全文获取类型
收费全文 | 941篇 |
免费 | 114篇 |
国内免费 | 31篇 |
专业分类
化学 | 405篇 |
晶体学 | 2篇 |
力学 | 26篇 |
综合类 | 41篇 |
数学 | 527篇 |
物理学 | 85篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 20篇 |
2021年 | 31篇 |
2020年 | 34篇 |
2019年 | 33篇 |
2018年 | 23篇 |
2017年 | 36篇 |
2016年 | 47篇 |
2015年 | 26篇 |
2014年 | 59篇 |
2013年 | 89篇 |
2012年 | 49篇 |
2011年 | 55篇 |
2010年 | 54篇 |
2009年 | 64篇 |
2008年 | 36篇 |
2007年 | 49篇 |
2006年 | 43篇 |
2005年 | 40篇 |
2004年 | 35篇 |
2003年 | 29篇 |
2002年 | 23篇 |
2001年 | 29篇 |
2000年 | 15篇 |
1999年 | 23篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 19篇 |
1995年 | 1篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1086条查询结果,搜索用时 15 毫秒
981.
Research progress and frontiers of magnetic-mediated hyperthermia (MMH) are presented, along with clinical trials in Germany, the US, Japan, and China. Special attention is focused on MMH mediated by magnetic nanoparticles, and multifunctional magnetic devices for cancer multimodality treatment are also introduced. 相似文献
982.
Carla Vilela Armando J. D. Silvestre Alessandro Gandini 《Journal of polymer science. Part A, Polymer chemistry》2013,51(10):2260-2270
Novel trifunctional monomers based on renewable resources were prepared and subsequently polymerized via the Diels‐Alder (DA) polycondensation between furan and maleimide complementary moieties. Three basic approaches were considered for these nonlinear DA polycondensations, namely the use of (i) a bisfuran monomer in combination with a trismaleimide (A2 + B3 system) and (ii) a trisfuran monomer in conjunction with a bismaleimide (A3 + B2 system) leading to branched or crosslinked materials, and (iii) the use of monomers incorporating both furan and maleimide end groups (A2B or AB2 systems), which lead to hyperbranched structures. The application of the retro‐DA reaction to the ensuing polymers confirmed their thermoreversible character. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
983.
Donald H. Negri 《Natural Resource Modeling》1990,4(4):521-537
This paper computes open loop and subgame perfect Nash equilibria for an infinite horizon, common property resource model with congestion and stock externalities. The model permits the comparison of the game-theoretic approach and the traditional commons literature, which preceded the widespread recognition of the games, because the underlying assumptions are equivalent. With access to the commons restricted, the subgame perfect equilibrium captures the inefficiency associated with the strategic scramble to capture the resource reserves the open loop does not. Under sole ownership, the two equilibrium concepts coincide with the surplus maximizing extraction policy. In free access, the extraction strategies under both equilibrium concepts coincide with complete rent dissipation. 相似文献
984.
Peter Hall 《Journal of multivariate analysis》1986,19(2)
This paper is devoted to tests for uniformity based on sum-functions of m-spacings, where m diverges to infinity as the sample size, n, increases. It is shown that if m diverges at a slower rate than n1/2 then the commonly used sum-function will detect alternatives distant (mn)−1/4 from the uniform. This result fails if m diverges more quickly than n1/2, and in that situation the statistic must be modified. The case where m/n → , 0 < < 1, is also considered, and it is shown that the test has adequate power against local and fixed alternatives if and only if is irrational. 相似文献
985.
Fully understand the chemical science and reasonable use of existing resources is an important premise to chemical science popularization. This paper summarizes the current resource types of popular science of chemistry in China. The chemical science resources in China are sorted out and analyzed, including China Association for Science and Technology of chemical science, popular science base of scientific research institutes and universities, scientific public class and the chemical science online open courses, and WeChat public platform chemical resources. This paper will provide a meaningful introduction of chemical science resources for the public, and provide valuable reference for the practice of chemical science in China. 相似文献
986.
Theorems of the alternative for multifunctions with applications to optimization: General results 总被引:2,自引:0,他引:2
F. Giannessi 《Journal of Optimization Theory and Applications》1987,55(2):233-256
Theorems of the alternative and separation theorems have been shown to be very useful concepts in constrained extremum problems (see, for instance, Refs. 1–12). Their use has stressed the concept of image of a constrained extremum problem, which has turned out to be a powerful and promising tool for investigating the main aspects of optimization (see Refs. 13 and 19). It should be pointed out that, in this approach, a finite-dimensional image problem can be associated to the given extremum problem, even if this is infinite-dimensional and provided that its constraints are expressed by functionals. Such a development can be carried on by means of theorems of the alternative for systems of single-valued functions.In this paper, theorems of the alternative for systems of multifunctions are studied, some general properties are stated, and connections with known results investigated. It is shown how the present approach can be used to analyze extremum problems, where the image of the domain of the constraining functions belongs to a functional space. Such a development will be carried on in a subsequent paper.Useful discussions with O. Ferrero and C. Zlinescu are gratefully acknowledged. 相似文献
987.
Lü Gui-Qin 《结构化学》2007,26(3)
Two new borate compounds, C4H10N2·B6O8(OH)2 1 and (NH3CH2CH2NH3)B5O8(OH)2, have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR, elemental analysis and thermal analysis. Compound 1 crystallizes in the monoclinic system, space group P21/c, with a = 8.3318(17), b = 6.2118(12), c = 12.479(3) (A), β = 108.96(3)°, V = 610.8(2) (A)3, Mr = 313.02, Z = 2, Dc= 1.702 g/cm3, μ = 0.150 mm-1, F(000) = 320, R = 0.0387and wR = 0.0924. Its layered structure is linked by infinite covalently coordinated neutral sheets with 3,20-membered window system, which are built up from alternative B6O8(OH)2 subunits donated by two piperzazine nitrogen donors. 2 crystallizes in monoclinic, space group Cc, with a =6.7207(13), b = 11.481(2), c = 12.564(3) (A),β = 95.25(3)°, V= 965.4(3) (A)3, Mr= 261.18, Z= 4, Dc=1.797 g/cm3, μ = 0.164 mm-1, F(000) = 536, R = 0.0396 and wR = 0.0752. Its oxoborate structure is generated from the sheets of 3,9-membered boron rings bonded diamine molecules through electrostatic and H-bonding interactions to form a two-dimensional layered network. 相似文献
988.
In this paper, several methods based on electronic educational resources have been presented for teaching structural chemistry. The constructions of multimedia materials, VRML models, teaching videos and website can not only improve the classroom effect, but also provide the students with a useful post-class learning platform. Meanwhile, further teaching reforms can be made on the foundations of these techniques. 相似文献
989.
Linchon B. Mehta Kunal K. Wadgaonkar 《Journal of Dispersion Science and Technology》2019,40(5):756-765
The present work focuses on the ability of 2-hydroxyethyl methacrylate (HEMA), isobornyl methacrylate (IBOMA) and methyl methacrylate (MMA) as reactive diluents to replace styrene in unsaturated polyester resin based on itaconic acid, sebacic acid, 1,4-Butanediol, 1,6-Hexanediol and glycerol. The structural analysis confirmed the presence of itaconate linkages in the UPs. The synthesized resins were characterized by infrared spectroscopy and their physiochemical properties such as appearance, viscosity, acid value, %volatile content, curing characteristics like gel time, peak exotherm temperature and total cure time. Among all the resins formed; the resin based on 1,6-Hexanediol showed optimum molecular weight and viscosity needed for final application. The cured resins were investigated for their thermal stability by thermo-gravimetric analysis which revealed that all the diluted resins had good thermal stability. From the results it could be concluded that styrene-free bio-based unsaturated polyester resin can be synthesized having properties equivalent to the commercial styrene based resin.GRAPHICAL ABSTRACT 相似文献
990.
Advancements in the area of conducting polymers have been towards their application as effective corrosion protective coatings to replace the use of heavy metals as additives in the coatings industries, which are now considered to be an environmental as well as health hazard. With the aim to utilize a sustainable resource based polymer for the development of an anti‐corrosive conducting coating material, coconut oil based conducting blend coatings of polyaniline and poly(esteramide urethane) were prepared by loading different ratios (2, 4 and 8 wt%) of polyaniline in poly(esteramide urethane). Then their physico‐chemical, thermal, morphological, conductivity and anti‐corrosive coating characteristics were investigated. The effect of a 2 year environmental aging process on the coated samples was analyzed by thermal methods as well as by corrosion studies. Results showed that the corrosion protective performance of the blend coatings was far superior than that of plane poly(esteramide urethane). These coatings showed enhanced corrosion protection in acid as well as alkaline environments upto 360 and 192 hr respectively. Conductivity of the blends was found to be in the range 2.5 × 10?5–5.7 × 10?4 S/cm?1. An increase in the thermal stability of the blend coatings and a decrease in their conductivity was noticed in the aged samples which was attributed to the crosslinking effect. The corrosion protective performance of the coatings remained almost unaffected even after 2 years of aging. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献