全文获取类型
收费全文 | 21147篇 |
免费 | 1850篇 |
国内免费 | 5篇 |
专业分类
23002篇 |
出版年
2023年 | 89篇 |
2022年 | 239篇 |
2021年 | 442篇 |
2020年 | 237篇 |
2019年 | 319篇 |
2018年 | 433篇 |
2017年 | 370篇 |
2016年 | 657篇 |
2015年 | 1054篇 |
2014年 | 1209篇 |
2013年 | 1454篇 |
2012年 | 1807篇 |
2011年 | 1699篇 |
2010年 | 1100篇 |
2009年 | 959篇 |
2008年 | 1296篇 |
2007年 | 1332篇 |
2006年 | 1147篇 |
2005年 | 1091篇 |
2004年 | 1070篇 |
2003年 | 979篇 |
2002年 | 932篇 |
2001年 | 237篇 |
2000年 | 189篇 |
1999年 | 183篇 |
1998年 | 248篇 |
1997年 | 172篇 |
1996年 | 147篇 |
1995年 | 139篇 |
1994年 | 127篇 |
1993年 | 116篇 |
1992年 | 103篇 |
1991年 | 97篇 |
1990年 | 102篇 |
1989年 | 71篇 |
1988年 | 65篇 |
1987年 | 73篇 |
1986年 | 61篇 |
1985年 | 59篇 |
1984年 | 63篇 |
1983年 | 75篇 |
1982年 | 51篇 |
1981年 | 43篇 |
1980年 | 52篇 |
1979年 | 43篇 |
1978年 | 61篇 |
1977年 | 46篇 |
1976年 | 44篇 |
1974年 | 52篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
101.
The predominant spoilage fungi of dried and high-moisture prunes were members of the Aspergillus glaucus group and Xeromyces bisporus. Chrysosporium spp. were also important. At the mean pH of prune flesh (3.8) and at 25 C, X. bisporus grew at water activities (aw) down to 0.605, and Chrysosporium fastidium grew to 0.686. Germination was always followed by growth, but within the 120-day incubation period, the minimum aw permitting asexual sporulation was usually higher than that permitting germination. Sexual sporulation often required an even higher aw. The water requirements of aspergilli were appreciably greater at this pH than near neutrality, no species germinating below 0.738 aw. This was probably a consequence of a high spore-death rate during incubation at low aw and pH. 相似文献
102.
Peter Hirsch 《Archives of microbiology》1968,60(3):201-216
Summary Budding bacteria from aquatic or terrestrial habitats were found to accumulate ferric oxide hydrate (ferric hydroxide) on their cell surfaces. Metal paper clips served as the source of oxidizable iron. Pure cultures deposited ferric hydroxide during growth on sea water medium at a pH of 7.8, but not in a mineral salts medium of normal ionic strength, of pH 7.2, and without NaCl, although some active strains came from fresh water or soil.Ferric iron deposition was found to be initiated at primary active sites on the cell surface; the hyphae and rods eventually become completely encased by the heavy coat.The presence of iron depositing, budding bacteria in fresh water, brackish water or sea water indicates an ubiquitous distribution of these microorganisms.Actively depositing isolates from marine environments are more closely related to Pedomicrobium than to Hyphomicrobium spp. because of their multiple formation of hyphae from rod-shaped swarmer cells. A taxonomic and cultural study of these new forms is in progress. 相似文献
103.
Summary The locomotory turns of the beetle Tenebrio molitor were recorded from free walking animals which were held in stationary position and orientation by means of a tread compensator. Striped patterns revolved around an animal elicit optomotor responses which undergo an inversion at smaller stripe widths. The position of the inversion point characterizes the resolving power of the motion detectors, and corresponds to a 6.5° average angle between the optical axes of interacting elements in the motion detecting device. This indirectly determined value is consistent with the anatomically measured 7° average angle between the axes of neighbouring ommatidia in the Tenebrio compound eye. 相似文献
104.
105.
Summary Since viable intergeneric hybrids between the chicken (Gallus domesticus) and the pheasant (Phasianus colchicus) have been reported, as well as interfamilial hybrids between the chicken and the turkey (Meleagris gallopavo), the chromosome complements of the pheasant and the turkey were compared with that of the chicken. In these three species belonging to the order Galli, the Z-chromosomes appeared to be identical, while the autosomal complements of the pheasant and the turkey differed radically from that of the chicken. It was noted with some surprise that the pheasant of the family Phasianidae and the turkey of the family Meleagridae have very similar chromosome complements, at least so far as gross morphology of somatic metaphase chromosomes is concerned.This work was supported in part by grant C-5138 from the National Cancer Institute, U.S. Public Health Service, and grant C-17601 from the National Science Foundation.The authors gratefully acknowledge the generosity of Rea's Game Birds, Paramount, California, who supplied the pheasant chicks, and the McPherin Hatcheries, Sunnymead, California, who furnished the turkey chicks. The authors also appreciate the editorial assistance of'Patricia A. Ray. 相似文献
106.
Christian Stenseth 《Entomologia Experimentalis et Applicata》1965,8(1):33-38
Summary The effect of temperatures below 0° C on different stages of the two-spotted spider mite, and in particular on active adult females, has been investigated.Survival of active females at-5° was higher at approximately 100% relative humidity than at a lower degree of humidity. Higher rates of survival were also caused by acclimation of active females and larvae for one day at +5° before storage at-15°. No differences in cold-hardiness were found in active females from an organophosphorous resistant strain and a susceptible strain, and the ability to survive depended on the time-temperature exposures (see Fig. 3).Eggs were killed very rapidly at-15° C, while larvae survived longer exposures than active females. Compared at the LT50 level females in diapause survived three times the exposure endured by acclimated active females.Supercooling points measured at a rate of cooling of 2° C per minute were highest in diapausing females and lowest in eggs. Acclimation had no effect on the supercooling points of active females. All stages were killed by freezing. It seems likely that the difference in survival between acclimated and not acclimated active females at-15° is caused by different ability to live in a supercooled state.
Zusammenfassung Es wurde die Wirkung von Temperaturen unter 0° auf verschiedene Stadien der Bohnenspinnmilbe, insbesondere auf aktive erwachsene Weibchen untersucht.Die Überlebensrate aktiver Weibchen war bei nahezu hundertprozentiger relativer Luftfeuchtigkeit höher als bei niederer Feuchtigkeit. Höhere Überlebensraten wurden auch durch Akklimatisation aktiver Weibchen und Larven für einen Tag bei 5° vor der Behandlung mit-15° erreicht. Es wurden keine Unterschiede in der Kältewiderstandfähigkeit aktiver Weibchen eines phosphorsäureesterresistenten und eines anfälligen Stammes gefunden. Die Überlebensfähigkeit hängt von Dauer und Temperatur der Einwirkung ab.Eier wurden von-15° sehr schnell abgetötet, während Larven längere Einwirkungszeiten überlebten als aktive Weibchen. Bei einem Vergleich der LT50 überlebten diapausierende Weibchen dreimal längere Einwirkungszeiten, als sie von akklimatisierten aktiven Weibchen ertragen wurden.Unterkühlungspunkte—gemessen bei einer Abkühlungsrate von 2° pro Minute—lagen bei diapausierenden Weibchen am höchsten und bei Eiern am niedrigsten.Akklimatisierung hatte keinen Einfluß auf die Unterkühlungspunkte aktiver Weibchen. Durch Gefrieren wurden alle Stadien getötet. Es erscheint möglich, daß der Unterschied im Überleben akklimatisierter und nichtakklimatisierter Weibchen bei-15° durch die verschiedene Fähigkeit bedingt ist, in einem unterkühlten Zustande zu leben.相似文献
107.
108.
A preliminary electron microscope study of human neuromuscular junction is presented. The biopsy material was taken from the palmarus longus, and fixed routinely in osmium tetroxide and embedded in methacrylate. The structure of the motor endings and the relationship of the synaptic vesicles to the axolemmal membrane are described. The synaptic clefts are filled with an homogeneous material in continuity with the basement membrane covering the muscle fiber. The subneural apparatus is described, and special attention is paid to a vesicular component present in the sarcoplasm of the junctional area, which differs from synaptic vesicles and is presumed to be a derivate of the sarcoplasmic reticulum. 相似文献
109.
Christian Berg Hans Dieter Knapp Ulrich Messner Wolfgang Wiehle 《Folia Geobotanica》1989,24(3):297-304
(Bellevalia ciliata was recorded in north-east Bulgaria south of the Dobrudsha, within field and steppe vegetation. Vegetation records and a distribution map are presented. Based on taxonomic studies it is proposed to combineB. ciliata, B. sarmatica (Pall.) Wor. andB. speciosa Wor. under the oldest nameB. ciliata (Cyr.) Nees. 相似文献
110.
Robert Y. Kanterman Christian C. Felder Douglas E. Brenneman Alice L. Ma Sandra Fitzgerald Julius Axelrod 《Journal of neurochemistry》1990,54(4):1225-1232
The alpha 1-adrenergic receptor has been shown to mediate the release of arachidonic acid in FRTL5 thyroid cells and MDCK kidney cells. In primary cultures of spinal cord cells, norepinephrine stimulated release of arachidonic acid (from neurons only) and turnover of inositol phospholipids (from neurons and glia) via alpha 1-adrenergic receptors. These two responses were dissociated by treatment with phorbol ester and pertussis toxin, which inhibited production of inositol phosphates with no appreciable effect on release of arachidonic acid. Extracellular calcium was required for release of arachidonic acid, but not for production of inositol phosphates. The calcium channel blockers nifedipine and verapamil inhibited release of arachidonic acid only. However, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), a compound that blocks intracellular calcium release, diminished production of inositol phosphates, but had little effect on release of arachidonic acid. These results suggest that alpha 1-adrenergic receptors couple to release of arachidonic acid in primary cultures of spinal cord cells by a mechanism independent of activation of phospholipase C, possibly via the activation of phospholipase A2. 相似文献