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   2139篇
  免费   176篇
  国内免费   3篇
耳鼻咽喉   17篇
儿科学   93篇
妇产科学   73篇
基础医学   307篇
口腔科学   93篇
临床医学   169篇
内科学   413篇
皮肤病学   16篇
神经病学   193篇
特种医学   65篇
外科学   329篇
综合类   39篇
一般理论   2篇
预防医学   218篇
眼科学   60篇
药学   99篇
中国医学   14篇
肿瘤学   118篇
  2022年   25篇
  2021年   34篇
  2020年   25篇
  2019年   39篇
  2018年   49篇
  2017年   38篇
  2016年   37篇
  2015年   47篇
  2014年   55篇
  2013年   83篇
  2012年   115篇
  2011年   132篇
  2010年   86篇
  2009年   47篇
  2008年   121篇
  2007年   105篇
  2006年   118篇
  2005年   112篇
  2004年   112篇
  2003年   112篇
  2002年   92篇
  2001年   47篇
  2000年   49篇
  1999年   46篇
  1998年   32篇
  1997年   23篇
  1996年   18篇
  1995年   16篇
  1994年   13篇
  1992年   22篇
  1991年   29篇
  1990年   26篇
  1989年   24篇
  1988年   27篇
  1987年   27篇
  1986年   21篇
  1985年   25篇
  1984年   30篇
  1983年   17篇
  1982年   17篇
  1981年   16篇
  1980年   13篇
  1979年   16篇
  1978年   19篇
  1977年   15篇
  1976年   10篇
  1975年   16篇
  1974年   16篇
  1973年   13篇
  1972年   12篇
排序方式: 共有2318条查询结果,搜索用时 171 毫秒
991.
Earlier exploratory work on a scoring algorithm for the Reasons for Drinking Questionnaire [Zywiak, W. H., Westerberg, V. S., Connors, G. J., & Maisto, S. A. (2003). Exploratory findings from the Reasons for Drinking Questionnaire. Journal of Substance Abuse Treatment, 25, 287–292.] presented a number of interesting findings, but was limited by a fairly low consistency in type of relapse between the first relapse and the second relapse (63%). This scoring algorithm objectively classifies alcohol relapses into one of three types (negative affect, social pressure, or craving/cued). While examining gender differences in the type of first relapse, evidence indicating that relapses were more consistent for men (81%) than for women (44%) was uncovered. For initial posttreatment relapses, women were more likely to have negative affect relapses, and men were more likely to have social pressure relapses. For men, negative affect relapses were predicted by the Beck Depression Inventory score. For women, negative affect relapses were predicted by the Alcohol Dependence Scale score, and craving/cued relapses were predicted by situational craving.  相似文献   
992.
BACKGROUND: Characterizing virus-host interactions during self-limited infectious mononucleosis could explain how Epstein-Barr virus (EBV) replication is normally controlled and provide insight into why certain immunocompromised patients fail to contain it. METHODS: University students had an average of 7 clinical and virologic evaluations during acute infectious mononucleosis. EBV was quantified in 697 samples of oral wash fluid, whole blood, peripheral blood mononuclear cells (PBMCs), and plasma by a real-time (TaqMan) polymerase chain reaction (qEBV) assay developed in our laboratory. RESULTS: Twenty of 25 subjects had serologically confirmed primary EBV infection. EBV was cleared from whole blood by a first-order process with a median half-life of 3 days, and its quantity was associated with severity of illness (r2=0.82). Oral shedding persisted at a median of >or=1x104 copies/mL for 32 weeks and was unrelated to severity of illness. Subjects with nonprimary EBV infection shed virus intermittently, and median quantities for all samples became undetectable within 4 weeks. CONCLUSIONS: Using a novel qEBV assay, we demonstrated that young adults with primary EBV infection rapidly cleared virus from blood but not from the oropharynx. High oral concentrations of EBV in asymptomatic persons who have resumed normal activities support the concept that infectious mononucleosis is most likely acquired by kissing.  相似文献   
993.
The chemokine coreceptors play a significant role in HIV entry and pathogenesis. The V3 region of HIV envelope glycoprotein is considered as a principal determinant for viral phenotype and tropism. The present study describes lack of association between the V3 genotype and viral phenotype of 18 Indian HIV-2 isolates. The viruses were isolated, confirmed by PCR and the HIV subtypes were determined by sequencing V3 region of the env gene. The coreceptor usage and syncytium inducing (SI) capacity of isolates was determined. Our study indicated that CCR5 coreceptor usage and NSI phenotype is predominant among Indian HIV-2 isolates obtained from patients in the early stage of infection. Two of the four HIV-2 isolates obtained from the late stage patients were SI and dual tropic. Phylogenetic analysis of these isolates revealed close relatedness to the isolates from western and southern India.  相似文献   
994.
995.
996.
997.
The study was designed to examine whether dynamic measurements of inhibin B and oestradiol following single administration of buserelin acetate were correlated with the ovarian response to stimulation in IVF. A total of 37 patients undergoing IVF treatment was studied when the long protocol was started in the early follicular phase. Blood samples were taken twice: on day 2 of the menstrual cycle, before the first s.c. administration of buserelin acetate 0.5 mg and on day 3, 24 h later. Inhibin B and oestradiol concentrations were compared with the ovarian response to stimulation. The ovarian response was defined in two ways: 'number of oocytes/total recombinant (r) follicle stimulating hormone (FSH) dose'; and 'square-root (number of follicles/total rFSH dose)'. The following measurements were highly correlated with the ovarian response to stimulation: increase in oestradiol (day 3-day 2 oestradiol concentration) [correlation coefficient (r) = 0.68, P: < 0.0001] and sum of inhibin B (day 2 + day 3 inhibin B concentrations) (r = 0.6, P: < 0.0001). Age and basal concentrations of FSH and inhibin B were inferior to the above measurements in terms of correlation with the ovarian response. In conclusion, dynamic measurements of inhibin B and oestradiol following single administration of buserelin acetate were highly correlated with the ovarian response to stimulation for IVF treatment.  相似文献   
998.
PURPOSE: To determine the prevalence of hepatitis C virus antibodies (anti-HCV) in patients with sickle cell disease. PATIENTS AND METHODS: Between 1983 and 2001, 150 patients from the Howard University Hospital Center for Sickle Cell Disease were screened for HCV antibody (52% women, 48% men, mean age 34 years). Frozen serum samples from 56 adult sickle cell patients who had participated in previous surveys (1983-92) of HIV and HTLV-1 serology and who were tested in 1992 for anti-HCV antibody--when commercial ELISA test (Ortho) became available--were included in this paper. Of the 150 patients in the study, 132 had sickle cell anemia genotype (SS), 15 had sickle cell hemoglobin-C disease (SC) and three had sickle beta thalassemia. Clinical charts were reviewed for history of blood transfusion, IV drug abuse, homosexuality, tattooing, iron overload, and alcohol abuse. RESULTS: Antibodies to HCV were detected in 53 patients (35.3%). Of the 55 patients who had frozen serum samples tested in 1992, 32 (58%) were reactive for anti-HCV, while only 21 of the 95 patients (22%) tested after 1992 were positive for HCV antibodies (P<0.001). Thirty-nine of 77 patients (51%) who received more than 10 units of packed red blood cells were positive for HCV antibody, and only 14 of 61 patients (23%) who received less than 10 units of packed red blood cells transfusion were positive for HCV antibodies (P<0.001). None of the 12 patients who never received transfusion were positive for HCV antibody. In the 53 anti-HCV positive patients, the mean alanine amino-transferase (ALT) value was 98- and 81 U/L, respectively, for males and females. These values were normal for the HCV-antibody negative patients. The aspartate amino-transferase (AST) and the total bilirubin were also higher in the anti-HCV positive patients compared to patients in the anti-HCV negative group. Forty-four patients (57.1%) who were transfused more than 10 units developed iron overload defined by a serum ferritin level higher than 1,000 ng/ml. A total of 20 of the patients with iron overload underwent liver biopsies. Seven of these 20 patients (35%) were HCV positive. These patients often had more severe liver disease and higher degree of iron deposition. CONCLUSION: The prevalence of HCV antibody and iron overload is directly related to the number of blood transfusions in patients with sickle cell disease. The prevalence of HCV infection has decreased significantly, since blood donor screening for HCV became available. Chronic HCV infection and iron overload place sickle cell patients at risk for significant liver disease.  相似文献   
999.
The distributed model of face processing proposes an anatomical dissociation between brain regions that encode invariant aspects of faces, such as identity, and those that encode changeable aspects of faces, such as expression. We tested for a neuroanatomical dissociation for identity and expression in face perception using a functional MRI (fMRI) adaptation paradigm. Repeating identity across face pairs led to reduced fMRI signal in fusiform cortex and posterior superior temporal sulcus (STS), whereas repeating emotional expression across pairs led to reduced signal in a more anterior region of STS. These results provide neuroanatomical evidence for the distributed model of face processing and highlight a dissociation within right STS between a caudal segment coding identity and a more rostral region coding emotional expression.  相似文献   
1000.
The use of cryopreserved human embryos in gene expression studies provides an additional source to the scarce embryos available for research. To validate their use we have implemented a quantitative RT-PCR to characterize the levels of the tuberous sclerosis, TSC2 gene in fresh and frozen-thawed human embryos. Frozen embryos were thawed using two different clinical protocols. In fresh embryos 9.95 fg of TSC2 cDNA was present in the unfertilized oocyte, which was comparable to the level on day 2 of preimplantation development. On day 3 there was a significant drop (P<0.001) to 6.8 fg, followed by an increase in cDNA levels to 10.8 fg (P<0.01) on day 6 at the expanded blastocyst stage. Day 2 frozen embryos possessed 50% less (P<0.001) TSC2 mRNA in comparison to the fresh embryos using thawing protocol one (from frozen to 37 degrees C) and 25% less TSC2 mRNA (P<0.01) with thawing protocol 2 (from frozen to room temperature). After culturing day 2 frozen embryos for an additional day they showed mRNA levels comparable with fresh day 3 embryos. There was no significant difference in the levels of TSC2 mRNA between fresh and frozen day 3 human embryos with either thawing protocol. This study demonstrates that cryopreservation does affect the normal pattern of gene expression during human preimplantation development, and that intact frozen-thawed embryos are not equivalent to their non-frozen counterparts. Furthermore human embryos frozen on day 2 appear to be more susceptible to temperature change than embryos frozen on day 3.  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