全文获取类型
收费全文 | 3449篇 |
免费 | 278篇 |
国内免费 | 214篇 |
出版年
2023年 | 87篇 |
2022年 | 104篇 |
2021年 | 100篇 |
2020年 | 92篇 |
2019年 | 121篇 |
2018年 | 145篇 |
2017年 | 102篇 |
2016年 | 91篇 |
2015年 | 85篇 |
2014年 | 253篇 |
2013年 | 253篇 |
2012年 | 190篇 |
2011年 | 212篇 |
2010年 | 165篇 |
2009年 | 180篇 |
2008年 | 193篇 |
2007年 | 223篇 |
2006年 | 141篇 |
2005年 | 114篇 |
2004年 | 86篇 |
2003年 | 78篇 |
2002年 | 55篇 |
2001年 | 45篇 |
2000年 | 40篇 |
1999年 | 47篇 |
1998年 | 33篇 |
1997年 | 24篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 42篇 |
1992年 | 31篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 26篇 |
1984年 | 46篇 |
1983年 | 31篇 |
1982年 | 40篇 |
1981年 | 34篇 |
1980年 | 44篇 |
1979年 | 38篇 |
1978年 | 24篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1974年 | 23篇 |
1973年 | 19篇 |
排序方式: 共有3941条查询结果,搜索用时 15 毫秒
81.
Isolation and complete nucleotide sequence of the gene for bovine parathyroid hormone 总被引:7,自引:0,他引:7
The structure of the bovine parathyroid hormone (PTH) gene has been analyzed by Southern blot hybridization of genomic DNA and by nucleotide sequence analysis of a cloned PTH gene. In the Southern analysis, several restriction enzymes produced single fragments that hybridized to PTH cDNA suggesting that there is a single bovine PTH gene. The restriction map of the cloned gene is the same as that determined by Southern blot analysis of bovine DNA. The sequence of 3154 bp of the cloned gene has been determined including 510 bp and 139 bp in the 5' and 3' flanking regions, respectively. The gene contains two introns which separate three exons that code primarily for: (i) the 5' untranslated region, (ii) the pre-sequence of preProPTH, and (iii) PTH and the 3' untranslated region. The gene contains 68% A + T and unusually long stretches of 100- to 150-bp sequences containing alternating A and T nucleotides in the 5' flanking region and intron A. The 5' flanking region contains two TATA sequences, both of which appear to be functional as determined by S1 nuclease mapping. Compared to the rat and human genes, the locations of the introns are identical but the sizes differ. Comparable human and bovine sequences in the flanking regions and introns are about 80% homologous. 相似文献
82.
83.
The conversion of both parental- and progeny-nascent open circular M13 RF DNA into covalently closed RF I is drastically reduced in an mutant deficient in the 5′ → 3′ exonuclease associated with DNA polymerase I. The nascent progeny RF DNA also contains a significant proportion of fragments of smaller than unit length. 相似文献
84.
Localization of retinoic acid-binding protein in nuclei 总被引:5,自引:0,他引:5
B P Sani 《Biochemical and biophysical research communications》1977,75(1):7-12
Retinoic acid-binding component has been detected in the nuclei of chick embryo skin. The physicochemical properties of this macromolecule are in agreement with the properties of the retinoic acid-binding protein isolated from tissue cytosol. Although no binding protein could be detected in normal colon or lung tissue, nuclei isolated from a transplantable colon tumor and Lewis lung carcinoma contained this protein. 相似文献
85.
L.C. Boffa J. Karn G. Vidali V.G. Allfrey 《Biochemical and biophysical research communications》1977,74(3):969-976
Nuclear proteins have been fractionated into five distinct classes according to their extractability from rat liver nuclei at different pH and salt concentrations. The fractions have been analyzed for their amino acid composition which shows the presence of NG, NG-dimethylarginine, in sizable amount, in non-histone nuclear proteins (NHNP). This modification is most prominent in proteins which are found associated with rapidly-labeled heterogeneous RNA (HnRNP proteins). 相似文献
86.
M T Hansen 《Mutation research》1982,106(2):209-216
The sensitivity to psoralen plus near-ultraviolet radiation (PUVA) was compared in a pair of E. coli strains differing at the acrA locus. Survival was determined for both bacteria and phage lambda. AcrA mutant cells were 40 times more sensitive than wild type to the lethal effect of PUVA. Free lambda phage exposed to PUVA survived as well when plated on acrA mutants as on wild type. In contrast, prophage lambda CI857 ind carried in lysogenic acrA strains was hypersensitive to PUVA. The enhanced sensitivity of bacterial and lambda DNA, when inside acrA cells, was paralleled by an increased photobinding of radiolabelled psoralens in the mutant. Binding was increased specifically to DNA rather than to nucleic acids in general. The difference in psoralen-binding ability determined by the acrA gene persisted after permeabilizing treatment of the cells. The results suggest that the acrA mutation causes an alteration specifically in the environment of the cellular DNA so as to allow increased intercalation and photobinding of psoralens. 相似文献
87.
Marie Kselíková Tomáš Mařík Bedřich Bíbr Jaroslav Lener 《Biological trace element research》1980,2(1):57-64
This study describes the interaction of molybdenum with blood components. Molybdenum-99 was added to blood, and after four
washings, 3% of the total radioactivity was found in red cells. More specifically, the radioactivity was determined to be
associated with the cell membrane.
Molybdenum-99 in the +VI form did not interact with the human erythrocyte membrane; however, Mo(V) forms did interact. Of
five different compounds, the highes uptake was observed with a brown Mo(V)-ascorbate complex generated from Mo(VI) and ascorbic
acid in the molar ratio 1∶20. A membrane suspension of Mo-ascorbate-treated human erythrocytes was prepared and the solubilized
proteins were separated on a polyacrylamide gel in the presence of sodium dodecyl sulfate (SDS). Molybdenum-99 binding to
spectrin was demonstrated, as well as some minor interactions with membrane hemoglobin and bands 6 and 8. 相似文献
88.
Quang Khai Huynh Ryuzo Sakakibara Takehiko Watanabe Hiroshi Wada 《Biochemical and biophysical research communications》1980,97(2):474-479
The complete amino acid sequence of the mitochondrial glutamic oxaloacetic transaminase isozyme from rat liver is presented. The sequence contained 401 amino acid residues, 10 of which are methionine. Cyanogen bromide cleavage of mitochondrial glutamic oxaloacetic transaminase produced 12 peptides, one of which contained an internal homoserine residue resulting from incomplete cleavage by cyanogen bromide. The calculated molecular weight was 44,358. The sequence showed 94% homology with that of the corresponding isozyme from pig heart. These findings support the conclusion that the rate of evolution of the mitochondrial isozymes is lower than that of their cytosolic isozymes. 相似文献
89.
Restriction mapping and nucleotide sequence analysis of several defective, interfering particles of bacteriophage f1 are described. These particles contain the nucleotide sequences corresponding to the carboxyl terminus of gene IV and the amino-terminus of gene II and the intergenic space between them. Tandem duplication of a portion of this intergenic space generates defective particles with novel nucleotide sequences not found in wild-type f1. This duplication is shown to contain the origin of complementary strand synthesis. Our results suggest that the duplication occurs at the site of gene II protein action, i.e. the origin of viral strand synthesis. A model is presented for the generation of these duplications in defective particles. 相似文献
90.
Nitrous acid (NA) induced mutations efficiently in mitDNA, conferring resistance to erythromycin and weakly induces mit- mutations. In some strains of yeast it also enhanced rho- mutations. The frequencies of nuclear and mitochondrial mutations induced with NA are compared. 相似文献