全文获取类型
收费全文 | 2285篇 |
免费 | 77篇 |
国内免费 | 20篇 |
专业分类
化学 | 1355篇 |
晶体学 | 27篇 |
力学 | 46篇 |
数学 | 433篇 |
物理学 | 521篇 |
出版年
2022年 | 22篇 |
2021年 | 22篇 |
2020年 | 41篇 |
2019年 | 55篇 |
2018年 | 31篇 |
2017年 | 25篇 |
2016年 | 69篇 |
2015年 | 43篇 |
2014年 | 50篇 |
2013年 | 118篇 |
2012年 | 119篇 |
2011年 | 128篇 |
2010年 | 71篇 |
2009年 | 60篇 |
2008年 | 139篇 |
2007年 | 119篇 |
2006年 | 138篇 |
2005年 | 129篇 |
2004年 | 89篇 |
2003年 | 86篇 |
2002年 | 76篇 |
2001年 | 25篇 |
2000年 | 30篇 |
1999年 | 22篇 |
1998年 | 26篇 |
1997年 | 33篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 31篇 |
1993年 | 23篇 |
1992年 | 22篇 |
1991年 | 26篇 |
1990年 | 22篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1985年 | 29篇 |
1984年 | 34篇 |
1983年 | 19篇 |
1982年 | 27篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1974年 | 27篇 |
1973年 | 17篇 |
1972年 | 15篇 |
排序方式: 共有2382条查询结果,搜索用时 15 毫秒
131.
Nonlinear Dynamics - This paper addresses the problem of trajectory tracking control of an underactuated surface vessel moving in a two-dimensional space in the presence of unknown disturbances. In... 相似文献
132.
Rory?H.?Uibel Emily?C.?Heider Jennifer?L.?Gasser Joel?M.?HarrisEmail author Edward?M.?Eyring Sergio?Petrucci 《Journal of solution chemistry》2005,34(5):499-514
Advances have been made recently in broadening the accessible ultrasonic absorption frequency range and improving the detectability of minor species present in solution using Raman spectroscopy. Development of chemometric techniques in these areas needs to keep pace with the improvement of these experimental methods. Refinements in the analysis of ultrasonic and Raman data based on multivariable least squares and factor analysis, respectively, are examined to investigate the kinetics of zinc thiocyanate complex formation in water. Analysis of ultrasonic absorption relaxation spectra verified that the observed process in aqueous Zn(SCN)2 involves substitution of water from the first coordination shell of Zn2+. Use of a multivariable least-squares error surface is described that enhances the reliability of assigned frequencies of ultrasonic absorption maxima. Factor analysis of Raman scattering data provided direct evidence that at least four complex species, such as Zn(SCN)+ and Zn(SCN)2, are simultaneously present in the aqueous zinc thiocyanate solutions. 相似文献
133.
134.
Behnaz Afzalian Joel T. Mague Maryam Mohamadi S. Yousef Ebrahimipour Behjat Pour amiri Esmat Tavakolinejad Kermani 《催化学报》2015,(7):1101-1108
Three complexes containing 2-pyrazinecarboxylate (pzca–), including [Ni(pzca)2(H2O)2], [Co(pzca)2(H2O)2], and [Cu(pzca)2(H2O)2], have been synthesized and characterized using physico-chemical and spectroscopic methods. Furthermore, the structure of each complex was determined by single-crystal X-ray diffraction. All three complexes have an octahedral geometry, where the metal ion chelated by two carboxylate oxygens, two nitrogen atoms belonging to pyrazinic acid molecules, and two oxygen atoms of two water molecules. The catalytic activities of these complex-es were also investigated in the green synthesis of 2H-indazolo[2,1-b]phthalazine-triones by the reaction of hydrazine hydrate with an arylaldehyde, phthalic anhydride, and dimedone in acetic acid. 相似文献
135.
Michael G. Neubauer William Watkins Joel Zeitlin 《Linear algebra and its applications》1998,280(2-3):109-127
The purpose of this paper is to exhibit new infinite families of D-optimal (0, 1)-matrices. We show that Hadamard designs lead to D-optimal matrices of size (j, mj) and (j − 1, mj), for certain integers j ≡ 3 (mod 4) and all positive integers m. For j a power of a prime and j ≡ 1 (mod 4), supplementary difference sets lead to D-optimal matrices of size (j, 2mj) and (j − 1, 2mj), for all positive integers m. We also show that for a given j and d sufficiently large, about half of the entries in each column of a D-optimal matrix are ones. This leads to a new relationship between D-optimality for (0, 1)-matrices and for (±1)-matrices. Known results about D-optimal (±1)-matrices are then used to obtain new D-optimal (0, 1)-matrices. 相似文献
136.
In mobile edge computing systems, the edge server placement problem is mainly tackled as a multi-objective optimization problem and solved with mixed integer programming, heuristic or meta-heuristic algorithms, etc. These methods, however, have profound defect implications such as poor scalability, local optimal solutions, and parameter tuning difficulties. To overcome these defects, we propose a novel edge server placement algorithm based on deep q-network and reinforcement learning, dubbed DQN-ESPA, which can achieve optimal placements without relying on previous placement experience. In DQN-ESPA, the edge server placement problem is modeled as a Markov decision process, which is formalized with the state space, action space and reward function, and it is subsequently solved using a reinforcement learning algorithm. Experimental results using real datasets from Shanghai Telecom show that DQN-ESPA outperforms state-of-the-art algorithms such as simulated annealing placement algorithm (SAPA), Top-K placement algorithm (TKPA), K-Means placement algorithm (KMPA), and random placement algorithm (RPA). In particular, with a comprehensive consideration of access delay and workload balance, DQN-ESPA achieves up to 13.40% and 15.54% better placement performance for 100 and 300 edge servers respectively. 相似文献
137.
138.
139.
Dr. Jingjun Hao Prof. Arnold L. Rheingold Marzieh Kavand Dr. Kipp J. van Schooten Prof. Christoph Boehme Dr. Marçal Capdevila‐Cortada Prof. Juan J. Novoa Eva Wöss Prof. Günther Knör Prof. Joel S. Miller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(35):12312-12315
The reaction of 2,3,5,6‐tetracyanopyridine (TCNPy) and Cr(C6H6)2 forms diamagnetic σ‐[TCNPy]22? possessing a 1.572(3) Å intrafragment sp3–sp3 bond. This is in contrast to the structurally related 1,2,4,5‐tetracyanobenzene and 1,2,4,5‐tetracyanopyrazine that form π‐dimer dianions possessing long, multicenter bonds. 相似文献
140.
Maja Ponikvar-Svet Diana N. Zeiger Loryn R. Keating Joel F. Liebman 《Structural chemistry》2012,23(6):2019-2037
In the current review of the journal Structural Chemistry, the contents of the issues 1–3 for the calendar year 2012 are related to thermochemistry. A brief thermochemical commentary is added to the summary of each article. 相似文献