全文获取类型
收费全文 | 207篇 |
免费 | 0篇 |
专业分类
系统科学 | 4篇 |
现状及发展 | 39篇 |
研究方法 | 37篇 |
综合类 | 114篇 |
自然研究 | 13篇 |
出版年
2021年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 3篇 |
2012年 | 7篇 |
2011年 | 31篇 |
2010年 | 3篇 |
2008年 | 11篇 |
2007年 | 21篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 6篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有207条查询结果,搜索用时 31 毫秒
91.
Bond J Roberts E Springell K Lizarraga SB Lizarraga S Scott S Higgins J Hampshire DJ Morrison EE Leal GF Silva EO Costa SM Baralle D Raponi M Karbani G Rashid Y Jafri H Bennett C Corry P Walsh CA Woods CG 《Nature genetics》2005,37(4):353-355
Autosomal recessive primary microcephaly is a potential model in which to research genes involved in human brain growth. We show that two forms of the disorder result from homozygous mutations in the genes CDK5RAP2 and CENPJ. We found neuroepithelial expression of the genes during prenatal neurogenesis and protein localization to the spindle poles of mitotic cells, suggesting that a centrosomal mechanism controls neuron number in the developing mammalian brain. 相似文献
92.
Functional analysis of secreted and transmembrane proteins critical to mouse development. 总被引:20,自引:0,他引:20
K J Mitchell K I Pinson O G Kelly J Brennan J Zupicich P Scherz P A Leighton L V Goodrich X Lu B J Avery P Tate K Dill E Pangilinan P Wakenight M Tessier-Lavigne W C Skarnes 《Nature genetics》2001,28(3):241-249
We describe the successful application of a modified gene-trap approach, the secretory trap, to systematically analyze the functions in vivo of large numbers of genes encoding secreted and membrane proteins. Secretory-trap insertions in embryonic stem cells can be transmitted to the germ line of mice with high efficiency and effectively mutate the target gene. Of 60 insertions analyzed in mice, one-third cause recessive lethal phenotypes affecting various stages of embryonic and postnatal development. Thus, secretory-trap mutagenesis can be used for a genome-wide functional analysis of cell signaling pathways that are critical for normal mammalian development and physiology. 相似文献
93.
We examined abundance and flight periodicity of 3 predators of bark beetles (Coleoptera: Curculionidae, Scolytinae), Temnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae), Enoclerus sphegeus (Fabricius) (Coleoptera: Cleridae), and E. lecontei (Wolcott) (Coleoptera: Cleridae), across an elevational gradient of ponderosa pine ( Pinus ponderosa Lawson) forests in north central Arizona. Predator populations were estimated at 10 sites in each of 3 elevation bands (low: 1600–1736 m; mid: 2058–2230 m; high: 2505–2651 m) for 3 years (2004–2006) using pheromone-baited funnel traps targeting 3 primary bark beetle species. We also investigated how predator abundance and flight seasonality related to those of 5 bark beetle species: Ips pini (Say), I. lecontei Swaine, Dendroctonus frontalis Zimmermann, D. brevicomis LeConte, and D. adjunctus Blandford. Temnochila chlorodia was most abundant in the low- and mid-elevation bands, whereas E. sphegeus was most abundant in the high-elevation band. Enoclerus lecontei showed no consistent elevational trend in abundance. Within each elevation band, changes in annual abundance of pooled predator species tracked shifts in abundance of pooled bark beetle species. In general, predator flight initiation coincided with or closely followed bark beetle flight initiation in the spring, but predator flight terminated before flight activity ended for most bark beetle species in the fall. In addition, the ratio of prey to predators was lowest in the summer and highest in the fall. This suggests that all bark beetle species examined may be provided temporal escape from their predators in the fall. For all 3 predator species, the pheromone-baited trap targeting D. brevicomis was less attractive than the pheromone-baited traps targeting I. pini and I. lecontei. 相似文献
94.
Assembly and function of the two ABC transporter proteins encoded in the human major histocompatibility complex. 总被引:30,自引:0,他引:30
A Kelly S H Powis L A Kerr I Mockridge T Elliott J Bastin B Uchanska-Ziegler A Ziegler J Trowsdale A Townsend 《Nature》1992,355(6361):641-644
Presentation of cytoplasmic antigens to class I-restricted cytotoxic T cells implied the existence of a specialized peptide transporter. For most class I heavy chains, association with peptides of the appropriate length is required for stable assembly with beta 2-microglobulin. Mutant cells RMA-S and .174/T2 neither assemble stable class I molecules nor present intracellular antigens, and we have suggested that they have lost a function required for the transport of short peptides from the cytosol to the endoplasmic reticulum. The genetic defect in .174 has been localized to a large deletion in the class II region of the major histocompatibility complex, within which two genes (RING4 and RING11) have been identified that code for 'ABC' (ATP-binding cassette) transporters. We report here that the protein products of these two genes assemble to form a complex. Defects in either protein result in the formation of unstable class I molecules and loss of presentation of intracellular antigens. The molecular defect in a new mutant, BM36.1, is shown to be in the ATP-binding domain of the RING11/PSF2 protein. This is in contrast to the mutant .134, which lacks the RING4/PSF1 protein. 相似文献
95.
多梯度复杂图像的分割 总被引:1,自引:1,他引:0
图像分割是一种重要的图像分析技术,它不仅得到人们广泛的重视和研究,也在实际中得到大量的应用。本文针对一些经典分割算法对多梯度复杂图像分割边缘定位不准确,易受噪声干扰的特点,提出了一种利用图像边缘区域对多梯度复杂图像进行自适应阈值分割的算法。通过对各种算法的比较,本算法抗干扰能力较强,稳定性好,而且完全自动,不需预先设定任何参数。对多种图像的实验表明本文方法十分有效。 相似文献
96.
97.
Planavsky NJ McGoldrick P Scott CT Li C Reinhard CT Kelly AE Chu X Bekker A Love GD Lyons TW 《Nature》2011,477(7365):448-451
The chemical composition of the ocean changed markedly with the oxidation of the Earth's surface, and this process has profoundly influenced the evolutionary and ecological history of life. The early Earth was characterized by a reducing ocean-atmosphere system, whereas the Phanerozoic eon (less than 542 million years ago) is known for a stable and oxygenated biosphere conducive to the radiation of animals. The redox characteristics of surface environments during Earth's middle age (1.8-1 billion years ago) are less well known, but it is generally assumed that the mid-Proterozoic was home to a globally sulphidic (euxinic) deep ocean. Here we present iron data from a suite of mid-Proterozoic marine mudstones. Contrary to the popular model, our results indicate that ferruginous (anoxic and Fe(2+)-rich) conditions were both spatially and temporally extensive across diverse palaeogeographic settings in the mid-Proterozoic ocean, inviting new models for the temporal distribution of iron formations and the availability of bioessential trace elements during a critical window for eukaryotic evolution. 相似文献
98.
Yokoyama S Woods SL Boyle GM Aoude LG MacGregor S Zismann V Gartside M Cust AE Haq R Harland M Taylor JC Duffy DL Holohan K Dutton-Regester K Palmer JM Bonazzi V Stark MS Symmons J Law MH Schmidt C Lanagan C O'Connor L Holland EA Schmid H Maskiell JA Jetann J Ferguson M Jenkins MA Kefford RF Giles GG Armstrong BK Aitken JF Hopper JL Whiteman DC Pharoah PD Easton DF Dunning AM Newton-Bishop JA Montgomery GW Martin NG Mann GJ Bishop DT Tsao H Trent JM Fisher DE Hayward NK Brown KM 《Nature》2011,480(7375):99-103
99.
Tom Flanagan Janet McIntyre-Mills Tony Made Kelly Mackenzie Charles Morse Gayle Underwood Ken Bausch 《Systemic Practice and Action Research》2012,25(2):171-193
Sustainability is not simply about changing practices but more centrally about agreeing to change practices together. To achieve
such an end, groups need to improve processes for making complex decisions together. An online course was designed and tested
linking students in the United States and in Australia. Students engaged in a re-enactment of deliberations based on Hasan
Ozbekhan’s “Predicament of Mankind,” which was constructed originally under assignment from the founders of the Club of Rome
in 1970. This re-enactment included contemporary research for examples of a set of 49 continuous critical problems of mankind,
asynchronous clarification of these problems using a wiki, pair-wise construction of a systems view of problems assessed to
be of highest priority by the class, narrative analysis of the structure, and creative suggestions for resolving the systems
problem based on resources available today. This report comments on the strengths and challenges identified in an initial
application of an approach for building collaborative and systems thinking skills through an online course in a general education
curriculum. Findings are particularly meaningful for contemporary policy makers as well as online educators. 相似文献
100.