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   2321篇
  免费   208篇
  国内免费   4篇
  2533篇
  2022年   28篇
  2021年   34篇
  2020年   17篇
  2019年   23篇
  2018年   30篇
  2017年   18篇
  2016年   45篇
  2015年   88篇
  2014年   113篇
  2013年   95篇
  2012年   171篇
  2011年   135篇
  2010年   89篇
  2009年   71篇
  2008年   133篇
  2007年   121篇
  2006年   125篇
  2005年   105篇
  2004年   93篇
  2003年   96篇
  2002年   78篇
  2001年   70篇
  2000年   62篇
  1999年   36篇
  1998年   19篇
  1997年   19篇
  1996年   19篇
  1995年   15篇
  1994年   22篇
  1993年   13篇
  1992年   32篇
  1991年   36篇
  1990年   23篇
  1989年   36篇
  1988年   38篇
  1987年   37篇
  1986年   37篇
  1985年   34篇
  1984年   23篇
  1983年   26篇
  1982年   21篇
  1981年   18篇
  1980年   13篇
  1979年   24篇
  1978年   14篇
  1977年   24篇
  1976年   15篇
  1974年   12篇
  1973年   17篇
  1971年   11篇
排序方式: 共有2533条查询结果,搜索用时 15 毫秒
21.
22.
Gene mapping by fluorescent in situ hybridization   总被引:6,自引:0,他引:6  
We describe a new method for the mapping of mammalian genes, utilizing in situ hybridization of mRNA to DNA of chromosomes. It involves the hydrogen bonding of the polyadenylic acid at the 3' end of hybridized mRNA to the polyuridylic acid tail of a highly fluorescent latex microsphere. The resultant double hybrid can be visualized by fluorescence microscopy. The chromosomal localization of human alpha + beta globin genes has been explored by this method. Our data point ot the long arms of chromosomes 4 and 5 as the loci for the human globin genes.  相似文献   
23.
24.
H C Cheung  C K Wang  N A Malik 《Biochemistry》1987,26(18):5904-5907
We have determined the free energy of formation of the binary complexes formed between skeletal troponin C and troponin T (TnC.TnT) and between troponin T and troponin I (TnT.TnI). This was accomplished by using TnC fluorescently modified at Cys-98 with N-(iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine for the first complex and TnI labeled at Cys-133 with the same probe for the other complex. The free energy of the ternary complex formed between troponin C and the binary complex TnT.TnI [TnC.(TnT.TnI)] was also measured by monitoring the emission of 5-(iodoacetamido)eosin attached to Cys-133 of the troponin I in TnT.TnI. The free energies were -9.0 kcal.mol-1 for TnC.TnT, -9.2 kcal.mol-1 for TnT.TnI, and -8.7 kcal.mol-1 for TnC.(TnT.TnI). In the presence of Mg2+ the free energies of TnC.TnT and TnC.(TnT.TnI) were -10.3 and -10.9 kcal.mol-1, respectively; in the presence of Ca2+ the corresponding free energies were -10.6 and -13.5 kcal.mol-1. Mg2+ and Ca2+ had negligible effect on the free energy of TnT.TnI. From these results the free energies of the formation of troponin from the three subunits were found to be -16.8 kcal.mol-1, -18.9 kcal.mol-1, and -21.6 kcal.mol-1 in the presence of EGTA, Mg2+, and Ca2+, respectively. Most of the free energy decrease caused by Ca2+ binding to the Ca2+-specific sites is derived from stabilization of the TnI-TnC linkage.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
25.
The effects of granulocyte depletion with hydroxyurea on pulmonary responsiveness to aerosol histamine were studied in 10 chronically instrumented unanesthetized sheep. Sheep were studied when granulocyte counts were normal (B), after 3 days of hydroxyurea but before granulocyte counts had dropped below 700 cells/mm3 (H), and after granulocyte counts had fallen below 200 cells/mm3 (D). Hydroxyurea itself had no effect on aerosol histamine responsiveness and the results were unaffected by the order of experimentation. All 10 sheep were less responsive (P less than 0.05) to aerosol histamine when granulocyte depleted effective dose of histamine that caused a reduction to 65% of control dynamic compliance (ED65Cdyn = 23.98 +/- 4.70 mg/ml) compared with base line (ED65Cdyn = 7.06 +/- 1.86 mg/ml). Those sheep initially most responsive to aerosol histamine had the greatest attenuation in their airway responsiveness to aerosol histamine (P less than 0.05). There was a significant negative correlation between absolute granulocyte counts in peripheral blood and pulmonary responsiveness to aerosol histamine during base-line (B) condition (r = -0.74, P less than 0.05) and for the data as a whole [r = -0.69, P less than 0.05 (B + H + D)]. Circulating granulocytes and/or pulmonary inflammation may contribute to pulmonary responsiveness to bronchial challenge.  相似文献   
26.
Proteomic analysis was applied to investigate the mechanism of the stimulatory effect of Tween 80 on the mycelial growth and exopolysaccharide production by an edible mushroom Pleurotus tuber-regium. 32 differentially expressed proteins were identified by one-dimension gel electrophoresis. Combined with our previous findings, the up-regulation of heat shock proteins might help to maintain cellular viability under environmental stress. The up-regulation of ATP:citrate lyase isoform 2 could suppress the activity of tricarboxylic acid cycle and, consequently, stimulate exopolysaccharide production. The present results provide important insight to the mechanism by which stimulatory agents (Tween 80) can increase the production of useful fungal metabolites and also fill the gap of our knowledge on the under-developed mushroom proteomics.  相似文献   
27.

Background  

Tumour regression observed in many conditional mouse models following oncogene inactivation provides the impetus to develop, and a platform to preclinically evaluate, novel therapeutics to inactivate specific oncogenes. Inactivating single oncogenes, such as c-Myc, can reverse even advanced tumours. Intriguingly, transient c-Myc inactivation proved sufficient for sustained osteosarcoma regression; the resulting osteocyte differentiation potentially explaining loss of c-Myc's oncogenic properties. But would this apply to other tumours?  相似文献   
28.
29.

Objective

To describe temporal changes in systolic, diastolic, and mean blood pressure (SBP, DBP, and MBP, respectively) in term and preterm infants immediately after birth.

Methods

Prospective observational two-center study. In term infants SBP, DBP, and MBP were assessed non-invasively every minute for the first 15 minutes, and in preterm infants every minute for the first 15 minutes, as well as at 20, 25, 30, 45, and 60 minutes after birth. Regression analyses were performed by gender and respiratory support in all neonates; and by mode of delivery, cord clamping time, and development of ultrasound-detected brain injury in preterm neonates.

Results

Term infants (n = 54) had a mean (SD) birth weight of 3298 (442) g and gestational age of 38 (1) weeks, and preterm infants (n = 94) weighed 1340 (672) g and were 30 (3) weeks gestation. Term infants’ SBP, DBP and MBP within the first 15 minutes after birth were independent of gender or respiratory support. Linear mixed regression analysis showed that preterm infants, who were female, born vaginally, had delayed cord clamping and did not require positive pressure ventilation nor develop periventricular injury or ventriculomegaly, had significantly higher SBP, DBP, and MBP at some measurement points within the first hour after birth.

Conclusions

We present novel reference ranges of BP immediately after birth in a cohort of term and preterm neonates. They may aid in optimization of cardiovascular support during early transition at all gestations.  相似文献   
30.
The expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) was studied in spleen lymphocytes isolated from male C57BL/6J mice of 6, 20, and 29 months of age. GM-CSF expression (biological activity and mRNA level) was maximum after culturing the lymphocytes for 45 hr with concanavalin A and phorbol myristate acetate. The induction of both GM-CSF activity and mRNA levels was observed to decline over 60% between 6 and 29 months of age. The age-related decline in the level of GM-CSF paralleled the age-related decline in the mRNA levels of interleukin-2 and interleukin-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