全文获取类型
收费全文 | 798701篇 |
免费 | 82904篇 |
国内免费 | 239篇 |
出版年
2018年 | 8002篇 |
2017年 | 7646篇 |
2016年 | 10748篇 |
2015年 | 13655篇 |
2014年 | 16254篇 |
2013年 | 23384篇 |
2012年 | 26292篇 |
2011年 | 27072篇 |
2010年 | 18477篇 |
2009年 | 17068篇 |
2008年 | 24177篇 |
2007年 | 25148篇 |
2006年 | 23470篇 |
2005年 | 22583篇 |
2004年 | 22335篇 |
2003年 | 21488篇 |
2002年 | 21011篇 |
2001年 | 34870篇 |
2000年 | 34320篇 |
1999年 | 27520篇 |
1998年 | 9914篇 |
1997年 | 9949篇 |
1996年 | 9565篇 |
1995年 | 9092篇 |
1994年 | 8772篇 |
1993年 | 8808篇 |
1992年 | 22437篇 |
1991年 | 22017篇 |
1990年 | 21446篇 |
1989年 | 20905篇 |
1988年 | 19166篇 |
1987年 | 18391篇 |
1986年 | 17149篇 |
1985年 | 17038篇 |
1984年 | 13995篇 |
1983年 | 12225篇 |
1982年 | 9287篇 |
1981年 | 8411篇 |
1980年 | 7791篇 |
1979年 | 12995篇 |
1978年 | 10256篇 |
1977年 | 9240篇 |
1976年 | 8837篇 |
1975年 | 9864篇 |
1974年 | 10542篇 |
1973年 | 10405篇 |
1972年 | 9512篇 |
1971年 | 8502篇 |
1970年 | 7427篇 |
1969年 | 7306篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
51.
52.
A. A. Gontcharov 《Hydrobiologia》1996,336(1-3):93-97
A survey of the freshwater algal flora of the Primorsky Region, Russian Far East, is presented. During more than 70 years
of investigations 1659 species (including varieties and forms 2276 taxa) belonging to 346 genera of different groups of algae
have been recorded from this territory. The Primorsky Region is rich in habitats attractive to algae-rivers, lakes, reservoirs,
and ponds. The details of the distribution of algae in different types of waterbodies have been examined. The algal flora
of the region is comparable to the areas, and its taxonomical structure is typical for Eurasia. From this territory some new
species and varieties have been described — Achnanthes chankensis, Cymbella ventricosa var. hankensis, Surirella alisoviana, and others. The flora includes some rare species — Fragilaria magocsyi, Perone dimorpha, and Heterothrix monochloron, and some endemics of Asia — Navicula scutelloides var. baicalensis, N. globulifera var. nipponica, Gomphonema sphaerophorum, and Surirella tientsinensis. 相似文献
53.
54.
N. H. Russel A. E. Hunter A. Haynes E. M. Bessell 《BMJ (Clinical research ed.)》1994,308(6945):1715-1716
55.
56.
One of the major problems faced by conservation biologists is the allocation of scarce resources to an overwhelmingly large number of species in need of preservation efforts. Both demographic and genetic information have been brought to bear on this problem; however, the role of information obtained from genetic markers has largely been limited to the characterization of gene frequencies and patterns of diversity. While the genetic consequences of rarity may be a contributing factor to endangerment, it is widely recognized that demographic factors often may be more important. Because patterns of genetic marker variation are influenced by the same demographic factors of interest to the conservation biologist, it is possible to extract useful demographic information from genetic marker data. Such an approach may be productive for determining plant mating systems, inbreeding depression, effective population size, and metapopulation structure. In many cases, however, data consisting only of marker frequencies are inadequate for these purposes. Development of genealogical based analytical methods coupled with studies of DNA sequence variation within and among populations is likely to yield the most information on demographic processes from genetic marker data. Indeed, in some cases it may be the only means of obtaining information on the long-term demographic properties that may be most useful for determining the future prospects of a species of interest. 相似文献
57.
Analysis of 'homes' occupied by juvenile Octopus vulgaris shows flexible behaviour which may indicate specialized intelligence and tool use. Octopuses occupied sheltered areas for a short time, average 10 days, but stayed longer in larger homes and in areas where preferred prey was available. They did not simply respond to perceptual characteristics of a site, but instead chose locations potentially suitable and modified them by removing rocks and sand and bringing in items partially to block the aperture. 相似文献
58.
59.
The genusLepidapedon is subdivided into several species groups and subgroups of species based on the vitelline distribution and the length of the excretory vesicle. The species in each of the subgroups are listed and keys to the species in most subgroups are given. The following north-eastern Atlantic species are described or redescribed:Lepidapedon rachion fromMelanogrammus aeglefinus, Gadus morhua, Aspitrigla cuculus, Merlangius merlangus andPollachius pollachius; L. cambrensis fromEnchelyopus cimbrius; L. sommervillae n. sp. fromTrachyrincus scabrus, T. murrayi andCoryphaenoides guentheri; L. elongatum fromGadus morhua; L. gaevskayae fromCoryphaenoides (Nematonurus) armatus; L. discoveryi n. sp. fromCoryphaenoides (Nematonurus) armatus; L. arlenae n. sp. fromTrachyrincus scabrus andT. murrayi; L. mariannae n. sp. fromGaidropsarus argentatus; Lepidapedon spp. innom (Elongatum-group) fromCoryphaenoides guentheri andCoryphaenoides (Chalinura) leptolepis; L. desclersae n. sp. fromLepidion eques; L. beveridgei fromCoryphaenoides (Nematonurus) armatus andC. (Chalinura) mediterraneus; andL. zubchenkoi fromCoryphaenoides (Chalinura) leptolepis andC. (C.) profundicolus. The phylogeny, host-specificity and zoogeography of the genus are briefly discussed. 相似文献
60.
M. Pons M. García A. Borell F. Garcia J. Egozcue M. A. Gorostiaga A. Delprat M. Mudry 《American journal of primatology》1995,37(4):325-331
Cytogenetic studies have been carried out in 39 specimens of C. apella of different origins. Three different morphologies, one affecting the long arm of chromosome 4 and two affecting pair 17, have been detected. In each case, they can be related by paracentric inversions. Heterochromatin polymorphisms affecting terminal or interstitial C+ regions have also been observed. The length of the terminal heterochromatic region in the long arms of chromosome 11 is variable in C. apella sp., in C. a. paraguayanus and absent in the C. a. nigritus specimens studied. Interstitial C + bands can be observed in the long arms of the biarmed chromosomes 4 and 6, and in the long arms of the acrocentric pairs 12, 13, 17, 18, 19, 20, and 21. Interstitial C + bands in the long arms of chromosomes 4, 12, 17, and 19 are present in all animals studied, although their size is variable, especially in the case of chromosomes 17 and 19. © 1995 Wiley-Liss, Inc. 相似文献