全文获取类型
收费全文 | 31213篇 |
免费 | 85篇 |
国内免费 | 117篇 |
专业分类
系统科学 | 137篇 |
丛书文集 | 379篇 |
教育与普及 | 72篇 |
理论与方法论 | 103篇 |
现状及发展 | 14312篇 |
研究方法 | 1261篇 |
综合类 | 14806篇 |
自然研究 | 345篇 |
出版年
2013年 | 203篇 |
2012年 | 400篇 |
2011年 | 741篇 |
2008年 | 514篇 |
2007年 | 562篇 |
2006年 | 583篇 |
2005年 | 570篇 |
2004年 | 631篇 |
2003年 | 542篇 |
2002年 | 505篇 |
2001年 | 975篇 |
2000年 | 940篇 |
1999年 | 611篇 |
1994年 | 371篇 |
1992年 | 580篇 |
1991年 | 432篇 |
1990年 | 495篇 |
1989年 | 465篇 |
1988年 | 413篇 |
1987年 | 482篇 |
1986年 | 515篇 |
1985年 | 646篇 |
1984年 | 471篇 |
1983年 | 436篇 |
1982年 | 411篇 |
1981年 | 401篇 |
1980年 | 409篇 |
1979年 | 1053篇 |
1978年 | 834篇 |
1977年 | 764篇 |
1976年 | 630篇 |
1975年 | 695篇 |
1974年 | 916篇 |
1973年 | 790篇 |
1972年 | 770篇 |
1971年 | 901篇 |
1970年 | 1174篇 |
1969年 | 905篇 |
1968年 | 914篇 |
1967年 | 886篇 |
1966年 | 762篇 |
1965年 | 608篇 |
1964年 | 194篇 |
1959年 | 319篇 |
1958年 | 541篇 |
1957年 | 387篇 |
1956年 | 321篇 |
1955年 | 317篇 |
1954年 | 309篇 |
1948年 | 235篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
531.
In 1985, more than thirty geomorphologists, planetary scientists, and remote sensing specialists gathered at a conference center in Oracle, Arizona, to discuss an emerging area of research that they called “mega-geomorphology.” Building on a conference of the same name held in London in 1981, they argued that new techniques of remote sensing and insights emerging from the study of extraterrestrial planets had created opportunities for geomorphology to broaden its spatial and temporal scope. This new approach was, however, neither unproblematic nor uncontested. In the discussions around mega-geomorphology that took place in the mid-1980s, the perceived conflict between the use of remote-sensing techniques to observe phenomena on vast spatial scales, on one hand, and the disciplinary centrality of fieldwork and field experience to geomorphology, on the other, was a recurrent theme. In response, mega-geomorphologists attempted to re-situate fieldwork and re-narrate disciplinary histories in such a way as to make remote sensing and planetary science not only compatible with geomorphological traditions but also means of revitalizing them. Only partially successful, these attempts reveal that the process of adopting a planetary perspective in geomorphology, as in other earth sciences, was neither straightforward nor inevitable. They also show how the field and fieldwork could remain central to geomorphology while also being extensively revised in light of new technical possibilities and theoretical frameworks. 相似文献
532.
533.
534.
Antoni Camins Javier G. Pizarro Daniel Alvira Javier Gutierrez-Cuesta Aurelio Vazquez de la Torre Jaume Folch Francesc X. Sureda Ester Verdaguer Felix Junyent Joaquín Jordán Isidre Ferrer Mercè Pallàs 《Cellular and molecular life sciences : CMLS》2010,67(22):3865-3882
In the present study we demonstrated that neurotoxin MPP+-induced DNA damage is followed by ataxia telangiectasia muted (ATM) activation either in cerebellar granule cells (CGC) or in B65 cell line. In CGC, the selective ATM inhibitor KU-55933 showed neuroprotective effects against MPP+-induced neuronal cell loss and apoptosis, lending support to the key role of ATM in experimental models of Parkinson’s disease. Likewise, we showed that knockdown of ATM levels in neuroblastoma B65 cells using an ATM-specific siRNA attenuates the phosphorylation of retinoblastoma protein without affecting other cell-cycle proteins involved in the G0/G1 cell-cycle phase. Moreover, we demonstrated DNA damage, in human brain samples of PD patients. These findings support a model in which MPP+ leads to ATM activation with a subsequent DNA damage response and activation of pRb. Therefore, this study demonstrates a new link between DNA damage by MPP+ and cell-cycle re-entry through retinoblastoma protein phosphorylation. 相似文献
535.
Nicole Schwarz Jessica Pruessmeyer Franz M. Hess Daniela Dreymueller Elena Pantaler Anne Koelsch Reinhard Windoffer Matthias Voss Alisina Sarabi Christian Weber Antonio S. Sechi Stefan Uhlig Andreas Ludwig 《Cellular and molecular life sciences : CMLS》2010,67(24):4233-4248
The surface-expressed transmembrane CX3C chemokine ligand 1 (CX3CL1/fractalkine) induces firm adhesion of leukocytes expressing its receptor CX3CR1. After shedding by the disintegrins and metalloproteinases (ADAM) 10 and 17, CX3CL1 also acts as soluble leukocyte chemoattractant. Here, we demonstrate that transmembrane CX3CL1 expressed on both endothelial and epithelial cells induces leukocyte transmigration. To investigate the underlying mechanism, we generated CX3CR1 variants lacking the intracellular aspartate-arginine-tyrosine (DRY) motif or the intracellular C-terminus which led to a defect in intracellular calcium response and impaired ligand uptake, respectively. While both variants effectively mediated firm cell adhesion, they failed to induce transmigration and rather mediated retention of leukocytes on the CX3CL1-expressing cell layer. Targeting of ADAM10 led to increased adhesion but reduced transmigration in response to transmembrane CX3CL1, while transmigration towards soluble CX3CL1 was not affected. Thus, transmembrane CX3CL1 mediates leukocyte transmigration via the DRY motif and C-terminus of CX3CR1 and the activity of ADAM10. 相似文献
536.
Triosephosphate isomerase: a highly evolved biocatalyst 总被引:1,自引:0,他引:1
R. K. Wierenga E. G. Kapetaniou R. Venkatesan 《Cellular and molecular life sciences : CMLS》2010,67(23):3961-3982
Triosephosphate isomerase (TIM) is a perfectly evolved enzyme which very fast interconverts dihydroxyacetone phosphate and d-glyceraldehyde-3-phosphate. Its catalytic site is at the dimer interface, but the four catalytic residues, Asn11, Lys13, His95 and Glu167, are from the same subunit. Glu167 is the catalytic base. An important feature of the TIM active site is the concerted closure of loop-6 and loop-7 on ligand binding, shielding the catalytic site from bulk solvent. The buried active site stabilises the enediolate intermediate. The catalytic residue Glu167 is at the beginning of loop-6. On closure of loop-6, the Glu167 carboxylate moiety moves approximately 2 Å to the substrate. The dynamic properties of the Glu167 side chain in the enzyme substrate complex are a key feature of the proton shuttling mechanism. Two proton shuttling mechanisms, the classical and the criss-cross mechanism, are responsible for the interconversion of the substrates of this enolising enzyme. 相似文献
537.
Potassium and sodium transport in non-animal cells: the Trk/Ktr/HKT transporter family 总被引:1,自引:1,他引:0
C. Corratgé-Faillie M. Jabnoune S. Zimmermann A.-A. Véry C. Fizames H. Sentenac 《Cellular and molecular life sciences : CMLS》2010,67(15):2511-2532
Bacterial Trk and Ktr, fungal Trk and plant HKT form a family of membrane transporters permeable to K+ and/or Na+ and characterized by a common structure probably derived from an ancestral K+ channel subunit. This transporter family, specific of non-animal cells, displays a large diversity in terms of ionic permeability,
affinity and energetic coupling (H+–K+ or Na+–K+ symport, K+ or Na+ uniport), which might reflect a high need for adaptation in organisms living in fluctuating or dilute environments. Trk/Ktr/HKT
transporters are involved in diverse functions, from K+ or Na+ uptake to membrane potential control, adaptation to osmotic or salt stress, or Na+ recirculation from shoots to roots in plants. Structural analyses of bacterial Ktr point to multimeric structures physically
interacting with regulatory subunits. Elucidation of Trk/Ktr/HKT protein structures along with characterization of mutated
transporters could highlight functional and evolutionary relationships between ion channels and transporters displaying channel-like
features. 相似文献
538.
Large intergenic non-coding RNA-RoR modulates reprogramming of human induced pluripotent stem cells 总被引:1,自引:0,他引:1
539.
The developmental dynamics of the maize leaf transcriptome 总被引:5,自引:0,他引:5
540.
Genome-wide association studies of 14 agronomic traits in rice landraces 总被引:20,自引:0,他引:20
Huang X Wei X Sang T Zhao Q Feng Q Zhao Y Li C Zhu C Lu T Zhang Z Li M Fan D Guo Y Wang A Wang L Deng L Li W Lu Y Weng Q Liu K Huang T Zhou T Jing Y Li W Lin Z Buckler ES Qian Q Zhang QF Li J Han B 《Nature genetics》2010,42(11):961-967
Uncovering the genetic basis of agronomic traits in crop landraces that have adapted to various agro-climatic conditions is important to world food security. Here we have identified ~ 3.6 million SNPs by sequencing 517 rice landraces and constructed a high-density haplotype map of the rice genome using a novel data-imputation method. We performed genome-wide association studies (GWAS) for 14 agronomic traits in the population of Oryza sativa indica subspecies. The loci identified through GWAS explained ~ 36% of the phenotypic variance, on average. The peak signals at six loci were tied closely to previously identified genes. This study provides a fundamental resource for rice genetics research and breeding, and demonstrates that an approach integrating second-generation genome sequencing and GWAS can be used as a powerful complementary strategy to classical biparental cross-mapping for dissecting complex traits in rice. 相似文献