全文获取类型
收费全文 | 27362篇 |
免费 | 4250篇 |
国内免费 | 2408篇 |
专业分类
化学 | 5741篇 |
晶体学 | 150篇 |
力学 | 3365篇 |
综合类 | 684篇 |
数学 | 14216篇 |
物理学 | 9864篇 |
出版年
2024年 | 38篇 |
2023年 | 279篇 |
2022年 | 426篇 |
2021年 | 629篇 |
2020年 | 724篇 |
2019年 | 697篇 |
2018年 | 669篇 |
2017年 | 987篇 |
2016年 | 1106篇 |
2015年 | 874篇 |
2014年 | 1472篇 |
2013年 | 2014篇 |
2012年 | 1454篇 |
2011年 | 1700篇 |
2010年 | 1518篇 |
2009年 | 1693篇 |
2008年 | 1889篇 |
2007年 | 1953篇 |
2006年 | 1614篇 |
2005年 | 1481篇 |
2004年 | 1375篇 |
2003年 | 1174篇 |
2002年 | 1190篇 |
2001年 | 983篇 |
2000年 | 871篇 |
1999年 | 808篇 |
1998年 | 701篇 |
1997年 | 617篇 |
1996年 | 501篇 |
1995年 | 461篇 |
1994年 | 311篇 |
1993年 | 273篇 |
1992年 | 204篇 |
1991年 | 241篇 |
1990年 | 153篇 |
1989年 | 115篇 |
1988年 | 140篇 |
1987年 | 100篇 |
1986年 | 79篇 |
1985年 | 92篇 |
1984年 | 76篇 |
1983年 | 46篇 |
1982年 | 50篇 |
1981年 | 50篇 |
1980年 | 38篇 |
1979年 | 44篇 |
1978年 | 29篇 |
1977年 | 16篇 |
1976年 | 15篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Jing Zhang Shuhui Wang Jacques Lalevée Fabrice Morlet-Savary Elizabeth S.-H. Lam Bernadette Graff Jing Liu Feiyue Xing Pu Xiao 《Journal of polymer science. Part A, Polymer chemistry》2020,58(6):792-802
The photoinitiation abilities of three 1,2-diketones [i.e., acenaphthenequinone ( ANPQ ), aceanthrenequinone ( AATQ ), and 9,10-phenanthrenequinone ( PANQ )]-based photoinitiating systems [PISs, with additives such as iodonium salt, N-vinylcarbazole (NVK), tertiary amine, and phenacyl bromide (R-Br)] for cationic photopolymerization and free-radical photopolymerization under the irradiation of ultraviolet (UV; 392 nm) or blue (455 nm) light-emitting diode (LED) bulb are investigated. All 1,2-diketones studied exhibit ground state absorption that match with the emission spectra of UV (392 nm) or blue LED (455 nm) better than that of the well-known blue-light-sensitive photoinitiator camphorquinone (CQ). In particular, AATQ /iodonium salt/NVK can show high photoinitiating ability (with epoxide conversion yield >70%) under the UV light irradiation due to the effect of NVK. In addition, 1,2-diketone/iodonium salt (and optional NVK) systems are capable of initiating free-radical photopolymerization of methacrylates, with conversions of 50–58%. Furthermore, some 1,2-diketone/tertiary amine (and optional R-Br) combinations are found to demonstrate high efficiency to initiate free-radical photopolymerization, and 71% of methacrylate conversion can be achieved with PANQ /tertiary amine/R-Br PIS. Some 1,2-ketone-based PISs can even exhibit higher efficiency than the CQ-based systems. The photochemical mechanism of the radical generation from the 1,2-diketone-based PISs is investigated and found to be consistent with the related photopolymerization efficiency. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 792–802 相似文献
992.
A variety of heterobiaryl compounds have been synthesized by the Suzuki‐Miyaura coupling reactions of heteroaryl halides with potassium aryltrifluoroborates. Pd (OAc)2 was found to be highly efficient for the Suzuki‐Miyaura coupling reactions of various heteroaryl halides with potassium aryltrifluoroborates in aqueous systems, delivering the corresponding heterobiaryl compounds in good to excellent yields. 相似文献
993.
In this article, we study for the ‐realization of the vector‐valued Schrödinger operator . Using a noncommutative version of the Dore–Venni theorem due to Monniaux and Prüss, we prove that the ‐realization of , defined on the intersection of the natural domains of the differential and multiplication operators which form , generates a strongly continuous contraction semigroup on . We also study additional properties of the semigroup such as extension to L1, positivity, ultracontractivity and prove that the generator has compact resolvent. 相似文献
994.
In this paper, for a finite group, we investigate to what extent its directed (resp. undirected) reduced power graph determines its directed power graph (resp. reduced power graph). Moreover, we investigate the determination of the orders of the elements of a finite group from its directed (resp. undirected) reduced power graph. Consequently, we show that some classes of finite groups are recognizable from their undirected reduced power graphs. Also, we study the relationship between the isomorphism classes of groups corresponding to the equivalence relations induced by the isomorphism of each of these graphs on the set of all finite groups. 相似文献
995.
In 2001, J.-M. Le Bars disproved the zero-one law (that says that every sentence from a certain logic is either true asymptotically almost surely (a.a.s.), or false a.a.s.) for existential monadic second order sentences (EMSO) on undirected graphs. He proved that there exists an EMSO sentence ? such that does not converge as (here, the probability distribution is uniform over the set of all graphs on the labeled set of vertices ). In the same paper, he conjectured that, for EMSO sentences with 2 first order variables, the zero-one law holds. In this paper, we disprove this conjecture. 相似文献
996.
Bilender P. Allahverdiev 《Mathematical Methods in the Applied Sciences》2019,42(1):229-236
In this study, maximal dissipative second‐order dynamic operators on semi‐infinite time scale are studied in the Hilbert space , that the extensions of a minimal symmetric operator in limit‐point case. We construct a self‐adjoint dilation of the dissipative operator together with its incoming and outgoing spectral representations so that we can determine the scattering function of the dilation as stated in the scheme of Lax‐Phillips. Moreover, we construct a functional model of the dissipative operator and identify its characteristic function in terms of the Weyl‐Titchmarsh function of a self‐adjoint second‐order dynamic operator. Finally, we prove the theorems on completeness of the system of root functions of the dissipative and accumulative dynamic operators. 相似文献
997.
Stevo Stevi Bratislav Iri
anin Witold Kosmala Zdenk marda 《Mathematical Methods in the Applied Sciences》2019,42(5):1687-1701
Some formulas for well‐defined solutions to four very special cases of a nonlinear fifth‐order difference equation have been presented recently in this journal, where some of them were proved by the method of induction, some are only quoted, and no any theory behind the formulas was given. Here, we show in an elegant constructive way how the general solution to the difference equation can be obtained, from which the special cases very easily follow, which is also demonstrated here. We also give some comments on the local stability results on the special cases of the nonlinear fifth‐order difference equation previously publish in this journal. 相似文献
998.
In this paper, the existence and multiplicity of positive solutions is established for Schrödinger‐Poisson system of the form where 0 ∈ Ω is a smooth bounded domain in , , and λ > 0 is a real parameter. Combining with the variational method and Nehari manifold method, two positive solutions of the system are obtained. 相似文献
999.
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
1000.
A mixed hp FEM for the approximation of fourth‐order singularly perturbed problems on smooth domains
P. Constantinou S. Franz L. Ludwig C. Xenophontos 《Numerical Methods for Partial Differential Equations》2019,35(1):114-127
We consider fourth‐order singularly perturbed problems posed on smooth domains and the approximation of their solution by a mixed Finite Element Method on the so‐called Spectral Boundary Layer Mesh. We show that the method converges uniformly, with respect to the singular perturbation parameter, at an exponential rate when the error is measured in the energy norm. Numerical examples illustrate our theoretical findings. 相似文献