全文获取类型
收费全文 | 617篇 |
免费 | 24篇 |
国内免费 | 10篇 |
专业分类
化学 | 478篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 92篇 |
物理学 | 68篇 |
出版年
2023年 | 6篇 |
2021年 | 5篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 28篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 18篇 |
2012年 | 35篇 |
2011年 | 54篇 |
2010年 | 29篇 |
2009年 | 25篇 |
2008年 | 41篇 |
2007年 | 40篇 |
2006年 | 43篇 |
2005年 | 36篇 |
2004年 | 34篇 |
2003年 | 30篇 |
2002年 | 18篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 11篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1990年 | 5篇 |
1984年 | 2篇 |
1981年 | 2篇 |
1967年 | 2篇 |
1917年 | 2篇 |
1915年 | 2篇 |
1904年 | 2篇 |
1903年 | 2篇 |
1901年 | 2篇 |
1896年 | 2篇 |
1886年 | 3篇 |
1884年 | 2篇 |
1880年 | 4篇 |
1879年 | 4篇 |
1878年 | 4篇 |
1877年 | 5篇 |
1876年 | 7篇 |
1874年 | 4篇 |
1865年 | 2篇 |
排序方式: 共有651条查询结果,搜索用时 46 毫秒
81.
Rob Stevenson 《Foundations of Computational Mathematics》2007,7(2):245-269
In this paper an adaptive finite element method is constructed for solving elliptic equations that has optimal computational
complexity. Whenever, for some s > 0, the solution can be approximated within a tolerance ε > 0 in energy norm by a continuous
piecewise linear function on some partition with O(ε-1/s) triangles, and one knows how to approximate the right-hand side in the dual norm with the same rate with piecewise constants,
then the adaptive method produces approximations that converge with this rate, taking a number of operations that is of the
order of the number of triangles in the output partition. The method is similar in spirit to that from by Morin, Nochetto, and Siebert, and so in particular it does not rely on a recurrent coarsening of the partitions. Although
the Poisson equation in two dimensions with piecewise linear approximation is considered, the results generalize in several
respects. 相似文献
82.
L. Rob 《Czechoslovak Journal of Physics》1966,16(3):249-254
The paper describes the measurement of the differential cross-section for pp scattering at an energy of 8 GeV. The results of the paper agree well with the assumption that there exists a real part of the scattering amplitude that is 33% of the imaginary part. 相似文献
83.
Rob Stevenson 《Numerische Mathematik》1993,66(1):373-398
Summary We analyse multi-grid applied to anisotropic equations within the framework of smoothing and approximation-properties developed by Hack busch. For a model anisotropic equation on a square, we give an up-till-now missing proof of an estimate concerning the approximation property which is essential to show robustness. Furthermore, we show a corresponding estimate for a model anisotropic equation on an L-shaped domain. The existing estimates for the smoothing property are not suitable to prove robustness for either 2-cyclic Gauss-Seidel smoothers or for less regular problems such as our second model equation. For both cases, we give sharper estimates. By combination of our results concerning smoothing- and approximation-properties, robustness of W-cycle multi-grid applied to both our model equations will follow for a number of smoothers. 相似文献
84.
In [Found. Comput. Math., 2 (2002), pp. 203-245], Cohen, Dahmen, and DeVore proposed an adaptive wavelet algorithm for solving general operator equations. Assuming that the operator defines a boundedly invertible mapping between a Hilbert space and its dual, and that a Riesz basis of wavelet type for this Hilbert space is available, the operator equation is transformed into an equivalent well-posed infinite matrix-vector system. This system is solved by an iterative method, where each application of the infinite stiffness matrix is replaced by an adaptive approximation. It was shown that if the errors of the best linear combinations from the wavelet basis with terms are for some , which is determined by the Besov regularity of the solution and the order of the wavelet basis, then approximations yielded by the adaptive method with terms also have errors of . Moreover, their computation takes only operations, provided , with being a measure of how well the infinite stiffness matrix with respect to the wavelet basis can be approximated by computable sparse matrices. Under appropriate conditions on the wavelet basis, for both differential and singular integral operators and for the relevant range of , in [SIAM J. Math. Anal., 35(5) (2004), pp. 1110-1132] we showed that , assuming that each entry of the stiffness matrix is exactly available at unit cost.
Generally these entries have to be approximated using numerical quadrature. In this paper, restricting ourselves to differential operators, we develop a numerical integration scheme that computes these entries giving an additional error that is consistent with the approximation error, whereas in each column the average computational cost per entry is . As a consequence, we can conclude that the adaptive wavelet algorithm has optimal computational complexity.
85.
Wu W Daszykowski M Walczak B Sweatman BC Connor SC Haselden JN Crowther DJ Gill RW Lutz MW 《Journal of chemical information and modeling》2006,46(2):863-875
Proton nuclear magnetic resonance (1H NMR) spectroscopic analysis of mixtures has been used extensively for a variety of applications ranging from the analysis of plant extracts, wine, and food to the evaluation of toxicity in animals. For example, NMR analysis of urine samples has been used extensively for biomarker discovery and, more simply, for the construction of classification models of toxicity, disease, and biochemical phenotype. However, NMR spectra of complex mixtures typically show unwanted local peak shifts caused by matrix and instrument variability, which must be compensated for prior to statistical analysis and interpretation of the data. One approach is to align the spectral peaks across the data set. An efficient and fast warping algorithm is required as the signals typically contain ca. 32,000-64,000 data points and there can be several thousand spectra in a data set. As demonstrated in our study, the iterative fuzzy warping algorithm fulfills these requirements and can be used on-line for an alignment of the NMR spectra. Correlation coefficients between the aligned and target spectra are used as the evaluation function for the algorithm, and its performance is compared with those of other published warping methods. 相似文献
86.
An exactly solvable model of multisite condensed-phase vibrational relaxation was studied in Paper I (Peter, S.; Evans, D. G.; Coalson, R. D. J. Phys. Chem. B 2006, 110, 18758.), where it was shown that long-time steady-state site populations of a degenerate N-level system are not equal (hence, they are non-Boltzmann) and depend on the initial preparation of the system and the number of sites that it comprises. Here we consider a generalization of the model to the case of a nondegenerate three-level system coupled to a high-dimensional bath: such a model system has direct relevance to a large class of donor-bridge-acceptor electron transfer processes. Because the quantum dynamics of this system cannot be computed analytically, we compare numerically exact path integral calculations to the predictions of second-order time-local relaxation theory. For modest system-bath coupling strengths, the two sets of results are in excellent agreement. They show that non-Boltzmann long-time steady-state site populations are obtained when the level splitting is small but nonzero, whereas at larger values of the system bias (asymmetry) these populations become Boltzmann distributed. 相似文献
87.
Rob J. Hyndman David M. Bashtannyk Gary K. Grunwald 《Journal of computational and graphical statistics》2013,22(4):315-336
Abstract We consider the kernel estimator of conditional density and derive its asymptotic bias, variance, and mean-square error. Optimal bandwidths (with respect to integrated mean-square error) are found and it is shown that the convergence rate of the density estimator is order n –2/3. We also note that the conditional mean function obtained from the estimator is equivalent to a kernel smoother. Given the undesirable bias properties of kernel smoothers, we seek a modified conditional density estimator that has mean equivalent to some other nonparametric regression smoother with better bias properties. It is also shown that our modified estimator has smaller mean square error than the standard estimator in some commonly occurring situations. Finally, three graphical methods for visualizing conditional density estimators are discussed and applied to a data set consisting of maximum daily temperatures in Melbourne, Australia. 相似文献
88.
We first present prima facie evidence for the predictions generated by the mixture of distributions hypothesis, using daily German stock returns and their corresponding daily trading volumes and number of trades. These last two variables are used as proxies for the stochastic rate of information arrival when one wishes to explain GARCH effects by adhering to the mixture of distributions hypothesis. We show that there is no need for these proxies when the stochastic rate of information arrival follows an inverted gamma distribution. Daily trading volume and the daily number of trades, however, empirically provide an explanation for the occurrence of conditional heteroskedasticity of the GARCH form. We estimate several specifications where daily trading volume is included in the conditional variance equation additively and multiplicatively. The new multiplicative specification clearly outperforms the additive specification. 相似文献
89.
Min Tu Helge Reinsch Sabina Rodríguez‐Hermida Rhea Verbeke Timothe Stassin Werner Egger Marcel Dickmann Bjorn Dieu Johan Hofkens Ivo F. J. Vankelecom Norbert Stock Rob Ameloot 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2445-2449
Metal–organic frameworks (MOFs) enable the design of host–guest systems with specific properties. In this work, we show how the confinement of anthracene in a well‐chosen MOF host leads to reversible yellow‐to‐purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host–guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications. 相似文献
90.
Niels J. Hauwert Tamara A. M. Mocking Daniel DaCostaPereira Ken Lion Yara Huppelschoten Henry F. Vischer Iwan J. P. DeEsch Maikel Wijtmans Rob Leurs 《Angewandte Chemie (International ed. in English)》2019,58(14):4531-4535
Spatiotemporal control over biochemical signaling processes involving G protein‐coupled receptors (GPCRs) is highly desired for dissecting their complex intracellular signaling. We developed sixteen photoswitchable ligands for the human histamine H3 receptor (hH3R). Upon illumination, key compound 65 decreases its affinity for the hH3R by 8.5‐fold and its potency in hH3R‐mediated Gi protein activation by over 20‐fold, with the trans and cis isomer both acting as full agonist. In real‐time two‐electrode voltage clamp experiments in Xenopus oocytes, 65 shows rapid light‐induced modulation of hH3R activity. Ligand 65 shows good binding selectivity amongst the histamine receptor subfamily and has good photolytic stability. In all, 65 (VUF15000) is the first photoswitchable GPCR agonist confirmed to be modulated through its affinity and potency upon photoswitching while maintaining its intrinsic activity, rendering it a new chemical biology tool for spatiotemporal control of GPCR activation. 相似文献