全文获取类型
收费全文 | 2335篇 |
免费 | 259篇 |
专业分类
2594篇 |
出版年
2023年 | 6篇 |
2022年 | 20篇 |
2021年 | 34篇 |
2020年 | 26篇 |
2019年 | 35篇 |
2018年 | 44篇 |
2017年 | 49篇 |
2016年 | 75篇 |
2015年 | 101篇 |
2014年 | 105篇 |
2013年 | 122篇 |
2012年 | 127篇 |
2011年 | 142篇 |
2010年 | 100篇 |
2009年 | 79篇 |
2008年 | 116篇 |
2007年 | 111篇 |
2006年 | 105篇 |
2005年 | 127篇 |
2004年 | 101篇 |
2003年 | 95篇 |
2002年 | 96篇 |
2001年 | 77篇 |
2000年 | 71篇 |
1999年 | 71篇 |
1998年 | 40篇 |
1997年 | 29篇 |
1996年 | 25篇 |
1995年 | 26篇 |
1994年 | 16篇 |
1993年 | 17篇 |
1992年 | 40篇 |
1991年 | 32篇 |
1990年 | 39篇 |
1989年 | 39篇 |
1988年 | 40篇 |
1987年 | 24篇 |
1986年 | 29篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1971年 | 8篇 |
排序方式: 共有2594条查询结果,搜索用时 0 毫秒
981.
Phospholipid composition and 32P metabolism were studied in oocytes and early developing embryos of the toad, Bufo arenarum, Hensel. The content and distribution of phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidic acid, sphingomyelin, phosphatidylserine, and diphosphatidylglycerol in embryos, whole oocytes, and the subcellular fractions of both were determined. Phosphatidylcholine and phosphatidylethanolamine were the major constituents of yolk platelet. Diphosphatidylglycerol was confined to the mitochondrial fraction, where it represented about 7% of the total phosphoacylglycerols. Relatively large amounts of sphingomyelin were found in microsomal and postmicrosomal supernatants. After in vivo labeling with 32P, the early development of individual phospholipids in subcellular fractions and in whole eggs was followed. The greatest uptake was found in mitochondrial and yolk platelet fractions. A steady increase in the amount of 32P present in phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol was seen in the whole embryo from oocyte to late gastrula stage and in all subcellular fractions. Phosphatidic acid exhibited a slight decrease in specific activity, except in the yolk platelet fraction. This high 32P incorporation would indicate a rapid and uneven polar headgroup turnover determined by phospholipid class and subcellular fraction. At the same time, the phospholipid content of the subcellular fractions studied remained unchanged during early embryogenesis. Moreover, 32P was actively incorporated into the individual phospholipids in the absence of measurable net synthesis. 相似文献
982.
HeLa cells doubly infected with Semliki Forest virus (SFV) and poliovirus synthesize either more poliovirus proteins or more SFV late proteins depending on the time of super-infection with poliovirus. Under some conditions, the infected cells translate uncapped poliovirus mRNA and capped 26S mRNA from SFV simultaneously, even though host protein synthesis has been shut down. Vesicular stomatitis virus (VSV) protein synthesis is depressed drastically when VSV-infected cells are super-infected with poliovirus. In cells doubly infected with VSV and encephalomyocarditis (EMC) virus or with VSV and SFV, dominance of one of the viruses depends on the time of addition of the challenge virus. The influence of external conditions on the relative translation of capped or uncapped viral mRNA in doubly infected cells has also been analysed. 相似文献
983.
Ethionine-resistant mutants ofCandida utilis CCY-158 overproducing methionine have been isolated. In these mutants the intracellular methionine concentration decreased significantly during the stationary phase. The wild-type strain CCY-158 and the ethionine-resistant mutants isolated were able to use methionine as the nitrogen source but not as the carbon source. From these ethionine-resistant mutants we isolated mutants unable to use methionine as nitrogen source (Mec- mutants), the principal alteration being at the level of methionine uptake. Some of the Mec mutants lost also the ability to use other amino acids as nitrogen source. 相似文献
984.
Specific Detection of Arcobacter and Campylobacter Strains in Water and Sewage by PCR and Fluorescent In Situ Hybridization
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)
Yolanda Moreno Salut Botella Jos Luis Alonso María A. Ferrús Manuel Hernndez Javier Hernndez 《Applied microbiology》2003,69(2):1181-1186
The aim of this study was to evaluate PCR and fluorescent in situ hybridization (FISH) techniques for detecting Arcobacter and Campylobacter strains in river water and wastewater samples. Both 16S and 23S rRNA sequence data were used to design specific primers and oligonucleotide probes for PCR and FISH analyses, respectively. In order to assess the suitability of the methods, the assays were performed on naturally and artificially contaminated samples and compared with the isolation of cells on selective media. The detection range of PCR and FISH assays varied between 1 cell/ml (after enrichment) to 103 cells/ml (without enrichment). According to our results, both rRNA-based techniques have the potential to be used as quick and sensitive methods for detection of campylobacters in environmental samples. 相似文献
985.
Leeanne E. Alonso 《Biotropica》1998,30(2):201-213
Striking variation in ant occupation of a facultative ant-plant, Conostegia setosa (Melastomataceae), was found at three scales: local spatial, geographic, and temporal. C. setosa provides housing for ants and grows in groups of stems (clones). The ant occupants of 14 C. setosa clones were censused four times over a 14-mo period at the La Selva Biological Station, Costa Rica, and twice over a 9-mo period at the Nusagandi Station, Panama. Twelve facultative ant species occupied C. setosa stems at La Selva, compared to six facultative and one obligate species at Nusagandi. Occupancy (as % of stems ever occupied/clone) was higher at Nusagandi (median = 89%) compared to La Selva (65%). Occupancy varied among clones at La Selva but not at Nusagandi. C. setosa clones differed between sites, with larger clones and more small stems/clone at La Selva. Occupancy was influenced by clone structure; larger clones contained more ant species at both sites and had lower occupancy at La Selva. Occupancy was highest in larger stems and lowest in small stems at both sites. Temporally, percent occupation/clone did not differ among censuses at either site, but overall occupancy was lower in the dry season at La Selva. Turnover in ant occupants was higher at La Selva than at Nusagandi. The variation observed in this study is likely due to a number of factors, including differences between sites in plant population structure and history, differences between and within sites in ant faunas and their nesting requirements, and changes over space and time in microclimatic variables. Such high variation at multiple scales draws attention to the importance of long-term comparative studies of facultative animal-plant interactions. 相似文献
986.
Elizabeth Laran José Maria Requena Antonio Jimenez-Ruiz Manuel Carlos Lopez Carlos Alonso 《Chromosoma》1990,99(5):315-320
Multiple interactions of members of the hsp70 family with cellular components have already been described. We present, however, the first evidence that upon heat shock treatment hsp70 molecules interact with specific chromosomal subdivisions of the polytene chromosomes ofDrosophila hydei. After a heat shock treatment of 20 min the protein binds to subdivision 3-58D1 and to the heat shock inducible subdivisions 2-48B3–6 and 2-48C1–2. Hsp70 molecules were also observed in subdivision 3-58D1 during recovery at 25°C but not in subdivisions 2-48B3–6 and 2-48C1–2. Our data suggest that this interaction is stress specific. DNase and RNase experiments suggest, moreover, that the hsp70 molecules bind to RNA from ribonucleoproteins (RNPs) in subdivisions 2-48B3–6 and 2-48C1–2 and to DNA in subdivision 3-58D1. The DNA sequences in subdivision 3-58D1 seem to have the potential to adopt the Z-DNA conformation. 相似文献
987.
A study of Trypanosomatidae GC distribution and codon usage is presented. The codon usage patterns in coincidence with the phylogenetical data are similar in Crithidia and Leishmania, whereas they are more divergent in Trypanosoma brucei and T. cruzi. The analysis of the GC mutational pressure in these organisms reveals that T. brucei, and to a lesser extent T. cruzi, have evolved towards a more balanced use of all bases, whereas Leishmania and Crithidia retain features of a primeval genetic apparatus. Tables with the approximated GC mutational pressure in homologous genes, and codon usage in Trypanosomatidae are presented. 相似文献
988.
989.
J. R. Castro P. L. Petti I. K. Daftari J. M. Collier T. Renner B. Ludewigt W. Chu S. Pitluck T. Fleming J. Alonso E. Blakely 《Radiation and environmental biophysics》1992,31(3):233-240
Summary The feasibility of dynamic conformal heavy charged particle radiotherapy has been investigated at UCLBL, and shows high promise of: 1. an improved therapeutic ratio and 2. reduction in the number of treatment portals required for efficient treatment delivery. Assessment of dose to tumor and critical structures for several anatomical sites have been carried out using a normal tissue complication algorithm developed at LBL. For high-LET charged particle treatment delivery, dynamic conformal therapy using a raster scanned beam with variable modulation and multileaf collimator appears to be the optimal technique for treatment delivery.Paper given on the fourth workshop on Heavy Charged Particles in Biology and Medicine GSI, Darmstadt, FRG, September 23–25,1991. Supported in part by NIH-NCI Grant CA19138 and DOE Contract DE-AC03-76SF00098 相似文献
990.
C. Alonso 《Entomologia Experimentalis et Applicata》1971,14(1):73-82
The injection of gibberellic acid (GA3) into larvae of Drosophila hydei can affect the pattern of gene activities in a specific manner. This became clear from a study on the pattern of puffs in the giant chromosomes of the larval salivary glands.Depending upon the age of the larvae injected, either of two new puffs, 72B or 21B, appeared. Not only was the activity of these chromosome regions stimulated but the activity of some normally occurring puffs specific for the period shortly before puparium formation was affected. If GA3 was injected during the period shortly before puparium formation further development became influenced as revealed by a significant reduction in the number of flies emerging from treated animals.
Zusammenfassung Es wurde die Wirkung verschiedener Konzentrationen von Gibberellinsäure (GA3) nach Injektion in Drosophila-Larven unterschiedlichen Alters untersucht. Konzentrationen von 3 g/Larve und höher führten bei jungen und mittleren Larven des 3. Stadiums zur Ausbildung eines neuen Puffs (72B) in den polytänen Chromosomen der Speicheldrüse. Diese Reaktion wurde in 15–20% der Larven beobachtet.In späteren Stadien der Entwicklung kurz vor der Pupariumbildung wird nach Injektion von 1 g/Larve ein weiterer Puff (21B) in 10% der Larven induziert. Der Prozentsatz der Larven die diesen Puff 3 Stunden nach der Injektion aufweisen, nimmt mit steigender GA3-Konzentration zu. Nach Injektion von 5–6 g/Larve war der Puff 21B in 80% der Tiere enthalten.Zur selben Zeit ließ sich eine Beinflussing der Aktivität von zwei Puffs nachweisen, die für die Periode der Pupariumbildung spezifisch sind. Die Aktivität dieser Puffs wird durch die Injektion von GA3 herabgesetzt.GA3 bewirkt nicht nur die Induktion neuer Puffs, sondern außerdem eine Verzögerung der Entwicklung. Nach der Injektion von 2 g/Larve verzögert sich die Zeit der Pupariumbildung um 2–10 Stunden. Die Zahl der Fliegen, die aus Larven schlüpfte, die kurz vor der Pupariumbildung eine Injektion von mehr als 3 g GA3 erhielten, war deutlich herabgesetzt. Es wird vermutet, daß GA3 eine spezifische Wirkung auf die Aktivität des Genoms ausübt und damit eine Beeinflussung der normalen Entwicklung bewirkt.相似文献