全文获取类型
收费全文 | 1014篇 |
免费 | 0篇 |
专业分类
系统科学 | 13篇 |
教育与普及 | 1篇 |
理论与方法论 | 18篇 |
现状及发展 | 365篇 |
研究方法 | 169篇 |
综合类 | 442篇 |
自然研究 | 6篇 |
出版年
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2014年 | 11篇 |
2013年 | 10篇 |
2012年 | 58篇 |
2011年 | 72篇 |
2010年 | 26篇 |
2009年 | 6篇 |
2008年 | 38篇 |
2007年 | 52篇 |
2006年 | 54篇 |
2005年 | 50篇 |
2004年 | 27篇 |
2003年 | 28篇 |
2002年 | 40篇 |
2001年 | 32篇 |
2000年 | 41篇 |
1999年 | 34篇 |
1992年 | 31篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 20篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1972年 | 14篇 |
1971年 | 15篇 |
1970年 | 14篇 |
1969年 | 12篇 |
1968年 | 9篇 |
1967年 | 11篇 |
1966年 | 8篇 |
1964年 | 6篇 |
1960年 | 4篇 |
1956年 | 6篇 |
1947年 | 4篇 |
排序方式: 共有1014条查询结果,搜索用时 546 毫秒
171.
Pascal AA Liu Z Broess K van Oort B van Amerongen H Wang C Horton P Robert B Chang W Ruban A 《Nature》2005,436(7047):134-137
In order to maximize their use of light energy in photosynthesis, plants have molecules that act as light-harvesting antennae, which collect light quanta and deliver them to the reaction centres, where energy conversion into a chemical form takes place. The functioning of the antenna responds to the extreme changes in the intensity of sunlight encountered in nature. In shade, light is efficiently harvested in photosynthesis. However, in full sunlight, much of the energy absorbed is not needed and there are vitally important switches to specific antenna states, which safely dissipate the excess energy as heat. This is essential for plant survival, because it provides protection against the potential photo-damage of the photosynthetic membrane. But whereas the features that establish high photosynthetic efficiency have been highlighted, almost nothing is known about the molecular nature of the dissipative states. Recently, the atomic structure of the major plant light-harvesting antenna protein, LHCII, has been determined by X-ray crystallography. Here we demonstrate that this is the structure of a dissipative state of LHCII. We present a spectroscopic analysis of this crystal form, and identify the specific changes in configuration of its pigment population that give LHCII the intrinsic capability to regulate energy flow. This provides a molecular basis for understanding the control of photosynthetic light-harvesting. 相似文献
172.
173.
van Rossum DB Patterson RL Sharma S Barrow RK Kornberg M Gill DL Snyder SH 《Nature》2005,434(7029):99-104
Many ion channels are regulated by lipids, but prominent motifs for lipid binding have not been identified in most ion channels. Recently, we reported that phospholipase Cgamma1 (PLC-gamma1) binds to and regulates TRPC3 channels, components of agonist-induced Ca2+ entry into cells. This interaction requires a domain in PLC-gamma1 that includes a partial pleckstrin homology (PH) domain-a consensus lipid-binding and protein-binding sequence. We have developed a gestalt algorithm to detect hitherto 'invisible' PH and PH-like domains, and now report that the partial PH domain of PLC-gamma1 interacts with a complementary partial PH-like domain in TRPC3 to elicit lipid binding and cell-surface expression of TRPC3. Our findings imply a far greater abundance of PH domains than previously appreciated, and suggest that intermolecular PH-like domains represent a widespread signalling mode. 相似文献
174.
175.
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
176.
van Delden RA ter Wiel MK Pollard MM Vicario J Koumura N Feringa BL 《Nature》2005,437(7063):1337-1340
Molecules capable of mimicking the function of a wide range of mechanical devices have been fabricated, with motors that can induce mechanical movement attracting particular attention. Such molecular motors convert light or chemical energy into directional rotary or linear motion, and are usually prepared and operated in solution. But if they are to be used as nanomachines that can do useful work, it seems essential to construct systems that can function on a surface, like a recently reported linear artificial muscle. Surface-mounted rotors have been realized and limited directionality in their motion predicted. Here we demonstrate that a light-driven molecular motor capable of repetitive unidirectional rotation can be mounted on the surface of gold nanoparticles. The motor design uses a chiral helical alkene with an upper half that serves as a propeller and is connected through a carbon-carbon double bond (the rotation axis) to a lower half that serves as a stator. The stator carries two thiol-functionalized 'legs', which then bind the entire motor molecule to a gold surface. NMR spectroscopy reveals that two photo-induced cis-trans isomerizations of the central double bond, each followed by a thermal helix inversion to prevent reverse rotation, induce a full and unidirectional 360 degrees rotation of the propeller with respect to the surface-mounted lower half of the system. 相似文献
177.
178.
179.
P. van Caneghem 《Cellular and molecular life sciences : CMLS》1964,20(12):699-700
Zusammenfassung An Cystamin-injizierten Ratten (i.p.) wurde das Ausmass der Schutzwirkung, in zeitlicher Abhängigkeit, bei lokaler Röntgenbestrahlung, auf das Haarwachstum untersucht. Eine maximale Schutzwirkung wurde nach 10 min gefunden. Sie nimmt von da an langsam ab und ist selbst 60 min nach der Cystamininjektion noch nachweisbar. 相似文献
180.
Résumé La capacité de transport de la bilirubine dans le foie de rat a été mesurée par différents auteurs. Dans nos expériments leT
m
était variable selon les conditions expérimentales. En stabilisant la température à 38 C pendant les 10 h qui suivent l'opération, le Tm s'avère 50% plus élevé que les valeurs données dans la littérature. En plus la valeur du Tm était étroitement correlée au débit biliaire. 相似文献