全文获取类型
收费全文 | 89篇 |
免费 | 23篇 |
国内免费 | 68篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 5篇 |
2012年 | 5篇 |
2011年 | 3篇 |
2010年 | 12篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 12篇 |
2005年 | 5篇 |
2004年 | 1篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有180条查询结果,搜索用时 15 毫秒
31.
32.
因遭受滥垦及过度放牧破坏的中国北方农牧交错带亟待进行植被的恢复和重建.本文从为该区域植被的恢复与重建提供植物物种上的支持出发,对适宜该区域生长与分布的乔、灌、草种进行了生态区划.生态区划的原则概括为4条:生态保育优先、有利生产发展、适地适树适草以及参考行政区划边界.在该原则指导下,依据限定农牧交错带植物生长和分布的主要生态因子:年最低日均温、年大于0℃积温、湿润度指数(年降水量与年大于0℃积温之比)、反映区域地表组成物质、地形及气候特征影响的土壤类型等,将农牧交错带划分为7个不同的生态区域,依次为:Ⅰ.松辽平原西部及大兴安岭山地区,Ⅱ.辽河上游风沙区,Ⅲ.蒙古高原中、东部及冀西北山地区,Ⅳ.吕梁山、太行山、燕山山地区,Ⅴ.鄂尔多斯高原风沙区,Ⅵ.陕北、陇东黄土高原区,Ⅶ.陇中及青海高原东部黄土区.在上述分区的基础上,对以往文献报道中出现的适宜该区域生长和分布的乔、灌、草,包括乡土种和人工栽培或引种的外来种,按其生态习性分别进行了细致的甄别选择,并在文中择其精要予以列出. 相似文献
33.
黄土高原东北缘的鼠类及某区划的研究 总被引:2,自引:0,他引:2
位于山西省东北部和河北省冀北山地张家口的黄土高原东北缘地区的鼠类,过去曾经有Thomas(1908;1909)、Allen(1938;1940)、Ho(何锡瑞,1934)、张俊等(1965)、郑宝赉等(1966)、柳枢(1977)、梁俊勋(1983)等报道。 相似文献
34.
The Rosaceae is one of the five largest families of Xizang flora, consisting of
30 genera with 242 species, the total number of species is slightly less than those of
Compositae, Graminae, Leguminosae and Ericaceae in Xizang, amounting to 62.5% of
the total number of genera and 28% of the total number of species of the rosaceous flora
in China.
The four subfamilies of Rosaceae including primitive, intermediate and advanced
groups have been found in Xizang. These groups consist of 11 types of floristic elements, i.e. 4 genera belong to cosmopolitan, 9 genera belong to North Temperate, 3, E.
Asian-N. American, 3 Sino-Himalayan, 3 Sino-Japanesa, 2 Old World Temperate, 1
Temperate Asian, 2 Mediterranean-W. and O. Asian, 1 C. Asian, I Tropical Asian and 1
endemic to China. It is obvious that Rosaceae in Xizang comprises holarctic, Ancient Mediterranean and paleotropical elements, among which the temperate components are the
most dominant. The characteristics of the floristic composition of Rosaceae in Xizang
may be summarized as follows:
(1) Xizang abounds in both genera and species of the family which are diverse in
forms, including the primitive, intermediate and advanced groups, (2) The geographical elements are rather complex, mostly belonging to the temperate, among which the
Sino- Himalayan components and the elements endemic to China are dominant, (3) The
proportion of plants endemic to China and distributed in Xizang is much higher than
those endemic to Xizang itself, but there exist newly arisen species and infraspecific
forms or varieties which show that the speciation is apparently still active in Xizang.
The rosaceous flora of Xizang is a combination of old and new floristic elements, based
on the old floristic components, affected by the upheaval of the Himalayas, the differentiation and speciation have been taking place in the long history.
The geographical distribution of Rosaceae in Xizang may be divided into 5 regions,
i.e. the northeastern, southeastern, southern, northwestern and northern. The rosaceous
plants are most abundant in the southeastern area, next in southern area, fewer in the
northeastern and very rare in the northwestern and northern regions. The general tendency of the distribution of Rosaceae in Xizang is that the number of species gradually
decreases from the southeast to the northwest and the habit gradually changes from
trees, shrubs and herbaceous plants in the southeast to cushion-like scrubs and dwarf
perennial herbs in the northwest. These facts clearly show that the uplift of the Himalayas has deeply affected the phytogeographical distribution of Xizang Rosaceae.
The rosaceous flora of Xizang has close relationships with those of the adjoring
regions, i.e. Yunnan and Sichuan. Besides, it is connected with floras of Nepal, Sikkim,
Bhutan nothern Buram and nothern India, but silghtly influenced by the Ancient Mediterranean flora. 相似文献
35.
36.
Octavio R. Rojas-Soto Othón Alcántara-Ayala Adolfo G. Navarro 《Journal of Biogeography》2003,30(3):449-461
Aim To analyse the distributional patterns of the Baja California Peninsula's resident avifauna, and to generate a regionalization based on a method that uses a parsimony analysis (parsimony analysis of endemicity, PAE) of point data and modelled potential distributions. Location The Baja California Peninsula, Mexico. Methods A data base was constructed containing records of 113 species of resident terrestrial birds present in the Baja California Peninsula. Records and localities were obtained from the literature and from specimens housed in scientific collections world‐wide. Raw data points and potential distribution maps obtained using the software Genetic Algorithms for Rule‐set Prediction (GARP), were analysed with PAE. Results The data base consisted of 4164 unique records (only one combination of species/locality) belonging to 113 terrestrial resident bird species, in a total of 809 localities. From the point distribution matrix, the analysis generated 500 equally parsimonious trees, from which a strict consensus cladogram with 967 steps was obtained. The cladogram shows a basal polytomy and some geographical correspondence of a few resolved groups obtained in the analysis. These results do not allow the recognition of areas defined by avifaunistic associations. From the potential distribution matrix, the analysis generated 501 equally parsimonious trees, and a strict consensus cladogram of 516 steps was obtained. The cladogram shows a higher resolution because of the number of resolved groups with better geographical correspondence and therefore regions are well‐defined. Main conclusions The correspondence of some groupings of species suggest their validity as areas with biogeographical (historical and/or ecological) meaning. This regionalization in the Baja California avifauna seems to be consistent with previous regionalizations for other groups. Hence, PAE is a useful tool for area categorization if reliable point records and prediction tools are available. Our results suggest that the geographical definition is much better using potential data generated by GARP, particularly when they are contrasted with the results from point data. Thus, this is an excellent alternative for developing biogeographical studies, as well as for improving the use of data from scientific collections and other sources of biodiversity information. 相似文献
37.
38.
Biotic homogeneity of putative biogeographic units in the Neotropics: A test with Sapotaceae 下载免费PDF全文
Julieth Serrano James E. Richardson Terence D. Pennington Rocio Cortes‐B Dairon Cardenas Alan Elliott Ivan Jimenez 《Diversity & distributions》2018,24(8):1121-1135
Aim
To evaluate Morrone's (2001, Biogeografia de America Latina y el Caribe. Zaragoza, Spain: CYTED, ORCYT‐UNESCO, Sociedad Entomológica Aragonesa (SEA)) Neotropical regionalization by testing the prediction that biotas are more homogeneous within than among biogeographic units.Location
Neotropics.Methods
We conducted pairwise comparisons of beta diversity of Sapotaceae species within and between biogeographic units in the hierarchical regionalization proposed by Morrone (2001, Biogeografia de America Latina y el Caribe. Zaragoza, Spain: CYTED, ORCYT‐UNESCO, Sociedad Entomológica Aragonesa (SEA)), at a spatial resolution of 1‐degree cells. We used a null model to control differences in sampling effort across 1‐degree cells and performed beta‐diversity comparisons conditional on geographic distance to control for distance decay of biotic similarity.Results
None of the biogeographic units proposed by Morrone (2001, Biogeografia de America Latina y el Caribe. Zaragoza, Spain: CYTED, ORCYT‐UNESCO, Sociedad Entomológica Aragonesa (SEA)) was biotically homogeneous with respect to all other units at the same hierarchical level. This was the case even for units commonly reported to be isolated and to host distinctive taxa like “Choco.” However, five of 45 biogeographic units were biotically homogenous relative to several other units. These units were “Cuba,” “Chaco,” “Varzea,” “Cauca” and “Costa Pacífica Mexicana.” Also, beta diversity within units was often lower than beta diversity between units at relatively short geographic distances.Main conclusions
The distribution of Sapotaceae species showed generally low biotic homogeneity within Morrone's (2001, Biogeografia de America Latina y el Caribe. Zaragoza, Spain: CYTED, ORCYT‐UNESCO, Sociedad Entomológica Aragonesa (SEA)) biogeographic units and did not support his biogeographic regionalization. This result suggests a strong role for dispersal and biotic interchange among biogeographic units and across barriers like the Andes. It also casts doubt on the usefulness of Morrone's (2001, Biogeografia de America Latina y el Caribe. Zaragoza, Spain: CYTED, ORCYT‐UNESCO, Sociedad Entomológica Aragonesa (SEA)) biogeographic units as tools for the identification of priority areas for the conservation of biodiversity. However, relatively high biotic homogeneity within some biogeographic units suggests that they capture significant spatial patterns. In particular, noteworthy biotic homogeneity within “Cuba,” “Cauca” and “Costa Pacifica Mexicana” could be explained by isolation. Also, in “Costa Pacifica Mexicana,” patterns of biotic homogeneity could reflect closer affinities to humid lowland montane forest in Central America than to lowland rain forest in South America. Finally, substantial biotic homogeneity within “Varzea” could result from common adaptation to edaphic environments near the Amazon River.39.
Susumu Matsushita 《Development, growth & differentiation》1996,38(3):247-255
Developmental changes in mesodermal activity to induce intestine-like differentiation expressing sucrase antigen in the endoderm and changes in endodermal reactivity to such an activity in the digestive tract of the chick embryo were analyzed. Digestive-tract endoderms of embryos at 3 days of incubation were highly responsive to the inductive effect of the 5 day duodenal mesenchyme, with the stomach endoderm lying nearest to the intestine having the highest reactivity. Endodermal reactivity decreased with increasing age. It was almost absent in the endoderm of the esophagus or proventriculus of 6 day embryos and in the endoderm of the gizzard of 7 day embryos. The activity of the mesoderm to induce intestine-like differentiation in 5 day gizzard endoderm was high in the 5–10 day duodenal mesenchyme, but was rarely found in 14 day duodenal mesenchyme. This activity was specific to intestinal mesenchymes, among which the duodenal mesenchyme had the highest activity in 5 day embryos. The 3 day intestinal mesenchyme may already have the inductive activity. The presumptive intestinal mesoderm of 1.5 day embryos seemed to have a slight or no activity, but it may have intestinal identity and may manifest a high inductive activity later. 相似文献
40.