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991.
992.
J C De la Torre 《Nature》1968,219(5157):954-955
993.
994.
Resurrecting ancestral alcohol dehydrogenases from yeast 总被引:1,自引:0,他引:1
Thomson JM Gaucher EA Burgan MF De Kee DW Li T Aris JP Benner SA 《Nature genetics》2005,37(6):630-635
Modern yeast living in fleshy fruits rapidly convert sugars into bulk ethanol through pyruvate. Pyruvate loses carbon dioxide to produce acetaldehyde, which is reduced by alcohol dehydrogenase 1 (Adh1) to ethanol, which accumulates. Yeast later consumes the accumulated ethanol, exploiting Adh2, an Adh1 homolog differing by 24 (of 348) amino acids. As many microorganisms cannot grow in ethanol, accumulated ethanol may help yeast defend resources in the fruit. We report here the resurrection of the last common ancestor of Adh1 and Adh2, called Adh(A). The kinetic behavior of Adh(A) suggests that the ancestor was optimized to make (not consume) ethanol. This is consistent with the hypothesis that before the Adh1-Adh2 duplication, yeast did not accumulate ethanol for later consumption but rather used Adh(A) to recycle NADH generated in the glycolytic pathway. Silent nucleotide dating suggests that the Adh1-Adh2 duplication occurred near the time of duplication of several other proteins involved in the accumulation of ethanol, possibly in the Cretaceous age when fleshy fruits arose. These results help to connect the chemical behavior of these enzymes through systems analysis to a time of global ecosystem change, a small but useful step towards a planetary systems biology. 相似文献
995.
A syndrome of altered cardiovascular, craniofacial, neurocognitive and skeletal development caused by mutations in TGFBR1 or TGFBR2 总被引:18,自引:0,他引:18
Loeys BL Chen J Neptune ER Judge DP Podowski M Holm T Meyers J Leitch CC Katsanis N Sharifi N Xu FL Myers LA Spevak PJ Cameron DE De Backer J Hellemans J Chen Y Davis EC Webb CL Kress W Coucke P Rifkin DB De Paepe AM Dietz HC 《Nature genetics》2005,37(3):275-281
We report heterozygous mutations in the genes encoding either type I or type II transforming growth factor beta receptor in ten families with a newly described human phenotype that includes widespread perturbations in cardiovascular, craniofacial, neurocognitive and skeletal development. Despite evidence that receptors derived from selected mutated alleles cannot support TGFbeta signal propagation, cells derived from individuals heterozygous with respect to these mutations did not show altered kinetics of the acute phase response to administered ligand. Furthermore, tissues derived from affected individuals showed increased expression of both collagen and connective tissue growth factor, as well as nuclear enrichment of phosphorylated Smad2, indicative of increased TGFbeta signaling. These data definitively implicate perturbation of TGFbeta signaling in many common human phenotypes, including craniosynostosis, cleft palate, arterial aneurysms, congenital heart disease and mental retardation, and suggest that comprehensive mechanistic insight will require consideration of both primary and compensatory events. 相似文献
996.
997.
Jarillo-Herrero P Kong J van der Zant HS Dekker C Kouwenhoven LP De Franceschi S 《Nature》2005,434(7032):484-488
Progress in the fabrication of nanometre-scale electronic devices is opening new opportunities to uncover deeper aspects of the Kondo effect--a characteristic phenomenon in the physics of strongly correlated electrons. Artificial single-impurity Kondo systems have been realized in various nanostructures, including semiconductor quantum dots, carbon nanotubes and individual molecules. The Kondo effect is usually regarded as a spin-related phenomenon, namely the coherent exchange of the spin between a localized state and a Fermi sea of delocalized electrons. In principle, however, the role of the spin could be replaced by other degrees of freedom, such as an orbital quantum number. Here we show that the unique electronic structure of carbon nanotubes enables the observation of a purely orbital Kondo effect. We use a magnetic field to tune spin-polarized states into orbital degeneracy and conclude that the orbital quantum number is conserved during tunnelling. When orbital and spin degeneracies are present simultaneously, we observe a strongly enhanced Kondo effect, with a multiple splitting of the Kondo resonance at finite field and predicted to obey a so-called SU4 symmetry. 相似文献
998.
Europe-wide reduction in primary productivity caused by the heat and drought in 2003 总被引:22,自引:0,他引:22
Ciais P Reichstein M Viovy N Granier A Ogée J Allard V Aubinet M Buchmann N Bernhofer C Carrara A Chevallier F De Noblet N Friend AD Friedlingstein P Grünwald T Heinesch B Keronen P Knohl A Krinner G Loustau D Manca G Matteucci G Miglietta F Ourcival JM Papale D Pilegaard K Rambal S Seufert G Soussana JF Sanz MJ Schulze ED Vesala T Valentini R 《Nature》2005,437(7058):529-533
Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr(-1)) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes. 相似文献
999.
XI Qingxin LIU De'an ZHI Ya'nan ZHU Luan LIU Liren 《科学通报(英文版)》2005,50(24):2799-2803
A reversible electrochromic effect accompanying domain-inversion during the electrical poling process in LiNbO3: Ru: Fe crystals at room temperature has been observed. In electrode area, both electrochromism and domain-inversion occur alternately, and electrochromism is also reversible during back-switch poling, which is experimentally verified and whose mechanism is briefly explained using a microstrncture ferroelectric model. In addition, because of the enhancing elcctrochromic effect, different from the undoped LiNbO3 crystals, the coercive filed (21.0 kV/mm or so) measured in LiNbO3: Ru: Fe is lower than its breakdown field, thus providing a possible new technique for realizing the domain-inversion by constant electric field rather than a pulsed one. 相似文献
1000.
Summary A novel iridoid glycoside, ipolamiide fromStachytarpheta mutabilis was identified and found to inhibit feeding by several insect species. It is active at concentrations well below those occurring naturally. 相似文献