全文获取类型
收费全文 | 2487篇 |
免费 | 123篇 |
国内免费 | 2篇 |
出版年
2023年 | 5篇 |
2021年 | 21篇 |
2020年 | 16篇 |
2019年 | 21篇 |
2018年 | 35篇 |
2017年 | 20篇 |
2016年 | 46篇 |
2015年 | 85篇 |
2014年 | 82篇 |
2013年 | 165篇 |
2012年 | 161篇 |
2011年 | 139篇 |
2010年 | 81篇 |
2009年 | 110篇 |
2008年 | 140篇 |
2007年 | 157篇 |
2006年 | 145篇 |
2005年 | 159篇 |
2004年 | 146篇 |
2003年 | 148篇 |
2002年 | 153篇 |
2001年 | 42篇 |
2000年 | 41篇 |
1999年 | 44篇 |
1998年 | 38篇 |
1997年 | 37篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 20篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 10篇 |
1975年 | 4篇 |
1971年 | 4篇 |
1965年 | 3篇 |
排序方式: 共有2612条查询结果,搜索用时 15 毫秒
1.
Abstract. A technique for fine-scale vegetation mapping with the aid of low-altitude aerial photography was developed. The procedure is as follows: 1. The site is divided into a lattice pattern - in case the site is too large to fit into a single photograph with satisfactory resolution. The coordinates of every lattice point are surveyed to be used as control points for geometric correction. A photograph of each block of the lattice is taken using a remote-controlled camera system lifted by a captive helium balloon. 2. The vegetation is classified on the basis of a phytosociological survey. 3. The shapes and locations of vegetation patches appearing in the photographs are entered into a computer, using a digitizer. A geometric correction is carried out through coordinate transformation referring to the coordinates of the control points and subsequently a draft vegetation map is produced. Finally, discrepancies are corrected and the map is coloured to produce the final version of the vegetation map. This technique was applied to vegetation mapping at a bar, 500 m wide and 2 km long, in the river Yoshino in Shikoku, Japan. A fine-scale vegetation map was obtained and used to analyse the influence of plants on geomorphic processes and community-specific hydrogeomorphic conditions on the bar. 相似文献
2.
Uptake of sodium cefoxitin, D-phenylalanine and insulin into human red blood cells was significantly enhanced by the presence of salicylate and 5-methoxysalicylate in the medium. The mechanism of adjuvant action appeared to depend on an affinity between the adjuvant and the protein fraction in the erythrocyte membrane. The inhibitory effect of DIDS and phlorizin on the salicylate-enhanced uptake of these compounds strongly suggests that the ability of salicylate to permeate the membrane may be essential for it to act as an adjuvant. 相似文献
3.
4.
Circulating tumor cells (CTCs), shed from primary tumors and disseminated into peripheral blood, are playing a major role in metastasis. Even after isolation of CTCs from blood, the target cells are mixed with a population of other cell types. Here, we propose a new method for analyses of cell mixture at the single-cell level using a microfluidic device that contains arrayed electroactive microwells. Dielectrophoretic (DEP) force, induced by the electrodes patterned on the bottom surface of the microwells, allows efficient trapping and stable positioning of single cells for high-throughput biochemical analyses. We demonstrated that various on-chip analyses including immunostaining, viability/apoptosis assay and fluorescent in situ hybridization (FISH) at the single-cell level could be conducted just by applying specific reagents for each assay. Our simple method should greatly help discrimination and analysis of rare cancer cells among a population of blood cells. 相似文献
5.
6.
7.
Summary An activated carbon column was utilized for the synthesis of disaccharides by use of a reversed hydrolysis activity of an immobilized -galactosidase column in order to shift the equilibrium to the direction of condensation. The yields of lactulose and allo-lactulose from galactose and fructose, and N-acetyl lactosamine and N-acetyl allolactosamine from galactose and N-acetyl glucosamine, were 11.3% and 10.0%, respectively. 相似文献
8.
Abstract Biovar A strains of Fusobacterium necrophorum exhibited high hydrophobicity when examined by the method of Rosenberg et al. Biovar B strains showed a lower cell surface hydrophobicity than biovar A strains. Biovar B strains were divided into 2 groups according to their hydrophobic activity. The strains of biovar A and the first group of biovar B were increasingly removed from aqueous phase to octane phase by increasing the volume of octane, but the turbidity of the second group of biovar B was not significantly affected. The hydrophobicity of biovar A strains decreased on heating at 60 and 100°C for 30 min. 相似文献
9.
ß-Tubulins from fourteen benomyl-resistant strainsof the homobasidiomycete Coprinus cinereus, which carry thebenA, benB, benC or benD mutations, were analyzed by urea SDS-PAGEor isoelectric focusing and subsequent immunoblot analysis.Electrophoretic aberrations in a major ß-tubulin isotype,denoted ß1 were found in two strains, BEN154 and BEN215,both of which carry benomyl resistance mutations in benA + Theaberrations of ß1 in BEN154 and BEN215 cosegregatedwith benomyl resistance among the progeny of outcrosses of BEN154 and BEN215 to wild type, indicating that the ß1aberrations were caused by the benA mutations. Both the mutantand wild-type ß1 tubulins were present in the heterozygousdikaryons, BEN 154/wild-type and BEN215/wild-type, ruling outpost-translational modification as a possible cause for theaberrations in ß1. Thus, we conclude that benA isa structural gene for ß1. Transhyphal migration ofnuclei in dikaryosis was blocked in the mycelia of BEN 154 andin its progeny that carried benA (ß1 mutation), demonstratingthat microtubules are involved in the migration process. Nuclearmigration in dikaryosis seems to differ in terms of mechanism,at least in part, from the migration of tetrad nuclei from basidiainto prespores during formation of basidiospores and from themigration of nuclei from basidiospores into hyphae during germination,because a benA mutation blocked the former without affectingthe latter two processes. (Received May 19, 1989; Accepted August 30, 1989) 相似文献
10.
Oka Kotaro; Ikeshima Hiroko; Ishikawa Hideo; Ohta Eiji; Sakata Makoto 《Plant & cell physiology》1988,29(5):771-775
We showed that the surface charge density of protoplasts canbe estimated by the 9-aminoacridine method. The estimated surfacecharge density of the protoplasts isolated from elongating regionsof Vigna mungo root was 39 ? 8 mC/m2. The negative surfacecharge density increased when protoplasts were treated withglutaraldehyde or when EDTA was added to the protoplast suspensionmedium. These results support the validity of our estimationof the surface charge density of protoplasts by the 9-aminoacridinemethod. The concentration of amino groups at the surface ofthe protoplasts was estimated to be 34 mC/m2. (Received June 19, 1987; Accepted April 11, 1988) 相似文献