全文获取类型
收费全文 | 373篇 |
免费 | 7篇 |
国内免费 | 1篇 |
出版年
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 6篇 |
2010年 | 12篇 |
2009年 | 16篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 4篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1972年 | 3篇 |
1968年 | 3篇 |
1959年 | 3篇 |
1958年 | 5篇 |
1957年 | 9篇 |
1956年 | 6篇 |
1955年 | 5篇 |
1954年 | 12篇 |
1953年 | 19篇 |
1952年 | 8篇 |
1951年 | 7篇 |
1950年 | 5篇 |
1949年 | 11篇 |
1948年 | 8篇 |
1947年 | 3篇 |
排序方式: 共有381条查询结果,搜索用时 31 毫秒
51.
WILLIAM E. MITCHELL 《American anthropologist》2005,107(1):177-180
52.
A device was designed to mark the growth zones of elongating seedling stems rapidly and accurately without exposing the tissue to mechanical stress. The device consists of a spring-loaded clamp, two plastic, grooved holders attached to either side of the open end of the clamp, a narrow foam pad to cushion and support the plant tissue, and a narrow nylon marking head. The marking head contains flat-topped ridges, 0·5 mm in width, machined such that the ridges are 2 mm (± 0·1) apart. Marking is accomplished using India ink. The procedure is rapid, precise, relatively inexpensive to build and operate, and does not require sophisticated or expensive instrumentation to obtain meaningful data. With practice, up to 100 seedlings may be uniformly marked in one hour. Tests using dark-grown soybean (Glycine max), sunflower (Helianthus annuus), and pea (Pisum sativum) show that the device does not itself cause a reduction in growth. 相似文献
53.
The Mahalanobis distance and elliptic distributions 总被引:3,自引:0,他引:3
54.
55.
56.
57.
Traditional views about the origin of eukaryotes and relationshipsbetween major "kingdoms" reflect interpretations of the fossilrecord and comparisons of phenotypic characters. This perspectiveis challenged by phylogenetic frameworks inferred from comparisonsof macromolecular sequences which share a common ancestry. Similaritiesbetween ribosomal RNA genes demonstrate that instead of beingrelatively recent biological inventions, eukaryotes representa discrete lineage that may be as old as the archaebacterialand eubacterial lines of descent. The diversity of protistansmall subunit rRNA sequences exceeds that seen within the entireprokaryotic world. The earliest branching lineages include diplomonads,microsporidians, and tritrichomonads. Yet, other major protistangroups diverged relatively late in the evolutionary historyof nucleated cells. Rather than being a concise evolutionaryassemblage, the Protista should be regarded as a collectionof paraphyletic lineages. In contrast, the Fungi, Plantae, andAnimalia are independent monophyletic groupings. They originatednearly simultaneously during a relatively recent period characterizedby a massive diversification of forms. This novel view of eukaryoticevolution suggests that a reliance upon large phenotypic differencesin delineating kingdoms can obscure true genealogical relationships.Instead of dividing eukaryotes into four or more major divisions,they should be considered as a single kingdom that encompassesa progression of independently diverging lineages. 相似文献
58.
JONES RUSSELL S.; COE LAURA L.; MONTGOMERY LADONNA; MITCHELL CARY A. 《Annals of botany》1990,66(6):617-622
Physical agitation applied as periodic seismic stress (shaking)reduced stem clongation, leaf expansion, and biomass accumulationby vegetative soybeans. Level of photon flux (PPF) influencedthe type and extent of plant response to mechanical stress.Plant parts responded differently as PPF varied between 135and 592 µmol m2 S1. Stem length was significantlyreduced by seismic stress at 135 µmol m2 s1but this effect was insignificant at higher PPFs. Reduced stemlength resulted from an inhibition of internode elongation.Stem diameter was unaffected by stress at the PPFs tested. Incontrast to effects on stem elongation, leaf area was insensitiveto stress treatments at 135 µmol m2 S1 butwas progressively inhibited by stress as PPF increased. Statisticallysignificant reductions in shoot f. wt and d. wt by seismic stressoccurred only at 295 µmol m2 S1. Root biomassaccumulation was not affected by seismic stress at any PPF usedin this study. Glycine max (L.) Merr. cv. Century 84, mechanical stress, photosynthetic photon flux, seismic stress, soybean 相似文献
59.
Comparison of the Surface Proteins and Glycoproteins On Erythrocytes of Calves Before and During Infection With Babesia Bovis 总被引:3,自引:0,他引:3
RUSSELL J. HOWARD BARRY J. RODWELL PATRICIA M. SMITH L. L. CALLOW GRAHAM F. MITCHELL 《The Journal of eukaryotic microbiology》1980,27(2):241-247
The surface proteins and glycoproteins on red cells from normal and Babesia bovis-infected calf blood have been compared. Several radiolabeling probes were used to label specifically external membrane molecules which were then separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified by autoradiography or fluorography. No differences were observed among the Coomassie Blue-stained membrane proteins of erythrocytes from individual uninfected calves. Comparison of red cells from these animals also indicated no qualitative differences in the surface proteins with accessible tyrosyl residues labeled by lactoperoxidase-catalyzed radioiodnation, although some quantitative variation in the uptake of radioactivity into particular proteins was observed. the major radioiodinated bands on normal bovine erythrocytes had Mr of 165, 130, 90, and 45 kiloDaltons. However, labeling of surface glycoproteins by the periodate/[3H]NaBH4 and galactose oxidase (± neuraminidase)/[3H]NaBH4 methods showed significant differences in the surface proteins of red cells from individual uninfected calves. of 14 animals tested, 5 had major labeled glycoproteins of unique Mr. No changes were observed in radioiodinated surface proteins of total red cell samples from infected calves with 0.5-6% parasitemia. Radioiodination of concentrated infected red cells from the same samples (concentrated by selective hypotonic lysis of uninfected erythrocytes in KC1) resulted in the labeling of 3 new surface proteins, with Mr of 118, 115, and 60 kiloDaltons. the same new 125I-labeled bands were identified on infected cells from 3 avirulent strains of B. bovis used in vaccine production. Furthermore, in concentrated infected cells there was very poor radiolabeling of major bands strongly labeled on uninfected cells (Mr 165, 130, and 90 kiloDaltons), suggesting parasite-induced loss of these proteins. Although there were some differences in 3H-labeled surface glycoproteins of red cells from normal and. B. bovis -infected blood, they were restricted to minor labeled bands and were not seen consistently. the labeled surface glycoproteins of concentrated infected cells were very similar to those of the uninfected red blood cells from infected blood. 相似文献
60.