全文获取类型
收费全文 | 19338篇 |
免费 | 1552篇 |
国内免费 | 681篇 |
专业分类
化学 | 5480篇 |
晶体学 | 17篇 |
力学 | 1099篇 |
综合类 | 77篇 |
数学 | 9461篇 |
物理学 | 5437篇 |
出版年
2024年 | 22篇 |
2023年 | 198篇 |
2022年 | 326篇 |
2021年 | 417篇 |
2020年 | 462篇 |
2019年 | 488篇 |
2018年 | 347篇 |
2017年 | 410篇 |
2016年 | 630篇 |
2015年 | 533篇 |
2014年 | 865篇 |
2013年 | 1496篇 |
2012年 | 876篇 |
2011年 | 954篇 |
2010年 | 873篇 |
2009年 | 1197篇 |
2008年 | 1352篇 |
2007年 | 1345篇 |
2006年 | 1052篇 |
2005年 | 779篇 |
2004年 | 691篇 |
2003年 | 706篇 |
2002年 | 696篇 |
2001年 | 512篇 |
2000年 | 539篇 |
1999年 | 440篇 |
1998年 | 447篇 |
1997年 | 325篇 |
1996年 | 306篇 |
1995年 | 238篇 |
1994年 | 258篇 |
1993年 | 212篇 |
1992年 | 196篇 |
1991年 | 124篇 |
1990年 | 120篇 |
1989年 | 111篇 |
1988年 | 123篇 |
1987年 | 85篇 |
1986年 | 92篇 |
1985年 | 135篇 |
1984年 | 107篇 |
1983年 | 35篇 |
1982年 | 92篇 |
1981年 | 65篇 |
1980年 | 65篇 |
1979年 | 60篇 |
1978年 | 48篇 |
1977年 | 44篇 |
1976年 | 36篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
212.
《Tetrahedron letters》2019,60(52):151357
In this work, the host–guest interaction between calixpyridinium and the anionic anticancer drug methotrexate disodium was explored in water. Unexpectedly, an interesting anisotropic needle-like rather than an ordinary isotropic spherical supramolecular amphiphilic assembly was fabricated by the complexation of calixpyridinium with methotrexate disodium. It is the second anionic guest to be discovered to form the non-spherical supramolecular assembly upon complexation with calixpyridinium. This discovery implies the possibility to construct various topological nanostructures based on the host–guest interactions between calixpyridinium and the anionic drugs in the future. The resulting calixpyridinium–drug assemblies with different morphologies may have the diverse potentials to adjust the efficacies of anionic drugs. 相似文献
213.
本文通过将高阶非线性自治微分方程转化为Lurie型控制系统的方法,借助于Popov的频率判据,得到了它们全局渐近稳定的判别准则,推广了文[1]的结果. 相似文献
214.
The MReaDy program was designed for studying Multiprocess Reactive Dynamic systems, that is, complex chemical systems involving different and concurrent reactions. It builds a global potential energy surface integrating a variety of potential energy surfaces, each one of them representing an elementary reaction expected to play a role in the chemical process. For each elementary reaction, energy continuity problems may happen in the transition between potential energy surfaces due to differences in the functional form for each of the fragments, especially if built by different authors. A N‐dimensional switch function is introduced in MReaDy in order to overcome such a problem. As an example, results of a collision trajectory calculation for H2 + OH → H3O are presented, showing smooth transition in the potential energy, leading to conservation in the total energy. Calculations for a hydrogen combustion system from 1000 K up to 4000 K shows a variation of 0.012% when compared to the total energy of the system. © 2016 Wiley Periodicals, Inc. 相似文献
215.
Facile Assembly of Benzo[b]naphtho[2,3‐d]azocin‐6(5 H)‐ones by a Palladium‐Catalyzed Double Carbometalation 下载免费PDF全文
The palladium‐catalyzed reaction of 2‐alkynylanilines with 2‐(2‐bromobenzylidene)cyclobutanone as an efficient route to 7,8‐dihydrobenzo[b]naphtho[2,3‐d]azocin‐6(5 H)‐ones was developed. The fused eight‐membered ring was constructed conveniently. During the reaction process, double carbometalation was involved, which resulted in excellent selectivity with the formation of three new bonds. This transformation is highly efficient and leads to fused polycycles in good to excellent yields with good functional group tolerance. 相似文献
216.
Yang Jiao Wan‐Lu Li Dr. Jiang‐Fei Xu Dr. Guangtong Wang Prof. Jun Li Prof. Zhiqiang Wang Prof. Xi Zhang 《Angewandte Chemie (International ed. in English)》2016,55(31):8933-8937
Tuning the activity of radicals is crucial for radical reactions and radical‐based materials. Herein, we report a supramolecular strategy to accelerate the Fenton reaction through the construction of supramolecularly activated radical cations. As a proof of the concept, cucurbit[7]uril (CB[7]) was introduced, through host–guest interactions, onto each side of a derivative of 1,4‐diketopyrrolo[3,4‐c]pyrrole (DPP), a model dye for Fenton oxidation. The DPP radical cation, the key intermediate in the oxidation process, was activated by the electrostatically negative carbonyl groups of CB[7]. The activation induced a drastic decrease in the apparent activation energy and greatly increased the reaction rate. This facile supramolecular strategy is a promising method for promoting radical reactions. It may also open up a new route for the catalytic oxidation of organic pollutants for water purification and widen the realm of supramolecular catalysis. 相似文献
217.
利用相关函数(CF)-超球谐(HH)-广义Laguerre(GLF)方法直接求解类氦离子n1,3P(n=1,2,3)低躺激发态的Schrodinger方程,得氦原子的本征能量分别为-2.13317Eh (13P),-2.12383Eh(11P),-2.05810Eh(23P),-2.05516Eh(21P),-2.03235Eh(33P)和-2.03109Eh(31P),它们与文献值在........第6位上很好地吻合。这说明CFHHGLF方法也适用于类氦离子1,3P激发态。还给出了总角动量L=1的对称超球谐基函数和有关矩阵元的解析式。 相似文献
218.
María T. Viciosa José L. Gómez Ribelles Madalena Dionísio 《European Polymer Journal》2008,44(1):155-170
A detailed dielectric characterization of n-ethylene glycol dimethacrylate monomers with n = 2 and 4 is provided. Besides the α relaxation associated to the glass transition, two secondary relaxation processes were detected: the γ process assigned to the twisting motions within the ethylene glycol moiety, and the β process related with hindered rotations of carboxylic groups. While the relaxation time of the γ process is independent of the size of the ethylene glycol group, the β process deviates to higher times with increasing n. Upon polymerization the α process goes to extinction, faster in the 4-ethylene monomer, with a concomitant depletion of the β process that remains at higher polymerization degrees relatively to the α process, thus acting as a more sensitive probe to evaluate conversion. The height decrease of α and β processes of monomers with the polymerization progress, occurs without significant changes of position. At intermediate states of polymerization, a new relaxation process evolves being only detectable in a narrow temperature range. In the end, the polymer networks show, in addition to the γpol relaxation identical to the γ relaxation of the monomer, a βpol relaxation with similar features to the β relaxation found in poly n-alkyl methacrylates originated by a π flip of the ester unit accompanied by a restricted main chain rearrangement. The main dielectric relaxation corresponding to the swollen polymer network should appear at quite high temperatures already in early stages of the polymerization process because phase segregation occurs and only a limited amount of liquid monomer plasticizes the newly formed material. 相似文献
219.
Gadenne B Semeraro M Yebeutchou RM Tancini F Pirondini L Dalcanale E Credi A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(29):8964-8971
The phosphorus-bridged cavitand 1 self-assembles very efficiently in CH2Cl2 with either the monopyridinium guest 2+ or the bispyridinium guest 3(2+). In the first case a 1:1 complex is obtained, whereas in the second case both 1:1 and 2:1 host-guest complexes are observed. The association between 1 and either one of the guests causes the quenching of the cavitand fluorescence; in the case of the adduct between 1 and 3(2+), the fluorescence of the latter is also quenched. Cavitand complexation is found to affect the reduction potential values of the electroactive guests. Voltammetric and spectroelectrochemical measurements show that upon one-electron reduction both guests are released from the cavity of 1. Owing to the chemical reversibility of such redox processes, the supramolecular complexes can be re-assembled upon removal of the extra electron from the guest. Systems of this kind are promising for the construction of switchable nanoscale devices and self-assembling supramolecular materials, the structure and properties of which can be reversibly controlled by electrochemical stimuli. 相似文献
220.
Guldi DM Rahman GM Qin S Tchoul M Ford WT Marcaccio M Paolucci D Paolucci F Campidelli S Prato M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(8):2152-2161
Dispersible single-walled carbon nanotubes grafted with poly(4-vinylpyridine), SWNT-PVP, were tested in coordination assays with zinc tetraphenylporphyrin (ZnP). Kinetic and spectroscopic evidence corroborates the successful formation of a SWNT-PVPZnP nanohybrid. Within this SWNT-PVPZnP nanohybrid, static electron-transfer quenching (2.0+/-0.1) x 10(9) s(-1) converts the photoexcited-ZnP chromophore into a radical-ion-pair state with a microsecond lifetime, namely one-electron oxidized-ZnP and reduced-SWNT. 相似文献