全文获取类型
收费全文 | 16266篇 |
免费 | 1241篇 |
国内免费 | 6篇 |
出版年
2023年 | 135篇 |
2022年 | 114篇 |
2021年 | 277篇 |
2020年 | 214篇 |
2019年 | 236篇 |
2018年 | 420篇 |
2017年 | 401篇 |
2016年 | 479篇 |
2015年 | 569篇 |
2014年 | 655篇 |
2013年 | 940篇 |
2012年 | 1276篇 |
2011年 | 1306篇 |
2010年 | 774篇 |
2009年 | 619篇 |
2008年 | 1092篇 |
2007年 | 1120篇 |
2006年 | 1069篇 |
2005年 | 961篇 |
2004年 | 936篇 |
2003年 | 880篇 |
2002年 | 770篇 |
2001年 | 182篇 |
2000年 | 243篇 |
1999年 | 182篇 |
1998年 | 146篇 |
1997年 | 93篇 |
1996年 | 101篇 |
1995年 | 109篇 |
1994年 | 89篇 |
1993年 | 79篇 |
1992年 | 93篇 |
1991年 | 73篇 |
1990年 | 68篇 |
1989年 | 50篇 |
1988年 | 48篇 |
1987年 | 46篇 |
1986年 | 36篇 |
1985年 | 48篇 |
1984年 | 59篇 |
1983年 | 38篇 |
1982年 | 51篇 |
1981年 | 48篇 |
1980年 | 53篇 |
1979年 | 41篇 |
1978年 | 42篇 |
1977年 | 35篇 |
1976年 | 38篇 |
1975年 | 38篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
J. Couturier B. Dutrillaux Pascale Garber Odile Raoul Marie-Françoise Croquette J. C. Fourlinnie E. Maillard 《Human genetics》1979,49(3):319-326
Summary A familial translocation t(X;21)(q2700;q11) is studied. A girl, trisomic for almost all the chromosome 21, has a mildly abnormal phenotype. A second girl, phenotypically abnormal, is monosomic for the juxtacentromeric region of chromosome 21 only. A comparison of the replication pattern and of the activity of superoxide dismutase (gene located on chromosome 21) shows a clear correlation between late replication, gene inactivation and phenotype expression of chromosome 21.This work has been supported by CNRS (ERA 47) 相似文献
212.
213.
Selective, double irradiation allows the assignment of most 13C-n.m.r. signals in a series of per-O-acetyl disaccharides composed of two D-glucose residues linked α-(1→3), β-(1→3), α-(1→4), β-(1→4), α-(1→6), β-(1→6), and α,α-(1→1). The main influences that affect the chemical shifts are discussed and the spectra of β-cellobiose octaacetate and β-maltose octaacetate are compared to those of cellulose and amylose triacetate, respectively, to show the possibilities and limitations of a disaccharide model for the interpretation of the 13C-spectrum of a polymer. 相似文献
214.
Treatment of 2,5-anhydro-1-bromo-1-deoxy-2,3-O-isopropylidene-1-p-nitrophenylhydrazono-d-ribose with methyl acetylenecarboxylate gave methyl 3-(2,3-O-isopropylidene-β-d-erythrofuranosyl)-1-p-nitrophenylpyrazole- (8) and 5-carboxylate (9). Amidification at C-5 of 8 was easier than at C-4 of 9. Similarly, dimethyl 3-(2,3-O-isopropylidene-β-d-erythrofuranosyl)- 1 - p-nitrophenylpyrazole-4,5-dicarboxylate gave specifically a 5-carbamoyl derivative, the structure of which was established by comparison of the 13C-n.m.r.spectrum with those of a series of glycosylpyrazoles. The correlation between the experimental values of the chemical shifts of the carbon atoms of the pyrazole ring and the values calculated by addition of the contributions of the various groups linked to the ring was better (R 0.98) than the correlations obtained by calculation by the CNDO/2 method of the total electron population (R 0.92) or of the π-electron population of each carbon atom (R 0.85). 相似文献
215.
The manner in which centromere regions of mitotic chromosomes are distributed with respect to the age of their DNA was studied. Cells of the Indian deer, Muntiacus muntjak, were grown in the presence of bromodeoxyuridine (BrdU) for two generations and stained with the fluorescent dye Hoechst 33258. Chromatids containing granddaughter DNA appear dim when compared with those containing grandparental DNA. The frequencies of the various anaphase patterns of bright and dim centromere regions were binomially distributed, indicating random distribution of chromatids with respect to the age of their DNA templates. 相似文献
216.
217.
218.
Antônio A. Lins Mesquita Wanderley Gonçlves De Oliveira Rosa M. Taveira Neiva Otto R. Gottlieb 《Phytochemistry》1975,14(3):803-806
The wood of Tovomita pyrifolium (Guttiferae) contains the novel tovopyrifolins A [1,6-dihydroxy-7-methoxy-5-prenyl-6′,6′-dimethylpyrano (2′,3′:3,2)xanthone], B (1,5-dihydroxy-3,4-dimethoxyxanthone) and C (1,3,5-trihydroxy-2-methoxyxanthone) and also the known tovophyllins A and B [structure revised to 1,6-dihydroxy-5-prenyl-6′, 6′-dimethylpyrano(2′,3′:3,2)-6″,6″-dimethylpyrano(2″,3″:7,8)xanthone]. 相似文献
219.
J. François 《Journal of insect physiology》1975,21(9):1535-1546
The introduction of inert foreign objects into the thorax of the thysanuran Thermobia domestica provoked the formation of a cellular capsule, the development and fine structure of which were examined.Encapsulation at first simply results from the accumulation of blood cells around the implant. It is possible to distinguish 48 hr later four regions in the cellular capsule: (1) An exterior layer including normal haemocytes. (2) An intermediate layer formed by homogeneous intercellular electron-dense material and by stretched haemocytes. These haemocytes have numerous microtubules, without any granular particles, and are linked together by desmosomes. (3) An interior layer of cells in the process of necrosis and rich in lysosomes. (4) A very thin limiting layer tentatively interpreted as melanin.The large number of haemocytes devoid of the specific features of the fibroblasts and the very important reduction of the acellular material without collagen fibrils distinguish clearly the cellular capsules of the Insecta from the granuloma of the Vertebrata and other groups. 相似文献
220.