全文获取类型
收费全文 | 16566篇 |
免费 | 3430篇 |
国内免费 | 4299篇 |
专业分类
化学 | 12451篇 |
晶体学 | 456篇 |
力学 | 1201篇 |
综合类 | 360篇 |
数学 | 2108篇 |
物理学 | 7719篇 |
出版年
2024年 | 44篇 |
2023年 | 255篇 |
2022年 | 615篇 |
2021年 | 624篇 |
2020年 | 639篇 |
2019年 | 646篇 |
2018年 | 585篇 |
2017年 | 705篇 |
2016年 | 732篇 |
2015年 | 880篇 |
2014年 | 1062篇 |
2013年 | 1372篇 |
2012年 | 1587篇 |
2011年 | 1656篇 |
2010年 | 1360篇 |
2009年 | 1419篇 |
2008年 | 1453篇 |
2007年 | 1260篇 |
2006年 | 1287篇 |
2005年 | 1057篇 |
2004年 | 753篇 |
2003年 | 533篇 |
2002年 | 557篇 |
2001年 | 601篇 |
2000年 | 563篇 |
1999年 | 385篇 |
1998年 | 243篇 |
1997年 | 203篇 |
1996年 | 153篇 |
1995年 | 143篇 |
1994年 | 141篇 |
1993年 | 126篇 |
1992年 | 116篇 |
1991年 | 80篇 |
1990年 | 84篇 |
1989年 | 62篇 |
1988年 | 56篇 |
1987年 | 40篇 |
1986年 | 35篇 |
1985年 | 29篇 |
1984年 | 35篇 |
1983年 | 24篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1977年 | 5篇 |
1965年 | 4篇 |
1959年 | 4篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Cyanobenzaldehydes (m-,o-,p-) were synthesized by oxidation of corresponding tolunitriles with molecular oxygen,catalyzed by cobalt acetate and sodium bromide. 相似文献
122.
热处理对聚乙烯/炭黑导电复合体系形态结构及PTC特性的影响 总被引:11,自引:3,他引:11
借助WAXD、SAXD和DSC等手段研究了炭黑与聚乙烯复合体系在不同热处理条件下的结晶行为及聚集态结构的大尺寸效应对PTC特性的影响。由此提出,不仅结晶度大小,而且聚集大尺寸效应性能对PTC行性有重要影响的新观点。 相似文献
123.
以Mg(NO3)2,Ca(NO3)2,Eu(NO3)3,Bi(NO3)3和Si(OC2H5)4为反应物,采用溶胶-凝胶法,在比较低的温度,首次合成0.701molMgO-0.175molCaO-1.25molSiO2:0.06molEu^3+,0.002molBi^3+(加入Li^+作为电荷补偿剂)发光体,得到了最佳合成条件,研究了由溶胶向凝胶转变和凝胶向发光晶体的转变过程,探讨了发光体在不同激光 相似文献
124.
A Novel Dimeric Coumarin from Clausena lenis 总被引:1,自引:0,他引:1
HongPingHE ShunTingCHEN YueMaoSHEN ChangXiangCHEN YiBinZHAO XiaoJiangHAO 《中国化学快报》2003,14(11):1150-1153
A novel dimeric coumarin (1), a dimeric of seselin named diseselin A, was isolated from the aerial part of Clausena lenis. The structure was elucidated based on the MS, 1D and 2D NMR data. 相似文献
125.
Discharge performance of K2FeO4 electrode under different conditions was studied by the constant electric current discharge method. The electrochemical characteristics of K2FeO4 electrode were investigated for the first time by means of cyclic voltammetry. The results show that the K2FeO4 electrode made at moderate pressure (20MPa) and discharged at lower current has better discharge performance. It is also found that K2FeO4 electrode is significantly rechargeable. 相似文献
126.
127.
在以加氢汽油为溶剂,MoCl_3(C_7H_(15)COO)_2(Mo)为主催化剂,(i-Bu)_2AlO〈O〉(Al)为助催化剂合成1,2-聚丁二烯的二元催化体系中,添加BF_3CH3·OEt_2等,对体系的催化活性影响显著。以的混合物为第三组份加入催化体系,较大幅度提高了钼系催化体系的活性。在Mo/Bd=8.0×10~(-5)(摩尔比),聚合5小时,丁二烯转化率可达到70%。初步搞清了钼催化体系合成的1,2-聚丁二烯中产生凝胶的条件,推测了凝胶的生成原因,考察了聚合条件对催化活性、分子量及微观结构含量的影响。 相似文献
128.
A parallel solution combustion synthesis technique was developed for combinatorial materials studies. The vigorous combustion reactions were successfully limited in the microreactors by using a substrate-net-mask microreactor system and the lowest adoptable furnace temperature. Using this technique, a luminescent materials library of Y3Al5O12/Tb(chi) was synthesized with the aid of an ink-jet delivery system. Structure and luminescence characterizations were implemented using X-ray diffraction and UV/X-ray spectroscopies, respectively. The results show that this technique is reliable and applicable to combinatorial study of powder materials with high synthesis temperature. 相似文献
129.
The rates at which aluminum was removed from the N- and C-terminal monoaluminum ovotransferrins by pyrophosphate were evaluated by UV difference spectra in 0.01 mol/L Hepes, pH=7.4 and at 37℃. Pesudo first-order rate constants as a function of pyrophosphate concentration were measured. The results indicate that the pathways of aluminum removal are different. For the N-terminal binding site, aluminum removal follows simple saturation kinetics, while the removal of aluminum from the C-terminal binding site reverts to the combination of saturation and first-order kinetics. The saturation component is consistent with a rate-limiting conformational change in the protein as has been reported. We propose that the first-order kinetics mechanism is attributed to a pre-equilibrium process. The rate constants of saturation kinetics are accelerated from both terminals with the addition of 0.1 mol/L chloride to the monoaluminum ovotransferrin solutions, whereas the rates of the first-order kinetics are decreased for the C-terminal binding site. The effect of chloride ionic strength causes a continuing increase on kobs for the N- and C-terminal binding sites. Moreover, the kinetics behavior of the N-terminal is more easily affected by chloride than that of the C-terminal. In the experiment presumably the N-terminal site is apparently kinetically more labile than the C-terminal site. 相似文献
130.
Neonatal rats have taken in lead, during the period from their parturition to their weaning, from the milk of dams fed with water containing 0.2% lead acetate solutions. The alterations in the temporal response properties of retinal ganglion cells in adult rats (90 days) following the lead exposure at their developing stage have been studied. The results of this investigation demonstrate that the lead exposure in neonatal rats causes decreases in the optimal temporal frequency, bandwidth at half amplitude, temporal resolution and response phase of the retinal ganglion cells in adult rats. Compared with the sustained cells, the transient cells have a much greater alteration in temporal response properties. 相似文献