全文获取类型
收费全文 | 1368篇 |
免费 | 128篇 |
专业分类
1496篇 |
出版年
2023年 | 6篇 |
2022年 | 14篇 |
2021年 | 36篇 |
2020年 | 29篇 |
2019年 | 29篇 |
2018年 | 55篇 |
2017年 | 34篇 |
2016年 | 37篇 |
2015年 | 85篇 |
2014年 | 68篇 |
2013年 | 94篇 |
2012年 | 122篇 |
2011年 | 91篇 |
2010年 | 63篇 |
2009年 | 63篇 |
2008年 | 93篇 |
2007年 | 74篇 |
2006年 | 80篇 |
2005年 | 58篇 |
2004年 | 42篇 |
2003年 | 48篇 |
2002年 | 51篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 18篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 15篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 2篇 |
1968年 | 2篇 |
1964年 | 3篇 |
排序方式: 共有1496条查询结果,搜索用时 0 毫秒
11.
Ninety-six CD-1 male rats were exposed to gamma-ray doses (0-25 Gy) in increments of 5 Gy. One femur, the surgically exteriorized GI tract, and the oral cavity were shielded during irradiation to protect against acute mortality from injury to the hematopoietic system, small intestine, and oral cavity. In addition, the thoraxes of half of the animals from each dose group were shielded. At approximately monthly intervals from 2 to 10 months after irradiation the hematocrit, plasma urea nitrogen (PUN), and 51Cr-EDTA clearance were measured. During the study 20 thorax-shielded and 19 thorax-irradiated animals died. All rats whose thoraxes received 25 Gy irradiation and three out of seven rats whose thoraxes received 20 Gy died 1 to 3 months postirradiation with massive pleural fluid accumulation. Shielding the thoraxes prevented this mode of death at these doses. Kidney injury was judged to be the primary cause of death of all thorax-shielded animals and 15- and 20-Gy thorax-irradiated animals. Animals with kidney damage had elevated PUN and reduced 51Cr-EDTA clearance and hematocrits. The relative merits of each of these end points in assessing radiation-induced kidney injury after total-body exposure are discussed. 相似文献
12.
Effect of CryIC toxin from Bacillus thuringiensis on larval feeding behavior of Spodoptera exigua 总被引:1,自引:0,他引:1
Mariano Berdegué John T. Trumble William J. Moar 《Entomologia Experimentalis et Applicata》1996,80(2):389-401
The lack of data on the effect of Bacillus thuringiensis (B.t.) toxins on larval feeding behavior of the pest Spodoptera exigua (Hübner) (Noctuidae: Amphypyrini) prompted us to investigate the effect of three delivery systems of CryIC, a commercial formulation, inclusion bodies, and the activated CryIC toxin. The commercial formulation was the least and CryIC toxin the most lethal form to neonates of susceptible colonies. All but two of the treatments in choice tests with neonates and third instars showed significant avoidance of B.t. treated diet, with greater proportion of larvae from susceptible (UCR-S and AUBURN-S) and resistant (AUBURN-R) colonies on untreated diet than on diet treated with any of the CryIC forms and concentrations tested. Furthermore, third instars consumed significantly more control than treated diet for all CryIC forms, colonies and concentrations. The avoidance of CryIC toxin by neonates and third instars strongly suggests that CryIC, which also is present in the commercial formulation and in the inclusion bodies, is responsible for eliciting avoidance behavior by S. exigua larvae. Behavioral observations of third instars in a no-choice test on either treated or control diet indicated that questing behavior in susceptible larvae appears to be positively related with presence of CryIC toxin in the diet. Furthermore, resistant third instars were on the whole more active than susceptible thirds on both treated and control diet. Resistant thirds raised on CryIC treated diet (AUBURN-RC) spent more time eating treated diet than resistant larvae raised on control diet (AUBURN-R), suggesting that diet conditioning plays an important role on feeding behavior of S. exigua. The implications of these results are discussed. 相似文献
13.
Characterization of Monoclonal Antibodies Specific for Erwinia carotovora subsp. atroseptica and Comparison of Serological Methods for Its Sensitive Detection on Potato Tubers 总被引:1,自引:0,他引:1 下载免费PDF全文
María Teresa Gorris Benito Alarcon María M. Lopez Mariano Cambra 《Applied microbiology》1994,60(6):2076-2085
Seven monoclonal antibodies (MAbs) to Erwinia carotovora subsp. atroseptica have been produced. One, called 4G4, reacted with high specificity for serogroup I of E. carotovora subsp. atroseptica, the most common serogroup on potato tubers in different serological assays. Eighty-six strains belonging to different E. carotovora subsp. atroseptica serogroups were assayed. Some strains of serogroup XXII also reacted positively. No cross-reactions were observed against other species of plant pathogenic bacteria or 162 saprophytic bacteria from potato tubers. Only one strain of E. chrysanthemi from potato cross-reacted. A comparison of several serological techniques to detect E. carotovora subsp. atroseptica on potato tubers was performed with MAb 4G4 or polyclonal antibodies. The organism was extracted directly from potato peels of artificially inoculated tubers by soaking or selective enrichment under anaerobiosis in a medium with polypectate. MAb 4G4 was able to detect specifically 240 E. carotovora subsp. atroseptica cells per ml by indirect immunofluorescence and immunofluorescence colony staining and after soaking by ELISA-DAS (double-antibody sandwich enzyme-linked immunosorbent assay) after enrichment. The same amount of cells was detected by using immunolectrotransfer with polyclonal antibodies, and E. carotovora subsp. atroseptica and subsp. carotovora were distinguished by the latter technique. ELISA-DAS using MAb 4G4 with an enrichment step also efficiently detected E. carotovora subsp. atroseptica in naturally infected tubers and plants. 相似文献
14.
Eugenio Vitrano Antonio Cupane Maurizio Leone Valeria Militello Lorenzo Cordone Benedetto Salvato Mariano Beltramini Luigi Bubacco Gian Paolo Rocco 《European biophysics journal : EBJ》1993,22(3):157-167
In this work we report the optical absorption spectra of three cobalt-substituted derivatives of hemocyanin (He) from Carcinus maenas, in the temperature range 300–20 K. The derivatives studied are the mononuclear (Co2+)-He with a single cobalt ion in the CuA site, the binuclear (Co2+)2-He and the binuclear mixed metal (Co2+-Cu1+)-He. At low temperature three main bands are clearly resolved; the temperature dependence of their zeroth, first and second moments sheds light on the stereodynamic properties in the surroundings of the chromophore. Within the limits of the reported analysis, in the binuclear derivatives the motions coupled to the chromophore appear to be essentially harmonic in the whole temperature range investigated; moreover the data are consistent with the presence of an exogenous ligand strongly bound to the two metal ions. For the mononuclear derivative an essentially harmonic behavior is evident only up to 200 K where the data are consistent with the presence of an exogenous ligand much less strongly bound, while at higher temperatures the behavior of the spectra indicates the onset of very large anharmonic contributions to motions, that plausibly involve the above exogenous ligand and, quite likely, the entire active site.Abbreviations He
Hemocyanin
- M0
zeroth moment
- M1
first moment
- M2
second moment
- (Co2–)2-He
binuclear bicobalt hemocyanin derivative
- (Co2+)-He
mononuclear monocobalt hemocyanin derivative
- (Co2+-Cu1+)-He
binuclear mixed metals hemocyanin derivative
- LFT
ligand field theory
- CT
charge transfer
- EPR
electronic paramagnetic resonance
- XANES
X-ray absorption near edge structure
Correspondence to: L. Cordone 相似文献
15.
Influence of external factors on secondary embryogenesis and germination in somatic embryos from leaves of Quercus suber 总被引:2,自引:0,他引:2
Bárbara Fernández-Guijarro Cristina Celestino Mariano Toribio 《Plant Cell, Tissue and Organ Culture》1995,41(2):99-106
Somatic embryogenesis was obtained in cultures of leaves from young seedlings of Quercus suber L. A two-stage process, in which benzyladenine and naphthaleneacetic acid were added first at high and then at low concentrations, was required to initiate the process. Somatic embryos arose when the explants were subsequently placed on medium lacking plant growth regulators. The embryogenic lines remained productive, by means of secondary embryogenesis, on medium without growth regulators. However, this repetitive induction was influenced by the macronutrient composition of the culture medium. Both low total nitrogen content and high reduced nitrogen concentration decreased the percentage of somatic embryos that showed secondary embryogenesis. Our results suggest that alternate culture on medium that increases embryo proliferation and a low salt medium prohibiting embryo formation will partially synchronize embryo development. Chilling slightly reduced secondary embryogenesis but gave a modest increase in germination. Maturation under light followed by storage at 4 °C for at least 30 days gave the best results in switching embryos from an embryogenic pathway to a germinative one. Under these conditions 15% of embryos showed coordinated root and shoot growth and 35% formed either shoots or mostly roots. These percentages were higher than those of embryos matured in darkness. This result indicates that a specific treatment is required after maturation and before chilling to activate the switch from secondary embryo formation to germination.Abbreviations BA
benzyladenine
- NAA
naphthaleneacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- BA
indolebutyric acid
- MS
Murashige & Skoog (1962) medium
- SH
Schenk & Hildebrandt (1972) medium
- G
Gamborg (1966, PRL-4-C) medium (macronutrients in mg l–1: NaH2PO4·H2O, 90; Na2HPO4, 30; KCl, 300; (NH4)2SO4, 200; MgSO4·7H2O, 250; KNO3, 1000, CaCl2·2H2O, 150)
- PGR
plant growth regulator 相似文献
16.
Alessandro Sisto Fabio Bonelli Felice Centini Christopher I. Fincham Edoardo Potier Edith Monteagudo Paolo Lombardi Federico Arcamone Cristina Goso Stefano Manzini Alessandro Giolitti Carlo A. Maggi Mariano Venanzi Basilio Pispisa 《Biopolymers》1995,36(4):511-524
In the course of a program aimed at synthesizing novel, potent NK-1 tachykinin receptor antagonists, we developed upon a bioactive model by comparing the low energy structures of a series of peptide and nonpeptide Substance P antagonists. The comparison was based on the super imposition of the aromatic rings, assuming that the rest of the molecule behaves predominantly as a template to arrange the key aromatic groups in the right spatial position. A series of 2-aminocyclohexane carboxylic acid analogues were then selected as the best templates for reproducing the postulated bioactive structure, leading to several pseudo-peptides with interesting biological activity. According to the molecular modeling, these compounds exhibit a neat parallel facing of the indolyl and naphthyl groups at about 3 Å distance. Ultraviolet absorption and steady state fluorescence measurements support this conclusion, showing a linear correlation between the spectral properties and the binding affinity of these analogues. Stacking of the indole ring with naphthalene gives rise to a complex characterized by a well-defined molar extinction coefficient. Consistently, steady state and lifetime fluorescence measurements suggest that the quenching process is ascribable to ground-state interactions between the chromophores. Implications of the π stacking propensity of aromatic groups in the biological activity of the compounds examined are briefly discussed. © 1995 John Wiley & Sons, Inc. 相似文献
17.
18.
Differential phosphorylation of band 3 and glycophorin in intact and extracted erythrocyte membranes
This report presents an analysis of the phosphorylation of human and rabbit erythrocyte membrane proteins which migrate in NaDodSO4-polyacrylamide gels in the area of the Coomassie Blue-stained proteins generally known as band 3. The phosphorylation of these proteins is of interest as band 3 has been implicated in transport processes. This study shows that there are at least three distinct phosphoproteins associated with the band 3 region of human erythrocyte membranes. These are band 2.9, the major band 3, and PAS-1. The phosphorylation of these proteins is differentially catalyzed by solubilized membrane and cytoplasmic cyclic AMP-dependent and -independent erythrocyte protein kinases. Band 2.9 is present and phosphorylated in unfractionated human and rabbit erythrocyte ghosts but not in NaI- or dimethylmaleic anhydride (DMMA)-extracted membranes. These latter membrane preparations are enriched in band 3 and in sialoglycoproteins. The NaI-extracted ghosts contain residual protein kinase activity which can catalyze the autophosphorylation of band 3 whereas the DMMA-extracted ghosts are usually devoid of any kinase activity. However, both NaI- and DMMA-extracted ghosts, as well as Triton X-100 extracts of the DMMA-extracted ghosts, can be phosphorylated by various erythrocyte protein kinases. The kinases which preferentially phosphorylate the major band 3 protein are inactive towards PAS-1 while the kinases active towards PAS-1 are less active towards band 3. The band 3 protein in the DMMA-extracted ghosts can be cross-linked with the Cu2+ -σ-phenanthroline complex. The cross-linking of band 3 does not affect its capacity to serve as a phosphoryl acceptor nor does phosphorylation affect the capacity of band 3 to form cross-links. In addition to band 2.9, the major band 3 and PAS-1, another minor protein component appears to be present in the band 3 region in human erythrocyte membranes. This protein is specifically phosphorylated by the cyclic AMP-dependent protein kinases isolated from the cytoplasm of rabbit erythrocytes. The rabbit erythrocyte membranes lack PAS-1 and the cyclic AMP-dependent protein kinase substrate. 相似文献
19.
Human interferon omega (omega) binds to the alpha/beta receptor. 总被引:2,自引:0,他引:2
It was proposed that human interferon omega (omega) binds to the interferon alpha/beta receptor but not to the interferon gamma receptor. However, since no studies were performed to provide direct evidence for this hypothesis, we carried out cross-linking experiments and saturation binding assays between a 32P-labeled human interferon-alpha (Hu-IFN-alpha) and unlabeled Hu-IFN-alpha A, -beta, -gamma, and -omega. These assays demonstrated that Hu-IFN-alpha A, -beta, and -omega, but not Hu-IFN-gamma, were able to block binding of 32P-labeled Hu-IFN-alpha A to human cells. These results indicate that Hu-IFN-omega binds to the alpha/beta receptor. 相似文献
20.
Antonio Baldini Dorothy A. Miller Viji Shridhar Mariano Rocchi Orlando J. Miller David C. Ward 《Chromosoma》1991,101(2):109-114
We have isolated an alpha satellite DNA clone, pG3.9, from gorilla DNA. Fluorescence in situ hybridization on banded chromosomes under high stringency conditions revealed that pG3.9 identifies homologous sequences at the centromeric region of ten gorilla chromosomes, and, with few exceptions, also recognizes the homologous chromosomes in human. A pG3.9-like alphoid DNA is present on a larger number of orangutan chromosomes, but, in contrast, is present on only tow chromosomes in the chimpanzee. These results show that the chromosomal subsets of related alpha satellite DNA sequences may undergo different patterns of evolution.by J.B. Rattner 相似文献