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   300443篇
  免费   21994篇
  国内免费   76篇
  2018年   3920篇
  2017年   3763篇
  2016年   4734篇
  2015年   4654篇
  2014年   6071篇
  2013年   8680篇
  2012年   10013篇
  2011年   10509篇
  2010年   7481篇
  2009年   6481篇
  2008年   9384篇
  2007年   9642篇
  2006年   9191篇
  2005年   8615篇
  2004年   8715篇
  2003年   8389篇
  2002年   8216篇
  2001年   12685篇
  2000年   12271篇
  1999年   9565篇
  1998年   3014篇
  1997年   2881篇
  1996年   2645篇
  1995年   2419篇
  1992年   7423篇
  1991年   7608篇
  1990年   7587篇
  1989年   7370篇
  1988年   6868篇
  1987年   6483篇
  1986年   5989篇
  1985年   6144篇
  1984年   4921篇
  1983年   4124篇
  1982年   2847篇
  1981年   2506篇
  1980年   2424篇
  1979年   4598篇
  1978年   3572篇
  1977年   3255篇
  1976年   3196篇
  1975年   3835篇
  1974年   4223篇
  1973年   4273篇
  1972年   3773篇
  1971年   3532篇
  1970年   3032篇
  1969年   3007篇
  1968年   2783篇
  1967年   2513篇
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
761.
IntroductionThe MIITOP-0607 protocol, studying the efficiency of administration of topotecan and myelosupressive [131I]-mIBG therapy in children affected by neuroblastoma, needed to assess irradiation risks on staff and family of children to obtain the agreement of the Autorité de sûreté nucléaire (ASN). Our aim was to quantify irradiation of the staff during preparation of the mIBG and to assay the irradiation and contamination of the accompanying persons.Patient and methodsRadiation exposure of the staff was measured during the preparation, transport and administration of the first treatment. Salivary and urinary excretions were monitored well as the atmospheric radioactivity. Radiation exposure and contamination of the accompanying persons were also measured.ResultsFinger dose of 3 mSv and whole body dose of 50 μSv were estimated for preparation of an 11.1 GBq syringe. Irradiation from urinary activity can be as low as 100 μSv if a dedicated device is used. Salivary excretion decreased rapidly during the first 24 hours. Atmospheric contamination always remained below 25 Bq m?3. Total irradiation of the accompanying persons is about 2.35 mSv for the two consecutive injections (9,3 and 11,1 GBq). Internal contamination occurred only once and corresponded to a 27 μSv whole body irradiation and 670 μSv thyroid irradiation.ConclusionThis study shows the safety of [131I]-mIBG treatments using high activities. The involved dose is not negligible but seems to be acceptable in the specific paediatric oncology context if radioprotection instructions are met and if optimization of protocols is performed.  相似文献   
762.
The pleiotropic effects of transgenesis includes different consequences of the insertion of a transgene that are not related to the direct action of its product. It is necessary to evaluate the outlook for the application in selection of the transgenic potato strain containing the bacterial chitinase gene chiA we created for studying the possible nonspecific influence of the introduction of the transgene on the phenotypical properties of the transgenic lines. In the present investigation we will consider the effect of the introduction of the chitinase transgene on such agronomically important characteristics as yield and nonspecific resistance.  相似文献   
763.
Zinchuk  V. V.  Biletskaya  E. S. 《Biophysics》2020,65(5):779-783
Biophysics - The effects of ozone on oxygen transport in the blood of experimental animals have been studied in vitro. Incubation of the blood with ozonated water at О3 concentrations of 2,...  相似文献   
764.
765.
Seinings of the lowland bed of a typical small river of Western Kamchatka demonstrated that of several methods for the census of juveniles of salmonids (Salmonidae) the most accurate result in comparison with complete removal is obtained by three-fold seining with calculation of abundance by the Zippin method. In comparison with a seine, a drive-in trap and electrofishing possess a lower average catching efficiency and a higher selectivity. The average density of fish estimated by the results of seining at the investigated stretch was 0.55–0.57 specimens/m2.  相似文献   
766.
The paper presents the analysis of the frequency, density, and distribution of recombination sites in the male meiosis of the domestic cat (Felis silvestris catus). The study was carried out using immunofluorescent staining of synaptonemal complex (SC) proteins, centromeric proteins and mismatch repair protein MLH1, a reliable marker of crossingover sites. We mapped 2633 sites of crossing over in 1098 individual autosomes. Based on these data, we estimated the total length of the genetic map of the domestic cat to be 2176 centimorgans. Positive correlation between the length of SC and the number of recombination sites common for mammalians was also found in the domestic cat. It was shown that this species was characterized by the highest density of recombination and the lowest interference in mammals.  相似文献   
767.
Routes of aquatic allochthonous inputs (aquatic subsidies) to detrital food webs are studied, as is the effect of aquatic subsidies on the functional and taxonomic structure of soil invertebrate communities in coastal ecosystems. The study took place in the coastal zone of an oxbow lake of the Pra River in the Oka Reserve. The results indicate a strong dependence of soil animals in the coastal habitats on aquatic subsidies. Isotopic analysis shows that aquatic resources enter soil food webs not only via predators feeding on flying insects or aquatic prey, but also via saprophages decomposing organic debris of aquatic origin. The contribution of aquatic subsidies to the energy balance of soil invertebrates decreases rapidly with increasing distance from the lake. The fraction of aquatic carbon in tissues of collembolans and saprophages is negligible already a few meters from the water edge. The dependence of predatory invertebrates on aquatic resources can be traced at somewhat greater distance (tens of meters).  相似文献   
768.
769.
770.
Aspartate transaminase level was significantly increased in intestine of experimentals that received multiple doses of infection. The level of alanine transaminase rose to a significant value in liver of mice infected with multiple doses. Rise of transaminases is correlated with the necrosis (disruption of intestina) hepatic cells in infected mice. Changes and/or the distribution of aspartate transaminase and alanine transaminase with regard to the dosage is discussed.  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