全文获取类型
收费全文 | 187篇 |
免费 | 35篇 |
国内免费 | 2篇 |
出版年
2022年 | 1篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 6篇 |
2008年 | 9篇 |
2007年 | 7篇 |
2006年 | 10篇 |
2005年 | 4篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 7篇 |
排序方式: 共有224条查询结果,搜索用时 15 毫秒
171.
MicroRNAs (miRNAs) are regulatory molecules that share both biosynthetic derivation (cleavage from short hairpin precursor RNAs) and functional roles (downregulation of specific mRNAs through targeted degradation and/or translational inhibition). A distinct family of small RNAs, termed siRNAs, have some common characteristics but exhibit distinct modes of biosynthesis and function. In this study, we report procedures for purification of a predominant species of miRNA-containing ribonucleoprotein complexes from Caenorhabditis elegans and demonstrate that this population is distinct from the predominant pool of siRNA-containing ribonucleoprotein complexes. An observed miRNP-associated RNA population consisting predominantly (>95%) of miRNAs supported the unique identity of miRNPs as biological effectors within the cell, provided clean material for analysis of changes in miRNA spectra during development, and provided strong evidence of miRNA character for a number of novel small RNAs. Likewise, the RNA spectrum derived from partial siRNP purification was useful in defining functional characteristics of this more diverse population of small RNAs. 相似文献
172.
Shi Y Sitkoff D Zhang J Han W Hu Z Stein PD Wang Y Kennedy LJ O'Connor SP Ahmad S Liu EC Seiler SM Lam PY Robl JA Macor JE Atwal KS Zahler R 《Bioorganic & medicinal chemistry letters》2007,17(21):5952-5958
The design and synthesis of a novel class of amino(methyl) pyrrolidine-based sulfonamides as potent and selective FXa inhibitors is reported. The amino(methyl) pyrrolidine scaffolds were designed based on the proposed bioisosterism to the piperazine core in known FXa inhibitors. The SAR study led to compound 15 as the most potent FXa inhibitor in this series, with an IC(50) of 5.5 nM and PT EC(2x) of 1.7 microM. The proposed binding models show that the pyrrolidine cores are in van der Waals contact with the enzyme surface, and the flexibility of amino(methyl) pyrrolidines allows the two nitrogen atoms to anchor both the P1 and P4 groups to fit similarly in the S1 and S4 pockets. 相似文献
173.
We have investigated the morphological effects of a genetic locus, Pgm1- t,
that affects the expression of a phosphoglucomutase locus (Pgm1) in liver
of rainbow trout (Salmo gairdneri). We have previously shown that embryos
with liver Pgm1 expression hatch earlier than those without liver Pgm1
expression. We predicted that this difference in developmental rate should
cause a reduction in meristic counts in the more rapidly developing fish
with liver Pgm1 expression. Eight meristic (countable) characters in nine
full-sib groups segregating for the presence or absence of liver Pgm1
expression are in agreement with this prediction. In eight of the nine
families, there is a significant difference in the multivariate
distribution of the eight meristic counts between full sibs with and
without liver Pgm1 expression. This separation in multivariate space is
based on a tendency for lower meristic counts in fish with liver Pgm1
expression. The magnitude of these morphological differences is similar to
that between two subspecies of cutthroat trout (Salmo clarki) that show
substantial genetic divergence at structural loci encoding enzymes (Nei's D
= 0.34). These data support the view that small changes in the
developmental process caused by genetic differences at regulatory genes can
have large effects on morphology.
相似文献
174.
Telomere terminal transferase activity in the hypotrichous ciliate Oxytricha nova and a model for replication of the ends of linear DNA molecules. 总被引:43,自引:12,他引:31
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)
We have found abundant telomere-specific terminal transferase activity in crude macronuclear extracts from vegetatively growing cells of the hypotrichous ciliate Oxytricha nova. This activity adds two to seven tandem repeats of the sequence GGGGTTTT (the Oxytricha telomeric repeat) to the 3' end of oligonucleotide primers ending in repeats of G4T4 and always adds the repeats in the proper phase. The activity requires the presence of micromolar amounts of dGTP and dTTP as well as single-stranded oligomer primers ending 3' with repeats of the Oxytricha telomeric sequence. A nuclease activity is present in the extracts which is closely balanced with telomere terminal transferase activity. We propose a simple model for replication of the ends of linear DNA molecules based on the telomere terminal transferase. 相似文献
175.
176.
The biosynthesis of alpha-isopropylmalate (alphaIPM) synthetase, IPM isomerase, and betaIPM dehydrogenase in Bacillus subtilis can be derepressed in leucine auxotrophs by limiting them for leucine. The derepression of the three enzymes is apparently coordinate. A class of mutants resistant to 4-azaleucine excretes leucine and has derepressed levels of all three enzymes. The azaleucine-resistance mutations may lie in a gene (azlA) encoding a repressor. Efforts to find mutations characteristic of a constitutive operator have been unsuccessful. No polar mutations have been found among nine leucine auxotrophs that have characteristics of frameshift mutations. The enzyme catalyzing the first step in leucine biosynthesis, alphaIPM synthetase, is sensitive to feedback inhibition by leucine. We conclude that leucine biosynthesis is controlled by the inhibition of the activity of the first biosynthetic enzyme by leucine, and by the repression of the synthesis of the first three biosynthetic enzymes by leucine. The repression of the three enzymes may be under the control of a single repressor and a single operator, or of a single repressor and a separate operator for each structural gene. 相似文献
177.
Bacillus subtilis has a constitutive system for the uptake of alpha-keto-beta-methylvalerate, alpha-ketoisovalerate, and (probably) alpha-ketoisocaproate. A mutation, kauA1, which blocks the uptake of alpha-keto-beta-methylvalerate and alpha-ketoisovalerate, is located between metB and citK on the B. subtilis chromosome. 相似文献
178.
Structure, composition, enzymatic activities of human erythrocyte and sarcoplasmic reticulum membrane films 总被引:2,自引:0,他引:2
Air/water interface films were obtained from human erythrocytes and rabbit sarcoplasmic reticulum membranes at 'zero surface pressure. according to Verger, R and Pattus, F. (Chem. Phys. Lipids (1976) 16, 285-291). The lipid and protein distribution of these membrane films suggest that the film composition is determined by the composition of the membrane and the mode of integration of its components. When kept at low surface pressure, slow film expansion occurred due to unfolding of proteins at the interface. This process can be stopped by compressing the films at a higher surface pressure than 15 dyn/cm. Acetylcholinesterase activity from human erythrocyte films is highly dependent on the condensation state of the film. Ca2+-ATPase from sarcoplasmic reticulum films was still activable by Ca2+. Freeze-fracture studies on erythrocyte membrane films suggest the such films are monolayers in which proteins are randomly distributed. 相似文献
179.
180.
The Bacillus subtilis ochre suppressor sup-3 is located in an operon of seven tRNA genes. 总被引:7,自引:5,他引:2
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Most Bacillus subtilis tRNA genes have been isolated from lambda libraries by use of probes that hybridize to tRNA or rRNA sequences. None of those genes map to the region of the sup-3 mutation. By cloning of the sup-3 allele, a cluster of seven tRNA genes (the trnS operon) that had not been isolated by other methods was identified. In principle, this approach could be used to isolate at least one more predicted tRNA-containing operon in this bacterium. The trnS operon was shown to contain tRNA genes for Asn (GUU), Ser (GCU), Glu (UUC), Gln (UUG), Lys (UUU), Leu (UAG), and Leu (GAG). The sup-3 mutation was found to be a T-to-A transversion that changes the anticodon of the lysine tRNA from 5'-UUU-3' to 5'-UUA-3'. This result agrees with previous work that determined that the sup-3 mutation causes lysine to be inserted at ochre nonsense mutations. 相似文献