全文获取类型
收费全文 | 7298篇 |
免费 | 186篇 |
国内免费 | 43篇 |
专业分类
化学 | 5563篇 |
晶体学 | 75篇 |
力学 | 88篇 |
数学 | 345篇 |
物理学 | 1456篇 |
出版年
2023年 | 37篇 |
2021年 | 73篇 |
2020年 | 90篇 |
2019年 | 103篇 |
2018年 | 64篇 |
2017年 | 49篇 |
2016年 | 117篇 |
2015年 | 134篇 |
2014年 | 145篇 |
2013年 | 341篇 |
2012年 | 365篇 |
2011年 | 468篇 |
2010年 | 233篇 |
2009年 | 272篇 |
2008年 | 483篇 |
2007年 | 418篇 |
2006年 | 479篇 |
2005年 | 405篇 |
2004年 | 372篇 |
2003年 | 344篇 |
2002年 | 337篇 |
2001年 | 175篇 |
2000年 | 163篇 |
1999年 | 114篇 |
1998年 | 81篇 |
1997年 | 87篇 |
1996年 | 85篇 |
1995年 | 69篇 |
1994年 | 80篇 |
1993年 | 82篇 |
1992年 | 92篇 |
1991年 | 77篇 |
1990年 | 67篇 |
1989年 | 67篇 |
1988年 | 56篇 |
1987年 | 69篇 |
1986年 | 57篇 |
1985年 | 81篇 |
1984年 | 77篇 |
1983年 | 50篇 |
1982年 | 46篇 |
1981年 | 65篇 |
1980年 | 51篇 |
1979年 | 62篇 |
1978年 | 56篇 |
1977年 | 34篇 |
1976年 | 40篇 |
1975年 | 39篇 |
1974年 | 38篇 |
1973年 | 30篇 |
排序方式: 共有7527条查询结果,搜索用时 15 毫秒
1.
Dr. Yogesh Kumar Maurya Dr. Pingchun Wei Takahide Shimada Dr. Kazuhisa Yamasumi Dr. Shigeki Mori Prof. Dr. Ko Furukawa Dr. Hajime Kusaba Prof. Dr. Tatsumi Ishihara Prof. Dr. Yongshu Xie Dr. Masatoshi Ishida Prof. Dr. Hiroyuki Furuta 《化学:亚洲杂志》2021,16(7):743-747
A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C−C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials. 相似文献
2.
Homohelicity induction of a series of propylene-linked zinc bilinone (ZnBL; linear tetrapyrrople-zinc(II) complex) dimers upon complexation with chiral amine and α-amino esters was investigated. Introduction of substituents such as dimethyl and diisobutyl to the central carbon of the propylene spacer gave rise to stabilization of the homohelical (PP and MM) conformers rather than the heterohelical (PM) conformer. As bulkiness of the substituent increased, stability of the homohelical conformers was raised. The preorganization of the homohelical structures led to significantly amplified homohelicity induction upon complexation with chiral amine and α-amino esters. 相似文献
3.
4.
Hiroyuki Saimoto Tomoyuki Onitsuka Satoko Okabe Minoru Morimoto 《Tetrahedron letters》2004,45(48):8777-8780
Treatment of 1,3-dihydroxyacetone and acrolein with aqueous KOH gave a tetrahydrofuran derivative, 1,4-dihydroxy-3,7-dioxabicyclo[3.3.0]octane, in 80% yield. Similarly, 6-alkyl substituted 1,4-dihydroxy-3,7-dioxabicyclo[3.3.0]octanes were obtained by reaction of 1,3-dihydroxyacetone with various α,β-unsaturated aldehydes. In the cases of long chain alkenals, the reaction was effectively accelerated in the presence of organic co-solvent. On the other hand, the corresponding tricyclic products were synthesized by reaction of 1,3-dihydroxyacetone with cyclic enones, such as 2-cyclopentenone and 2-cyclohexenone. This method was successfully applied to the reaction of a tetrulose in the absence of any protecting groups. 相似文献
5.
It is theoretically predicted that the Nernst coefficient is strongly suppressed and the thermal conductance is quantized in the quantum Hall regime of the two-dimensional electron gas. The Nernst effect is the induction of a thermomagnetic electromotive force in the y-direction under a temperature bias in the x-direction and a magnetic field in the z-direction. The quantum nature of the Nernst effect is analyzed with the use of a circulating edge current and is demonstrated numerically. The present system is a physical realization of the non-equilibrium steady state. 相似文献
6.
Yoshiko Oi Nakamura 《Surface science》1987,180(2-3):518-549
By using a quantized theory of non-radiative surface plasmon in a semi-infinite electron gas, where retardation is taken into account, the differential surface loss intensity of electrons in a metal foil is calculated for the case of non-normal incidence of electron to the metal surface. The result shows that the differential surface loss intensity neither has a zero at θ = 0 for the case of normal incidence nor has a zero at a forward direction (θ ≠ 0, φ = 0) for the case of non-normal incidence, whose existences were predicted by electrostatic theories, but diverges as 1/θ at θ = 0 for both cases. It is also shown that, when the angle of incidence is greater than a certain critical value, there is a region of direction to which incident electrons can be scattered by exciting any one of surface plasmons with three different wave vectors. 相似文献
7.
Dehydropeptides containing dehydroamino acid (ΔAA) are frequently found in natural resources with important biological activity. Herein, we report the selective synthesis of Z- and E-ΔAbu from l- and l-allo-threonine as starting materials through selenation and oxidative elimination. The detailed reaction mechanism of phosphine-assisted selenoether formation is also discussed. 相似文献
8.
Takayuki Yaegashi Shinya Yodoya Masahiko Nakamura Hiroki Takeshita Katsuhiko Takenaka Tomoo Shiomi 《Journal of polymer science. Part A, Polymer chemistry》2004,42(4):999-1007
Free‐radical homo‐ and copolymerization behavior of N,N‐diethyl‐2‐methylene‐3‐butenamide (DEA) was investigated. When the monomer was heated in bulk at 60 °C for 25 h without initiator, rubbery, solid gel was formed by the thermal polymerization. No such reaction was observed when the polymerization was carried out in 2 mol/L of benzene solution with with 1 mol % of azobisisobutyronitrile (AIBN) as an initiator. The polymerization rate (Rp) equation was Rp ∝ [DEA]1.1[AIBN]0.51, and the overall activation energy of polymerization was calculated 84.1 kJ/mol. The microstructure of the resulting polymer was exclusively a 1,4‐structure where both 1,4‐E and 1,4‐Z structures were included. From the product analysis of the telomerization with tert‐butylmercaptan as a telogen, the modes of monomer addition were estimated to be both 1,4‐ and 4,1‐addition. The copolymerizations of this monomer with styrene and/or chloroprene as comonomers were also carried out in benzene solution at 60 °C. In the copolymerization with styrene, the monomer reactivity ratios obtained were r1 = 5.83 and r2 = 0.05, and the Q and e values were Q = 8.4 and e = 0.33, respectively. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 999–1007, 2004 相似文献
9.
Lian-Chun Park Tatsuo Maruyama Noriho Kamiya Masahiro Goto Hiroyuki Kuma Naotaka Hamasaki 《Analytical sciences》2004,20(11):1609-1611
The emergence of drug-resistant hepatitis B virus (HBV) has been reported in patients with prolonged administration of lamivudine, which is a potent drug for the prevention of HBV infection. Lamivudine-resistant HBV has several types of mutations at the YMDD motif of its DNA polymerase. We successfully demonstrated that monitoring the hybridization behavior in nanostructured reverse micelles enables us to detect single nucleotide polymorphisms (SNPs). With the aid of reverse micelles, a model 40-mer oligonucleotide containing a single-base substitution was clearly distinguished from the normal, complementary oligonucleotide. In addition, we extended this technique to a high-throughput analysis. The results obtained with a 96-well micro-plate reader indicated the possibility of SNPs detection toward multiple samples of patients. 相似文献
10.
H. Yonemura S. Moribe K. Hayashi M. Noda H. Tokudome S. Yamada H. Nakamura 《Applied magnetic resonance》2003,23(3-4):289-307
Photoinduced intramolecular electron-transfer reactions in carbazole (Cz)-fullerene (C60) (Cz(8)C60) and phenothiazine (Ph)-C60 (Ph(n)C60 (n=8, 10, 12)) linked compounds have been investigated in benzene and benzonitrile by fluorescence, transient absorption, and time-resolved electron paramagnetic resonance measurements, and by magnetic field effects on the decay rate constants of the photogenerated biradicals. In benzonitrile, photoinduced intramolecular electron transfer from Cz to the singlet excited state of C60 (1C60 *) occurred in Cz(8)C60, but not to the triplet excited state (3C60 *), while the intramolecular electron-transfer to both1C60 * and3C60 * occurred in Ph(n)C60 (n=8, 10, 12). In benzene, on the other hand, no electron transfer to both1C60 * and3C60 * took place in all linked compounds. These results were interpreted in terms of the different Gibbs free energy changes in the two solvents. 相似文献