全文获取类型
收费全文 | 1129篇 |
免费 | 59篇 |
专业分类
1188篇 |
出版年
2023年 | 5篇 |
2022年 | 12篇 |
2021年 | 26篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 23篇 |
2017年 | 32篇 |
2016年 | 34篇 |
2015年 | 47篇 |
2014年 | 54篇 |
2013年 | 72篇 |
2012年 | 92篇 |
2011年 | 91篇 |
2010年 | 60篇 |
2009年 | 60篇 |
2008年 | 70篇 |
2007年 | 73篇 |
2006年 | 70篇 |
2005年 | 46篇 |
2004年 | 57篇 |
2003年 | 48篇 |
2002年 | 49篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有1188条查询结果,搜索用时 0 毫秒
41.
Cavalcante MC de Andrade LR Du Bocage Santos-Pinto C Straus AH Takahashi HK Allodi S Pavão MS 《Journal of structural biology》2002,137(3):313-321
In most ascidian species the oocytes are surrounded by two types of accessory cells called follicle cells and test cells. Test cells are located on the periphery of oocytes and remain in the perivitelline space during egg development until hatching. Heparin and histamine were previously described in the test cells of the ascidian Styela plicata. In the present study, electron microscopy techniques were used to characterize the ultrastructure of the S. plicata test cells and to localize heparin and histamine in these cells. Test cells contain several intracellular granules with unique ultrastructural features. They are formed by elongated filaments composed of serial globules with an electron-lucent circle, containing a central electron-dense spot. Immunocytochemistry showed that heparin and histamine colocalize at the border of granule filaments in the test cell. Compound 48/80, a potent secretagogue of heparin-containing mast cells, also induced degranulation of test cells. According to these results, we suggest that test cells represent ancient effector cells of the innate immunity in primitive chordates. 相似文献
42.
43.
Enhanced activity of the plasma membrane oxidoreductase in circulating lymphocytes from insulin-dependent diabetes mellitus patients 总被引:2,自引:0,他引:2
Lenaz G Paolucci U Fato R D'Aurelio M Parenti Castelli G Sgarbi G Biagini G Ragni L Salardi S Cacciari E 《Biochemical and biophysical research communications》2002,290(5):1589-1592
Circulating human lymphocytes contain a transmembrane oxidoreductase (PMOR) capable of reducing dichlorophenol indophenol (DCIP) by endogenous reductants, presumably NADH. Membranes from lymphocytes obtained from buffy coats contain a NADH DCIP reductase having a K(m) of about 1 microM and almost insensible to dicoumarol. The PMOR of lymphocytes from insulin-dependent diabetic patients is higher than that from age-matched controls and, in addition, has a dicoumarol-sensitive component, lacking in most controls, presumably due to membrane association of DT-diaphorase. The increase of PMOR in diabetes is likely due to overexpression of the enzyme, in view of the very low K(m) for NADH indicating that, in intact cells, the enzyme is practically saturated with the reductant substrate. 相似文献
44.
In this study we report preliminary data on the consumption of tannin-rich plants by sifakas (Propithecus verreauxi verreauxi) living in the Kirindy forest, western Madagascar. Sifakas spent most of their time feeding on only a few plant species.
The tannin intake during the period between the pregnancy and birth season was significantly higher in pregnant females or
females with lactating infants than in non-reproductive females and males. These periparturient females secured a larger proportion
of condensed tannins by short feeding bouts on plants not included in the group's limited preferred food species. The measured
increase in tannin intake is puzzling in light of the fact that tannins are commonly known for their protein-binding properties.
Since protein demands are highest in pregnant and lactating females, possible medicinal benefits of tannin ingestion are considered.
Tannin consumption is associated with an increase in body weight and stimulation of milk secretion. Veterinarians administer
tannins as an astringent, anti-hemorrhagic and anti-abortive. Their high potential as an alternative anthelminthic has also
recently been recognized. Thus, when viewed as self-medicating behavior, controlled increase in tannin intake could have multiple
prophylactic advantages for females during the periparturient period. The high selectivity in their plant choice, and the
presence of unusual feeding habits by a particular group of individuals (females with infants) limited in time (birth season),
suggests that an increase in tannin ingestion may be a self-medicating behavior with multiple directly adaptive benefits to
female reproduction.
Electronic Publication 相似文献
45.
Pure phloem sap of tomato leaves was collected by stylectomy.Glutamine and glutamate were the predominant free amino acidstranslocated by the phloem stream. In developing fruits glutaminecontent increased significantly, reaching 35% of the total freeamino acids. Comparison in the amino acid composition betweenthe two tissues are discussed. (Received October 6, 1997; Accepted January 27, 1998) 相似文献
46.
Angelo PC Nunes-Silva CG Brígido MM Azevedo JS Assunção EN Sousa AR Patrício FJ Rego MM Peixoto JC Oliveira WP Freitas DV Almeida ER Viana AM Souza AF Andrade EV Acosta PO Batista JS Walter ME Leomil L Anjos DA Coimbra RC Barbosa MH Honda E Pereira SS Silva A Pereira JO Silva ML Marins M Holanda FJ Abreu RM Pando SC Gonçalves JF Carvalho ML Leal-Mesquita ER da Silveira MA Batista WC Atroch AL França SC Porto JI Schneider MP 《Plant cell reports》2008,27(1):117-124
Guarana (Paullinia cupana var. sorbilis) is a plant native to the central Amazon basin. Roasted seed extracts have been used as medicinal beverages since pre-Colombian
times, due to their reputation as stimulants, aphrodisiacs, tonics, as well as protectors of the gastrointestinal tract. Guarana
plants are commercially cultivated exclusively in Brazil to supply the national carbonated soft-drink industry and natural
product stores around the world. In this report, we describe and discuss the annotation of 15,387 ESTs from guarana seeded-fruits,
highlighting sequences from the flavonoid and purine alkaloid pathways, and those related to biotic stress avoidance. This
is the largest set of sequences registered for the Sapindaceae family. 相似文献
47.
Summary The recessive embryo-lethal mutantdek-1 of maize, showing arrest of embryo development at the proembryo stage, lack of carotenoids and anthocyanins and absence in the endosperm of the aleurone layer, was characterized at a cytological level. Cytofluorimetric analysis excluded endoreduplication or polyploidization events in mutant embryonic cells, in spite of an evident increase in nucleolus and nucleus diameters.The data seem to point to an involvement ofDek-1 in the progression of the embryo toward specific developmental steps and in the differentiation of the aleurone layer in the endosperm. Cellular proliferation is not affected by the mutation, as is shown by DNA replication even after the arrest in development and by the possibility of inducing callus from mutant embryos.Abbreviation DAP
days after pollination 相似文献
48.
(20S)-[7,7,21,21-2H(4)]-3beta-(tert-Butyldimethylsilanyloxy)-20-methyl-pregn-5-en-21-ol, an intermediate for the preparation of deuterated isotopomers of sterols to be used as standards for biomedical studies, was prepared by reduction with dichloroaluminum deuteride of ethyl (20S)-3beta-(tert-butyldimethylsilanyloxy)-7-oxo-pregn-5-en-20-carboxylate. Using controlled experimental conditions, it has also been shown that the dichloroaluminum hydride reduction of a 7-keto steroid affords the corresponding 7beta-hydroxy derivative in a highly stereoselective manner. 相似文献
49.
Asolene platae (Ampullariidae) is a dioecious freshwater snail with subaquatic gelatinous egg masses that dwells in the Río de la Plata basin (Argentina). The aim of this study was to describe the inheritance mechanism of the colour variations of the shell and soft parts of this snail, and to study their potential use as a genetic marker. The wild-type phenotype presents dark pigments in the soft parts and in shell bands, whereas the yellow phenotype lacks dark pigments in the soft parts and also most dark bands in the shell, except for a subsutural and a periumbilical band. The data showed that the lack of pigments in A. platae is a recessive homozygotic condition with a simple Mendelian inheritance mechanism. Females of the wild-type phenotype had a higher number of bands than the males. The pigment of the bands of both phenotypes is located in the calcareous matrix of the shell. Using the lack of pigments as a genetic marker we demonstrated the existence of biparental egg masses in A. platae, hitherto known in only one species within the Ampullariidae. 相似文献
50.
Vaisburg A Bernstein N Frechette S Allan M Abou-Khalil E Leit S Moradei O Bouchain G Wang J Woo SH Fournel M Yan PT Trachy-Bourget MC Kalita A Beaulieu C Li Z MacLeod AR Besterman JM Delorme D 《Bioorganic & medicinal chemistry letters》2004,14(1):283-287
A variety of omega-substituted alkanoic acid (2-amino-phenyl)-amides were designed and synthesized. These compounds were shown to inhibit recombinant human histone deacetylases (HDACs) with IC(50) values in the low micromolar range and induce hyperacetylation of histones in whole cells. They induced expression of p21WAF1/Cip1 and caused cell-cycle arrest in human cancer cells. Compounds in this class showed efficacy in human tumor xenograft models. 相似文献