全文获取类型
收费全文 | 20018篇 |
免费 | 1043篇 |
国内免费 | 27篇 |
出版年
2023年 | 170篇 |
2022年 | 227篇 |
2021年 | 708篇 |
2020年 | 441篇 |
2019年 | 460篇 |
2018年 | 691篇 |
2017年 | 624篇 |
2016年 | 829篇 |
2015年 | 966篇 |
2014年 | 1203篇 |
2013年 | 1650篇 |
2012年 | 1739篇 |
2011年 | 1543篇 |
2010年 | 895篇 |
2009年 | 790篇 |
2008年 | 924篇 |
2007年 | 915篇 |
2006年 | 766篇 |
2005年 | 703篇 |
2004年 | 572篇 |
2003年 | 468篇 |
2002年 | 426篇 |
2001年 | 354篇 |
2000年 | 318篇 |
1999年 | 280篇 |
1998年 | 120篇 |
1997年 | 95篇 |
1996年 | 85篇 |
1995年 | 95篇 |
1994年 | 66篇 |
1993年 | 63篇 |
1992年 | 176篇 |
1991年 | 177篇 |
1990年 | 133篇 |
1989年 | 95篇 |
1988年 | 145篇 |
1987年 | 116篇 |
1986年 | 99篇 |
1985年 | 101篇 |
1984年 | 102篇 |
1983年 | 57篇 |
1982年 | 52篇 |
1981年 | 57篇 |
1980年 | 50篇 |
1979年 | 73篇 |
1978年 | 44篇 |
1977年 | 52篇 |
1976年 | 41篇 |
1975年 | 46篇 |
1974年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
41.
42.
43.
44.
Fine structure of reproductive glands in two primitive marine pulmonates (Basommatophora: Siphonariidae) 总被引:1,自引:0,他引:1
Purba Pal 《Acta zoologica》2007,88(2):145-152
Within the clade Euthyneura the marine basommatophorans are particularly neglected. More morphological and molecular studies are needed because their phylogenetic relationships with other pulmonates remain unresolved. The present study examines the most conspicuous reproductive gland, the glandular complex in two marine limpets, Siphonaria capensis and S. serrata (Pulmonata: Basommatophora) at both gross and fine structural levels. These two sympatric species with different developmental modes were selected to compare the structure and function of this enormous glandular structure. In both S. capensis and S. serrata, the glandular complex shows an undifferentiated state composed of an acidophilic albumen gland and a basophilic mucous gland. The glands contain secretory cells and supporting cells (= ciliated cells) that are highly ciliated. When the histochemical properties of the glandular complex were compared with those of siphonariid egg masses (of each species) it could be established that the albumen gland was responsible for the production of perivitelline fluid whereas the mucous gland secreted substances that help in the assembly of mucous layers surrounding the egg capsules. We suggest that the presence of a single glandular complex comprised of two glands is the most primitive organization of reproductive glands in pulmonates. Furthermore, the histology, fine structure and histochemistry of these glands are very similar to those of the reproductive glands of opisthobranchs. 相似文献
45.
46.
47.
Dipak Kumar Banerjee 《Journal of biosciences》1987,11(1-4):311-319
Radio-labelled amphomycin (3H-amphomycin) forms a complex with dolichylmonophosphate in presence of Ca2+. Complex formation has also been documented with retinylmonophosphate and perhydromonoeneretinylmonophosphate. Analysis of
the space-filling model suggested both fatty acylated aspartic acid residue at the N-terminus of the lipopeptide and phosphate
head group of dolichylmonophosphate are necessary for the complex formation. The binding ability of amphomycin is then utilized
to localize dolichylmonophosphate in the microsomal membrane. Studies with microsomal membranes from hen oviduct suggested
that dolichylmonophosphate is located in the cytoplasmic side of the membrane. 相似文献
48.
S. K. Podder A. Chakraborti K. Vijayalakshmi P. Lalit Kumar Singh 《Journal of biosciences》1987,11(1-4):495-502
To examine how surface Potential controls the reactivity of glycoconjugates at cell surface, the interaction of galactose-sPecific
lectinse.g. peanut agglutinin,Ricinus cummunis agglutinin with liPosomes bearing asialo GM1 were studied in the Presence of varying amount of ganglioside mixture, GMn. The Presence of 5% GMn causes comPlete slowing down of PreciPitin reaction and thereby make carbohydrate moiety of asialo GM1 comPletely inaccessiblei.e. ‘cryPtic’. In contrast the Presence of 1–2% GMn enhances the aPParent rate and amPlitude of the PreciPitin reaction as surface Potential becomes more negative. The relevance
of the findings has been discussed in relation to the exPression and involvement of the cell-surface sialic acid residues
during develoPment and differentiation. 相似文献
49.
The phylogenetic relationships among three derivative forms of the immigrans-Hirtodrosophila radiation viz. Chaetodrosophilella, Zaprionus and the immigrans species group are examined, by comparing the banding patterns of their polytene chromosomes and by analysing the nature of their heterochromatin. Based on the results of these studies it is concluded that D. quadrilineata has a very strong affinity with the members of the immigrans species group, while the genus Zaprionus represents a very distinct evolutionary lineage. This study further indicates that D. quadrilineata is a karyotypically primitive species having five pairs of rods and one pair of dots, while the karyotype of other members of the immigrans species group appears to have undergone modifications through fusions, fissions, inversions and the addition or deletion of heterochromatin to dots and other chromosomes. 相似文献
50.
Lack of dendritic Thy-1+ epidermal cells in mice with severe combined immunodeficiency disease 总被引:1,自引:0,他引:1
J L Nixon-Fulton P L Witte R E Tigelaar P R Bergstresser V Kumar 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(9):2902-2905
C.B-17 scid (severe combined immunodeficiency disease) mice were used to evaluate the relationship of dendritic Thy-1+ epidermal cells (EC) to T lymphocytes (deficient in scid) and to NK cells (replete in scid). Epidermis from scid mice was deficient in dendritic Thy-1+ cells as determined by immunofluorescent staining of epidermal whole mounts. Similarly, epidermal cell suspensions from scid mice failed to proliferate in response to Con A, as compared with epidermal cell suspensions from C.B-17 control mice. Transplantation of normal bone marrow into scid mice reconstituted morphologically identifiable dendritic Thy-1+ EC in whole mounts, as well as Con A responsiveness of EC suspensions, thus indicating that the deficiency in dendritic Thy-1+ EC in scid mice is at the precursor level. These studies demonstrate that Thy-1+ EC are more closely related to T lymphocytes than to NK cells. 相似文献