganglia and substantia nigra being the most intensely labelled areas. The development of these receptors throughout the human brain was mainly postnatal: low densities of [125I]GTI binding sites were observed at the fetal/neonatal stage in most regions analyzed, in contrast with the high levels of labelling found in infant and children's brains. Indeed, in a number of regions, including the globus pallidus, substantia nigra and visual cortex, a peak of overexpression of 5-HT1D receptors was observed in the first decade of life. Such overexpression could support a regulatory role for 5-HT1D receptors in advanced periods of the CNS developmental process. Our results also indicate that the administration of drugs acting on 5-HT1D receptors during the early postnatal period of life could result in modifications of their properties, as these receptors are already functional in this period.  相似文献   
100.
目的 评价血清肿瘤标志物甲胎蛋白(AFP)、癌胚抗原(CEA)、糖类抗原50(CA50)、糖类抗原19—9(CA19—9)、铁蛋白(SF)、神经元特异性烯醇化酶(NSE)、细胞角蛋白19片段(CYFlRA21—1)水平对肺癌诊断的临床价值。方法 测定72例肺癌患者和40例良性肺病患者的血清AFP、CEA、CA50、CA19—9、SF、NSE、CYFRA21—1水平,比较两组的差异。结果 肺癌组患者CEA、CA50、CA19—9、SF、NSE、CY—FRA21—1水平高于良性肺病组,AFP对肺癌的诊断价值不大。NSE CYF、RA21—1的联合检测具有良好的阳性和阴性预测值。六项联合检测的敏感性和准确性最高,但与两项联合检测的敏感性和准确性差异无统计学意义。结论 NSE CYFRA21—1的联合检测具有良好的临床应用前景。  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