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   2176篇
  免费   99篇
  国内免费   69篇
耳鼻咽喉   9篇
儿科学   84篇
妇产科学   18篇
基础医学   252篇
口腔科学   41篇
临床医学   267篇
内科学   496篇
皮肤病学   43篇
神经病学   160篇
特种医学   347篇
外科学   145篇
综合类   41篇
一般理论   14篇
预防医学   147篇
眼科学   51篇
药学   179篇
肿瘤学   50篇
  2021年   15篇
  2019年   14篇
  2018年   15篇
  2017年   13篇
  2016年   22篇
  2015年   31篇
  2014年   40篇
  2013年   47篇
  2012年   61篇
  2011年   67篇
  2010年   58篇
  2009年   74篇
  2008年   81篇
  2007年   123篇
  2006年   96篇
  2005年   69篇
  2004年   109篇
  2003年   104篇
  2002年   66篇
  2001年   77篇
  2000年   61篇
  1999年   51篇
  1998年   76篇
  1997年   85篇
  1996年   80篇
  1995年   65篇
  1994年   46篇
  1993年   52篇
  1992年   28篇
  1991年   28篇
  1990年   33篇
  1989年   58篇
  1988年   39篇
  1987年   53篇
  1986年   24篇
  1985年   37篇
  1984年   31篇
  1983年   34篇
  1982年   27篇
  1981年   28篇
  1980年   27篇
  1979年   10篇
  1978年   12篇
  1977年   13篇
  1976年   11篇
  1975年   19篇
  1974年   12篇
  1973年   9篇
  1972年   9篇
  1970年   9篇
排序方式: 共有2344条查询结果,搜索用时 15 毫秒
21.
The author proposes a general systems approach to the examination and understanding of family functioning. Scrutinizing the family as an open system with 1) evolutionary goals and tangible tasks, 2) a need for "semipermeable" boundaries, 3) cultural and subcultural communication modes, 4) leadership effectiveness, and 5) the nature and age-appropriateness of the affective bonds will enable clinical judgements about family functioning that indicate general system competencies and defects. Such a framework may also lead to a typology of family process because the major functions of the family as a system (creation, nurturance, enculturation, and guidance of the young into adulthood) can be evaluated regardless of symptoms or diagnoses.  相似文献   
22.
RATIONALE AND OBJECTIVES: To evaluate the diagnostic value of the new ultrasound mode "wide-band harmonic" (WBH) using an ultrasound contrast agent in blunt renal trauma in an animal model. METHODS: A defined blunt renal trauma was induced in 10 rabbits according to published standards. Ultrasound (B-mode, color and power Doppler, WBH) was performed before and after trauma, with and without using a contrast agent (Levovist). Ultrasound features were compared with histologic findings. RESULTS: In 2 of the 10 rabbits, three focal renal intraparenchymal lesions with diameters ranging from 1.0 to 1.8 mm were found that could be identified only using WBH with contrast. Six of the 10 rabbits developed a subcapsular hematoma with a thickness of up to 1.5 mm, which was identified by conventional B-mode as well as WBH. Histologic workup confirmed these findings of intraparenchymal hematomas and did not reveal further lesions. CONCLUSIONS: Only 20% of the experimental subjects developed parenchymal lesions with diameters of 1.0 mm or larger. All these lesions were identified only using WBH. These results indicate the potential to use WBH plus contrast for the diagnosis of blunt renal trauma.  相似文献   
23.
Objective: To evaluate the incidence and severity of apnoea and bradycardia in hospitalized preterm infants following immunization at 2 months of age, and identify risk factors.
Methodology: A prospective study of 98 preterm infants, of gestational age 24–31 weeks, immunized at approximately 2 months post natal age with diphtheria-tetanus-whole cell pertussis vaccine (DTPw) in the neonatal intensive care unit (NICU) at King George V Hospital Sydney. Half the infants also received Haemophilus influenzae type b conjugate vaccine (Hib) simultaneously. All infants were monitored for apnoea and bradycardia in the 24 h periods pre- and post immunization.
Results: Only one infant had apnoea and/or bradycardia pre-immunization compared with 17 post immunization. For 12 infants these events were brief, self-limiting and not associated with desaturations (oxygen saturation <90%). However, for five infants (30%) these events were associated with oxygen desaturation and two of these infants required supplemental oxygen. The group that had apnoea and/or bradycardia and the group that did not were not significantly different in terms of gestational age, birth weight and other variables. Infants who received Hib together with DTPw were less likely to have apnoea and/or bradycardia than those given DTPw alone.
Conclusion: When considering immunization for preterm infants, the benefits of early immunization must be balanced against the risk of apnoea and bradycardia. We recommend that the cardio-respiratory function of hospitalized infants born at less than 31 weeks gestation be monitored for 48 h post immunization.  相似文献   
24.
25.
蓣知子皂甙IV的结构   总被引:5,自引:1,他引:5  
从木通科木通属植物白木通[Akebia trifoliata(Thunb.)Koidz.var.australis(Diels)Rehd]种子的乙醇提取物中以硅胶层析等方法得四种三萜皂甙。其中甙IV是新天然产物,命名为蓣知子皂甙IV(yuzhiziosideIV)。根据化学和光谱分析,确定甙IV的结构为3-O-β-D-吡喃木糖基-(1→2)-a-L-吡喃阿拉伯糖齐墩果酸-28-O-β-D-吡喃葡萄糖基-(1→6)-β-D-吡喃葡萄糖酯甙。另外皂甙B(I)、皂甙C(II)和皂甙D(III)为已知物。这些化合物在白木通种子中均是首次得到。  相似文献   
26.
为了寻找毒性低、增敏作用强的乏氧细胞放射增敏剂,设计并合成了一系列5-溴-,5-甲基-,和5-未取代的3-硝基-1,2,4-三唑-1-乙酰胺类化合物,用HeLaS3细胞进行了体外试验。结果表明5-溴取代衍生物的增敏作用强于相应的5-甲基-或5-未取代的硝基三唑衍生物,但是它们的毒性亦增大。修饰1位乙酰胺侧链也可以改变化合物的增敏作用和亲脂性。在所测定的化合物中TA-101[2-(3-硝基-1-三唑基)乙酰胺]由于有高的增敏作用和低亲脂性,可能是一个有希望的放射增敏剂。  相似文献   
27.
28.
29.
Fraser  CC; Eaves  CJ; Szilvassy  SJ; Humphries  RK 《Blood》1990,76(6):1071-1076
A large number of biologic, technological, and clinical studies await the development of procedures that will allow totipotent hematopoietic stem cells to be expanded in vitro. Previous work has suggested that hematopoiesis can be reconstituted using transplants of cells from long- term marrow cultures. We have used retrovirus mediated gene transfer to demonstrate that marked totipotent hematopoietic stem cells are both maintained and can be amplified in such cultures, and then subsequently regenerate and sustain lympho-myeloid hematopoiesis in irradiated recipients. Marrow cells from 5-fluorouracil-treated male mice were infected with a recombinant virus carrying the neomycin resistence gene and seeded onto irradiated adherent layers of pre-established, long- term marrow cultures of female origin. At 4 weeks, cells from individual cultures were transplanted into single or multiple female recipients. Southern blot analysis of hematopoietic tissue 45 days posttransplantation showed retrovirally marked clones common to lymphoid and myeloid tissues in 14 of 23 mice examined. Strikingly, for 3 of 4 long-term cultures, multiple recipients of cells from a single flask showed marrow and thymus repopulation with the same unique retrovirally marked clone. These results establish the feasibility of retroviral-marking techniques to demonstrate the maintenance of totipotent lympho-myeloid stem cells for at least 4 weeks in the long- term marrow culture system and provide the first evidence of their proliferation in vitro. Therefore, such cultures may serve as a starting point for identifying factors that stimulate totipotent hematopoietic stem cell expansion.  相似文献   
30.
Choi  Y; Greenberg  SJ; Du  TL; Ward  PM; Overturf  PM; Brecher  ML; Ballow  M 《Blood》1996,87(6):2506-2512
B-cell acute lymphoblastic leukemia (B-ALL), more frequently than any other B-lineage neoplasm, exhibits oligoclonal Ig heavy chain (IgH) gene rearrangement in 15% to 43% of all cases studied. To study the molecular processes that promote multiple IgH rearrangements, a comprehensive sequence analysis of a B-ALL case was performed in which seven clonal IgH gene rearrangements were identified. The genetic profiles suggested that a single leukemic progenitor clone evolved into several subclones through dual processes of variable (VH) to preexisting diversity-joining (DJH) gene segment rearrangement and VH to VH gene replacement. Predominant IgH-V usage and the uniquely rearranged clonotype-specific VHDJH region gene sequences were identified using a novel DNA-based gene amplification strategy. Polymerase chain reaction (PCR) was directed by an IgH-J generic primer and a complement of family-specific IgH-V primers that defined the major B-cell IgH-V gene usage. Clonality of rearranged VHDJH bands was substantiated by high resolution denaturant gel electrophoretic analysis. Sequence patterns of the amplified VHDJH fragments segregated into two groups defined by common DJH sequences. Partial N region homology at the VHD junction as well as shared DJH sequences firmly established VH to VHDJH gene replacement as a mechanism generating clonal evolution in one group. In the second subset, oligoclonality was propagated by independent VH gene rearrangements to a common DJH precursor. The contributions of all clonal Ig-VHDJH repertoires for each group was approximately 50% and reflected a symmetric distribution of leukemic subclones generated by either process. Thus, oligoclonal rearrangements evolved by two independent, yet seemingly contemporaneous molecular genetic mechanisms. All seven clones displayed nonfunctional Ig-VHDJH recombinations. These observations may have relevance to the recombinatorial opportunities available during normal B-cell maturation.  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