全文获取类型
收费全文 | 19516篇 |
免费 | 1335篇 |
国内免费 | 3篇 |
专业分类
20854篇 |
出版年
2023年 | 126篇 |
2022年 | 250篇 |
2021年 | 423篇 |
2020年 | 312篇 |
2019年 | 398篇 |
2018年 | 483篇 |
2017年 | 433篇 |
2016年 | 718篇 |
2015年 | 1025篇 |
2014年 | 1085篇 |
2013年 | 1392篇 |
2012年 | 1624篇 |
2011年 | 1562篇 |
2010年 | 948篇 |
2009年 | 880篇 |
2008年 | 1150篇 |
2007年 | 1105篇 |
2006年 | 1051篇 |
2005年 | 927篇 |
2004年 | 848篇 |
2003年 | 817篇 |
2002年 | 763篇 |
2001年 | 178篇 |
2000年 | 128篇 |
1999年 | 161篇 |
1998年 | 169篇 |
1997年 | 170篇 |
1996年 | 158篇 |
1995年 | 120篇 |
1994年 | 116篇 |
1993年 | 112篇 |
1992年 | 89篇 |
1991年 | 87篇 |
1990年 | 81篇 |
1989年 | 55篇 |
1988年 | 49篇 |
1987年 | 48篇 |
1986年 | 40篇 |
1985年 | 67篇 |
1984年 | 58篇 |
1983年 | 64篇 |
1982年 | 64篇 |
1981年 | 69篇 |
1980年 | 44篇 |
1979年 | 43篇 |
1978年 | 44篇 |
1977年 | 32篇 |
1975年 | 34篇 |
1974年 | 35篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
G De Luca M E Tira S Rindi R Salvini G Cetta A A Castellani 《The Italian journal of biochemistry》1984,33(6):403-412
The PGs produced in the growth medium by skin fibroblast cultures from two O.I. affected patients were investigated. After density gradient centrifugation, in the most dense fraction two main families of molecules appeared. The patient with the more severe clinical picture showed a lower content of the PGs with the highest molecular weight. The GAG composition of PGs was different in the two patients. The more severely affected one showed an increase of HS and a decrease of ChS content, in agreement with the lower value of galactosamine to glucosamine ratio in urinary GAGs. 相似文献
72.
Dion tomasellii sp. nov. occurs with an interrupted distribution from Guerrero to central Sonora. It is characterized by falcate to subfalcate leaflets. The populations from Sonora and northern Sinaloa are segregated asD. tomasellii var.sonorense on the basis of their narrower and glaucous leaflets. 相似文献
73.
Antonio Gomez Sanchez Manuel Mancera Francisco Rosado Manuel Rico 《Carbohydrate research》1984,134(1):75-82
3,4,5,6,7-Penta-O-acetyl-1,2-dideoxy-1-nitro-d-gluco-hept-1-enitol reacts with methyl acetoacetate in an unusual Michael reaction, giving the normal adduct (6), and a bicyclic derivative (9) that arises from quasi-dimerization of the former when a high concentration of the base is used. Acetylation of compound 9 gives the hydroxylamine O-acetate (10).From the reactions of 3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitro-d-galacto-hept-1-enitol with ethyl and tert-butyl acetoacetate, the normal adducts (7 and 8) were isolated. The structures of compounds 6 to 10 were established on the basis of their spectral properties (u.v., i.r., mass, and 1H- and 13C-n.m.r.) 相似文献
74.
75.
Summary
Aspergillus sp strains from decaying lemons were tested for extracellular pectinase production, testing differently pretreated lemon peel as the carbon source instead of pectin. It was found that the production of extracellular polygalacturonase was about the same and that of pectinesterase substantially higher when unwashed fresh lemon peel was used instead of pectin. The culture filtrate obtained showed a clarifying capacity similar to that of a commercial pectinase preparation, but the vitamin C of the juice was less affected by the treatment. 相似文献
76.
Renny T. Franceschi Hector F.De Luca Donna L. Mercado 《Archives of biochemistry and biophysics》1983,222(2):504-517
The interaction of the 1α,25-dihydroxyvitamin D3 receptor with immobilized calf thymus DNA has been compared with its sedimentation properties on hypotonic sucrose gradients. Forty to sixty percent of total hormone:receptor complexes formed at 4 °C were retained by DNA-cellulose and could be eluted by 0.18 to 0.2 m KCl. In contrast, heating preparations to 25 °C rapidly and irreversibly converted receptor to a form which bound hormone and DEAE-cellulose normally, but was unable to associate with DNA. Similarly, the ability of receptor to aggregate to a 6 S species was labile at 25 °C. Stabilization of receptor in the DNA binding aggregating form was accomplished using Ca2+, Mg2+, Mn2+, or Na2MoO4 while several protease and phosphatase inhibitors were ineffective. An examination of DNA binding properties of aggregating and nonaggregating receptor forms revealed that only receptor competent to enter into aggregates could bind DNA suggesting that a functional nucleic acid binding site, and, hence, a nucleic acid interaction is necessary for aggregate formation. Consistent with this view, an RNA:receptor interaction appears to be involved in formation of the 6 S complex since removal of RNA by ribonuclease treatment or purification of receptor reduced aggregation, an effect that could be reversed by addition of purified RNA. 相似文献
77.
Emilio Román Galán Jaun A. Galbis Pérez Mariá A. Arévalo Arévalo 《Carbohydrate research》1983,116(2):255-262
The reaction between 2-(benzylamino)-2-deoxy-d-glycero-l-gluco-heptose and 5,5-dimethyl-1,3-cyclohexanedione yields 1-benzyl-4,5,6,7-tetrahydro-6,6-dimethyl-2-(d-galacto-pentitol-1-yl)-indol-4-one (2). Acid-catalyzed, intramolecular dehydration of 2 under kinetically controlled conditions gives 1-benzyl-4,5,6,7-tetrahydro-2-α-d-lyxofuranosyl-6,6-dimethylindol-4-one; the anomeric configuration of this compound is only suggested. When the dehydration reaction is conducted under thermodynamically controlled conditions, it produces a 1:1 mixture of the α- and β-d-lyxopyranosyl compounds. The structures of the new compounds were elucidated by chemical and physical methods. 相似文献
78.
Factors Determining Annual Changes in Bacterial Photosynthetic Pigments in Holomictic Lake Cisó, Spain 下载免费PDF全文
The pigments and biomass of anoxygenic phototrophic bacteria were measured during a year cycle in Lake Cisó (Girona, Spain). Two genera, Chromatium and Chlorobium, accounted for most of the bacterial population. The bacteria were present throughout the year despite complete mixing of the lake during fall and winter. This was possible because the sulfide production in the sediment was high enough to make the lake anaerobic to the very surface. Solar radiation, temperature, and biomass of Chromatium sp. were found to be important in determining pigment concentrations by correlation analysis. Sulfide concentration and biomass of Chlorobium spp. were found to be unimportant. A path analysis was performed to determine what percentage of the variability of pigments could be explained by the variables studied. Since a high percentage could be explained, it was possible to conclude that solar radiation, temperature, and biomass of Chromatium sp. were the main variables. 相似文献
79.
Systemic administration of the enkephalin analog FK 33.824 was previously shown to inhibit ACTH secretion in man. In this study, the direct action of this analog on cortisol release was studied. The enkephalin analog (1 uM and 10 uM) did not influence basal or ACTH-stimulated cortisol production by cultured isolated adrenocortical cells prepared from the hyperplastic adrenal glands from three patients with Cushing's disease. Naloxone (10 uM) had also no direct effect on cortisol release. It is concluded that the met-enkephalin analog used in this study and naloxone do affect the hypothalamo-pituitary-adrenal axis via a central effect. 相似文献
80.
Lucio Annunziato Salvatore Amoroso Gianfranco Di Renzo Filomena Argenzio Caterina Aurilio Antonio Grella Aldo Quattrone 《Life sciences》1983,33(26):2651-2655
In humans the release of growth hormone (GH) elicited by dopamine (DA) and DA agonists may represent a reliable model to assess change in sensitivity of DA receptors. We now report that in chronic alcoholics, 4–7 days after the suspension of alcohol consumption, the increase of GH response to DA infusion was higher than that seen in non alcoholic volunteers. The specificity of this GH response to DA administration was demonstrated by the use of domperidone, a novel peripheral antagonist of DA receptors. These results suggest the development of hyper-responsiveness of DA receptors involved in the control of GH secretion in chronic alcoholics during the later phases of the “withdrawal syndrome”. 相似文献