全文获取类型
收费全文 | 1345篇 |
免费 | 29篇 |
国内免费 | 9篇 |
专业分类
化学 | 773篇 |
晶体学 | 4篇 |
力学 | 80篇 |
数学 | 230篇 |
物理学 | 296篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 32篇 |
2021年 | 32篇 |
2020年 | 27篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 32篇 |
2016年 | 56篇 |
2015年 | 37篇 |
2014年 | 49篇 |
2013年 | 86篇 |
2012年 | 86篇 |
2011年 | 112篇 |
2010年 | 79篇 |
2009年 | 70篇 |
2008年 | 95篇 |
2007年 | 69篇 |
2006年 | 72篇 |
2005年 | 68篇 |
2004年 | 52篇 |
2003年 | 36篇 |
2002年 | 38篇 |
2001年 | 16篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1929年 | 1篇 |
1905年 | 2篇 |
1900年 | 2篇 |
排序方式: 共有1383条查询结果,搜索用时 0 毫秒
61.
62.
CaII Binding Regulates and Dominates the Reactivity of a Transition‐Metal‐Ion‐Dependent Diesterase from Mycobacterium tuberculosis 下载免费PDF全文
Dr. Marcelo M. Pedroso Prof. James A. Larrabee Dr. Fernanda Ely Shuhui E. Gwee Dr. Nataša Mitić Prof. David L. Ollis Prof. Lawrence R. Gahan Prof. Gerhard Schenk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):999-1009
The diesterase Rv0805 from Mycobacterium tuberculosis is a dinuclear metallohydrolase that plays an important role in signal transduction by controlling the intracellular levels of cyclic nucleotides. As Rv0805 is essential for mycobacterial growth it is a promising new target for the development of chemotherapeutics to treat tuberculosis. The in vivo metal‐ion composition of Rv0805 is subject to debate. Here, we demonstrate that the active site accommodates two divalent transition metal ions with binding affinities ranging from approximately 50 nm for MnII to about 600 nm for ZnII. In contrast, the enzyme GpdQ from Enterobacter aerogenes, despite having a coordination sphere identical to that of Rv0805, binds only one metal ion in the absence of substrate, thus demonstrating the significance of the outer sphere to modulate metal‐ion binding and enzymatic reactivity. CaII also binds tightly to Rv0805 (Kd≈40 nm ), but kinetic, calorimetric, and spectroscopic data indicate that two CaII ions bind at a site different from the dinuclear transition‐metal‐ion binding site. CaII acts as an activator of the enzymatic activity but is able to promote the hydrolysis of substrates even in the absence of transition‐metal ions, thus providing an effective strategy for the regulation of the enzymatic activity. 相似文献
63.
64.
Liu X McLaughlin AC de Miranda MP McInnes EJ Kilner CA Halcrow MA 《Chemical communications (Cambridge, England)》2002,(24):2978-2979
The complex [[Cu3(HpztBu)4(mu-pztBu)2(mu-F)2(mu 3-F)]2]F2 (HpztBu = 3[5]-tert-butylpyrazole) has a cyclic, C2v-symmetric hexacopper core. The two non-coordinated F- anions are encapsulated within cavities formed by three HpztBu ligands. 相似文献
65.
We describe the characteristics of a double-exposure specklegram obtained through a double-aperture system, by introduction of a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and visibility of the interferometric fringes in the Fourier plane are analyzed. An alternative interferometric technique for phase-object detection is proposed. 相似文献
66.
A post-processing technique is presented for correcting images undersampled in k-space. The method works by taking advantage of the image's background zeros (dynamically segmented through the application of a threshold) to extrapolate the missing k-space samples. The algorithm can produce good quality images from a small set of k-space frequencies with only a few iterations of simple matrix operations, using the image entropy as the focus criterion. It does not require any special patient preparation, extra pulse sequences, complex gradient programming or specialized hardware. This makes it a good candidate for any application that requires short scan times or where only few frequencies can be sampled. 相似文献
67.
The dynamics of small spherical neutrally buoyant particulate impurities immersed in a two-dimensional fluid flow are known to lead to particle accumulation in the regions of the flow in which vorticity dominates over strain, provided that the Stokes number of the particles is sufficiently small. If the flow is viewed as a Hamiltonian dynamical system, it can be seen that the accumulations occur in the nonchaotic parts of the phase space: the Kolmogorov-Arnold-Moser tori. This has suggested a generalization of these dynamics to Hamiltonian maps, dubbed a bailout embedding. In this paper we use a bailout embedding of the standard map to mimic the dynamics of neutrally buoyant impurities subject not only to drag but also to fluctuating forces modeled as white noise. We find that the generation of inhomogeneities associated with the separation of particle from fluid trajectories is enhanced by the presence of noise, so that they appear in much broader ranges of the Stokes number than those allowing spontaneous separation. (c) 2002 American Institute of Physics. 相似文献
68.
Craig F Ferris Tara Stolberg Praveen Kulkarni Murali Murugavel Robert Blanchard D Caroline Blanchard Marcelo Febo Mathew Brevard Neal G Simon 《BMC neuroscience》2008,9(1):111
Background
With the advent of functional magnetic resonance imaging (fMRI) in awake animals it is possible to resolve patterns of neuronal activity across the entire brain with high spatial and temporal resolution. Synchronized changes in neuronal activity across multiple brain areas can be viewed as functional neuroanatomical circuits coordinating the thoughts, memories and emotions for particular behaviors. To this end, fMRI in conscious rats combined with 3D computational analysis was used to identifying the putative distributed neural circuit involved in aggressive motivation and how this circuit is affected by drugs that block aggressive behavior. 相似文献69.
A Semigroup Crossed Product Arising in Number Theory 总被引:2,自引:0,他引:2
Recently Bost and Connes have studied an interesting C*-algebraicHecke algebra arising in number theory. Here it is shown thatthis algebra can be realised as a semigroup crossed product,and be profitably studied using methods developed by the authorsfor analysing Toeplitz algebras. One main result is a characterisationof faithful representations of the Hecke algebra. 相似文献
70.
Existence and asymptotic stability for evolution problems on manifolds with damping and source terms
Marcelo M. Cavalcanti Valéria N. Domingos Cavalcanti 《Journal of Mathematical Analysis and Applications》2004,291(1):109-127
One considers the nonlinear evolution equation with source and damping terms