全文获取类型
收费全文 | 27363篇 |
免费 | 15605篇 |
国内免费 | 5篇 |
出版年
2023年 | 31篇 |
2022年 | 122篇 |
2021年 | 440篇 |
2020年 | 2216篇 |
2019年 | 3739篇 |
2018年 | 3857篇 |
2017年 | 4141篇 |
2016年 | 4151篇 |
2015年 | 4102篇 |
2014年 | 3764篇 |
2013年 | 4175篇 |
2012年 | 1871篇 |
2011年 | 1594篇 |
2010年 | 3113篇 |
2009年 | 1834篇 |
2008年 | 758篇 |
2007年 | 339篇 |
2006年 | 345篇 |
2005年 | 391篇 |
2004年 | 370篇 |
2003年 | 336篇 |
2002年 | 307篇 |
2001年 | 268篇 |
2000年 | 201篇 |
1999年 | 157篇 |
1998年 | 31篇 |
1997年 | 23篇 |
1996年 | 18篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 7篇 |
1992年 | 32篇 |
1991年 | 19篇 |
1990年 | 9篇 |
1989年 | 16篇 |
1988年 | 9篇 |
1987年 | 23篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
121.
Nitrogen Source Regulates Glutamate Dehydrogenase NADP Synthesis in Neurospora crassa 总被引:8,自引:4,他引:4
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Georgina Hernndez Ray Snchez-Pescador Rafael Palacios Jaime Mora 《Journal of bacteriology》1983,154(1):524-528
Neurospora crassa glutamate dehydrogenase-NADP (EC 1.3.1.3) has a higher activity when mycelium is grown on ammonium or nitrate as nitrogen source than when grown on glutamate or glutamine. Quantitative immunoelectrophoresis established that, under all conditions, enzyme activity corresponded to enzyme concentration. Isotope incorporation studies demonstrated that the nitrogen source exerts its regulation at the level of de novo enzyme synthesis. 相似文献
122.
Selection of Wine Yeasts for Growth and Fermentation in the Presence of Ethanol and Sucrose 总被引:5,自引:3,他引:2
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tahía Benítez Lucas del Castillo Andrs Aguilera Jaime Conde E. Cerdolmedo 《Applied microbiology》1983,45(5):1429-1436
To optimize the conversion of carbohydrates to ethanol, strains of several Saccharomyces species were examined for the ability to grow and ferment in a range of sucrose and ethanol concentrations. A total of 632 wine yeasts, most of them isolated from wineries in Andalusia and Extremadura, southwestern Spain, were subjected to screening and selection. Growth and fermentative capacity in different ethanol and sucrose concentrations varied from one strain to another. There was no correlation between growth and fermentative capacity. The best 35 strains grew in 15% ethanol and fermented in 18% ethanol. Ethanol accumulated, although at a reduced rate, after the cells stopped growing. Most yeast strains were highly fermentative in 50% sucrose. Some of them effectively utilized the carbohydrates of the culture, yielding final ethanol concentrations of > 14%. Of the 35 selected strains, 16 were promising for genetic analysis and breeding because of their capacity to sporulate. These strains were homothallic, and their spores were viable. The meiotic products analyzed so far were also homothallic. 相似文献
123.
Antonio G. Gonzalez Jaime Bermejo Barrera Francisco J. Tolfdo Marante 《Phytochemistry》1983,22(4):1049-1050
The fruit bodies of the Basidiomycete Scleroderma polyrhizum have been shown to contain the steroids ergosta-4,6,8(14) 22-tetraen-3-one and 5α,8α-epidoxyergosta-6,22-dien-3β-ol and also palmitic and oleic acids. 相似文献
124.
Herbert M. Schulman Jaime Martinez-Medellin Rose Sidloi 《Biochimica et Biophysica Acta (BBA)/General Subjects》1974,343(3):529-534
The effect of three groups of metabolic inhibitors on the incorporation of Fe and release of bicarbonate from transferrin by rabbit reticulocytes was measured. Inhibitors which affect reticulocyte Fe and transferrin uptake to the same extent (sodium arsenite, N-ethylmaleimide and iodoacetamide); those which inhibit reticulocyte Fe uptake to a greater extent than transferrin uptake (NaN3, NaF, NaCN, rotenone, oligomycin, 2,4-dinitrophenol and cycloheximide); and compounds which after reticulocyte heme synthesis (CoCl2, isonicotinic acid hydrazide and hemin) were used. In each case the effect on Fe incorporation and bicarbonate release was the sameThus, additional evidence has been obtained for the idea that the reticulocyte-mediated release of Fe and bicarbonate from transferrin are tightly coupled. The results are consistent with the hypothesis that an enzymatic attack on transferrin-bound bicarbonate is involved in the removal of Fe from transferrin by erythroid cells. 相似文献
125.
I. Gillot B. Ciapa P. Payan G. De Renzis G. Nicaise C. Sardet 《Histochemistry and cell biology》1989,92(6):523-529
Summary Freeze-substitution was used to study the distribution of calcium in sea urchin eggs, and the validity of the technique was assessed. We followed the fate of both total and exchangeable calcium of sea urchin eggs in two species (Paracentrotus lividus and Arbacia lixula) after the various treatments needed for freeze-substitution and embedding. We compared the calcium content either by X-ray microanalysis of Epon-embedded sections of freeze-substituted eggs (6.2±0.71 mmoles/kg of Epon-embedded tissue) or by flame spectrometry analysis of living eggs (32.3±1.30 nmoles/mg protein). After standardization of units, both values lead to similar total calcium content. We also measured the movements of 45Ca from prelabelled eggs. Exchangeable 45Ca as well as total calcium appeared unaffected by the preparative treatment for X-ray microanalysis. In conclusion, our preparative technique for X-ray microanalysis can be considered appropriate for our material and allows us to undertake a subcellular quantification of calcium in various organelles. 相似文献
126.
Resistance to arsenic salts in aPseudomonas aeruginosa clinical isolate was shown to be determined by a 100 kb transferable plasmid. The resistance pattern included arsenate, arsenite, and antimonate ions. Arsenate and arsenite resistances were inducible by previous exposure of cultures to subinhibitory amounts of either of the two ions. Phosphate ions protectedP. aeruginosa cells from the toxic effects of arsenate but did not alter arsenite toxicity. 相似文献
127.
Sedimentation loss of phytoplankton cells from the mixed layer: effects of turbulence levels 总被引:2,自引:0,他引:2
In this paper, we describe a study of the role of turbulencein the loss by sedimentation of phytoplankton cells from themixed layer. The approach presented allows the quantificationof the sedimentation rate of phytoplankton in the whole rangeof turbulence levels of this layer. Two types of phytoplanktercan be distinguished according to the effect that turbulencecan exert on their sedimentation rate. The rate of those cellswhose settling velocity is lower than 1 m day1will not be modified by turbulence. The sedimentation rate ofcells with higher settling velocities can, however, be modifiedby the level of turbulence. A set of dimensionless numbers isgiven to delimit several processes that are important in thedynamics of phytoplankton sedimentation in a turbulent regime.The use of these dimensionless numbers suggests that an increasein the turbulence level in the mixed layer does not always implya decrease in the sedimentation rate of phytoplankton cells. 相似文献
128.
Summary Peptides labelled with the fluorophore cyanine 3 were used to study naturally expressed neuropeptide receptors by confocal
microscopy in continuous cell lines, primary cultures, and unfixed tissue. Swiss 3T3 fibroblasts bound cyanine 3-gastrin-releasing
peptide at 4°C, and internalized the peptide after 10 min at 37°C. Internalization was specific, since it was blocked by incubation
with unlabelled peptide. Primary cultures of myenteric neurons of the guinea pig incubated with cyanine 3-substance P at 4°C
had specific surface labelling. After 30 s at 37°C, the peptide was internalized into vesicles in both the soma and neurites.
Direct observation of live neurons showed movement of fluorescent vesicles to a perinuclear region after 30 min. Endocytosis
was associated with a loss of surface binding sites. Unfixed whole mounts of guinea pig and rat ileum were incubated with
cyanine 3-neurokinin A at 4°C. After 5 min at 37°C, Cy3-neurokinin A was specifically internalized in neurons and smooth muscle
cells. After 30 min, a perinuclear labelling occurred in some cells. Labelling in rat neurons was diminished by the NK3-R
antagonist SR142801. Thus, cyanine 3-neuropeptides are valuable tools to study expression and endocytosis of naturally expressed
receptors. 相似文献
129.
Delineation of the endocytic pathway of substance P and its seven-transmembrane domain NK1 receptor. 总被引:6,自引:1,他引:5
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
E F Grady A M Garland P D Gamp M Lovett D G Payan N W Bunnett 《Molecular biology of the cell》1995,6(5):509-524
Many of the actions of the neuropeptide substance P (SP) that are mediated by the neurokinin 1 receptor (NK1-R) desensitize and resensitize, which may be associated with NK1-R endocytosis and recycling. We delineated this endocytic pathway in transfected cells by confocal microscopy using cyanine 3-SP and NK1-R antibodies. SP and the NK1-R were internalized into the same clathrin immunoreactive vesicles, and then sorted into different compartments. The NK1-R was colocalized with a marker of early endosomes, but not with markers of late endosomes or lysosomes. We quantified the NK1-R at the cell surface by incubating cells with an antibody to an extracellular epitope. After exposure to SP, there was a loss and subsequent recovery of surface NK1-R. The loss was prevented by hypertonic sucrose and potassium depletion, inhibitors of clathrin-mediated endocytosis. Recovery was independent of new protein synthesis because it was unaffected by cycloheximide. Recovery required endosomal acidification because it was prevented by an H(+)-ATPase inhibitor. The fate of internalized 125I-SP was examined by chromatography. SP was intact at the cell surface and in early endosomes, but slowly degraded in perinuclear vesicles. We conclude that SP induces clathrin-dependent internalization of the NK1-R. The SP/NK1-R complex dissociates in acidified endosomes. SP is degraded, whereas the NK1-R recycles to the cell surface. 相似文献
130.