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   5829篇
  免费   699篇
  国内免费   3篇
  2021年   54篇
  2018年   53篇
  2016年   93篇
  2015年   120篇
  2014年   143篇
  2013年   192篇
  2012年   252篇
  2011年   191篇
  2010年   149篇
  2009年   142篇
  2008年   203篇
  2007年   204篇
  2006年   213篇
  2005年   194篇
  2004年   188篇
  2003年   181篇
  2002年   187篇
  2001年   199篇
  2000年   194篇
  1999年   165篇
  1998年   82篇
  1997年   107篇
  1996年   101篇
  1995年   89篇
  1994年   89篇
  1993年   88篇
  1992年   120篇
  1991年   113篇
  1990年   144篇
  1989年   123篇
  1988年   106篇
  1987年   115篇
  1986年   98篇
  1985年   123篇
  1984年   90篇
  1983年   72篇
  1982年   80篇
  1981年   69篇
  1980年   76篇
  1979年   85篇
  1978年   72篇
  1977年   65篇
  1976年   76篇
  1975年   70篇
  1974年   74篇
  1973年   73篇
  1972年   75篇
  1971年   62篇
  1969年   47篇
  1968年   51篇
排序方式: 共有6531条查询结果,搜索用时 15 毫秒
951.
The binding of [3H]prostaglandin E1 to membranes of clones of normal rat kidney fibroblasts (NRK cells) has been measured. Cell lines that responded to prostaglandin E1, such as NRK and NRK transformed with Schmitt-Ruppin strain of Rous sarcoma virus (SR-NRK cells), have a high affinity prostaglandin E1 binding site. Murine-sarcoma-virus-transformed lines of NRK cells are unresponsive to prostaglandin E1 and have reduced prostaglandin E1 binding. Exposure of cells to prostaglandin E1 results both in decreases prostaglandin E1 responsiveness and reduced prostaglandin E1 binding.Activation of adenylate cyclase is correlated to binding of prostaglandin E1 to receptors in both NRK and SR-NRK cell membranes. Mathematical models suggest that GTP decreases the affinity of hormone for its receptor while increasing the catalytic efficiency of adenylate cyclase, and that aggregates of occupied receptors may play an important role in the activation of adenylate cyclase.  相似文献   
952.
953.
Exposing pregnant sheep to an ambient temperature of 43 +/- 1 degree C for 8 h was associated with a 1-1.5 degrees C increase of maternal and fetal core temperatures, and a 11-fold and 3-5 fold increase in maternal and fetal plasma prolactin concentrations respectively. Hyperthermia did not change maternal or fetal plasma cortisol concentrations. We conclude that maternal and fetal hyperprolactinaemia may occur in late pregnancy during hyperthermic conditions and that the increase in fetal plasma prolactin is due to either increased secretion or decreased metabolic clearance of prolactin in the feto-placental compartment.  相似文献   
954.
There is no direct evidence to support the contention that contracting skeletal muscle and/or associated vasculature generates free radicals in exercising humans. The unique combination of isolated quadriceps exercise and the measurement of femoral arterial and venous free radical concentrations with the use of electron paramagnetic resonance (EPR) spectroscopy enabled this assumption to be tested in seven healthy men. Application of ex vivo spin trapping using alpha-phenyl-tert-butylnitrone (PBN) resulted in the detection of oxygen- or carbon-centered free radicals (a(N) = 1.38 +/- 0.01 mT and a(beta)(H) = 0.17 +/-0.01 mT, where a(N) and a(beta)(H) are the nitrogen and beta-hydrogen coupling constants, respectively) with consistently higher EPR signal intensities of the PBN spin adduct observed in the venous compared with the arterial circulation (P < 0.05). Incremental exercise further increased the venoarterial intensity difference [85 +/- 58 arbitrary units (AU) at 24 +/- 6% maximal work rate (WR(max)) vs. 387 +/- 214 AU at 69 +/- 7% WR(max); P < 0.05]. When combined with measured changes in femoral venous blood flow (Q), this resulted in a net adduct outflow of 130 +/- 118 and 1,146 +/- 582 AU/min (P < 0.05), which was positively associated with leg oxygen uptake (r(2) = 0.47, P < 0.05) and Q (r(2) = 0.47, P < 0.05). These results provide the first evidence for oxygen- or carbon-centered free radical outflow from an active muscle bed in humans.  相似文献   
955.
Background: An accurate assessment of ankle ligament kinematics is crucial in understanding the injury mechanisms and can help to improve the treatment of an injured ankle, especially when used in conjunction with robot-assisted therapy. A number of computational models have been developed and validated for assessing the kinematics of ankle ligaments. However, few of them can do real-time assessment to allow for an input into robotic rehabilitation programs. Method: An ankle computational model was proposed and validated to quantify the kinematics of ankle ligaments as the foot moves in real-time. This model consists of three bone segments with three rotational degrees of freedom (DOFs) and 12 ankle ligaments. This model uses inputs for three position variables that can be measured from sensors in many ankle robotic devices that detect postures within the foot–ankle environment and outputs the kinematics of ankle ligaments. Validation of this model in terms of ligament length and strain was conducted by comparing it with published data on cadaver anatomy and magnetic resonance imaging. Results: The model based on ligament lengths and strains is in concurrence with those from the published studies but is sensitive to ligament attachment positions. Conclusions: This ankle computational model has the potential to be used in robot-assisted therapy for real-time assessment of ligament kinematics. The results provide information regarding the quantification of kinematics associated with ankle ligaments related to the disability level and can be used for optimizing the robotic training trajectory.  相似文献   
956.
957.
958.
959.
960.
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