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   223939篇
  免费   14993篇
  国内免费   49篇
  238981篇
  2021年   1773篇
  2018年   3125篇
  2017年   3023篇
  2016年   3666篇
  2015年   3201篇
  2014年   4437篇
  2013年   6321篇
  2012年   7542篇
  2011年   8060篇
  2010年   5721篇
  2009年   4876篇
  2008年   7197篇
  2007年   7477篇
  2006年   7178篇
  2005年   6703篇
  2004年   6848篇
  2003年   6567篇
  2002年   6524篇
  2001年   9274篇
  2000年   8953篇
  1999年   6987篇
  1998年   2122篇
  1997年   1953篇
  1996年   1819篇
  1992年   5467篇
  1991年   5677篇
  1990年   5650篇
  1989年   5620篇
  1988年   5212篇
  1987年   4862篇
  1986年   4442篇
  1985年   4677篇
  1984年   3696篇
  1983年   3025篇
  1982年   2013篇
  1981年   1722篇
  1980年   1725篇
  1979年   3338篇
  1978年   2576篇
  1977年   2375篇
  1976年   2330篇
  1975年   2826篇
  1974年   3117篇
  1973年   3084篇
  1972年   2746篇
  1971年   2604篇
  1970年   2212篇
  1969年   2158篇
  1968年   2031篇
  1967年   1797篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Proteases with the thrombolytic activity were studied in 212 strains of actinomycetes isolated from different soils of the Soviet Union. The cultures belonged to the genera Micromonospora, Nocardia and Streptomyces. Proteases were synthesized by 41% of the studied actinomycetes and some of their strains completely dissolved in vitro artificially obtained blood thrombi within 120-240 min. In the Streptomyces genus, more active strains were found in the groups Flavus, Fradia and Globisporus. The groups Olivaceus, Violaceus and Viridis had less active strains.  相似文献   
82.
The infection of Planorbarius banaticus with sporocysts of Cotylurus cornutus is accompanied by an increase in aldolase activity of molluscs' haemolymph of 1.2 fold. In solutions of nitroammofoska (0.1, 1 and 10 mg/1) the activity of this ferment in infected individuals increases much higher than in non-infected ones. This results in fast carbohydrate expenditures by molluscs, intermediate hosts of trematodes, and their death from exhaustion.  相似文献   
83.
Infravesical obstruction in 300 male patients was determined by prostatic sclerosis (PS). PS is a polyetiological disease developing more frequently as a result of prostatitis, autoimmune, allergic and congestive factors. Sclerosis and shriveling of the gland cause topographo-anatomic changes in the infravesical area, well revealed during a combined roentgeno-urological study. Direct signs of PS are the following: stenosis, deformity and shortening of the prostatic part of the urethra, a high position of the lower outline of the bladder resembling braces over the public symphysis; indirect signs: change of the bladder shape, megacyst, trabecular mucosa and diverticulosis, congestion in the upper urinary tracts, uni- or bilateral urethero-hydronephrosis.  相似文献   
84.
The effects of corticotropin-releasing hormone (CRH) injected into the dorsal neostriatum on the open-field and shuttle-box behavior were studied in rats with high (Koltushi high avoidance, KHA) and low (Koltushi low avoidance, KLA) capability for avoidance learning. The effects of this hormone on the behavior of these rat strains were different. In KLA rats with passive strategy of behavior the CRH injection led to a rapid locomotor activation in the open field, while the rats with active behavioral strategy (KHA) reacted to the injection by a significant decrease in locomotion and change for the passive mode of behavior. The same CRH effects on locomotion were obtained in the shuttle-box experiments. Moreover, in the KLA rats the neurohormone injection resulted in an improvement of avoidance learning in contrast to the KHA rats, in which CRH substantially impaired avoidance learning. The obtained evidence is discussed in terms of the important role of striatal CRH in the choice of behavioral strategy in stress.  相似文献   
85.
X-IRRADIATION of mammalian cells in culture yields a survival curve of the threshold type (for review see ref. 1). It isjnter-esting to ask how one can enhance the radiation response by small changes of the physical environment of the cells, as can be done chemically, for example, by incorporation of 5-bromo-deoxyuridine into DNA1,2. Elevation of the temperature is a likely prospect for enhancement of radiosensitivity for the following reasons. It is known that proteins are heat labile and that temperature sensitive mutants of bacteria and phage can be obtained for many different enzymes3 which are operative at 37° C but not at 42° or 43°C. For example4, DNA polymerase is reversibly temperature sensitive; it is rendered inoperative above 42°C, but will be functional again when the temperature is lowered. It is not unreasonable to expect that temperature sensitive mutations for many enzymes occur frequently and that the use of temperatures somewhat higher than the normal range at which the cells grow might disclose sensitivities for specific enzymes in normal cells of higher organisms.  相似文献   
86.
87.
88.
89.
90.
Content of dopamine in the striatum; of serotonin, 5-hydroxyindolacetic acid and noradrenaline in the hypothalamus, striatum and midbrain was studied in three groups of minks from population of an animal farm, differing by their reaction to humans (cowardly, calm, aggressive). The reaction to humans was estimated by a system of marks at the attempt to catch the mink with a mitten. Aggressive animals had a lowered level of serotonin in the hypothalamus and striatum, a lesser content of serotonin metabolite--5-hydroxyindolacetic acid in the striatum. Minks of different groups did not differ by noradrenaline content, but dopamine level in the striatum of cowardly minks was higher than in calm and aggressive animals. Conclusion is made that polymorphism of behaviour corresponds to polymorphism of the state of monoaminergic systems.  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