全文获取类型
收费全文 | 269篇 |
免费 | 15篇 |
专业分类
284篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 14篇 |
2012年 | 37篇 |
2011年 | 26篇 |
2010年 | 9篇 |
2009年 | 6篇 |
2008年 | 24篇 |
2007年 | 17篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有284条查询结果,搜索用时 15 毫秒
51.
52.
Rudi Verovnik Branko Micevski Dirk Maes Irma Wynhoff Chris Van Swaay Martin Warren 《Journal of Insect Conservation》2013,17(5):941-947
The Macedonian Grayling is listed as critically endangered in the recent IUCN Red List of European butterflies because of its extreme rarity and habitat loss due to quarrying. This categorisation was, however, based on rather limited knowledge on its actual distribution, population size and habitat requirements. In 2012, we conducted field surveys to acquire more information. We found the species at six new sites extending its known range of suitable habitat to just under 10 km2. The daily population size was estimated using capture-mark-recapture method in the most densely populated part of the Pletvar pass site at more than 650 individuals. Adults proved to be extremely sedentary, not moving far even within the continuous habitat on the same slope. Oviposition was observed on dry plant material and in a rock crevice close to the potential larval host plant Festuca sp. Quarrying is confirmed to be the main threat to the habitat of the Macedonian Grayling with five out of seven populated sites containing active marble quarries. Due to the enlargement of the known area of occupancy, its threat status would now be estimated at endangered. Despite the restricted knowledge about its distribution and trends in the population size, the IUCN criteria proved to be applicable to determine the threat status of a rare and localized butterfly such as Pseudochazara cingovskii. Its original assessment of being called the most threatened butterfly in Europe resulted in immediate research project and subsequent actions that will undoubtedly help to conserve it in the future. 相似文献
53.
Aerobiologia - In this study, we have compared time series of pollen concentration originating from two Hirst-type volumetric samplers that were equipped with different sampling heads. To collect... 相似文献
54.
Quantitative coral damage assessment by means of line transects was performed in several northern Red Sea coral reef sites in Israel (Eilat) and Egypt (Hurghada area). Reefs with high and low visitor frequency were compared. For both reef systems, breakage was found to be the most common damage category, being significantly higher on highly frequented reefs. Also, all observed damage (breakage, tissue loss, algal overgrowth) was most frequent within the first ten meters depth. A significant difference in the amount of corals overgrown by algae was found on the reefs near Hurghada as compared to all other reefs. Algal overgrowth was correlated with the occurrence of tissue loss and breakage, being considered as a consequence of pollution or the former damage types. In all cases of damage, Acropora was the most frequently affected genus, while Millepora dichotoma was the most affected species. 相似文献
55.
Study of the carbohydrate part of yeast acid phosphatase 总被引:2,自引:0,他引:2
Branko Kozulić Slobodan Barbarić Blanka Ries Pavao Mildner 《Biochemical and biophysical research communications》1984,122(3):1083-1090
It has been found that the carbohydrate part of acid phosphatase from yeast Saccharomyces cerevisiae consists of 16 N-glycosidically linked carbohydrate chains containing from 14 to about 150 mannose units. The presence of very small amounts of O-glycosidically linked chains was indicated. Acetolysis studies pointed to a high similarity in the structure of acid phosphatase and mannan carbohydrate chains. A new method is described for cross-linking of acid phosphatase specifically via carbohydrate chains. The possibility to cross-link the enzyme subunits intramolecularly is in accordance with the suggestion that carbohydrate chains play a role in subunit associations. 相似文献
56.
Stefanie Kimbacher Ingrid Gerstl Branko Velimirov Sylvia Hagemann 《Molecular genetics and genomics : MGG》2009,282(2):165-172
P transposons belong to the eukaryotic DNA transposons, which are transposed by a cut and paste mechanism using a P-element-coded transposase. They have been detected in Drosophila, and reside as single copies and stable homologous sequences in many vertebrate species. We present the P elements Pcin1, Pcin2 and Pcin3 from Ciona intestinalis, a species of the most primitive chordates, and compare them with those from Ciona savignyi. They showed typical DNA transposon structures, namely terminal inverted repeats and target site duplications. The coding
region of Pcin1 consisted of 13 small exons that could be translated into a P-transposon-homologous protein. C. intestinalis and C. savignyi displayed nearly the same phenotype. However, their P elements were highly divergent and the assumed P transposase from C. intestinalis was more closely related to the transposase from Drosophila melanogaster than to the transposase of C. savignyi. The present study showed that P elements with typical features of transposable DNA elements may be found already at the base of the chordate lineage.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
57.
Cepika AM Soldo Jureša D Morović Vergles J Malenica B Santak M Kapitanović S Mayer M Anić B Sentić M Gagro A 《Cellular immunology》2012,276(1-2):196-203
Arsenal of pattern-recognition receptors alongside antibody production machinery make B cells vulnerable to autoimmune response if an autoantigen elicits both pathways in a self-sustained fashion. Systemic lupus erythematosus is an autoimmune disease characterized by autoantibodies to DNA, RNA and related structures. Murine studies demonstrated autoreactive B cell activation upon TLR9 stimulation with DNA-containing immune complexes. This activation could be abolished with chloroquine, a drug used in SLE treatment that also blocks TLR9 signaling. We investigated whether chloroquine modulates TLR9 expression, circulating DNA levels and B cell-related cytokines in newly discovered, untreated SLE patients. TLR9 was measured in peripheral blood B cells by flow cytometry, serum DNA by real-time PCR, and IL-10 and BAFF by ELISA before treatment, after 3weeks on corticosteroids, and 3months after introduction of chloroquine. We found that circulating DNA is higher in SLE patients than in controls in every time-point and decreases significantly after chloroquine treatment. Untreated patients had higher serum IL-10 than controls or patients on corticosteroids. Also, corticosteroids decreased and chloroquine completely abolished CpG-mediated CD86 upregulation on B cells and IL-10 secretion in PBMC culture. Providing the TLR9 pathway activation demonstrates its importance in pathogenesis of human SLE, this data supports continuation of chloroquine in SLE treatment protocol. In addition, observed modulation of cytokine and DNA levels after immunomodulatory treatment prompts for inclusion of untreated patients in studies of human immune disorders. 相似文献
58.
Two novel 4‐substituted camphidine derivatives 10a , b have been prepared from (+)‐camphor ( 1 ) in five steps, the Beckmann rearrangement being the bottleneck of the synthesis. Isoborneol derivative 5b , formed as a side product during the hydrogenation of arylidene ketone 3b , under Beckmann rearrangement conditions yielded interesting novel rearrangement products 11 and 12 . (1S)‐(+)‐Camphorquinone ( 13 ) was transformed into diamines 15 and 16 in two steps, the former being cyclized into an imidazoline salt 17 , an N‐heterocyclic carbene precursor. The structures of all novel compounds have been meticulously characterized using NMR techniques and/or single crystal X‐ray analysis. Chirality 24:778–788, 2012. © 2012 Wiley Periodicals, Inc. 相似文献
59.
This article presents an overview of HIV/AIDS epidemiology and surveillance in Croatia 20 years after the first documented case of AIDS in the country. Here we describe strategies employed for HIV/AIDS surveillance in Croatia as well as preliminary results of HIV seroprevalence among most-at-risk populations (MARPs) research conducted by the Infectious Diseases Epidemiology Service at the Croatian National Institute of Public Health (CNIPH). Croatia has a low incidence and prevalence of HIV and AIDS. At the end of 2005, there were 553 documented cases of HIV infection, 239 of which progressed to AIDS. In Croatia, AIDS is being registered within MARPs only and dominantly among men who have sex with men (MSM). AIDS patients and HIV infected persons are found in all parts of the country. Crude prevalence of HIV among MARPs was found to be 0.9%. It is necessary to continue with current prevention and control measures in the country, and to create a culture of awareness and precaution, a strategy that has proven effective in reducing risk of HIV infection. 相似文献
60.