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   181篇
  免费   8篇
  国内免费   1篇
  190篇
  2023年   1篇
  2021年   2篇
  2020年   2篇
  2019年   1篇
  2018年   1篇
  2017年   1篇
  2016年   2篇
  2015年   6篇
  2014年   15篇
  2013年   11篇
  2012年   11篇
  2011年   10篇
  2010年   8篇
  2009年   8篇
  2008年   14篇
  2007年   9篇
  2006年   15篇
  2005年   5篇
  2004年   4篇
  2003年   5篇
  2002年   8篇
  2001年   4篇
  2000年   4篇
  1999年   4篇
  1998年   14篇
  1997年   1篇
  1996年   4篇
  1995年   3篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1983年   2篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1977年   1篇
  1976年   2篇
  1975年   1篇
排序方式: 共有190条查询结果,搜索用时 15 毫秒
51.
52.
TORGEIR NYGÅRD 《Ibis》1999,141(1):85-90
Eggshell thickness is often expressed by means of an index based on the length, breadth and weight of the shell. The effect of the blow-hole and egg eccentricity on Ratcliffe's shell thickness index was investigated in a sample of 585 eggs from six raptor species. Corrections for the size of the hole and egg eccentricity are proposed, as is a combined formula to correct both sources of error at the same time. It is shown that by using these formulae, considerable improvements in estimates of shell thinning are obtained. These may be especially useful when sample sizes are small, which is often the case when working with species that have been reduced in numbers.  相似文献   
53.
54.
DNA sequence analysis confirms the distinction between Parablennius ruber and Parablennius gattorugine , simultaneously validating the presence of the former species in Western Europe where it has been reported for >150 years. A possible scenario involving speciation of P. ruber at the Azores and subsequent transport of larvae to Europe, a process that may be still occurring nowadays, could explain this pattern of occurrence.  相似文献   
55.
Larvae and juveniles of long sardine, Triportheus auritus, from the lower Amazon river was described, evaluating ontogenetic changes in their external mor­phology, pigmentation, fin development, morphometry, and meristics. A total of 93 individuals, 83 larvae and 10 juveniles were analyzed, they were captured monthly between 2014 and 2019 in the Amazon river channel and in macrophytes aquatic stands in the alluvial plains located in the lower Amazon River. From each specimen, morphometric and meristic data were measured and then the growth pattern between morphometric variables was analyzed. The larvae have an elongated body in a fusiform shape, superior mouth, simple nostril, pigmented spherical eyes and long intestine, surpassing the median region of the body. Initial pigmentation is scarce, but intensifies through development forming a pattern composed of three longitudinal bands concentrated in the ventral, cephalo-dorsal and lateral line regions. There are also pigments in the mandible, surrounding the mouth, under the swim bladder, intestine and fins. The sequence of complete fin formation is: caudal, anal, dorsal, pectoral and pelvic. The total number of myomeres ranged from 45 to 48 (25–29 preanal and 17–22 postanal). Morphometric relationships indicated differential growth for measurable morphometric parameters, with abrupt growth of snout length, head length and body height in the transition from flexion to postflexion stages. The pre-dorsal distance showed a decrease in the growth rate at the threshold from the larval to the juvenile period. The pre-pectoral and pre-anal distances showed negative allometric growth. In conclusion, the combination of body shape pigmentation pattern and, the formation sequence of fins allow the identification of the genus and coupled with the number of myomeres, morphometric relationships, and ray numbers of the anal fin ensure the differentiation of T. auritus from the other congeneric species. The metamorphosis occurred mainly at the end of the larval period and it is related to changes in the physiological and ecomorphological characteristics of the species.  相似文献   
56.
The genetic relationships of a population of brook lamprey Lampetra planeri from Spain were analysed using a fragment of the mitochondrial non-coding region in order to describe its relationships with other European Lampetra populations. DNA sequences were obtained from ten larvae, all corresponding to a single private haplotype. Its closest haplotype differed by five mutations and was found in several samples of Lampetra fluviatlis, both from the North Sea and the Baltic. These results argue for the great conservation value of this brook lamprey population, likely originated from L. fluviatilis ancestors.  相似文献   
57.
58.
In this paper we present ACTUS2, the second version of ACTUS (Analysis of Contingency Tables Using Simulation). ACTUS2 has many new features, including analysis of data in which dependencies that make some combinations of properties impossible are hypothesized. Because ACTUS2 explicitly simulates such hypotheses, it can be used without loss of accuracy to analyze small amounts of data in large tables with many zeros or very low frequencies. We illustrate these features with two studies of animal behavior: interactions of male individuals with other individuals in groups of captive, mature Triturus marmoratus pygmaeus (newts); and agonistic interactions between pairs of male juvenile Diplodus sargus (the sparid fish, white sea-bream). Both significantly frequent, and significantly infrequent, co-occurrences that had biologically meaningful interpretations were revealed.  相似文献   
59.
60.
Harmonisation of reference intervals for routine general chemistry analytes has been a goal for many years. Analytical bias may prevent this harmonisation. To determine if analytical bias is present when comparing methods, the use of commutable samples, or samples that have the same properties as the clinical samples routinely analysed, should be used as reference samples to eliminate the possibility of matrix effect. The use of commutable samples has improved the identification of unacceptable analytical performance in the Netherlands and Spain. The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) has undertaken a pilot study using commutable samples in an attempt to determine not only country specific reference intervals but to make them comparable between countries. Australia and New Zealand, through the Australasian Association of Clinical Biochemists (AACB), have also undertaken an assessment of analytical bias using commutable samples and determined that of the 27 general chemistry analytes studied, 19 showed sufficiently small between method biases as to not prevent harmonisation of reference intervals. Application of evidence based approaches including the determination of analytical bias using commutable material is necessary when seeking to harmonise reference intervals.  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