全文获取类型
收费全文 | 7039篇 |
免费 | 676篇 |
国内免费 | 3篇 |
出版年
2023年 | 36篇 |
2022年 | 61篇 |
2021年 | 130篇 |
2020年 | 89篇 |
2019年 | 107篇 |
2018年 | 128篇 |
2017年 | 115篇 |
2016年 | 184篇 |
2015年 | 278篇 |
2014年 | 288篇 |
2013年 | 389篇 |
2012年 | 478篇 |
2011年 | 444篇 |
2010年 | 344篇 |
2009年 | 270篇 |
2008年 | 413篇 |
2007年 | 399篇 |
2006年 | 348篇 |
2005年 | 358篇 |
2004年 | 299篇 |
2003年 | 270篇 |
2002年 | 279篇 |
2001年 | 129篇 |
2000年 | 88篇 |
1999年 | 100篇 |
1998年 | 101篇 |
1997年 | 65篇 |
1996年 | 89篇 |
1995年 | 70篇 |
1994年 | 64篇 |
1993年 | 63篇 |
1992年 | 86篇 |
1991年 | 78篇 |
1990年 | 62篇 |
1989年 | 66篇 |
1988年 | 62篇 |
1987年 | 72篇 |
1986年 | 48篇 |
1985年 | 76篇 |
1984年 | 51篇 |
1983年 | 53篇 |
1982年 | 51篇 |
1981年 | 29篇 |
1980年 | 40篇 |
1979年 | 35篇 |
1978年 | 28篇 |
1977年 | 39篇 |
1976年 | 33篇 |
1975年 | 28篇 |
1973年 | 32篇 |
排序方式: 共有7718条查询结果,搜索用时 62 毫秒
1.
2.
3.
G S Aulakh E B Stephens D L Rose J G Tully M F Barile 《Journal of bacteriology》1983,153(3):1338-1341
3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically. 相似文献
4.
The Asian Tree Toad genus Pedostibes, as currently understood, exhibits a conspicuously disjunct distribution, posing several immediate questions relating to the biogeography and taxonomy of this poorly known group. The type species, P. tuberculosus and P. kempi, are known only from India, whereas P. hosii, P. rugosus, and P. everetti are restricted to Southeast Asia. Several studies have shown that these allopatric groups are polyphyletic, with the Indian Pedostibes embedded within a primarily South Asian clade of toads, containing the genera Adenomus, Xanthophryne, and Duttaphrynus. Southeast Asian Pedostibes on the other hand, are nested within a Southeast Asian clade, which is the sister lineage to the Southeast Asian river toad genus Phrynoidis. We demonstrate that Indian and Southeast Asian Pedostibes are not only allopatric and polyphyletic, but also exhibit significant differences in morphology and reproductive mode, indicating that the Southeast Asian species’ are not congeneric with the true Pedostibes of India. As a taxonomic solution, we describe a new genus, Rentapia
gen. nov. to accommodate the Southeast Asian species. 相似文献
5.
The distribution of grooming and touching behaviours was recorded in a group of captive ring-tailed lemurs. Grooming was found
to be performed chiefly by older, higher ranking animals; touching (i.e., “reach out and touch” behaviour) was directed primarily
by younger, low ranking animals to older, high ranking individuals. It is suggested that such touching is a submissive gesture
in this species. 相似文献
6.
Peter J Stephens 《BMJ (Clinical research ed.)》2005,330(7506):1508-1509
7.
Sandra L. Almeyda Zambrano Eben N. Broadbent Sam Shanee Noga Shanee Anneke Deluycker Michael Steinberg Scott A. Ford Alma Hernndez Jaramillo Robin Fernandez‐Hilario Carolina Lagos Castillo Angelica M. Almeyda Zambrano 《American journal of primatology》2019,81(8)
Habitat loss is one of the main threats to wildlife. Therefore, knowledge of habitat use and preference is essential for the design of conservation strategies and identification of priority sites for the protection of endangered species. The yellow‐tailed woolly monkey (Lagothrix flavicauda Humboldt, 1812), categorized as Critically Endangered on the IUCN Red List, is endemic to montane forests in northern Peru where its habitat is greatly threatened. We assessed how habitat use and preference in L. flavicauda are linked to forest structure and composition. The study took place near La Esperanza, in the Amazonas region, Peru. Our objective was to identify characteristics of habitat most utilized by L. flavicauda to provide information that will be useful for the selection of priority sites for conservation measures. Using presence records collected from May 2013 to February 2014 for one group of L. flavicauda, we classified the study site into three different use zones: low‐use, medium‐use, and high‐use. We assessed forest structure and composition for all use zones using 0.1 ha Gentry vegetation transects. Results show high levels of variation in plant species composition across the three use zones. Plants used as food resources had considerably greater density, dominance, and ecological importance in high‐use zones. High‐use zones presented similar structure to medium‐ and low‐use zones; thus it remains difficult to assess the influence of forest structure on habitat preference. We recommend focusing conservation efforts on areas with a similar floristic composition to the high‐use zones recorded in this study and suggest utilizing key alimentation species for reforestation efforts. 相似文献
8.
Food sharing: a model of manipulation by harassment 总被引:3,自引:1,他引:2
Most analyses of food-sharing behavior invoke complex explanationssuch as indirect and delayed benefits for sharing via kin selectionand reciprocal altruism. However, food sharing can be a moregeneral phenomenon accounted for by more parsimonious, mutualisticexplanations. We propose a game theoretical model of a generalsharing situation in which food owners share because it is
in their own self-interestthey avoid high costs associatedwith beggar harassment. When beggars harass, owners may benefitfrom sharing part of the food if their consumption rate islow relative to the rate of cost accrual. Our model predictsthat harassment can be a profitable strategy for beggars if
they reap some direct benefits from harassing other than sharedfood (such as picking up scraps). Therefore, beggars may manipulatethe owner's fitness payoffs in such a way as to make sharingmutualistic. 相似文献
9.
10.
C A Tyson D L Story R J Stephens 《Biochemical and biophysical research communications》1983,114(2):511-517
Ultrastructural data are presented on time-course changes in isolated rat hepatocyte suspensions exposed either to 1.2 or 1.8 mM CCl4 for up to 1 h. The subcellular changes at the lower concentration, but not the higher, are shown to closely parallel those reported to occur in rat hepatocytes following ingestion of CCl4. 相似文献