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   13341篇
  免费   1056篇
  国内免费   2篇
  14399篇
  2023年   69篇
  2022年   156篇
  2021年   270篇
  2020年   160篇
  2019年   192篇
  2018年   259篇
  2017年   253篇
  2016年   411篇
  2015年   666篇
  2014年   765篇
  2013年   922篇
  2012年   1253篇
  2011年   1159篇
  2010年   701篇
  2009年   620篇
  2008年   892篇
  2007年   929篇
  2006年   776篇
  2005年   758篇
  2004年   669篇
  2003年   638篇
  2002年   629篇
  2001年   108篇
  2000年   77篇
  1999年   103篇
  1998年   144篇
  1997年   88篇
  1996年   75篇
  1995年   70篇
  1994年   71篇
  1993年   71篇
  1992年   51篇
  1991年   47篇
  1990年   42篇
  1989年   26篇
  1988年   24篇
  1987年   22篇
  1986年   23篇
  1985年   15篇
  1984年   22篇
  1983年   19篇
  1982年   8篇
  1981年   17篇
  1980年   14篇
  1979年   10篇
  1978年   11篇
  1975年   8篇
  1971年   11篇
  1969年   8篇
  1966年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
We investigated an Alu element at the end of intron 8 of the human vitamin D-binding protein (hDBP, group-specific component, GC) gene that shows a polymorphic poly(A) tail due to a variable number of tandem repeats (AluVpA) forming the 3 end of this member of the most abundant class of short interspersed repeated DNA element (SINES). The Alu element sequence in intron 8 of the GC gene was identical in all three common GC alleles (GC*1F, GC*1S, and GC*2) and could be classified as an Alu-Sa or Alu class-II sequence. The polymerase chain reaction was used to amplify selectively a fragment of about 200 bp containing the identified (TAAA)n repeat from genomic DNA of 188 unrelated human subjects. The size of the amplified products was determined by polyacrylamide gel electrophoresis. Four alleles (named GC-18*6, GC-I8*8, GC-I8*10, and GC-18*11) were found that differed in size by multiples of four nucleotides. The allele frequencies ranged from 0.0053 to 0.8511 and the observed heterozygosity was 26%. The stable inheritance of this polymorphic patterned poly(A) sequence was confirmed by a segregation study of a highly informative family with 19 members. Statistically significant linkage disequilibrium between the AluVpA and the GC isoelectric focusing (IEF) phenotypes was found in a sample of 188 unrelated individuals and delta values were calculated from the observed haplotype distribution.  相似文献   
13.
The life cycle of the Antarctic Dry Valley soil nematode, Scottnema lindsayae (Timm 1971) was studied in laboratory culture at two temperatures, 10°C and 15°C. Soil yeast and bacteria isolated with the nematodes were used as the food source. The species reproduced sexually. The higher temperature had a negative effect on the life cycle. The number of eggs per female and the number of juveniles developing per female were greater at 10°C than at 15°C. Juveniles developed faster at 10°C and four juvenile stages were observed outside of the egg at both temperatures. The unusually long life cycle (218 d at 10°C) suggests that more than one austral summer may be required for successful completion. An increase in Dry Valley soil temperatures associated with potential global environmental change may have detrimental effects on soil nematodes.  相似文献   
14.
Summary Cats were treated with high doses of chloroquine for one year during which the ocular fundus was periodically examined. After completion of the treatment, the tapetal cells were investigated by light and electron microscopy. Prolonged treatment with the retinotoxic drug chloroquine reduced the light reflection of the fundus, and examination by light and electron microscopy revealed a destruction of the rod-like structures in the cytoplasm of the tapetal cells.  相似文献   
15.
Genetic variation of a codominantly inherited pancreas protease, designated CTRA-1, was discovered in the house mouse by isoelectric focusing in polyacrylamide gels. Phenotype CTRA-1A was found in MOLH/Fre and in the majority of common laboratory mouse strains. Phenotype CTRA-1B was found in PWD/Ph. It was characterized by the absence of a corresponding protease band. A third phenotype, CTRA-1C, was observed in IS/Cam and a fourth phenotype, CTRA-1D, was detected in SEG/1. CTRA-1 was found only in the pancreas and may represent the A form of chymotrypsin. The enzyme was shown to be controlled by the presumed structural locus Ctra-1 located on chromosome 8. From two backcross series, including a total of 274 animals, the gene order (Es-1, Es-9)-3.9 +/- 1.7%-Got-2-3.9 +/- 1.7%-(Es-2, Es-7, Es-23)-0.7 +/- 0.5%- Ctra-1-6.3 +/- 2.2%-Prt-2 was established.  相似文献   
16.
Zusammenfassung Die Analyse von Sequenzunterschieden in mitochondrieller und genomischer DNA von Vögeln mittels Restriktionsenzymen eröffnet völlig neue Perspektiven für systematische, populationsgenetische und verhaltensökologische Forschung. Diese Methode ist der elektrophoretischen Untersuchung von Isoenzymen und der DNA-DNA-Hybridisierung vielfach überlegen. Das Prinzip, der technische Ablauf und die theoretischen Vorteile werden erläutert. Einige bisherige Untersuchungen dienen als Beispiele für vielversprechende Anwendungsmöglichkeiten in der Ornithologie. Die Einrichtung eines Schwerpunktlabors für solche Arbeiten wird vorgeschlagen, um technische und personelle Ausstattung optimal nutzen zu können.
Restriction enzyme analysis of DNA: principle and possible applications in ornithology
Summary The analysis of restriction fragment length polymorphisms in mitochondrial and genomic DNA of birds opens up a large new field of research for ornithologists. The method is in most contexts superior to electrophoretic analysis of allozymes and an important complement to DNA-DNA hybridization. Its principle, the technical procedures and theoretical advantages are briefly explained. Some recent studies are reviewed and potential applications outlined. Ornithological institutions in Germany should set up a central laboratory for such research to use personnel and technical equipment most efficiently.
  相似文献   
17.
18.
Recent studies have shown that surfactant components, in particular the collectins surfactant protein (SP)-A and -D, modulate the phagocytosis of various pathogens by alveolar macrophages. This interaction might be important not only for the elimination of pathogens but also for the elimination of inhaled allergens and might explain anti-inflammatory effects of SP-A and SP-D in allergic airway inflammation. We investigated the effect of surfactant components on the phagocytosis of allergen-containing pollen starch granules (PSG) by alveolar macrophages. PSG were isolated from Dactylis glomerata or Phleum pratense, two common grass pollen allergens, and incubated with either rat or human alveolar macrophages in the presence of recombinant human SP-A, SP-A purified from patients suffering from alveolar proteinosis, a recombinant fragment of human SP-D, dodecameric recombinant rat SP-D, or the commercially available surfactant preparations Curosurf and Alveofact. Dodecameric rat recombinant SP-D enhanced binding and phagocytosis of the PSG by alveolar macrophages, whereas the recombinant fragment of human SP-D, SP-A, or the surfactant lipid preparations had no effect. In addition, recombinant rat SP-D bound to the surface of the PSG and induced aggregation. Binding, aggregation, and enhancement of phagocytosis by recombinant rat SP-D was completely blocked by EDTA and inhibited by d-maltose and to a lesser extent by d-galactose, indicating the involvement of the carbohydrate recognition domain of SP-D in these functions. The modulation of allergen phagocytosis by SP-D might play an important role in allergen clearance from the lung and thereby modulate the allergic inflammation of asthma.  相似文献   
19.
20.
The complete amino acid sequence of apolipophorin-III (apoLp-III), a lipid-binding hemolymph protein from the greater wax moth,Galleria mellonella, was determined by protein sequencing. The mature protein consists of 163 amino acid residues forming a protein of 18,075.5 Da. Its sequence is similar to apoLp-III from other Lepidopteran species, but remarkably different from the apoLp-IIIs of insects from other orders. As shown by mass spectrometric analysis, the protein carries no modifications. Thus, all of its known physiological functions, including its recently discovered immune response-stimulating activity, must reside in the protein itself.  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