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   8380篇
  免费   802篇
  国内免费   38篇
耳鼻咽喉   59篇
儿科学   266篇
妇产科学   151篇
基础医学   1157篇
口腔科学   198篇
临床医学   1014篇
内科学   1713篇
皮肤病学   103篇
神经病学   606篇
特种医学   280篇
外科学   1363篇
综合类   244篇
一般理论   9篇
预防医学   871篇
眼科学   101篇
药学   562篇
肿瘤学   523篇
  2021年   91篇
  2020年   66篇
  2019年   103篇
  2018年   139篇
  2017年   84篇
  2016年   86篇
  2015年   107篇
  2014年   157篇
  2013年   260篇
  2012年   362篇
  2011年   368篇
  2010年   189篇
  2009年   200篇
  2008年   375篇
  2007年   394篇
  2006年   413篇
  2005年   368篇
  2004年   356篇
  2003年   312篇
  2002年   342篇
  2001年   297篇
  2000年   277篇
  1999年   228篇
  1998年   130篇
  1997年   119篇
  1996年   105篇
  1995年   95篇
  1994年   76篇
  1993年   107篇
  1992年   200篇
  1991年   174篇
  1990年   207篇
  1989年   176篇
  1988年   158篇
  1987年   156篇
  1986年   141篇
  1985年   160篇
  1984年   124篇
  1983年   89篇
  1982年   67篇
  1981年   68篇
  1979年   115篇
  1978年   85篇
  1976年   72篇
  1975年   76篇
  1974年   86篇
  1973年   82篇
  1972年   87篇
  1970年   67篇
  1969年   81篇
排序方式: 共有9220条查询结果,搜索用时 31 毫秒
71.
Prior reports suggest an ambivalence regarding treatment in individuals with Post-Traumatic Stress Disorder (PTSD). A model that accommodates such ambivalence is the Transtheoretical Model of Behavior Change (TTM, also known as the Stages-of-Change Model). Fifty veterans presenting for treatment completed self-report measures (94% response rate) that assessed disorder variables and constructs relating to the TTM. While the relationships between the components of each specific construct were found to be consistent with the findings of other studies and a number of predicted relationships between variables were confirmed, many results were inconsistent with the TTM. Notwithstanding questions about the suitability of the self-report measures, the unique characteristics of the veteran sample and the small sample size, the results suggest that the assumptions of the TTM were not met in veterans with PTSD. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
72.
Five commercial kits for the determination of folate and six kits for the determination of vitamin B12 were investigated. Their performance has been compared with microbiological methods for the two vitamins and with a non-commercial radioisotopic method for B12. The results show the importance of the determination of the reference range for an individual laboratory for each method. The precision of the kits varied appreciably, as did their performance using specimens from patients with different haematological disorders. In particular, certain kits failed to detect all patients with pernicious anaemia. The relative accuracy of the kits was assessed. Various factors which should be taken into account in the final selection of a satisfactory kit are discussed.  相似文献   
73.
AIMS: To study the expression of Ki-67 and cytokeratin 20 (CK20) in a group of hyperplastic polyps (including a group with "atypical" features) with the aim of determining whether upper crypt Ki-67 staining and lower crypt CK20 staining correlated with these atypical features, as assessed by light microscopy. METHODS: Fifty seven formalin fixed, paraffin wax embedded hyperplastic colorectal polyps from 53 patients were selected on histological grounds; these comprised 26 typical polyps and 31 with atypical features, which included nuclear hyperchromatism, basal crowding, and increased mitotic activity. These polyps were examined using a standard immunohistochemical method with antibodies against CK20 and Ki-67. Comparisons were made with normal mucosa, adenomatous polyps, and carcinomas. RESULTS: Of the 26 typical polyps, 17 showed the usual pattern of lower crypt Ki-67 and upper crypt CK20 staining; one with upper crypt Ki-67 staining but normal surface CK20 staining; seven with Ki-67 confined to the lower half of crypts but with scattered lower crypt CK20; and one with both upper crypt Ki-67 staining, together with scattered CK20 basal staining. Of the 31 polyps with atypical features, 11 showed the usual staining pattern of lower crypt Ki-67 staining and surface staining with CK20; two showed Ki-67 staining extending into the upper half of crypts, but with a normal surface staining with CK20; 14 showed Ki-67 confined to the lower half of crypts, but scattered lower crypt staining with CK20; and four showed upper crypt Ki-67 staining together with scattered CK20 lower crypt staining. CONCLUSIONS: The normal pattern of lower crypt Ki-67 and upper crypt CK20 was seen in 28 of the 57 hyperplastic polyps and, in general, this corresponded with standard light microscopic appearances. Twenty one of the 57 polyps showed lower crypt mosaic CK20 staining, which in general corresponded with basal abnormalities on light microscopy, although seven specimens had normal appearances. Two smaller subsets emerged, one showing upper crypt Ki-67 staining in the presence of normal CK20 expression (three cases) and another in which a combination of lower crypt CK20 and upper crypt Ki-67 expression was seen (five cases). This last pattern was similar to that of neoplastic polyps and raises the possibility that a subgroup of hyperplastic polyps exists that may be a variant with malignant potential. Further studies with markers of mismatch repair genes and K-ras mutations may help to clarify this issue.  相似文献   
74.
Recently, in-vitro maturation (IVM) of immature human oocytes recovered from non-stimulated follicles has been applied in the treatment of infertility. However, in previous reports, very few embryos cultured in conventional medium have reached the expanded blastocyst stage following in-vitro maturation and fertilization (IVM/IVF). The objective of this study was to investigate whether the developmental competence of human embryos following IVM/IVF could be enhanced by the use of a human ampullary cell co-culture system. Immature human oocytes were aspirated from small follicles at Caesarean section and then cultured in medium containing human menopausal gonadotrophin for 36 to 48 h, followed by insemination. Zygotes were randomly cultured either in conventional culture medium alone or in the co-culture system. Of 48 embryos cultured in conventional medium alone, all arrested at the 2-16- cell stage on day 3 after insemination. Of 46 embryos cultured in the co-culture system, 26 embryos (56.5%) arrested at the 2-16-cell stage. Six embryos (13%) developed to the morula stage. Fourteen embryos (30.4%) developed to expanded blastocysts and two blastocysts were hatching on day 7 after insemination. We conclude that co-culture significantly enhances the development of blastocysts in embryos resulting from IVM/IVF.   相似文献   
75.
Four commercially available acridinium ester-labeled DNA probes directed against rRNA were evaluated for their ability to identify Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, and Cryptococcus neoformans in culture. rRNA was extracted by sonication of 1- to 2-mm2 portions of cultures of fungi in two chaotropic reagents with glass beads. Following a heat inactivation step, the extracts were hybridized in solution with probes specific for each pathogen. The acridinium ester reporter moiety of nonhybridized probe was selectively hydrolyzed, and chemiluminescence of specific DNA:RNA hybrids was quantitated in relative light units with a luminometer. A positive identification required a relative light unit value of > or = 50,000. Sensitivity and specificity of the probes were determined by probing cultures of the respective pathogenic fungi (target) and nontarget fungi. Both mycelial and yeast forms of the dimorphic fungi (B. dermatitidis and H. capsulatum) were tested. For B. dermatitidis, sensitivity and specificity were 87.8 and 100%, respectively (74 target and 219 nontarget fungi tested). For C. immitis, sensitivity and specificity were 99.2 and 100%, respectively (122 target and 164 nontarget fungi tested). For H. capsulatum, sensitivity and specificity were 100 and 100%, respectively (86 target and 154 nontarget fungi tested). For C. neoformans, sensitivity and specificity were 97 and 100%, respectively (100 target and 230 nontarget fungi tested). For B. dermatitidis, C. immitis, and C. neoformans, repeat testing increased the respective sensitivities to 97.3, 100, and 100%. The high sensitivities and specificities of the probes, the relatively short time (less than 1 h) required to perform the assay, and the availability of standardized reagent kits make the acridinium ester-labeled DNA probes well suited to laboratories in need of a rapid method to identify these fungal pathogens. Further, use of the probes to identify pathogenic fungi as soon as colonies appear on primary recovery media significantly shortens the time to reporting.  相似文献   
76.
The aim of the present work was to evaluate the induction and localization of Stat1, interferon (IFN) regulatory factor-1 (IRF-1), and IRF-2 after IFN-gamma exposure of human breast cancer cell lines, SKBR3, MDA468, MCF7, and BT20. Results from growth assays, Western staining, electrophoretic mobility shift assay (EMSA), and immunohistochemical staining were collated to test our hypothesis that immunohistochemical analysis of Stat1, IRF-1, and IRF-2 would provide additional information about the functionality of the IFN-gamma signaling pathway in human tumor lines. EMSA results showed that in each of four cell lines, Stat1 expression was increased and demonstrated functional activity after IFN-gamma stimulation. Western and EMSA analysis showed upregulation of IRF-1 but not IRF-2 in each cell line. Confocal microscopy of cells stained for Stat1, IRF-1, and IRF-2 confirmed the results and also provided novel information about the intracellular localization of proteins and intercellular variations in responses. The proportion of cells with IRF-1 stimulation and translocation was positively correlated with the IFN-gamma growth suppression in vitro. In conclusion, using four independent assays, we have demonstrated that heterogeneity in IFN-gamma-mediated upregulation of signal transduction proteins can be detected in vitro and that these differences can explain distinct cellular growth effects.  相似文献   
77.
In a double-blind, randomized, and placebo-controlled previous trial, the efficacy of Vi-rEPA for typhoid fever in 2- to 5-year-olds was 89.0% for 46 months. Vi-rEPA contained 25 microg of Vi and induced a greater-than-eightfold rise in immunoglobulin G (IgG) anti-Vi in all of the vaccinees tested. In this investigation, we conducted a dosage-immunogenicity study of 5, 12.5, and 25 microg of Vi-rEPA in this age group. Two doses of Vi-rEPA were injected 6 weeks apart. Blood samples were taken before and at 10 weeks (4 weeks after the second injection) and 1 year later. All postimmunization geometric mean (GM) levels were higher than the preimmune levels (P < 0.0001). At 10 weeks, the GM IgG anti-Vi level elicited by 25 microg (102 EU/ml) was higher than those elicited by 12.5 microg (74.7 EU/ml) and 5 microg (43 EU/ml) (P < 0.004): all of the children had > or = 3.52 EU/ml (estimated minimum protective level). One year later, the levels declined about sevenfold (13.3 and 11.3 versus 6.43 EU/ml, P < 0.0001) but remained significantly higher than the preimmune levels (P < 0.0001), and >96% of the children had a greater-than-eightfold rise. This study also confirmed the safety and consistent immunogenicity of the four lots of Vi-rEPA used in this and previous trials.  相似文献   
78.
Individual preparations of affinity purified anti-F(ab')2 antibodies and anti-Fc antibodies isolated from the sera of patients with rheumatoid arthritis (RA), were examined for reactivity with the Fab and Fc fragments of human IgG. Western blot assays demonstrated specific interaction of affinity-purified anti-Fab antibodies with both Fab and Fc molecules. Approximately one-half of the anti-Fab antibody preparations studied contained IgG antibodies reactive with Fab and Fc fragments in ELISA, suggesting the existence of naturally occurring epibody-like autoantibodies in these patients. Thirteen of 14 affinity-purified anti-Fc antibody preparations contained IgG cross-reactive with Fab molecules in ELISA. Double-adsorption assays on affinity columns demonstrated that a minimum of 14%, and possibly as much as 50%, of the IgG anti-Fab antibodies reacted with the Fc of IgG. Conversely, a minimum of 12%, and possibly as much as 70%, of the IgG anti-Fc antibodies reacted with IgG Fab molecules. Anti-Fab antibodies isolated from non-RA individuals also exhibited anti-Fc reactivity in ELISA, demonstrating the presence of these dual-reactive antibodies in other autoimmune and normal individuals. These studies establish the presence of naturally occurring IgG autoantibodies reactive with both the Fab and Fc fragments of human IgG. Their existence emphasizes the potential of anti-immunoglobulin antibodies to recognize a multiplicity of antigens, possibly including other members of the immunoglobulin supergene family.  相似文献   
79.
A patient with aplastic anemia received an ABO incompatible bone marrow transplant (BMT) from an HLA identical sibling. Weekly HLA antibody screens were performed as part of the BMT protocol. At the time of transplant, a hemolytic anti-Le(a) was detected in the Le (a-b-) donor. The Le (a-b+) recipient had no red cell or LCT antibody. A hemolytic anti-Le(a) was detected in the recipient on day 8, but no LCT reactivity was noted at this time. On day 15, the LCT panel demonstrated reactivity with 9 of 50 panel cells without apparent HLA specificity. Graft vs. host disease (GVHD) was present on the skin at this time. The dose of cyclosporin A was increased, but by day 20 the GVHD worsened and the LCT titers increased to 8. This strong reactivity was noted only in the Le (a+) panel members (12/50) and was neutralized with commercial Lewis substance. On day 34 there was no evidence of GVHD, but the lymphocytotoxic anti-Lea continued to be present. The patient began experiencing renal and gastrointestinal difficulties by day 48, and expired on day 60. In renal transplants the kidneys retain their Lewis type and secrete Lewis substance in the urine. In our experience BMT patients retain their Lewis type regardless of the type of the donor. The Lewis system has been linked to renal allograft rejection, and Lewis antigens may function as transplantation antigens in BMT patients as well. In addition, lymphocytotoxic Lewis antibodies can mask other significant HLA antibodies and must be identified when screening patients in need of plateletpheresis products.  相似文献   
80.
Giemsa staining for cysts and trophozoites of Pneumocystis carinii.   总被引:1,自引:0,他引:1       下载免费PDF全文
Although Giemsa staining has been routinely used for the detection of trophozoites and intracystic bodies in smears of bronchoalveolar lavage fluid (BAL) from patients with Pneumocystis carinii pneumonia, it does not normally stain the cyst wall. For detection of the cysts other stains such as toluidine Blue 'O' and methenamine silver must be used as well. Sulphation of smears before staining with Giemsa allows cysts to be visualised, thus enabling a single stain to be used to show all the stages of BAL or sputum, which is particularly useful, considering the increase in the prevalence of P carinii pneumonia in conjunction with the spread of AIDS.  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