全文获取类型
收费全文 | 11963篇 |
免费 | 1663篇 |
国内免费 | 1806篇 |
专业分类
化学 | 9386篇 |
晶体学 | 171篇 |
力学 | 748篇 |
综合类 | 162篇 |
数学 | 1338篇 |
物理学 | 3627篇 |
出版年
2024年 | 16篇 |
2023年 | 177篇 |
2022年 | 387篇 |
2021年 | 377篇 |
2020年 | 468篇 |
2019年 | 434篇 |
2018年 | 357篇 |
2017年 | 354篇 |
2016年 | 531篇 |
2015年 | 515篇 |
2014年 | 638篇 |
2013年 | 855篇 |
2012年 | 981篇 |
2011年 | 1064篇 |
2010年 | 820篇 |
2009年 | 718篇 |
2008年 | 842篇 |
2007年 | 781篇 |
2006年 | 745篇 |
2005年 | 587篇 |
2004年 | 534篇 |
2003年 | 445篇 |
2002年 | 456篇 |
2001年 | 364篇 |
2000年 | 274篇 |
1999年 | 264篇 |
1998年 | 189篇 |
1997年 | 170篇 |
1996年 | 160篇 |
1995年 | 121篇 |
1994年 | 96篇 |
1993年 | 111篇 |
1992年 | 87篇 |
1991年 | 80篇 |
1990年 | 75篇 |
1989年 | 55篇 |
1988年 | 35篇 |
1987年 | 30篇 |
1986年 | 30篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 26篇 |
1982年 | 19篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1978年 | 9篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1973年 | 9篇 |
1972年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Baijun Liu Gilles P. Robertson Michael D. Guiver Yi‐Ming Sun Yin‐Ling Liu Juin‐Yih Lai Serguei Mikhailenko Serge Kaliaguine 《Journal of Polymer Science.Polymer Physics》2006,44(16):2299-2310
A series of sulfonated poly(aryl ether ether ketone ketone)s statistical copolymers with high molecular weights were synthesized via an aromatic nucleophilic substitution polymerization. The sulfonation content (SC), defined as the number of sulfonic acid groups contained in an average repeat unit, could be controlled by the feed ratios of monomers. Flexible and strong membranes in sodium sulfonate form could be prepared by the solution casting method, and readily transformed to their proton forms by treating them in 2 N sulfuric acid. The polymers showed high Tgs, which increased with an increase in SC. Membranes prepared from the present sulfonated poly(ether ether ketone ketone) copolymers containing the hexafluoroisopropylidene moiety (SPEEKK‐6F) and copolymers containing the pendant 3,5‐ditrifluoromethylphenyl moiety (SPEEKK‐6FP) had lower water uptakes and lower swelling ratios in comparison with previously prepared copolymers containing 6F units. All of the polymers possessed proton conductivities higher than 1 × 10?2 S/cm at room temperature, and proton conductivity values of several polymers were comparable to that of Nafion at high relative humidity. Their thermal stability, oxidative stability, and mechanical properties were also evaluated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2299–2310, 2006 相似文献
82.
83.
A single hair sample preparation protocol modified from reported method was developed and used to prepare longitudinally sectioned hair for ToF-SIMS analysis. Preliminary results demonstrate that ToF-SIMS is capable of providing molecular distribution of fragment ions from intrinsic constituents as well as external chemicals like the hair dye ingredients used in this study. The observation of pPDA and H2PO4− penetrating into the internal region of hair might initiate a renewed interest in exposure study. 相似文献
84.
The difficulty suffered in optimization-based algorithms for the solution of nonlinear equations lies in that the traditional
methods for solving the optimization problem have been mainly concerned with finding a stationary point or a local minimizer
of the underlying optimization problem, which is not necessarily a solution of the equations. One method to overcome this
difficulty is the Lagrangian globalization (LG for simplicity) method. This paper extends the LG method to nonsmooth equations
with bound constraints. The absolute system of equations is introduced. A so-called Projected Generalized-Gradient Direction (PGGD) is constructed and proved to be a descent direction of the reformulated nonsmooth optimization problem. This projected
approach keeps the feasibility of the iterates. The convergence of the new algorithm is established by specializing the PGGD.
Numerical tests are given.
This author's work was done when she was visiting The Hong Kong Polytechnic University.
His work is also supported by the Research Grant Council of Hong Kong. 相似文献
85.
7-Hydroxyderivativesofcholesteroldisplayawidevarietyofbiologicalactivities'-',mostofwhicharerelatedtothephysiologicalcontrolofcholesterolbiosynthesisandantitumoractivity.Inearlyreports',the7-hydroxycholesterolswerepreparedbythesequenceofacetylation,allylicchromicoxidation,andhydridereduction.Generally,theproductisamixtureof7a-and76-epimerswhichisdifficulttobeseparated.V.Kumaretal5improvedthisprocedurebyusingstereospecificreducingreagentsinsteadofthesimplehydride.7a-and7o-epimerscouldbeobtained… 相似文献
86.
Conflict resolution methodology is discussed with fuzzified Pareto frontier. Four solution concepts, namely, the Nash solution, the generalized Nash solution, the Kalai-Smorodinsky concept, and a solution method based on a special bargaining process are examined. The solutions are also fuzzy, the corresponding payoff values are fuzzy numbers, the membership functions of which are determined. Three particular cases are considered in the paper. Linear, quadratic, and general nonlinear Pareto frontiers with known shape are examined. 相似文献
87.
88.
89.