全文获取类型
收费全文 | 2384篇 |
免费 | 160篇 |
国内免费 | 2篇 |
专业分类
2546篇 |
出版年
2023年 | 11篇 |
2022年 | 23篇 |
2021年 | 48篇 |
2020年 | 26篇 |
2019年 | 43篇 |
2018年 | 47篇 |
2017年 | 41篇 |
2016年 | 72篇 |
2015年 | 100篇 |
2014年 | 111篇 |
2013年 | 146篇 |
2012年 | 181篇 |
2011年 | 170篇 |
2010年 | 102篇 |
2009年 | 105篇 |
2008年 | 145篇 |
2007年 | 132篇 |
2006年 | 127篇 |
2005年 | 113篇 |
2004年 | 128篇 |
2003年 | 110篇 |
2002年 | 105篇 |
2001年 | 29篇 |
2000年 | 21篇 |
1999年 | 27篇 |
1998年 | 14篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 24篇 |
1991年 | 8篇 |
1990年 | 25篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1986年 | 17篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 14篇 |
1977年 | 10篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1972年 | 8篇 |
1971年 | 7篇 |
排序方式: 共有2546条查询结果,搜索用时 0 毫秒
21.
Summary The neuro-endocrine cells of fish skin and respiratory surfaces, and their bioactive secretion as far as is known, are reviewed, and compared with similar elements in tetrapods, particularly amphibians. In the skin of teleost fish, immunohistochemistry has shown that Merkel cells react for serotonin, neuron-specific enolase and enkephalins. The pharmacology is not established in dipnoans or lampreys. In some teleosts, neuromasts react for substance P and leu-enkephalins; substance P is also reported from some ampullary organs (electroreceptors). Taste buds of teleosts may react for enkephalin and substance P. Basal cells of taste buds react for serotonin and neuron-specific enolase. Some unicellular skin glands of teleosts express bioactive compounds, including serotonin and some peptides; this ectopic expression is paralleled in amphibian skin glands. The dipnoan Protopterus has innervated pulmonary neuro-endocrine cells in the pneumatic duct region with dense-cored vesicles. In Polypterus and Amia the lungs have serotonin-positive neuro-endocrine cells that are apparently not innervated. In fish gills, a closed type of neuro-endocrine cell reacts for serotonin, an open type for enkephalins and some calcium-binding proteins (calbindin, calmodulin and S-100 protein). The functions of neuro-endocrine cells in fishes await investigation, but it is assumed they are regulatory. 相似文献
22.
At altitudes between 1300 m to 2100 m in the Etna massif (Sicily), an endemic species of theBetula genus,Betula aetnensis Rafin, grows in a well-defined microclimatical context. Aboveground biomass and nutrient content studies within one stand revealed no significant differences from the otherBetula species, normally found in colder more temperate climate regions.Throughout the studied sites, biomass production, nutrient cycling and various structural or physiological characteristics (leaf area index) varied very little.Other researches indicate that the originality ofBetula aetnensis lies more in the histological or anatomical characteristics of its water conducting system which enables the species to adapt to Mediterranean-climate summer droughts in the Etna massif.
Riassunto Sull'Etna, tra 1300 e 2100 m d'altitudine, in una zona microclimaticamente ben definita del versante nordorientale, si rinviene laBetula aetnensis Rafin.Dallo studio della fitomassa e della mineralomassa aerea del bosco di Monte Baracca, è emerso che non vi sono differenze notevoli con le altre specie indagate del genereBetula, più caratteristiche dei climi temperati e freddi.La produzione di biomassa, cosi come la gestione degli elementi nutritivi, è molto simile ai diversi popolamenti già indagati, cosi come certe caratteistiche strutturali e fisiologiche (leaf area index).L'originalità dellaBetula aetnensis è da ricercarsi nel vantaggio che ne ricava, a livello endogeno, sfruttando le caratteristiche istologiche ed anatomiche del suo apparato conduttore, che le consentono un efficace ed eccellente adattamento alle condizioni di siccità estive particolari del clima mediterraneo del vulcano.相似文献
23.
Enterocin 226NWC, a bacteriocin produced by Enterococcus faecalis 226, active against Listeria monocytogenes 总被引:2,自引:0,他引:2
F. Villani G. Salzano Elena Sorrentino Olimpia Pepe P. Marino S. Coppola 《Journal of applied microbiology》1993,74(4):380-387
F. VILLANI, G. SALZANO, E. SORRENTINO, O. PEPE, P. MARINO AND S. COPPOLA. 1993. Enterococcus faecalis 226, isolated from natural whey cultures utilized as starters in the manufacture of mozzarella cheese from water-buffalo milk, produces a bacteriocin designated enterocin 226NWC. The bacteriocin was isolated from culture supernatant fluids of the producer strain and was active against strains of the same species and Listeria monocytogenes, but not against useful lactic acid bacteria. Enterocin 226NWC is a protein with an apparent molecular weight of about 5800; it is relatively heat-stable and has a bactericidal mode of action. Listeria monocytogenes, growing in the presence of the enterocin 226NWC producer strain in broth and in reconstituted skim milk, was inhibited. 相似文献
24.
Fiorito Serena Collevecchio Chiara Epifano Francesco Genovese Salvatore Palumbo Lucia 《Phytochemistry Reviews》2023,22(1):73-84
Phytochemistry Reviews - Oxyprenylated secondary metabolites of plant, fungal, and microbial origin have emerged as biologically active natural compounds with a great potential for the next future.... 相似文献
25.
Pietro Cugini Loredana Di Palma Salvatore Di Simone Piernatale Lucia Paola Battisti Alessandro Coppola Giuseppe Leone 《Chronobiology international》1993,10(1):73-78
This study aimed to explore the 24-h patterns of stroke volume, cardiac output, and peripheral vascular resistance along with other correlated variables, such as left ventricular ejection time, ejection velocity index, thoracic fluid index, heart rate, and blood pressure. The study was performed on 12 clinically healthy subjects by means of a noninvasive beat-to-beat monitoring using the thoracic electric bioimpedance technique associated with the automated sphygmomano-metric recording. Time data series were analyzed by means of chronobiological procedures. The results documented the occurrence of a circadian rhythm for all the variables investigated, giving relevance to the beat-to-beat bioperiodicity of cardiac output and peripheral vascular resistance. Temporal quantification of the investigated variables may be useful for a better insight of the chronophysiology of the cardiovascular apparatus. 相似文献
26.
Arpana Agrawal Sarah J. Brislin Kathleen K. Bucholz Danielle Dick Ronald P. Hart Emma C. Johnson Jacquelyn Meyers Jessica Salvatore Paul Slesinger COGA Collaborators Laura Almasy Tatiana Foroud Alison Goate Victor Hesselbrock John Kramer Samuel Kuperman Alison K. Merikangas John I. Nurnberger Jay Tischfield Howard J. Edenberg Bernice Porjesz 《Genes, Brain & Behavior》2023,22(5):e12864
27.
Antibody staining was observed in the electron microscope by means of untagged antibody and osmium fixation. The antibody was visualized as a change in morphology due to its deposition on the antigenic structures. Glycerinated chicken breast muscle was stained with antimyosin, anti-H-meromyosin, and antiactin. The staining patterns obtained by electron microscopy were consistent with those previously demonstrated by fluorescence microscopy. A second method was used for confirmation of antibody staining. This consisted of extraction of unstained portions of the sarcomere with 0.6 M potassium iodide, 10-4 M adenosine triphosphate solution. Stained regions of the sarcomere remained intact because of insolubility of the combined antigen and antibody. 相似文献
28.
Aeromonas hydrophila secretes several extracellular proteins that are associated with virulence including an enterotoxin, a protease, and the hole-forming toxin, aerolysin. These degradative enzymes and toxins are exported by a conserved pathway found in many Gram-negative bacteria. In Pseudomonas aeruginosa this export pathway and type IV pilus biogenesis are dependent on the product of the pilD gene. PilD is a bifunctional enzyme that processes components of the extracellular secretory pathway as well as a type IV prepilin. An A. hydrophila genomic library was transferred into a P. aeruginosa pilD mutant that is defective for type IV pilus biogenesis. The A. hydrophila pilD homologue, tapD , was identified by its ability to complement the pilD mutation in P. aeruginosa . Transconjugants containing tapD were sensitive to the type IV pilus-specific phage, PO4. Sequence data revealed that tapD is part of a cluster of genes ( tapABCD ) that are homologous to P. aeruginosa type IV pilus biogenesis genes ( pilABCD ). We showed that TapB and TapC are functionally homologous to P. aeruginosa PilB and PilC, the first such functional complementation of pilus assembly demonstrated between bacteria that express type IV pili. In vitro studies revealed that TapD has both endopeptidase and N -methyltransferase activities using P. aeruginosa prepilin as substrate. Furthermore, we show that tapD is required for extracellular secretion of aerolysin and protease, indicating that tapD may play an important role in the virulence of A. hydrophila 相似文献
29.
Two-dimensional close packing of purified bovine rhodopsin, made by the Langmuir-Blodgett technique, was characterized by small angle x-ray scattering and nanogravimetric measurements. The area occupied by a molecule of rhodopsin in the film was approximately 1100 Angstrum2 and the periodicity of the layers resulted in 59 Angstrum. The circular dichroism measurements showed that bleached rhodopsin in Langmuir-Blodgett film had high thermal stability, in fact, reaching a temperature of 150 degrees C without a loss of the secondary structure. Moreover, when the film was made up in the dark, rhodopsin maintained its stability up to at least 200 degrees C and its characteristic absorbance peak at 500 nm up to about 90 degrees C. 相似文献
30.
Lipophosphoglycan (LPG) is the predominant surface glycoconjugateof Leishmania promastigotes and consists of a capped polymerof Gal(ß1,4)Man( 相似文献