全文获取类型
收费全文 | 6034篇 |
免费 | 695篇 |
专业分类
6729篇 |
出版年
2021年 | 76篇 |
2018年 | 56篇 |
2016年 | 85篇 |
2015年 | 153篇 |
2014年 | 143篇 |
2013年 | 232篇 |
2012年 | 248篇 |
2011年 | 245篇 |
2010年 | 151篇 |
2009年 | 156篇 |
2008年 | 204篇 |
2007年 | 231篇 |
2006年 | 227篇 |
2005年 | 200篇 |
2004年 | 209篇 |
2003年 | 178篇 |
2002年 | 209篇 |
2001年 | 189篇 |
2000年 | 193篇 |
1999年 | 174篇 |
1998年 | 99篇 |
1997年 | 84篇 |
1995年 | 80篇 |
1994年 | 66篇 |
1993年 | 92篇 |
1992年 | 157篇 |
1991年 | 130篇 |
1990年 | 141篇 |
1989年 | 117篇 |
1988年 | 106篇 |
1987年 | 108篇 |
1986年 | 95篇 |
1985年 | 107篇 |
1984年 | 100篇 |
1983年 | 82篇 |
1982年 | 71篇 |
1981年 | 62篇 |
1980年 | 76篇 |
1979年 | 90篇 |
1978年 | 72篇 |
1977年 | 75篇 |
1976年 | 65篇 |
1975年 | 71篇 |
1974年 | 81篇 |
1973年 | 88篇 |
1972年 | 61篇 |
1971年 | 54篇 |
1970年 | 58篇 |
1968年 | 48篇 |
1967年 | 47篇 |
排序方式: 共有6729条查询结果,搜索用时 15 毫秒
81.
P. D. Needham R. G. Atkinson B. A. M. Morris R. C. Gardner A. P. Gleave 《Plant cell reports》1998,17(8):631-639
We have constructed a binary vector containing elements of the monopartite geminivirus, tobacco yellow dwarf virus (TYDV).
The vector is designed to be stably integrated into the plant genome, via Agrobacterium-mediated transfer. Upon expression of the viral replication-associated protein the TYDV elements are released from the T-DNA
and then replicate episomally. We refer to these released forms as multicopy plant episomes (MPE). Tobacco plants (Nicotiana tabacum cv `Samsun') transformed with the vector showed MPE release and subsequent episomal replication in 6 of 11 of these plants.
An MPE vector containing the uidA gene faithfully replicated and maintained the reporter gene, even though the construct was considerably larger than the wild-type
TYDV genome. Histochemical staining revealed a speckled GUS expression phenotype which could be correlated with MPE replication.
Received: 11 July 1997 / Revision received: 4 November 1997 / Accepted: 8 December 1997 相似文献
82.
Garcia BA Hake SB Diaz RL Kauer M Morris SA Recht J Shabanowitz J Mishra N Strahl BD Allis CD Hunt DF 《The Journal of biological chemistry》2007,282(10):7641-7655
Post-translational modifications (PTMs) of histones play an important role in many cellular processes, notably gene regulation. Using a combination of mass spectrometric and immunobiochemical approaches, we show that the PTM profile of histone H3 differs significantly among the various model organisms examined. Unicellular eukaryotes, such as Saccharomyces cerevisiae (yeast) and Tetrahymena thermophila (Tet), for example, contain more activation than silencing marks as compared with mammalian cells (mouse and human), which are generally enriched in PTMs more often associated with gene silencing. Close examination reveals that many of the better-known modified lysines (Lys) can be either methylated or acetylated and that the overall modification patterns become more complex from unicellular eukaryotes to mammals. Additionally, novel species-specific H3 PTMs from wild-type asynchronously grown cells are also detected by mass spectrometry. Our results suggest that some PTMs are more conserved than previously thought, including H3K9me1 and H4K20me2 in yeast and H3K27me1, -me2, and -me3 in Tet. On histone H4, methylation at Lys-20 showed a similar pattern as H3 methylation at Lys-9, with mammals containing more methylation than the unicellular organisms. Additionally, modification profiles of H4 acetylation were very similar among the organisms examined. 相似文献
83.
Low molecular weight polar complexes were shown to be formed from 3H-aldosterone in both kidney and liver subcellular fractions, the majority being present in the cytosol fractions. Significant differences were observed between the quantities of polar complexes present in kidney subcellular fractions from intact and adrenalectomized male rats and also between the quantities of these kidney polar complexes from spironolactone treated male rats. 3H-aldosterone macro-molecule complexes were shown to exist in appreciable quantities only in the kidney cytosol fractions of adrenalectomized male rats. These gel filtration studies also showed the 3H-aldosterone labeled macromolecule complexes to consist of two protein peaks; one of high molecular weight and the other of lower molecular weight (~50,000 mol. wt.). The amount of 3H-aldosterone labeled protein complexes in kidney cytosol was greatly reduced when adrenalectomized rats were pretreated with spironolactone. 相似文献
84.
85.
H G Morris S A Rusnak J C Selner K Barzens J Barnes 《Journal of cyclic nucleotide research》1977,3(6):439-446
Cyclic AMP was measured in leukocytes of normal and asthmatic subjects before and after one week of treatment with equal amounts of ephedrine. During the control and placebo periods, the measurements of cyclic AMP in leukocytes of asthmatic subjects were similar to those of normal individuals. After one week of treatment with ephedrine, both groups exhibited suppression of the leukocyte cyclic AMP response to adrenergic stimulation in vitro: however, the suppression of response was significantly greater in asthmatic subjects (p less than .u1). Subcutaneous administration of epinephrine was followed by further suppression of the leukocyte cyclic AMP response to in vitro stimulation which was similar in both groups during all treatment periods. The results indicate that in vivo exposure to adrenergic medications is followed by desensitization of the leukocyte responses to subsequent adrenergic stimulation in vitro. After administration of small doses of medication, the severity and/or duration of desensitization is significantly greater in asthmatic leukocytes. 相似文献
86.
87.
Morris J. Robins Mirna C. Samano Vicente Samano 《Nucleosides, nucleotides & nucleic acids》2013,32(3-5):485-493
Abstract Ribonucleotide reductases are essential for the de novo biosynthesis of the 2′-deoxynucleotide components of DNA. These enzymes have complex cofactors and execute novel chemistry involving C2′ via radical abstraction of H3′. Mechanistic aspects of these transformations and selected nucleotide analogues that cause mechanism-based inactivation of ribonucleotide reductases are discussed. 相似文献
88.
I. R. Bradbury P. V. R. Snelgrove P. Bentzen B. de Young R. S. Gregory C. J. Morris 《Journal of fish biology》2009,75(6):1393-1409
The interplay between structural connectivity ( i.e. habitat continuity) and functional connectivity ( i.e. dispersal probability) in marine fishes was examined in a coastal fjord (Holyrood Pond, Newfoundland, Canada) that is completely isolated from the North Atlantic Ocean for most of the year. Genetic differentiation was described in three species (rainbow smelt Osmerus mordax , white hake Urophycis tenuis and Atlantic cod Gadus morhua ) with contrasting life histories using seven to 10 microsatellite loci and a protein-coding locus, Pan I ( G. morhua ). Analysis of microsatellite differentiation indicated clear genetic differences between the fjord and coastal regions; however, the magnitude of difference was no more elevated than adjacent bays and was not enhanced by the fjord's isolation. Osmerus mordax was characterized by the highest structure overall with moderate differentiation between the fjord and St Mary's Bay ( F ST c. 0·047). In contrast, U. tenuis and G. morhua displayed weak differentiation ( F ST < 0·01). Nonetheless, these populations did demonstrate high rates (< 75%) of Bayesian self-assignment. Furthermore, elevated differentiation was observed at the Pan I locus in G. morhua between the fjord and other coastal locations. Interestingly, locus-specific genetic differentiation and expected heterozygosity were negatively associated in O. mordax , in contrast to the positive associations observed in U. tenuis and G. morhua . Gene flow in these species is apparently unencumbered by limited structural connectivity, yet the observed differentiation suggests that population structuring exists over small scales despite high dispersal potential. 相似文献
89.
Isabella Steffensen William R. Bates Catherine E. Morris 《Development, growth & differentiation》1991,33(5):437-442
Certain developmental events are thought to be controlled by mechanical tension, but the nature of the transduction mechanism for sensing and responding to tension changes is unknown. A good candidate for such a sensing system would be stretch-activated (SA) ion channels, a type of mechanosensitive (MS) ion channel found in many preparations including the oocytes or embryos of ascidians, fish, and amphibians. To test the hypothesis that SA channel activation is important for early embryogenesis, we treated amphibian and ascidian eggs and embryos with inhibitors of MS ion channels. Xenopus laevis eggs and embryos were treated with gadolinium (Gd3+ ) concentrations up to 100 times the Kd for SA channel inhibition. Boltenia villosa eggs and embryos were exposed to three agents (Gd3+ , tubocurarine, and gallamine) which are known to block SA channels in other organisms. None of these drugs interfered with morphogenesis in a manner that would suggest SA channel activity is critical to early embryogenesis. 相似文献
90.
T.E. Mansour P.G. Morris J. Feeney G.C.K. Roberts 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1982,721(4):336-340
31P-NMR techniques offer a useful method of studying changes in the metabolism of intact parasitic worms. The liver flukes, Fasciola hepatica, provide good quality 31P high resolution NMR spectra for at least 6 h under anaerobic conditions. The levels of ATP remain constant throughout this period. There is no signal for phosphocreatine or phosphoarginine. In contrast to the findings in mammalian tissues, there is a distinct peak for the terminal phosphate of ADP. A number of signals are observed in the phosphodiester region of the spectrum the largest of which is identified as l-α-glycerophosphoryl choline. Serotonin (5-hydroxytryptamine) causes an appreciable increase in the levels of sugar phosphates when the flukes are incubated in the absence of glucose. The addition of glucose also causes a marked increase in the signals for the hexose phosphate. 相似文献