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   445380篇
  免费   51508篇
  国内免费   744篇
  497632篇
  2018年   4163篇
  2017年   4006篇
  2016年   5711篇
  2015年   8251篇
  2014年   9601篇
  2013年   12940篇
  2012年   15333篇
  2011年   15792篇
  2010年   10455篇
  2009年   9491篇
  2008年   13843篇
  2007年   14291篇
  2006年   13428篇
  2005年   12803篇
  2004年   12863篇
  2003年   12007篇
  2002年   11660篇
  2001年   18918篇
  2000年   18849篇
  1999年   15072篇
  1998年   5622篇
  1997年   5631篇
  1996年   5358篇
  1995年   5150篇
  1994年   4849篇
  1993年   4852篇
  1992年   12473篇
  1991年   12434篇
  1990年   12193篇
  1989年   11661篇
  1988年   10832篇
  1987年   10202篇
  1986年   9732篇
  1985年   9500篇
  1984年   7876篇
  1983年   6828篇
  1982年   5135篇
  1981年   4626篇
  1980年   4311篇
  1979年   7348篇
  1978年   5964篇
  1977年   5290篇
  1976年   4959篇
  1975年   5769篇
  1974年   6301篇
  1973年   6120篇
  1972年   5458篇
  1971年   5075篇
  1970年   4274篇
  1969年   4202篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Extensibility, contractile function and resistance to excess calcium of the right atrium myocardium were studied in normotensive Wistar-Kyoto and August rats and in spontaneously hypertensive rats (SHR). It was shown that long-term stress results in a decrease in the measured parameters in normotensive animals. SHR do not show any stress-induced disturbances. It was discovered that in intact SHR rats, the myocardium has a greater resistance to excess calcium, indirect evidence for higher efficiency of the Ca-pump of the sarcoplasmic reticulum in cardiomyocytes of SHR animals, which is apparently a constituent part of the mechanism of such animals' heart increased resistance to stress-induced damage.  相似文献   
82.
THE TIMING OF DIVISION IN CHLAMYDOMONAS   总被引:3,自引:2,他引:1  
  相似文献   
83.
The neutrophil-stimulating properties of 38 S. aureus strains and 32 S. epidermidis strains were studied in the reaction of luminol-mediated chemiluminescence. All S. aureus strains and 29 S. epidermidis strains were found to possess neutrophil-stimulating activity, the mean activity index for S. aureus being significantly higher. The stimulating activity of the strains varied within a wide range (the variation coefficient was 120.0 +/- 21.9%) and did not correlate with the content of protein A in bacterial cells and the degree of their hydrophoby. The opsonization of staphylococci with normal human serum enhanced the neutrophil reaction 1.5- to 100-fold and simultaneously leveled out the chemiluminescence indices in experiments with different strains (the variation coefficient was 8.0 +/- 1.5%). The nature of the neutrophil-stimulating effect of staphylococci and its relationship to the exploratory reactions of phagocytes are discussed.  相似文献   
84.
85.
86.
Samples of marine pleuston were collected from the sea-surface along considerable sections of the track of Eye of the Wind during its 2-year circumnavigational expedition 'Operation Drake' from November 1978 to October 1980. One hundred and eleven of the tow samples contained insects of the genus Halobates . They were assigned to four oceanic species: H. micans, H. sericeus, H. germanus and H. splendens; two coastal species: H. maculatus, H. princeps, and one undescribed species. Various development stages of the oceanic species were found. The locations, time of collection and surface temperatures where sea-skaters were collected are tabulated. Distributional boundaries and population densities of the oceanic species collected are discussed.  相似文献   
87.
88.
Rosette and single-element strain gauges were implanted on the tibia in 2 dogs and recordings were made during locomotion on a treadmill. At foot contact and during the swing phase of locomotion, bone strains were low and directions of the principal strains were variable. There was a large shift in the directions of the principal strains at the beginning of the stance phase and bone strains were considerably higher. Peak strain occurred midway through the stance phase. At that time, the maximum principal strain (tension) was directed upwards and anteriorly between 30 and 60 degrees with respect to the long axis of the tibia. These bone strain patterns in the dog are similar to those found in sheep while both differ markedly from those found in humans.  相似文献   
89.
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation.  相似文献   
90.
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