全文获取类型
收费全文 | 6161篇 |
免费 | 1135篇 |
国内免费 | 2191篇 |
专业分类
化学 | 5917篇 |
晶体学 | 126篇 |
力学 | 374篇 |
综合类 | 97篇 |
数学 | 609篇 |
物理学 | 2364篇 |
出版年
2024年 | 16篇 |
2023年 | 58篇 |
2022年 | 157篇 |
2021年 | 169篇 |
2020年 | 226篇 |
2019年 | 244篇 |
2018年 | 188篇 |
2017年 | 183篇 |
2016年 | 251篇 |
2015年 | 267篇 |
2014年 | 339篇 |
2013年 | 630篇 |
2012年 | 646篇 |
2011年 | 627篇 |
2010年 | 416篇 |
2009年 | 562篇 |
2008年 | 428篇 |
2007年 | 383篇 |
2006年 | 349篇 |
2005年 | 385篇 |
2004年 | 694篇 |
2003年 | 468篇 |
2002年 | 483篇 |
2001年 | 247篇 |
2000年 | 148篇 |
1999年 | 185篇 |
1998年 | 164篇 |
1997年 | 131篇 |
1996年 | 99篇 |
1995年 | 56篇 |
1994年 | 50篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 18篇 |
1990年 | 22篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1970年 | 5篇 |
1931年 | 3篇 |
1909年 | 3篇 |
排序方式: 共有9487条查询结果,搜索用时 10 毫秒
91.
Study of Tea Digitized Chromatographic Fingerprint Spectra Using Micellar Electrokinetic Chromatography 总被引:1,自引:0,他引:1
IntroductionTeaisthemostwidelyconsumedbeverageinpeople’slife .Theheightenedpopularityofthisbeveragethroughouttheworldinrecentyearsmaybedueinparttotheevidenceofarelationshipbetweenteaconsumptionandpreventionofcertainformsofhumandisease .Themaincomponentsofteaarepolyphenoliccompounds ,commonlyknownascatechins ,whichrepresentagroupofcom poundsbelongingtotheflavonoidfamily .Thesecom poundsarewidelydistributedinthetealeavesandconsti tuteupto 30 %ofthedryleafweight.1Muchinteresthasbeenfocusedoncat… 相似文献
92.
水煤气变换反应的微观动力学分析──Cu基催化剂上H_2S中毒失活原因的 Monte Carlo 模拟研究 总被引:1,自引:0,他引:1
用BOCMP方法及MonteCarlo模拟技术,对H2S导致Cu基催化剂失活的原因进行了计算分析。研究结果表明,当原料气中存在H2S时,WGS反应的活化能明显高于无H2S时的活化能,随着表面H2S浓度的增大(θ=0,0.10,0.25),反应的活化能也逐渐变大(其大小比为1∶1.34∶3.3),究其原因可归结为H2S的存在使得反应物分子的吸附热减小,从而使H2O的解离吸附(WGS反应的速控步骤)活化能增大。 相似文献
93.
Yuan LF Yang J Wang H Zeng C Li Q Wang B Hou JG Zhu Q Chen DM 《Journal of the American Chemical Society》2003,125(1):169-172
Orientationally ordered structures of two-dimensional (2D) C(60) at low temperature have been investigated theoretically and experimentally. Using total energy optimization with a phenomenological potential, we find the ground state is a close packed hexagonal lattice in which all the molecules have the same orientation. Several local minima of the potential energy surface are found to be associated with other 1 x 1 lattices as well as 2 x 2 lattices. The energies of the orientational domain boundaries of the 1x1 lattices are also computed, and two kinds of which yield negative values. A majority of these theoretical findings are confirmed by our low-temperature scanning tunneling microscopy study of a 2D C(60) array supported on a self-assembled monolayer. 相似文献
94.
IntroductionTheintramolecularenergytransferprocessandmechanismofrareearthcomplexeswithβ-diketoneshavebeengeneralystudiedandac... 相似文献
95.
LING Daren LIU Bing WU Guoqi Department of Applied Chemistry Jiangsu Institute of Petrochemical Technology Changzhou China 《Chinese Journal of Reactive Polymers》2002,(1)
1. INTRODUCTION When investigating contaminated sites it is often essential to determine specific pollutants in a large number of ambient air samples. Amongst these sites, polycylic aromatic hydrocarbons (PAHs) are a major class of compounds that hav… 相似文献
96.
离子性指数、极化效应指数烷烃^13C NMR化学位移的 关系研究 总被引:5,自引:0,他引:5
定义了烷烃分子中碳原子的离子性指数(INI),用离子性指数(INI)、极化效应指数(PEI)及N^i~H(i=αβΥ)结构信息参数研究了烷烃的^13CNMR化学位移模型,结果表明,烷烃^13CNMR化学位移(CS)可用下式来定量描述:CS=194.6156-37.7394(INI)+98.6505(ΣPEI)+27.1630(INI/ΣPEI)-652.9106(ΣPEI/INI)+0.7735N^α~H+2.2468N^β~H-0.1742N^γ~H。用上式估算了304个碳原子的化学位移,平均绝对误差仅为0.77δ,标准差0.9860δ,预测值与实验值非常吻合。 相似文献
97.
利用原位红外技术研究了CH3OH、CO、O2等在Pd/γAl2O3上的吸附情况及CH3OH和O2共吸附时表面物种的变化,结果表明:表面纯净的Pd/γAl2O3催化剂对甲醇具有很好的解离吸附性能,在无氧条件下,CH3OH可在其上脱氢产生HCHO及CO。Pd对O2的吸附力强,氧均以解离方式吸附于Pd/γAl2O3上。当吸附的[CH3O]与[O]在Pd/γAl2O3上相互作用时,可产生HCHO、CO、甲二氧基、甲酸根等中间物种 相似文献
98.
We report the time courses of five solid-phase reactions obtained using single bead FTIR microspectroscopy. This time-resolved information aided in the determination of the required reaction time, the nature of the solid-phase reaction, and resin property, effectively assisting in the initial phase of our combinatorial chemistry efforts. Our results showed that solid-phase organic reactions proceed faster than generally speculated. In addition, we have shown that reactions on the surface and in the interior of the bead occur at the same rate for reactions studied. The reaction on the TentaGel resin was shown to be not faster than reactions on Wang resin, suggesting that the diffusion of the substrate into polystyrene bead copolymerized with 1% divinylbenzene is not rate-limiting. Finally, the capability of obtaining IR spectra from the partial surface of a single bead demonstrated the femtomolar detection limit of single bead FTIR microspectroscopy. 相似文献
99.
Yuan L Feng W Yamato K Sanford AR Xu D Guo H Gong B 《Journal of the American Chemical Society》2004,126(36):11120-11121
Highly efficient, one-step macrocyclizations leading to the formation of macrocyclic hexa(aramides) in high yields (69-82%) are described. The one-step macrocyclizations were facilitated by the preorganization or folding of the backbones of uncyclized precursors in the course of macrocyclization. The preorganization of backbones was achieved by the presence of localized three-centered hydrogen bonds that were adopted in the design of a class of closely related, backbone-rigidified foldamers. The macrocyclization involved reactions between diacid chloride 1 and diamine 2. The crude reaction mixtures and products were conveniently examined by mass spectrometric method (MALDI-TOF). Compared to most traditional one-step macrocyclizations that usually require high dilution conditions and often lead to very low overall yields of the desired products, cyclic hexamers 3 were obtained as the overwhelmingly major product under a variety of reaction conditions, suggesting the generality of this approach. 相似文献
100.
A novel organic-inorganic hybrid compound {[Cu(2,2′-bpy)2]2Mo8O26} has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group, Pna21,with a=2.4164(5),b=1.8281(4),c=1.1877(2)nm,V=5.247(2)nm^3,Z=4,and final R1=0.0331,wR2=0.0727.The structure consists of discrete {[Cu(2,2′-bpy)2]2Mo8O26} clusters,constructed from a β-octamolybdate subunit[Mo8O26]^4- covalently bonded to two [Cu(2,2′-bpy)2]^2 coordination complex cations via bridging oxo groups.In addition,the spectroscopic properties and thernal behavior of this compound have been investigated by spectroscopic techniques (UV-vis,IR,Raman and EPR spectra) and TG analysis. 相似文献