全文获取类型
收费全文 | 10918篇 |
免费 | 622篇 |
国内免费 | 2083篇 |
专业分类
化学 | 10077篇 |
晶体学 | 185篇 |
力学 | 150篇 |
综合类 | 90篇 |
数学 | 1350篇 |
物理学 | 1771篇 |
出版年
2024年 | 11篇 |
2023年 | 122篇 |
2022年 | 308篇 |
2021年 | 245篇 |
2020年 | 245篇 |
2019年 | 254篇 |
2018年 | 226篇 |
2017年 | 283篇 |
2016年 | 301篇 |
2015年 | 249篇 |
2014年 | 320篇 |
2013年 | 819篇 |
2012年 | 575篇 |
2011年 | 721篇 |
2010年 | 615篇 |
2009年 | 818篇 |
2008年 | 795篇 |
2007年 | 761篇 |
2006年 | 708篇 |
2005年 | 644篇 |
2004年 | 654篇 |
2003年 | 490篇 |
2002年 | 451篇 |
2001年 | 333篇 |
2000年 | 350篇 |
1999年 | 260篇 |
1998年 | 220篇 |
1997年 | 242篇 |
1996年 | 208篇 |
1995年 | 229篇 |
1994年 | 207篇 |
1993年 | 173篇 |
1992年 | 157篇 |
1991年 | 115篇 |
1990年 | 87篇 |
1989年 | 88篇 |
1988年 | 56篇 |
1987年 | 30篇 |
1986年 | 45篇 |
1985年 | 23篇 |
1984年 | 27篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1981年 | 29篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
采用SCF-X_α-MS方法, 对于C(2×2)S/Fe(001)吸附体系, 选择Fe_5S和Fe_9S两种原子簇模型, 研究了该吸附体系的电子结构、吸附成键特征及其相互作用图象。结果表明, S吸附于Fe(001)单晶表面具有较强的定域性质, S原子与底物Fe原子之间的吸附相互作用主要表现为S(3p)-Fe(4s,3d)之间的轨道相互作用。通过对表面吸附键长的优化, 其结果与X.S.Zhang等的ARPEFS的实验结果一致。 相似文献
102.
On a New Copper Cobalt Borate Oxide with Isolated B2O5 Units: Cu2Co(B2O5)O Single crystals of a new compound with the empirical formula Cu2CoB2O6 were obtained by using a B2O3 flux technique. X-ray single crystal technique led to a new structure type. Cu2CoB2O6 crystallizes monoclinic, space group C-P21/c (No. 14); a = 3.2250(6); b = 14.847(1); c = 9.1171(6) Å; β = 93.67°; Z = 4. All metal sites are octahedrally coordinated and form a two dimensional framework consisting of edge sharing octahedra ribbons. In addition one observes isolated B2O5-units and oxygen which is not coordinated to boron. The far relation to the crystal structure of the mineral Warwickite is illustrated. 相似文献
103.
Yu. V. Tomilov I. V. Kostyuchenko E. V. Shulishov O. M. Nefedov 《Russian Chemical Bulletin》1998,47(4):666-668
The reaction of diazocyclopropane generatedin situ with vinyl bromide occurs as regioselective 1,3-dipolar cycloaddition to give 5-bromospiro(1-pyrazoline-3,1′-cyclopropane)
in ∼60% yield. Reactions of the latter with nucleophilic reagents, which can occur both with retention and opening of the
cyclopropane ring, were studied.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 688–690, April 1998. 相似文献
104.
Enthalpies of dissolution of benzo-15-crown-5 ether (B15C5) in mixtures of acetonitrile with water and in solutions of NaI and NaBPh4 (I=0.05 mol dm–3) in these mixtures were measured at 298.15 K. From the obtained results and appropriate literature data, the thermodynamic functions of B15C5/Na+ complex formation in acetonitrile-water mixtures were determined. The enthalpies of transfer of the complex B15C5/Na+ from pure acetonitrile to the examined mixtures were calculated and are discussed. 相似文献
105.
Designing peptide inhibitors of the p53-MDM2 interaction against cancer is of wide interest. Computational modeling and virtual screening are a well established step in the rational design of small molecules. But they face challenges for binding flexible peptide molecules that fold upon binding. We look at the ability of five different peptides, three of which are intrinsically disordered, to bind to MDM2 with a new Bayesian inference approach (MELD × MD). The method is able to capture the folding upon binding mechanism and differentiate binding preferences between the five peptides. Processing the ensembles with statistical mechanics tools depicts the most likely bound conformations and hints at differences in the binding mechanism. Finally, the study shows the importance of capturing two driving forces to binding in this system: the ability of peptides to adopt bound conformations () and the interaction between interface residues (). 相似文献
106.
V. A. Yanchenko A. M. Demchenko M. O. Lozinskii 《Chemistry of Heterocyclic Compounds》2004,40(4):516-518
We propose a method for obtaining derivatives of 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine by alkylation of 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol by substituted -chloroacetanilides, followed by cyclization of the intermediate by phosphorus oxychloride. 相似文献
107.
2'-azido-2'-deoxyribonucleoside 5'-diphosphates are mechanism-based inhibitors of Ribonucleotide Reductase. Considerable effort has been made to elucidate their mechanism of inhibition, which is still controversial and not fully understood. Previous studies have detected the formation of a radical intermediate when the inhibitors interact with the enzyme, and several authors have proposed possible structures for this radical. We have conducted a theoretical study of the possible reactions involved, which allowed us to identify the structure of the new radical among the several proposals. A new reactional path is also proposed that is the most kinetically favored to yield this radical and ultimately inactivate the enzyme. The energetic involved in this mechanism, both for radical formation and radical decay, as well as the calculated Hyperfine Coupling Constants for the radical intermediate, are in agreement with the correspondent experimental values. This mechanistic alternative is fully coherent with remaining experimental data. 相似文献
108.
Cerium-doped terbium aluminum garnet phosphors, Tb3Al5O12:Ce3+ (TAG:Ce3+), were prepared with different methods: co-precipitation (CP), half dry-half wet (HDHW), sol-combustion (SC) and Pechini method plus conventional solid state reaction (SS) method. Comparative study on the phase-formation, particle size, morphologies and luminescent characteristics of the phosphors synthesized with different methods was carried out by means of XRD, FE-SEM and photoluminescence (PL) analysis and SC method was confirmed by the comparison of the results to be an easy and an effective process for preparing efficient and nano-sized Tb3Al5O12:Ce3+ phosphors. Various factors influencing particle size, morphology and PL of the phosphors, such as precursor preparation, reaction temperature and heating time, were also investigated. Light-emitting diodes (LEDs) were fabricated with each phosphor and a ∼460 nm emitting InGaN chip. The LEDs from SS, HDHW and CP exhibit strong white emission while those from SC and Pechini emit yellow, revealing that the emission characteristics of LEDs are influenced not only by the morphology and the particle size of the phosphors, but also by the preparing process of the phosphors. 相似文献
109.
Gertraud Chiste Helmut Egg Klemens Kraus Elisabeth Pipitz Elisabeth Spanyar 《Monatshefte für Chemie / Chemical Monthly》1991,122(6-7):537-544
Summary A new method for the synthesis of 1,2-diaryl-1,2-dihydro-5-methyl-3H-pyrazol-3-ones3 and 4-acetyl-1,2-diaryl-1,2-dihydro-5-methyl-3H-pyrazol-3-ones5 is presented. The reaction of 4,4-disubstituted 1,2-diarylhydrazines1 with acetic anhydride in the presence of an equimolar amount of 4-(dimethylamino)pyridine leads to mixtures of the corresponding acetyl derivatives2 and3. Under the same conditions, 2,2-disubstituted 1,2-diarylhydrazines yield mixtures of3 and5.
4-(Dimethylamino)pyridin-katalysierte Reaktion von 1,2-Diarylhydrazinen mit Essigsäureanhydrid
Zusammenfassung Eine neue Methode zur Synthese von 1,2-Diaryl-1,2-dihydro-5-methyl-3H-pyrazol-3-onen3 und 4-Acetyl-1,2-diaryl-1,2-dihydro-5-methyl-3H-pyrazol-3-onen5 wird beschrieben. Die Reaktion von 4,4-disubstituierten 1,2-Diaryl-hydrazinen1 mit Essigsäureanhydrid führt in Gegenwart eines Äquivalentes 4-(Dimethylamino)pyridin zu Gemischen der entsprechenden Acetylderivate2 und3. Unter den gleichen Bedingungen werden aus 2,2-disubstituierten 1,2-Diarylhydrazinen Gemische aus3 und5 erhalten.相似文献
110.
Microwave synthesis,characterization and catalytic properties of titanium-incorporated ZSM-5 zeolite
Taihuan Jin Young Kyu Hwang Do-Young Hong Sung Hwa Jhung Jin-Soo Hwang San-Eon Park Young Ho Kim Jong-San Chang 《Research on Chemical Intermediates》2007,33(6):501-512
Titanium-incorporated ZSM-5 zeolites (Si/Al = 50–200 and Si/Ti = 70) were successfully synthesized in a one-step sol-gel process
under microwave irradiation. The characteristics of Ti-ZSM-5 zeolites were investigated using X-ray power diffraction, UV/Vis-DRS,
FT-IR spectroscopy and solid-state 27Al-NMR to monitor the physico-chemical properties. Simultaneously, the acidic properties were characterized by the NH3-TPD profile. The characterization results revealed that the Ti4+ and Al3+ ions were well incorporated into the framework of Ti-ZSM-5 zeolite. The prepared zeolite was moderately active but selective
in the dehydration of methanol to dimethyl ether. 相似文献