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   613篇
  免费   42篇
  国内免费   2篇
  657篇
  2023年   4篇
  2022年   6篇
  2021年   14篇
  2020年   11篇
  2019年   4篇
  2018年   8篇
  2017年   4篇
  2016年   16篇
  2015年   54篇
  2014年   41篇
  2013年   54篇
  2012年   54篇
  2011年   49篇
  2010年   36篇
  2009年   31篇
  2008年   42篇
  2007年   36篇
  2006年   26篇
  2005年   33篇
  2004年   23篇
  2003年   17篇
  2002年   21篇
  2001年   1篇
  2000年   4篇
  1999年   6篇
  1998年   7篇
  1997年   3篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1993年   1篇
  1991年   2篇
  1989年   4篇
  1988年   1篇
  1987年   2篇
  1985年   1篇
  1984年   1篇
  1982年   5篇
  1974年   2篇
  1971年   21篇
  1970年   7篇
排序方式: 共有657条查询结果,搜索用时 15 毫秒
121.
Many raptor species are considered to be generalists, taking a range of prey species. However, longitudinal dietary records are often scarce, although necessary for characterizing niche width of species at population and individual levels. Quantifying raptor diets at large spatio‐temporal scales is often necessary for refining conservation efforts, although it can be particularly difficult and may involve a great effort by conventional means. Therefore, we adopted the analysis of stable isotopes in tissues of predators and their potential food sources as a complementary methodology for assessing animals' diet. We examined the isotopic composition (δ13C and δ15N) of White‐tailed Eagles Haliaeetus albicilla from Germany, Finland and Greenland to detect patterns of dietary variation and quantify diet composition. The isotopic analysis included liver and muscle samples from Eagles of the three populations together with 16 potential food sources in the German population. Our results suggested dietary differences between German and Greenlandic Eagles, in accordance with the availability of freshwater and marine habitats in each population. Within the German population, we found seasonal shifts in isotopic ratios, suggesting the birds responded to temporal changes in food availabilities, and age‐related isotopic differences, indicating different diets in adults and juveniles. Isotopic values of liver and muscle tissues collected from the same animal showed intra‐individual short‐term changes in the German and Finnish but not Greenlandic population. This suggests that local feeding niches of this generalist predator may vary with local food supplies, which determines the niche width (from generalist to specialist) at the individual level. Our results also revealed that game mammal carcasses constitute an important food source (29.5% of diet) for the German Eagle population during the winter half‐year corresponding to the hunting season. This result is of relevance to management and conservation because the White‐tailed Eagle and other raptor species are affected by the ingestion of lead ammunition from shot mammalian carcasses.  相似文献   
122.
123.
The red list has become a ubiquitous tool in the conservation of species. We analyzed contemporary trends in the threat levels of European orchids, in total 166 species characterized in 27 national red lists, in relation to their reproductive biology and growth form, distribution area, and land cover where they occur. We found that species in central Europe are more threatened than those in the northern, southern, or Atlantic parts of Europe, while species were least threatened in southern Europe. Nectarless and tuberous species are significantly more threatened than nectariferous and rhizomatous taxa. Land cover (ratios of artificial land cover, area of pastures and grasslands, forests and inland wetlands) also significantly impacted the threat level. A bigger share of artificial land cover increases threat, and a bigger share of pasture and grassland lowers it. Unexpectedly, a bigger share of inland wetland area in a country increased threat level, which we believe may be due to the threatened nature of wetlands themselves relative to other natural land cover types. Finally, species occurring in multiple countries are on average less threatened. We believe that large‐scale analysis of current IUCN national red lists as based on their specific categories and criteria may particularly inform the development of coordinated regional or larger‐scale management strategies. In this case, we advocate for a coordinated EU protection and restoration strategy particularly aimed at central European orchids and those occurring in wetland area.  相似文献   
124.
Zusammenfassung Es werden Befunde aus einer Sippe mit PGI-Defizienz mitgeteilt. Die beiden Patienten haben eine nichtsphärocytäre hämolytische Anämie, sie besitzen den homozygoten Phänotypus PGI9. Die Eltern sind heterozygot PGI 9-1. Der Zymogrammvergleich von Eltern und Kindern spricht für die Hypothese, daß die PGI ein dimeres Molekül sei, das normalerweise aus identischen Polypeptidketten aufgebaut ist.
Formal genetics of phosphoglucoseisomerase investigations of a family with PGI-Deficiency
Summary In a family two children exhibited a non-sphaerocytic hemolytic anemia; they revealed the homozygous phenotype PGI9. The parents are heterozygous PGI 9-1. The comparison of the zymogram pattern of both parents and children allows the conclusion that the PGI molecule is a dimer which has identical subunits in homozygous individuals.


Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.  相似文献   
125.
126.
127.
Zusammenfassung Die Adenosindesaminasen der Primaten zeigen eine genetisch determinierte Variabilität. Bei der Untersuchung von 327 subhumanen Primaten (289 Simiae der Alten Welt, 38 Prosimiae) konnten wir neun Adenosindesaminase-Varianten nachweisen, die auf Grund ihrer unterschiedlichen elektrophoretischen Wandergeschwindigkeit als ADA 6, ADA 4, ADA 2, ADA 2, ADA 1, ADA 3, ADA 5, ADA 5 und ADA 7 bezeichnet werden. Die Verteilung der verschiedenen Phänotypen wurde ermittelt.
Red cell enzymes of primatesAdenosine deamisnase (EC: 3.5.4.4.)
Summary The polymorphism of adenosine deaminase has been investigated in 327 subhuman Primates (289 Old World Monkeys and 38 Prosimians). Nine adenosine deaminase variants were found to be present, which on the basis of their different electrophoretic mobilities were designated ADA 6, ADA 4, ADA 2, ADA 2, ADA 1, ADA 3, ADA 5, ADA 5 and ADA 7. The distribution of these various phenotypes has been estimated.


Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.  相似文献   
128.
Zusammenfassung Die NADH-Diaphorasen in Erythrocyten der Primaten lassen eine transspezifische Variabilität erkennen, die durch Ladungsunterschiede bedingt wird. Mit der Stärkegelelektrophorese können sechs verschiedene Enzym-Varianten differenziert werden. Die Verteilung der verschiedenen NADH-Diaphorase-Phänotypen von 425 subhumanen Primaten wurde ermittelt.
Transspecific variability of NADH-diaphorases in primates
Summary The NADH-Diaphorases in the erythrocytes of Primates show a transspecific variability, caused by differences in charge. Six kinds of genetically determined enzymes are distinguishable by means of starchgel-electrophoresis. The distribution of the various NADH-Diaphorase phenotypes in 425 subhuman Primates was estimated.


Direktor: Prof. Dr. Dr. H. Ritter

Direktor: Prof. Dr. Dr. h. c. B. Grzimek

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.  相似文献   
129.
Findings of early cerebral amyloid‐β deposition in mice after peripheral injection of amyloid‐β‐containing brain extracts, and in humans following cadaveric human growth hormone treatment raised concerns that amyloid‐β aggregates and possibly Alzheimer’s disease may be transmissible between individuals. Yet, proof that Aβ actually reaches the brain from the peripheral injection site is lacking. Here, we use a proteomic approach combining stable isotope labeling of mammals and targeted mass spectrometry. Specifically, we generate 13C‐isotope‐labeled brain extracts from mice expressing human amyloid‐β and track 13C‐lysine‐labeled amyloid‐β after intraperitoneal administration into young amyloid precursor protein‐transgenic mice. We detect injected amyloid‐β in the liver and lymphoid tissues for up to 100 days. In contrast, injected 13C‐lysine‐labeled amyloid‐β is not detectable in the brain whereas the mice incorporate 13C‐lysine from the donor brain extracts into endogenous amyloid‐β. Using a highly sensitive and specific proteomic approach, we demonstrate that amyloid‐β does not reach the brain from the periphery. Our study argues against potential transmissibility of Alzheimer’s disease while opening new avenues to uncover mechanisms of pathophysiological protein deposition.  相似文献   
130.
The cytoskeleton is connected to the nuclear interior by LINC (linker of nucleoskeleton and cytoskeleton) complexes located in the nuclear envelope. These complexes consist of SUN proteins and nesprins present in the inner and outer nuclear membrane respectively. Whereas SUN proteins can bind the nuclear lamina, members of the nesprin protein family connect the nucleus to different components of the cytoskeleton. Nesprin-1 and -2 can establish a direct link with actin filaments, whereas nesprin-4 associates indirectly with microtubules through its interaction with kinesin-1. Nesprin-3 is the only family member known that can link the nuclear envelope to intermediate filaments. This indirect interaction is mediated by the binding of nesprin-3 to the cytoskeletal linker protein plectin. Furthermore, nesprin-3 can connect the nucleus to microtubules by its interactions with BPAG1 (bullous pemphigoid antigen 1) and MACF (microtubule-actin cross-linking factor). In contrast with the active roles that nesprin-1, -2 and -4 have in actin- and microtubule-dependent nuclear positioning, the role of nesprin-3 is likely to be more passive. We suggest that it helps to stabilize the anchorage of the nucleus within the cytoplasm and maintain the structural integrity and shape of the nucleus.  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