全文获取类型
收费全文 | 361篇 |
免费 | 10篇 |
国内免费 | 7篇 |
专业分类
化学 | 266篇 |
晶体学 | 4篇 |
力学 | 11篇 |
综合类 | 1篇 |
数学 | 40篇 |
物理学 | 56篇 |
出版年
2023年 | 1篇 |
2022年 | 21篇 |
2021年 | 12篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 18篇 |
2012年 | 25篇 |
2011年 | 32篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 23篇 |
2006年 | 24篇 |
2005年 | 18篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有378条查询结果,搜索用时 31 毫秒
41.
The usage of ordinal scales (sometimes called ‘semi-quantitative’ scales) for performing measurements in the area of applied
chemical metrology and quality assurance is widespread. This paper presents a method for handling actions such as calibration,
measuring systems’ capabilities comparison and reproducibility evaluation as a comparison between two measuring systems (MSs)
referring to a known/unknown reference standard. The strength of the agreement between these MSs is evaluated through two
known versions of Cohen’s kappa statistics (the traditional one and the modified one). The effectiveness of these statistics
from the metrological point of view is examined, and the preferability of the modified kappa statistics is demonstrated via
an example. 相似文献
42.
Yi L Zhang P Ji X Liang Y Wang Y Zhou Z Chen B 《Chemical & pharmaceutical bulletin》2011,59(7):839-843
The article reports a simple, sensitive and fast LC/MS method for the analysis of L-arginine (L-Arg), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) in human plasma. The homoarginine was used as the internal standard (IS). The chromatographic separation was achieved on C??(150 mm×2.1 mm, 5 μm) column with a mobile phase consisting of ammonium acetate (0.25 mmol/l) and methanol (93 : 7, v/v), at a flow rate of 0.2 ml/min. L-Arg, ADMA and SDMA were well separated by LC/MS with selective ion mode (SIM). The method was successfully applied to type 2 diabetes mellitus (T2DM) study. Twenty-one healthy controls and twenty-two T2DM patients before and after treatment two years were investigated. The results indicated that the level of ADMA in T2DM was significantly higher than that in healthy controls. Furthermore, ADMA has important association with the development of cardiovascular diseases. 相似文献
43.
We employ a one-electron, tight-binding model of an electrode-molecule-electrode junction to explore the fundamental relationship between adsorption geometry and electron transport, producing exact results (within this model). By varying the chemisorption location (e.g., atop a surface atom or in a hollow site between surface atoms) and the molecule-electrode coupling, we find that the largest currents are realized when the molecule (i) is highly coordinated by the surface and (ii) has favorable overlap with electrode states near the Fermi level. We also show the importance of electrode-induced molecular level shifting for certain adsorption geometries, which can cause molecular levels far from the Fermi level to conduct better than those near the Fermi level. Since all of these factors are greatly influenced by the chemical moiety used to link the molecule to an electrode, these results present a set of guidelines to help choose "alligator clips" for molecular electronic devices. 相似文献
44.
Zhu B Yuan F Li R Li Y Wei Q Ma Z Du B Zhang X 《Chemical communications (Cambridge, England)》2011,47(25):7098-7100
A simple but highly selective colorimetric and ratiometric fluorescent chemodosimeter was designed and synthesized to detect fluoride ions (F(-)) in aqueous solution and living cells by virtue of the strong affinity of F(-) toward silicon. 相似文献
45.
Mabkhot YN Al-Majid AM Alamary AS Warad I Sedigi Y 《Molecules (Basel, Switzerland)》2011,16(6):5142-5148
Facile and convenient syntheses of bisdimethylthieno[2,3-b]thiophen-2,5-diyl bis(oxazole-2-amine), bis(1H-imidazol-2-amine), bis((3a)-H-indole),[1,2-a]pyrimidine), bis(1H-imidazo[1,2-b][1,2,4]triazole) and bis(9H-benzo[d]imidazo[1,2-a]imidazole) derivatives incorporating a thieno[2,3-b]thiophene moiety from the versatile and readily accessible 1,1'(3,4-dimethylthieno[2,3-b]thiophene-2,5-diyl)-bis(2-bromo-ethanone) (1) are described. 相似文献
46.
K. Raychaudhuri D. Jensen F. Lomanno D. McIntyre M. Rabin G. Bunce S.P. Yamin P.T. Cox J. Dworkin O.E. Overseth K. Heller Y. Makdisi 《Physics letters. [Part B]》1980,90(3):319-323
We report measurements of inclusive Λ polarization, produced by unpolarized protons incident at several momenta (20, 24, and 28.5 GeV/c) onto hydrogen, deuterium, and beryllium targets. A large polarization from hydrogen, P = ?0.34 ± 0.06 at pPT = 1.2 GeV/c, establishes the fact that inclusive Λ polarization arises from p-p collisions. 相似文献
47.
Dexuan Xie Suresh B. Singh Eugene M. Fluder Tamar Schlick 《Mathematical Programming》2003,95(1):161-185
The similarity and diversity sampling problems are two challenging optimization tasks that arise in the analysis of chemical
databases. As a first step to their solution, we propose an efficient projection/ refinement protocol based on the principal
component analysis (PCA) and the truncated-Newton minimization method implemented by our package TNPACK (PCA/TNPACK). We show
that PCA can provide the same initial guess as the singular value decomposition (SVD) for the optimization task of solving
the distance-geometry optimization problem if each column of a database matrix has a mean of zero. Hence, our PCA/TNPACK approach
is analogous to the SVD/TNPACK projection/refinement protocol that we developed recently for visualizing large chemical databases.
Using PCA/TNPACK and the Merck MDDR database (MDL Drug Data Report), we further investigate the projection/refinement procedure
with regards to the preservation of the original clusters of chemical compounds, the accuracy of similarity and diversity
sampling of chemical compounds, and the potential application in the study of structure activity relationships. We also explore
by simple experiments accuracy and efficiency aspects of the PCA/TNPACK procedure compared to those of a global optimization
algorithm (simulated annealing, as implemented by the program package SIMANN) in terms of producing the projection mapping
of a database. Numerical results show that the 2D PCA/TNPACK mapping can preserve the distance relationships of the original
database and is thus valuable as a first step in similarity and diversity applications. Of course, the generation of a global
rather than local minimizer and its interpretation in terms of pharameceutical applications remains a challenge. Since all
numerical tests are performed on the Merck MDDR database, results are representative of realistic cases encountered in the
field of drug design, and may help analyze properties of medicinal compounds.
Received: December 21, 2000 / Accepted: August 19, 2002 Published online: September 27, 2002
Mathematics Subject Classification (2000): 65K10, 62H25, 92C50 相似文献
48.
This paper introduces a new computational method for molecular dynamics. The method combines the Backward-Euler scheme for the solution of stiff differential equations with a Langevin-equation approach to the establishment of thermal equilibrium. The method allows the user to choose a cutoff frequency ωc. Vibrational modes with frequencies below ωc will be fully excited (receive a mean energy of kT per mode), while modes with frequencies greater than ωc will be effectively frozen by the method. By setting ωc = kT/h, one can obtain reasonable agreement with the quantum-mechanical energy distribution among the various modes, despite the classical character of the computation. 相似文献
49.
Tamar Burak 《Israel Journal of Mathematics》1973,16(4):404-417
Fort ∈ [a, b], letA(t) be the unbounded operator inH
0,p
(G) associated with an elliptic-boundary value problem that satisfies Agmon’s conditions on the rays λ=±iτ, τ ≥0. Existence and uniqueness results are obtained for weak and strict solutions of two-point problems of the type (du/dt)−A(t) u(t) =f(t),E
1(α)u (α)=u
α,E
2 (β)u (β)=u
β. Here [α, β) χ- [a, b],E
1 (α) andE
2 (β) are spectral projections associated withA(α) andA(β) respectively, andA(α)E
1 (α) and =A (β)E
2 (β) are infinitesimal generators of analytic semigroups. WhenA(t) andf(t) are analytic in a convex, complex neighborhoodO of [a, b] we show that for someθ
i
,i=1,2, any solution ofdu/dt =A(t)u (t)=f(t) in [a, b] is analytic and satisfies the above equation in the setO∩{t; t ≠ a, t ≠ b, | arg (t −a) | <θ
1, | arg (b −t) |θ
2}.
Research partially supported by N. N. F. grant at Brandeis University. 相似文献
50.
Tamar Lando 《Annals of Pure and Applied Logic》2018,169(4):277-311
Space, as we typically represent it in mathematics and physics, is composed of dimensionless, indivisible points. On an alternative, region-based approach to space, extended regions together with the relations of ‘parthood’ and ‘contact’ are taken as primitive; points are represented as mathematical abstractions from regions.Region-based theories of space have been traditionally modeled in regular closed (or regular open) algebras, in work that goes back to [5] and [21]. Recently, logics for region-based theories of space were developed in [3] and [19]. It was shown that these logics have both a nice topological and relational semantics, and that the minimal logic for contact algebras, (defined below), is complete for both.The present paper explores the question of completeness of and its extensions for individual topological spaces of interest: the real line, Cantor space, the rationals, and the infinite binary tree. A second aim is to study a different, algebraic model of logics for region-based theories of space, based on the Lebesgue measure algebra (or algebra of Borel subsets of the real line modulo sets of Lebesgue measure zero). As a model for point-free space, the algebra was first discussed in [2]. The main results of the paper are that is weakly complete for any zero-dimensional, dense-in-itself metric space (including, e.g., Cantor space and the rationals); the extension is weakly complete for the real line and the Lebesgue measure contact algebra. We also prove that the logic is weakly complete for the infinite binary tree. 相似文献