全文获取类型
收费全文 | 1171篇 |
免费 | 65篇 |
国内免费 | 2篇 |
专业分类
化学 | 717篇 |
晶体学 | 5篇 |
力学 | 23篇 |
数学 | 300篇 |
物理学 | 193篇 |
出版年
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 17篇 |
2020年 | 18篇 |
2019年 | 31篇 |
2018年 | 33篇 |
2017年 | 26篇 |
2016年 | 86篇 |
2015年 | 45篇 |
2014年 | 52篇 |
2013年 | 85篇 |
2012年 | 101篇 |
2011年 | 105篇 |
2010年 | 49篇 |
2009年 | 47篇 |
2008年 | 75篇 |
2007年 | 56篇 |
2006年 | 60篇 |
2005年 | 53篇 |
2004年 | 36篇 |
2003年 | 29篇 |
2002年 | 21篇 |
2001年 | 11篇 |
2000年 | 16篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1978年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1963年 | 2篇 |
1912年 | 2篇 |
排序方式: 共有1238条查询结果,搜索用时 31 毫秒
91.
An efficient and operationally simple synthesis of the neodolestane diterpenoids (±)-heptemerone G and (±)-guanacastepene A is reported. The common tricyclic scaffold (±)-4 was prepared from 2-methylcyclopent-2-en-1-one via 23 isolated intermediates in 5.1% yield. The key features include a novel annulation sequence combining tandem conjugate addition, methylenation, and metathesis reaction and completely diastereoselective transformation of the azulene derivative 23 into rings AB building block 32. Stereochemistry of alkylation of both saturated trans-azulene enolate 38 and its α,β-unsaturated counterpart 48 was examined. Rather surprisingly, a different facial selectivity was recorded. Several synthetic methods were modified or developed, including an alternative methodology for the Wharton-type rearrangement, ketalization of epimerizable ketone under mild conditions, and efficient alkylation of a ketone via its kinetic enolate. 相似文献
92.
Zofia?Krystyna?DrzazgaEmail author Karina?Maciejewska Katarzyna?Michalik Micha??Kaszuba Barbara?Nowińska 《Journal of fluorescence》2011,21(3):883-886
The influence of antiretroviral drug zidovudine treatment during pregnancy on mandible development in newborn rats was studied. The fluorescence of mandibles from 7-, 14-
and 28-days old individuals was measured by means of fiber-optical fluorescence analyzer with 407 nm laser excitation. Obtained
results revealed disturbing effect of maternal zidovudine administration on mandible fluorescence intensity which should decrease with bone development. Small changes in fluorescence
of porphyrin forms are maintaining in the first month of newborns life while the changes observed in 440–585 nm range disappear. 相似文献
93.
Leszek Krzemień Krzysztof Brzozowski Marcin Witkowski Micha? Zawada 《Optics Communications》2011,284(5):1247-1253
We present a method of Doppler-free laser frequency stabilization based on magnetically assisted rotation spectroscopy (MARS) which combines the Doppler-free velocity-selective optical pumping (VSOP) and magnetic rotation spectroscopy. The stabilization is demonstrated for the atomic rubidium transitions at 780 nm. The proposed method is largely independent of stray magnetic fields and does not require any modulation of the laser frequency. Moreover, the discussed method allows one to choose between locking the laser exactly to the line center, or with a magnetically-controlled shift to an arbitrary frequency detuned by up to several natural linewidths. This feature is useful in many situations, e.g. for laser cooling experiments. In addition to presenting the principle of the method, its theoretical background and peculiarities inherent to the repopulation VSOP are discussed. 相似文献
94.
Nixon M Friedman M Ronen E Friesem AA Davidson N Kanter I 《Physical review letters》2011,106(22):223901
We experimentally investigate the phase dynamics of laser networks with homogenous time-delayed mutual coupling and establish the fundamental rules that govern their state of synchronization. We identified a specific substructure that imposes its synchronization state on the entire network and show that for any coupling configuration the network forms at most two synchronized clusters. Our results indicate that the synchronization state of the network is a nonlocal phenomenon and cannot be deduced by decomposing the network into smaller substructures, each with its individual synchronization state. 相似文献
95.
Lau RK Ménard M Okawachi Y Foster MA Turner-Foster AC Salem R Lipson M Gaeta AL 《Optics letters》2011,36(7):1263-1265
We report the first demonstration of cw wavelength conversion from the telecommunications band to the mid-IR (MIR) region via four-wave mixing in silicon nanowaveguides. We measure a parametric bandwidth of 748 nm by converting a 1636 nm signal to produce a 2384 nm idler and show continuously tunable wavelength conversion from 1792 to 2116 nm. This report indicates that the advantages of silicon photonics may be leveraged to create devices for a large range of MIR applications that require cw operation. 相似文献
96.
In this Letter, we introduce an algorithm that overcomes limitations in shape measurement by holographic microscopic methods in cases of micro-optical elements with high NA, such as microlenses. The presented algorithm provides a simple method for shape reconstruction from interferometrically measured phase. The algorithm is based on the analysis of local ray transition through the measured object. We develop algorithms for holographic configurations working in transmission and reflection. The accuracy of the developed algorithms is proved by experiments and extensive simulations. We present an experiment in a holographic Mach-Zehnder configuration where we have measured and successfully reconstructed the height distribution of spherical and cylindrical microlenses with NA up to 0.3. 相似文献
97.
98.
The present paper contains a martingale representation theorem for set-valued martingales defined on a filtered probability space with a filtration generated by a Brownian motion. It is proved that such type martingales can be defined by some generalized set-valued stochastic integrals with respect to a given Brownian motion. The main result of the paper is preceded by short part devoted to the definition and some properties of generalized set-valued stochastic integrals. 相似文献
99.
A generalized Nevanlinna function Q(z) with one negative square has precisely one generalized zero of nonpositive type in the closed extended upper halfplane. The fractional linear transformation defined by Qτ(z)=(Q(z)−τ)/(1+τQ(z)), τ∈R∪{∞}, is a generalized Nevanlinna function with one negative square. Its generalized zero of nonpositive type α(τ) as a function of τ is being studied. In particular, it is shown that it is continuous and its behavior in the points where the function extends through the real line is investigated. 相似文献
100.
Michał Kozak 《Mathematical Logic Quarterly》2014,60(4-5):319-334
We study the sequent system mentioned in the author's work 18 as CyInFL with ‘intuitionistic’ sequents. We explore the connection between this system and symmetric constructive logic of Zaslavsky 40 and develop an algebraic semantics for both of them. In contrast to the previous work, we prove the strong completeness theorem for CyInFL with ‘intuitionistic’ sequents and all of its basic variants, including variants with contraction. We also show how the defined classes of structures are related to cyclic involutive FL‐algebras and Nelson FLew‐algebras. In particular, we prove the definitional equivalence of symmetric constructive FLewc‐algebras (algebraic models of symmetric constructive logic) and Nelson FLew‐algebras (algebras introduced by Spinks and Veroff 33 , 34 as the termwise equivalent definition of Nelson algebras). Because of the strong completeness theorem that covers all basic variants of CyInFL with ‘intuitionistic’ sequents, we rename this sequent system to symmetric constructive full Lambek calculus (). We verify the decidability of this system and its basic variants, as we did in the case of their distributive cousins 18 . As a consequence we obtain that the corresponding theories of (distributive and nondistributive) symmetric constructive FL‐algebras are decidable. 相似文献