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   1269篇
  免费   97篇
  国内免费   125篇
  2023年   17篇
  2022年   31篇
  2021年   41篇
  2020年   54篇
  2019年   65篇
  2018年   61篇
  2017年   55篇
  2016年   55篇
  2015年   52篇
  2014年   50篇
  2013年   147篇
  2012年   47篇
  2011年   46篇
  2010年   39篇
  2009年   70篇
  2008年   57篇
  2007年   69篇
  2006年   66篇
  2005年   37篇
  2004年   45篇
  2003年   47篇
  2002年   35篇
  2001年   23篇
  2000年   17篇
  1999年   10篇
  1998年   10篇
  1997年   19篇
  1996年   7篇
  1995年   16篇
  1994年   9篇
  1993年   13篇
  1992年   11篇
  1991年   5篇
  1990年   16篇
  1989年   8篇
  1988年   4篇
  1987年   11篇
  1986年   10篇
  1985年   9篇
  1984年   18篇
  1983年   13篇
  1982年   15篇
  1981年   12篇
  1980年   10篇
  1979年   8篇
  1978年   9篇
  1976年   4篇
  1975年   3篇
  1974年   5篇
  1973年   6篇
排序方式: 共有1491条查询结果,搜索用时 15 毫秒
181.
182.
East Coast fever is a lymphoproliferative disease caused by the tick-borne protozoan parasite Theileria parva. The sporozoite stage of this parasite, harboured and released from the salivary glands of the tick Rhipicephalus appendiculatus during feeding, invades and establishes infection in bovine lymphocytes. Blocking this initial stage of invasion presents a promising vaccine strategy for control of East Coast fever and can in part be achieved by targeting the major sporozoite surface protein p67. To support research on the biology of T. parva and the identification of additional candidate vaccine antigens, we report on the sporozoite proteome as defined by LC–MS/MS analysis. In total, 4780 proteins were identified in an enriched preparation of sporozoites. Of these, 2007 were identified as T. parva proteins, representing close to 50% of the total predicted parasite proteome. The remaining 2773 proteins were derived from the tick vector. The identified sporozoite proteins include a set of known T. parva antigens targeted by antibodies and cytotoxic T cells from cattle that are immune to East Coast fever. We also identified proteins predicted to be orthologs of Plasmodium falciparum sporozoite surface molecules and invasion organelle proteins, and proteins that may contribute to the phenomenon of bovine lymphocyte transformation. Overall, these data establish a protein expression profile of T. parva sporozoites as an important starting point for further study of a parasitic species which has considerable agricultural impact.  相似文献   
183.
184.
Habitat loss via human activity has fragmented populations of the golden snub-nosed monkey (Rhinopithecus roxellana), and thus affected patterns of gene flow. We investigated in-depth a single troop in the Qinling Mountains, central China, two major histocompatibility complex (MHC) class II loci, DQA1 and DQB1, and compared the resulting data with data from troops from the wider Qinling Mountains region. We found that a novel DQB1 allele was only present in the study troop and relatively few divergent alleles at the DQA1 and DQB1 loci were present compared with the wider population. The inbreeding coefficient (Fis) at the MHC region was lower than previous measurements, which may have reflected different sampling strategies. However, R. roxellana has relatively high diversity in MHC genes, even though it has probably experienced serious past population bottlenecks and reduced gene flow between populations. We also found that some alleles present in the wider population had been lost in the study troop, and suggest that conservation management strategies be implemented to increase gene flow between troops in order to increase genetic variation.  相似文献   
185.
Although the Omani Owl Strix butleri (A. O. Hume, 1878) was previously reported from southern Iran, this note details the first confirmed records of this species from Mashhad (Khorasan) and Jam (Bushehr) in 2015, after recent revision of the taxonomy of this species in the Middle East.  相似文献   
186.
187.
Although archaeobotanical sampling and recovery programmes are a relatively recent implementation in East African archaeology, results from sites where they have been carried out follow a similar trend. This is one of abundant recovery of wood charcoal, but very little in the way of other macroscopic plant remains. Restricted archaeological evidence and ethnographic interviews show the importance of grains, in particular finger millet (Eleusine coracana), for the Bunyoro people of Uganda in pre-colonial times. It has been suggested that one of the possible reasons why finger millet is not being recovered in quantity from archaeological contexts is because the processing of this crop does not involve heating and hence there is not the chance of being deposited in charred form in the archaeological record. Recent ethnographic work on finger millet processing in Uganda shows that it is exposed to heat and potential charring during cleaning and preparation of the grain for either storage or cooking, and this regime is discussed in terms of its activities and products. These findings reinforce the need for archaeobotanists and archaeologists working in this region to look for other possible causes of the scarcity of macroscopic plant remains, and also the importance of considering integrated evidence for agricultural activity on prehistoric sites.  相似文献   
188.
There are two peat fields, the Maohebei peat field and Daziying peat field, both situated in the delta of the lower reaches of the Liao River in the Eastern Hebei Plain, North China. The peat bogs were deposited at 10000–3500 years ago. From the point view of vegetational history, the pollen assemblage zones correlated with the radiocarbon dating materials are established. On this basis the profile may be divided into three zonation systems. Zone M-l, 10000–9000 14C yr. BP. The temperate needle leaf and deciduous woodlots scattered among herbs, with a mild and cool climate. It can be correlated to the Boreal or the Anathermal interval. Zone M-2, 9000–5000 BP. Pinus and Quercum mixtumum ( Quercus, Ulmus, Tilia, Corylus) woodland and Vermuth steppes, with warm and semihumid climate. And about 7500 BP a maximum warm took place. It can be correlated to the Atlantic. Zone M-3, 5000–3500 BP. Pinus-Quercus woodland and Vermuth steppes with warm and semihumid, correlated to Subboreal. Both M-2 and M-3 can corrspond to the Hypsithermal interval of the Holocene subdivisions, i.e. the Optimum. In this interval some subtropical elements sppeare in the assemblage, such as Myrica, Antidesma, and Fagara which reflect that the weather might be warmer than that of the present in the same region. Some ecological dynamics of the vegetation are expressed in the assemblages. When climate became warm from Boreal to Atlantic, Corylus increased a little earlier than other deciduous but soon decreased. Ulmus declined at 5000 BP. This reflects situation is just the same as in North Europe. The woodland destroyed by human activities in culture and agiculture might be an important factor of vegetational and environmental changes. However the great increase of Pinus and Artemisia following the decrease of Ulmus and Tilia gives effective support to the tendency of climatic change, becaming cooler and drier in the Sub- boreal of Hypsithermal interval. This is an attempt to establish the pollen percentage diagram and pollen influx diagram by mean of exotic pollen. The pollen influx record shows similarities to that of the pollen percentages. However, the pollen influx is more obvious in representing the vegetation and environment changes.  相似文献   
189.
190.
New data and records of the genus Chrysotoxum Meigen, 1803 are reported, arising from taxonomic and faunistic examination of adult specimens collected from 1920 to 2011 from four northeastern provinces of Turkey (Erzurum, Bayburt, Kars, and Artvin), and from the neighboring countries of Armenia, Azerbaijan and Iran. Three new species are described: Chrysotoxum antennalis Vuji?, Nedeljkovi? &; Hayat sp. n., C. clausseni Vuji?, Nedeljkovi? &; Hayat sp. n. and C. persicum Vuji?, Nedeljkovi? &; Hayat sp. n. The first two are known only from northeastern Turkey, and the third also occurs in Armenia, Azerbaijan and Iran. These new species have in common an antenna with the basoflagellomere being shorter than the scape and pedicel together.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:4C264678-8E47-4DE0-AC7D-91DABC597BCD  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