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   397篇
  免费   14篇
  国内免费   29篇
耳鼻咽喉   5篇
儿科学   26篇
妇产科学   5篇
基础医学   25篇
口腔科学   11篇
临床医学   38篇
内科学   81篇
皮肤病学   15篇
神经病学   14篇
特种医学   54篇
外科学   43篇
综合类   59篇
预防医学   12篇
眼科学   2篇
药学   32篇
肿瘤学   18篇
  2023年   1篇
  2022年   2篇
  2021年   4篇
  2020年   1篇
  2019年   4篇
  2016年   3篇
  2015年   6篇
  2014年   11篇
  2013年   9篇
  2012年   10篇
  2011年   9篇
  2010年   19篇
  2009年   18篇
  2008年   20篇
  2007年   24篇
  2006年   25篇
  2005年   14篇
  2004年   11篇
  2003年   6篇
  2002年   6篇
  2001年   7篇
  2000年   4篇
  1999年   6篇
  1998年   29篇
  1997年   35篇
  1996年   30篇
  1995年   18篇
  1994年   13篇
  1993年   18篇
  1992年   5篇
  1990年   4篇
  1989年   11篇
  1988年   5篇
  1987年   7篇
  1986年   3篇
  1985年   13篇
  1984年   3篇
  1983年   4篇
  1982年   5篇
  1981年   6篇
  1980年   1篇
  1978年   4篇
  1977年   2篇
  1975年   3篇
  1970年   1篇
排序方式: 共有440条查询结果,搜索用时 0 毫秒
91.
OBJECTIVE: To estimate prevalence of xerophthalmia and to assess dietary intake of vitamin A in Indian children aged under 6 y. DESIGN: Cross sectional study. STUDY SETTING: Urban slums under Urban Health Centre affiliated to Department of Preventive and Social Medicine, Government Medical College, Nagpur, India. PARTICIPANTS: The study included 1094 all children under 6 y of age, from two randomly selected urban slums. METHODS: Xerophthalmia was diagnosed on the basis of ocular signs and symptoms (WHO recommendations). Dietary intake of vitamin A was assessed by using one year recall method recommended by International Vitamin A Consultative Group. RESULTS: Prevalence of xerophthalmia was estimated to be 8.7%. Nine hundred and ninety-five (90.9%) study subjects were identified as inhabitants consuming dietary vitamin A at below recommended levels. (UPF score < 210). Five hundred and ninety-three (54.2%) study subjects were consuming dietary vitamin A at approximately less than 200 RE/d (UPF score < 120) while 402 (36.2%) were consuming approximately 200-300 RE/d (UPF score 120-210). The prevalence of xerophthalmia was found to be decreasing as the score of usual pattern of food consumption (UPF) increased. CONCLUSIONS: Children with a dietary intake represented by a UPF score of less than 120 were at high risk of developing xerophthalmia, whereas, those consuming vitamin A equal to a UPF score greater than 120 were at comparatively less risk despite being below the recommended levels.  相似文献   
92.
93.
Background This study of patients with multivalvular lesions was undertaken to assess optimal surgical management and identify risk factors for prognosis. Methods Five hundred and twenty one patients underwent valve repair or replacement surgery between January’90 and December’98. Mean age was 30.19±12.2 years and 342 were males. All patients had dyspnoea on exertion, 467 (89.6%) were in New York Heart Association (NYHA) Class III and 47 (9.0%) were in Class IV. Congestive Heart Failure in 67 (12.3%) and prior cardiac procedure in 66 (12.2%) were other risk factors. The valves affected were mitral and aortic in 483 (Group 1), mitral and tricuspid in 43 (Group II) and mitral, aortic and tricuspid in 40 (Group III) patients. Surgical procedures included, several different combinations using repair or replacement with prosthetic or biological substitutes. Results Operative mortality was 9.8% (51 patients). Follow up (1 to 108 months, mean 45 months) was 94% complete. Late mortality occurred in 48 patients (10.4%). Causes included, left ventricular dysfunction (n=21), valve thrombosis (n=10) and, endocarditis (n=8). Freedom from late events was 50.7±8.5% at 9 years. At their last visit 40 patients were in Class IV, 18 were in Class III, 59 in Class II and the remaining in Class I (NYHA). Conclusions Important predictors of early mortality were NYHA Class IV, congestive heart failure, tricuspid valve disease and prior cardiac surgery. Left ventricular dysfunction was an important determinant of late outcome.  相似文献   
94.
95.
Hamaguchi  N; Bajaj  SP; Smith  KJ; Stafford  DW 《Blood》1994,84(6):1837-1842
The purpose of this study is to determine which residues of the factor IXa heavy chain are important for interaction with the cofactor of factor IXa, factor VIIIa. Because the monoclonal antibody (MoAb) FXC008 inhibits interaction between factors IXa and VIIIa, and because it also reacts with residues 181-310 of the factor IXa heavy chain, we used the computer-modelled structure of the factor IXa heavy chain to select charged surface residues likely to interact with FXC008 and/or factor VIIIa. We made mutations in the region of residues 181-310 of the heavy chain of factor IX, and replaced these amino acids individually with those located at the same position in factor X. The mutated factor IX retained complete clotting activity and thus interacted normally with factor VIIIa. Five mutant proteins (factor IXK214F, factor IXK228R, factor IXE240Q, factor IXK247V, and factor IXN260K) reacted with heavy chain-specific MoAbs FXC008 and A-5. Neither factor IXD276K nor factor IXR248H bound to FXC008. Factor IXR252V had reduced affinity to FXC008. Our results suggest the following: (1) factor IXa residues 214, 228, 240, 247, 248, 252, 260, and 276 are not involved in specific interaction with factor VIIIa; and (2) the FXC008 and factor VIIIa binding sites may not share critical residues.  相似文献   
96.
97.
An abnormal increase in numbers of CCGG sites methylated in the 5' region of the human calcitonin (CT) gene occurred in tumor cell DNA samples from 90% (17 of 19) of patients with non-Hodgkin's T and B cell lymphoid neoplasms and in 95% (21 of 22) of tumor cell DNA samples from patients with acute nonlymphocytic leukemia (ANLL). The changes were not seen in patients with chronic myelogenous leukemia (0 of 9). The abnormal methylation patterns appear to be a property only of transformed or malignant cells since they were not found in DNA from nonneoplastic adult tissues including sperm, early myeloid progenitor cells, benign lymphoid hyperplasia, peripheral lymphocytes stimulated to divide, or early myeloid progenitor cells (obtained by immunoaffinity using anti-My-10 antibody), but they did appear after Epstein-Barr virus transformation of lymphocytes. Moreover, during the course of therapy in patients with ANLL, the hypermethylation pattern reflects the presence of the leukemic clone even in normal-appearing granulocytes derived from this clone. The increased methylation of the CT gene may then provide an important molecular marker for biologic events in human cell transformation or tumor progression and may prove clinically useful in monitoring patients with lymphoid and acute myelogenous neoplasms.  相似文献   
98.
The present study was designed to test the psychometric properties of the RAQoL, a rheumatoid arthritis (RA)-specific quality of life (QoL) instrument. All stages of the development were conducted simultaneously in The Netherlands and the UK. The content of the draft measure was derived from qualitative interviews with RA patients in both countries. The final version of the RAQoL has 30 items with a 'yes'/'no' response format and takes approximately 6 min to complete. Both language versions have high internal consistency and test-retest reliability (> 0.9), and good sensitivity to discriminate between groups with various disease activity and severity. Given the excellent psychometric properties of the new instrument, it will prove to be a valuable tool for assessing quality of life in clinical trials and for monitoring patients in routine clinical practice.   相似文献   
99.
Quadros  EV; Sai  P; Rothenberg  SP 《Blood》1993,81(5):1239-1245
Transcobalamin II (TCII) is a cobalamin (Cbl, vitamin B12)-binding protein in mammalian plasma that facilitates the cellular uptake of the vitamin. To obtain human TCII in sufficient quantity for analytical studies, the complementary DNA (cDNA) encoding TCII was inserted into the plasmid PVL 1393, and the baculovirus expressing TCII was obtained by homologous recombination in Spodoptera frugiperda (SF9) insect cells by cotransfection with the wildtype virus. Under optimized conditions, SF9 cells infected with the recombinant virus secreted 2 to 4 micrograms of TCII per milliliter of culture medium. TCII did not accumulate in the SF9 cells and seemed to be constitutively secreted as observed previously in cultured human endothelial cells. The purified recombinant TCII has the same molecular weight by SDS-PAGE as purified human TCII. The recombinant TCII cross-reacts with an antiserum to native human TCII, binds Cbl and facilitates the uptake of Cbl in eukaryotic cells by binding to the receptor for TCII-Cbl on the plasma membrane of K562 cells. Amino acid sequence analysis of the purified recombinant TCII identified two polypeptides, one identical to the amino acid sequence deduced from the cDNA and a second lacking the first and second N-terminal residues. These sequences are identical to two TCII polypeptides purified from Cohn fraction III of pooled human plasma. The two forms of recombinant TCII have the same isoelectric points as the two predominant isoprotein forms of TCII in human serum. Since the baculovirus construct contains a single cDNA that can encode only one amino acid sequence, the two isoproteins in recombinant TCII must be generated by a mechanism other than allele specific expression. A plausible mechanism for generating isoproteins of nonglycosylated peptides, such as TCII, may be by splicing of the leader peptide at alternative sites.  相似文献   
100.
The Transfusion Safety Study (TSS) and the National Heart, Lung, and Blood Institute (NHLBI) established a repository of approximately 200,000 sera from blood donors in late 1984 and early 1985. Collections were made in the four metropolitan areas with the highest prevalence of AIDS. Retrospective testing showed an overall anti-HIV-1 prevalence of 16 cases per 10,000 donations. In this study, the predictive value of a negative initial enzyme-linked immunoassay was estimated from both quality control specimens and the rescreening of 13,461 sera to be greater than 99.99 percent with respect to technical error. Among anti-HIV-1-positive persons, there was a 1.3- to 1.5-fold excess of first-time donors. The anti-HIV-1 prevalence among donors showed that infection was more common among young men than suggested by national reporting of AIDS cases. Anti-HIV-1 prevalence varied among the four metropolitan areas less than did reported AIDS cases, but, by 1987, the differences in the latter had decreased. Anti-HIV-1 prevalence in collection areas outside of the four major cities differed much more widely than that among the cities themselves. The TSS/NHLBI Donor Repository will remain available for the indefinite future for further evaluation of screening procedures for HIV-1 and other viruses for which transfusion is found to be an important route of transmission.  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