全文获取类型
收费全文 | 177篇 |
免费 | 0篇 |
专业分类
系统科学 | 2篇 |
理论与方法论 | 1篇 |
现状及发展 | 29篇 |
研究方法 | 29篇 |
综合类 | 114篇 |
自然研究 | 2篇 |
出版年
2020年 | 1篇 |
2013年 | 2篇 |
2012年 | 5篇 |
2011年 | 9篇 |
2010年 | 1篇 |
2008年 | 15篇 |
2007年 | 6篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 6篇 |
1969年 | 1篇 |
1968年 | 3篇 |
1967年 | 6篇 |
1966年 | 1篇 |
1965年 | 3篇 |
1963年 | 1篇 |
排序方式: 共有177条查询结果,搜索用时 15 毫秒
41.
A semiconductor source of triggered entangled photon pairs 总被引:1,自引:0,他引:1
Entangled photon pairs are an important resource in quantum optics, and are essential for quantum information applications such as quantum key distribution and controlled quantum logic operations. The radiative decay of biexcitons-that is, states consisting of two bound electron-hole pairs-in a quantum dot has been proposed as a source of triggered polarization-entangled photon pairs. To date, however, experiments have indicated that a splitting of the intermediate exciton energy yields only classically correlated emission. Here we demonstrate triggered photon pair emission from single quantum dots suggestive of polarization entanglement. We achieve this by tuning the splitting to zero, through either application of an in-plane magnetic field or careful control of growth conditions. Entangled photon pairs generated 'on demand' have significant fundamental advantages over other schemes, which can suffer from multiple pair emission, or require post-selection techniques or the use of photon-number discriminating detectors. Furthermore, control over the pair generation time is essential for scaling many quantum information schemes beyond a few gates. Our results suggest that a triggered entangled photon pair source could be implemented by a simple semiconductor light-emitting diode. 相似文献
42.
Gissen P Johnson CA Morgan NV Stapelbroek JM Forshew T Cooper WN McKiernan PJ Klomp LW Morris AA Wraith JE McClean P Lynch SA Thompson RJ Lo B Quarrell OW Di Rocco M Trembath RC Mandel H Wali S Karet FE Knisely AS Houwen RH Kelly DA Maher ER 《Nature genetics》2004,36(4):400-404
ARC syndrome (OMIM 208085) is an autosomal recessive multisystem disorder characterized by neurogenic arthrogryposis multiplex congenita, renal tubular dysfunction and neonatal cholestasis with bile duct hypoplasia and low gamma glutamyl transpeptidase (gGT) activity. Platelet dysfunction is common. Affected infants do not thrive and usually die in the first year of life. To elucidate the molecular basis of ARC, we mapped the disease to a 7-cM interval on 15q26.1 and then identified germline mutations in the gene VPS33B in 14 kindreds with ARC. VPS33B encodes a homolog of the class C yeast vacuolar protein sorting gene, Vps33, that contains a Sec1-like domain important in the regulation of vesicle-to-target SNARE complex formation and subsequent membrane fusion. 相似文献
43.
Ionic liquids and eutectic mixtures as solvent and template in synthesis of zeolite analogues 总被引:3,自引:0,他引:3
The challenges associated with synthesizing porous materials mean that new classes of zeolites (zeotypes)-such as aluminosilicate zeolites and zeolite analogues-together with new methods of preparing known zeotypes, continue to be of great importance. Normally these materials are prepared hydrothermally with water as the solvent in a sealed autoclave under autogenous pressure. The reaction mixture usually includes an organic template or 'structure-directing agent' that guides the synthesis pathway towards particular structures. Here we report the preparation of aluminophosphate zeolite analogues by using ionic liquids and eutectic mixtures. An imidazolium-based ionic liquid acts as both solvent and template, leading to four zeotype frameworks under different experimental conditions. The structural characteristics of the materials can be traced back to the solvent chemistry used. Because of the vanishingly low vapour pressure of ionic liquids, synthesis takes place at ambient pressure, eliminating safety concerns associated with high hydrothermal pressures. The ionic liquid can also be recycled for further use. A choline chloride/urea eutectic mixture is also used in the preparation of a new zeotype framework. 相似文献
44.
Cooper S 《Cellular and molecular life sciences : CMLS》2003,60(6):1099-1106
An analysis of different classes of forced or batch synchronization methods reveals why these methods, in theory, do not produce synchronized cultures. Cells may be aligned for a particular property after specific treatments, but these aligned cells do not correspond to any particular cell age during the normal cell cycle. The experimental methods analyzed are those that arrest cells with a G1 phase amount of DNA, those that inhibit DNA synthesis, and those that arrest cells at mitosis. Release of arrested cells from inhibition does not produce cells reflecting cells during the normal division cycle. Thus, cells produced by batch or forcing methods are not experimental models for analysis of the normal cell cycle. 相似文献
45.
Disruption of the actin cytoskeleton in yeast capping protein mutants 总被引:42,自引:0,他引:42
Capping protein controls the addition of actin subunits to the barbed end of actin filaments and nucleates actin polymerization in vitro. Capping protein has been identified in all eukaryotic cells examined so far; it is a heterodimer with subunits of relative molecular masses 32,000-36,000 (alpha-subunit) and 28,000-32,000 (beta-subunit). In skeletal muscle, capping protein (CapZ) probably binds the barbed ends of actin filaments at the Z line. The in vivo role of this protein in non-muscle cells is not known. We report here the characterization of CAP2, the single gene encoding the beta-subunit of capping protein in Saccharomyces cerevisiae. Yeast cells in which the CAP2 gene was disrupted by an insertion or a deletion had an abnormal actin distribution, including the loss of actin cables. The mutant cells were round and large, with a heterogeneous size distribution, and, although viable, grew more slowly than congenic wild-type cells. Chitin, a cell wall component restricted to the mother-bud junction in wild-type budding yeast, was found on the entire mother cell surface in the mutants. The phenotype of CAP2 disruption resembled that of temperature-sensitive mutations in the yeast actin gene ACT1, indicating that capping protein regulates actin-filament distribution in vivo. 相似文献
46.
p53 mutant mice that display early ageing-associated phenotypes. 总被引:56,自引:0,他引:56
Stuart D Tyner Sundaresan Venkatachalam Jene Choi Stephen Jones Nader Ghebranious Herbert Igelmann Xiongbin Lu Gabrielle Soron Benjamin Cooper Cory Brayton Sang Hee Park Timothy Thompson Gerard Karsenty Allan Bradley Lawrence A Donehower 《Nature》2002,415(6867):45-53
The p53 tumour suppressor is activated by numerous stressors to induce apoptosis, cell cycle arrest, or senescence. To study the biological effects of altered p53 function, we generated mice with a deletion mutation in the first six exons of the p53 gene that express a truncated RNA capable of encoding a carboxy-terminal p53 fragment. This mutation confers phenotypes consistent with activated p53 rather than inactivated p53. Mutant (p53+/m) mice exhibit enhanced resistance to spontaneous tumours compared with wild-type (p53+/+) littermates. As p53+/m mice age, they display an early onset of phenotypes associated with ageing. These include reduced longevity, osteoporosis, generalized organ atrophy and a diminished stress tolerance. A second line of transgenic mice containing a temperature-sensitive mutant allele of p53 also exhibits early ageing phenotypes. These data suggest that p53 has a role in regulating organismal ageing. 相似文献
47.
D W Cooper 《Nature》1971,230(5292):292-294
48.
Bovee D Zhou Y Haugen E Wu Z Hayden HS Gillett W Tuzun E Cooper GM Sampas N Phelps K Levy R Morrison VA Sprague J Jewett D Buckley D Subramaniam S Chang J Smith DR Olson MV Eichler EE Kaul R 《Nature genetics》2008,40(1):96-101
The human genome sequence has been finished to very high standards; however, more than 340 gaps remained when the finished genome was published by the International Human Genome Sequencing Consortium in 2004. Using fosmid resources generated from multiple individuals, we targeted gaps in the euchromatic part of the human genome. Here we report 2,488,842 bp of previously unknown euchromatic sequence, 363,114 bp of which close 26 of 250 euchromatic gaps, or 10%, including two remaining euchromatic gaps on chromosome 19. Eight (30.7%) of the closed gaps were found to be polymorphic. These sequences allow complete annotation of several human genes as well as the assignment of mRNAs. The gap sequences are 2.3-fold enriched in segmentally duplicated sequences compared to the whole genome. Our analysis confirms that not all gaps within 'finished' genomes are recalcitrant to subcloning and suggests that the paired-end-sequenced fosmid libraries could prove to be a rich resource for completion of the human euchromatic genome. 相似文献
49.
A genome-wide association study of nonsynonymous SNPs identifies a type 1 diabetes locus in the interferon-induced helicase (IFIH1) region 总被引:1,自引:0,他引:1
Smyth DJ Cooper JD Bailey R Field S Burren O Smink LJ Guja C Ionescu-Tirgoviste C Widmer B Dunger DB Savage DA Walker NM Clayton DG Todd JA 《Nature genetics》2006,38(6):617-619
In this study we report convincing statistical support for a sixth type 1 diabetes (T1D) locus in the innate immunity viral RNA receptor gene region IFIH1 (also known as mda-5 or Helicard) on chromosome 2q24.3. We found the association in an interim analysis of a genome-wide nonsynonymous SNP (nsSNP) scan, and we validated it in a case-control collection and replicated it in an independent family collection. In 4,253 cases, 5,842 controls and 2,134 parent-child trio genotypes, the risk ratio for the minor allele of the nsSNP rs1990760 A --> G (A946T) was 0.86 (95% confidence interval = 0.82-0.90) at P = 1.42 x 10(-10). 相似文献
50.
Xue QG Itoh N Schey KL Li YL Cooper RK La Peyre JF 《Cellular and molecular life sciences : CMLS》2007,64(1):82-95
A new lysozyme (cv-lysozyme 2) with a MALDI molecular mass of 12 984.6 Da was purified from crystalline styles and digestive
glands of eastern oysters (Crassostrea virginica) and its cDNA sequenced. Quantitative real time RT-PCR detected cv-lysozyme 2 gene expression primarily in digestive gland
tissues, and in situ hybridization located cv-lysozyme 2 gene expression in basophil cells of digestive tubules. Cv-lysozyme 2 showed high amino
acid sequence similarity to other bivalve mollusk lysozymes, including cv-lysozyme 1, a lysozyme recently purified from C. virginica plasma. Differences between cv-lysozyme 2 and cv-lysozyme 1 molecular characteristics, enzymatic properties, antibacterial
activities, distribution in the oyster body and site of gene expression indicate that the main role of cv-lysozyme 2 is in
digestion. While showing that a bivalve mollusk employs different lysozymes for different functions, findings in this study
suggest adaptive evolution of i type lysozymes for nutrition.
Received 30 August 2006; received after revision 14 October 2006; accepted 6 November 2006 相似文献