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   10376篇
  免费   25篇
  国内免费   41篇
系统科学   51篇
丛书文集   48篇
教育与普及   30篇
理论与方法论   25篇
现状及发展   3989篇
研究方法   540篇
综合类   5571篇
自然研究   188篇
  2012年   167篇
  2011年   356篇
  2010年   67篇
  2009年   55篇
  2008年   177篇
  2007年   219篇
  2006年   210篇
  2005年   232篇
  2004年   220篇
  2003年   201篇
  2002年   215篇
  2001年   432篇
  2000年   439篇
  1999年   295篇
  1996年   52篇
  1994年   269篇
  1992年   254篇
  1991年   202篇
  1990年   231篇
  1989年   192篇
  1988年   186篇
  1987年   190篇
  1986年   202篇
  1985年   269篇
  1984年   202篇
  1983年   164篇
  1982年   136篇
  1981年   140篇
  1980年   144篇
  1979年   325篇
  1978年   266篇
  1977年   216篇
  1976年   192篇
  1975年   194篇
  1974年   206篇
  1973年   176篇
  1972年   207篇
  1971年   248篇
  1970年   305篇
  1969年   229篇
  1968年   227篇
  1967年   194篇
  1966年   223篇
  1965年   149篇
  1959年   75篇
  1958年   123篇
  1957年   81篇
  1956年   58篇
  1954年   62篇
  1948年   57篇
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
991.
As one of his first acts upon becoming Astronomer Royal in 1835, George Airy made moves to set up a new observatory at Greenwich to study the Earth’s magnetic field. This paper uses Airy’s correspondence to argue that, while members of the reform movement in British science were putting pressure on the Royal Observatory to branch out into geomagnetism and meteorology, Airy established the magnetic observatory on his own initiative, ahead of Alexander von Humboldt’s request for British participation in the worldwide magnetic charting project that later became known as the ‘Magnetic Crusade’. That the Greenwich magnetic observatory did not become operational until 1839 was due to a series of incidental factors that provide a case study in the technical and political obstacles to be overcome in building a new government observatory. Airy attached less importance to meteorology than he did to geomagnetism. In 1840, he set up a full programme of meteorological observations at Greenwich – and thus turned his magnetic observatory into the ‘Magnetic and Meteorological department’ – only as the price of foiling an attempt by Edward Sabine and others in the London scientific elite to found a rival magnetic and meteorological observatory. Studying the origins of Airy’s Magnetic and Meteorological department highlights how important the context of other institutions and trends in science is to understanding the development of Britain’s national observatory.  相似文献   
992.
993.

Introduction

Tff3 peptide exerts important functions in cytoprotection and restitution of the gastrointestinal (GI) tract epithelia. Moreover, its presence in the rodent inner ear and involvement in the hearing process was demonstrated recently. However, its role in the auditory system still remains elusive. Our previous results showed a deterioration of hearing with age in Tff3-deficient animals.

Results

Present detailed analysis of auditory brain stem response (ABR) measurements and immunohistochemical study of selected functional proteins indicated a normal function and phenotype of the cochlea in Tff3 mutants. However, a microarray-based screening of tissue derived from the auditory central nervous system revealed an alteration of securin (Pttg1) and serpina3n expression between wild-type and Tff3 knock-out animals. This was confirmed by qRT-PCR, immunostaining and western blots.

Conclusions

We found highly down-regulated Pttg1 and up-regulated serpina3n expression as a consequence of genetically deleting Tff3 in mice, indicating a potential role of these factors during the development of presbyacusis.  相似文献   
994.
Patterns of colonization by macroinvertebrates were examined in two streams that differ in flow regime: a snowmelt system and a mesic groundwater system. Experiments were conducted during spring runoff, summer baseflow, and winter baseflow using artificial substrata. Colonization patterns reflected seasonal changes in benthic macroinvertebrate assemblages and life histories in each stream. The density and biomass of benthic organisms were approximately 3X greater in winter than in either spring or summer for both streams. Similarly, colonization was greater in winter than in spring or summer for both streams. In spring, colonization patterns were different between streams, with colonization being imperceptible in the snowmelt stream. Macroinvertebrate abundance fluctuated during the summer colonization experiment at both sites, resulting from a complex interplay among population emergence, recruitment, and/or movement. Assemblages in the snowmelt system primarily comprised mobile or ruderal taxa, such as Beatis tricaudatus and Chironomidae, whereas relatively sessile taxa, such as Glossoma nigrior , were predominant in the mesic groundwater system. Seasonal patterns of colonization differed among stream types primarily because of the profound interplay of flow regime and temperature on benthic community structure and organism life history.  相似文献   
995.
We examined crop contents of 217 Gray Partridge ( Perdix perdix ) collected during a two-year period in eastern South Dakota. Row crop grains (corn, sunflowers) dominated late fall, winter, and spring diets. Small grains (oats, barley, wheat, rye) were rarely consumed although fields of small grains were widely available. During a severe winter when waste row crop grains were buried by snow, partridge consumed more leafy vegetation. Insects dominated the early summer diet, while foxtail ( Setaria spp.) seeds were a major late summer and early fall food.  相似文献   
996.
Functional impairment of DNA damage response pathways leads to increased genomic instability. Here we describe the centrosomal protein CEP152 as a new regulator of genomic integrity and cellular response to DNA damage. Using homozygosity mapping and exome sequencing, we identified CEP152 mutations in Seckel syndrome and showed that impaired CEP152 function leads to accumulation of genomic defects resulting from replicative stress through enhanced activation of ATM signaling and increased H2AX phosphorylation.  相似文献   
997.
998.
999.
Ageing, fitness and neurocognitive function.   总被引:18,自引:0,他引:18  
  相似文献   
1000.
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