全文获取类型
收费全文 | 7280篇 |
免费 | 586篇 |
国内免费 | 29篇 |
专业分类
7895篇 |
出版年
2022年 | 67篇 |
2021年 | 92篇 |
2020年 | 79篇 |
2019年 | 59篇 |
2018年 | 132篇 |
2017年 | 120篇 |
2016年 | 181篇 |
2015年 | 298篇 |
2014年 | 330篇 |
2013年 | 399篇 |
2012年 | 520篇 |
2011年 | 507篇 |
2010年 | 350篇 |
2009年 | 277篇 |
2008年 | 420篇 |
2007年 | 365篇 |
2006年 | 332篇 |
2005年 | 330篇 |
2004年 | 330篇 |
2003年 | 296篇 |
2002年 | 313篇 |
2001年 | 145篇 |
2000年 | 146篇 |
1999年 | 116篇 |
1998年 | 64篇 |
1997年 | 60篇 |
1996年 | 74篇 |
1995年 | 46篇 |
1994年 | 47篇 |
1993年 | 48篇 |
1992年 | 74篇 |
1991年 | 89篇 |
1990年 | 75篇 |
1989年 | 56篇 |
1988年 | 44篇 |
1987年 | 49篇 |
1986年 | 58篇 |
1985年 | 40篇 |
1984年 | 36篇 |
1982年 | 37篇 |
1981年 | 47篇 |
1980年 | 35篇 |
1979年 | 45篇 |
1978年 | 35篇 |
1977年 | 36篇 |
1975年 | 45篇 |
1973年 | 35篇 |
1972年 | 33篇 |
1971年 | 42篇 |
1968年 | 34篇 |
排序方式: 共有7895条查询结果,搜索用时 33 毫秒
21.
Harald Witte 《Zoomorphology》1978,91(2):157-189
Zusammenfassung Das Gnathosoma von sieben Arten der Milbenfamilie Erythraeidae wurde untersucht. Die postembryonale Entwicklung der Cuticula-Strukturen, der Muskulatur und der Drüsen wird beschrieben.Das Gnathosoma der Larven weist Cheliceren auf, die aus Grundglied und klauenförmigem Digitus mobilis bestehen. Sie liegen dem Infracapitulum dorsal auf und inserieren an einem Paar Capitular-Apophysen. Bei den Protound Tritonymphen unterliegt das Gnathosoma der Histolyse und wird anschließend jeweils neu ausgebildet. Bei der Deutonymphe und beim Adultus ist es gegenüber der Larve stark abgewandelt: Die Tracheenstämme sind aus den Capitular-Apophysen der Larve abzuleiten. Die Stech-Cheliceren entsprechen dem Grundglied der larvalen Cheliceren, und ihre medialen Protraktoren gehen aus den Levator-Muskeln der Cheliceren der Larve hervor.Der Weg der Sekrete der podocephalischen und infracapitulären Drüsen über die Dorsalfläche des Infracapitulum erfährt mit dem Erwerb schmaler Stech-Cheliceren eine radikale Umstellung des Schutzes gegen Austrocknung. Während bei der Larve die breiten Cheliceren-Grundglieder den Sekretweg überdecken, und der Raum zwischen den Grundgliedern und dem Infracapi-tulum zusätzlich durch das ölartige Sekret der Intercheliceraldrüse ausgefüllt wird, schließen sich bei der Deutonymphe und beim Adultus die Lateralkiele der Genae über den Stech-Cheliceren zusammen, und der hintere Abschnitt des Cervix wird in das Idiosoma eingesenkt. Dadurch wird der Cervix zu einem internen Cervicalkanal umgebildet.Der Mundraum wird bei den aktiven Stadien durch die lipidartigen Sekrete der Buccal- und Labialdrüsen geschützt.Die phylogenetischen Beziehungen der Parasitengona innerhalb der Prostigmata und der Erythraeidae innerhalb der Parasitengona werden diskutiert.
Postembryonic development and functional anatomy of the gnathosoma in the family Erythraeidae (Acarina, Prostigmata)
Summary The gnathosoma of seven species of the Erythraeidae was investigated. The postembryonic development of the cuticular structures, the musculature and the glands are described.In the larval gnathosoma, the chelicerae consist of a basal segment and a claw. They rest upon the dorsal surface of the infracapitulum. The basal segments are attached to a pair of capitular apophyses (sigmoid pieces). During the two molts larva to protonymph and deutonymph to tritonymph, the gnathosoma is histolysed. Directly afterwards it is rebuilt. Compared to the larva, in the deutonymph and in the adult it undergoes profound changes: The capitular apophyses are transformed to parts of the tracheae, the basal segment of each chelicera to a styliform chelicera, and the levator muscles of the chelicerae to medial protractors of the styliform chelicerae.The secretions of the podocephalic and infracapitular glands proceed along the dorsal surface of the infracapitulum to the buccal cavity. In the larva, the way of the secretions is protected against desiccation by the broad basal segments of the chelicerae, that cover the infracapitulum. In addition the oily secretion of the intercheliceral gland seals the space between the infracapitulum and the chelicerae. By obtaining styliform chelicerae the protection against desiccation undergoes a radical change: The lateral ridges of the infracapitulum join above the chelicerae, and the posterior part of the cervix is transferred back into the idiosoma. Thus the cervix is transformed into an internal canal.In the active instars, the buccal cavity is protected by the lipid-like secretions of the buccal glands and labial glands.The phylogenetic relationships of the Parasitengona within the Prostigmata, and of the Erythraeidae within the Parasitengona are discussed.相似文献
22.
A new diol glucoside, 2-β-d-glucopyranosyloxy-2-methylpropanol, the first reported naturally occurring monoglucoside of an aliphatic dihydric alcohol, was isolated from pods of Acacia sieberana var. woodii. Structure elucidation was based on 1 H and 13C NMR spectroscopy, and enzymatic analyses. The compound was hydrolysed very slowly by almond β-glucosidase, but cleaved by a β-glucuronidase enzyme complex from Helix pomatia. 相似文献
23.
The transport system for organic acids in the kidney is not fully developed in the neonatal period. The effect of repeated administrations of ethacrynic acid on the renal excretion of p-aminohippurate (PAH) was studied in rats of different ages. Pretreatment with ethacrynic acid was followed by an increase in the renal excretion of PAH in 33-, 55-, 105- and 240-day-old rats but not in newborn rats. In 55-day-old rats the increase in renal excretion of PAH after pretreatment with ethacrynic acid was not associated with any consistent change of the glomerular filtration rate. It is concluded from these results that the stimulation of transport processes in the kidney by ethacrynic acid and some other drugs is linked with their affinity to tissue proteins. 相似文献
24.
R S Dreizin V Strizová T I Ponomareva L Syr?cek E M Vikhnovich N M Borovkova G V Geine E V Klimanskaya M Br?cková L Kuncová V Berkovicová 《Journal of hygiene, epidemiology, microbiology, and immunology》1979,23(2):174-185
Virological, serological and immunofluorescence studies revealed circulation of rhinoviruses of the strains 1A, 1B, 2, 3, 7, 9, 10, 12, 13, 14, 16-23, 27, 29-33, 42, 48, 53, 56, 60 and 69 on the territory of Czechoslovakia and the Soviet Union. According to virological results, type 48 predominated and was followed in frequency of occurrence by types 27, 14 and 16 in the USSR and 30, 1A and 31 in the CSSR. RV infection in adults with ARD diseases was the aetiology in 28.5% of cases. Among the causative agents of acute rhinitis, rhinosinusitis and otitis, rhinovirus infection makes up a large proportion. Interrelation has been found between rhinovirus infection and chronic inflammation of the mucosa of the nose, the accessory sinuses and the ears. Prolonged course of rhinovirus infection and isolation of the virus in the late stages of disease (1-4 months after its onset) support the presumption that rhinoviruses promote chronicity of inflammation. RV was isolated from patients with chronic pneumonia from the lower respiratory passages (bronchial secretion). Rhinoviraemia was found in a child who died of ARD. 相似文献
25.
P. Brönnimann 《Pal?ontologische Zeitschrift》1977,51(1-2):94-101
Favreina tabasensis n. sp., a Crustacean (Decapoda) coprolite with numerous longitudinal canals is described from the Upper Jurassic of the Tabas area, east-central Iran. The same favreine form-species is also recorded and figured from the Neocomian of the Dinarids, Bata, Montenegro, Jugoslavia. Further, a lectotype is proposed forFavreina prusensis (Paréjas) from the Upper Portlandian of the region of Lake Apolyont, Turkey.Favreina montana Elliott from the Albian Qamchuqa formation, Gund-i-Shikavt, Erbil Liwa, northern Iraq, is considered as a nomen dubium non conservandum. 相似文献
26.
Retinoic acid modulates gap junctional permeability: a comparative study of dye spreading and ionic coupling in cultured cells 总被引:1,自引:0,他引:1
All-trans retinoic acid (RA), which was recently identified as a morphogen, affects gap junctional permeability in a dose- and time-dependent manner. In five different established mammalian cell lines (FL, BRL, BICR/M1Rk, HEL37, BT5C1) 100 mumol/liter RA reduced Lucifer yellow spreading within 30 min to 20-50% of the control. Ionic coupling, however, remained almost unaffected under the same conditions. Freeze-fractured membranes of untreated and RA-treated cells were similar with regard to frequency and sizes of gap junction plaques. With concentrations of less than 10 mumol/liter RA the dye spreading increased significantly in the human amniotic cell line FL, pointing to a possible modulatory effect of RA on junctional communication. 相似文献
27.
28.
Summary Diffusates from flower buds, flower fruits, and scape segments, and extracts of flower stalks of Narcissus pseudonarcissus contain an auxin active in the Avena geo-curvature test. The auxin behaved like indole-3-acetic acid (IAA) in thin-layer chromatography (TLC) with neutral and basic solvents on different adsorbents. After TLC, the auxin of the extracts showed chromogenic reactions identical with those of IAA; in gas-liquid chromatography on two different columns, the purified substance, after methylation, appeared at the retention time of IAA methyl ester. The auxin content of the extracts has been estimated to be equivalent to ca. 10 g IAA kg–1 fresh weight. Diffusates, collected at the basal end of excised flowering apices and of scape segments at different developmental stages, showed highest auxin activity when collected from old buds and young flowers, and from the basal, rapidly elongating scape regions. The diffusible auxin obtained from scape segments was very likely produced by the segments themselves. Thus, the shoot of Narcissus appears to possess two different sites of auxin production, namely, the apical region represented by the flower bud, the flower or the fruit, and the scape.Abbreviations IAA
indole-3-acetic acid
- IAA-OMe
indole-3-acetic-acid methyl ester
- TLC
thin-layer chromatography
- GLC
gas-liquid chromatography 相似文献
29.
30.
Harald Sioli 《International Review of Hydrobiology》1973,58(6):943-944