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   1148篇
  免费   92篇
  国内免费   1篇
  2022年   5篇
  2021年   13篇
  2020年   6篇
  2019年   11篇
  2018年   10篇
  2017年   14篇
  2016年   25篇
  2015年   40篇
  2014年   63篇
  2013年   54篇
  2012年   71篇
  2011年   53篇
  2010年   53篇
  2009年   36篇
  2008年   44篇
  2007年   52篇
  2006年   59篇
  2005年   55篇
  2004年   40篇
  2003年   41篇
  2002年   48篇
  2001年   45篇
  2000年   45篇
  1999年   48篇
  1998年   11篇
  1997年   16篇
  1996年   17篇
  1995年   11篇
  1994年   5篇
  1993年   11篇
  1992年   27篇
  1991年   21篇
  1990年   14篇
  1989年   20篇
  1988年   8篇
  1987年   7篇
  1986年   8篇
  1985年   21篇
  1984年   10篇
  1983年   12篇
  1981年   5篇
  1979年   7篇
  1977年   5篇
  1976年   8篇
  1975年   5篇
  1974年   6篇
  1973年   6篇
  1969年   6篇
  1965年   4篇
  1955年   4篇
排序方式: 共有1241条查询结果,搜索用时 15 毫秒
31.
We have studied, by the gel mobility shift assay, the interaction of DNA binding proteins with a fragment of the proximal promoter (from nucleotides -177 to -47) of the androgen-regulated canine prostate arginine esterase gene. Several shifted bands were obtained using nuclear extracts from various tissues. In the case of the prostate, the intensity of some of the shifted bands was decreased or increased when the extracts were prepared from animals that had been castrated 12 days earlier. Several of the DNA-protein complexes could be assigned to an interaction with part or all of the sequence GGGGGTGGGGG from-124 to -114. We also obtained evidence for the presence of protein(s) interacting with an Sp1 motif present in the same fragment. These results suggest that some ubiquitous factors different from the androgen receptors could be involved in the regulation of the arginine esterase gene.  相似文献   
32.
To study alterations in cellular gene expression in mouse kidney cell cultures infected with simian virus 40 (SV40) or polyomavirus, we performed a differential screening of a mouse kidney cDNA library with probes prepared from mRNAs of virus-infected and mock-infected cells. We isolated and characterized cDNA recombinant pKT13 which detected increased mRNA levels in infected cells. Sequence analysis of pKT13 revealed close to 100% homology with the 3'-end of mouse fibronectin (FN) mRNA. Since primary cultures of baby mouse kidney cells have been extensively characterized in our laboratories, we studied FN gene expression at different stages of uninfected and virus-infected cultures. High levels of FN and of its mRNA were found in the kidneys of suckling mice, while in primary cultures of proliferating epithelial kidney cells the expression of FN was very low until the cultures became confluent. Thereafter FN increased and reached high levels in cells which were irreversibly arrested in phase Go and which had apparently exhausted their finite division potential. Infection of confluent cultures with polyomavirus or SV40 resulted in a further stimulation of FN gene expression. However, during abortive infection with SV40, FN mRNA and FN levels decreased with emergence of transformed cells and were low in an established SV40-transformed mouse kidney cell line. These changes in FN gene expression suggest that high levels of FN might be indicative in vivo for terminal differentiation and in vitro for cellular senescence.  相似文献   
33.
The epididymis of adult rams is the primary source of alpha-glucosidase in seminal plasma. Two breeds of rams were selected to ascertain whether the enzyme was under androgenic control during adult life of rams. Opposite variations between serum testosterone and alpha-glucosidase were recorded over a period of 16 months in Suffolk and Finnish Landrace. In addition, the highest percentage of sperm motility was associated with a low alpha-glucosidase content of seminal plasma. Data from this study suggest that seasonal variations of testosterone in adult rams exert a negative control on the presence of alpha-glucosidase in semen.  相似文献   
34.
P. LeBlanc  B. Tremblay  D. D'Amours  G. Tremblay 《CMAJ》1982,126(11):1300-1305
A program of reconditioning through walking was prescribed for 130 patients following an exercise test on a treadmill 3 weeks after a myocardial infarction. At 8 and at 12 weeks the patients again underwent an exercise test. The protocol is safe and permits the detection of angina, arrhythmias and dyspnea during the exercise, thus avoiding delays in treatment. The heart rate and the systolic blood pressure were measured at the end of each stage of the test and after 3 minutes of recuperation. About 75% of the patients attained the target energy output of the two submaximal tests (4 and 7 mets at 3 and 8 weeks respectively); an output of 7 mets permits a patient to resume his or her usual daily activities. The results of the tests at 3 and 12 weeks (the latter a maximal test) showed that the probability of an aerobic capacity of 7 mets or greater at 12 weeks is 86% if the 3-week test is completed. Clinical observations alone did not have the same prognostic value 3 weeks after the infarction.  相似文献   
35.
A plasma inhibitor of tonin activity in the rat, was purified by ammonium sulfate precipitation, ion-exchange of chromatography, and gel filtration. Its purity was investigated by analytical electrophoresis on polyacrylamide gel and by ultracentrifugation sedimentation velocity. The molecular weight (360 000) of the purified inhibitor was determined by sodium dodecyl sulfate electrophoresis and its isoelectric point (4.5) by gel isoelectrofocusing. The Stokes radius (640 nm) was evaluated by gel filtration studies and a frictional ratio (f/fo) of 1.95 was calculated from the molecular weight and Stokes radius. Kinetic studies using angiotensin I as substrate showed that the inhibition of tonin by the purified inhibitor was noncompetitive and does not exceed 70%. Electrophoresis showed the same mobility for [125I]tonin bound to plasma proteins and for [125I]tonin bound to the purified inhibitor. The inhibitor may be a protein resembling half of the dimeric protease inhibitor rat alpha 1-macroglobulin or human alpha 2-macroglobulin.  相似文献   
36.
The effect of 6-hydroxydopamine (6-OH-dopamine) and of a cholesterol rich diet on the plasma and aortic cholesterol of female rats were studied. Both the diet and the 6-OH-dopamine produced an important increase in plasmatic and aortic cholesterol. A synergistic effect of these two treatments was observed on the plasma but not on the aortic cholesterol. The mechanism by which 6-OH-dopamine produces hypercholesterolemia and a increase in aortic cholesterol remains to be explained.  相似文献   
37.
This study is concerned with the computation of aortic pulse wave velocity based on simultaneous recordings of the aortic pressure gradient and first-time derivative of aortic pressure. These variables were recorded by means of a double-lumen catheter introduced in the aorta of four anesthetized closed chest dogs, and connected to critically damped manometer systems. Results of aortic pulse wave velocity were then compared: (i) to the true phase velocity obtained from spectra of apparent phase velocity, and (ii) to the pulse wave velocity computed from the time shift between maximum slopes of the pressure wave. From the aortic valves to 37 cm down the aortic trunk, pulse wave velocity increased from 410-460 cm/s to approximately 600-800 cm/s. Based on the wave propagation equation presented of Bramwell and Hill (Bramwell, J.C., and Hill, A. V. 1922. Proc. R. Soc. 93, 298-306), volumetric extensibility coefficients were computed from pulse wave velocity data. Results indicated that, from the aortic valves to 37 cm down to the aorta, the mean volumetric extensibility decreased from 0.43-0.56% deltaV/cm H2O to 0.16-0.25% deltaV/cm H2O (1 cm H2O = 94.1 N/m2).  相似文献   
38.
The effect of catecholamine-depleting pretreatments, reserpine, and 6-hydroxydopamine (6-OH-DA) on left ventricular pressure (LVP) and the inotropic response to graded doses of ouabain (up to 300 mug/0.05 ml) was studied in isolated perfused rat and guinea-pig hearts. In rats, reserpine and 6-OH-DA depleted the cardiac content of catecholamine, but did not increase initial LVP and did not reduce the inotropic response to the highest dose of ouabain. It is concluded that in isolated rat hearts, these catecholamine-depleting pretreatments nearly abolish the inotropic response to ouabain, and this effect appears to be mediated mainly through an increase in initial LVP. The reason why catecholamine depletion failed to increase initial LVP in guinea pigs remains unexplained.  相似文献   
39.
To characterize by a mathematical model the dynamics of adrenocortical responses to ACTH, the concentration of plasma corticosterone was measured following a series of injections and perfusions of ACTH to dexamethasone-treated male rats. A similar slope was observed during the rise of plasma corticosterone following graded pulse inputs, and the steady-state corticosterone secretion rate was shown to increase proportionally to the perfusion rate of ACTH up to saturation corresponding to maximal secretion. The data will be used, concurrently with our model of the dynamics of plasma cortiscosterone, for the identification of a mathematical model of the adrenocortical response to ACTH.  相似文献   
40.
We have studied the cytosolic phospholipase A2 (cPLA2) of human U937 cells by radiation inactivation in order to characterize the functional form of the native enzyme by a method that was independent of the discrepancies observed by SDS-PAGE and cDNA cloning. The Radiation Inactivation Size of cPLA2 was reproducible and gave a value of 76,800-80,100 daltons. We eluted the active enzyme from polyacrylamide-gradient gel electrophoresis at a molecular weight of 77,000, confirming the irradiation result. We conclude that cPLA2 is active as the monomeric enzyme and is composed of a single major functional domain that is sensitive to irradiation.  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