全文获取类型
收费全文 | 13008篇 |
免费 | 1416篇 |
国内免费 | 7篇 |
专业分类
14431篇 |
出版年
2022年 | 87篇 |
2021年 | 157篇 |
2020年 | 159篇 |
2019年 | 236篇 |
2018年 | 263篇 |
2017年 | 275篇 |
2016年 | 358篇 |
2015年 | 577篇 |
2014年 | 596篇 |
2013年 | 812篇 |
2012年 | 809篇 |
2011年 | 715篇 |
2010年 | 577篇 |
2009年 | 524篇 |
2008年 | 627篇 |
2007年 | 641篇 |
2006年 | 622篇 |
2005年 | 668篇 |
2004年 | 629篇 |
2003年 | 688篇 |
2002年 | 691篇 |
2001年 | 129篇 |
2000年 | 117篇 |
1999年 | 168篇 |
1998年 | 212篇 |
1997年 | 157篇 |
1996年 | 149篇 |
1995年 | 150篇 |
1994年 | 126篇 |
1993年 | 96篇 |
1992年 | 140篇 |
1991年 | 110篇 |
1990年 | 97篇 |
1989年 | 102篇 |
1988年 | 86篇 |
1987年 | 91篇 |
1986年 | 85篇 |
1985年 | 105篇 |
1984年 | 114篇 |
1983年 | 92篇 |
1982年 | 111篇 |
1981年 | 127篇 |
1980年 | 94篇 |
1979年 | 100篇 |
1978年 | 97篇 |
1977年 | 84篇 |
1976年 | 88篇 |
1975年 | 55篇 |
1974年 | 74篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Abstract— Young mice treated with hydrocortisone (50 mg/kg) subcutaneously for 10 days showed a doubling of brain glucose. Brain phospho-creatine, glucose-6-phosphate, and ATP increased slightly. Brain glycogen and lactate were unchanged. Total energy reserve of the brain was 23 per cent higher than the control value. Liver glycogen was increased 47 per cent; liver and blood glucose levels were 11 per cent lower than in control animals. Since the animals showed no evidence of sedation, these findings suggest a facilitated transport of glucose from blood into the brain under the influence of hydrocortisone. Other possible explanations include an inhibition of the hexose monophosphate shunt and a proportionate decrease in both the oxidative and glycolytic pathways of the brain, but it was concluded that these explanations are less likely. 相似文献
103.
Jean J. Pasteels 《Cell and tissue research》1969,102(4):594-600
Résumé Dans toutes les cellules mucipares de la branchie de Mytilus edulis L., quelques grains de secretion montrent une activité phosphatasique acide, décelée par la méthode cytochimique de Gomori appliquée au microscope électronique. A la proximité de ces grains se trouvent des dictyosomes golgiens où une activité phosphatasique se décèle dans les parties latérales des cisternes et dans les vésicules qui en émanent. Au moment de l'excrétion, tous les grains de sécrétion confluent et la phosphatase acide active est incluse dans l'amas de mucus expulsé dans la cavité palléale. Le rôle digestif de ces amas — et non purement mécanique — peut ainsi être considéré comme hautement probable. De telles manifestations enzymatiques sont totalement absentes dans le tapis muqueux ainsi que dans les cellules qui le constituent.
Excretion of acidic phosphatase by the goblet-cells of the gill of Mytilus edulis L.An electron microscopic study
Summary Acidic phosphatase activity detected by the Gomori method applied to E.M., has been found in a few secretion granules of each goblet cell of the gill of Mytilus edulis L. In the close proximity of those granules golgian dictyosomes always occur, with acidic phosphatase activity in the lateral parts of the cisternae and in the vesicles arising from the latter. When the mucus is extruded, active and non active secretion granules are mixed and thus, acidic phosphatase activity is regularly found in the mucous tufts extruded into the palleal cavity. Therefore the digestive role — and not merely mechanic — of the mucous tufts may be considered as highly probable. Conversely, the secretion granules from which arises the continuous mucous cover of the epithelium and this cover also, are entirely devoid of any acidic phosphatase activity.相似文献
104.
Platelet aggregation has been related to blood coagulation studies in patients on nicoumalone, a coumarin anticoagulant. Aggregation studies were performed by means of Chandler''s tube and the adenosine diphosphate (A.D.P.)-induced optical density method. Platelet aggregation in Chandler''s tube has been shown to be quite different from A.D.P. aggregation and to be dependent on the “intrinsic” (blood) clotting system. When the intrinsic system was depressed by coumarin anticoagulant, aggregation was delayed in Chandler''s tube, but patients with a predominantly “extrinsic” (tissue) system defect gave normal results even when their prothrombin time was excessively prolonged. In contrast there was an increased response to A.D.P. in the anticoagulated patients.The study emphasizes the different mechanisms of platelet aggregation, which we have referred to as coagulation-induced and A.D.P.-induced aggregation. It also shows the limitations of routine control of oral anticoagulants by prothrombin time alone, as the coagulation-induced platelet aggregation appears to be quantitatively related to the overall level of clotting factors in the intrinsic system and independent of the extrinsic system. 相似文献
105.
Reductive Pentose Cycle and Formate Assimilation in Rhodopseudomonas palustris 总被引:2,自引:0,他引:2 下载免费PDF全文
Rhodopseudomonas palustris assimilated formate autotrophically as carbon dioxide and hydrogen arising from the activity of the formic hydrogenlyase system. Kinetic analyses of cell suspensions pulse-labeled with (14)C-formate or (14)C-bicarbonate showed similar distributions of incorporated radioactivity. In both cases phosphate esters were the first assimilation products. Ribulose diphosphate carboxylase, phosphoribose isomerase, and phosphoribulokinase, characteristic enzymes of the reductive pentose cycle, were present in extracts of cells grown on formate. 相似文献
106.
Jean Hubert 《Cell and tissue research》1970,107(2):265-283
Résumé Les gonocytes primaires sont relativement pauvres en polysomes et l'ergastoplasme granulaire est très réduit. Le reticulum endoplasmique de type lisse se développe au cours du développement embryonnaire. L'appareil de Golgi est bien représenté et localisé au niveau de la calotte juxtanucléaire mitochondriale. Les liposomes cytoplasmiques sont très nombreux.Cette étude précise la structure du nucléole «annulaire» et de la «masse paranucléolaire» observés en microscopic photonique. Des modifications nucléolaires sont constatées au cours du développement embryonnaire. Certains aspects ultrastructuraux sont vraisemblablement en rapport avec le déplacement autonome des gonocytes. La signification physiologique du nucléole «annulaire» et de la «masse paranucléolaire» est envisagée.
Ultrastructural study on the primordial germ cells during embryonic development of Lacerta vivipara Jacquin
Summary The primordial germ cells of Lacerta vivipara have relatively few free polysomes and little ergastoplasm. Smooth endoplasmic reticulum increases during embryonic development. The Golgi apparatus is well developed and lies close to the mitochondrial juxtanuclear cap. This study shows the ultrastructure of the ring-shaped nucleoli and the masse paranucléolaire. Modifications in nucleolar structure are observed during embryonic development. Some ultrastructural features are probably related to the ameboid movement of the primordial germ cells. The physiological meaning of the ring-shaped nucleoli and the masse paranucléolaire is considered.
Avec la collaboration technique de Mme. M. Hubert. 相似文献
107.
Differential Tolerance of Streptomycetes to Sodium Chloride as a Taxonomic Aid 总被引:2,自引:1,他引:1 下载免费PDF全文
A survey was made of the NaCl tolerance of approximately 1,300 Streptomyces strains belonging to 313 species. The growth medium of the organisms was supplemented with a graded series of NaCl concentrations (4, 7, 10, and 13%). Only 1.8% of the species could not tolerate 4% NaCl; 26.9% could grow at a maximum of 4%; 49.7% could tolerate a maximum of 7%; 18.8% could grow at a maximum of 10%; and only 2.8% could tolerate 13% NaCl. In evaluating the relationships of NaCl tolerance to various taxonomic features, higher tolerance was statistically associated with the "yellow" and possibly the "white"-spored streptomycetes, whereas the "red"-spored series tended to have lesser tolerance. Higher tolerance was also indicated for spiny-spored species, as a group, than for smooth-spored forms. Likewise, nonproducers of melanin, collectively, were more NaCl tolerant than melanin-producing species. Uniformity of test responses between strains of species studied suggested the usefulness of NaCl tolerance as a taxonomic criterion. 相似文献
108.
Jojoba plants of the selection ‘Vista’ were grown for two years in the greenhouse at four levels of soil salinity. All plants reached anthesis with no symptom of major injury because of the treatments. The following changes were noted on treated plants: Leaves were thicker, with larger secretory and palisade cells. They had fewer stomata per unit area, smaller vascular cylinder and vascular cells, and discontinuous layers of secretory cells. Stems were thinner, with smaller pith diameter, smaller pith cells, and smaller vessel elements. Both leaves and stems had a higher moisture content. A higher accumulation of Cl and Na ions was observed in both leaves and stems. Mg ions decreased in leaves but increased in stems. Ca ions increased in leaves only. 相似文献
109.
110.