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   20827篇
  免费   3472篇
  国内免费   2435篇
化学   14530篇
晶体学   212篇
力学   1505篇
综合类   200篇
数学   2381篇
物理学   7906篇
  2024年   47篇
  2023年   390篇
  2022年   456篇
  2021年   694篇
  2020年   831篇
  2019年   801篇
  2018年   671篇
  2017年   570篇
  2016年   976篇
  2015年   988篇
  2014年   1156篇
  2013年   1515篇
  2012年   1823篇
  2011年   2027篇
  2010年   1280篇
  2009年   1232篇
  2008年   1255篇
  2007年   1165篇
  2006年   1142篇
  2005年   953篇
  2004年   849篇
  2003年   620篇
  2002年   589篇
  2001年   521篇
  2000年   463篇
  1999年   466篇
  1998年   399篇
  1997年   332篇
  1996年   344篇
  1995年   321篇
  1994年   297篇
  1993年   234篇
  1992年   245篇
  1991年   203篇
  1990年   180篇
  1989年   154篇
  1988年   91篇
  1987年   89篇
  1986年   74篇
  1985年   76篇
  1984年   42篇
  1983年   44篇
  1982年   37篇
  1981年   22篇
  1980年   15篇
  1979年   8篇
  1977年   5篇
  1975年   6篇
  1969年   4篇
  1957年   8篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
A n‐type conjugated polymer containing naphthalene diimide (NDI) and 1,3,4‐thiadiazole (TZ) moieties, named PNTZ, has been synthesized and applied for all‐polymer solar cells (all‐PSCs). By the incorporation of TZ unit into the polymer main chains, the lowest unoccupied molecular orbital level of this polymer has been adjusted effectively. In addition, the electron‐acceptor PNTZ shows a broad absorption spectrum in the range of 300–700 nm, and possesses complementary absorption spectrum with the electron‐donor PTB7‐Th. On the basis of PNTZ as the acceptor and PTB7‐Th as the donor, the all‐PSCs are fabricated. After optimization, the well blend morphologies with a continuous D/A interpenetrating network are observed and the best all‐PSC device exhibits a power conversion efficiency of 4.35% with a high short‐circuit current density of 13.26 mA cm?2. This research demonstrates that the TZ‐containing polymer PNTZ is a promising non‐fullerene acceptor for high efficiency all‐PSCs. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 990–996  相似文献   
992.
In this article, various energies and geometries of pure platinum nanoparticles and those of platinum nanoparticles with adsorbed OH were investigated. Fourteen different platinum clusters of 3–40 atoms were studied using spin-unrestricted density functional theory (DFT) with a double numerical plus polarization basis set. This range of sizes gave enough information for establishing the general trends that were the primary goal of the study. Three different shapes of platinum clusters were presented, and the effect of cluster size on binding energy, total energy, and HOMO–LUMO energy gap was investigated. Subsequently, same calculations were performed for those selected Pt clusters with OH adsorbate on the surface. The results show that the stability of both the pure clusters and the clusters with adsorbed OH molecule increases with an increase of cluster size. This fact indicates that direct influence of the size of Pt cluster on the reaction rate is possible, and the understanding of how cluster size would affect binding energy is important. As expected, the effect of cluster size on total energy of molecule was shown to be a linear function independent of cluster type. We also found that optimized (stable) Pt clusters were bigger in size than that of the initial clusters, or clusters with bulk geometry.  相似文献   
993.
994.
995.
996.
Soft set theory based on its extension   总被引:2,自引:0,他引:2  
In this paper, we point out a defect that the definitions of soft subset and soft intersection in Maji’s paper are partial definitions, and then we introduce extension of soft set to redefine and simplify operations between soft sets. At last, we obtain some algebraic properties of new soft operations.  相似文献   
997.
We study Leibniz algebras graded by finite root systems of type C l .  相似文献   
998.
999.
We report herein an improved Pfitzinger reaction for the synthesis of highly functionalized quinaldines from 1,3-dicarbonyl compounds, isatins and alcohols mediated by TMSCl. This synthesis involves cyclization and esterification in one-step cascade process for the formation of a carboxylate (CO2R) at the 4-position of quinaldine ring. Moreover, this procedure shows highly efficient, good functional group tolerance, operational simplicity, environment-friendly and feasibility of scale up.  相似文献   
1000.
In this paper, plasma concentration, plasma protein binding rate, body distribution, and excretion of both oral and intravenous administration of rats were determined by high performance liquid chromatography (HPLC) combining with UV detector. The blood drug concentration of oral and intravenous administration was summarized. The bioavailability of T1/2 was approximately 0.75?hr. At the meanwhile, the bioavailability was about 18.84?±?2.21%. The plasma protein binding rate of 1-methyl hydantoin was about 24.36?±?0.93%, belonging to low protein binding drug. The result shows that 1-methyl hydantoin can be rapidly distributed in various organs and tissues and quickly eliminated within 6?hr without accumulation in the organs. Its discharge from the urine and feces was 16.58?±?4.48% and 3.37?±?0.71%, respectively. All of the results showed that the recovery rate, liner relationship, specificity, stability, and precision of the method were good. The study also proved that 1-methyl hydantoin has been eliminated quite faster in rats.  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