全文获取类型
收费全文 | 7356篇 |
免费 | 527篇 |
国内免费 | 1篇 |
出版年
2023年 | 39篇 |
2022年 | 101篇 |
2021年 | 186篇 |
2020年 | 138篇 |
2019年 | 166篇 |
2018年 | 214篇 |
2017年 | 166篇 |
2016年 | 287篇 |
2015年 | 462篇 |
2014年 | 455篇 |
2013年 | 599篇 |
2012年 | 672篇 |
2011年 | 651篇 |
2010年 | 362篇 |
2009年 | 324篇 |
2008年 | 412篇 |
2007年 | 387篇 |
2006年 | 353篇 |
2005年 | 316篇 |
2004年 | 272篇 |
2003年 | 227篇 |
2002年 | 249篇 |
2001年 | 58篇 |
2000年 | 40篇 |
1999年 | 55篇 |
1998年 | 58篇 |
1997年 | 31篇 |
1996年 | 40篇 |
1995年 | 26篇 |
1994年 | 29篇 |
1993年 | 28篇 |
1992年 | 36篇 |
1991年 | 31篇 |
1990年 | 35篇 |
1989年 | 31篇 |
1988年 | 23篇 |
1987年 | 23篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1977年 | 23篇 |
1976年 | 13篇 |
1973年 | 19篇 |
1972年 | 16篇 |
1967年 | 12篇 |
排序方式: 共有7884条查询结果,搜索用时 31 毫秒
41.
Summary A new probabilistic learning machine for pattern recognition is described. The machine operates on the basis of random criteria obtained from special pseudorandom generators. The input, particularly versatile due to the use of an image dissector, allows a random scan for which normal television storage pick-up tubes are not suitable. The computation data section, completely automatic, uses two ferrite core memories with a capacity of 64,000 bits. Consequently it is possible to obtain very quick recognizing cycles for a maximum of 16 classes of 256 learning examples each. Preliminary experiments are reported, some of which, like the recognition of meteorological events by the analysis of absolute baric topography maps, could already be suitable for practical application of the machine.This work was supported by Consiglio Nazionale delle Ricerche (C.N.R.) through the Gruppo Nazionale Cibernetica (G.N.C.). 相似文献
42.
43.
V O Palmieri A Velardi N Morelli P Portincasa D Patimo G Palasciano 《Bollettino della Società italiana di biologia sperimentale》1990,66(6):551-558
The Authors describe an optimized procedure for the isolation of rat pancreatic acini and the preliminary results concerning the functional characterization of the cells. Isolation is carried out by two sequential digestive steps in a KREBS modified medium containing collagenase, separated by an intermediate step in which acini separation is fostered by incubation in a Ca++ free medium containing the Ca++ chelator EDTA. Final separation is obtained through the application of mechanical forces by aspirating the suspension in plastic pipettes. The choice of the collagenase, the duration and the entity of the mechanical dissociation strength are the main modifications to the classic procedure and allow to obtain a very high yield of cells maintaining their ability to secrete enzymes for a long period (6-7 hours). Functional characterization is completed mainly by the determination of the amylase release stimulated by increasing doses of cholecystokinin. 相似文献
44.
Márcia Camargo-De-Morais Marta De Freitas Angela G. De Mattos Nádia Schröder Ana C. Zilles Carla S. F. Lisboa Nice Arteni Armando Barlem Rejane Schierholt Guilherme Zwetsch Carlos A. B. Souza Regina Pessoa-Pureur Carlos A. Netto 《Neurochemical research》1996,21(5):595-602
Neurofilaments subunits (NF-H, NF-M, NF-L) and glial fibrillary acidic protein (GFAP) were investigated in the hippocampus
of rats after distinct periods of reperfusion (1 to 15 days) following 20 min of transient global forebrain ischemia in the
rat. In vitro [14Ca]leucine incorporation was not altered until 48 h after the ischemic insult, however concentration of intermediate filament
subunits significantly decreased in this period. Three days after the insult, leucine incorporation significantly increased
while the concentration NF-H, NF-M, and NF-L were still diminished after 15 days of reperfusion. In vitro incorporation of32P into NF-M and NF-L suffered immediately after ischemia, but returned to control values after two days of reperfusion. GFAP
levels decreased immediately after ischemia but quickly recovered and significantly peaked from 7 to 10 days after the insult.
These results suggest that transient ischemia followed by reperfusion causes proteolysis of intermediate filaments in the
hippocampus, and that proteolysis could be facilitated by diminished phosphorylation levels of NF-M and NF-L. 相似文献
45.
Yeast mitochondria lacking the phosphate carrier/p32 are blocked in phosphate transport but can import preproteins after regeneration of a membrane potential. 总被引:4,自引:1,他引:3
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
V Zara K Dietmeier A Palmisano A Vozza J Rassow F Palmieri N Pfanner 《Molecular and cellular biology》1996,16(11):6524-6531
Two different functions have been proposed for the phosphate carrier protein/p32 of Saccharomyces cerevisiae mitochondria: transport of phosphate and requirement for import of precursor proteins into mitochondria. We characterized a yeast mutant lacking the gene for the phosphate carrier/p32 and found both a block in the import of phosphate and a strong reduction in the import of preproteins transported to the mitochondrial inner membrane and matrix. Binding of preproteins to the surface of mutant mitochondria and import of outer membrane proteins were not inhibited, indicating that the inhibition of protein import occurred after the recognition step at the outer membrane. The membrane potential across the inner membrane of the mutant mitochondria was strongly reduced. Restoration of the membrane potential restored preprotein import but did not affect the block of phosphate transport of the mutant mitochondria. We conclude that the inhibition of protein import into mitochondria lacking the phosphate carrier/p32 is indirectly caused by a reduction of the mitochondrial membrane potential (delta(gamma)), and we propose a model that the reduction of delta(psi) is due to the defective phosphate import, suggesting that phosphate transport is the primary function of the phosphate carrier/p32. 相似文献
46.
47.
Immaculada Martin Josep A. Villena Marta Giralt Roser Iglesias Teresa Mampel Octavi Vińas Francesc Villarroya 《Molecular and cellular biochemistry》1996,154(2):107-111
The action of thyroid hormones on the expression of the mitochondrial ATP synthase -subunit gene (ATPsyn) is controversial. We detected a binding site for the thyroid hormone receptor between-366 and-380 in the human ATPsyn gene by DNase I footprint analysis and band-shift assays. However, expression vectors in which the chloramphenicol acetyl transferase (CAT) reporter gene is driven by the 5 upstream region of ATPsyn gene were unresponsive to T3 when transiently transfected to HepG2 or GH4C1 cells. CAT constructs driven by the rat phosphoenolpyruvate carboxykinase (PEPCK) or the growth hormone (GH) promoters were stimulated several fold by T3 in parallel experiments. It is proposed that the biological effects of thyroid hormones on the ATPsyn expression occur through indirect mechanisms. 相似文献
48.
Summary Endoproteinase(s) was isolated from a freeze-dried powder of larvae of Ostrinia nubilalis using reverse micellar solutions. The inhibition of proteinase was studied in reverse micelles with commercial Bowman-Birk soybean trypsin inhibitor and three trypsin inhibitors recently isolated from ripe cruciferous seeds. 相似文献
49.
Abstract The digestive tract and its endocytotic activity in the catenulid Stenostomum grande were studied by electron microscopy. The pharynx was typical of the simplex type. At the mouth, between the integumental epithelium and the pharyngeal epithelium proper, was a transition zone. Among the epithelial cells of this transition were monociliated sensory cells and the necks of bucco-pharyngeal secretory cells of two types. The pharyngeal epithelium proper was densely ciliated, with long ciliary rootlets and mitochondria. It was surrounded by two layers of muscles. The gastrodermis consisted of phagocytes and typical secretory Minotian cells. It was underlain by a delicate basal lamina and muscle fibers. Distinctive of the phagocytes was the presence of differentiated cilia, cup-shaped mitochondria, and vacuoles with dense inclusions. Morphological differences between pharyngeal and gastrodermal cilia suggest functional differences. Experiments using latex beads as tracers and the identification of acid phosphatase in cytoplasmic vacuoles pointed to a high level of endocytotic and digestive activity in the phagocytes. Our data demonstrate that the basic structure of the digestive tract in S. grande conforms well to that of other free-living platyhelminths, but it does have ultrastructural peculiarities. 相似文献