全文获取类型
收费全文 | 12037篇 |
免费 | 1464篇 |
国内免费 | 1037篇 |
专业分类
化学 | 8575篇 |
晶体学 | 53篇 |
力学 | 1802篇 |
综合类 | 178篇 |
数学 | 640篇 |
物理学 | 3290篇 |
出版年
2024年 | 27篇 |
2023年 | 137篇 |
2022年 | 335篇 |
2021年 | 372篇 |
2020年 | 498篇 |
2019年 | 406篇 |
2018年 | 409篇 |
2017年 | 434篇 |
2016年 | 572篇 |
2015年 | 528篇 |
2014年 | 629篇 |
2013年 | 1214篇 |
2012年 | 785篇 |
2011年 | 724篇 |
2010年 | 527篇 |
2009年 | 597篇 |
2008年 | 570篇 |
2007年 | 671篇 |
2006年 | 575篇 |
2005年 | 570篇 |
2004年 | 493篇 |
2003年 | 430篇 |
2002年 | 394篇 |
2001年 | 302篇 |
2000年 | 293篇 |
1999年 | 279篇 |
1998年 | 239篇 |
1997年 | 210篇 |
1996年 | 185篇 |
1995年 | 179篇 |
1994年 | 115篇 |
1993年 | 140篇 |
1992年 | 109篇 |
1991年 | 86篇 |
1990年 | 71篇 |
1989年 | 59篇 |
1988年 | 55篇 |
1987年 | 53篇 |
1986年 | 40篇 |
1985年 | 35篇 |
1984年 | 33篇 |
1983年 | 10篇 |
1982年 | 23篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1976年 | 12篇 |
1973年 | 12篇 |
1972年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 562 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.
PinHuaLI LeiWANG MinWANG JinCanYAN 《中国化学快报》2004,15(11):1295-1298
A Glaser coupling reaction of terminal alkynes in the presence of nickel chloride withoutany organics and bases in hot water has been developed, which produces the correspondinghomo-coupling products in good yields. 相似文献
33.
34.
The Modeling of Velocity Enhancement in Polymer Flooding 总被引:1,自引:0,他引:1
In single-phase polymer flooding experiments it has repeatedly been observed that the average velocity of the polymer molecules is higher than the average velocity of the water molecules. This effect is incorporated in many conventional Enhanced Oil Recovery (EOR) simulators by the introduction of a constant velocity enhancement factor. In this paper we show that, in absence of dispersion, a constant enhancement factor in the mathematical model for two-phase polymer flow (Buckley--Leverett displacement) leads to ill-posedness of the model equations. We propose a saturation dependent enhancement factor, derived from a model based on percolation concepts, for which this problem does not occur. 相似文献
35.
36.
Butyltins were analyzed in waters from California river and lake marinas and were detected at the part per trillion (ppt) level in most locations. The tributyltin:dibutyltin (TBT/DBT) ratios in the fresh waters were similar to those in their saline counterparts indicating like rates of degradation in the two salinity regimes. 相似文献
37.
Alp E. E. Sturhahn W. Toellner T. S. Zhao J. Hu M. Brown D. E. 《Hyperfine Interactions》2002,144(1-4):3-20
Nuclear resonant inelastic X-ray scattering of synchrotron radiation is being applied to ever widening areas ranging from
geophysics to biophysics and materials science. Since its first demonstration in 1995 using the 57Fe resonance, the technique has now been applied to materials containing 83Kr, 151Eu, 119Sn, and 161Dy isotopes. The energy resolution has been reduced to under a millielectronvolt. This, in turn, has enabled new types of
measurements like Debye velocity of sound, as well as the study of origins of non-Debye behavior in presence of other low-energy
excitations. The effect of atomic disorder on phonon density of states has been studied in detail. The flux increase due to
the improved X-ray sources, crystal monochromators, and time-resolved detectors has been exploited for reducing sample sizes
to nano-gram levels, or using samples with dilute resonant nuclei like myoglobin, or even monolayers. Incorporation of micro-focusing
optics to the existing experimental setup enables experiments under high pressure using diamond-anvil cells. In this article,
we will review these developments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
本文针对一类非饱和土壤水流问题,提出了基于二次插值的特征差分格式,得到了严谨的L2模误差估计.并作了数值试验,指明方法的有效性. 相似文献
39.
40.
功能性丙烯酸/MBAM体系共聚产物的研制 总被引:2,自引:0,他引:2
以丙烯酸和MBAM为主要原料,经聚合,合成了一种高性能的具有良好保水性能的聚合产物,其保水量达到750~1000倍.50℃以下有良好的保水性能,28℃以下有极好的保水性能,并研究了工艺条件对该产品性能的影响因素. 相似文献