全文获取类型
收费全文 | 2133篇 |
免费 | 80篇 |
国内免费 | 13篇 |
专业分类
化学 | 1354篇 |
晶体学 | 16篇 |
力学 | 72篇 |
数学 | 285篇 |
物理学 | 499篇 |
出版年
2023年 | 13篇 |
2022年 | 21篇 |
2021年 | 40篇 |
2020年 | 28篇 |
2019年 | 28篇 |
2018年 | 26篇 |
2017年 | 29篇 |
2016年 | 54篇 |
2015年 | 59篇 |
2014年 | 59篇 |
2013年 | 94篇 |
2012年 | 124篇 |
2011年 | 156篇 |
2010年 | 84篇 |
2009年 | 96篇 |
2008年 | 137篇 |
2007年 | 150篇 |
2006年 | 146篇 |
2005年 | 105篇 |
2004年 | 79篇 |
2003年 | 66篇 |
2002年 | 54篇 |
2001年 | 52篇 |
2000年 | 58篇 |
1999年 | 34篇 |
1998年 | 28篇 |
1997年 | 26篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1934年 | 6篇 |
1930年 | 4篇 |
排序方式: 共有2226条查询结果,搜索用时 343 毫秒
1.
2.
3.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
4.
Rafael R. del Río Castillo 《Communications in Mathematical Physics》1991,142(2):421-431
In this work we study the behavior of embedded eigenvalues of Sturm-Liouville problems in the half axis under local perturbations. When the derivative of the spectral function is strictly positive, we prove that the embedded eigenvalues either disappear or remain fixed. In this case we show that local perturbations cannot add eigenvalues in the continuous spectrum. If the condition on the spectral function is removed then a local perturbation can add infinitely many eigenvalues. 相似文献
5.
Summary We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most
finitely additive integration theories. 相似文献
6.
Fabiano Severo Rodembusch Ndya Pesce da Silveira Dimitrios Samios Leandra Franciscato Campo Valter Stefani 《Journal of Polymer Science.Polymer Physics》2003,41(4):341-350
The solution behavior of new copolymers of methyl methacrylate and benzazole dyes emitting fluorescence because of an intramolecular proton‐transfer mechanism in the electronically excited state has been investigated by static light scattering, fluorescence spectroscopy, ultraviolet–visible, and gel permeation chromatography. In the dilute regime, with tetrahydrofuran (THF) and chloroform as solvents, the copolymers behave as typical polydisperse linear chains in good solvents. The analysis of the osmotic modulus for concentrated solutions in THF (c ≥ 60 g L?1) indicates the existence of an interchain association mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 341–350, 2003 相似文献
7.
8.
9.
We study bounds on averages of spectral functions corresponding to Sturm-Liouville operators on the half line for different boundary conditions. As a consequence constraints are obtained which imply existence of singular spectrum embedded in a.c. spectrum for sets of boundary conditions with positive measure and potentials vanishing in an interval [0,N]. These constraints are related to estimates on the measure of sets where the spectral density is positive. 相似文献
10.
The effects of n‐hexanol, n‐pentanol, and n‐butanol on the critical micelle concentration (cmc), on the micellar ionization degree (α), and on the rate of the reaction methyl 4‐nitrobenzenesulfonate + Br? have been investigated in cetyltrimethylammonium bromide (CTAB) aqueous solutions. An increase in the alcohol concentration present in the solution produces a decrease in the cmc and an increase in the micellar ionization degree. Kinetic data show that the observed rate constant decreases as alcohol concentration increases. This result was rationalized by considering variations in the equilibrium binding constant of the methyl 4‐nitrobenzenesulfonate molecules to the micelles, variations in the interfacial bromide ion concentration, and variations in the characteristics of the water–alcohol bulk phase provoked by the presence of alcohols. When these operative factors are considered, kinetic data in this and other works show that the second‐order rate constants in the micellar pseudophases of water–alcohol micellar solutions are quite similar to those estimated in the absence of alcohols. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 634–641, 2004 相似文献