全文获取类型
收费全文 | 1532篇 |
免费 | 151篇 |
国内免费 | 164篇 |
专业分类
1847篇 |
出版年
2024年 | 14篇 |
2023年 | 21篇 |
2022年 | 35篇 |
2021年 | 28篇 |
2020年 | 76篇 |
2019年 | 65篇 |
2018年 | 67篇 |
2017年 | 60篇 |
2016年 | 40篇 |
2015年 | 48篇 |
2014年 | 98篇 |
2013年 | 108篇 |
2012年 | 76篇 |
2011年 | 69篇 |
2010年 | 46篇 |
2009年 | 68篇 |
2008年 | 74篇 |
2007年 | 64篇 |
2006年 | 80篇 |
2005年 | 56篇 |
2004年 | 61篇 |
2003年 | 40篇 |
2002年 | 33篇 |
2001年 | 40篇 |
2000年 | 26篇 |
1999年 | 18篇 |
1998年 | 22篇 |
1997年 | 27篇 |
1996年 | 22篇 |
1995年 | 25篇 |
1994年 | 16篇 |
1993年 | 25篇 |
1992年 | 23篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1974年 | 10篇 |
排序方式: 共有1847条查询结果,搜索用时 15 毫秒
81.
Gábriel R Lesauter J Bánvölgyi T Petrovics G Silver R Witkovsky P 《Cell and tissue research》2004,315(2):181-186
We investigated parvalbumin immunoreactivity (PA-IR) in the retinas of rats maintained on a 12:12 h light:dark cycle, or after being placed in constant darkness for 24–72 h. Retinas were harvested at zeitgeber and circadian times 02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 h. PA-IR was found primarily in retinal amacrine cells of the AII subtype. In a light/dark cycle, PA-IR showed a clear rhythm, with a low near zeitgeber time (ZT) 10:00 h and a peak near ZT 18:00 h. The ratio of immunofluorescence intensities at these timepoints was >15-fold. When animals were kept in complete darkness for 1–3 days, the rhythm of PA-IR was still preserved, but was progressively reduced in amplitude. The rhythm of PA-IR inferred from immunohistochemical data was confirmed by Western blots. We conclude that PA-IR in the rat retina shows an underlying circadian rhythm that is enhanced by cyclic light. The regulation may involve translocation of the protein between cell compartments and/or new protein synthesis.This study was supported by an OTKA grant (T 34160), NIH grants NS 37919 (R.S.) and ET 03570, NSF grant IBN-96418886 (R.S.), and grants from the Helen Hoffritz Charitable Trust and Research to Prevent Blindness, Inc. R.G. was also in receipt of a János Bolyai fellowship 相似文献
82.
The jaw muscle (i.e., masticatory, suprahyoid, and extrinsic tongue) anatomy and mass were examined in four genera of Old World hamsters (cricetine murids), Mesocricetus, Cricetulus, Tscherskia, and Phodopus. The masseter was the largest and most complicated of the muscles examined. In the superficial layer, a few ventral fibers form a small medially turned portion with an insertion site more similar to those of sciurids than of other murids. In Mesocricetus, the superficial layer has a discrete anteroventral portion that has not been reported for other murid rodents. Examination of the fiber attachment sites indicated that the deep layer contains four parts and the medial layer contains three parts. The deep layer originates from two aponeuroses that are firmly connected to each other at their anterior ends and lie along the zygomatic arch. The aponeurosis of insertion for the deep layer is situated along the masseteric ridge and the dorsal border of the angular process, but is absent in its middle part, consistent with reports in two relatives, sigmodontine and arvicoline murids. In cricetine murids, unlike in other rodents, fibers insert on the dorsal narrow strip of the posterior mandibular aponeurosis, not on its broad medial aspect. The relative mass of some masticatory and suprahyoid muscles is related to body mass. Small species (Cricetulus and Phodopus) have relatively larger masseter and mylohyoid muscles and smaller temporalis and geniohyoid muscles than large species (Mesocricetus and Tscherskia). 相似文献
83.
Stewart SG Bausek N Wohlrab F Schneider WJ Janet Horrocks A Wishart GJ 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2004,137(4):657-663
The interaction of chicken spermatozoa with the inner perivitelline layer from different avian species in vitro during a 5 min co-incubation was measured as the number of points of hydrolysis produced per unit area of inner perivitelline layer. The average degree of interaction, as a proportion of that between chicken spermatozoa and their homologous inner perivitelline layer, was: equal to or greater than 100% within Galliformes (chicken, turkey, quail, pheasant, peafowl and guineafowl); 44% within Anseriformes (goose, duck); and less than 30% in Passeriformes (Zebra Finch) and Columbiformes (collared-dove). The homologue of the putative chicken sperm-binding proteins, chicken ZP1 and ZP3, were identified by Western blotting with anti-chicken ZP1/ZP3 antibody in the perivitelline layers of all species. The functional cross-reactivity between chicken spermatozoa and heterologous inner perivitelline layer appeared to be linked to known phylogenetic distance between the species, although it was not related to the relative affinity of the different ZP3 homologues for anti-chicken ZP3. This work demonstrates that sperm interaction with the egg investment does not represent such a stringent species-specific barrier in birds as it does in mammals and marine invertebrates. This may be a factor in the frequency of hybrid production in birds. 相似文献
84.
Drapc1 expression during mouse embryonic development 总被引:2,自引:0,他引:2
We identified the mouse homolog of human DRAPC1 (APCDD1) gene, shown to be a target of Wnt/beta-catenin signaling pathway in cancer cell lines. Analysis of its spatiotemporal expression in mouse embryos from E7.5 to E14 showed that Drapc1 is expressed during development of the extraembryonic structures, nervous system, vascular system and inner ear. In addition, Drapc1 is expressed in the mesenchyme of several developing organs at sites of epithelio-mesenchymal interactions. Drapc1 expression was also found in the hair follicles of the adult mouse skin. Similarity of Drapc1 expression pattern to location of active beta-catenin in developing mouse embryo further suggests that mouse Drapc1 is a novel in vivo target gene of Wnt/beta-catenin signaling pathway. 相似文献
85.
Anti-IL-13 monoclonal antibody inhibits airway hyperresponsiveness, inflammation and airway remodeling 总被引:8,自引:0,他引:8
Yang G Volk A Petley T Emmell E Giles-Komar J Shang X Li J Das AM Shealy D Griswold DE Li L 《Cytokine》2004,28(6):224-232
Asthma is a chronic inflammatory disease characterized by reversible bronchial constriction, pulmonary inflammation and airway remodeling. Current standard therapies for asthma provide symptomatic control but fail to target the underlying disease pathology. Furthermore, no therapeutic agent is effective in preventing airway remodeling. Interleukin 13 (IL-13) is a pleiotropic cytokine produced mainly by T cells. A substantial amount of evidence suggests that IL-13 plays a critical role in the pathogenesis of asthma. Therefore, a neutralizing anti-IL-13 monoclonal antibody could provide therapeutic benefits to asthmatic patients. To test the concept we have generated a neutralizing rat anti-mouse IL-13 monoclonal antibody, and evaluated its effects in a chronic mouse model of asthma. Chronic asthma-like response was induced in ovalbumin (OVA) sensitized mice by repeated intranasal OVA challenges. After weeks of challenge, mice developed airway hyperresponsiveness (AHR) to methacholine stimulation, severe airway inflammation, hyper mucus production, and subepithelial fibrosis. When given at the time of each intranasal OVA challenge, anti-IL-13 antibody significantly suppressed AHR, eosinophil infiltration, proinflammatory cytokine/chemokine production, serum IgE, and most interestingly, airway remodeling. Taken together, these results strongly suggest that a neutralizing anti-human IL-13 monoclonal antibody could be an effective therapeutic agent for asthma. 相似文献
86.
The crystal structure of a yeast hypothetical protein with sequence similarity to CN hydrolases has been determined to 2.4 A resolution by the multiwavelength anomalous dispersion (MAD) method. The protein folds as a four-layer alphabetabetaalpha sandwich and exists as a dimer in the crystal and in solution. It was selected in a structural genomics project as representative of CN hydrolases at a time when no structures had been determined for members of this family. Structures for two other members of the family have since been reported and the three proteins have similar topology and dimerization modes, which are distinct from those of other alphabetabetaalpha proteins whose structures are known. The dimers form an unusual eight-layer alphabetabetaalpha:alphabetabetaalpha structure. Although the precise enzymatic reactions catalyzed by the yeast protein are not known, considerable information about the active site may be deduced from conserved sequence motifs, comparative biochemical information, and comparison with known structures of hydrolase active sites. As with serine hydrolases, the active-site nucleophile (cysteine in this case) is positioned on a nucleophile elbow. 相似文献
87.
Corneas of tadpole, mouse, rat, guinea pig, rabbit, cat, cattle, and human were examined by TEM and SEM in a comparative study. The differences between species were noted mainly by using TEM. Bowman's layer showed a tendency to be well developed in higher mammals. Tadpoles lack a Bowman's layer, lower mammals have a thin Bowman's layer, and higher mammals have a thick Bowman's layer. The boundary between the substantia propria and Descemet's membrane was distinct in higher mammals. On the other hand, there are no differences in thickness of the collagen fibrils that constitute Bowman's layer and those of the substantia propria. NaOH digestion was utilized for SEM preparation. SEM imaging revealed a textured appearance of the epithelial side of Bowman's layer. In Descemet's membrane, fibrous long spacing (FLS) fiber-like structures, which are arranged in parallel to the endothelium, were observed by both TEM and SEM. To our knowledge, this is the first report of SEM observations of FLS fiber-like structures on the endothelial surface of Descemet's membrane. SEM at a plane normal to the plane of the cornea showed that Descemet's membrane has a piled laminar structure. Descemet's membrane is closely associated with the collagen layer of the substantia propria. Collagen fibrils invading from the substantia propria into Descemet's membrane were observed with both TEM and SEM. 相似文献
88.
The spatial and temporal patterns of post-embryonal cell growth and cell division were characterised in excised cotyledons
of vegetable marrow (Cucurbita pepo L. var. giromontia Alef.) incubated in water. The concurrent roles of these two processes in cotyledon growth were determined using paradermal
sections of the first palisade layer of developing cotyledons. Tissue specificity was observed in the pattern of cell division.
The daughter cells derived from an initial cell, which had already differentiated before imbibition of the seeds, were tightly
packed in a cluster, which enabled us to monitor cell division during early cotyledon development. Heterogeneity of cell size
was recognised during the process of cell proliferation in the cluster, suggesting that cell division is uncoupled from control
of cell size. There was significantly more cell division in the marginal part of the cotyledons than in other parts, suggesting
high activity of the marginal meristem. Light enhanced cell and cotyledon enlargement, but had no effect on the number of
divisions. This study elucidated the cellular basis of post-germinative Cucurbita cotyledon morphogenesis and development.
Electronic Publication 相似文献
89.
Hemphill A Stettler M Walker M Siles-Lucas M Fink R Gottstein B 《Trends in parasitology》2002,18(10):445-451
This article reviews the use of an in vitro culture model for the maintenance and proliferation of Echinococcus multilocularis metacestodes and the formation of protoscoleces. This model has been used to identify and characterize parasite molecules involved in host-parasite interactions, and is a suitable tool to perform in vitro drug-screening assays. The development of a simple and easy-to-handle assay to determine the effects of drugs on parasite viability, without the need for time-consuming animal experimentation, has opened the way for larger-scale in vitro drug screening. 相似文献
90.
The purpose of the study was to investigate the effect of hydroxypropyl beta cyclodextrin (HPβCD) on aqueous solubility, stability,
and in vitro corneal permeation of acyl ester prodrugs of ganciclovir (GCV). Aqueous solubility and stability of acyl ester
prodrugs of Ganciclovir (GCV) were evaluated in pH 7.4 isotonic phosphate buffer solution (IPBS) in the presence and absence
of HPβCD. Butyryl cholinesterase-mediated enzymatic hydrolysis of the GCV prodrugs was studied using various percentage w/v
HPβCD. In vitro corneal permeation of GCV and its prodrugs (with and without 5% HPβCD) across isolated rabbit cornea was studied
using side-by-side diffusion cells. HPβCD-prodrug complexation was of the AL type with values for complexation constants ranging between 12 and 108 M−1. Considerable improvement in chemical and enzymatic stability of the GCV prodrugs was observed in the presence of HPβCD.
The stabilizing effect of HPβCD was found to depend on the degree of complexation and the degradation rate of prodrug within
the complex. Five percent w/v HPβCD was found to enhance the corneal permeation of only the most lipophilic prodrug GCV dibutyrate
(2.5-fold compared with 0% HPβCD). All other prodrugs showed little or no difference in transport in the presence of 5% w/v
HPβCD. Agitation in the donor chamber largely influenced the transport kinetics of GCV dibutyrate across cornea. Results indicate
the presence of an unstirred aqueous diffusion layer at the corneal surface that restricts the transport of the highly lipophilic
GCV dibutyrate prodrug. HPβCD improves corneal permeation by solubilizing the hydrophobic prodrug and delivering it across
the mucin layer at the corneal surface. 相似文献