全文获取类型
收费全文 | 2779篇 |
免费 | 98篇 |
国内免费 | 15篇 |
专业分类
化学 | 1864篇 |
晶体学 | 89篇 |
力学 | 66篇 |
数学 | 268篇 |
物理学 | 605篇 |
出版年
2023年 | 22篇 |
2022年 | 47篇 |
2021年 | 69篇 |
2020年 | 75篇 |
2019年 | 65篇 |
2018年 | 67篇 |
2017年 | 62篇 |
2016年 | 107篇 |
2015年 | 59篇 |
2014年 | 92篇 |
2013年 | 197篇 |
2012年 | 171篇 |
2011年 | 178篇 |
2010年 | 111篇 |
2009年 | 100篇 |
2008年 | 137篇 |
2007年 | 128篇 |
2006年 | 111篇 |
2005年 | 97篇 |
2004年 | 78篇 |
2003年 | 70篇 |
2002年 | 59篇 |
2001年 | 44篇 |
2000年 | 64篇 |
1999年 | 77篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 20篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 18篇 |
1977年 | 29篇 |
1976年 | 22篇 |
1974年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有2892条查询结果,搜索用时 109 毫秒
121.
Mohanad A. Hussein Dr. Uyen P. N. Tran Dr. Vien T. Huynh Dr. Junming Ho Dr. Mohan Bhadbhade Prof. Dr. Herbert Mayr Dr. Thanh V. Nguyen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(4):1471-1475
Tropylium bromide undergoes noncatalyzed, regioselective additions to a large variety of Michael acceptors. In this way, acrylic esters are converted into β-bromo-α-cycloheptatrienylpropionic esters. The reactions are interpreted as nucleophilic attack of bromide ions at the electron-deficient olefins and the approach of the tropylium ion to the incipient carbanion. Quantum chemical calculations were performed to elucidate the analogy to the amine- or phosphine-catalyzed Rauhut–Currier reactions. Subsequent synthetic transformations of the bromo-cycloheptatrienylated adducts are reported. 相似文献
122.
Amit Vijay Sasane Dr. Antony Sekar Kulandai Raj Tzu-Hsuan Chao Dr. Mu-Jeng Chen Dr. Rai-Shung Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(70):16932-16938
Gold-catalyzed oxidations of propargyl alcohols with nitrones by using a P(tBu)2(o-biphenyl)Au+ catalyst, afforded bicyclic annulation products from the Mannich reactions of gold enolates. The same reactions of propargyl amines with nitrones by using the same gold catalyst gave distinct oxoarylation products. Our DFT calculations indicate that oxidation of propargyl alcohols with nitrones by using electron-rich gold catalysts lead only to gold carbenes, which can generate gold enolates or oxoarylation intermediates with enolate species having a barrier smaller than that of oxoarylation species. 相似文献
123.
Jing He Mohan Yu Maofu Pang Yanqing Fan Zhe Lian Dr. Ying Wang Prof. Wenguang Wang Prof. Yajun Liu Prof. Hua Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(13):e202103832
Structural designs combining cycloparaphenylenes (CPPs) backbone with planar chiral [2.2]paracyclophane ([2.2]PCP) lead to optical-active chiral macrocycles with intriguing properties. X-ray crystal analysis revealed aesthetic necklace-shaped structures and size-dependent packages with long-range channels. The macrocycles exhibit unique photophysical properties with high fluorescence quantum yield of up to 82 %, and the fluorescent color varies with ring size. In addition, size-dependent chiroptical properties with moderately large CPL dissymmetry factor of 10−3 and CPL brightness in the range of 30–40 M−1 cm−1 were observed. 相似文献
124.
Rajneesh Mohan Karthikeyan Krishnamoorthy Sang-Jae Kim 《Solid State Communications》2012,152(5):375-380
Cu-doped ZnO nanorods with different Cu concentrations were synthesized through the vapor transport method. The synthesized nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV–vis spectroscopy. The XRD results revealed that Cu was successfully doped into ZnO lattice. The FE-SEM images showed that the undoped ZnO has needle like morphology whereas Cu-doped ZnO samples have rod like morphology with an average diameter and length of 60–90 nm and 1.5–3 μm respectively. The red shift in band edge absorption peak in UV-vis absorbance spectrum with increasing Cu content also confirm the doping of Cu in ZnO nanorods. The photocatalytic activity of pure and Cu-doped ZnO samples was studied by the photodegradation of resazurin (Rz) dye. Both pure ZnO and the Cu-doped ZnO nanorods effectively removed the Rz in a short time. This photodegradation of Rz followed the pseudo-first-order reaction kinetics. ZnO nanorods with increasing Cu doping exhibit enhanced photocatalytic activity. The pseudo-first-order reaction rate constant for 15 % Cu-doped ZnO is equal to 10.17×10?2min?1 about double of that with pure ZnO. The increased photocatalytic activity of Cu-doped ZnO is attributed to intrinsic oxygen vacancies due to high surface to volume ratio in nanorods and extrinsic defect due to Cu doping. 相似文献
125.
Organic halides absorbed without solvent onto sodium phenylsulfinate on alumina (1) gave phenylsulfones (2) under microwave or ultrasound activation. 相似文献
126.
127.
128.
129.
M.V. Madhubabu R. Shankar T. Krishna Y. Satish Kumar Y. Chiranjeevi Ch. Muralikrishna H. Rama Mohan Satish S. More M.V. Basaveswara Rao Raghunadh Akula 《Tetrahedron: Asymmetry》2017,28(12):1803-1807
A convergent approach towards the synthesis of the 2-alkyl-substituted tetrahydroquinoline alkaloid (?)-cuspareine via enantiospecific construction of the (R)-benzyl 2-formyl-3,4-dihydroquinoline-1(2H)-carboxylate. We have achieved an efficient enantiospecific synthesis of (?)-cuspareine starting from known key starting materials. The reactions employed for individual transformations are simple and high yielding, and the strategy could potentially be easily extended. 相似文献
130.
Bianchi Type-III cosmological models for perfect fluid distribution with time dependent displacement field in the framework
of Lyra geometry are investigated. To get the deterministic model of the universe, we have assumed two conditions (i) shear
(σ) is proportional to the expansion (θ). This leads to B=C
n
where B and C are metric potentials and n is a constant. (ii) Universe is filled with barotropic fluid distribution which leads to p=γ
ρ, 0≤γ≤1, p being isotropic pressure and ρ the energy density. The physical and geometrical aspects of the model with a special case and singularities in the models
are also discussed. 相似文献