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   906篇
  免费   78篇
  国内免费   86篇
化学   561篇
晶体学   1篇
力学   13篇
综合类   2篇
数学   358篇
物理学   135篇
  2023年   11篇
  2022年   28篇
  2021年   36篇
  2020年   23篇
  2019年   23篇
  2018年   17篇
  2017年   14篇
  2016年   33篇
  2015年   33篇
  2014年   35篇
  2013年   59篇
  2012年   46篇
  2011年   54篇
  2010年   40篇
  2009年   71篇
  2008年   52篇
  2007年   62篇
  2006年   45篇
  2005年   45篇
  2004年   42篇
  2003年   36篇
  2002年   30篇
  2001年   20篇
  2000年   20篇
  1999年   38篇
  1998年   16篇
  1997年   17篇
  1996年   23篇
  1995年   11篇
  1994年   15篇
  1993年   8篇
  1992年   13篇
  1991年   9篇
  1990年   6篇
  1989年   5篇
  1988年   3篇
  1987年   3篇
  1986年   1篇
  1985年   4篇
  1984年   2篇
  1983年   2篇
  1982年   5篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
排序方式: 共有1070条查询结果,搜索用时 15 毫秒
121.
本文简要介绍了7×35cm~2多灯丝大面积源的供电保护系统,给出了该系统的基本设计思想,电源简化原理图及主要电路特点和已达到的技术指标。  相似文献   
122.
The potentiometric response characteristics of zinc ion selective PVC-based membrane electrode employing 1,12,14-triaza-5,8-dioxo-3(4),9(10)-dibenzoyl-1,12,14-triene as an inophore was investigated. The proposed electrode exhibits a Nernstian behavior with a slope of 29.2 ± 0.4 mV per decade with a working concentration range of 1.3 × 10?7–1.0 × 10?1 mol L?1 and a detection limit of 1.0 × 10?8 mol L?1. The membrane having the composition as TDODBCPT:O-NPOE:PVC:OA; 7:57:30:6 wt.% exhibits the best results. It has a fast response time of 7 s and can be used for at least 100 days without any considerable divergence in potential. The proposed electrode show good discrimination of Zn2+ ion from diverse ions. The potential response remains constant over a pH range of 3.5–9.2. The electrode found well work under laboratory conditions. The proposed sensor directly used for determination of zinc ions in human hair sample, wastewater and an indicator electrode with EDTA titration.  相似文献   
123.
The aim of this paper is to complement existing oscillation results for third-order neutral delay differential equations by establishing sufficient conditions for nonexistence of so-called Kneser solutions. Combining newly obtained results with existing ones, we attain oscillation of all solutions of the studied equations.  相似文献   
124.
In this note, we prove the existence and uniqueness of the solution to neutral stochastic functional differential equations with infinite delay (INSFDEs in short) in which the initial value belongs to the phase space BC((-,0]Rd), which denotes the family of bounded continuous Rd-value functions φ defined on (-,0] with norm ||φ||=sup-<θ?0|φ(θ)|, under some Carathéodory-type conditions on the coefficients by means of the successive approximation. Especially, we extend the results appeared in Ren et al. [Y. Ren, S. Lu, N. Xia, Remarks on the existence and uniqueness of the solutions to stochastic functional differential equations with infinite delay, J. Comput. Appl. Math. 220 (2008) 364-372], Ren and Xia [Y. Ren, N. Xia, Existence, uniqueness and stability of the solutions to neutral stochastic functional differential equations with infinite delay, Appl. Math. Comput. 210 (2009) 72-79] and Zhou and Xue [S. Zhou, M. Xue, The existence and uniqueness of the solutions for neutral stochastic functional differential equations with infinite delay, Math. Appl. 21 (2008) 75-83].  相似文献   
125.
This paper is concerned with the numerical solution of delay differential equations (DDEs). We focus on the stability of general linear methods for systems of neutral DDEs with multiple delays. A type of interpolation procedure is considered for general linear methods. Linear stability properties of general linear methods with this interpolation procedure are investigated. Many extant results are unified.  相似文献   
126.
为HL-2A 装置中性束注入器研制了引出束功率为1MW 的射频离子源。在测试平台上,实验离子源已经成功引出了束能量和束电流分别为35keV 和12.4A、束质子比为79%、脉宽为100ms 的氢离子束,达到了设计束功率要求的44%。在射频离子源实验平台上,利用多普勒频移光谱方法测量了离子源引出束流成分比例,对比了束流成分和射频离子源引出束流之间的关系。实验数据分析表明,在10A 引出束流的情况下,离子流成分 H+ 1、H+ 2 和H+ 3 分别为75%、18%和7%。并且当引出束流从3.3A 升至10.4A 时,H+ 1 从37%升至78%,而H+ 3 则从19%降至9%。  相似文献   
127.
具有无穷时滞中立型泛函微分方程概周期解的存在性   总被引:1,自引:0,他引:1  
袁荣 《数学学报》1996,39(5):707-717
对具有无穷时滞中立型泛函微分方程,本文利用Liapunov泛函,建立概周期解的存在性定理.  相似文献   
128.
通过大块液膜体系研究了四烷基锡的碳链长度、载体浓度.NO_2~-浓度及抗衡离子等因素对NO_2~_穿透含四烷基锡的液膜的传质速率的影响,讨论了它们与四烷基锡为载体的离子电极性能间的关系。NO_2~-通过四烷基锡为载体的液膜的迁移规律符合离子对传输模式。  相似文献   
129.
《Mendeleev Communications》2022,32(3):354-356
The novel conjugates of cholesterol with cobalt – bis(dicarbollide) were synthesized by the ring-opening reactions of the cyclic oxonium derivatives of [3,3′-Co(C2B9H11)2] with the OH group of cholesterol 2-hydroxyethyl ether. The compounds obtained were tested for toxicity to glioblastoma U-87 MG cells and human embryo fibroblasts FECH-15 cells  相似文献   
130.
We report boronate-caged guanidine-lipid 1 that activates liposomes for cellular delivery only upon uncaging of this compound by reactive oxygen species (ROS) to produce cationic lipid products. These liposomes are designed to mimic the exceptional cell delivery properties of cell-penetrating peptides (CPPs), while the inclusion of the boronate cage is designed to enhance selectivity such that cell entry will only be activated in the presence of ROS. Boronate uncaging by hydrogen peroxide was verified by mass spectrometry and zeta potential (ZP) measurements. A microplate-based fluorescence assay was developed to study the ROS-mediated vesicle interactions between 1 -liposomes and anionic membranes, which were further elucidated via dynamic light scattering (DLS) analysis. Cellular delivery studies utilizing fluorescence microscopy demonstrated significant enhancements in cellular delivery only when 1 -liposomes were incubated with hydrogen peroxide. Our results showcase that lipid 1 exhibits strong potential as an ROS-responsive liposomal platform for targeted drug delivery applications.  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