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   23925篇
  免费   3965篇
  国内免费   3023篇
化学   17222篇
晶体学   252篇
力学   1668篇
综合类   165篇
数学   2637篇
物理学   8969篇
  2024年   88篇
  2023年   502篇
  2022年   912篇
  2021年   919篇
  2020年   976篇
  2019年   922篇
  2018年   835篇
  2017年   770篇
  2016年   1231篇
  2015年   1098篇
  2014年   1400篇
  2013年   1754篇
  2012年   2141篇
  2011年   2176篇
  2010年   1460篇
  2009年   1391篇
  2008年   1644篇
  2007年   1416篇
  2006年   1253篇
  2005年   1128篇
  2004年   814篇
  2003年   673篇
  2002年   648篇
  2001年   542篇
  2000年   463篇
  1999年   476篇
  1998年   403篇
  1997年   362篇
  1996年   398篇
  1995年   384篇
  1994年   293篇
  1993年   229篇
  1992年   230篇
  1991年   208篇
  1990年   175篇
  1989年   133篇
  1988年   113篇
  1987年   95篇
  1986年   63篇
  1985年   62篇
  1984年   38篇
  1983年   32篇
  1982年   17篇
  1981年   21篇
  1980年   10篇
  1978年   2篇
  1972年   1篇
  1959年   1篇
  1957年   8篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Ag colloidal nanoparticles coated with Eu(TTA)3 · 2H2O complexes were prepared, and it was found that Eu(TTA)3 · 2H2O complexes J-aggregate was formed on the surface of Ag nanoparticles according to a red shift (18.2 nm) in UV–Vis spectra. However, there had similar excitation wavelength, which was attributed to existence of Ag nanoparticles. Highly luminescent properties of Ag colloidal nanoparticles were observed, and it was believed to result from low energy transfer between Eu(III) complexes and Ag and the large electromagnetic field arising from the excitation of surface plasmon polariton of Ag nanoparticles.  相似文献   
92.
来用连续加料法,以二元醇-KOH为引发剂合成一组不同组成的环氧乙烷-环氧丙烷无规共聚醚,并用核磁共振、红外光谱、示差扫描量热计和热失重等方法对其本体聚合物,用浊点和表面张力测定的方法对其水溶液,进行系统的表征。  相似文献   
93.
微合金钢中稀土对沉淀相和性能的影响   总被引:3,自引:5,他引:3  
在Nb(Ti,V)微合金钢中,主要沉淀相分别为Nb(C,N),(Nb,Ti)(C,N)和V(C,N)。稀土降低沉淀相完全溶解的温度,增大奥氏体中沉淀相析出的孕育期,降低析出速率,抑制奥氏体中沉淀相的析出,在铁素体相区,稀土提高沉淀相的析出速率和数量,促进沉淀相的析出,其中稀土对铌沉淀相析出的作用影响最强。锻态钢中,稀土有促进细化球化析出相的作用,随稀土含量增加,沉淀相析出数量增加,但过量稀土,促进作用又减弱,稀土在保持微合金钢强度的情况下,显著改善其冲击韧性,尤其是低温韧性,微合金钢中添加适量稀土可获得更佳的综合性能。  相似文献   
94.
95.
Reaction of transition metal formate M(HCOO)(2).2H2O (M = Mn, Co, Ni) with 4,4'-bpy (4,4-bipyridine) has led to four new compounds with the formula M(HCOO)2(4,4'-bpy).nH2O (M = Mn, Co (1.Mn, 2.Co), n = 0; M = Co, Ni (3.Co, 4.Ni), n = 5). Compounds 1.Mn and 2.Co are isomorphous and crystallized in the tetragonal crystal system with the chiral space group P4(1)2(1)2. They are of three-dimensional diamondoid structure connected by anti-anti formate with 4,4'-bpy in the cavities of the framework reinforcing the intermetallic connections; the diamond-like net was observed also in their azide analogue (Mn(N3)2(4,4'-bpy)). Compounds 3.Co and 4.Ni are isomorphous also but crystallized in the monoclinic crystal system with the space group Cc. Both structures are uninterpenetrated 3D "CdSO4" type with big channels, constructed by anti-anti formate and 4,4'-bpy. This type of net was not observed in their azide analogue. Residing in the channels, water molecules form a new type of 1D tape constructed by vertex-sharing cyclic pentamers. Magnetic measurements were performed on all of these four compounds. 1.Mn and 2.Co are weak ferromagnets with the critical temperature Tc = 5.3 and 7.4 K, respectively. 3.Co is an antiferromagnet with Neel temperature TN = 3.0 K, and 4.Ni is a weak ferromagnet below 20 K. Hysteresis loop can be observed for 2.Co and 4.Ni at 1.8 K. As an analogue of azide, formate can be used to construct molecular architectures, which structurally and magnetically have great similarities to and also differences from those of azide. This offers a promising method for the design of new molecular architectures with formate.  相似文献   
96.
A novel method, modified matrix solid-phase dispersion (MMSPD), has been developed for quantitative analysis of organophosphorus pesticide residues in soil. It was based on matrix solid-phase dispersion (MSPD) and continuous liquid-solid extraction (continuous LSE), using Florisil as sorbent and dichloromethane as the recycling solvent. Two soils with different texture and physicochemical properties were studied to validate the method. The effect of residence time of pesticides in soil was also studied. MMSPD was compared with MSPD and continuous LSE respectively. Determination was carried out by gas chromatography with nitrogen-phosphorus detection (GC-NPD). The method gave recoveries ranging from 72–105% with relative standard deviations (RSDs) lower than 15% for the pesticides studied. The limits of detection (LODs) ranged from 0.1 to 0.6 ng g−1. Two pesticide residues have been detected in real soil samples from Fujian, China, using MMSPD. The pesticides were confirmed by gas chromatography-mass spectrometry (GC-MS) in a selected-ion monitoring (SIM) mode. Revised: 4 and 9 April 2006  相似文献   
97.
合成了六种轻希土硫氰酸盐与标题不饱和冠醚的新固体配合物,进行了元素分析,摩尔电导率、DTA、UV、IR和XPS等表征.对Ln(NCS)3·L和Ln(NCS)3的XPS研究中,得到它们组成原子芯能级电子(Ln3d5/2,Ols,Nls,S2p)的结合能信息;观察到除Y3d5/2外Ln3d5/2(Ln=La、Ce、Pr、Nd、和Sm)的伴峰结构,Ln3d5/2结合能与原子序数呈线性关系,并推断类似化合物Pm3d5/2结合能在1035eV附近.  相似文献   
98.
Single crystal tin nano-rod arrays were fabricated by the electrodeposition method when amphiphilic triblock copolymer P123 was used as a soft template at a concentration much lower than that for forming a liquid crystalline phase.  相似文献   
99.
本非水电池体系由Li负极、多孔石墨电极和电解质溶液组成;电解质溶液由无机溶剂POCl_3(或有机溶剂硝基苯)和溶解在该溶剂中的活性物质(KIBr_2)及支持电解质构成。该电池体系的开路电压为8.50伏左右,放电性能良好,可望在实际中得到应用。此外,对电池体系的反应机理也作了初步的探讨。  相似文献   
100.
用共振电离飞行时间质谱仪分析土壤中超痕量气态金   总被引:2,自引:0,他引:2  
采用激光共振电离飞行时间质谱技术(简称RIS-TOF技术)对土壤中超痕量气态金的含量进行了分析研究。RIS-TOF谱仪具有极高的灵敏度和很强的选择性,避免了对样品的预富集过程。本文给出了该谱仪对金元素的检测限和65个土壤中气态金样品的分析结果,以及用中子活化法随机抽样检查的结果。  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