全文获取类型
收费全文 | 4755篇 |
免费 | 238篇 |
国内免费 | 5篇 |
出版年
2022年 | 19篇 |
2021年 | 39篇 |
2020年 | 25篇 |
2019年 | 31篇 |
2018年 | 54篇 |
2017年 | 40篇 |
2016年 | 91篇 |
2015年 | 116篇 |
2014年 | 152篇 |
2013年 | 363篇 |
2012年 | 231篇 |
2011年 | 254篇 |
2010年 | 157篇 |
2009年 | 167篇 |
2008年 | 269篇 |
2007年 | 277篇 |
2006年 | 299篇 |
2005年 | 279篇 |
2004年 | 282篇 |
2003年 | 275篇 |
2002年 | 286篇 |
2001年 | 50篇 |
2000年 | 60篇 |
1999年 | 57篇 |
1998年 | 58篇 |
1997年 | 60篇 |
1996年 | 55篇 |
1995年 | 73篇 |
1994年 | 51篇 |
1993年 | 62篇 |
1992年 | 63篇 |
1991年 | 42篇 |
1990年 | 50篇 |
1989年 | 46篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 25篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 42篇 |
1982年 | 40篇 |
1981年 | 50篇 |
1980年 | 45篇 |
1979年 | 21篇 |
1978年 | 31篇 |
1977年 | 25篇 |
1976年 | 24篇 |
1975年 | 18篇 |
1974年 | 23篇 |
1973年 | 19篇 |
排序方式: 共有4998条查询结果,搜索用时 718 毫秒
71.
Toshio Ariga Shama Bhat Takashi Kanda Masanaga Yamawaki Tadashi Tai Yasunori Kushi Takeshi Kasama Shizuo Handa Robert K. Yu 《Glycoconjugate journal》1996,13(2):135-145
We analysed the glycolipid composition of glioma cells (N-370 FG cells), which are derived from a culture of transformed human fetal glial cells. The neutral and acidic glycolipid fractions were isolated by column chromatography on DEAE-Sephadex and analysed by high-performance thin-layer chromatography (HPTLC). The neutral glycolipid fraction contained 1.6 µg of lipid-bound glucose/galactose per mg protein and consisted of GlcCer (11.4% of total neutral glycolipids), GalCer (21.5%), LacCer (21.4%), Gb4 (21.1%), and three unknown neutral glycolipids (23%). These unknown glycolipids were characterized as Lewisx (fucosylneolactonorpentaosyl ceramide; Lex), difucosylneolactonorhexaosyl ceramide (dimeric Lex), and neolactonorhexaosyl ceramide (nLc6) by an HPTLC-overlay method for glycolipids using specific mouse anti-glycolipid antibodies against glycolipid and/or liquid-secondary ion (LSI) mass spectrometry. The ganglioside fraction contained 0.6 µg of lipid-bound sialic acid per mg protein with GD1a as the predominant ganglioside species (83% of the total gangliosides) and GM3, GM2, and GM1 as minor components. Trace amounts of sialyl-Lex and the complex type of sialyl-Lex derivatives were also present. Immunocytochemical studies revealed that GD1a and GalCer were primarily localized on the surface of cell bodies. Interestingly, Lex glycolipids and sialyl-Lex were localized not only on the cell bodies but also on short cell processes. Especially, sialyl-Lex glycolipid was located on the tip of fine cellular processes. The unique localization of the Lex glycolipids suggests that they may be involved in cellular differentiation and initiation of cellular growth in this cell line. 相似文献
72.
Structural characterization of sulfated and sialyl Lewis (Le)-type glycosphingolipids performed by fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectrometry is described. Both FAB and ESI collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of acidic glycosphingolipids allowed identification of the sulfated or sialyl sugar, and provided information on the saccharide chain sequence. The negative-ion tandem FABMS of sulfated Le-type glycosphingolipids having the non-reducing end trisaccharide ion as the precursor can be used to differentiate the Lea- and LeX-type oligosaccharides. The ESI CID-MS/MS of multiple-charged ions provided even more detailed structural information, and some of the useful daughter ions appeared with higherm/z values than the precusor because of a lower charge-state. These methodologies can be applied to the structural analyses of glycoconjugates with much larger molecular masses and higher polarity, such as the poly-sulfated and sialyl analogues.Abbreviations CID
collision-induced dissociation
- ESI
electrospray ionization
- FABMS
fast atom bombardment mass spectrometry
- Fuc
fucose
- Gal
galactose
- GlcNAc
N-acetylglucosamine
- Le
Lewis
- Lea
Lewisa
- LeX
LewisX
- MS/MS
mass spectrometry/mass spectrometry
- NeuAc
N-acetylneuraminic acid
- 3-SO4-Lea
3-sulfated Lea pentaosyl ceramide
- 3-SO4-LeX
3-sulfated LeX pentaosyl ceramide
- 2,3-SO4-LeX
2,3-disulfated LeX pentaosyl ceramide
- 3-S-Lea
3-sialyl Lea pentaosyl ceramide
- 3-S-Lex
3-sialyl LeX heptaosyl ceramide
- 3-S-LeX-LeX
3-sialyl-Lex-Lex octaosyl ceramide. 相似文献
73.
The heterobasidiomycetous yeastRhodotorula glutinis was able to grow in medium containing a high concentration of LiCl. This character ofR. glutinis was presumed to be attributable to its ability to incorporate [14C]-adenine and [14C]-leucine into nucleic acids and proteins, respectively, in the presence of LiCl. Intracellular levels of Li+ and Cl– ions, production and accumulation of glycerol as an osmoregulator, and respiration in the LiCl-stressed condition were almost the same in the tolerant yeastR. glutinis and the sensitive yeastRhodosporidium sphaerocarpum. 相似文献
74.
75.
Anti-human immunodeficiency virus type 1 activity of phosphorothioate analogs of oligodeoxynucleotides: penetration and localization of oligodeoxynucleotides in HIV-1-infected MOLT-4 cells. 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
H Nakashima Y Shoji S G Kim J Shimada Y Mizushima M Ito N Yamamoto H Takaku 《Nucleic acids research》1994,22(23):5004-5010
76.
Hideo Yamanari Tatsuo Suganuma Takeshi Iwamura Norio Kitamura Shoji Taniguchi Toshiaki Setoguchi 《Experimental cell research》1994,211(2)
The interaction between the extracellular matrix and human tumor-cell clones S2-013 and S2-020, derived from a pancreatic cancer cell line (SUIT-2), was examined in vitro, using various cell differentiation-promoting matrices in two- and three-dimensional cultures. S2-013 cells (well-differentiated tubular adenocarcinoma in xenografts in nude mice) cultured in Matrigel formed glandular structures. Ultrastructural observation revealed a morphological polarity of cells and a distinct basal lamina. On the other hand, S2-020 cells (poorly differentiated tubular adenocarcinoma in xenografts) cultured in Matrigel formed neither glandular structures nor a basal lamina, but only cell aggregates. The morphology of these two sublines cultured in Matrigel expressed the histological degree of differentiation which they presented in nude mice. In contrast, in type I collagen gel, S2-013 cells formed glandular structures without a basal lamina, and in soft agar, they were able to form neither glandular structures nor a basal lamina. S2-020 cells cultured in type I collagen gel or soft agar formed the same simple cell aggregates as in Matrigel. Matrices used in a three-dimensional culture influenced the degree of differentiation in S2-013 cells but had no effect on the morphological differentiation in S2-020 cells. To detect the factors which induce basal lamina formation, S2-013 cells were cultured on a microporous membrane coated with extracellular matrix components such as laminin, type IV collagen, and fibronectin. S2-013 cells formed a basal lamina only on the laminin. These cell lines may be useful in investigating the mechanisms regulating the formation of glandular structures and basal lamina. 相似文献
77.
Kivoshi Ohkawa Tae Hirakawa-Sakurai Kensuke Joh Tadashi Asakura Koji Takada Makoto Matsuda 《Neurochemical research》1994,19(10):1231-1235
Murine polyclonal antibody against purified bovine brain pyridoxal kinase (EC 2.7.1.35) was generated and showed cross-reactivity with rabbit brain pyridoxal kinase. This antibody was used to immunohistochemically examine the distribution of pyridoxal kinase in the rabbit brain. The cytoplasm of neuronal cells and neuroglial cells in the cerebral cortex, hippocampal region, brain nuclei and cerebellar cortex showed positive staining with various degrees of intensity. The neuronal cells and surrounding fibers in some brain nuclei, such as the area tegmentalis ventralis or the substantia nigra, showed intense staining. The neuronal cells of the hippocampal region showed somewhat weak reactivity, but some with intense reactivity were found sparsely distributed and positive staining fiber networks of a very low density were also observed. 相似文献
78.
Hideaki Kabuto Isao Yokoi Mineo Takei Tadashi Kurimoto Akitane Mori 《Neurochemical research》1994,19(4):463-467
Serotonin (5-HT) plays an important role in the seizures of El mice since the seizure threshold of El mice correlates with the 5-HT concentration in the central nervous system. In this study, the anticonvulsant effect of a 5-HT reuptake blocker, citalopram, was evaluated behaviorally and biochemically. El mouse convulsions were inhibited by oral administration of citalopram for 2 weeks. Citalopram increased tryptophan and tyrosine amounts, and decreased the 5-HT, 5-hydroxy-indoleacetic acid, kynurenine, and dopamine amounts in the brain. These findings show that citalopram depresses monoaminergic metabolism. Given the known convulsant effect of kynurenine, it is suggested that its decrease by citalopram may involve attenuation of El mice seizures. 相似文献
79.
Cloning, nucleotide sequence and expression of a hemolysin gene of Clostridium septicum 总被引:4,自引:0,他引:4
Abstract A genomic library of Clostridium septicum NCTC547 strain was made in Escherichia coli by means of λgt10. The DNA insert of a hemolysin-positive (Hly+ ) λ-clone was transferred into pUC19. The resulting plasmid, pCS21, confers a Hly+ phenotype on E. coli . Crude lysates of E. coli (pCS21) possessed a strong lytic activity on human erythrocytes and also a lethal effect on mice, characteristic of an α toxin. Nucleotide sequence analysis revealed that the insert DNA (5.2 kb) in pCS21 included at least one open reading frame of 1380 bp. The coding frame for hemolysin was predicted to be 1329 bp in size and to encode a protein of 49.8 kDa. It coincided with the molecular mass (48 kDa) of the α toxin secreted by C. septicum . Taken together, the data indicated that plasmid pCS21 indeed encoded an α toxin gene of C. septicum . 相似文献
80.
Chloroplast DNA (cpDNA) restriction site variation was examined in five species ofDesmodium subgenusPodocarpium (Leguminosae; Papilionoideae; Desmodieae). Twenty four phylogenetically informative cpDNA mutations were scored. The cladistic
analysis of characters based on the 24 mutations resulted in the most parsimonious tree which supports the monophyly of the
subgenus.Desmodium elegans of subgenusDollinera was the sister group of subgenusPodocarpium in this tree. The groupings obtained from the cpDNA characters were consistent with the present infrageneric classification
system for the subgenus except for the infraspecific taxa ofD. podocarpum. Three groups withinD. podocarpum, which were incongruent with the infraspecific classification of the species, were distinguished by a total of four site
mutations. The first group consisted of subsp.podocarpum, subsp.fallax, and subsp.oxyphyllum var.oxyphyllum; the second subsp.oxyphyllum var.oxyphyllum; and the last subsp.oxyphyllum var.oxyphyllum and var.mandshuricum. 相似文献