全文获取类型
收费全文 | 265752篇 |
免费 | 4760篇 |
国内免费 | 1351篇 |
专业分类
化学 | 150857篇 |
晶体学 | 3549篇 |
力学 | 10214篇 |
综合类 | 47篇 |
数学 | 31054篇 |
物理学 | 76142篇 |
出版年
2021年 | 2360篇 |
2020年 | 2849篇 |
2019年 | 3072篇 |
2018年 | 4337篇 |
2017年 | 4063篇 |
2016年 | 5964篇 |
2015年 | 3955篇 |
2014年 | 5478篇 |
2013年 | 12427篇 |
2012年 | 10517篇 |
2011年 | 12161篇 |
2010年 | 8362篇 |
2009年 | 7869篇 |
2008年 | 11287篇 |
2007年 | 11286篇 |
2006年 | 10390篇 |
2005年 | 9595篇 |
2004年 | 8432篇 |
2003年 | 7448篇 |
2002年 | 7113篇 |
2001年 | 6831篇 |
2000年 | 5467篇 |
1999年 | 4077篇 |
1998年 | 3478篇 |
1997年 | 3480篇 |
1996年 | 3396篇 |
1995年 | 2687篇 |
1994年 | 2830篇 |
1993年 | 2875篇 |
1992年 | 3023篇 |
1991年 | 3021篇 |
1990年 | 2881篇 |
1989年 | 2867篇 |
1988年 | 2736篇 |
1987年 | 2706篇 |
1986年 | 2587篇 |
1985年 | 3404篇 |
1984年 | 3524篇 |
1983年 | 2787篇 |
1982年 | 3133篇 |
1981年 | 3001篇 |
1980年 | 2765篇 |
1979年 | 2956篇 |
1978年 | 3055篇 |
1977年 | 3039篇 |
1976年 | 3064篇 |
1975年 | 2897篇 |
1974年 | 2888篇 |
1973年 | 3029篇 |
1972年 | 1963篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Doklady Physics - In this paper, we study the statistical characteristics of the Riemann wave and the integral of it. Such problems arise in the physics of fronts’ propagation, in particular,... 相似文献
142.
Norbornene derivatives from a metal‐free,strain‐promoted cycloaddition reaction: New building blocks for ring‐opening metathesis polymerization reactions
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Christopher E. Hobbs Binhong Lin Thomas Malinski 《Journal of polymer science. Part A, Polymer chemistry》2015,53(20):2357-2362
The preparation of new ring opening metathesis polymerization (ROMP) monomers using a 1,3‐dipolar cycloaddition between aryl azides and norbornadiene is described. Various norbornenetriazolines, obtained through a solvent‐and catalyst‐free reaction, can subsequently be incorporated into polymer backbones through ROMP reactions. Furthermore, thermal decomposition of the triazoline moiety can allow for further polymer functionalization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2357–2362 相似文献
143.
144.
145.
G.E. Farr 《Discrete Mathematics》2019,342(5):1510-1519
This paper continues the study of combinatorial properties of binary functions — that is, functions such that , where is a finite set. Binary functions have previously been shown to admit families of transforms that generalise duality, including a trinity transform, and families of associated minor operations that generalise deletion and contraction, with both these families parameterised by the complex numbers. Binary function representations exist for graphs (via the indicator functions of their cutset spaces) and indeed arbitrary matroids (as shown by the author previously). In this paper, we characterise degenerate elements – analogues of loops and coloops – in binary functions, with respect to any set of minor operations from our complex-parameterised family. We then apply this to study the relationship between binary functions and Tutte’s alternating dimaps, which also support a trinity transform and three associated minor operations. It is shown that only the simplest alternating dimaps have binary representations of the form we consider, which seems to be the most direct type of representation. The question of whether there exist other, more sophisticated types of binary function representations for alternating dimaps is left open. 相似文献
146.
We consider the problem of estimating a large rank-one tensor u ⊗k ∈ (ℝn)⊗k , k ≥ 3 , in Gaussian noise. Earlier work characterized a critical signal-to-noise ratio λ Bayes = O(1) above which an ideal estimator achieves strictly positive correlation with the unknown vector of interest. Remarkably, no polynomial-time algorithm is known that achieved this goal unless λ ≥ Cn(k − 2)/4 , and even powerful semidefinite programming relaxations appear to fail for 1 ≪ λ ≪ n(k − 2)/4 . In order to elucidate this behavior, we consider the maximum likelihood estimator, which requires maximizing a degree-k homogeneous polynomial over the unit sphere in n dimensions. We compute the expected number of critical points and local maxima of this objective function and show that it is exponential in the dimensions n , and give exact formulas for the exponential growth rate. We show that (for λ larger than a constant) critical points are either very close to the unknown vector u or are confined in a band of width Θ(λ−1/(k − 1)) around the maximum circle that is orthogonal to u . For local maxima, this band shrinks to be of size Θ(λ−1/(k − 2)) . These “uninformative” local maxima are likely to cause the failure of optimization algorithms. © 2019 Wiley Periodicals, Inc. 相似文献
147.
Thomas Wittmann Dr. Renée Siegel Nele Reimer Dr. Wolfgang Milius Prof. Dr. Norbert Stock Prof. Dr. Jürgen Senker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):314-323
The resistance of metal–organic frameworks towards water is a very critical issue concerning their practical use. Recently, it was shown for microporous MOFs that the water stability could be increased by introducing hydrophobic pendant groups. Here, we demonstrate a remarkable stabilisation of the mesoporous MOF Al‐MIL‐101‐NH2 by postsynthetic modification with phenyl isocyanate. In this process 86 % of the amino groups were converted into phenylurea units. As a consequence, the long‐term stability of Al‐MIL‐101‐URPh in liquid water could be extended beyond a week. In water saturated atmospheres Al‐MIL‐101‐URPh decomposed at least 12‐times slower than the unfunctionalised analogue. To study the underlying processes both materials were characterised by Ar, N2 and H2O sorption measurements, powder X‐ray diffraction, thermogravimetric and chemical analysis as well as solid‐state NMR and IR spectroscopy. Postsynthetic modification decreased the BET equivalent surface area from 3363 to 1555 m2 g?1 for Al‐MIL‐101‐URPh and reduced the mean diameters of the mesopores by 0.6 nm without degrading the structure significantly and reducing thermal stability. In spite of similar water uptake capacities, the relative humidity‐dependent uptake of Al‐MIL‐101‐URPh is slowed and occurs at higher relative humidity values. In combination with 1H‐27Al D ‐HMQC NMR spectroscopy experiments this favours a shielding mechanism of the Al clusters by the pendant phenyl groups and rules out pore blocking. 相似文献
148.
Differential inequalities for polynomials generalizing the well-known Smirnov, Rahman, Schmeisser, and Bernstein inequalities are obtained.
相似文献149.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
150.
Thermodynamic study of transthyretin association (wild‐type and senile forms) with heparan sulfate proteoglycan: pH effect and implication of the reactive histidine residue
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ambre Geneste Claire André Nadine Magy‐Bertrand Lydie Lethier Gharbi Tijani Yves Claude Guillaume 《Biomedical chromatography : BMC》2015,29(4):514-522
The tetramer destabilization of transthyretin into monomers and its fibrillation are phenomena leading to amyloid deposition. Heparan sulfate proteoglycan (HSPG) has been found in all amyloid deposits. A chromatographic approach was developed to compare binding parameters between wild‐type transthyretin (wtTTR) and an amyloidogenic transthyretin (sTTR). Results showed a greater affinity of sTTR for HSPG at pH 7.4 compared with wtTTR owing to the monomeric form of sTTR. Analysis of the thermodynamic parameters showed that van der Waals interactions were involved at the complex interface for both transthyretin forms. For sTTR, results from the plot representing the number of protons exchanged vs pH showed that the binding mechanism was pH‐dependent with a critical value at a pH 6.5. This observation was due to the protonation of a histidine residue as an imidazolium cation, which was not accessible when TTR was in its tetrameric structure. At pH >6.5, dehydration at the binding interface and several contacts between nonpolar groups of sTTR and HSPG were also coupled to binding for an optimal hydrogen‐bond network. At pH <6.5, the protonation of the His residue from sTTR monomer when pH decreased broke the hydrogen‐bond network, leading to its destabilization and thus producing slight conformational changes in the sTTR monomer structure. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献