全文获取类型
收费全文 | 25940篇 |
免费 | 1368篇 |
国内免费 | 34篇 |
出版年
2023年 | 190篇 |
2022年 | 336篇 |
2021年 | 846篇 |
2020年 | 499篇 |
2019年 | 536篇 |
2018年 | 795篇 |
2017年 | 727篇 |
2016年 | 968篇 |
2015年 | 1147篇 |
2014年 | 1467篇 |
2013年 | 1951篇 |
2012年 | 2094篇 |
2011年 | 1850篇 |
2010年 | 1119篇 |
2009年 | 966篇 |
2008年 | 1170篇 |
2007年 | 1132篇 |
2006年 | 932篇 |
2005年 | 921篇 |
2004年 | 725篇 |
2003年 | 671篇 |
2002年 | 595篇 |
2001年 | 500篇 |
2000年 | 445篇 |
1999年 | 409篇 |
1998年 | 179篇 |
1997年 | 133篇 |
1996年 | 133篇 |
1995年 | 134篇 |
1994年 | 112篇 |
1993年 | 104篇 |
1992年 | 285篇 |
1991年 | 247篇 |
1990年 | 248篇 |
1989年 | 190篇 |
1988年 | 231篇 |
1987年 | 192篇 |
1986年 | 164篇 |
1985年 | 176篇 |
1984年 | 165篇 |
1983年 | 114篇 |
1982年 | 111篇 |
1981年 | 133篇 |
1980年 | 110篇 |
1979年 | 152篇 |
1978年 | 97篇 |
1977年 | 111篇 |
1975年 | 92篇 |
1974年 | 97篇 |
1973年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
51.
52.
53.
Study of the oviduct of the pied myna (Sturnus contra contra) throughout the year reveals that oviductal weight, length, surface epithelial height and glycogen content are low during August to January (nonbreeding phase), partially increase during February to April (pre-breeding phase), maximally increase in May (breeding phase) and decrease in June and July (post-breeding phase). In the nesting cycle, there is greatest growth in all the regions of the oviduct from early nest-building to the egg-laying period and this is followed by rapid involution during incubation and nestling periods. Some notable features in the oviduct of the pied myna are described: 1) All five regions of the oviduct (infundibulum, magnum, isthmus, uterus, and vagina) are clearly distinguishable when studied from serial sections of the oviduct even during the nonbreeding phase of the annual ovarian cycle. 2) There is a strong correlation between initiation of tubular gland formation and the onset of nestbuilding activity. 3) The distal part of the magnum is differentiated into a 'mucous region' having well developed basal nonciliated cells. 4) A sixth zone can be identified between the magnum and isthmus. Sperm hostlike glands exist at the cranial end of the zone. 5) Several circular epithelial invaginations are evident in the intermucosal folds and their size decreases in centripetal order in the vagina. 6) The pattern and degree of regression are different in various regions of the oviduct. A close synchrony between ovarian and oviducal cycles is indicated in the pied myna (Sturnus contra contra). 相似文献
54.
55.
Omkar G. Mishra S. Srivastava A. K. Gupta S. K. Singh 《Journal of Applied Entomology》2005,129(4):217-220
Abstract: This study investigated prey consumption, egg production, percent progeny loss, reproductive, pre- and post-reproductive periods, reproductive time ratio, reproductive rate and bioconversion efficiency of four aphidophagous ladybirds, viz. Cheilomenes sexmaculata (Fabricius), Coccinella septempunctata Linnaeus, Coccinella transversalis Fabricius and Propylea dissecta (Mulsant) on Dolichos lablab Linnaeus infested with cowpea aphid, Aphis craccivora Koch. C. sexmaculata had the highest bioconversion efficiency, reproductive rate and reproductive time ratio followed in rank order by P. dissecta , C. transversalis and C. septempunctata . This study indicates that C. sexmaculata has a narrow ecological relationship with A. craccivora . The increased allocation of resources to reproduction as indicated through a high reproductive time ratio and high bioconversion efficiency of C. sexmaculata and P. dissecta suggest that they may be better adapted to compete for this prey with larger species like C. transversalis and C. septempunctata . 相似文献
56.
57.
58.
P. K. Gupta P. M. Priyadarshan 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(6):893-898
Summary Triticales (XTriticosecale Wittmack) at three ploidy levels (8x, 6x, 4x, x=7) were crossed with diploid rye (Secale cereale L.) to produce a solitary hypopentaploid hybrid (2n=32), and a number of tetraploid (2n=4x=28) and triploid (2n=3x=21) hybrids. The hybrids exhibited a morphology which was intermediate between the parents. The number of bivalents ranged from 1–7 (4.65 per cell) in hypopentaploid, from 2–12 (7.13 per cell) in tetraploid and from 4–9 (6.84 per cell) in triploid hybrids. In 4x and 3x hybrids, trivalents and quadrivalents were also observed at low frequencies (range 0–1; mean 0.01–0.03 per cell). Chiasmata frequency was highest in triploid hybrids (12.44 per cell), lowest in hypopentaploid (5.37 per cell) and intermediate in tetraploids (10.54 per cell). More than 711 were found in 39.7% pollen mother cells (PMC's) in the 4x hybrids and in 5.0% PMCs in 3x hybrids. It is concluded that an increase in the relative proportion of wheat chromosomes in the hybrids had a slight suppression effect on homologous as well as homoeologous pairing of rye chromosomes. Contrary to this, the relative increase in rye complement promoted homoeologous pairing between wheat chromosomes. In triploid hybrids, the chiasmata frequency as well as the c value were the highest, suggesting that in tetraploid hybrids rye chromosomes had a reduced pairing (low frequency of ring bivalents). 相似文献
59.
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
60.
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