全文获取类型
收费全文 | 8174篇 |
免费 | 904篇 |
国内免费 | 541篇 |
专业分类
化学 | 562篇 |
晶体学 | 19篇 |
力学 | 545篇 |
综合类 | 78篇 |
数学 | 801篇 |
物理学 | 2499篇 |
综合类 | 5115篇 |
出版年
2024年 | 16篇 |
2023年 | 54篇 |
2022年 | 113篇 |
2021年 | 129篇 |
2020年 | 150篇 |
2019年 | 166篇 |
2018年 | 177篇 |
2017年 | 254篇 |
2016年 | 270篇 |
2015年 | 316篇 |
2014年 | 484篇 |
2013年 | 470篇 |
2012年 | 522篇 |
2011年 | 582篇 |
2010年 | 435篇 |
2009年 | 472篇 |
2008年 | 497篇 |
2007年 | 573篇 |
2006年 | 535篇 |
2005年 | 510篇 |
2004年 | 411篇 |
2003年 | 372篇 |
2002年 | 346篇 |
2001年 | 260篇 |
2000年 | 258篇 |
1999年 | 187篇 |
1998年 | 156篇 |
1997年 | 138篇 |
1996年 | 134篇 |
1995年 | 103篇 |
1994年 | 103篇 |
1993年 | 71篇 |
1992年 | 67篇 |
1991年 | 60篇 |
1990年 | 57篇 |
1989年 | 41篇 |
1988年 | 41篇 |
1987年 | 33篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有9619条查询结果,搜索用时 15 毫秒
991.
992.
为滤除数字图像中的椒盐噪声,在图像灰度空间上引入模糊划分和像素点灰度值检测噪声,进而利用滤波窗口内非噪声点灰度值描述中心点的灰度水平.依据改进重心去模糊法设计一种模糊滤波器,模拟实验表明该滤波器可以有效地滤除图像中的椒盐噪声. 相似文献
993.
刘春辉 《山东大学学报(理学版)》2014,(10)
研究了BL代数的区间值(∈,∈∨q)-模糊滤子理论。在BL代数中引入区间值(∈,∈∨q)-模糊对合滤子和区间值(∈,∈∨q)-模糊结合滤子两类新概念,获得了它们的几个等价刻画。详细讨论了BL代数中各类区间值(∈,∈∨q)-模糊滤子间的关系,证明了一个区间值模糊集为区间值(∈,∈∨q)-模糊布尔(关联)滤子当且仅当它既是区间值(∈,∈∨q)-模糊正关联滤子又是区间值(∈,∈∨q)-模糊对合滤子的结论。 相似文献
994.
995.
996.
997.
Wenger D Gerecke AC Heeb NV Naegeli H Zenobi R 《Analytical and bioanalytical chemistry》2008,390(8):2021-2029
An in vitro reporter gene assay based on human breast cancer T47D cells (ER-CALUX) was applied to examine the ability of diesel exhaust to induce or inhibit estrogen receptor (ER)-mediated gene expression. Exhaust from a heavy-duty diesel engine was either treated by iron- or copper/iron-catalyzed diesel particulate filters (DPFs) or studied as unfiltered exhaust. Collected samples included particle-bound and semivolatile constituents of diesel exhaust. Our findings show that all of the samples contained compounds that were able to induce ER-mediated gene expression as well as compounds that suppressed the activity of the endogenous hormone 17beta-estradiol (E2). Estrogenic activity prevailed over antiestrogenic activity. We found an overall ER-mediated activity of 1.63 +/- 0.31 ng E2 CALUX equivalents (E2-CEQs) per m(3) of unfiltered exhaust. In filtered exhaust, we measured 0.74 +/- 0.07 (iron-catalyzed DPF) and 0.55 +/- 0.09 ng E2-CEQ m(-3) (copper/iron-catalyzed DPF), corresponding to reductions in estrogenic activity of 55 and 66%, respectively. Our study demonstrates that both catalytic DPFs lowered the ER-mediated endocrine-disrupting potential of diesel exhaust. 相似文献
998.
Marcel Wild 《Semigroup Forum》2008,76(2):268-275
For any positive integers M and N we define a selfdually ordered band ℬ(M,N) of cardinality
and ask whether or not it is lattice-ordered. The origin of ℬ(M,N) in nonlinear signal processing is outlined. 相似文献
999.
燃煤电站布袋除尘器和静电除尘器脱汞性能比较 总被引:8,自引:0,他引:8
采用国际上通用的Ontario Hydro方法(OHM)对中国五个燃煤电站布袋除尘器(FF)/静电除尘器(ESP)前、后的烟气进行采样,应用美国EPA标准方法测定了烟气中Hg0、Hg2+和HgP的浓度。应用DMA80测定固体样品(煤、底灰、ESP飞灰)中的汞浓度。由汞平衡得出各个环节中汞所占的份额。由此得到FF和ESP脱除烟气中汞的性能。安装FF的电站1和2的综合脱除效率约为80%和20%,安装ESP的电站3、4和5的综合脱除效率分别为6%、20%和4%左右。这说明FF比ESP有更加优良的脱汞性能,而且FF/ESP脱除烟气中的汞受到很多因素的影响。 相似文献
1000.
FANG Ji-Min WANG Zhi-Quan GONG Wen-Qi YANG Hong-Gang MENG Ya-Wen ZHANG Xiao-Zhen 《中国化学》2008,26(3):459-462
Hydrolysis reaction of Fe(NO3)3 at a high temperature in the presence of urea as the homogeneous precipitant was studied. With the prepared ceramic filter balls loaded with α-Fe2O3 after high temperature calcination, the loading of α-Fe2O3 on the porous ceramic filter balls from Fe(NO3)3 solutions of different concentrations and mechanical stability of the loaded α-Fe2O3 were studied. The product was characterized using XRD and SEM. Adsorption experiments were conducted to evaluate the performance of the product in adsorbing NH3-N. It turned out that the specific surface area of the ceramic filter balls loaded with α-Fe2O3 had increased to 36.5387 m2/g from original 4.6127 m2/g. When the concentration of Fe(NO3)3 was 0.40 mol/L, the loading of α-Fe2O3 on the ceramic filter balls accounted for 8.4% of the total mass of the adsorbent and α-Fe2O3 was adsorbed on the filter balls very well. The adsorption isotherm of NH3-N on the ceramic filter ball adsorbent loaded with α-Fe2O3 was of Langmuir type. The saturated adsorption capacity was 3.33 mg/L, and the adsorption constant K was 0.1873. NH3-N was adsorbed by α-Fe2O3 more easily, which was a kind of specific adsorption. 相似文献