全文获取类型
收费全文 | 122190篇 |
免费 | 1764篇 |
国内免费 | 549篇 |
专业分类
化学 | 41735篇 |
晶体学 | 1039篇 |
力学 | 7563篇 |
综合类 | 1篇 |
数学 | 33985篇 |
物理学 | 21262篇 |
无线电 | 18918篇 |
出版年
2023年 | 329篇 |
2022年 | 422篇 |
2021年 | 692篇 |
2020年 | 602篇 |
2019年 | 631篇 |
2018年 | 12172篇 |
2017年 | 11835篇 |
2016年 | 7846篇 |
2015年 | 1697篇 |
2014年 | 1422篇 |
2013年 | 2207篇 |
2012年 | 6337篇 |
2011年 | 13881篇 |
2010年 | 8283篇 |
2009年 | 8264篇 |
2008年 | 9259篇 |
2007年 | 11632篇 |
2006年 | 2212篇 |
2005年 | 3429篇 |
2004年 | 3361篇 |
2003年 | 3515篇 |
2002年 | 2404篇 |
2001年 | 1260篇 |
2000年 | 1160篇 |
1999年 | 789篇 |
1998年 | 686篇 |
1997年 | 673篇 |
1996年 | 741篇 |
1995年 | 554篇 |
1994年 | 499篇 |
1993年 | 497篇 |
1992年 | 444篇 |
1991年 | 395篇 |
1990年 | 314篇 |
1989年 | 289篇 |
1988年 | 273篇 |
1987年 | 216篇 |
1986年 | 177篇 |
1985年 | 244篇 |
1984年 | 193篇 |
1983年 | 167篇 |
1982年 | 192篇 |
1981年 | 154篇 |
1980年 | 149篇 |
1979年 | 123篇 |
1978年 | 141篇 |
1977年 | 122篇 |
1976年 | 122篇 |
1975年 | 134篇 |
1973年 | 145篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A. Di Giacomo E. Meggiolaro Yu. A. Simonov A. I. Veselov 《Physics of Atomic Nuclei》2007,70(5):908-924
It is argued that strong dynamics in the quark-gluon plasma and bound states of quarks and gluons is mostly due to nonperturbative
effects described by field correlators. The emphasis in the paper is made on two explicit calculations of these effects from
first principles—one analytic using gluelump Green’s functions and another using independent lattice data on correlators.
The resulting hadron spectra are investigated in the range T
c
≤ T < 2T
c
. The spectra of charmonia, bottomonia, light s
mesons, glueballs, and quark-gluon states calculated numerically are in general agreement with lattice MEM data. The possible
role of these bound states in the thermodynamics of quark—gluon plasma is discussed.
The text was submitted by the authors in English. 相似文献
992.
In this paper we study the semileptonic decays of the Bc meson in the light-cone sum rule (LCSR) approach. The result for each channel depends on the corresponding distribution amplitude
(DA) of the final meson. For the case of Bc decaying into a pseudoscalar meson, to twist-3 accuracy only the leading twist distribution amplitude is involved if we start
from a chiral current. If we choose a suitable chiral current in the vector meson case, the main twist-3 contributions are
also eliminated and we can consider the leading twist contribution only. The leading twist distribution amplitudes of the
charmonium and other heavy mesons are given by a model approach in a reasonable way. Employing this charmonium distribution
amplitude we find a cross section that is consistent with Belle and BaBar data. Based on this model, we calculate the form factors for various Bc decay modes in the corresponding regions. Extrapolating the form factors to the whole kinetic regions, we get the decay widths
and branching ratios for various Bc decay modes including their τ modes when they are kinematically accessible.
PACS 13.20.He; 13.20.Fc; 11.55.Hx 相似文献
993.
994.
Zhongzhi Zhang Shuigeng Zhou Tao Zou Lichao Chen Jihong Guan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):259-264
We make a mapping from Sierpinski fractals to a new class
of networks, the incompatibility networks, which are scale-free,
small-world, disassortative, and maximal planar graphs. Some
relevant characteristics of the networks such as degree
distribution, clustering coefficient, average path length, and
degree correlations are computed analytically and found to be
peculiarly rich. The method of network representation can be applied
to some real-life systems making it possible to study the complexity
of real networked systems within the framework of complex network
theory. 相似文献
995.
Philippe Pinel Bertrand Thirion Sébastien Meriaux Antoinette Jobert Julien Serres Denis Le Bihan Jean-Baptiste Poline Stanislas Dehaene 《BMC neuroscience》2007,8(1):91
Background
Although cognitive processes such as reading and calculation are associated with reproducible cerebral networks, inter-individual variability is considerable. Understanding the origins of this variability will require the elaboration of large multimodal databases compiling behavioral, anatomical, genetic and functional neuroimaging data over hundreds of subjects. With this goal in mind, we designed a simple and fast acquisition procedure based on a 5-minute functional magnetic resonance imaging (fMRI) sequence that can be run as easily and as systematically as an anatomical scan, and is therefore used in every subject undergoing fMRI in our laboratory. This protocol captures the cerebral bases of auditory and visual perception, motor actions, reading, language comprehension and mental calculation at an individual level. 相似文献996.
Background
The involvement of different NMDA receptor (NMDAR) subunits has been implicated in several forms of synaptic plasticity. However, it is still controversial to what extent the involvement is specific, and little is known about the role of NMDAR subunits in certain "non-conventional" forms of plasticity. In this study we used subunit-specific blockers to test the roles of NR2A- and NR2B-containing NMDARs in a type of chemical long-term depression (LTD) induced by brief bath application of the NMDAR agonist NMDA to hippocampal slices from 12–18 days old rats. For comparison, we also examined other forms of plasticity, including a "slow LTD" induced by 0.1 Hz stimulation under low Mg2+ conditions as well as long-term potentiation (LTP). 相似文献997.
Adult neurogenesis and specific replacement of interneuron subtypes in the mouse main olfactory bulb
Background
New neurons are generated in the adult brain from stem cells found in the subventricular zone (SVZ). These cells proliferate in the SVZ, generating neuroblasts which then migrate to the main olfactory bulb (MOB), ending their migration in the glomerular layer (GLL) and the granule cell layer (GCL) of the MOB. Neuronal populations in these layers undergo turnover throughout life, but whether all neuronal subtypes found in these areas are replaced and when neurons begin to express subtype-specific markers is not known. 相似文献998.
Smell is often regarded as an ancillary perception in primates, who seem so dominated by their sense of vision. In this paper, we will portray some aspects of the significance of olfaction to human life and speculate on what evolutionary factors contribute to keeping it alive. We then outline the functional architecture of olfactory sensory neurons and their signal transduction pathways, which are the primary detectors that render olfactory perception possible. Throughout the phylogenetic tree, olfactory neurons, at their apical tip, are either decorated with cilia or with microvilli. The significance of this dichotomy is unknown. It is generally assumed that mammalian olfactory neurons are of the ciliary type only. The existence of so-called olfactory microvillar cells in mammals, however, is well documented, but their nature remains unclear and their function orphaned. This paper discusses the possibility, that in the main olfactory epithelium of mammals ciliated and microvillar sensory cells exist concurrently. We review evidence related to this hypothesis and ask, what function olfactory microvillar cells might have and what signalling mechanisms they use. 相似文献
999.
Background
Numerous electrophysiological, ultrastructural, and immunocytochemical studies on rodent taste buds have been carried out on rat taste buds. In recent years, however, the mouse has become the species of choice for molecular and other studies on sensory transduction in taste buds. Do rat and mouse taste buds have the same cell types, sensory transduction markers and synaptic proteins? In the present study we have used antisera directed against PLCβ2, α-gustducin, serotonin (5-HT), PGP 9.5 and synaptobrevin-2 to determine the percentages of taste cells expressing these markers in taste buds in both rodent species. We also determined the numbers of taste cells in the taste buds as well as taste bud volume.Results
There are significant differences (p < 0.05) between mouse and rat taste buds in the percentages of taste cells displaying immunoreactivity for all five markers. Rat taste buds display significantly more immunoreactivity than mice for PLCβ2 (31.8% vs 19.6%), α-gustducin (18% vs 14.6%), and synaptobrevin-2 (31.2% vs 26.3%). Mice, however, have more cells that display immunoreactivity to 5-HT (15.9% vs 13.7%) and PGP 9.5 (14.3% vs 9.4%). Mouse taste buds contain an average of 85.8 taste cells vs 68.4 taste cells in rat taste buds. The average volume of a mouse taste bud (42,000 μm3) is smaller than a rat taste bud (64,200 μm3). The numerical density of taste cells in mouse circumvallate taste buds (2.1 cells/1000 μm3) is significantly higher than that in the rat (1.2 cells/1000 μm3).Conclusion
These results suggest that rats and mice differ significantly in the percentages of taste cells expressing signaling molecules. We speculate that these observed dissimilarities may reflect differences in their gustatory processing.1000.
Salvatore D'Aniello George H Fisher Enza Topo Gabriele Ferrandino Jordi Garcia-Fernàndez Antimo D'Aniello 《BMC neuroscience》2007,8(1):109