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   423699篇
  免费   47737篇
  国内免费   153篇
  2018年   3914篇
  2016年   5298篇
  2015年   6925篇
  2014年   8204篇
  2013年   11279篇
  2012年   12843篇
  2011年   13296篇
  2010年   9106篇
  2009年   8455篇
  2008年   12150篇
  2007年   12649篇
  2006年   11865篇
  2005年   11350篇
  2004年   11379篇
  2003年   10679篇
  2002年   10473篇
  2001年   17444篇
  2000年   17454篇
  1999年   13826篇
  1998年   4848篇
  1997年   5086篇
  1996年   4756篇
  1995年   4625篇
  1994年   4495篇
  1993年   4546篇
  1992年   11619篇
  1991年   11544篇
  1990年   11295篇
  1989年   10909篇
  1988年   10497篇
  1987年   10080篇
  1986年   9369篇
  1985年   9237篇
  1984年   7750篇
  1983年   6704篇
  1982年   5166篇
  1981年   4618篇
  1980年   4461篇
  1979年   7424篇
  1978年   5864篇
  1977年   5393篇
  1976年   5200篇
  1975年   5610篇
  1974年   6307篇
  1973年   6166篇
  1972年   5764篇
  1971年   5227篇
  1970年   4633篇
  1969年   4576篇
  1968年   4420篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The results of the investigations of radioactive contamination after the Chernobyl catastrophe and subsequent iodine prophylaxis on the thyroid gland function and morphology in Northeast Poland. The aim of the study was to determine whether kalium iodine in one dose during radioactive contamination in Poland limited the radioactive dose in the thyroid gland and if significant disadvantageous side-effects in the intrathyroid and extrathyroid occurred. Additionally during the studies we tried to determine if radioactive iodine contamination which occurred in the region of the Medical Academy in Bia?ystok caused an increase in thyroid disease. It is interesting to note the different results obtained after radioactive contamination with the results from the investigations in this same territory in 1983-1985. In 1983-1985, before the Chernobyl catastrophe, 6,921 persons in Northeast Poland were investigated. In 1986-1988, immediately after the disaster 4,010 persons were investigated. The main study according to grant No MZ-XVII was carried out in three provinces: Bia?ystok, Suwa?ki and Olsztyn. In this investigation 10,011 persons born before April 26, 1986 and after January 1, 1936 participated, 5,789 townspeople and 4,222 villagers, 3,987 children up to 16 years of age it the time of the disaster 1,973 boys and 2,009 girls; 6,024 adults 2,509 men and 3,516 women were drawn from a register. Committed doses to the thyroid in the investigated region were one of the highest in Poland and depended on age group and were depended on time of prophylaxis non proportional. Iodine prophylaxis was provided mainly with one dose of Lugol solution about 90%, 95% children and 30% adults took iodine. The majority of the population (53.3%-74%) were given iodine in April. From May 1st to 5th 23.0-43.4% received iodine, but after May 5th very few persons. Iodine was well tolerated, but Lugol Solution was better tolerated than other kinds of iodine. Only 241 (4.4%) cases had side effects, mainly vomiting (143), symptoms such as stomach ache, diarrhea, dyspnoe, skinrash etc. in lesser numbers. 12% (29 persons) were seen by a physician. In the investigated population were 200 pregnant women aged 19-40 years of which the majority (177) delivered full term healthy babies. Only 1 interrupted pregnancy and 7 had spontaneous abortion. Changes in the thyroid were noticed by 187 persons (2.3%-11.7%) most of which were enlargement of the thyroid, but only a few were confirmed by a physician. In the studied population from 1989 to 1990 over 30% of the population had struma.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
52.
The predominant consequences of mu-opioid-receptor activation are depression of both neuronal activity and transmitter release. Mu-Opioid agonists have previously been observed to increase a potassium conductance and to inhibit adenylate cyclase. We now report that activation of mu-opioid receptors directly decreases the N-type calcium-channel current in a differentiated, human neuroblastoma cell line (SH-SY5Y). The coupling between the mu-opioid receptor and the calcium channel involves a pertussis toxin-sensitive G protein and is independent of changes in adenylate cyclase activity. The inhibition of the calcium-channel current is voltage dependent because it is largely overcome by strong membrane depolarization. It is not associated with changes in the kinetics of current inactivation. Therefore, the mu-receptor belongs to the superfamily of G-protein-coupled, inhibitory neurotransmitter receptors which modulate the activity of calcium and potassium channels and adenylate cyclase.  相似文献   
53.
The mago nashi (mago) locus is a newly identified strict maternal effect, grandchildless-like, gene in Drosophila melanogaster. In homozygous mutant mago females reared at 17 degrees C, mago+ function is reduced, the inviable embryos lack abdominal segments and 84-98% of the embryos die. In contrast, at 25 degrees C, some mago alleles produce a novel gene product capable of inducing the formation of symmetrical double abdomen embryos. Reciprocal temperature-shift experiments indicate that the temperature-sensitive period is during oogenetic stages 7-14. Furthermore, embryos collected from mago1 homozygous females contain no apparent functional posterior determinants in the posterior pole. In viable F1 progeny from mago mutant females, regardless of genotype and temperature, polar granules are reduced or absent and germ cells fail to form (the grandchildless-like phenotype). Thus, we propose that the mago+ product is a component of the posterior determinative system, required during oogenesis, both for germ cell determination and delineation of the longitudinal axis of the embryo.  相似文献   
54.
Genes for the major histocompatibility complex (MHC) were localized by fluorescence in situ hybridization to the long arm of rhesus monkey chromosome 5. This localization contradicts previous reports, based on genetic investigation of somatic cell hybrids, that placed the MHC on chromosome 2 of this species. In the chimpanzee, the MHC loci were localized to 5p21.3, corresponding precisely to their location on human chromosome 6p21.3.  相似文献   
55.
56.
The structure and mathematical model of PARATI, a detailed computer programme developed for the assessment of the radiological consequences of an accidental contamination of urban areas, is described with respect to the scenarios used for the estimation of exposure fields in a village or town, the models for the initial and secondary contamination with the radionuclide 137Cs, the concepts for calculating the resulting radiation exposures and the changes with time of the contamination and radiation fields. Kerma rates at various locations in tropical urban areas are given, and the contribution of different contaminated surfaces to these rates after dry or wet deposition are discussed. Received: 12 April 1996 / Accepted in revised form: 30 August 1996  相似文献   
57.
A search for quantitative trait loci for ovulation rate in cattle   总被引:4,自引:0,他引:4  
Seventy-seven polymorphic microsatellites were analysed in offspring of three elite sires that were part of the foundation of an experimental population selected for twinning rate at the US Meat Animal Research Center, Clay Center, Nebraska. All females were assessed for ovulation rate by rectal palpation of corpora lutea over 8–10 consecutive oestrous cycles from approximately 12 to 18 months of age, and associations between ovulation rate and sire allele were examined in each of the three sire groups. A preliminary analysis was performed using selectively genotyped daughters of each sire. Markers found significant or approaching significance were also genotyped in all daughters, sons and granddaughters of these sires. A test of marker associations limited to the granddaughter data provided an independent confirmation of marker effect and significance relative to the initial test with daughter data. Putative ovulation rate quantitative trait loci were detected on chromosomes 7 and 23. Marker UWCA20 on chromosome 7 was associated with an effect in excess of one phenotypic standard deviation and accounted for approximately 10% of phenotypic variation ovulation rate. Marker CYP21 (steroid 21-hydroxylase) on chromosome 23 was associated with an effect of slightly less than half a phenotypic standard deviation and accounted for approximately 4% of phenotypic variation.  相似文献   
58.
59.
60.
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