全文获取类型
收费全文 | 350篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
丛书文集 | 1篇 |
教育与普及 | 1篇 |
现状及发展 | 80篇 |
研究方法 | 43篇 |
综合类 | 210篇 |
自然研究 | 16篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2012年 | 9篇 |
2011年 | 33篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 16篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 25篇 |
2001年 | 21篇 |
2000年 | 24篇 |
1999年 | 14篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 12篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1971年 | 5篇 |
1970年 | 12篇 |
1969年 | 9篇 |
1968年 | 3篇 |
1967年 | 5篇 |
1966年 | 6篇 |
1965年 | 4篇 |
1964年 | 3篇 |
1962年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有351条查询结果,搜索用时 78 毫秒
281.
Mid-depth recirculation observed in the interior Labrador and Irminger seas by direct velocity measurements 总被引:1,自引:0,他引:1
The Labrador Sea is one of the sites where convection exports surface water to the deep ocean in winter as part of the thermohaline circulation. Labrador Sea water is characteristically cold and fresh, and it can be traced at intermediate depths (500-2,000 m) across the North Atlantic Ocean, to the south and to the east of the Labrador Sea. Widespread observations of the ocean currents that lead to this distribution of Labrador Sea water have, however, been difficult and therefore scarce. We have used more than 200 subsurface floats to measure directly basin-wide horizontal velocities at various depths in the Labrador and Irminger seas. We observe unanticipated recirculations of the mid-depth (approximately 700 m) cyclonic boundary currents in both basins, leading to an anticyclonic flow in the interior of the Labrador basin. About 40% of the floats from the region of deep convection left the basin within one year and were rapidly transported in the anticyclonic flow to the Irminger basin, and also eastwards into the subpolar gyre. Surprisingly, the float tracks did not clearly depict the deep western boundary current, which is the expected main pathway of Labrador Sea water in the thermohaline circulation. Rather, the flow along the boundary near Flemish Cap is dominated by eddies that transport water offshore. Our detailed observations of the velocity structure with a high data coverage suggest that we may have to revise our picture of the formation and spreading of Labrador Sea water, and future studies with similar instrumentation will allow new insights on the intermediate depth ocean circulation. 相似文献
282.
Mutations in an oocyte-derived growth factor gene (BMP15) cause increased ovulation rate and infertility in a dosage-sensitive manner 总被引:43,自引:0,他引:43
Galloway SM McNatty KP Cambridge LM Laitinen MP Juengel JL Jokiranta TS McLaren RJ Luiro K Dodds KG Montgomery GW Beattie AE Davis GH Ritvos O 《Nature genetics》2000,25(3):279-283
Multiple ovulations are uncommon in humans, cattle and many breeds of sheep. Pituitary gonadotrophins and as yet unidentified ovarian factors precisely regulate follicular development so that, normally, only one follicle is selected to ovulate. The Inverdale (FecXI) sheep, however, carries a naturally occurring X-linked mutation that causes increased ovulation rate and twin and triplet births in heterozygotes (FecXI/FecX+; ref. 1), but primary ovarian failure in homozygotes (FecXI/FecXI; ref. 2). Germ-cell development, formation of the follicle and the earliest stages of follicular growth are normal in FecXI/FecXI sheep, but follicular development beyond the primary stage is impaired. A second family unrelated to the Inverdale sheep also has the same X-linked phenotype (Hanna, FecXH). Crossing FecXI with FecXH animals produces FecXI/FecXH infertile females phenotypically indistinguishable from FecXI/FecXI females. We report here that the FecXI locus maps to an orthologous chromosomal region syntenic to human Xp11.2-11.4, which contains BMP15, encoding bone morphogenetic protein 15 (also known as growth differentiation factor 9B (GDF9B)). Whereas BMP15 is a member of the transforming growth factor beta (TGFbeta) superfamily and is specifically expressed in oocytes, its function is unknown. We show that independent germline point mutations exist in FecXI and FecXH carriers. These findings establish that BMP15 is essential for female fertility and that natural mutations in an ovary-derived factor can cause both increased ovulation rate and infertility phenotypes in a dosage-sensitive manner. 相似文献
283.
284.
285.
Mapping T-cell receptor-peptide contacts by variant peptide immunization of single-chain transgenics. 总被引:58,自引:0,他引:58
To test models of T-cell recognition, mice transgenic for T-cell receptor alpha or beta chain have been immunized with variant peptides that force changes in the resulting T-cell response. In particular, charge substitutions on the peptide often elicit reciprocal charges in the junctional (CDR3) sequences of T-cell receptor V alpha or V beta chains, indicating direct T-cell receptor-peptide contact, and allowing derivation of a topology for the T-cell receptor-MHC interaction. At one position on the peptide, variants transformed a homogeneous V beta response into a very heterogeneous one. 相似文献
286.
≈37 kaBP大气中宇宙成因同位素含量增加的古里雅冰芯证据 总被引:4,自引:1,他引:3
证实了≈37kaBP青藏高原古里雅冰芯记录中这于宙成因同位素^36Cl含量峰值的存在,并认为该峰值是^36Cl在大气中产生速率增加导致的,而不是净积累速率变化影响的结果。发现这一峰值事件与气候变冷相伴出现。 相似文献
287.
The mouse mahogany locus encodes a transmembrane form of human attractin 总被引:16,自引:0,他引:16
Gunn TM Miller KA He L Hyman RW Davis RW Azarani A Schlossman SF Duke-Cohan JS Barsh GS 《Nature》1999,398(6723):152-156
288.
Impaired T(H)17 cell differentiation in subjects with autosomal dominant hyper-IgE syndrome 总被引:1,自引:0,他引:1
Milner JD Brenchley JM Laurence A Freeman AF Hill BJ Elias KM Kanno Y Spalding C Elloumi HZ Paulson ML Davis J Hsu A Asher AI O'Shea J Holland SM Paul WE Douek DC 《Nature》2008,452(7188):773-776
289.
The genome of the model beetle and pest Tribolium castaneum 总被引:6,自引:0,他引:6
Tribolium Genome Sequencing Consortium Richards S Gibbs RA Weinstock GM Brown SJ Denell R Beeman RW Gibbs R Beeman RW Brown SJ Bucher G Friedrich M Grimmelikhuijzen CJ Klingler M Lorenzen M Richards S Roth S Schröder R Tautz D Zdobnov EM Muzny D Gibbs RA Weinstock GM Attaway T Bell S Buhay CJ Chandrabose MN Chavez D Clerk-Blankenburg KP Cree A Dao M Davis C Chacko J Dinh H Dugan-Rocha S Fowler G Garner TT Garnes J Gnirke A Hawes A Hernandez J Hines S Holder M Hume J Jhangiani SN Joshi V Khan ZM 《Nature》2008,452(7190):949-955
Tribolium castaneum is a member of the most species-rich eukaryotic order, a powerful model organism for the study of generalized insect development, and an important pest of stored agricultural products. We describe its genome sequence here. This omnivorous beetle has evolved the ability to interact with a diverse chemical environment, as shown by large expansions in odorant and gustatory receptors, as well as P450 and other detoxification enzymes. Development in Tribolium is more representative of other insects than is Drosophila, a fact reflected in gene content and function. For example, Tribolium has retained more ancestral genes involved in cell-cell communication than Drosophila, some being expressed in the growth zone crucial for axial elongation in short-germ development. Systemic RNA interference in T. castaneum functions differently from that in Caenorhabditis elegans, but nevertheless offers similar power for the elucidation of gene function and identification of targets for selective insect control. 相似文献
290.
M Krauthammer Y Kong BH Ha P Evans A Bacchiocchi JP McCusker E Cheng MJ Davis G Goh M Choi S Ariyan D Narayan K Dutton-Regester A Capatana EC Holman M Bosenberg M Sznol HM Kluger DE Brash DF Stern MA Materin RS Lo S Mane S Ma KK Kidd NK Hayward RP Lifton J Schlessinger TJ Boggon R Halaban 《Nature genetics》2012,44(9):1006-1014
We characterized the mutational landscape of melanoma, the form of skin cancer with the highest mortality rate, by sequencing the exomes of 147 melanomas. Sun-exposed melanomas had markedly more ultraviolet (UV)-like C>T somatic mutations compared to sun-shielded acral, mucosal and uveal melanomas. Among the newly identified cancer genes was PPP6C, encoding a serine/threonine phosphatase, which harbored mutations that clustered in the active site in 12% of sun-exposed melanomas, exclusively in tumors with mutations in BRAF or NRAS. Notably, we identified a recurrent UV-signature, an activating mutation in RAC1 in 9.2% of sun-exposed melanomas. This activating mutation, the third most frequent in our cohort of sun-exposed melanoma after those of BRAF and NRAS, changes Pro29 to serine (RAC1(P29S)) in the highly conserved switch I domain. Crystal structures, and biochemical and functional studies of RAC1(P29S) showed that the alteration releases the conformational restraint conferred by the conserved proline, causes an increased binding of the protein to downstream effectors, and promotes melanocyte proliferation and migration. These findings raise the possibility that pharmacological inhibition of downstream effectors of RAC1 signaling could be of therapeutic benefit. 相似文献