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   35081篇
  免费   5573篇
  国内免费   4781篇
化学   25402篇
晶体学   557篇
力学   2157篇
综合类   402篇
数学   3925篇
物理学   12992篇
  2024年   21篇
  2023年   564篇
  2022年   744篇
  2021年   1026篇
  2020年   1257篇
  2019年   1315篇
  2018年   1123篇
  2017年   1189篇
  2016年   1614篇
  2015年   1663篇
  2014年   1890篇
  2013年   2579篇
  2012年   3022篇
  2011年   3193篇
  2010年   2203篇
  2009年   2217篇
  2008年   2485篇
  2007年   2297篇
  2006年   2143篇
  2005年   1698篇
  2004年   1442篇
  2003年   1213篇
  2002年   1275篇
  2001年   1010篇
  2000年   805篇
  1999年   768篇
  1998年   597篇
  1997年   531篇
  1996年   563篇
  1995年   462篇
  1994年   456篇
  1993年   352篇
  1992年   295篇
  1991年   274篇
  1990年   204篇
  1989年   166篇
  1988年   140篇
  1987年   115篇
  1986年   113篇
  1985年   102篇
  1984年   64篇
  1983年   53篇
  1982年   40篇
  1981年   31篇
  1980年   33篇
  1979年   20篇
  1978年   10篇
  1977年   8篇
  1975年   8篇
  1936年   8篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Fuzzy Optimization and Decision Making - Seepage equation in fissured porous media is a partial differential equation describing the variation of pressure of a given area over time. In traditional...  相似文献   
2.
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   
3.
Three nonfused ring electron acceptors (NFREAs) TTC6,TT-C8T and TT-TC8 were purposefully designed and synthesized.The molecular geometry can be adjusted by the steric hindrance of lateral substituents.According to the DFT calculations,from TTC6 to TT-C8T and TT-TC8,planarity of the molecular backbone is gradually improved,accompanying with the enhancing of intramolecular charge transfer effect.As for TT-TC8,the two phenyl substituents are almost perpendicular to the molecular backbone,which endues the acceptor with good solubility and suppresses it to form over-aggregation.Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film.As a result,TT-TC8 based devices afford the highest PCE of 13.13%,which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs.  相似文献   
4.
5.
Zhang  F.  Yi  S. H.  Niu  H. B.  Lu  X. G.  Wang  X. X. 《Fluid Dynamics》2021,56(3):383-392
Fluid Dynamics - To predict the boundary layer transition on swept wings, experimental and numerical researches were conducted to obtained the accurate boundary layer transition front and to...  相似文献   
6.
Annals of Operations Research - The main purpose of this study was to explore the impact of peace dividends on global changes in national productivity. First, this study assessed changes in...  相似文献   
7.
The high-entropy materials have raised much attention in recent years due to their extraordinary performances in mechanical, catalysis, energy storage fields. Herein, a new type of high-entropy hydroxides (e.g., NiFeCoMnAl(OH)x) that are amorphous and capable of broad solar absorption is reported. A facile one-pot co-precipitation method is employed to synthesize these amorphous high-entropy hydroxides (a-HEHOs) under ambient conditions. The a-HEHOs thus obtained display widely tunable bandgap (e.g., from 2.6 to 1.1 eV) due to their high-entropy and amorphous characteristics, enabling efficient light absorbance and photothermal conversion in the solar regime. Further solar water evaporation measurements show that the a-HEHOs delivered a considerable energy conversion efficiency of 55%, comparable to black titanium oxides that are synthesized using more complex and expensive methods.  相似文献   
8.
Han  Xiaoyang  Shen  Han-Wei  Li  Guan  Lu  Xuyi  Shan  Guihua  Wang  Yangang 《显形杂志》2021,24(3):615-629
Journal of Visualization - Convolutional neural networks (CNNs) have achieved breakthrough performance in image recognition and classification. However, it is still a challenge for CNNs to classify...  相似文献   
9.
Wang  Guowei  Ge  Mengyan  Lu  Lulu  Jia  Ya  Zhao  Yunjie 《Nonlinear dynamics》2021,103(3):2627-2643
Nonlinear Dynamics - The hybrid neural model provides a computationally effective and biophysics-based neuron behavior model, which maintains its simplicity by incorporating the dynamics...  相似文献   
10.
Yuan  Gonglin  Li  Pengyuan  Lu  Junyu 《Numerical Algorithms》2022,91(1):353-365
Numerical Algorithms - The BFGS method, which has great numerical stability, is one of the quasi-Newton line search methods. However, the global convergence of the BFGS method with a Wolfe line...  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