全文获取类型
收费全文 | 246篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 5篇 |
教育与普及 | 1篇 |
现状及发展 | 60篇 |
研究方法 | 19篇 |
综合类 | 152篇 |
自然研究 | 11篇 |
出版年
2014年 | 1篇 |
2013年 | 2篇 |
2012年 | 9篇 |
2011年 | 18篇 |
2010年 | 5篇 |
2008年 | 12篇 |
2007年 | 4篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 16篇 |
1969年 | 3篇 |
1968年 | 10篇 |
1967年 | 6篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有248条查询结果,搜索用时 234 毫秒
61.
Li Tiegang Liu Zhenxia M. A. Hall Y. Saito S. Berne Cang Shuxi Cheng Zhenbo 《科学通报(英文版)》2002,47(7):599-603
The equatorial Pacific upwelling zone has been suspected of playing an important role in the global atmospheric CO2 changes associated with glacial-interglacial cycles.In order to assess the influencing scope of the surface water deglacial δ13C minimum in the tropical Iow-latitude Pacific,the core DGKS9603, collected from the middle Okinawa Trough, was examined for δ13C records of planktonic foraminifera N. dutertrei and G. ruber. The planktonic foraminiferal δ13C records show a clear decreasing event from 20 to 6 cal. kaBP., which is characterized by long duration of about 14 ka and amplitude shift of 0.4 × 10-3. Its minimum value occurred at 15.7 cai kaBP. The event shows fairly synchrony with the surface water deglacial δ13C minimum identiffed in the tropical Pacific and its marginal seas. Because there is no evidence in planktonic foraminiferal fauna and δ18O records for upwelling and river runoff enhancement,the broad deglacial δ13C minimum event in planktonic foraminiferal records revealed in core DGKS9603 might have been the direct influencing result of the deglacial surface water of the tropical Pacific. The identification for the event in the Okinawa Trough provides new evidence that the water evolution in the tropical low-latitude Pacific plays a key role in large regional, even global carbon cycle. 相似文献
62.
Several authors (King and Rebelo, 1993; Cogley and Nason, 1995) have questioned the use of exponentially weighted moving average filters such as the Hodrick–Prescott filter in decomposing a series into a trend and cycle, claiming that they lead to the observation of spurious or induced cycles and to misinterpretation of stylized facts. However, little has been done to propose different methods of estimation or other ways of defining trend extraction. This paper has two main contributions. First, we suggest that the decomposition between the trend and cycle has not been done in an appropriate way. Second, we argue for a general to specific approach based on a more general filter, the stochastic trend model, that allows us to estimate all the parameters of the model rather than fixing them arbitrarily, as is done with mainly of the commonly used filters. We illustrate the properties of the proposed technique relative to the conventional ones by employing a Monte Carlo study. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
63.
Noel Edwards Catriona M. H. Anderson Nichola J. Conlon Andrew K. Watson Rebecca J. Hall Timothy R. Cheek T. Martin Embley David T. Thwaites 《Cellular and molecular life sciences : CMLS》2018,75(5):921-938
Amino acid transporters are essential components of prokaryote and eukaryote cells, possess distinct physiological functions, and differ markedly in substrate specificity. Amino acid transporters can be both drug targets and drug transporters (bioavailability, targeting) with many monogenic disorders resulting from dysfunctional membrane transport. The largest collection of amino acid transporters (including the mammalian SLC6, SLC7, SLC32, SLC36, and SLC38 families), across all kingdoms of life, is within the Amino acid-Polyamine-organoCation (APC) superfamily. The LeuT-fold is a paradigm structure for APC superfamily amino acid transporters and carriers of sugars, neurotransmitters, electrolytes, osmolytes, vitamins, micronutrients, signalling molecules, and organic and fatty acids. Each transporter is specific for a unique sub-set of solutes, specificity being determined by how well a substrate fits into each binding pocket. However, the molecular basis of substrate selectivity remains, by and large, elusive. Using an integrated computational and experimental approach, we demonstrate that a single position within the LeuT-fold can play a crucial role in determining substrate specificity in mammalian and arthropod amino acid transporters within the APC superfamily. Systematic mutation of the amino acid residue occupying the equivalent position to LeuT V104 titrates binding pocket space resulting in dramatic changes in substrate selectivity in exemplar APC amino acid transporters including PAT2 (SLC36A2) and SNAT5 (SLC38A5). Our work demonstrates how a single residue/site within an archetypal structural motif can alter substrate affinity and selectivity within this important superfamily of diverse membrane transporters. 相似文献
64.
65.
Cotton RG; Human Variome Project Appelbe W Auerbach AD Becker K Bodmer W Boone DJ Boulyjenkov V Brahmachari S Brody L Brookes A Brown AF Byers P Cantu JM Cassiman JJ Claustres M Concannon P Cotton RG den Dunnen JT Flicek P Gibbs R Hall J Hasler J Katz M Kwok PY Laradi S Lindblom A Maglott D Marsh S Masimirembwa CM Minoshima S de Ramirez AM Pagon R Ramesar R Ravine D Richards S Rimoin D Ring HZ Scriver CR Sherry S Shimizu N Stein L Tadmouri GO Taylor G Watson M 《Nature genetics》2007,39(4):433-436
Lists of variations in genomic DNA and their effects have been kept for some time and have been used in diagnostics and research. Although these lists have been carefully gathered and curated, there has been little standardization and coordination, complicating their use. Given the myriad possible variations in the estimated 24,000 genes in the human genome, it would be useful to have standard criteria for databases of variation. Incomplete collection and ascertainment of variants demonstrates a need for a universally accessible system. These and other problems led to the World Heath Organization-cosponsored meeting on June 20-23, 2006 in Melbourne, Australia, which launched the Human Variome Project. This meeting addressed all areas of human genetics relevant to collection of information on variation and its effects. Members of each of eight sessions (the clinic and phenotype, the diagnostic laboratory, the research laboratory, curation and collection, informatics, relevance to the emerging world, integration and federation and funding and sustainability) developed a number of recommendations that were then organized into a total of 96 recommendations to act as a foundation for future work worldwide. Here we summarize the background of the project, the meeting and its recommendations. 相似文献
66.
67.
Whole-genome sequence of Schistosoma haematobium 总被引:1,自引:0,他引:1
Young ND Jex AR Li B Liu S Yang L Xiong Z Li Y Cantacessi C Hall RS Xu X Chen F Wu X Zerlotini A Oliveira G Hofmann A Zhang G Fang X Kang Y Campbell BE Loukas A Ranganathan S Rollinson D Rinaldi G Brindley PJ Yang H Wang J Wang J Gasser RB 《Nature genetics》2012,44(2):221-225
Schistosomiasis is a neglected tropical disease caused by blood flukes (genus Schistosoma; schistosomes) and affecting 200 million people worldwide. No vaccines are available, and treatment relies on one drug, praziquantel. Schistosoma haematobium has come into the spotlight as a major cause of urogenital disease, as an agent linked to bladder cancer and as a predisposing factor for HIV/AIDS. The parasite is transmitted to humans from freshwater snails. Worms dwell in blood vessels and release eggs that become embedded in the bladder wall to elicit chronic immune-mediated disease and induce squamous cell carcinoma. Here we sequenced the 385-Mb genome of S. haematobium using Illumina-based technology at 74-fold coverage and compared it to sequences from related parasites. We included genome annotation based on function, gene ontology, networking and pathway mapping. This genome now provides an unprecedented resource for many fundamental research areas and shows great promise for the design of new disease interventions. 相似文献
68.
The frequency and intensity of wildfire in the western United States has increased over the last century, creating a heterogeneous mosaic of landscapes in various stages of recovery. The 2002 Hayman Fire was one of the largest wildfires in Colorado history and was unprecedented for its speed and intensity, with over 50%–70% of the burn area classified as moderate to high severity where much of the canopy crown was consumed. We evaluated the short-term impact of the Hayman Fire on ecological properties in montane stream ecosystems in the summers of 2003 and 2004, one and two years post-fire. Fire significantly altered surface temperature, dissolved oxygen concentration, and the chemical composition of stream water, including concentrations of nitrate, phosphate, and mineral salts. However, fire did not have significant impacts on stream conductivity, pH, or total concentrations of cations or anions during our study period. Streams in the burn area contained fewer benthic macroinvertebrate taxa compared to unburned streams during the year after fire and contained lower invertebrate densities and biomass compared to reference streams 2 years post-fire. Average C:N ratio of the benthic macroinvertebrate community was significantly and negatively related to stream nitrate concentration, possibly due to a shift in community composition or invertebrate nitrogen acquisition in fire-affected streams. 相似文献
69.
70.
1,2,4-Triazolidine-3,5-diones and the 3,5-isoxazolidinedione were observed to be potent inhibitors of rat lens aldose reductase activity. In vivo in streptozotocin-diabetic rats, selected agents at 20 mg/kg/day, orally for 21 days reduced significantly the sorbitol levels of rbc, lens and sciatic nerves, suggesting that these derivatives may have some usefulness to treat clinical complications of diabetes mellitus. 相似文献