全文获取类型
收费全文 | 46923篇 |
免费 | 2322篇 |
国内免费 | 5188篇 |
专业分类
化学 | 40796篇 |
晶体学 | 759篇 |
力学 | 221篇 |
综合类 | 196篇 |
数学 | 6893篇 |
物理学 | 5568篇 |
出版年
2024年 | 105篇 |
2023年 | 380篇 |
2022年 | 887篇 |
2021年 | 872篇 |
2020年 | 1042篇 |
2019年 | 2037篇 |
2018年 | 1130篇 |
2017年 | 1874篇 |
2016年 | 1358篇 |
2015年 | 1221篇 |
2014年 | 1623篇 |
2013年 | 3416篇 |
2012年 | 3247篇 |
2011年 | 2710篇 |
2010年 | 2046篇 |
2009年 | 2583篇 |
2008年 | 2863篇 |
2007年 | 3061篇 |
2006年 | 2658篇 |
2005年 | 2312篇 |
2004年 | 2265篇 |
2003年 | 1860篇 |
2002年 | 1540篇 |
2001年 | 1311篇 |
2000年 | 1283篇 |
1999年 | 1118篇 |
1998年 | 981篇 |
1997年 | 855篇 |
1996年 | 775篇 |
1995年 | 829篇 |
1994年 | 606篇 |
1993年 | 556篇 |
1992年 | 489篇 |
1991年 | 342篇 |
1990年 | 311篇 |
1989年 | 307篇 |
1988年 | 217篇 |
1987年 | 186篇 |
1986年 | 198篇 |
1985年 | 188篇 |
1984年 | 147篇 |
1983年 | 68篇 |
1982年 | 99篇 |
1981年 | 88篇 |
1980年 | 74篇 |
1979年 | 83篇 |
1978年 | 54篇 |
1977年 | 55篇 |
1976年 | 37篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The behavior of hexafluoroacetone ethoxycarbonylimine in cyclocondensation with different binucleophiles of the amidine type, viz., amino derivatives of N- and N,S-heterocycles, was studied. A preparative method for the synthesis of previously unknown annelated 2,2-bis(trifluoromethyl)-1,3,5-triazinones was developed. 相似文献
72.
73.
根据在自由基引发剂存在下,8,9-苯并-2-亚甲基-1,4,6-三氧螺(4,4)壬烷(Ⅰ)可能存在的竞争反应,推导了动力学方程式。用红外光谱法测定了单体的消失速率和苯酞的生成速率。实验结果与推导动力学方程式相符。进一步证明了单体(Ⅰ)的增长反应由加成聚合和开环—异构化—加成这两个反应组成。这两个反应对总速率的相对贡献与单体浓度有关。得到了共聚物的结构。 相似文献
74.
Gengliang Yang Zhiwei Li Dexian Wang Zhefeng Zhang Erdong Liu Yi Chen 《Chromatographia》2002,56(7-8):515-518
Summary A high-performance liquid chromatographic method was developed for the chiral separation of a new anti-diabetic agent, N-(trans-4-isopropylcyclohexylcarbonyl)-D-phenylalanine,
and its L-enantiomer. The separation was performed on a Sumichiral OA-3300 column. Optimized mobile phase was 0.025 mol.L−1 ammonium acetate in methanol solution. UV detection was at 210 nm. Baseline chiral separation was obtained within 12 minutes.
The detection limits are 80 pg for the D-enantiomer and 120 pg for the L-enantiomer. RSD of the method was below 1% (n=5). 相似文献
75.
Joan Fraga-DubreuilJean Pierre Bazureau 《Tetrahedron》2003,59(32):6121-6130
The first report of the use of task-specific ionic liquid as synthetic equivalent of ionic liquid-phase matrice for the preparation of a small library of 4-thiazolidinones is reported in this paper. The starting (ethyleneglycol)ionic liquid-phase is functionalized in good yields with 4-(formylphenoxy)butyric acid by using usual esterification reaction conditions (DCC/DMAP as catalyst). The synthesis of the ionic liquid-phase bound 4-thiazolidinones was performed by a one-pot three-component condensation under microwave dielectric heating. The final cleavage under microwave/catalysis strategy provides the expected 4-thiazolidinones in high purity after flash-chromatography purification. According to the ionic liquid-phase organic synthesis (IoLiPOS) methodology, it was found that optimized reaction conditions were performed by standard analytical methods (NMR, TLC). The 1H, 13C NMR spectrum of some representative 4-thiazolidinones and ionic liquid-phase bound benzaldehyde are also reported. 相似文献
76.
Fátima Nunes Serralha José Madeira Lopes Francisco Lemos Duarte Prazeres Maria Aires-Barros Joo Rocha Joaquim Cabral Fernando Ramôa Ribeiro 《Reaction Kinetics and Catalysis Letters》2000,69(2):217-222
Novel [CrIII(amp)(bipy)(Cl)] (1) (H2amp = N-(hydroxyphenyl)salicyldimine; bipy = 2,2-bipyridyl) and [CrIII(app)(bipy)(Cl)]+ (2) (H2app = N-(hydroxyphenyl)pyridine-2-carboxaldimine; bipy = 2,2-bipyridyl) complexes have been synthesized and characterized by physico-chemical methods. Complexes 1 and 2 have been employed as catalysts in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). The significance of the results with respect to oxo-functionalization of C-H bonds both in unsaturated and saturated hydrocarbons is noted. 相似文献
77.
K L Madhok 《Journal of Chemical Sciences》1982,91(2):165-171
Nicke(II) chloride reacts with N,N′-diarylformamidino-N′-arylcarbamides thiocarbamides and N-benzoylformamidino-N′-arylcarbamides,
thiocarbamides forming complexes of the general formula [Ni (Ar.NH.C (NH) NH.C.X. NH.R)2] Cl2 (R=phenyl, orthotolyl and paratolyl; Ar=benzoyl; X=S,O) and [Ni (R.NH.C.X.NH.C (N.Ph.).NH.Ph.)2] Cl2 (R=phenyl, orthotolyl, paratolyl; Ph=phenyl; X=S, O). The ligands when oxidized with iodine undergo ring closure to related
3,5-diarylamino 1,2,4-thiadiazolidines and 3,5-diarylamino-1,2,4-diazolidines, while the complexes are not susceptible to
oxidation. This confirms the binding in complexes is through sulphur and oxygen of the ligands. 相似文献
78.
79.
JIANG Qi-Jun 《结构化学》2005,24(10):1140-1144
1 INTRODUCTION The electron-transfer reaction of C60 derivatives, especially light-induced electron-transfer reaction, has been an active research field for a long time. Many researches are focused on the long-live charge- separated state caused by electron-transfer[1]. And several electron-transfers between electron donor and C60 or intramolecular electron-transfer have been confirmed. As an example, TTF-C60 is proved to be a short-live charge-separated compound[2].Due to the excelle… 相似文献
80.
Hao Li 《Tetrahedron letters》2007,48(12):2209-2211
2,2′-Disubstituted ferrocenecarboxaldehydes are subjected to zinc-mediated allylation to form homoallylic ferrocenyl alcohols. The effects of ortho-substituted functional groups on facial selectivities of planar chiral aldehydes were studied and it was found that the corresponding homoallylic alcohols were obtained as single diastereomers in excellent yields. 相似文献