全文获取类型
收费全文 | 3480篇 |
免费 | 196篇 |
国内免费 | 7篇 |
出版年
2021年 | 42篇 |
2020年 | 24篇 |
2019年 | 36篇 |
2018年 | 51篇 |
2017年 | 37篇 |
2016年 | 70篇 |
2015年 | 110篇 |
2014年 | 141篇 |
2013年 | 221篇 |
2012年 | 215篇 |
2011年 | 183篇 |
2010年 | 102篇 |
2009年 | 101篇 |
2008年 | 194篇 |
2007年 | 223篇 |
2006年 | 188篇 |
2005年 | 199篇 |
2004年 | 195篇 |
2003年 | 173篇 |
2002年 | 167篇 |
2001年 | 69篇 |
2000年 | 89篇 |
1999年 | 59篇 |
1998年 | 45篇 |
1997年 | 34篇 |
1996年 | 30篇 |
1995年 | 31篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 63篇 |
1991年 | 55篇 |
1990年 | 58篇 |
1989年 | 46篇 |
1988年 | 48篇 |
1987年 | 36篇 |
1986年 | 28篇 |
1985年 | 23篇 |
1984年 | 28篇 |
1983年 | 28篇 |
1982年 | 19篇 |
1981年 | 27篇 |
1980年 | 21篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1971年 | 9篇 |
1969年 | 9篇 |
1968年 | 10篇 |
排序方式: 共有3683条查询结果,搜索用时 265 毫秒
51.
52.
53.
54.
S Kashiwamura T Koyama T Matsuo M Steinmetz M Kimoto N Sakaguchi 《Journal of immunology (Baltimore, Md. : 1950)》1990,145(1):337-343
Genomic DNA clones containing the B cell-specific murine mb-1 gene were isolated and a 5.6-kb BamH I fragment was characterized. It is 5629 bp long and contains five exons: an exon containing the 5' untranslated and the coding sequence of the signal peptide, an exon of 294 bp, which contains most of the extracellular sequence of the MB-1 protein, a 119-bp long exon coding mainly for the transmembrane portion, and two exons of 69 bp and 427 bp encoding the cytoplasmic domain and the 3'-untranslated region, respectively. The mb-1 gene does not contain a "TATA box" found in many eukaryotic promoters. The 5'-flanking region has sequence stretches homologous to IgVH 5'-promoter regions and a bcl 2 intron sequence. It contains the decanucleotide sequence (ATGGCAAATA) almost identical to the octamer motif of IgVH promoters. A B cell-specific DNase I-hypersensitive site was found in the 3'-flanking region indicating that this region might be involved in B cell-specific expression of mb-1. Southern blot analysis of genomic liver DNA with the cloned mb-1 cDNA suggests the existence of another mb-1-related gene segment. 相似文献
55.
Substance P (SP)-like immunoreactivity was examined in the lower labial mucosa of the mouse by using the whole-mount technique. The density and design of subepithelial nerve plexuses containing SP differed depending on portions of the lower labial mucosa. 相似文献
56.
Purification and characterization of a peptide C-terminal alpha-amidating enzyme from porcine atrium
In many peptide hormones and neuropeptides, the carboxy-terminal alpha-amide structure is essential in eliciting biological activity. Here we report the purification and characterization of an alpha-amidating enzyme from porcine atrium, in which a high concentration of alpha-amidating activity was detected. The enzyme was purified to homogeneity from the membrane fraction of porcine atria by five steps of chromatography, including an affinity chromatography using a Sepharose column coupled with a substrate, Tyr-Phe-Gly. The purified enzyme was found to be composed of a single polypeptide chain with an apparent molecular weight of 92,000. This enzyme converted several synthetic peptides with C-terminal glycine to the corresponding des-glycine peptide alpha-amides. 相似文献
57.
K Kitamura K Uyeda F C Hartman K Kangawa H Matsuo 《The Journal of biological chemistry》1989,264(11):6344-6348
Fructose-6-P binding sites of rat liver and bovine heart Fru-6-P,2-kinase:Fru-2,6-bisphosphatase were investigated with an affinity labeling reagent, N-bromoacetylethanolamine phosphate. The rat liver enzyme was inactivated 97% by the reagent in 60 min, and the rate of inactivation followed pseudo-first order kinetics. The bovine heart enzyme was inactivated 90% within 60 min, but the inactivation rate followed pseudo-first order up to 80% inactivation and then became nonlinear. The presence of fructose-6-P retarded the extent of the inactivation to approximately 40% in 60 min. In order to determine the amino acid sequence of the fructose-6-P binding site, both enzymes were reacted with N-bromo[14C]acetylethanolamine-P and digested with trypsin; radiolabeled tryptic peptides were isolated and sequenced. A single 14C-labeled peptide was isolated from the rat liver enzyme, and the amino acid sequence of the peptide was determined as Lys-Gln-Cys-Ala-Leu-Ala-Leu-Lys. A major and two minor peptides were isolated from bovine heart enzyme whose amino acid sequences were Lys-Gln-Cys-Ala-Leu-Val-Ala-Leu-Lys, Arg-Ile-Glu-Cys-Tyr-Lys, and Ile-Glu-Cys-Tyr-Lys, respectively. In all cases, N-bromoacetylethanolamine-P had alkylated the cysteine residues. The amount of bromo[14C]acetylethanolamine-P incorporated into rat liver and beef heart was 1.3 mol/mol of subunit and 2.1 mol/mol of subunit, respectively, and the incorporations in the presence of Fru-6-P were reduced to 0.34 mol/mol of subunit and 0.9 mol/mol of subunit, respectively. Thus, the main fructose-6-P binding site of rat liver and bovine heart enzymes was identical except for a single amino acid substitution of valine for alanine in the latter enzyme. This peptide corresponded to residues 105 to 113 from the N terminus of the known amino acid sequence of rat liver enzyme, but since the complete sequence of bovine heart enzyme is not known, the location of the same peptide in the heart enzyme cannot be assigned. 相似文献
58.
Vanillin and its isomer o-vanillin have an effect on the adaptive and SOS responses, as well as mutagenesis, induced in Escherichia coli by N-methyl-N-nitrosourea (MNU) and UV irradiation, potentiating in some cases and suppressing in others. o-Vanillin markedly inhibited the MNU-induced adaptive response, while both vanillins potentiated the UV-induced SOS response. These phenomena appear to be responsible for the comutagenic or antimutagenic role of these chemicals in MNU and UV mutagenesis. 相似文献
59.
The interactions of benzoquinones with the reduced forms ofthe bound plastoquinone acceptors, QA and QB, were studied withoxygen-evolving photosystem II (PS II) particles from the thermophiliccyanobacterium Synechococcus elongatus, which largely lack poolplastoquinone molecules [Takahashi and Katoh (1986) Biochim.Biophys. Acta 845: 183]. Oxygen evolution in the presence ofvarious electron acceptors was determined and flash-inducedchanges in absorbance in the blue region were analyzed in termsof difference spectra, dependence on the concentration of benzoquinoneand on temperature, and sensitivity to 3-(3,4-dichlorophenyl)-1,1-dimethylurea(DCMU). The more hydrophobic the quinone molecule, the higherwas the rate of oxygen evolution, and the maximum rate of 3,000µmoles O2.(mg chlorophyll)1.h1 was recordedin the presence of phenyl- and dichloro-p-benzoquinones. DCMUinhibited oxygen evolution by more than 95%. However, spectrophotometricstudies revealed that, even though electrons were transferredto benzoquinones predominantly via the direct oxidation of by added benzoquinones occurred in such a way as to indicate thatabout 40% of PS II reaction centers were not associated withfunctional QB sites. was very stable in the presence of ferricyanide. However, benzoquinonesinduced the slow oxidation of . The characteristics of the benzoquinone reductioin in thePS II preparation is discussed.
1Present address: Department of Life Sciences, Faculty of Science,Himeji Institute of Technology, Shosha 2167, Himejishi, Hyogo-ken,671-22 Japan (Received May 8, 1990; Accepted August 14, 1990) 相似文献
60.
A simple technique for reconstruction of the umbilicus, using a conchal cartilage composite graft 总被引:1,自引:0,他引:1
A simple technique to reconstruct the umbilicus is reported in which a conchal cartilage composite graft, such as that used in tragus construction in the treatment of microtia, was employed with a very satisfactory result. 相似文献