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   186354篇
  免费   30321篇
  国内免费   18659篇
化学   125557篇
晶体学   1884篇
力学   12646篇
综合类   1078篇
数学   23801篇
物理学   70368篇
  2024年   193篇
  2023年   3370篇
  2022年   3784篇
  2021年   5901篇
  2020年   7068篇
  2019年   6810篇
  2018年   6041篇
  2017年   5604篇
  2016年   8610篇
  2015年   8243篇
  2014年   10122篇
  2013年   13519篇
  2012年   16604篇
  2011年   17405篇
  2010年   11721篇
  2009年   11104篇
  2008年   12046篇
  2007年   10902篇
  2006年   10110篇
  2005年   8527篇
  2004年   6507篇
  2003年   5211篇
  2002年   4854篇
  2001年   4028篇
  2000年   3534篇
  1999年   4054篇
  1998年   3421篇
  1997年   3207篇
  1996年   3315篇
  1995年   2813篇
  1994年   2614篇
  1993年   2170篇
  1992年   1942篇
  1991年   1768篇
  1990年   1444篇
  1989年   1105篇
  1988年   902篇
  1987年   749篇
  1986年   720篇
  1985年   614篇
  1984年   472篇
  1983年   306篇
  1982年   274篇
  1981年   226篇
  1980年   191篇
  1979年   104篇
  1978年   104篇
  1977年   110篇
  1976年   108篇
  1973年   99篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
3,4-Difluorobenzyl(1-ethyl-5-(4-((4-hydroxypiperidin-1-yl)-methyl)thiazol-2-yl)-1H-indol-3-yl)carbamate (NAI59), a small molecule with outstanding therapeutic effectiveness to anti-pulmonary fibrosis, was developed as an autotaxin inhibitor candidate compound. To evaluate the pharmacokinetics and plasma protein binding of NAI59, a UPLC–MS/MS method was developed to quantify NAI59 in plasma and phosphate-buffered saline. The calibration curve linearity ranged from 9.95 to 1990.00 ng/mL in plasma. The accuracy was −6.8 to 5.9%, and the intra- and inter-day precision was within 15%. The matrix effect and recovery, as well as dilution integrity, were within the criteria. The chromatographic and mass spectrometric conditions were also feasible to determine phosphate-buffered saline samples, and it has been proved that this method exhibits good precision and accuracy in the range of 9.95–497.50 ng/mL in phosphate-buffered saline. This study is the first to determine the pharmacokinetics, absolute bioavailability, and plasma protein binding of NAI59 in rats using this established method. Therefore, the pharmacokinetic profiles of NAI59 showed a dose-dependent relationship after oral administration, and the absolute bioavailability in rats was 6.3%. In addition, the results of protein binding showed that the combining capacity of NAI59 with plasma protein attained 90% and increased with the increase in drug concentration.  相似文献   
32.
In this paper,we first construct compact embeddedλ-hypersurfaces with the topology of torus which are calledλ-torus in Euclidean spaces?n^+1.Then,we give many compact immersedλ-hypersurfaces in Euclidean spaces?n^+1.  相似文献   
33.
Li  Jun  Zheng  Dayong  Wei  Ning  Sun  Yunfeng  Liu  Li  Yuan  Yuan  Jiang  Qinghua 《Chemistry of Natural Compounds》2022,58(4):650-652
Chemistry of Natural Compounds - A new quassinoid, dehydrobruceantinol B (1), was isolated from the seeds of Brucea javanica, together with two known compounds, bruceantinol (2) and bruceine A (3)....  相似文献   
34.
The molecular geometries and dissociation energies of AnO (An = Bk–Lr) molecules were first obtained at thecoupled-cluster single-, double-, and perturbative triple-excitations [CCSD(T)] level of theory. Four hybrid functionals,B3LYP, M06-2X, TPSSh, and PBE0, were also employed in the calculations for the sake of comparison. In comparison ofthe CCSD(T) results, B3LYP, TPSSh, and PBE0 functionals can obtain more appropriate results than M06-2X and MP2.The analyses on molecular orbitals show that the 7s, 6d, and 5f atomic orbitals of actinide (An) atoms participate in thebonding of An–O bonds. The partial covalent nature between An and O atoms is revealed by QTAIM analyses.  相似文献   
35.
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   
36.
Sun  Qinqin  Wang  Xiuye  Yang  Guolai  Chen  Ye-Hwa  Ma  Fai 《Nonlinear dynamics》2022,109(3):1629-1650
Nonlinear Dynamics - This paper proposes an optimal parameter design of control scheme for mechanical systems by adopting the Stackelberg game theory. The goal of the control is to drive the...  相似文献   
37.
Wang  Xigui  Ruan  Jiafu  Wang  Yongmei  Ji  Shue  An  Siyuan 《Meccanica》2021,56(2):303-316
Meccanica - In gear pair actual alternating meshing process, the comprehensive errors of the transmission system and the thermal elastic deformation of the teeth body cause the gears in the meshing...  相似文献   
38.
Annals of the Institute of Statistical Mathematics - In this paper, a model averaging approach is developed for the linear regression models with response missing at random. It is shown that the...  相似文献   
39.
Xu  Mengtao  Li  Changyou  Sun  Yang  Yang  Tianzhi  Zhang  Hongzhuang  Liu  Zhendong  Liu  Haiyang  Li  Zhenyuan  Zhang  Yimin 《Nonlinear dynamics》2021,105(4):3061-3092
Nonlinear Dynamics - Investigation of the dynamic characteristics of linear guideway is essential for enhancing structural performance of machine tools. However, few mechanical models are...  相似文献   
40.
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