首页 | 官方网站   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   15125篇
  免费   978篇
  国内免费   92篇
医药卫生   16195篇
  2024年   7篇
  2023年   105篇
  2022年   168篇
  2021年   464篇
  2020年   287篇
  2019年   377篇
  2018年   421篇
  2017年   369篇
  2016年   402篇
  2015年   500篇
  2014年   611篇
  2013年   734篇
  2012年   1217篇
  2011年   1219篇
  2010年   713篇
  2009年   627篇
  2008年   1050篇
  2007年   1043篇
  2006年   1016篇
  2005年   938篇
  2004年   885篇
  2003年   864篇
  2002年   761篇
  2001年   104篇
  2000年   94篇
  1999年   131篇
  1998年   159篇
  1997年   113篇
  1996年   102篇
  1995年   102篇
  1994年   79篇
  1993年   74篇
  1992年   59篇
  1991年   45篇
  1990年   38篇
  1989年   51篇
  1988年   25篇
  1987年   20篇
  1986年   30篇
  1985年   21篇
  1984年   30篇
  1983年   24篇
  1982年   18篇
  1981年   18篇
  1980年   16篇
  1979年   11篇
  1977年   8篇
  1976年   7篇
  1974年   5篇
  1963年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Objectives: To evaluate and to compare the bleeding patterns obtained with two regimens of hormone replacement therapy given to early postmenopausal women with asymptomatic uterine leiomyomas. Methods: In this randomised prospective 1-year study 50 early postmenopausal women with one to four asymptomatic uterine leiomyomas were enrolled into two study-groups to take two regimens of hormone replacement therapy for 12 28-day cycles: (A) Tibolone, 2.5 mg/day; (B) conjugated equine estrogens (CEE), 0.625 mg/day plus medroxyprogesterone acetate (MPA), 5 mg/day. The bleeding patterns and the changes in uterine volume of the 47 outpatients who completed the study were evaluated and compared. Results: Amenorrhea incidence was higher in group A (75.0% of the cycles) than in group B (65.6% of the cycles), while irregular bleeding and irregular spotting incidences were higher in group B (29.7 and 4.7% of the cycles, respectively) compared to group A (22.6 and 2.4% of the cycles, respectively). The mean bleeding and spotting lengths were not statistically different between patients in group A and those in group B. Finally, at the end of the study period transvaginal ultrasonography showed no significant change in leiomyoma size. Conclusions: The results demonstrate that, in early postmenopausal patients with asymptomatic uterine leiomyomas, Tibolone treatment seems to be preferable compared to CEE–MPA continuous combined treatment in relation to the lesser occurrence of irregular bleeding. Furthermore, neither Tibolone nor CEE–MPA therapy, at the doses used here, promote fibroid growth.  相似文献   
42.
Although the transfection of B7-1 cDNA into a few mouse tumor cell lines can induce anti-tumor T cell immunity, its expression alone is ineffective in many other tumor cell lines tested. We were interested to study what factors limit B7-1 co-stimulatory activity, and decided to investigate whether B7-1 requires the cooperation of ICAM-1 to provide the minimal co-stimulatory signal for establishing an efficient anti-tumor immunity. We show that the transfection of B7-1 cDNA into three ICAM-1+ (plasmocytoma J558L, T lymphomas EL-4 and RMA), but not into two ICAM-1? tumor cell lines (adenocarcinoma TS/A and melanoma B16.F1), is sufficient to induce their complete rejection in syngeneic mice. The expression of ICAM-1 is necessary for the rejection of the B7 expressing tumors, since the primary response elicited by B7-1+ EL-4 and RMA clones expressing reduced levels of ICAM-1 is severely reduced. Furthermore, super-transfection of ICAM-1 cDNA into B7-1+ adenocarcinoma and melanoma clones optimizes their primary rejection. Histologic examination of transfected tumors reveals that B7-1 and ICAM-1 exert a potent pro-inflammatory activity. The intra-tumor infiltration is composed of both eosinophils and lymphomono-cytes, and is already massive 5 days after the tumor challenge. The primary rejection of the B7-1+ ICAM-1+ tumors depends critically on CD8+ T cells, natural killer cells and granulocytes, but is independent of CD4+ T cells. Remarkably, in addition to its effects on the early phases of the immune response, the co-expression of ICAM-1 and B7-1 on tumors is also necessary for the efficient induction of a memory response. In fact, only the primary challenge with B7-1+, ICAM-1+ tumor cells protects the majority of the mice from a second injection of parental tumor cells. Collectively, our findings indicate that B7-1 and ICAM-1 are fundamental components for triggering the primary rejection of tumors and establishing a protective memory response. These findings may help to define new strategies for the rational application of co-stimulation in tumor immunotherapy.  相似文献   
43.
The phenotypes and genetic determinants for macrolide resistance were determined for 167 erythromycin-resistant Streptococcus pyogenes strains. A cMLS phenotype was shown in 18% of the erythromycin-resistant strains, while inducible resistance was apparent in 31% and the M phenotype was apparent in 50%. The emm gene type of this set of resistant isolates and that of 48 erythromycin-sensitive isolates were determined. emm2 and emm48 were recorded only in the resistant strains of the M phenotype, while approximately all of the strains harboring the emm22 gene had the cMLS phenotype. More than 80% of the emm89-positive strains had the iMLS phenotype, and the same portion of emm4 strains presented the M phenotype. emm3 is recorded only among sensitive strains. The distribution of frequencies of the genetic determinant for the virulence factor M protein was significantly different both among organisms of different types of resistance and between resistant and sensitive populations of S. pyogenes under study.  相似文献   
44.
Vitamin E affects cell death in adult rat dentate gyrus   总被引:1,自引:0,他引:1  
We have previously reported the presence of dying cells in the granule cell layer (GCL) of adult rat dentate gyrus (DG), where neurogenesis occurs. In particular, we found that cell death in the GCL increased in vitamin E deficiency and decreased in vitamin E supplementation. These findings were regarded as related to changes in neurogenesis rate, which in turn was influenced by vitamin E availability; a neuroprotective effect of vitamin E on cell death was also proposed. In order to verify this latter hypothesis, we have studied cell death in all layers of DG in vitamin E-deficient and vitamin E-supplemented rats and in control rats at different ages, using TUNEL and nick translation techniques. The phenotype of TUNEL-positive cells was characterized and the existence of dying BrdU-positive cells was investigated. Dying cells with neuronal phenotype were observed throughout the DG in all experimental groups. The number of TUNEL-positive cells decreased from juvenile to adult age. A higher number of TUNEL-positive cells in vitamin E-deficient rats and a lower number in vitamin E-supplemented rats, with respect to age-matched controls, were found; moreover, in these groups, TUNEL-positive cells had a different percentage distribution in the different layers of the DG. Our results confirm the occurrence of cell death in DG, demonstrate that cell death affects neuronal cells and support the hypothesis that the effect of vitamin E on cell death is not related to neurogenesis.  相似文献   
45.
A boy aged 8 years, 10 months presented with refractory anemia. Bone marrow investigation revealed monolobular megakaryocytes. Cytogenetic analysis showed a clonal abnormality: 46, XY, del(5)(q14q32). This is the youngest individual ever reported with this disorder. A year after diagnosis, while on treatment with human recombinant erythropoietin, the bone marrow showed an excess of blasts. No bone marrow donor could be found. Transformation to acute myelomonocytic leukemia occurred 3 months later. In spite of intensive chemotherapy, the child died of progressive disease with massive splenomegaly and jaundice. The case illustrates that the 5q- syndrome can occur de novo in children. The outcome in this child was poor, which may reflect a difference from the adult 5q- syndrome or may possibly be related to the erythropoietin the child received.  相似文献   
46.
OBJECTIVE: Lymphoepithelioma-like carcinoma (LELC) is an undifferentiated carcinoma with a dense lymphoid stroma. It has been reported in diverse organs and shows variable association with Epstein-Barr virus (EBV). Only a few EBV positive cases have been observed in the hepatobiliary system, all of which were considered to be cholangiocarcinomas. We report a unique case of hepatocellular LELC arising in a cirrhotic liver with EBV demonstrated in the tumor cells. METHODS AND RESULTS: A 39-year-old Hispanic female underwent an orthotopic liver transplant for end stage liver disease secondary to chronic hepatitis C. A high-grade hepatocellular carcinoma with a dense lymphocytic infiltrate was found in the explant as well as in a portal lymph node. Three months posttransplant, the patient developed numerous hepatic nodules with enlarged periaortic and portacaval lymph nodes. Biopsy of the hepatic nodules showed a recurrent hepatocellular carcinoma devoid of a dense lymphocytic infiltrate. Both the primary and recurrent tumors were positive for EBV by molecular studies. The patient eventually expired from liver failure over a 6-week period. CONCLUSION: This case represents the first report of EBV-positive hepatocellular LELC. It is particularly interesting given the precipitous clinical outcome, which was possibly related to immunosuppresive therapy.  相似文献   
47.
Autosomal-recessive osteopetrosis is a severe genetic disease caused by osteoclast failure. Approximately 50% of the patients harbor mutations of the ATP6i gene, encoding for the osteoclast-specific a3 subunit of V-ATPase. We found inactivating ATP6i mutations in four patients, and three of these were novel. Patients shared macrocephaly, growth retardation and optic nerve alteration, osteosclerotic and endobone patterns, and high alkaline phosphatase and parathyroid hormone levels. Bone biopsies revealed primary spongiosa lined with active osteoblasts and high numbers of tartrate-resistant acid phosphatase (TRAP)-positive, a3 subunit-negative, morphologically unremarkable osteoclasts, some of which located in shallow Howship lacunae. Scarce hematopoietic cells and abundant fibrous tissue containing TRAP-positive putative osteoclast precursors were noted. In vitro osteoclasts were a3-negative, morphologically normal, with prominent clear zones and actin rings, and TRAP activity more elevated than in control patients. Podosomes, alphaVbeta3 receptor, c-Src, and PYK2 were unremarkable. Consistent with the finding in the bone biopsies, these cells excavated pits faintly stained with toluidine blue, indicating inefficient bone resorption. Bone marrow transplantation was successful in all patients, and posttransplant osteoclasts showed rescue of a3 subunit immunoreactivity.  相似文献   
48.
This report describes the C-to-B capsular switching in four Neisseria meningitidis strains belonging to the electrophoretic type 37 (ET-37) complex. In particular, one strain belonged to the new sequence type 1860, which was first detected in the year 2000 in Italy and is now frequently isolated. The presence of switched serogroup B strains deserves special attention if they prove as able to spread as their serogroup C progenitors belonging to the hypervirulent ET-37 complex.  相似文献   
49.
The "golden path", produced by the Human Genome Project effort, is composed of a collection of overlapping and fully sequenced BAC/PAC clones covering almost completely the human genome. These clones can be advantageously exploited as fluorescence in situ hybridization (FISH) probes for the characterization of rearrangements frequently found in tumors. Breakpoint characterization can be further refined by generating additional smaller FISH probes through LONG-PCR amplification of specific DNA segments, 5-10 kb in size, using appropriate BAC/PAC probes as template. We report here an example of this approach that has been used to characterize a complex Ph-negative chronic myeloid leukemia (CML Ph-) case in which the BCR/ABL fusion gene was found located on chromosome 9.  相似文献   
50.
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-23

京公网安备 11010802026262号