全文获取类型
收费全文 | 15466篇 |
免费 | 747篇 |
国内免费 | 145篇 |
专业分类
化学 | 10397篇 |
晶体学 | 102篇 |
力学 | 431篇 |
数学 | 2761篇 |
物理学 | 2667篇 |
出版年
2023年 | 140篇 |
2022年 | 104篇 |
2021年 | 299篇 |
2020年 | 403篇 |
2019年 | 386篇 |
2018年 | 256篇 |
2017年 | 223篇 |
2016年 | 607篇 |
2015年 | 480篇 |
2014年 | 567篇 |
2013年 | 873篇 |
2012年 | 1125篇 |
2011年 | 1315篇 |
2010年 | 678篇 |
2009年 | 585篇 |
2008年 | 989篇 |
2007年 | 948篇 |
2006年 | 940篇 |
2005年 | 840篇 |
2004年 | 729篇 |
2003年 | 498篇 |
2002年 | 463篇 |
2001年 | 129篇 |
2000年 | 113篇 |
1999年 | 110篇 |
1998年 | 84篇 |
1997年 | 105篇 |
1996年 | 147篇 |
1995年 | 105篇 |
1994年 | 109篇 |
1993年 | 118篇 |
1992年 | 82篇 |
1991年 | 92篇 |
1990年 | 69篇 |
1989年 | 68篇 |
1988年 | 83篇 |
1987年 | 68篇 |
1986年 | 63篇 |
1985年 | 98篇 |
1984年 | 104篇 |
1982年 | 114篇 |
1981年 | 122篇 |
1980年 | 96篇 |
1979年 | 84篇 |
1978年 | 113篇 |
1977年 | 92篇 |
1976年 | 73篇 |
1975年 | 71篇 |
1974年 | 64篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Georghiou Angelos Kuhn Daniel Wiesemann Wolfram 《Computational Management Science》2019,16(4):545-576
Computational Management Science - Dynamic decision-making under uncertainty has a long and distinguished history in operations research. Due to the curse of dimensionality, solution schemes that... 相似文献
53.
Daniel Grinberg Sabrina Siddique Minh‐Quyen Le Richard Liang Jean‐Fabien Capsal Pierre‐Jean Cottinet 《Journal of Polymer Science.Polymer Physics》2019,57(2):109-115
Additive manufacturing (AM), otherwise known as three‐dimensional (3D) printing, is driving major innovations in many areas, such as engineering, manufacturing, art, education, and medicine. Although a considerable amount of progress has been made in this field, additional research work is required to overcome various remaining challenges. Recently, one of the actively researched areas lies in the AM of smart materials and structures. Electroactive materials incorporated in 3D printing have given birth to 4D printing, where 3D printed structures can perform as actuating and/or sensing systems, making it possible to deliver electrical signals under external mechanical stimuli and vice versa. In this paper, we present a lightweight, low cost piezoelectric material based on the dispersion of inorganic ferroelectric submicron particles in a polymer matrix. We report on how the proposed material is compatible with the AM process. Finally, we discuss its potential applications for healthcare, especially in smart implants prostheses. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 109–115 相似文献
54.
Dr. Daniel Brodbeck Dr. Sonia Álvarez-Barcia Dr. Jan Meisner Dr. Florian Broghammer Julian Klepp Dr. Delphine Garnier Dr. Wolfgang Frey Prof. Dr. Johannes Kästner Prof. Dr. René Peters 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(6):1515-1524
Asymmetric 1,2-additions of cyanide yield enantioenriched cyanohydrins as versatile chiral building blocks. Next to HCN, volatile organic cyanide sources are usually used. Among them, cyanoformates are more attractive on technical scale than TMSCN for cost reasons, but catalytic productivity is usually lower. Here, the development of a new strategy for cyanations is described, in which this activity disadvantage is overcome. A Lewis acidic Al center cooperates with an aprotic onium moiety within a remarkably robust bifunctional Al–F–salen complex. This allowed for unprecedented turnover numbers of up to 104. DFT studies suggest an unexpected unique trimolecular pathway in which the ammonium bound cyanide attacks the aldehyde, which itself is activated by the carbonyl group of the cyanoformate binding to the Al center. In addition, a novel practical carboxycyanation method was developed that makes use of KCN as the sole cyanide source. The use of a pyrocarbonate as carboxylating reagent provided the best results. 相似文献
55.
Reversible Activation of Water by an Air- and Moisture-Stable Frustrated Rhodium Nitrogen Lewis Pair
Dr. María Carmona Dr. Joaquina Ferrer Dr. Ricardo Rodríguez Dr. Vincenzo Passarelli Prof. Dr. Fernando J. Lahoz Dr. Pilar García-Orduña Dr. Laura Cañadillas-Delgado Prof. Dr. Daniel Carmona 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13665-13670
[Cp*Rh(κ3N,N′,P- L )][SbF6] (Cp*=C5Me5), bearing a guanidine-derived phosphano ligand L , behaves as a “dormant” frustrated Lewis pair and activates H2 and H2O in a reversible manner. When D2O is employed, a facile H/D exchange at the Cp* ring takes place through sequential C(sp3)−H bond activation. 相似文献
56.
Claudianor O. Alves Daniel C. de Morais Filho Giovany M. Figueiredo 《Mathematical Methods in the Applied Sciences》2019,42(14):4862-4875
In this work, we prove the existence of positive solution for the following class of problems where λ>0 and is a potential satisfying some conditions. Using the variational method developed by Szulkin for functionals, which are the sum of a C1 functional with a convex lower semicontinuous functional, we prove that for each large enough λ>0, there exists a positive solution for the problem, and that, as λ→+∞, such solutions converge to a positive solution of the limit problem defined on the domain Ω=int(V?1({0})). 相似文献
57.
The edge‐percolation and vertex‐percolation random graph models start with an arbitrary graph G, and randomly delete edges or vertices of G with some fixed probability. We study the computational complexity of problems whose inputs are obtained by applying percolation to worst‐case instances. Specifically, we show that a number of classical ‐hard problems on graphs remain essentially as hard on percolated instances as they are in the worst‐case (assuming ). We also prove hardness results for other ‐hard problems such as Constraint Satisfaction Problems and Subset‐Sum, with suitable definitions of random deletions. Along the way, we establish that for any given graph G the independence number and the chromatic number are robust to percolation in the following sense. Given a graph G, let be the graph obtained by randomly deleting edges of G with some probability . We show that if is small, then remains small with probability at least 0.99. Similarly, we show that if is large, then remains large with probability at least 0.99. We believe these results are of independent interest. 相似文献
58.
59.
Let k be a field and let Λ be an indecomposable finite dimensional k-algebra such that there is a stable equivalence of Morita type between Λ and a self-injective split basic Nakayama algebra over k. We show that every indecomposable finitely generated Λ-module V has a universal deformation ring and we describe explicitly as a quotient ring of a power series ring over k in finitely many variables. This result applies in particular to Brauer tree algebras, and hence to p-modular blocks of finite groups with cyclic defect groups. 相似文献
60.
Massimo Brochetta Tania Borsari Sukdev Bag Dr. Sadhan Jana Siddhartha Maiti Prof. Dr. Alessio Porta Prof. Dr. Daniel B. Werz Prof. Dr. Giuseppe Zanoni Prof. Dr. Debabrata Maiti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(44):10323-10327
The development of efficient and mild methods for the synthesis of organofluorine compounds is of foremost interest in various fields of chemistry. A direct pyrimidine-based selective meta-C−H perfluoroalkenylation of arenes involving several commercially available perfluoroolefins is described. The synthetic versatility of the protocol is demonstrated by an extensive substrate scope including different benzylsulfonyl, alkylarene and phenylacetic acid scaffolds. The generality of this methodology including the meta-C−H perfluoroalkenylation of Ibuprofen, the facile cleavage of the directing group and gram-scale reactions are presented. 相似文献