全文获取类型
收费全文 | 254篇 |
免费 | 0篇 |
专业分类
系统科学 | 4篇 |
现状及发展 | 131篇 |
研究方法 | 11篇 |
综合类 | 101篇 |
自然研究 | 7篇 |
出版年
2014年 | 3篇 |
2012年 | 5篇 |
2011年 | 16篇 |
2010年 | 3篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1990年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1981年 | 4篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1970年 | 7篇 |
1969年 | 6篇 |
1968年 | 5篇 |
1967年 | 5篇 |
1966年 | 6篇 |
1965年 | 5篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1960年 | 2篇 |
1959年 | 1篇 |
1958年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
1948年 | 3篇 |
1947年 | 6篇 |
1946年 | 3篇 |
排序方式: 共有254条查询结果,搜索用时 0 毫秒
1.
J A Martignetti A A Aqeel W A Sewairi C E Boumah M Kambouris S A Mayouf K V Sheth W A Eid O Dowling J Harris M J Glucksman S Bahabri B F Meyer R J Desnick 《Nature genetics》2001,28(3):261-265
The inherited osteolyses or 'vanishing bone' syndromes are a group of rare disorders of unknown etiology characterized by destruction and resorption of affected bones. The multicentric osteolyses are notable for interphalangeal joint erosions that mimic severe juvenile rheumatoid arthritis (OMIMs 166300, 259600, 259610 and 277950). We recently described an autosomal recessive form of multicentric osteolysis with carpal and tarsal resorption, crippling arthritic changes, marked osteoporosis, palmar and plantar subcutaneous nodules and distinctive facies in a number of consanguineous Saudi Arabian families. We localized the disease gene to 16q12-21 by using members of these families for a genome-wide search for homozygous-by-descent microsatellite markers. Haplotype analysis narrowed the critical region to a 1.2-cM region that spans the gene encoding MMP-2 (gelatinase A, collagenase type IV; (ref. 3). We detected no MMP2 enzymatic activity in the serum or fibroblasts of affected family members. We identified two family-specific homoallelic MMP2 mutations: R101H and Y244X. The nonsense mutation effects a deletion of the substrate-binding and catalytic sites and the fibronectin type II-like and hemopexin/TIMP2 binding domains. Based on molecular modeling, the missense mutation disrupts hydrogen bond formation within the highly conserved prodomain adjacent to the catalytic zinc ion. 相似文献
2.
3.
Bos KI Schuenemann VJ Golding GB Burbano HA Waglechner N Coombes BK McPhee JB DeWitte SN Meyer M Schmedes S Wood J Earn DJ Herring DA Bauer P Poinar HN Krause J 《Nature》2011,478(7370):506-510
Technological advances in DNA recovery and sequencing have drastically expanded the scope of genetic analyses of ancient specimens to the extent that full genomic investigations are now feasible and are quickly becoming standard. This trend has important implications for infectious disease research because genomic data from ancient microbes may help to elucidate mechanisms of pathogen evolution and adaptation for emerging and re-emerging infections. Here we report a reconstructed ancient genome of Yersinia pestis at 30-fold average coverage from Black Death victims securely dated to episodes of pestilence-associated mortality in London, England, 1348-1350. Genetic architecture and phylogenetic analysis indicate that the ancient organism is ancestral to most extant strains and sits very close to the ancestral node of all Y. pestis commonly associated with human infection. Temporal estimates suggest that the Black Death of 1347-1351 was the main historical event responsible for the introduction and widespread dissemination of the ancestor to all currently circulating Y. pestis strains pathogenic to humans, and further indicates that contemporary Y. pestis epidemics have their origins in the medieval era. Comparisons against modern genomes reveal no unique derived positions in the medieval organism, indicating that the perceived increased virulence of the disease during the Black Death may not have been due to bacterial phenotype. These findings support the notion that factors other than microbial genetics, such as environment, vector dynamics and host susceptibility, should be at the forefront of epidemiological discussions regarding emerging Y. pestis infections. 相似文献
4.
Learning causes a change in how information is processed by neuronal circuits. Whereas synaptic plasticity, an important cellular mechanism, has been studied in great detail, we know much less about how learning is implemented at the level of neuronal circuits and, in particular, how interactions between distinct types of neurons within local networks contribute to the process of learning. Here we show that acquisition of associative fear memories depends on the recruitment of a disinhibitory microcircuit in the mouse auditory cortex. Fear-conditioning-associated disinhibition in auditory cortex is driven by foot-shock-mediated cholinergic activation of layer 1 interneurons, in turn generating inhibition of layer 2/3 parvalbumin-positive interneurons. Importantly, pharmacological or optogenetic block of pyramidal neuron disinhibition abolishes fear learning. Together, these data demonstrate that stimulus convergence in the auditory cortex is necessary for associative fear learning to complex tones, define the circuit elements mediating this convergence and suggest that layer-1-mediated disinhibition is an important mechanism underlying learning and information processing in neocortical circuits. 相似文献
5.
Spatio-temporal transcriptome of the human brain 总被引:1,自引:0,他引:1
6.
Effect of conditioned media on nerve cell differentiation 总被引:2,自引:0,他引:2
M. Sensenbrenner G. G. Jaros G. Moonen B. J. Meyer 《Cellular and molecular life sciences : CMLS》1980,36(6):660-662
Summary Glial conditioned medium strongly stimulates the morphological maturation of cultured neuronal cells, while fibroblast and meningeal conditioned media have weaker effects.Acknowledgment. We acknowledge the expert technical assistance of Mrs M.F. Knoetgen. 相似文献
7.
K. H. Le Quan-Bui Marie-Aude Devynck Marie-Gabrielle Pernollet D. Ben-Ishay P. Meyer 《Cellular and molecular life sciences : CMLS》1981,37(2):169-170
Summary The cardiac catecholamine content of Sabra rats and their 2 genetically derived substrains, hypertension prone and resistant rats, was studied by high pressure liquid chromatography and electrochemical detection. Both in the control period and after sodium and DOCA administration the cardiac noradrenaline level is higher in hypertension resistant rats than in Sabra rats, and also higher than in hypertension prone rats. This finding suggests that a reduction of the cardiac sympathetic nervous tone is involved in the genetic resistance to sodium. 相似文献
8.
Western US ponderosa pine forests have recently suffered extensive stand-replacing fires followed by hillslope erosion and sedimentation. These fires are usually attributed to increased stand density as a result of fire suppression, grazing and other land use, and are often considered uncharacteristic or unprecedented. Tree-ring records from the past 500 years indicate that before Euro-American settlement, frequent, low-severity fires maintained open stands. However, the pre-settlement period between about ad 1500 and ad 1900 was also generally colder than present, raising the possibility that rapid twentieth-century warming promoted recent catastrophic fires. Here we date fire-related sediment deposits in alluvial fans in central Idaho to reconstruct Holocene fire history in xeric ponderosa pine forests and examine links to climate. We find that colder periods experienced frequent low-severity fires, probably fuelled by increased understory growth. Warmer periods experienced severe droughts, stand-replacing fires and large debris-flow events that comprise a large component of long-term erosion and coincide with similar events in sub-alpine forests of Yellowstone National Park. Our results suggest that given the powerful influence of climate, restoration of processes typical of pre-settlement times may be difficult in a warmer future that promotes severe fires. 相似文献
9.
Walder RY Landau D Meyer P Shalev H Tsolia M Borochowitz Z Boettger MB Beck GE Englehardt RK Carmi R Sheffield VC 《Nature genetics》2002,31(2):171-174
Familial hypomagnesemia with secondary hypocalcemia (OMIM 602014) is an autosomal recessive disease that results in electrolyte abnormalities shortly after birth. Affected individuals show severe hypomagnesemia and hypocalcemia, which lead to seizures and tetany. The disorder has been thought to be caused by a defect in the intestinal absorption of magnesium, rather than by abnormal renal loss of magnesium. Restoring the concentrations of serum magnesium to normal values by high-dose magnesium supplementation can overcome the apparent defect in magnesium absorption and in serum concentrations of calcium. Life-long magnesium supplementation is required to overcome the defect in magnesium handling by these individuals. We previously mapped the gene locus to chromosome 9q in three large inbred kindreds from Israel. Here we report that mutation of TRPM6 causes hypomagnesemia with secondary hypocalcemia and show that individuals carrying mutations in this gene have abnormal renal magnesium excretion. 相似文献
10.
Experimental demonstration of a robust,high-fidelity geometric two ion-qubit phase gate 总被引:8,自引:0,他引:8
Leibfried D DeMarco B Meyer V Lucas D Barrett M Britton J Itano WM Jelenković B Langer C Rosenband T Wineland DJ 《Nature》2003,422(6930):412-415
Universal logic gates for two quantum bits (qubits) form an essential ingredient of quantum computation. Dynamical gates have been proposed in the context of trapped ions; however, geometric phase gates (which change only the phase of the physical qubits) offer potential practical advantages because they have higher intrinsic resistance to certain small errors and might enable faster gate implementation. Here we demonstrate a universal geometric pi-phase gate between two beryllium ion-qubits, based on coherent displacements induced by an optical dipole force. The displacements depend on the internal atomic states; the motional state of the ions is unimportant provided that they remain in the regime in which the force can be considered constant over the extent of each ion's wave packet. By combining the gate with single-qubit rotations, we have prepared ions in an entangled Bell state with 97% fidelity-about six times better than in a previous experiment demonstrating a universal gate between two ion-qubits. The particular properties of the gate make it attractive for a multiplexed trap architecture that would enable scaling to large numbers of ion-qubits. 相似文献