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   11464篇
  免费   268篇
  国内免费   1篇
  11733篇
  2020年   71篇
  2019年   77篇
  2018年   241篇
  2017年   202篇
  2016年   276篇
  2015年   270篇
  2014年   355篇
  2013年   451篇
  2012年   435篇
  2011年   463篇
  2010年   292篇
  2009年   201篇
  2008年   303篇
  2007年   339篇
  2006年   336篇
  2005年   313篇
  2004年   259篇
  2003年   305篇
  2002年   276篇
  2001年   264篇
  2000年   219篇
  1999年   169篇
  1998年   73篇
  1992年   227篇
  1991年   214篇
  1990年   171篇
  1989年   200篇
  1988年   224篇
  1987年   233篇
  1986年   208篇
  1985年   238篇
  1984年   192篇
  1983年   157篇
  1982年   79篇
  1980年   81篇
  1979年   234篇
  1978年   153篇
  1977年   135篇
  1976年   136篇
  1975年   162篇
  1974年   263篇
  1973年   257篇
  1972年   243篇
  1971年   240篇
  1970年   252篇
  1969年   242篇
  1968年   184篇
  1967年   185篇
  1966年   165篇
  1965年   123篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
The group of aged subjects being 66 to 97 years old was compared with the middle-age group with regard to various immunological and cytochemical indices related to lymphocytes and neutrophils. The aged showed a lowered count and percentage of T cells, increased count and percentage of "non-B, non-T" lymphocytes, increased percentage of B cells. These alterations in the composition of lymphocyte subpopulation were associated with characteristic patterns of damage affecting the enzyme-positive lysosomal apparatus of lymphocytes with regard to acid phosphatase, beta-glucuronidase and N-acetyl-beta-D-glucosaminidase. There was a hundredfold smaller number of cells having intact enzyme-positive lysosomes in the aged than in the group of comparison. The changes mentioned above were also associated with the intracellular accumulation of glycogen in lymphocytes, decreased concentration of IgG and IgM in the serum and various changes in IgA concentration. Neutrophils of the aged were fewer in the blood of the aged than in younger subjects. However, an increased activity of myeloperoxidase, alkaline phosphatase, N-acetyl-beta-D-glucosaminidase, and an increased content of glycogen and lipids could be found in these cells. NBT-positive neutrophil numbers in the aged were lowered if the stimulated test was used and if there were no changes of the spontaneous test.  相似文献   
73.
Pineal involvement in the regulation of adrenocortical mitotic activity has recently been suggested. It has been shown that melatonin (Mel) decreased the mean mitotic activity rate (MMAR) of the adrenal cortex both in vivo and in organ culture. The goal of the present study was to test the influence of pinealectomy (PX) and/or Mel-treatment on the MMAR of adrenocortical cells, as well as on the adrenal weight in rats. The stathmokinetic method was used in the study. It was found that PX significantly increased the MMAR of the adrenocortical cells. Moreover, Mel suppressed the proliferogenic effect of PX on the rat adrenocortical cells. Melatonin alone did not significantly affect the mitotic activity of the adrenal cortex. None of the three experimental procedures, i.e. Mel, PX and Mel-treatment of pinealectomized animals significantly affected the adrenal weight. The present data suggest that Mel may be involved in the inhibitory control of adrenocortical cell proliferation.  相似文献   
74.
The fate of young individuals (to 45 years) with a history of myocardial infarction during 12 years was analysed with the aid of a questionnaire containing questions of both social and medical character. Sudden cardiac death or the second infarction were the most frequent causes of death during the first two years following myocardial infarction. Change in the physical activity mainly involved the return to work. Only 47% of young men and 29.8% of women started full-time jobs. They mainly belonged to so-called white collars. The lack of patients' physicians permission was a main cause of the abstinence of young men from the occupation. A position within the family and social activity usually remained unchanged in the majority of patients, but every third patient greatly reduced sexual activity. Every third patients continued smoking, and did not observe recommended diet despite the systematical medical check-ups. The course of the disease is unclear in the majority of young patients. It is often deformed and requires further, detailed information on young patients' style of life.  相似文献   
75.
Lithium concentration was determined in both sputum and blood serum of 31 patients treated with lithium carbonate. It was found that lithium concentration rate in the sputum/blood serum is 2.17 +/- 0.16, and is constant in all patients, except one, for a long time. A high correlation index between lithium concentration in the sputum and blood serum (r = 0.9025, and without two assays in the above mentioned patient r = 0.9858) as well as stability of sputum/serum lithium levels enable -- in the opinion of the authors -- to control lithium concentration in the body, using sputum for the assays. These assays are easy to perform with the aid of the kit called "Salivette" (Sarstedt, Germany). Its principle was discussed, too.  相似文献   
76.
Lead chloride (10-5 M) inhibited the growth of the main root, the duration of development, the number and growth of lateral roots, primary and trifoliate leaves, and also the mitotic index in root apical meristems. Lead strongly inhibited root growth rate, mainly by reducing the number of dividing cells. Other mechanisms of this inhibition are discussed.  相似文献   
77.
Isolated, cultured rat neonatal cardiac myocytes were placed in medium supplemented with mitochondrial respiratory inhibitor potassium cyanide which caused a rapid adenosine triphosphate (ATP) depletion. These myocytes with the impaired energy metabolism ("hypoxia-like state") were exposed to unstimulated human neutrophils. Effect of human neutrophils on the myocytes in the "hypoxia-like state" was quantified as a total change in the amount of ATP in cardiac cells. After 5 hours of incubation of neutrophils with the myocytes in the "hypoxia-like state" an additional decrease (of 50 per cent) in ATP content was observed. Since catalase (which destroys hydrogen peroxide) prevented the further decline in ATP level in the myocytes with impaired energy metabolism, it seem that hydrogen peroxide and possibly their products are responsible for this effect. These results suggest that unstimulated human neutrophils after activation by the contact with injured cardiac cells caused further decrease of ATP level in target cells.  相似文献   
78.
Six chronic uremic patients on regular hemodialysis treatment were given recombinant human erythropoietin (r-huEPO) in a dose of 50 U/kg of body weight intravenously thrice weekly for 14 weeks. Following r-huEPO therapy, unstimulated whole blood superoxide anion ( 2) generation did not change significantly, while opsonized zymosan-stimulated whole blood 2 generation increased. At the same time, erythrocyte superoxide dismutase and, in particular, glutathione peroxidase activities were found to be reducing with concomitant lowering of erythrocyte malonydialdehyde (MDA) concentrations and increase in plasma MDA concentrations.  相似文献   
79.
80.
Two classes of phosphonopeptides, those containing P-terminal 9-aminofluoren-9-ylphos-phonic acid and those of dialkyl 9-aminofluoren-9-ylphosphine oxides, influence plant growth according to different mechanisms. The effect of these compounds on the growth of several bacterial species, including the photosynthetic bacteriumRhodospirillum rubrum, as well as on the activity of photosystems 1 and 2 in isolatedPisum sativum andSpirodela oligorrhiza chloroplasts was studied. The peptides of free, unblocked 9-aminofluoren-9-ylphosphonic acid acted in a morphactin-like manner, whereas those of dialkyl 9-aminofluoren-9-ylphosphine oxides influenced photosynthesis indirectly.  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