全文获取类型
收费全文 | 2611篇 |
免费 | 304篇 |
国内免费 | 288篇 |
专业分类
化学 | 1509篇 |
晶体学 | 54篇 |
力学 | 390篇 |
综合类 | 25篇 |
数学 | 257篇 |
物理学 | 968篇 |
出版年
2024年 | 4篇 |
2023年 | 37篇 |
2022年 | 95篇 |
2021年 | 71篇 |
2020年 | 71篇 |
2019年 | 75篇 |
2018年 | 77篇 |
2017年 | 97篇 |
2016年 | 105篇 |
2015年 | 89篇 |
2014年 | 124篇 |
2013年 | 241篇 |
2012年 | 143篇 |
2011年 | 170篇 |
2010年 | 110篇 |
2009年 | 151篇 |
2008年 | 154篇 |
2007年 | 128篇 |
2006年 | 155篇 |
2005年 | 151篇 |
2004年 | 133篇 |
2003年 | 106篇 |
2002年 | 71篇 |
2001年 | 77篇 |
2000年 | 62篇 |
1999年 | 60篇 |
1998年 | 58篇 |
1997年 | 56篇 |
1996年 | 48篇 |
1995年 | 50篇 |
1994年 | 37篇 |
1993年 | 35篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1973年 | 2篇 |
1959年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有3203条查询结果,搜索用时 46 毫秒
971.
972.
《Ultrasonics sonochemistry》2014,21(6):1988-1993
Even though much knowledge on acoustic cavitation and its application has been accumulated over the past decades, further research is still required to develop industrial uses of acoustic cavitation. It is because the available information is mainly based on small-scale sonoreactors and the design and optimization of sonoreactors for large-scale applications have not been widely studied. In this study, the effects of liquid height/volume, initial concentration of the reactant and input acoustic power on sonochemical oxidation reactions including iodide ion oxidation, As(III) oxidation, and hydrogen peroxide generation were investigated using a 291 kHz sonoreactor with various liquid height/volumes (50, 100, 200, 300, 500, and 1000 mL) and input powers (23, 40, and 82 W). As the liquid height/volume and the input power changed, the power density varied from 23 to 1640 W/L and the maximum cavitation yields of triiodide ion for 23, 40, and 82 W were observed at 0.05, 0.1, and 0.2/0.3 L, respectively. It was found that low power was more effective for the small volume and the large volume required high power level and the moderate power density, approximately 400 W/L, was suggested for the sonochemical oxidation of iodide ion in the 291 kHz sonoreactor in this study. Similar results were observed in the generation of hydrogen peroxide and the sonochemical oxidation of As(III) to As(V). It was also revealed that KI dosimetry could be applicable for the estimation of the sonochemical reactions of non-volatile compounds such as As(III). 相似文献
973.
Consequent entanglement concentration of a less-entangled electronic cluster state with controlled-not gates 下载免费PDF全文
We present a highly efficient entanglement concentration protocol (ECP) for a four-electron system in a less-entangled cluster state. In this ECP, we only require one pair of less-entangled electron cluster states and one ancillary electron to complete the task. With the help of the controlled-not (CNOT) gate, the concentrated maximally entangled state can be retained for further application with some success probability. On the other hand, the discarded items can be reused to obtain a high success probability. All the features make this ECP useful in the current quantum information field. 相似文献
974.
975.
976.
采用高温溶剂热法制备了一系列不同Yb3+掺杂浓度的上转换发光纳米粒子β-NaYF4∶Yb,Tm和核壳结构的β-NaYF4∶Yb,Tm@β-NaYF4∶Yb纳米粒子。采用X射线衍射(XRD)、场发射扫描电镜(FESEM)、光致发光(PL)谱对材料的物相结构、形貌特征和发光性质进行了表征和研究,并特别研究了温度对材料发光性能的影响。结果表明:保持Tm3+浓度不变,随着Yb3+掺杂浓度的增加,β-NaYF4∶Yb,Tm的发光强度先增大后减小。当Yb3+掺杂摩尔分数为30%时,474 nm和645 nm处的发光强度达到最大值;当Yb3+掺杂摩尔分数为50%时,450 nm和692 nm处的发光强度达到最大值。在β-NaYF4∶Yb(30%),Tm上包裹一层β-NaYF4∶Yb壳层后,其发光显著增强,随壳层Yb3+摩尔分数的增加,发光强度也是先增大后减小。当壳层Yb3+摩尔分数为10%时,核壳结构纳米粒子的发光强度达到最大值;当壳层Yb3+摩尔分数达到40%时,核壳结构纳米粒子的发光强度已经低于未包裹时。将样品进行热处理后,荧光增强。样品的发光强度随环境温度的升高,红光变弱,蓝光增强。采用原位聚合法将β-NaYF4∶Yb,Tm纳米粒子与PMMA制成复合材料后,仍能保持较好的透明度和发光强度。 相似文献
977.
利用线性光学元器件对光场量子态进行操纵,可以实现远程的量子纠缠调控和量子通讯.通过分析光学分束器对相干态光场的作用,发现当初始光场态是两个两部分纠缠态的直乘时,让其中的两模通过光学分束器作用后再对其进行光子计数,另外两模将会塌缩到新的纠缠态.基于这个特点,提出了一个实现部分纠缠相干态纠缠浓缩的方案.在这个方案中,两个部分纠缠相干态被用来作为量子信道,通过光学分束器作用后对光场进行光子数探测时,如果测量到光场的两模分别处于奇光子数态和零光子数态,则光场另外的两模将塌缩到最大纠缠态,从而完成纠缠浓缩的过程.计算结果表明,对于纠缠相干态,无论其初始的纠缠是多么微弱,利用这种方法总有一定的几率可以从中提纯出最大纠缠态. 相似文献
978.
In this paper,we study the existence and concentration of weak solutions to the p-Laplacian type elliptic problem-εp△pu+V(z)|u|p-2u-f(u)=0 in Ω,u=0 on ■Ω,u0 in Ω,Np2,where Ω is a domain in RN,possibly unbounded,with empty or smooth boundary,εis a small positive parameter,f∈C1(R+,R)is of subcritical and V:RN→R is a locally Hlder continuous function which is bounded from below,away from zero,such that infΛVmin ■ΛV for some open bounded subset Λ of Ω.We prove that there is anε00 such that for anyε∈(0,ε0],the above mentioned problem possesses a weak solution uεwith exponential decay.Moreover,uεconcentrates around a minimum point of the potential V inΛ.Our result generalizes a similar result by del Pino and Felmer(1996)for semilinear elliptic equations to the p-Laplacian type problem. 相似文献
979.
研究了一含临界指数的p(x)-Laplace方程的Dirichlet边值问题,运用推广的集中紧致性原理,并结合山路引理得到了该问题非平凡弱解的存在性结果. 相似文献
980.
Let Z(F) be the number of solutions of a random k‐satisfiability formula F with n variables and clause density α. Assume that the probability that F is unsatisfiable is for some . We show that (possibly excluding a countable set of “exceptional” α's) the number of solutions concentrates, i.e., there exists a non‐random function such that, for any , we have with high probability. In particular, the assumption holds for all , which proves the above concentration claim in the whole satisfiability regime of random 2‐SAT. We also extend these results to a broad class of constraint satisfaction problems. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 45, 362–382, 2014 相似文献