全文获取类型
收费全文 | 2075篇 |
免费 | 129篇 |
出版年
2022年 | 6篇 |
2021年 | 22篇 |
2020年 | 5篇 |
2019年 | 13篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 33篇 |
2015年 | 67篇 |
2014年 | 89篇 |
2013年 | 85篇 |
2012年 | 140篇 |
2011年 | 151篇 |
2010年 | 103篇 |
2009年 | 83篇 |
2008年 | 124篇 |
2007年 | 127篇 |
2006年 | 145篇 |
2005年 | 125篇 |
2004年 | 130篇 |
2003年 | 134篇 |
2002年 | 105篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 23篇 |
1997年 | 29篇 |
1996年 | 32篇 |
1995年 | 18篇 |
1994年 | 16篇 |
1993年 | 17篇 |
1992年 | 26篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1980年 | 12篇 |
1979年 | 16篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 9篇 |
1971年 | 10篇 |
排序方式: 共有2204条查询结果,搜索用时 15 毫秒
51.
Morphogenesis and expression of the alpha and beta keratin polypeptides are controlled by epidermal-dermal interactions during development of avian skin derivatives. We have examined the relationship between morphogenesis of the embryonic feather and expression of the feather alpha and beta keratins by routine histology, indirect-immunofluorescence, and SDS-PAGE. Initially beta keratins are expressed only in the feather sheath. Following barb ridge morphogenesis beta keratins can be detected in the barb ridge, coincident with the differentiation of barb ridge cells into eight distinct morphological types. Beta keratinization occurs in gradients; from feather apex to base, and from periphery of the barb ridge to the interior. The onset of beta keratinization in the barb ridges is paralleled by an increase in the major feather beta keratin polypeptides, as detected by SDS-PAGE. The alpha keratins are present in both the periderm and feather sheath at early stages of feather development, but become greatly reduced after hatching, when the down feather emerges from the sheath. 相似文献
52.
53.
Qing-Sheng Ma Andrew W. B. Johnston Gerd Hombrecher J. Allan Downie 《Molecular & general genetics : MGG》1982,187(1):166-171
Summary Mutants of Rhizobium leguminosarum which failed to fix nitrogen within nodules on peas were isolated following the insertion of the transposon Tn5 into pRL1JI, a Rhizobium plasmid known to carry the genes for nitrogenase. The sites of the Tn5 insertions were identified by restriction endonuclease mapping of cloned fragments of DNA from the mutant strains. One group of mutants was located within 4 kilobases of the structural genes for nitrogenase and another was located about 30 kilobases from this region. Two mutants from the first group, one of which appeared to be affected in a nitrogenase gene, induced nodules that contained bacterioids, but the number of plant cells containing bacteroids was less than in a normal nodule. Another group of mutants, which was located about 30 kilobases from the nitrogenase genes failed to form bacterioids. Electron microscopy of the nodules induced by these mutants indicated that there was a defect in their release from infection threads. 相似文献
54.
Gerd N. La Mar Kiyoshi Nagai Thomas Jue David L. Budd K. Gersonde H. Sick T. Kagimoto A. Hayashi F. Taketa 《Biochemical and biophysical research communications》1980,96(3):1172-1177
The proton nmr spectra of the synthetic valency hybrids, α2(β+CN)2, (α+CN)2β2 of hemoglobin A and the natural valency hybrids of the mutant hemoglobins Boston, Iwate and Milwaukee have led to the unambiguous assignment of the two proximal histidyl imidazole exchangeable proton signals at 64 and 76 ppm to individual α and β subunits, respectively. New single non-exchangeable proton resonances detected in the extreme downfield region of the spectra of Hbs Boston and Iwate are tentatively assigned to the coordinated tyrosine of the mutated α chains. 相似文献
55.
56.
Below-ground carbon distribution in barley (Hordeum vulgare L.) with and without nitrogen fertilization 总被引:5,自引:0,他引:5
Gerd Johansson 《Plant and Soil》1992,144(1):93-99
The distribution of net assimilated C in barley (Hordeum vulgare L.) grown at two N-levels was determined in a growth chamber. The N-fertilization involved 0 and 3.61 mol N g-1 dry soil. After growth for seven weeks in an atmosphere with continuously 14C-labelled CO2, 14C was determined in shoots, roots, rhizosphere respiration and soil. At the low N-level, 32% of the net assimilated 14C was translocated below ground, whereas at the high N-level 27% was translocated below ground. The release of C from roots (root respiration, microbial respiration originating from decomposition of 14C-labelled root material and 14C remaining in soil) was greater with no N-supply (19% of net assimilated 14C) than in the treatment with N-supply (15%). Thus, the effect of N-supply on both translocation of assimilated 14C below ground and the release of 14C from growing roots was relatively small. 相似文献
57.
Summary In man, apolipoprotein A-IV is characterized by a genetically determined polymorphism controlled by two codominant alleles. Two isoforms of this apolipoprotein, designated A-IV-1 and A-IV-2, can be identified by isoelectric focusing. Among 1000 healthy factory workers participating in an epidemiological study, A-IV-1 (genotype 1-1) was observed in 85%; A-IV-2 (genotype 2-2), in 0.5%; and A-IV-1 in combination with A-IV-2 (genotype 1–2), in 14%. In four nonrelated subjects, an apolipoprotein A-IV variant (A-IV-Münster), characterized by a slightly more basic isoelectric focusing behavior than A-IV-2, was detected in combination either with A-IV-1 or A-IV-2. Mendelian inheritance of this variant could be demonstrated. 相似文献
58.
Genetic control of human apolipoprotein E polymorphism: Comparison of one-and two-dimensional techniques of isoprotein analysis 总被引:16,自引:0,他引:16
Summary Genetic polymorphism of human apolipoprotein E (apo E) has previously been demonstrated by one-dimensional isoelectric focusing (Utermann et al. 1977b) and by two-dimensional electrophoresis of apolipoproteins (Zannis et al. 1981), but the relationship between the results obtained by these methods remained unclear. We therefore performed comparative phenotyping by one-dimensional and two-dimensional electrophoresis. Apoproteins from very low-density lipoproteins (apo VLDL) prepared by ultracentrifugation or from an apo Erich lipoprotein fraction prepared by heparin/Mg++ precipitation, were used as a source of apo E. Six common phenotypes designated apo E-4/4, apo E-N/N, apo E-D/D, apo E-4/N, apo E-4/D, and apo E-N/D were differentiated irrespective of the technique used or the source of apolipoproteins, but the two-dimensional electrophoresis of apo VLDL and apo VLDL which had been treated with neuraminidase was the key for the correct genetic interpretation of those phenotypes exhibiting the E4 isoform of the protein. Each phenotype is characterized by the presence of either one or two of three major isoforms E2, E3, and E4 and by the presence of several minor sialylated forms of these proteins (apo Es) that have higher apparent molecular weights. The unsialylated major isoform apo E2 does not only differ in charge but also has a higher apparent mol.wt. (about 34,500) than the major isoforms apo E3 and apo E4 (mol. wt. about 33,000). Family studies including 90 matings with a total of 203 offspring confirmed the genetic one locus model of Zannis et al. (1981). Apo E phenotypes are controlled by three autosomal codominant alleles apo Ed, apo En, and apo E4 that specify for the E2, E3, and E4 isoforms respectively. Phenotypes apo E-D/D,-N/N, and-4/4 represent homozygotes and phenotypes apo E-4/N,-4/D, and-N/D heterozygotes for these alleles.The frequencies of apo E alleles in 1031 blood donors were apo E4=0.150, apo En=0.773, and apo Ed=0.077. Homozygosity for the allele apo Ed is associated with hyperlipoproteinemia type III. Hence a large number of the population (about 1%) are at risk for this specific lipoprotein disorder that is associated with premature atherosclerosis and xanthomatosis. 相似文献
59.
60.
Biological activity of the antitumor protein neocarzinostatin coupled to a monoclonal antibody by N-succinimidyl 3-(2-pyridyldithio)-propionate 总被引:6,自引:0,他引:6
Gundram Jung Wolfgang Köhnlein Gerd Lüders 《Biochemical and biophysical research communications》1981,101(2):599-606
The chromophore free apoprotein of neocarzinostatin was coupled to monoclonal IgG1 antibody using N-Succinimidyl 3-(2-pyridyldithio)-propionate as heterobifunctional reagent. After coupling active chromophore was reassociated with the apoprotein. We present here experimental evidence that the hybrid protein retains biological activity as measured by the degradation of T2-DNA and bacteriostatic action. 相似文献