全文获取类型
收费全文 | 1107篇 |
免费 | 54篇 |
国内免费 | 5篇 |
专业分类
化学 | 908篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 132篇 |
物理学 | 114篇 |
出版年
2023年 | 8篇 |
2022年 | 34篇 |
2021年 | 37篇 |
2020年 | 32篇 |
2019年 | 32篇 |
2018年 | 24篇 |
2017年 | 23篇 |
2016年 | 50篇 |
2015年 | 36篇 |
2014年 | 32篇 |
2013年 | 66篇 |
2012年 | 84篇 |
2011年 | 104篇 |
2010年 | 48篇 |
2009年 | 39篇 |
2008年 | 84篇 |
2007年 | 79篇 |
2006年 | 60篇 |
2005年 | 54篇 |
2004年 | 47篇 |
2003年 | 39篇 |
2002年 | 31篇 |
2001年 | 9篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1935年 | 1篇 |
1934年 | 2篇 |
排序方式: 共有1166条查询结果,搜索用时 15 毫秒
71.
72.
Patterns typical of Fraunhofer and Fresnel diffractive scattering and of rainbow scattering are considered for elastic nucleus-nucleus scattering in the region of intermediate energies. The interference contributions to the respective differential cross section that are responsible for the formation of these patterns are singled out on the basis of the S-matrix approach. 相似文献
73.
Jorge Labella Gonzalo Durn-Sampedro M. Victoria Martínez-Díaz Toms Torres 《Chemical science》2020,11(39):10778
Here we report gold(i)-catalyzed cycloisomerization as a new powerful synthetic tool for the preparation of π-extended BODIPY derivatives. The catalytic system PPhF3AuCl/AgSbF6 enables the synthesis of [b]-[2,1]naphtho-fused-BODIPYs (2a–2c) under mild conditions, in excellent yields and short reaction times. The reaction is totally regioselective to the 6-endo-dig product and for the α-position of the BODIPY, which is both the kinetically and thermodynamically favored pathway, as supported by the free energy profile calculated by means of Density Functional Theory (DFT). Moreover, this methodology also allows the synthesis of two new families of [b]-aryl-fused-BODIPYs, namely, [3,4]phenanthro- (2e and 2f) and [1,2]naphtho-fused (2g) BODIPYs. Their molecular and electronic structures were established by NMR and UV-vis spectroscopies as well as single-crystal X-ray diffraction analysis. As can be noted from the X-ray structures, 2a, 2e and 2g present interesting structural differences at both the molecular and packing level. Interestingly, despite being isomers, the UV/vis spectra of 2a and 2g revealed significant differences in their electronic structures. The origin of this finding was studied by Time-Dependent DFT calculations. Calculated DFT Nuclear Independent Chemical Shift (NICS(0)) values also supported the different electronic structures of 2a and 2g.Here we report gold(i)-catalyzed cycloisomerization as a new powerful synthetic tool for the preparation of π-extended BODIPY derivatives. 相似文献
74.
Nicholas E. Leadbeater Sharon J. Pillsbury Erik Shanahan Victoria A. Williams 《Tetrahedron》2005,61(14):3565-3585
In the light of the controversy in the area and since reports using simultaneous cooling in conjunction with microwave heating are appearing in the literature, we were keen to assess the methodology, looking at temperature measurement issues as well as the use of the technique in three classes of reaction, namely a Heck coupling, a Diels-Alder cycloaddition and a Michael addition. We present our initial findings here. 相似文献
75.
76.
77.
left order in Q and Q is a semigroup of left quotients of S if every q∈Q can be written as q=a^*b for some a, b∈S where a^* denotes the inverse of a in a subgroup of Q and if,
in addition, every square-cancellable element of S lies in a subgroup of Q. Perhaps surprisingly, a semigroup, even a commutative
cancellative semigroup, can have non-isomorphic semigroups of left quotients. We show that if S is a cancellative left order
in Q then Q is completely regular and the {\cal D}-classes of Q are left groups. The semigroup S is right reversible and its
group of left quotients is the minimum semigroup of left quotients of S.
The authors are grateful to the ARC for its generous financial support. 相似文献
78.
Victoria Gesheva 《Applied biochemistry and biotechnology》2009,158(1):20-24
Experimental mathematical designs were applied for optimization of a nutrient medium for biosynthesis of the antifungal antibiotic
AK-111-81 by phosphate-deregulated mutant of Streptomyces hygroscopicus 111-81. Antifungal antibiotic AK-111-81 possesses well-expressed activity against Fusarium graminearum and other phytopathogenic fungi. The level of the production of the antibiotic AK-111-81 on this medium is more than three
times higher than on the initial medium. The optimized quantitative composition of the nutrient culture media is (g/l): glucose,
20; soy meal, 18; ammonium succinate, 3; CaCO3, 1. 相似文献
79.
Victoria Ivanova Thierry Boghosian Olivier Rabin 《Accreditation and quality assurance》2007,12(9):491-493
This article provides a brief perspective of the World Anti-Doping Agency (WADA) in the context of the fight against doping
in sport and of the WADA Proficiency Testing Program as an essential element of the World Anti-Doping Program. The WADA Proficiency
Testing Program exists within the framework of the WADA-accredited laboratories and is aimed at improving the effectiveness
of the fight against doping by testing the ability of the laboratories to reliably identify and measure the substances and
methods defined in the WADA Prohibited List. The paper provides an overview of the WADA Proficiency Testing scheme with respect
to organization, test composition and evaluation of anti-doping methods and techniques. Scientific research is mentioned in
the context of WADA’s involvement in generating reference materials for improvement of analytical activities of the WADA-accredited
laboratories. WADA’s funding of a reference material for 19-norandrosterone in human urine is illustrated as an example. 相似文献
80.
Victoria Volkis Elena Smolensky Anatoli Lisovskii Moris S. Eisen 《Journal of polymer science. Part A, Polymer chemistry》2005,43(19):4505-4516
The effect of solvents (toluene, dichloromethane, and hexane) was studied on the polymerization of propylene with the octahedral complexes bis(trimethylsilyl)benzamidinate titanium dichloride(a), bis(acetylacetonate) titanium dichloride(b), and bis(diethylamino) titanium di‐2‐(diphenylphosphanylamino)pyridine as catalytic precursors and methylalumoxane as the cocatalyst. For comparison, the polymerization was also performed in plain liquid propylene without the addition of any solvent. The obtained polymers were fractionated by refluxing hexane. The activity of the complexes and the molecular weights and tacticities of the whole polymers and their different fractions were the studied parameters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4505–4516, 2005 相似文献