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   649884篇
  免费   80784篇
  国内免费   361篇
  2016年   6988篇
  2015年   10104篇
  2014年   11768篇
  2013年   16858篇
  2012年   18828篇
  2011年   19114篇
  2010年   13008篇
  2009年   12103篇
  2008年   17046篇
  2007年   17579篇
  2006年   16449篇
  2005年   16014篇
  2004年   15520篇
  2003年   15644篇
  2002年   14951篇
  2001年   27653篇
  2000年   27860篇
  1999年   22458篇
  1998年   8284篇
  1997年   8896篇
  1996年   8247篇
  1995年   8019篇
  1994年   7929篇
  1993年   8064篇
  1992年   19416篇
  1991年   19065篇
  1990年   18324篇
  1989年   18105篇
  1988年   16654篇
  1987年   16359篇
  1986年   15222篇
  1985年   15366篇
  1984年   12890篇
  1983年   11307篇
  1982年   8908篇
  1981年   8216篇
  1980年   7690篇
  1979年   12648篇
  1978年   10065篇
  1977年   9350篇
  1976年   8871篇
  1975年   9722篇
  1974年   10279篇
  1973年   10132篇
  1972年   9328篇
  1971年   8471篇
  1970年   7265篇
  1969年   7169篇
  1968年   6395篇
  1967年   5594篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
Journal of Physiology and Biochemistry - Infants born small for gestational age (SGA) are at increased risk of perinatal morbidity, persistent short stature, and metabolic alterations in later...  相似文献   
992.
993.
994.
995.
The effects of natural blooms of Heterosigma akashiwo on freshwater-and saltwater-acclimated juvenile chinook salmon were assessed. Rates of fish mortality in the blooms were independent of acclimation of fish to seawater and the ambient oxygen levels, but were dependent on concentration of algae and ambient water temperatures. No pathological abnormality to gills or other internal organs in the fish were evident. Aeration or oxygenation of fish cages did not enhance or inhibit fish survival in a H. akashiwo bloom. Cause of death was considered to be due to a labile ichthyotoxic agent.  相似文献   
996.
Mesodermal cell differentiation begins in response to an inductive interaction early in frog development. In parallel with the recent finding that certain peptide growth factors can induce mesoderm, early cellular and genetic responses to the induction have been discovered. I review here recent work on these responses, work that aims to understand how cells respond to inducers to form the complex pattern of the vertebrate mesoderm.  相似文献   
997.
The generation and characterization of new sheep-hamster cell hybrids is reported from the fusion of sheep white blood cells with six different hamster auxotrophs. Selection from these and previously generated cell hybrids has led to the production of a panel of 30 hybrids covering the complete sheep genome of 28 chromosomes. Over half of the cell hybrids in this panel contain single sheep chromosomes. By complementation, the following new assignments have been made using the panel: phosphoribosyl N-formylglycinamide amidotransferase (PRFGA) to sheep chromosome (chr) 11; adenylosuccinate synthetase (ADSS) to sheep chr 12; adenylosuccinate lyase (ADSL) to sheep chr 3q; 3-hydroxy-3-methylglutaryl-coenzyme A synthase (HMGCS) to sheep chr 16; dihydrofolate reductase (DHFR) to sheep chr 5; and adenine phosphoribosyltransferase (APRT) to sheep chr 14. The gene phosphoribosylaminoinidazole-carboxamide formyltransferase/Inosinicase (PRACFT) has now been regionally assigned to chr 2q. By isozyme analysis, phosphogluconate dehydrogenase (PGD) was assigned to sheep chr 12, anchoring the sheep syntenic group U1 to this chromosome, and mannose phosphate isomerase (MPI) was assigned to sheep chr 18. Furthermore, the chromosomal assignment of 110 microsatellites was confirmed using this cell panel.  相似文献   
998.
Summary Bacteria from recreational waters collected from two Lake Erie beaches in Dunkirk, New York were plated onto m Endo LES media. The 16S rRNA gene was then amplified from coliform and non-coliform bacteria using the polymerase chain reaction. The PCR products were characterized by restriction fragment length polymorphism (RFLP) analysis. A total of 8 RFLP groups were identified from the analysis of 920 samples and selected PCR products from each group were sequenced. The DNA sequence analysis indicated that more than half of the bacteria identified as coliforms on the m Endo plates belonged to the genus Aeromonas from the family Aeromonadaceae. Most of the remaining coliforms were from the Enterobacteriaceae. The data indicate that m Endo agar plates allow the growth of non-coliform bacteria, especially Aeromonas species.  相似文献   
999.
To clarify the mechanisms of Nosema ceranae parasitism, we deep-sequenced both honey bee host and parasite mRNAs throughout a complete 6-day infection cycle. By time-series analysis, 1122 parasite genes were significantly differently expressed during the reproduction cycle, clustering into 4 expression patterns. We found reactive mitochondrial oxygen species modulator 1 of the host to be significantly down regulated during the entire infection period. Our data support the hypothesis that apoptosis of honey bee cells was suppressed during infection. We further analyzed genome-wide genetic diversity of this parasite by comparing samples collected from the same site in 2007 and 2013. The number of SNP positions per gene and the proportion of non-synonymous substitutions per gene were significantly reduced over this time period, suggesting purifying selection on the parasite genome and supporting the hypothesis that a subset of N. ceranae strains might be dominating infection.  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