全文获取类型
收费全文 | 13560篇 |
免费 | 1286篇 |
国内免费 | 1114篇 |
专业分类
化学 | 9524篇 |
晶体学 | 88篇 |
力学 | 56篇 |
综合类 | 53篇 |
数学 | 4890篇 |
物理学 | 1349篇 |
出版年
2024年 | 30篇 |
2023年 | 290篇 |
2022年 | 210篇 |
2021年 | 227篇 |
2020年 | 453篇 |
2019年 | 451篇 |
2018年 | 453篇 |
2017年 | 305篇 |
2016年 | 504篇 |
2015年 | 601篇 |
2014年 | 823篇 |
2013年 | 1217篇 |
2012年 | 766篇 |
2011年 | 902篇 |
2010年 | 779篇 |
2009年 | 848篇 |
2008年 | 911篇 |
2007年 | 867篇 |
2006年 | 707篇 |
2005年 | 514篇 |
2004年 | 481篇 |
2003年 | 476篇 |
2002年 | 409篇 |
2001年 | 285篇 |
2000年 | 265篇 |
1999年 | 267篇 |
1998年 | 241篇 |
1997年 | 157篇 |
1996年 | 168篇 |
1995年 | 211篇 |
1994年 | 170篇 |
1993年 | 123篇 |
1992年 | 129篇 |
1991年 | 64篇 |
1990年 | 62篇 |
1989年 | 54篇 |
1988年 | 53篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 56篇 |
1984年 | 46篇 |
1982年 | 53篇 |
1981年 | 40篇 |
1980年 | 30篇 |
1979年 | 36篇 |
1978年 | 34篇 |
1977年 | 25篇 |
1976年 | 29篇 |
1975年 | 19篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Yongkang Quan Prof. Guorong Wang Dujuan Li Prof. Zhiliang Jin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(66):16448-16460
At present, inefficient charge separation of single photocatalyst impedes the development of photocatalytic hydrogen evolution. In this work, the CoSX/NiCo-LDH core-shell co-catalyst was cleverly designed, which exhibit high activity and high stability of hydrogen evolution in anhydrous ethanol system when coupled with CdS. Under visible light (λ≥420 nm) irradiation, the 3 %Co/NiCo/CdS composite photocatalyst exhibits a surprisingly high photocatalytic hydrogen evolution rate of 20.67 mmol g−1 h−1, which is 59 times than that of the original CdS. Continuous light for 20 h still showed good cycle stability. In addition, the 3 %Co/NiCo/CdS composite catalyst also shows good hydrogen evolution performance under the Na2S/Na2SO3 and lactic acid system. The fluorescence (PL), ultraviolet-visible diffuse reflectance (UV-vis) and photoelectrochemical tests show that the coupling of CdS and CoSX/NiCo-LDH not only accelerates the effective transfer of charges, but also greatly increases the absorption range of CdS to visible light. Therefore, the hydrogen evolution activity of the composite photocatalyst has been significantly improved. This work will provide new insights for the construction of new co-catalysts and the development of composite catalysts for hydrogen evolution in multiple systems. 相似文献
962.
963.
Ko-Hsiu Lu Heng-Hsiung Wu Renn-Chia Lin Ya-Chiu Lin Peace Wun-Ang Lu Shun-Fa Yang Jia-Sin Yang 《Molecules (Basel, Switzerland)》2021,26(1)
Osteosarcoma, the most prevalent malignant bone tumor in the pediatric age group, is responsible for the great majority of cancer-associated deaths owing to its highly metastatic potential. The anti-metastatic effects of the new curcumin analogue L48H37 in human osteosarcoma are still unknown; hence, we investigated whether L48H37 represses human osteosarcoma cells’ biological behavior of migratory potential and invasive activities and attempted to delve into its underlying mechanisms. L48H37 up to 5 μM inhibited, without cytotoxicity, the motility, migration, and invasion of human osteosarcoma U2OS and MG-63 cells. In U2OS cells, the human protease array revealed an obvious decrease in urokinase plasminogen activator (uPA) expression after L48H37 treatment, and L48H37 actually reduced the level, protein and mRNA expression, and promoter activity of uPA dose-dependently. L48H37 decreased the phosphorylation of STAT3, JAK1, JAK2, and JAK3 in U2OS cells, but did not affect the phosphorylation of ERK, JNK, p38, and Akt. Using colivelin, an activator of STAT3, the L48H37-induced decrease in uPA and migratory potential could be countered as expected. Collectively, L48H37 represses the invasion and migration capabilities of U2OS and MG-63 cells by the suppression of uPA expression and the inhibition of JAK/STAT signaling. These results suggest that L48H37 may be a potential candidate for anti-metastatic treatment of human osteosarcoma. 相似文献
964.
Prof. Dr. Xiaoqing Liu Xue Li Prof. Dr. Xiaoqian Yao Prof. Dr. Weizhen Zhao Prof. Dr. Lei Liu 《Chemphyschem》2021,22(10):968-974
Nowadays, hydrogen activation by frustrated Lewis pairs (FLPs) and their applications are one of the emerging research topics in the field of catalysis. Previous studies have shown that the thermodynamics of this reaction is determined by electronic structures of FLPs and solvents. Herein, we investigated systems consisting of typical FLPs and ionic liquids (ILs), which are well known by their large number of types and excellent solvent effects. The density functional theory (DFT) calculations were performed to study the thermodynamics for H2 activation by both inter- and intra-molecular FLPs, as well as the individual components. The results show that the computed overall Gibbs free energies in ILs are more negative than that computed in toluene. Through the thermodynamics partitioning, we find that ILs favor the H−H cleavage elemental step over the elemental steps of proton attachment, hydride attachment and zwitterionic stabilization. Moreover, the results show that these effects are strongly dependent on the type of FLPs, where intra-molecular FLPs are more affected compared to the inter-molecular FLPs. 相似文献
965.
Hanen Khadhraoui Abdelhak Othmani Abdessalem Kouki Mouldi Zouaoui 《Electroanalysis》2021,33(1):152-159
In this work we report an easy and efficient way to fabricate nanostructured cobalt oxide (Co3O4) thin films as a non-enzymatic sensor for H2O2 detection. Co3O4 thin films were grown on ITO glass substrates via the sol-gel method and characterized with several techniques including X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and optical absorbance. The Co3O4 thin films’ performance regarding hydrogen peroxide detection was studied in a 0.1 M NaOH solution using two techniques, cyclic voltammetry (CV) and amperometry. The films exhibited a high sensitivity of 1450 μA.mM−1.cm−2, a wide linear range from 0.05 μM to 1.1 mM, and a very low detection limit of 18 nM. Likewise, the Co3O4 thin films produced showed an exceptional stability and a high selectivity. 相似文献
966.
N. N. Tonkikh K. V. Ryzhanova M. V. Petrova A. Strakovs 《Chemistry of Heterocyclic Compounds》2003,39(5):651-653
By reaction of 6-dimethylamino-5-oxo-2-phenyl-5,6,7,8-tetrahydroquinazoline with hydrazine, phenylhydrazine, 4-bromo-, 4-chlorophenylhydrazines, and also reaction of 6-dimethylaminomethylene-5-oxo-2-(4-pyridyl)-5,6,7,8-tetrahydroquinazoline with hydrazine, 4-methoxy- and 2-carboxyphenylhydrazines, we have obtained the corresponding 7-phenyl(4-pyridyl)-substituted 1H(2H)- or 1-aryl-4,5-dihydropyrazolo[3,4-f]quinazolines. Methylation of 7-phenyl-4,5-dihydro-1(2H)-pyrazolo[3,4-f]quinazoline by methyl iodide led to its 2-methyl derivative. 相似文献
967.
On dehydration of La[Co(CN)6]·5H2O, the color of the complex, changes from white to pale blue at around 230°C. Heating the pale blue specimen, the color changes
to deep blue at around 290°C. This deep blue specimen is easily rehydrated to a pink one. As reported previously, in the pale
blue specimen, Co3+ ions are situated in the center of the D4h crystal field formed by six CN- ions.
The deep blue specimen is due to the presence of [Co(CN)4]2- ions in which Co2+ was situated in a Td coordination field formed by four CN- ions and the Co-C bond length is 1.67 Ĺ. The pink species corresponded to trans-[Co(CN)4(H2O)2]2- and the bond lengths of Co-C and Co-O are 1.89 and 1.85 Ĺ, respectively.
The Raman spectra of the complex observed at 25°C displays two bands at 2157 and 2176 cm-1 associated with the vibration of C-N bond, and the band of 2157 cm-1 was split into two bands, 2150 and 2156 cm-1, at around 100°C. When the complex was heated to around 230°C, three new bands were observed at 2103, 2116 and 2141 cm-1.
The bands of 2103 and 2116 cm-1 were assigned to the stretching vibration of C=N bonding to Co2+. The band of 2141 cm-1 was assigned to the stretching vibration of the inverted CN- as follows: Co-C=N-La→Co-N=C-La. The activation energy for the inversion of CN- was estimated as 67 kJ mol-1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
968.
ZHANG Cong-jie CAO Ze-xing ** ZHANG Qian-er . State Key Laboratory for Physical Chemistry of Solid Surface Department of Chemistry Center for Theoretical Chemistry Xiamen University Xiamen P. R. China . Department of Chemistry Shanxi Normal University Linfen P. R. China 《高等学校化学研究》2003,(4)
IntroductionCarbon chains are among the most attractivecandidates as the carriers of the diffuse interstellarbands ( DIBs) [1] .To detect the carbon chains indark clouds and carbon stars[2 ] ,itis very importantto understand their electronic spectra.Maier andhis coworkers have measured the polyacetylenicradicals C2 n H( n=1— 4) and C2 n-1H( n=2— 6) bythe rotational spectroscopy[3 ,4] and the species n≤ 4have been detected in dark interstellar clouds[5,6] .In neon matrices,the B2 Π← X2… 相似文献
969.
Lam WH Jia G Lin Z Lau CP Eisenstein O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(12):2775-2782
Theoretical calculations on the metathesis process, [Tp(PH3)MR(eta 2-H[bond]CH3)] --> [Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe, Ru, and Os; R=H and CH3), have been systematically carried out to study their detailed reaction mechanisms. Other than the one-step mechanism via a four-center transition state and the two-step mechanism through an oxidative addition/reductive elimination pathway, a new one-step mechanism, with a transition state formed under oxidative addition, has been found. Based on the intrinsic reaction coordinate calculations, we found that the trajectories of the transferring hydrogen atom in the metathesis processes studied are similar to each other regardless of the nature of reaction mechanisms. 相似文献
970.
Summary The chromatographic mobility of 21H, 23H-porphine and its Ni(II), Cu(II), Zn(II) and Pd(II) complexes were investigated by high-performance thin-layer chromatography on an octadecyl-bonded, silica gel plate with various polar organic solvents including alcohols, acetonitrile, dimethylsulfoxide and propylenecarbonate. The mobility generally decreases according to the central metal ion of the complex as follows: Zn(II)>(free porphine)>Ni(II)>Pd(II)>Cu(II). Methanol is a good choice of solvent for the separation of these metal porphine complexes. Successful separation of porphine and the four metal complexes is accomplished within 13 min on a LiChrosorb RP-18 column with methanol eluent. 相似文献