全文获取类型
收费全文 | 36471篇 |
免费 | 2543篇 |
国内免费 | 7篇 |
专业分类
39021篇 |
出版年
2023年 | 200篇 |
2022年 | 344篇 |
2021年 | 630篇 |
2020年 | 470篇 |
2019年 | 515篇 |
2018年 | 1222篇 |
2017年 | 1064篇 |
2016年 | 1191篇 |
2015年 | 1607篇 |
2014年 | 1665篇 |
2013年 | 2170篇 |
2012年 | 2857篇 |
2011年 | 3101篇 |
2010年 | 1888篇 |
2009年 | 1724篇 |
2008年 | 1892篇 |
2007年 | 1833篇 |
2006年 | 1761篇 |
2005年 | 1550篇 |
2004年 | 1506篇 |
2003年 | 1324篇 |
2002年 | 1273篇 |
2001年 | 645篇 |
2000年 | 543篇 |
1999年 | 500篇 |
1998年 | 349篇 |
1997年 | 253篇 |
1996年 | 263篇 |
1995年 | 250篇 |
1994年 | 190篇 |
1993年 | 194篇 |
1992年 | 291篇 |
1991年 | 287篇 |
1990年 | 231篇 |
1989年 | 237篇 |
1988年 | 206篇 |
1987年 | 175篇 |
1986年 | 181篇 |
1985年 | 214篇 |
1984年 | 167篇 |
1983年 | 127篇 |
1982年 | 109篇 |
1981年 | 119篇 |
1980年 | 106篇 |
1979年 | 148篇 |
1978年 | 127篇 |
1976年 | 112篇 |
1975年 | 103篇 |
1974年 | 98篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
J Ignacio Andrés Jesús Alcázar José M Alonso Adolfo Díaz Javier Fernández Pilar Gil Laura Iturrino Encarna Matesanz Theo F Meert Anton Megens Victor K Sipido 《Bioorganic & medicinal chemistry letters》2002,12(2):249-253
Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described. 相似文献
42.
43.
Administration of choline chloride i.p. to rats causes a dose-dependent increase in the brain concentration of the neurotransmitter, acetylcholine (ACh). This increase is maximal (22% after a 60-mg/kg dose) 40 minutes after injection. These observations suggest that precursor availability may influence brain ACh synthesis, just as brain tryptophan and tyrosine levels have previously been shown to control the synthesis of brain serotonin and catecholamines. 相似文献
44.
Changes in quality of blood units containing one and a half or double amounts of glucose, stored at +4 degrees C for three weeks were analysed. An experimental preservative containing glucose and fructose (1 : 1) was also used. No other additives (purine or purine-nucleoside) were applied. A standard CPD preservative of the National Inst. of Haematology and Blood Transfusion was used as control. The pH, plasma free haemoglobin, K+ content, red blood cell (RBC) ATP and 2,3-DPG content, and RBC fragility index were determined in each sample. Increase of glucose concentration, the addition of fructose had a beneficial effect on blood pH, and on plasma free haemoglobin and K+ concentration. 150% glucose improved the 2,3-DPG maintenance in stored blood. 相似文献
45.
The proton NMR spectrum of glycine was monitored in D2O solution as a function of added Hg(II) concentration and pD. Reliable values were established for formation constants for the Hg(II):glycine 1:1 and 1:2 complexes and also for the mixed glycine/deuteroxy and glycine/chloride complexes. Ligand exchange kinetics are relatively slow, and it is possible to observe coupling to 199Hg through the coordinating nitrogen. The formation constants were used to calculate speciation over a range of ligand concentrations for the Hg(II)/glycine and Hg(II)/glycine/chloride systems. 相似文献
46.
L. Brzsnyi 《Biometrical journal. Biometrische Zeitschrift》1981,23(3):283-295
The paper deals with the analysis of 2 × 2 table measures and describes several new possibilities for applying them. An estimate is given for HELLMICH's asymmetric K-measure and a possible extension of the contingency concept in a special 2×2 case is presented. The concept introduced and the recommended computer application of the 2×2 table measures is supported by new results obtained for the relationship between jaw joint pains and noises examined earlier by F. SCHMID and C. ZSCHEGE. With a larger number of observations the opportunity arises for a deeper analysis of this dental problem using path analysis. The plan of evaluation and the conncetion between the variables examined is illustrated by a path-diagram. The association tables determined on the basis of the (C) values introduced during the examination of jaw joint disturbances using association analysis draw attention to the special role of the left side of mastication. The paper raises ideas for further generalisations and indicates where further research is needed. 相似文献
47.
48.
P Navarro-Rosinés C Roux A Bellemère 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》2001,324(5):443-451
An ultrastructural study of Weddellomyces epicallopisma (ascomata wall, asci, ascospores and vegetative hyphae), the first done on the family Dacampiaceae, confirms most of the observations made in light microscopy. Moreover it shows that ascospores are provided with an endospore (not visible in light microscope) and that the structure of the ascospore septum is more complex. The similarity of the wall structure between the ascospore and the hyphoid appendages, developed on the upper part of the ascoma, is emphasized. 相似文献
49.
A heterozygous mutant for the two- and six-rowed character was isolated in the barley cultivar Igri through application of sodium azide to isolated microspore cultures and posterior regeneration. Six-rowed and two-rowed homozygotic plants were subsequently identified in the self-pollinated M2 progenies of the original heterozygous M1. Detailed molecular markers confirmed the isogenic nature of this recovered mutant and the original cultivar Igri. A comparative study of the anther culture response of this six-rowed induced mutant vs. diploid 'Igri' was performed to assess whether the two- or six-rowed gene influences anther culture response in barley through a pleiotropic effect or via linkage disequilibrium. No significant differences for any of the recorded variables throughout the in vitro regeneration process were detected between the 'Igri' six-rowed mutant and any of their two-rowed isogenic lines. This suggests that row-type association with anther culture response in barley cultivars is due to the effect of a tight linkage with other genes directly responsible for androgenic response. 相似文献
50.