全文获取类型
收费全文 | 4326篇 |
免费 | 356篇 |
出版年
2022年 | 27篇 |
2021年 | 61篇 |
2020年 | 44篇 |
2019年 | 40篇 |
2018年 | 67篇 |
2017年 | 54篇 |
2016年 | 109篇 |
2015年 | 157篇 |
2014年 | 174篇 |
2013年 | 256篇 |
2012年 | 327篇 |
2011年 | 344篇 |
2010年 | 204篇 |
2009年 | 202篇 |
2008年 | 284篇 |
2007年 | 276篇 |
2006年 | 275篇 |
2005年 | 243篇 |
2004年 | 234篇 |
2003年 | 243篇 |
2002年 | 244篇 |
2001年 | 40篇 |
2000年 | 34篇 |
1999年 | 44篇 |
1998年 | 61篇 |
1997年 | 40篇 |
1996年 | 39篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 28篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 28篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1974年 | 16篇 |
1972年 | 13篇 |
1969年 | 9篇 |
排序方式: 共有4682条查询结果,搜索用时 31 毫秒
61.
Chandra M. Dwivedi Laurence T. Plante Roy L. Kisliuk Edward J. Pastore Surendra P. Verma Donald F.H. Wallach 《Archives of biochemistry and biophysics》1982,213(1):338-340
Dihydrofolate reductase from Lactobacillus casei and its complexes with NADPH and methotrexate yield well-resolved Raman spectra. The 1685-cm?1 Raman band assigned to the carboxamide of NADPH persists in the NADPH-enzyme binary complex but is absent from the NADPH-methotrexate-enzyme ternary complex. This is ascribed to stabilization of the polarized form of the carboxamide by H bonding to the NH and CO groups of Ala 6 and Ile 13 of the peptide backbone. 相似文献
62.
Isidrogalvia longiflora, a new combination based onAsagraea longiflora, is proposed. It is the first record ofIsidrogalvia from Bolivia. 相似文献
63.
Laurence J. Dorr 《Brittonia》1992,44(1):53-13
In 1843 S. B. Buckley (1809–1884) traveled up the St. Johns River, Florida in search of plants, shells, and possibly other
natural history objects. Buckley encountered many difficulties in interior Florida and his trip did not live up to his original
expectations. It was unfortunate that the took years to distribute his plant specimens, since few botanists or naturalists
had preceded him into that poorly explored region. 相似文献
64.
Laurence J. Dorr 《Brittonia》1992,44(1):1-13
In 1843 S. B. Buckley (1809–1884) traveled up the St. Johns River, Florida in search of plants, shells, and possibly other natural history objects. Buckley encountered many difficulties in interior Florida and his trip did not live up to his original expectations. It was unfortunate that the took years to distribute his plant specimens, since few botanists or naturalists had preceded him into that poorly explored region. 相似文献
65.
Summary The properties of surfactin, a biosurfactant lipopeptide, were highly modified in the presence of inorganic cations. The micellization of surfactin was favoured by monovalent and, especially by divalent cations with a modification of the molecular area at the air-water interface. Haemolysis of erythrocytes by surfactin was enhanced by low concentrations of divalent cations with an increase of the binding of the lipopeptide to membrane. Inorganic ions induced conformational rearrangements probably due to ion-surfactin associations which modify the surface-active properties. 相似文献
66.
Isolation and characterization of two individual glycoprotein components from human milk-fat-globule membranes. 下载免费PDF全文
Two individual glycoprotein components from human milk-fat-globule membranes (MFGM) has been purified by selectively extracting the membrane glycoproteins followed by lectin affinity chromatography and gel filtration on Sephadex G-200 in the presence of protein-disaggregating agents. The purified glycoprotein components, termed 'epithelial-membrane glycoprotein' (EMGP-155 and EMGP-39) have estimated molecular weights of 155 000 and 39 000 respectively, and yield a single band under reducing conditions on sodium dodecyl sulphate/polyacrylamide gel. EMGP-155 and EMGP-39 contain 21.0% and 7.0% carbohydrate by weight, with fucose (13.5%, 12.4%), mannose (3.7%, 6.2%), galactose (28.5%, 22.6%), N-acetylglucosamine (17.8%, 7.4%) and sialic acid (36.4%, 51.4%) of the carbohydrate moiety respectively. For both the glycoprotein components, aspartic and glutamic acid and serine are the major amino acid residues. 相似文献
67.
Johannes D. Veldhuis Patricia Klase Laurence M. Demers 《Prostaglandins & other lipid mediators》1982,23(3):319-327
Granulosa cells isolated from mature Graafian follicles of swine produced significant quantities of immunoreactive 6-keto-PGF1α under chemically defined conditions in vitro. Luteinizing hormone elicited a dose-dependent stimulation of 6-keto-PGF1α accumulation, but follicle stimulating hormone, prolactin, L-epinephrine, estradiol-17B, or PGE2 were devoid of effect. The time-dependent in vitro production of 6-keto-PGF1α by ovarian cells was susceptible to inhibition by indomethacin, U-51506, cycloheximide, and actinomycin D. These observations implicate granulosa cells in the specific and hormonally regulated production of prostacyclin. 相似文献
68.
69.
The status of Aesculus pavia var. flavescens, a set of yellow-flowered populations endemic to the Edwards Plateau of central Texas, was evaluated on the basis of comparative morphology, geography, flowering phenology, and pollination ecology. Plants of typical A. pavia have red, tubular flowers with exserted stamens and are effectively pollinated by ruby-throated hummingbirds. Plants of var. flavescens have yellow, campanulate flowers with included stamens that can be pollinated effectively by large bees. These ethological reproductive isolating mechanisms are further augmented by a difference in flowering time between the two sets of populations and by geographical restriction of the yellow-flowered plants to localities on the Edwards Plateau. The yellow and red-flowered plants constitute two morphologically distinct groups, despite evidence of limited introgression in counties along the Balcones Escarpment. A yellow-flowered plant discovered in coastal east Texas may indicate the mechanism by which var. flavescens originated, but this plant is much more closely comparable to typical red-flowered var. pavia than to the yellow-flowered plants on the Edwards Plateau. An evolutionary history of section Pavia of Aesculus is presented, and it is concluded that the yellow-flowered plants of central Texas are best regarded as a taxonomic variety. 相似文献
70.
Donald J. Brasch Hi Mui Chang Chaw T. Chuah Laurence D. Melton 《Carbohydrate research》1981,97(1):113-125
A galactan sulfate has been isolated from the seaweed Porphyra columbina, and its structure established by a combination of methylation, methanolysis, treatment with alkali followed by methylation, and 13C-n.m.r. spectroscopy. The polysaccharide belongs to the porphyran class, and consists of 3-linked β-d-galactosyl residues and 4-linked α-l-galactosyl residues. 3,6-Anhydro-l-galactose and l-galactose 6-sulfate residues total approximately half of the sugar units, the other half being made up of d-galactose and 6-O-methyl-d-galactose residues. Some evidence is presented that suggests that the galactan sulfate does not have a completely alternating structure. 相似文献