全文获取类型
收费全文 | 1138篇 |
免费 | 97篇 |
出版年
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 42篇 |
2014年 | 42篇 |
2013年 | 59篇 |
2012年 | 58篇 |
2011年 | 56篇 |
2010年 | 42篇 |
2009年 | 39篇 |
2008年 | 53篇 |
2007年 | 45篇 |
2006年 | 39篇 |
2005年 | 38篇 |
2004年 | 42篇 |
2003年 | 38篇 |
2002年 | 26篇 |
2001年 | 32篇 |
2000年 | 30篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1992年 | 16篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1975年 | 18篇 |
1969年 | 8篇 |
1966年 | 8篇 |
1964年 | 8篇 |
1963年 | 7篇 |
1961年 | 8篇 |
1956年 | 7篇 |
排序方式: 共有1235条查询结果,搜索用时 147 毫秒
91.
Somatic cell nuclear transfer in the pig: control of pronuclear formation and integration with improved methods for activation and maintenance of pregnancy 总被引:14,自引:0,他引:14
De Sousa PA Dobrinsky JR Zhu J Archibald AL Ainslie A Bosma W Bowering J Bracken J Ferrier PM Fletcher J Gasparrini B Harkness L Johnston P Ritchie M Ritchie WA Travers A Albertini D Dinnyes A King TJ Wilmut I 《Biology of reproduction》2002,66(3):642-650
To clone a pig from somatic cells, we first validated an electrical activation method for use on ovulated oocytes. We then evaluated delayed versus simultaneous activation (DA vs. SA) strategies, the use of 2 nuclear donor cells, and the use of cytoskeletal inhibitors during nuclear transfer. Using enucleated ovulated oocytes as cytoplasts for fetal fibroblast nuclei and transferring cloned embryos into a recipient within 2 h of activation, a 2-h delay between electrical fusion and activation yielded blastocysts more reliably and with a higher nuclear count than did SA. Comparable rates of development using DA were obtained following culture of embryos cloned from ovulated or in vitro-matured cytoplasts and fibroblast or cumulus nuclei. Treatment of cloned embryos with cytochalasin B (CB) postfusion and for 6 h after DA had no impact on blastocyst development as compared with CB treatment postfusion only. Inclusion of a microtubule inhibitor such as nocodozole with CB before and after DA improved nuclear retention and favored the formation of single pronuclei in experiments using a membrane dye to reliably monitor fusion. However, no improvement in blastocyst development was observed. Using fetal fibroblasts as nuclear donor cells, a live cloned piglet was produced in a pregnancy that was maintained by cotransfer of parthenogenetic embryos. 相似文献
92.
Multifactor dimensionality reduction software for detecting gene-gene and gene-environment interactions 总被引:14,自引:0,他引:14
MOTIVATION: Polymorphisms in human genes are being described in remarkable numbers. Determining which polymorphisms and which environmental factors are associated with common, complex diseases has become a daunting task. This is partly because the effect of any single genetic variation will likely be dependent on other genetic variations (gene-gene interaction or epistasis) and environmental factors (gene-environment interaction). Detecting and characterizing interactions among multiple factors is both a statistical and a computational challenge. To address this problem, we have developed a multifactor dimensionality reduction (MDR) method for collapsing high-dimensional genetic data into a single dimension thus permitting interactions to be detected in relatively small sample sizes. In this paper, we describe the MDR approach and an MDR software package. RESULTS: We developed a program that integrates MDR with a cross-validation strategy for estimating the classification and prediction error of multifactor models. The software can be used to analyze interactions among 2-15 genetic and/or environmental factors. The dataset may contain up to 500 total variables and a maximum of 4000 study subjects. AVAILABILITY: Information on obtaining the executable code, example data, example analysis, and documentation is available upon request. SUPPLEMENTARY INFORMATION: All supplementary information can be found at http://phg.mc.vanderbilt.edu/Software/MDR. 相似文献
93.
94.
Witzmann FA Bobb A Briggs GB Coppage HN Hess RA Li J Pedrick NM Ritchie GD Iii JR Still KR 《Proteomics》2003,3(6):1016-1027
We analyzed protein expression in preparations from whole testis in adult male Sprague-Dawley rats exposed for 6 h/d for 91 consecutive days to jet propulsion fuel-8 (JP-8) in the vapor phase (0, 250, 500, or 1000 mg/m(3) +/- 10%), simulating a range of possible human occupational exposures. Whole body inhalation exposures were carefully controlled to eliminate aerosol phase, and subjects were sacrificed within 48 h postexposure. Organ fractions were solubilized and separated via large-scale, high resolution two-dimensional electrophoresis, and gel patterns scanned, digitized and processed for statistical analysis. Seventy-six different testis proteins were significantly increased or decreased in abundance in vapor-exposed groups, compared to controls, and dose-response profiles were often nonlinear. A number of the proteins were identified by peptide mass fingerprinting and related to histopathological or physiological deficits shown in previously published studies to occur with repeated exposure to hydrocarbon fuels or solvents. These results demonstrate a significant effect of JP-8 exposure on protein expression, particularly in protein expression in the rodent testis, and suggest that a 91 d exposure to jet fuel vapor induces changes of equal or greater magnitude to those reported previously for shorter duration JP-8 aerosol exposures. 相似文献
95.
While K-ras is essential for mouse development, expression of the K-ras 4A splice variant is dispensable 下载免费PDF全文
Plowman SJ Williamson DJ O'Sullivan MJ Doig J Ritchie AM Harrison DJ Melton DW Arends MJ Hooper ML Patek CE 《Molecular and cellular biology》2003,23(24):9245-9250
In mammals, the three classical ras genes encode four highly homologous proteins, N-Ras, H-Ras, and the isoforms K-Ras 4A and 4B. Previous studies have shown that K-ras is essential for mouse development and that while K-ras 4A and 4B are expressed during development, K-ras 4A expression is regulated temporally and spatially and occurs in adult kidney, intestine, stomach, and liver. In the present study, the pattern of K-ras 4A expression was examined in a wide range of wild-type adult mouse tissues, and gene targeting was used to generate K-ras 4A-deficient mice to examine its role in development. It was found that K-ras 4A is also expressed in uterus, lung, pancreas, salivary glands, seminal vesicles, bone marrow cells, and cecum, where it was the major K-Ras isoform expressed. Mating between K-ras(tmDelta4A/+) mice produced viable K-ras(tmDelta4A/tmDelta4A) offspring with the expected Mendelian ratios of inheritance, and these mice expressed the K-ras 4B splice variant only. K-ras(tmDelta4A/tmDelta4A) mice were fertile and showed no histopathological abnormalities on inbred (129/Ola) or crossbred (129/Ola x C57BL/6) genetic backgrounds. The results demonstrate that K-Ras 4A, like H- and N-Ras, is dispensable for normal mouse development, at least in the presence of functional K-Ras 4B. 相似文献
96.
Johansen CA Farrow RA Morrisen A Foley P Bellis G Van Den Hurk AF Montgomery B Mackenzie JS Ritchie SA 《Medical and veterinary entomology》2003,17(1):102-111
Circumstantial evidence has implicated wind-borne mosquitoes (Diptera: Culicidae) in the introduction of Japanese encephalitis (JE) virus into Australia from the New Guinea mainland. A study was initiated on Saibai Island in the northern Torres Strait, during January and February 2000, to identify the potential source of insects collected in aerial (kytoon) and surface-level traps. Wind speed and direction were recorded to determine wind profiles during insect sampling. Northerly winds capable of carrying insects from New Guinea to Saibai Island were only present on three out of 18 nights sampled. Only three male mosquitoes, comprising two Verrallina funerea (Theobald) and one Ochlerotatus vigilax (Skuse), were collected in aerial samples, and were most likely of local origin. Culicoides midges were also collected in aerial nets and included gravid/parous C. bundyensis Lee and Reye, and one parous C. histrio Johannsen. Highest densities of arthropods (up to 1562/million m3) were on 30 January 2000 when NW winds, sustained for six hours, probably introduced midges from the New Guinea mainland. Adult mosquitoes (including three female Ve. funerea and a single female Ficalbia) and Culicoides (including two gravid C. bundyensis and one parous C. cordiger Macfie) were also collected in 2 m high mast nets during northerly surface winds. Although the results do not provide evidence that wind-blown mosquitoes introduced JE from New Guinea into Australia, they do not preclude that strong N winds associated with low pressure systems SW of the Torres Strait could have done so. However, results suggest that Culicoides were more likely than mosquitoes to reach high altitude and travel long distances during the light N winds experienced during the study. 相似文献
97.
98.
Ritchie H Lawrie LC Crombie PW Mosesson MW Booth NA 《The Journal of biological chemistry》2000,275(32):24915-24920
In this study, we identified lysine residues in the fibrinogen Aalpha chain that serve as substrates during transglutaminase (TG)-mediated cross-linking of plasminogen activator inhibitor 2 (PAI-2). Comparisons were made with alpha(2)-antiplasmin (alpha(2)-AP), which is known to cross-link to lysine 303 of the Aalpha chain. A 30-residue peptide containing Lys-303 specifically competed with fibrinogen for cross-linking to alpha(2)-AP but not for cross-linking to PAI-2. Further evidence that PAI-2 did not cross-link via Lys-303 was the cross-linking of PAI-2 to I-9 and des-alphaC fibrinogens, which lack 100 and 390 amino acids from the C terminus of the Aalpha chain, respectively. PAI-2 or alpha(2)-AP was cross-linked to fibrinogen and digested with trypsin or endopeptidase Glu-C, and the resulting peptides analyzed by mass spectrometry. Peptides detected were consistent with tissue TG (tTG)-mediated cross-linking of PAI-2 to lysines 148, 176, 183, 457 and factor XIIIa-mediated cross-linking of PAI-2 to lysines 148, 230, and 413 in the Aalpha chain. alpha(2)-AP was cross-linked only to lysine 303. Cross-linking of PAI-2 to fibrinogen did not compete with alpha(2)-AP, and the two proteins utilized different lysines in the Aalpha chain. Therefore, PAI-2 and alpha(2)-AP can cross-link simultaneously to the alpha polymers of a fibrin clot and promote resistance to lysis. 相似文献
99.
100.
Use of length heterogeneity PCR and fatty acid methyl ester profiles to characterize microbial communities in soil 总被引:29,自引:0,他引:29
Ritchie NJ Schutter ME Dick RP Myrold DD 《Applied and environmental microbiology》2000,66(4):1668-1675
In length heterogeneity PCR (LH-PCR) a fluorescently labeled primer is used to determine the relative amounts of amplified sequences originating from different microorganisms. Labeled fragments are separated by gel electrophoresis and detected by laser-induced fluorescence with an automated gene sequencer. We used LH-PCR to evaluate the composition of the soil microbial community. Four soils, which differed in terms of soil type and/or crop management practice, were studied. Previous data for microbial biomass, nitrogen and carbon contents, and nitrogen mineralization rates suggested that the microbial characteristics of these soils were different. One site received two different treatments: no-till and conventional till perennial ryegrass. The other sites were no-till continuous grass plots at separate locations with different soil types. Community composition was characterized by assessing the natural length heterogeneity in eubacterial sequences amplified from the 5' domain of the 16S rRNA gene and by determining fatty acid methyl ester (FAME) profiles. We found that LH-PCR results were reproducible. Both methods distinguished the three sites. The most abundant bacterial community members, based on cloned LH-PCR products, were members of the beta subclass of the class Proteobacteria, the Cytophaga-Flexibacter-Bacteriodes group, and the high-G+C-content gram-positive bacterial group. Strong correlations were found between LH-PCR results and FAME results. We found that the LH-PCR method is an efficient, reliable, and highly reproducible method that should be a useful tool in future assessments of microbial community composition. 相似文献