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   345篇
  免费   30篇
  2023年   1篇
  2022年   2篇
  2021年   6篇
  2020年   6篇
  2019年   15篇
  2018年   10篇
  2017年   8篇
  2016年   6篇
  2015年   20篇
  2014年   21篇
  2013年   20篇
  2012年   13篇
  2011年   20篇
  2010年   7篇
  2009年   15篇
  2008年   14篇
  2007年   17篇
  2006年   18篇
  2005年   16篇
  2004年   13篇
  2003年   8篇
  2002年   8篇
  2001年   16篇
  2000年   16篇
  1999年   8篇
  1998年   6篇
  1997年   3篇
  1996年   5篇
  1995年   6篇
  1994年   4篇
  1993年   4篇
  1992年   3篇
  1991年   7篇
  1990年   4篇
  1989年   3篇
  1988年   10篇
  1987年   1篇
  1986年   2篇
  1985年   4篇
  1983年   1篇
  1979年   2篇
  1977年   1篇
  1975年   1篇
  1971年   1篇
  1969年   1篇
  1968年   1篇
  1965年   1篇
排序方式: 共有375条查询结果,搜索用时 15 毫秒
91.
92.
Length–weight relationships (LWR) were estimated for 34 fish species belonging to 25 genera and 17 families, specimens were collected near the mouth of the Río Verde, Oaxaca, Mexico. All r2 values are statistically significant (P > 0.0001). The values of ‘b’ ranged from 2.55 and 3.3, within the usual range (2.5–3.5). This study provides the first LWR references for six species, and new maximum length records for eight species.  相似文献   
93.
The glutamine synthetase (EC 6.3.1.2) from the haloarchaeon Haloferax mediterranei has been purified and characterized in order to understand the ammonium assimilation in haloarchaea. Based on sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel-filtration chromatography, the enzyme consists of eight subunits of 51.7 kDa, suggesting that this enzyme belongs to the glutamine synthetase type II. The purified enzyme has been characterized with respect to its optimum temperature (45 degrees C) and pH value (8.0). The optimal NaCl or KCl concentrations for the reaction were 0.5 and 0.25 M, respectively. The effect of l-methionine-d, l-sulphoximine and different divalent metal ions has also been tested. The glutamine synthetase presented here is unusual; it shows the typical characteristic of eukaryotic and soil bacteria glutamine synthetases.  相似文献   
94.
95.
A new species of Acritopappus, A. buiquensis, is described and illustrated from Pernambuco State, Brazil. This is the second record for the genus in the State. The position of A. buiquensis in the genus is discussed.  相似文献   
96.
Three different amylolytic activities, designated AMY1, AMY2, and AMY3 were detected in the cytoplasm of the extreme halophilic archaeon Haloferax mediterranei grown in a starch containing medium. This organism had also been reported to excrete an α-amylase into the external medium in such conditions. The presence of these different enzymes which are also able to degrade starch may be related to the use of the available carbohydrates and maltodextrins, including the products obtained by the action of the extracellular amylase on starch that may be transported to the cytoplasm of the organism. The behavior of these intracellular hydrolytic enzymes on starch is reported here and compared with their extracellular counterpart. Two of these glycosidic activities (AMY1, AMY3) have also been purified and further characterized. As with other halophilic enzymes, they were salt dependent and displayed maximal activity at 3 M NaCl, and 50°C. The purification steps and molecular masses have also been reported. The other activity (AMY2) was also detected in extracts from cells grown in media with glycerol instead of starch and in a yeast extract medium. This enzyme was able to degrade starch yielding small oligosaccharides and displayed similar halophilic behavior with salt requirement in the range 1.5–3 M NaCl. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
97.
Systematic Monte Carlo simulations of simple lattice models show that the final stage of protein folding is an ordered process where native contacts get locked (i.e., the residues come into contact and remain in contact for the duration of the folding process) in a well‐defined order. The detailed study of the folding dynamics of protein‐like sequences designed as to exhibit different contact energy distributions, as well as different degrees of sequence optimization (i.e., participation of non‐native interactions in the folding process), reveals significant differences in the corresponding locking scenarios—the collection of native contacts and their average locking times, which are largely ascribable to the dynamics of non‐native contacts. Furthermore, strong evidence for a positive role played by non‐native contacts at an early folding stage was also found. Interestingly, for topologically simple target structures, a positive interplay between native and non‐native contacts is observed also toward the end of the folding process, suggesting that non‐native contacts may indeed affect the overall folding process. For target models exhibiting clear two‐state kinetics, the relation between the nucleation mechanism of folding and the locking scenario is investigated. Our results suggest that the stabilization of the folding transition state can be achieved through the establishment of a very small network of native contacts that are the first to lock during the folding process.  相似文献   
98.
Field experiments and surveys were conducted to evaluate the efficacy of releasing Fopius arisanus (Sonan) and Psyttalia fletcheri (Silvestri) parasitoids for suppression of Bactrocera cucurbitae (Coquillett) infesting wild Coccinia grandis L. In 2003 and 2004, P. fletcheri releases combined with natural emergence from wild fly populations resulted in better fly suppression, compared to the control site. While P. fletcheri developed freely on melon fly, F. arisanus was less successful at producing its own progeny, yet causing mortality and a twofold decrease in pupae recovered from ivy gourds. Concurrent releases of both parasitoids exerted a compounded suppressive effect on the melon fly population 2–3 times higher than during the pre-release phase. A similar, less obvious, pattern occurred in 2004, due to reduction of the ivy gourd fruit canopy. In 2005, only P. fletcheri was released, with greatly reduced impact, due to ivy gourd destruction and by growers leaving crop culls in fields, producing large numbers of melon flies unaffected by parasitoid releases.  相似文献   
99.

Background

Nepal is small in size but rich in bio-cultural diversity. The rugged terrain of the country is home to a number of unique assemblages of fauna, some of which are endemic. Not only faunal resources the country also harbors some very ancient populations whose interrelationship with these diverse faunal resources is very intimate and thus demands scientific study. Animals play important role in both material and spiritual spheres of their life. There are more than hundred groups of such populations in the country and the group Tamang is one of these. The present paper studies Tamang-animal relationships in central Nepal. There is a growing trend of scientific ethnozoological studies all across the globe, but this field is yet in its infancy in Nepal. The country is losing important fauna as well as ancient human cultures at the advent of development processes. As a result, ethnozoological knowledge is also teetering on the brink of extinction.

Methods

Ethnozoological data were collected by applying different participatory approaches techniques such as semi-structured interviews, participatory rural appraisal, key informant interviews and focus group discussions. Quantitative data were obtained by employing a household level questionnaire survey. Data were collected from the period of September 2004 to August 2005. Most of the animals were identified up to the species level with the help of standard taxonomic keys.

Results

The Tamang community treasures knowledge on various uses of 41 genera belonging to 28 families. Out of total number of animals, 14.6% belong to the Invertebrate group and the rest to the Vertebrate group. Of the total uses 58% fall in the food and medicinal use category, 16% in the magico-religious use category, 18% in the category of omen indication, and 2% each in the categories such as weather forecasting, trophy, ethnomusical and taboos.

Conclusions

The Tamang maintain strong ties with animals both at a material as well as spiritual level. While some animals are the sources of important traditional medicines, others are omen indicators and weather forecasters. High priority should be given in conservation of those animals which are of high consensus value to the community.  相似文献   
100.
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