全文获取类型
收费全文 | 859篇 |
免费 | 18篇 |
国内免费 | 12篇 |
专业分类
化学 | 481篇 |
力学 | 12篇 |
数学 | 260篇 |
物理学 | 136篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 23篇 |
2014年 | 15篇 |
2013年 | 49篇 |
2012年 | 44篇 |
2011年 | 41篇 |
2010年 | 31篇 |
2009年 | 22篇 |
2008年 | 56篇 |
2007年 | 42篇 |
2006年 | 49篇 |
2005年 | 39篇 |
2004年 | 35篇 |
2003年 | 33篇 |
2002年 | 28篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 22篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有889条查询结果,搜索用时 15 毫秒
71.
Ron Tzur 《The Journal of Mathematical Behavior》2004,23(1):93-114
Within a constructivist perspective, I conducted a teaching experiment with two fourth graders to study how a teacher and students can jointly produce the reversible fraction conception. Ongoing and retrospective analysis of the data revealed the non-trivial process by which students can abstract multiplicative reasoning about fractions. The study articulates a conception in a developmental sequence of iteration-based fraction conceptions and the teacher’s role in fostering such a conception in students. 相似文献
72.
Ron Buckmire 《Numerical Methods for Partial Differential Equations》2004,20(3):327-337
The boundary value problem Δu + λeu = 0 where u = 0 on the boundary is often referred to as “the Bratu problem.” The Bratu problem with cylindrical radial operators, also known as the cylindrical Bratu‐Gelfand problem, is considered here. It is a nonlinear eigenvalue problem with two known bifurcated solutions for λ < λc, no solutions for λ > λc and a unique solution when λ = λc. Numerical solutions to the Bratu‐Gelfand problem at the critical value of λc = 2 are computed using nonstandard finite‐difference schemes known as Mickens finite differences. Comparison of numerical results obtained by solving the Bratu‐Gelfand problem using a Mickens discretization with results obtained using standard finite differences for λ < 2 are given, which illustrate the superiority of the nonstandard scheme. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 20: 327–337, 2004 相似文献
73.
F. Bry (J. Combin. Theory Ser. B 34 (1983), 48–57) proved that a locally finite infinite n-connected factorizable graph has at least (n−1)! 1-factors and showed that for n = 2 this lower bound is sharp. We prove that for n≥3 any infinite n-connected factorizable graph has at least n! 1-factors (which is a sharp lower bound). 相似文献
74.
75.
Ron Shepard 《International journal of quantum chemistry》1991,40(6):865-887
The integral file structure used in the COLUMBUS Program System is described. This file structure is proposed for use as an interchange format for the exchange of information between various electronic structure codes. Access to the integral and density matrix arrays stored in the file structure is simplified by a supporting subroutine library. This library is portable across various computers and is readily available to programmers from the COLUMBUS distribution files. This library provides for the efficient processing of individual records, including the use of asynchronous I/O and the vectorized processing of packed orbital labels. The individual arrays are identified in a self-defining and extensible manner, allowing for the addition of new integral types as demanded by the application. The format of the individual records is also self-defining, allowing for the use of various packing and data compression methods within each record without burdening the calling program with unnecessary complications. 相似文献
76.
77.
Majors J. Badgett Barry Boyes Ron Orlando 《Journal of the American Society for Mass Spectrometry》2017,28(5):818-826
Peptides with deamidated asparagine residues and oxidized methionine residues are often not resolved sufficiently to allow quantitation of their native and modified forms using reversed phase (RP) chromatography. The accurate quantitation of these modifications is vital in protein biotherapeutic analysis because they can affect a protein’s function, activity, and stability. We demonstrate here that hydrophilic interaction liquid chromatography (HILIC) adequately and predictably separates peptides with these modifications from their native counterparts. Furthermore, coefficients describing the extent of the hydrophilicity of these modifications have been derived and were incorporated into a previously made peptide retention prediction model that is capable of predicting the retention times of peptides with and without these modifications. 相似文献
78.
Cho DS Gibson SC Bhandari D McNally ME Hoffman RM Cook KD Song L 《Rapid communications in mass spectrometry : RCM》2011,25(23):3575-3580
Batch slurry reactions are widely used in the industrial manufacturing of chemicals, pharmaceuticals, petrochemicals and polymers. However, onsite monitoring of batch slurry reactions is still not feasible in production plants due to the challenge in analyzing heterogeneous samples without complicated sample preparation procedures. In this study, direct analysis in real time mass spectrometry (DART-MS) has been evaluated for the onsite monitoring of a model batch slurry reaction. The results suggested that automation of the sampling process of DART-MS is important to achieve quantitative results. With a sampling technique of manual sample deposition on melting point capillaries followed by automatic sample introduction across the helium beam, relative standard deviation (RSD) of the protonated molecule signals from the reaction product of the model batch slurry reaction ranged from 6 to 30%. This RSD range is improved greatly over a sampling technique of manual sample deposition followed by manual sample introduction where the RSDs are up to 110%. Furthermore, with the semi-automated sampling approach, semi-quantitative analysis of slurry samples has been achieved. Better quantification is expected with a fully automated sampling approach. 相似文献
79.
Ron Aharoni Eli Berger Agelos Georgakopoulos Amitai Perlstein 《Journal of Combinatorial Theory, Series B》2011,101(1):1-17
We prove a strong version of the Max-Flow Min-Cut theorem for countable networks, namely that in every such network there exist a flow and a cut that are “orthogonal” to each other, in the sense that the flow saturates the cut and is zero on the reverse cut. If the network does not contain infinite trails then this flow can be chosen to be mundane, i.e. to be a sum of flows along finite paths. We show that in the presence of infinite trails there may be no orthogonal pair of a cut and a mundane flow. We finally show that for locally finite networks there is an orthogonal pair of a cut and a flow that satisfies Kirchhoff's first law also for ends. 相似文献
80.
Wang F Elbaz J Orbach R Magen N Willner I 《Journal of the American Chemical Society》2011,133(43):17149-17151
A systematic study of the amplified optical detection of DNA by Mg(2+)-dependent DNAzyme subunits is described. The use of two DNAzyme subunits and the respective fluorophore/quencher-modified substrate allows the detection of the target DNA with a sensitivity corresponding to 1 × 10(-9) M. The use of two functional hairpin structures that include the DNAzyme subunits in a caged, inactive configuration leads, in the presence of the target DNA, to the opening of one of the hairpins and to the activation of an autonomous cross-opening process of the two hairpins, which affords polymer DNA wires consisting of the Mg(2+)-dependent DNAzyme subunits. This amplification paradigm leads to the analysis of the target DNA with a sensitivity corresponding to 1 × 10(-14) M. The amplification mixture composed of the two hairpins can be implemented as a versatile sensing platform for analyzing any gene in the presence of the appropriate hairpin probe. This is exemplified with the detection of the BRCA1 oncogene. 相似文献