全文获取类型
收费全文 | 1311篇 |
免费 | 71篇 |
专业分类
1382篇 |
出版年
2023年 | 3篇 |
2022年 | 14篇 |
2021年 | 19篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 27篇 |
2017年 | 15篇 |
2016年 | 35篇 |
2015年 | 49篇 |
2014年 | 60篇 |
2013年 | 111篇 |
2012年 | 120篇 |
2011年 | 103篇 |
2010年 | 61篇 |
2009年 | 64篇 |
2008年 | 62篇 |
2007年 | 68篇 |
2006年 | 65篇 |
2005年 | 79篇 |
2004年 | 76篇 |
2003年 | 53篇 |
2002年 | 59篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 22篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1968年 | 3篇 |
1967年 | 4篇 |
1940年 | 1篇 |
排序方式: 共有1382条查询结果,搜索用时 15 毫秒
1.
2.
Homozygous typing cells (HTC) were primed, using responding and stimulating lymphocytes of the same HLA-D groups. These intra-HLA-D group primings showed strong specific responses. Restimulation by HLA-D heterozygous and homozygous cell panels showed no correlation between the restimulating determinant and HLA-D. On the other hand, an unrelated individual, not carrying Dw4 and primed to Dw4 HTC, is restimulated by three of four Dw4-HTC. Thus, one non-HLA-D-associated restimulating determinant and another HLA-D-associated determinant could be identified. The differences among the four Dw4 HTC recognized in secondary MLC could reflect either recognition of separate gene products or recognition of separate determinants on the same gene product. 相似文献
3.
Victor M. Luque-Almagro Verity J. Lyall Stuart J. Ferguson M. Dolores Roldán David J. Richardson Andrew J. Gates 《The Journal of biological chemistry》2013,288(41):29692-29702
Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression. 相似文献
4.
Dolores G. Evans Ph.D. Doyle J. Evans Jr. Tuomo K. Karjalainen Chao-Hung Lee 《Current microbiology》1991,23(2):71-74
Experiments were performed to study the effect of glucose on the production of the fimbrial colonization factor CFA/II of enterotoxigenicEscherichia coli (ETEC). The production of the CFA/II antigen was examined by electron microscopy, quantitative ELISA, and hemagglutination. The results showed that addition of 1% glucose to the growth medium drastically decreased CFA/II production, whereas addition of glycerol or sodium acetate did not have any effect. Bacteria grown in the presence of 1% glucose were essentially devoid of CFA/II fimbriae when examined under the electron microscope. Addition of 1 mM cAMP reversed the repressive effect of glucose, suggesting that the glucose suppression on CFA/II synthesis is via the mechanism of catabolite repression. 相似文献
5.
Pigment patterns in mutants affecting the biosynthesis of pteridines and xanthommatin in Drosophila melanogaster 总被引:3,自引:0,他引:3
Juan Ferré Francisco J. Silva M. Dolores Real José L. Ménsua 《Biochemical genetics》1986,24(7-8):545-569
Eye-color mutants of Drosophila melanogaster have been analyzed for their pigment content and related metabolites. Xanthommatin and dihydroxanthommatin (pigments causing brown eye color) were measured after selective extraction in acidified butanol. Pteridines (pigments causing red eye color) were quantitated after separation of 28 spots by thin-layer chromatography, most of which are pteridines and a few of which are fluorescent metabolites from the xanthommatin pathway. Pigment patterns have been studied in 45 loci. The pteridine pathway ramifies into two double branches giving rise to isoxanthopterin, drosopterins, and biopterin as final products. The regulatory relationship among the branches and the metabolic blockage of the mutants are discussed. The Hn locus is proposed to regulate pteridine synthesis in a step between pyruvoyltetrahydropterin and dihydropterin. The results also indicate that the synthesis and accumulation of xanthommatin in the eyes might be related to the synthesis of pteridines.Support for this work was provided to J.F. in part by a grant from the Ministerio de Universidades e Investigación (Spain) and to F.J.S. by a grant from the Ministerio de Educación y Ciencia (Spain). 相似文献
6.
Ruth C. Steinkamp Clarence L. Young Dolores Nyhus Arnold E. Greenberg 《The Western journal of medicine》1968,109(2):126-133
The amount of sodium ion in water used for ingestion may be critical in effective use of a low sodium dietary regimen. Waters containing not over 20 mg of sodium per liter are provided for in the sodium restricted diets set forth by the American Heart Association. For diets containing more than 500 mg of sodium a day, waters of greater sodium content may be used if proper dietary adjustments are made.While assessment of the long-term average sodium content of a community water supply is difficult, the determined values for sodium lend to classification within range categories. The larger community water supplies in California are presented within several range categories of sodium content.The more commonly used water softeners add sodium to water. The sodium-restricted patient should be cautioned against their use. Similar consideration should probably be given to water supplies of retirement communities where the potential for disorders requiring sodium restriction is greater than in the general population. 相似文献
7.
Jose Pontón Fernando L. Hernando Maria Dolores Moragues Pedro L. Barea Mara Gerloni Stefania Conti Paola Fisicaro Cristina Cantelli Luciano Polonelli 《Mycopathologia》1996,133(2):89-94
The presence of heat shock mannoproteins (HSMPs) reactive with sIgA was demonstrated in several C. albicans strains. The subculture of the C. albicans isolated from mucosal surfaces on Sabouraud's dextrose agar at 25 °C switched off the HSMP expression. A re-expression of the HSMPs was obtained in the same medium by shifting the temperature of incubation to 37 °C. However, expression of HSMPs in two strains isolated from deep infections was maintained during several subcultures on Sabouraud's dextrose agar at 25 °C. A glycoprotein of 200 kDa seemed to be the main HSMP reacting with vaginal sIgA. The data presented in this study suggest that factors other than temperature can influence the expression of C. albicans HSMPs and therefore these antigens should be referred as stress mannoproteins.Abbreviations HSMPs
heat shock mannoproteins
- MAb
monoclonal antibody
- sIgA
secretory IgA 相似文献
8.
Summary A protocol for obtaining regenerated fertile plants from mesophyll protoplasts of three lines of Matthiola incana is described. Protoplasts were isolated from leaves of 21–28 days old Matthiola plants grown in controlled environment. Sustained divisions were achieved when protoplasts were embedded in sodium alginate. Up to 2.0 % of the protoplasts developed into colonies which could be transferred to shoot regeneration media. More than 25 % of the obtained calluses regenerated shoots. About 4 % of these shoots could be rooted and after transfer to soil phenotypically normal plants have been obtained.Abbreviations 2,4-D
2,4-dichlorphenoxyacetic acid
- NAA
naphthalene acetic acid
- IAA
indole-3-acetic acid
- BAP
6-banzylaminopurine
- IPA
isopentenyladenine
- IPAR
isopentenyladenosine
- MES
(2-[N-morpholino]) ethanesulfonic acid 相似文献
9.
Dinucleotide repeat polymorphism at the D4S2458 locus close to the PKD2 locus on human chromosome 4q
Miguel Viribay Dolores Tellería Eladio Velasco Felipe Moreno José L. San Millán 《Human genetics》1995,95(5):601-602
A new polymorphic CA repeat sequence was identified within the candidate region fot the autosomal dominant polycystic kidney disease type 2 (PKD2) locus. It should be a useful marker in the localization of this gene. 相似文献
10.