全文获取类型
收费全文 | 6269篇 |
免费 | 662篇 |
国内免费 | 818篇 |
专业分类
7749篇 |
出版年
2024年 | 28篇 |
2023年 | 166篇 |
2022年 | 221篇 |
2021年 | 278篇 |
2020年 | 269篇 |
2019年 | 274篇 |
2018年 | 282篇 |
2017年 | 265篇 |
2016年 | 240篇 |
2015年 | 251篇 |
2014年 | 283篇 |
2013年 | 496篇 |
2012年 | 201篇 |
2011年 | 268篇 |
2010年 | 213篇 |
2009年 | 320篇 |
2008年 | 315篇 |
2007年 | 352篇 |
2006年 | 307篇 |
2005年 | 250篇 |
2004年 | 255篇 |
2003年 | 234篇 |
2002年 | 194篇 |
2001年 | 181篇 |
2000年 | 133篇 |
1999年 | 157篇 |
1998年 | 130篇 |
1997年 | 115篇 |
1996年 | 117篇 |
1995年 | 86篇 |
1994年 | 93篇 |
1993年 | 68篇 |
1992年 | 78篇 |
1991年 | 73篇 |
1990年 | 69篇 |
1989年 | 52篇 |
1988年 | 42篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 56篇 |
1984年 | 65篇 |
1983年 | 36篇 |
1982年 | 44篇 |
1981年 | 25篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 10篇 |
1975年 | 8篇 |
排序方式: 共有7749条查询结果,搜索用时 15 毫秒
1.
Metabolites of corticosteroids that contain the 21-oic acid moiety are found in human urine. The acids from neutral steroids and urinary pigments have been separated by passing the mixture through a column of polyethyleneimine cellulose. The acids adhering to the column are quantitatively eluted with dilute formic acid. The purified preparation is suitable for derivatization and chromatographic analysis. 相似文献
2.
R. Balabsubramanian G. Raghunathan 《International journal of biological macromolecules》1982,4(6):377-378
The distribution of regular secondary structures, viz. α-helices and β-strands, along the length of over 70 properties whose secondary structural details have been reported, has been analysed. The occurrence of these regular structures tends to be a maximum at the N- and C-termini. Our analysis suggests that both these free ends could possibly serve as nucleating centers for secondary structures and could play an important role in the folding of proteins. 相似文献
3.
Abstract: Phenylacetic acid, the major metabolite of phenylethylamine, has been identified and quantitated in rat brain regions by capillary column high-resolution gas chromatography mass spectrometry. Its distribution is heterogeneous and correlates with that of phenylethylamine. The values obtained were (ng/g ± SEM): whole brain, 31.2 ± 2.7; caudate nucleus, 64.6 ± 6.5; hypothalamus, 60.1 ± 7.4; cerebellum, 31.3 ± 2.9; brainstem, 33.1 ± 3.3, and the "rest," 27.6 ± 3.0. 相似文献
4.
Summary Using an aeroscope, airborne fungal spores were sampled for two years, 1987–1988 at Tiruchirapalli, Tamil Nadu, India. The aerospora components, their seasonal and annual variations in incidence in the air are discussed and a spore calendar for Tiruchirapalli is presented. 相似文献
5.
6.
7.
T.Kent Kirk 《Phytochemistry》1977,16(12):1983-1985
Betulachrysoquinone hemiketal was isolated from pre-extracted wood of Betula lutea Michx. inoculated with Phanerochaete chrysosporium Burds. Acid-catalysed hydrolysis of betulachrysoquinone hemiketal produced betulachrysoquinone which was shown to be 2-hydroxy-6-(13′-hydroxytetradecanyl)-p-benzoquinone. 相似文献
8.
JessicaA. Maisano 《Zoological Journal of the Linnean Society》2002,136(2):277-313
Postnatal patterns of skeletal development, includingthe sequence of appearance of ossification centres and the distributionof sesamoids, appear to be highly conserved species-level phenomenain squamates. As such, they are a potential source of charactersfor phylogenetic inquiry. These patterns, from 21 species representing14 crown squamate clades, form the basis for two analyses. In thefirst, the sequence of postnatal skeletal events is coded as charactersusing the sequence unit approach. This analysis reveals that thesequence of postnatal skeletal events might be useful for determiningrelationships at or above the level of crown clades, but not amongthem. The second analysis utilizes discrete data from postnatalskeletal development, such as the presence/absence of sesamoidsand the number of secondary centres in epiphyseal cartilages. Thesediscrete data appear capable of recovering the deeper divergenceswithin Squamata, but evolve too slowly to be informative at thelevel of crown clades. Thus, patterns of postnatal skeletal developmenthave the potential to help illuminate relationships throughout thesquamate tree. Further progress in this area will require the examinationof additional squamate species, the exploration of alternative codingschemes for developmental sequences, and comparable postnatal datafor Sphenodon . © 2002 The Linnean Societyof London, Zoological Journal of the Linnean Society, 2002, 136 ,277−313. 相似文献
9.
Wheat-spikes inoculated withN. indica at the boot-leaf stage produced secondary sporidia when later incubated (intact/detached) under moist conditions in the laboratory. Sporidia were also released from inoculated spikes in the field where sporidial release exhibited diurnal periodicity. More sporidia were trapped between 5–6 o'clock than during the later parts of the day but no sporidia were trapped between 14–18 o'clock. However, they could be trapped at any time of the day from the detached spikes incubated under moist conditions in the laboratory. Sporidia trapped in different experiments were invariably of the allantoid type and they proved viable and infective. Maximum sporidia developed on the outer glumes of florets, and this observation was supported by scanning electron microcope studies. Sporidia developed at 15 and 20°C but not at 30°C. These findings indicated that repeated cycles of sporidial production in spikes provided more inoculum than expected from soil-borne teliospores ofN. indica. 相似文献
10.
Conformational change of bovine serum albumin by heat treatment 总被引:1,自引:0,他引:1
Kunio Takeda Akira Wada Kazuo Yamamoto Yoshiko Moriyama Koichiro Aoki 《Journal of Protein Chemistry》1989,8(5):653-659
The thermal denaturation of bovine serum albumin (BSA) was studied at pH 2.8 and 7.0 in the range of 2–65°C. The relative proportions of -helix, -structure, and disordered structure in the protein conformation were determined as a function of temperature, by the curve-fitting method of circular dichroism spectra. With the rise of temperature at pH 7.0, the proportion of -helix decreased above 30°C and those of -structure and disordered structure increased in the same temperature range. The structural change was reversible in the temperature range below 45°C. However, the structural change was partially reversible upon cooling to room temperature subsequent to heating at 65°C. On the other hand, the structural change of BSA at pH 2.3 was completely reversible in the temperature range of 2–65°C, probably because the interactions between domains and between subdomains might disappear due to the acid expansion. The secondary structure of disulfide bridges-cleaved BSA remained unchanged during the heat treatment up to 65°C at pH 2.8 and 7.0. 相似文献