首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   108929篇
  免费   28879篇
  国内免费   20612篇
化学   70968篇
晶体学   1323篇
力学   7343篇
综合类   393篇
数学   14162篇
物理学   64231篇
  2023年   1408篇
  2022年   1457篇
  2021年   1648篇
  2020年   2289篇
  2019年   2683篇
  2018年   2590篇
  2017年   3082篇
  2016年   3803篇
  2015年   3933篇
  2014年   4182篇
  2013年   6458篇
  2012年   7201篇
  2011年   8903篇
  2010年   11311篇
  2009年   11497篇
  2008年   5591篇
  2007年   4781篇
  2006年   4342篇
  2005年   4425篇
  2004年   4939篇
  2003年   3995篇
  2002年   3801篇
  2001年   3887篇
  2000年   3018篇
  1999年   3332篇
  1998年   2772篇
  1997年   2518篇
  1996年   2806篇
  1995年   3220篇
  1994年   3179篇
  1993年   3200篇
  1992年   2715篇
  1991年   2365篇
  1990年   1988篇
  1989年   2028篇
  1988年   1990篇
  1987年   1260篇
  1986年   1288篇
  1985年   954篇
  1984年   1031篇
  1982年   939篇
  1981年   758篇
  1980年   781篇
  1979年   529篇
  1978年   534篇
  1977年   634篇
  1976年   1043篇
  1973年   436篇
  1972年   532篇
  1971年   433篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Acta Mathematica Sinica, English Series - We are interested in the existence and asymptotic behavior for the least energy solutions of the following fractional eigenvalue problem $$\left({\rm{P}}...  相似文献   
2.
Hu  Duo-Duo  Gao  Qian  Dai  Jing-Cheng  Cui  Ru  Li  Yuan-Bo  Li  Yuan-Ming  Zhou  Xiao-Guo  Bian  Kang-Jie  Wu  Bing-Bing  Zhang  Kai-Fan  Wang  Xi-Sheng  Li  Yan 《中国科学:化学(英文版)》2022,65(4):753-761
Science China Chemistry - A light-induced, nickel-catalyzed three-component arylsulfonation of 1,3-enynes in the absence of photocatalyst is reported. This methodology exhibited mild conditions,...  相似文献   
3.
Juglandis Mandshuricae Cortex is the bark of Juglans mandshurica Maxim., which has been used as a folk medicine plant in China and India. In this study, an ultra-high performance liquid chromatography–quadrupole/orbitrap high-resolution mass spectrometry method was developed to clarify and quantify the chemical profiling of Juglandis Mandshuricae Cortex rapidly. A total of 113 compounds were characterized. Among them, seven flavonoids were simultaneously quantified in 15 min, including myricetin, myricetrin, taxifolin, kaempferol, quercetin, quercitrin, and naringenin. The method was validated for accuracy, precision, and the limits of detection and quantification. All calibration curves showed a good linear relationship (r > 0.9990) within test ranges. The intra- and inter-day relative standard deviations were less than 2.16%. Accuracy validation showed that the recovery was between 95.6 and 101.3% with relative standard deviation values below 2.85%. The validated method was successfully applied to determine the contents of seven flavones in Juglandis Mandshuricae Cortex from seven sources and the contents of these places were calculated respectively. This method provides a theoretical basis for further developing the medicinal value of Juglandis Mandshuricae Cortex.  相似文献   
4.
5.
以全血样品为原料,探讨湿法消解-原子荧光法测定全血中的硒含量。血样经硝酸-高氯酸消解后,用硼氢化钠将硒还原成硒化氢,由氩气载入原子化器,产生的原子荧光强度与试液中硒元素含量在一定范围内呈正比,外标法定量。以消解效率为指标,优化样品的消解条件,测定血中硒在0-10μg/L范围内线性情况良好,相关系数为0.9992,最低检出限为0.143μg/L,相对标准偏差为1.51%-1.58%,平均加标回收率为90.86%-104.62%。血中硒的原子荧光测定法灵敏度高,精密度和稳定性好,可应用于血中硒的生物监测。  相似文献   
6.
陈华俊  朱鹏杰  陈咏雷  侯宝成 《中国物理 B》2022,31(2):27802-027802
We investigate theoretically Rabi-like splitting and Fano resonance in absorption spectra of quantum dots(QDs)based on a hybrid QD-semiconducting nanowire/superconductor(SNW/SC)device mediated by Majorana fermions(MFs).Under the condition of pump on-resonance and off-resonance,the absorption spectrum experiences the conversion from Fano resonance to Rabi-like splitting in different parametric regimes.In addition,the Fano resonances are accompanied by the rapid normal phase dispersion,which will indicate the coherent optical propagation.The results indicate that the group velocity index is tunable with controlling the interaction between the QD and MFs,which can reach the conversion between the fast-and slow-light.Fano resonance will be another method to detect MFs and our research may indicate prospective applications in quantum information processing based on the hybrid QD-SNW/SC devices.  相似文献   
7.
采用态平均(CASSCF)/高度相关多参考组(MRCI)方法,对N2分子A3Σu+、B3Пg、C3Пu电子态的势能、跃迁偶极矩进行了高度相关的精确计算.计算的势能在平衡位置附近与RKR拟合的势能曲线非常一致,获得的跃迁偶极矩与已有实验值符合很好。首次对A3Σu+、B3Пg、C3Пu电子态的振转光谱常数随振动量子数v的变化进行系统定量计算,其结果与已有的实验观测数据相符.同时,获得了N2分子第一正带系的0-1、0-2、1-0、1-2、1-3、2-0、2-1、2-3、3-0、3-1和3-2光谱带分别在300,3000,6000,10000K时的谱线强度,如1-0带在3000,6000,10000K时的高温谱线带强度分别为1.58543×10-16 cm-1/(分子 cm-2)、6.07889×10-17 cm-1/(分子 cm-2)和2.3781×10-17 cm-1/(分子 cm-2).这些结果对N2分子进一步的理论研究、实际应用和高温大气的建模与研究具都有一定的参考价值.  相似文献   
8.
Photocatalytic CO2 reduction to C1 fuels is considered to be an important way for alleviating increasingly serious energy crisis and environmental pollution. Due to the environment-friendly, simple preparation, easy formation of highly-stable metal-nitrogen(M-Nx) coordination bonds, and suitable band structure, polymeric carbon nitride-based single-atom catalysts(C3N4-based SACs) are expected to become a potential for CO2 reduction under visible-light irradiation. In this review, we summarize the recent advancement on C3N4-based SACs for photocatalytic CO2 reduction to C1 products, including the reaction mechanism for photocatalytic CO2 reduction to C1 products, the structure and synthesis methods of C3N4-based SACs and their applications toward photocatalytic CO2 reduction reaction(CO2RR) for C1 production. The current challenges and future opportunities of C3N4-based SACs for photoreduction of CO2 are also discussed.  相似文献   
9.
Considering the effect of stochasticity including white noise and colored noise, this paper aims to study a hybrid stochastic cholera epidemic model with waning vaccine-induced immunity and nonlinear telegraph perturbations. First, we derive a critical value ? 0 C related to the basic reproduction number ? 0 of the deterministic model. The key aim of this paper is to generalize the θ-stochastic criterion method proposed by the recent work (Han et al. in Chaos Solit Fract 140:110238, 2020) to eliminate nonlinear telegraph perturbations. Next, via constructing several θ-stochastic Lyapunov functions and using the generalized method, we further prove that the stochastic model have a unique ergodic stationary distribution under ? 0 C > 1. Results show that the prevention and control of cholera epidemic depend on low transmission rate and small telegraph perturbations. Finally, the corresponding numerical simulations are performed to illustrate our analytical results and a practical application on the Somalia cholera outbreak is shown at the end of this paper.  相似文献   
10.
为明确裂缝间相互作用对各向异性的影响,本文以Hudson模型为例分析了裂缝密度、裂缝倾角对地震波波场、弹性常数和Thomsen系数的影响规律,然后采用“基质-骨架-流体”组合化的方法进行了裂缝储层微观尺度的建模,并与实际测井资料进行了对比。结果表明该模型适用条件为低裂缝密度储层,二阶模型适用的裂缝密度范围比一阶模型大,但在裂缝密度过大时,二阶模型会出现不收敛的现象,模型便不再适用。裂缝储层纵横波速度随裂缝倾角增大而增大,纵波速度对裂缝倾角更为敏感。另外,在与实际测井曲线对比时,在高裂缝密度地层二阶模型的应用效果明显优于一阶模型,说明了在高裂缝密度储层考虑裂缝间的相互作用的必要性。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号