全文获取类型
收费全文 | 17700篇 |
免费 | 1664篇 |
国内免费 | 1350篇 |
专业分类
化学 | 13059篇 |
晶体学 | 204篇 |
力学 | 683篇 |
综合类 | 112篇 |
数学 | 2367篇 |
物理学 | 4289篇 |
出版年
2024年 | 16篇 |
2023年 | 213篇 |
2022年 | 304篇 |
2021年 | 576篇 |
2020年 | 595篇 |
2019年 | 558篇 |
2018年 | 444篇 |
2017年 | 456篇 |
2016年 | 774篇 |
2015年 | 703篇 |
2014年 | 850篇 |
2013年 | 1254篇 |
2012年 | 1589篇 |
2011年 | 1658篇 |
2010年 | 1175篇 |
2009年 | 1024篇 |
2008年 | 1291篇 |
2007年 | 1191篇 |
2006年 | 1080篇 |
2005年 | 911篇 |
2004年 | 792篇 |
2003年 | 562篇 |
2002年 | 511篇 |
2001年 | 291篇 |
2000年 | 233篇 |
1999年 | 237篇 |
1998年 | 169篇 |
1997年 | 150篇 |
1996年 | 151篇 |
1995年 | 124篇 |
1994年 | 89篇 |
1993年 | 95篇 |
1992年 | 87篇 |
1991年 | 82篇 |
1990年 | 60篇 |
1989年 | 46篇 |
1988年 | 41篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 43篇 |
1984年 | 33篇 |
1983年 | 23篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1975年 | 8篇 |
1970年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
31.
Cationic polymer as a kind of flocculant is widely applied in purification treatment of waste water. Because it has positive charge group, it is able to connect strongly the suspended matters, short cellulose and other microparticles. The research on synthesis of cationic polymer and application in treatment of waste water is very universal abroad. But domestic research on those is not general. The technology of synthesis of PEM is simple, and the production cost is low. It is easy to apply in treatment of waste water.Synthesis of PEM Emulsion FlocculantSome distilled water, PVA(poly(vinyl alcohol)), EA(ethyl acrylate), and K2S2O8(potassium persulfate) were put into reaction vessel. Kept stirring up under nitrogen. When heated the solution to 40℃, dropped the water solution of MTA[(2-methacryloxylethyl)trimethyl ammonium].Maintained the temperature at 70℃, reacted about 7-8 hours. Then got the PEM emulsion. Changed the ratio of EA and MTA. Obtained a series of PEM emulsions.Stability and Convertibility of PEM EmulsionThe test results showed that when the EA/MTA was 85/15, the PEM emulsion was most stable.When the total monomer quantity was 35%, the convertibility of PEM emulsion was the highest,i.e.98.6%.The MTA Copolymerization Ratio and Morphology of PEM EmulsionWhen the monomers EA/MTA=85/15 and total monomer quantity was 35%, the MTA copolymerization ratio of PEM emulsion was 95.15%(the highest), and the PEM emulsion was some microspheres with 100-180nm of diameter.The Test Results of PEM Emulsion in Treatment of Waste Water The PEM emulsion flocculant was applied in treatment of waste water of paper mill, and measured the precipitation time(t) and transmittancy(T). The test results were showed in table 1. The optimum value of PEM which was able to make the waste water of paper mill into clear water was 0.008%. 相似文献
32.
A theorem of Birkhoff‐Frink asserts that every algebraic closure operator on an ordinary set arises, from some algebraic structure on the set, as the corresponding generated subalgebra operator. However, for many‐sorted sets, i.e., indexed families of sets, such a theorem is not longer true without qualification. We characterize the corresponding many‐sorted closure operators as precisely the uniform algebraic operators. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
33.
The notion of Kuratowski convergence is applied to describe a kind of convergence in the context of holomorphic functions. We associate it to a convenient topology, explore its relation with the compact-open topology, thus providing a new set theoretic point of view of this classic topology, and present it in the framework of set-valued mappings. 相似文献
34.
35.
36.
37.
38.
Juan Pablo Vielma 《Operations Research Letters》2007,35(1):29-35
Two independent proofs of the polyhedrality of the split closure of mixed integer linear program have been previously presented. Unfortunately neither of these proofs is constructive. In this paper, we present a constructive version of this proof. We also show that split cuts dominate a family of inequalities introduced by Köppe and Weismantel. 相似文献
39.
三种群食物链交错扩散模型的整体 总被引:1,自引:0,他引:1
本文应用能量估计方法和Gagliardo-Nirenberg型不等式证明了一类强耦合反应扩散系统整体解的存在性和一致有界性,该系统是带自扩散和交错扩散项的三种群Lotka-Volterra食物链模型.通过构造Lyapunov函数给出了该模型正平衡点全局渐近稳定的充分条件. 相似文献
40.
Young Hee Geum Young Ik Kim Kang Sup Lee 《Journal of Applied Mathematics and Computing》2007,25(1-2):109-118
A parametric boundary equation is established for the principal period-2 bulb in the cubic Mandelbrot set. Using its geometry, an efficient escape-time algorithm which reduces the construction time for the period-2 bulbs in the cubic Mandelbrot set is introduced and the implementation graphic results display the fascinating fractal beauty 相似文献