全文获取类型
收费全文 | 2976篇 |
免费 | 250篇 |
出版年
2023年 | 18篇 |
2022年 | 23篇 |
2021年 | 73篇 |
2020年 | 47篇 |
2019年 | 40篇 |
2018年 | 58篇 |
2017年 | 64篇 |
2016年 | 106篇 |
2015年 | 133篇 |
2014年 | 171篇 |
2013年 | 190篇 |
2012年 | 231篇 |
2011年 | 234篇 |
2010年 | 173篇 |
2009年 | 169篇 |
2008年 | 207篇 |
2007年 | 163篇 |
2006年 | 163篇 |
2005年 | 142篇 |
2004年 | 156篇 |
2003年 | 140篇 |
2002年 | 123篇 |
2001年 | 50篇 |
2000年 | 40篇 |
1999年 | 43篇 |
1998年 | 18篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 15篇 |
1993年 | 9篇 |
1992年 | 31篇 |
1991年 | 17篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1968年 | 2篇 |
排序方式: 共有3226条查询结果,搜索用时 15 毫秒
1.
A 3-wk-old lamb died because of neurological disease. The predominant microscopic lesions were in the brain and spinal cord and consisted of nonsuppurative encephalomyelitis with severe gliosis throughout the gray and white matter. Immature and mature schizonts, 15.7 x 10.6 microns (8-30 x 6-18 microns), occurred in capillaries and were structurally similar to those of Sarcocystis tenella. 相似文献
2.
Retrograde transport is a critical mechanism for recycling certain membrane cargo. Following endocytosis from the plasma membrane, retrograde cargo is moved from early endosomes to Golgi followed by transport (recycling) back to the plasma membrane. The complete molecular and cellular mechanisms of retrograde transport remain unclear. The small GTPase RAB-6.2 mediates the retrograde recycling of the AMPA-type glutamate receptor (AMPAR) subunit GLR-1 in C. elegans neurons. Here we show that RAB-6.2 and a close paralog, RAB-6.1, together regulate retrograde transport in both neurons and non-neuronal tissue. Mutants for rab-6.1 or rab-6.2 fail to recycle GLR-1 receptors, resulting in GLR-1 turnover and behavioral defects indicative of diminished GLR-1 function. Loss of both rab-6.1 and rab-6.2 results in an additive effect on GLR-1 retrograde recycling, indicating that these two C. elegans Rab6 isoforms have overlapping functions. MIG-14 (Wntless) protein, which undergoes retrograde recycling, undergoes a similar degradation in intestinal epithelia in both rab-6.1 and rab-6.2 mutants, suggesting a broader role for these proteins in retrograde transport. Surprisingly, MIG-14 is localized to separate, spatially segregated endosomal compartments in rab-6.1 mutants compared to rab-6.2 mutants. Our results indicate that RAB-6.1 and RAB-6.2 have partially redundant functions in overall retrograde transport, but also have their own unique cellular- and subcellular functions. 相似文献
3.
The morphogenesis of lower end of tibia in chick is studied commonly but the process of ossification of the same has received very little attention so far. The present study is directed to throw some light on the appearance of ossification centers in the lower end of tibiotarsus of chick. The histology of lower end of tibiotarsus was studied by procuring developing tibiotarsi from chick embryos (20) of 6th day incubation till hatching and 3 post hatched chicks. The transparancies of chick embryos at different incubation periods and post hatched chicks were prepared by Dawson's Alizarin staining method. Three cartilage center (tibial, fibulare and intermedium) appeared in 6...9 days of incubation period in the tarsal region. These gradually fused with the lower end of tibia. Three ossification centres developed in the lower end of tibiotarsus. One for intermedium appeared on 16th day and two fotibial and fibulare on 20th day. All these three centres could be located in the transparancies of the chick embryos in tarsal region. The present study proves that the three cartilages centres maintain their individuality during the ossification process even though those fuse completely with the lower end of tibia in chick. The centers for tibial and fibulare are similar to epiphyseal centres of mammals in histological details. 相似文献
4.
Summary The toxicity of chromium and tin on growth, photosynthetic carbon-fixation, oxygen evolution, heterocyst differentiation and nitrogenase activity ofAnabaena doliolum and its interaction with bivalent cations has been studied. Some interacting cations, viz. Ca2+, Mg2+ and Mn2+, substantially antagonised the toxic effects of chromium and tin with reference to growth, heterocyst differentiation and nitrogenase activity in the following hierarchal sequence: Ca2+ > Mg2+ > Mn2+. However, the sequence of hierarchy was Mg2+ > Ca2+ > Mn2+ for carbon fixation and Mn2+ > Mg2+ > Ca2+ for photosynthetic oxygen evolution. Synergistically inhibitory patterns were noticed for all the parameters, viz. growth,14CO2 uptake, oxygen evolution, heterocyst differentiation and nitrogenase activity ofA. doliolum when Ni2+, Co2+ and Zn2+ were combined with the test metals in the growth medium. These cations followed the following sequence of synergistic inhibition: Ni2+ > Co2+ > Zn2+. Among all the interacting cations, Ca2+, Mg2+ and Mn2+ exhibited antagonistic effects which relieved the test cyanobacterium from metal toxicity. In contrast to this, Ni2+, CO2+ and Zn2+ showed synergistic inhibition which potentiating the toxicity of test metals in the N2-fixing cyanobacteriumA. doliolum. It is evident from the present study that bivalent cations, viz. Ca2+, Mg2+, Mn2+, Ni2+, Co2+ and Zn2+, may appreciably regulate the toxicity of heavy metals in N2-fixing cyanobacteria if present in aquatic media. 相似文献
5.
Five calves inoculated orally with 10(5)-10(6) sporocysts of Sarcocystis hominis from human feces were necropsied 10, 18, 24, 111, and 222 days postinoculation (DPI). Calves became febrile (greater than 40-41 C) between 10 and 24 DPI and developed mild anemia (packed cell volumes were reduced by 40% of initial values) between 29 and 57 DPI but otherwise remained clinically normal. Focal hepatitis, mesenteric lymphadenitis, and myocarditis were seen in calves at 10, 18, and 24 DPI. No stages of the parasite were found at any of these times except for a few merozoites in macrophages associated with myocardial lesions in the calf necropsied 24 DPI. Mature sarcocysts at 111 and 222 DPI were up to 950 microm long and their walls were up to 6 microm thick. They were found only in skeletal muscles. One immature sarcocyst was seen in the myocardium of the calf at 222 DPI. 相似文献
6.
Philippe Fragu Colette Brianon Catherine Fourr Jrme Clerc Odile Casiraghi Josette Jeusset Frdrique Omri Sylvain Halpern 《Biology of the cell / under the auspices of the European Cell Biology Organization》1992,74(1):5-18
We attempted to indicate the requirements for biomedical applications of SIMS microscopy. Sample preparation methodology should preserve both the structural and the chemical integrity of the tissue. Furthermore, it is often necessary to correlate ionic and light microscope images. This implies a common methodological approach to sample preparation for both microscopes. The use of low or high mass resolution depends on the elements studied and their concentrations. To improve the acquisition and processing of images, digital imaging systems have to be designed and require both ionic and optical image superimposition. However, the images do not accurately reflect element concentration; a relative quantitative approach is possible by measuring secondary ion beam intensity. Using an internal reference element (carbon) and standard curves the results are expressed in micrograms/mg of tissue. Despite their limited lateral resolution (0.5 microns) the actual SIMS microscopes are very suitable for the resolution of biomedical problems posed by action modes and drug localization in human pathology. SIMS microscopy should provide a new tool for metabolic radiotherapy by facilitating dose evaluation. The advent of high lateral resolution SIMS imaging (less than 0.1 microns) should open up new fields in biomedical investigation. 相似文献
7.
Sabine Lhernould Yannis Karamanos Sylvain Bourgerie Gerard Strecker Raymond Julien Henri Morvan 《Glycoconjugate journal》1992,9(4):191-197
We have previously isolated mannoside and xylomannoside oligosaccharides with one or two terminal reducingN-acetylglucosamine residues from the extracellular medium of white campion (Silene alba) suspension culture. We have now demonstrated the presence of peptide-N
4-(N-acetylglucosaminyl)asparagine amidase (PNGase) activity in cell extracts as well in the culture medium that could explain the production of those compounds. An additional xylomannoside, (GlcNAc)Man3(Xyl)GlcNAc(Fuc)GlcNAc, was characterized, and1H- and13C-NMR assignments for the oligosaccharide Man3(Xyl)GlcNAc(Fuc)GlcNAc were obtained using homonuclear and heteronuclear spectroscopy (COSY).Abbreviations Endo
endo--N-acetylglucosaminidase
- Fuc
fucose
- GlcNAc
N-acetylglucosamine
- Man
mannose
- NMR
nuclear magnetic resonance
- PNGase
peptide-N
4-(N-acetylglucosaminyl)asparagine amidase
- Xyl
xylose 相似文献
8.
Influence of maize root mucilage on soil aggregate stability 总被引:9,自引:0,他引:9
This study was undertaken to determine the effects of root exudates on soil aggregate stability. Root mucilage was collected
from two-month old maize plants (Zea mays L.) Mucilage and glucose solutions were added at a rate of 2.45 g C kg−1 dry soil to silty clay and silt loam soils. Amended soils, placed in serum flasks, were incubated for 42 d with a drying-wetting
cycle after 21 d. Evolved CO2 was measured periodically as well as the water-stable aggregates and soluble sugar and polysaccharide content of the soil.
In mucilage-amended soils CO2 evolution started with a lag phase of 2–3 days, which was not observed in glucose-amended soils. There was then a sharp increase
in evolved CO2 up to day 7. During the second incubation period there were only small differences in evolved C between treatments. Incorporation
of mucilage in both soils resulted in a spectacular and immediate increase in soil aggregate stability. Thereafter, the percent
of water-stable aggregates quickly decreased parallel to microbial degradation. On completion of the incubation, aggregate
stability in the silty clay soil was still significantly higher in the presence of mucilage than in the control. This work
supports the assumption that freshly released mucilage is able to stick very rapidly to soil particles and may protect the
newly formed aggregates against water destruction. On the silty clay, microbial activity contributes to a stabilization of
these established organo-mineral bounds. 相似文献
9.
Evidence suggesting that the ARS elements associated with silencers of the yeast mating-type locus HML do not function as chromosomal DNA replication origins. 总被引:41,自引:21,他引:20 下载免费PDF全文
D D Dubey L R Davis S A Greenfeder L Y Ong J G Zhu J R Broach C S Newlon J A Huberman 《Molecular and cellular biology》1991,11(10):5346-5355
10.
Disc-shaped plaques were found in the primary cyst wall of sarcocysts of Sarcocystis hemionilatrantis in mule deer in Montana. Ultrastructurally, the plaques were 190.5 nm in diameter, 161.6 nm thick and consisted of six distinct layers with microfilaments arising from the innermost layer. These unusual plaques have not been reported previously for any species of Sarcocystis. 相似文献