全文获取类型
收费全文 | 1826篇 |
免费 | 59篇 |
国内免费 | 16篇 |
专业分类
化学 | 1145篇 |
晶体学 | 31篇 |
力学 | 65篇 |
数学 | 280篇 |
物理学 | 380篇 |
出版年
2021年 | 16篇 |
2020年 | 23篇 |
2019年 | 14篇 |
2017年 | 12篇 |
2016年 | 40篇 |
2015年 | 41篇 |
2014年 | 25篇 |
2013年 | 78篇 |
2012年 | 72篇 |
2011年 | 96篇 |
2010年 | 36篇 |
2009年 | 37篇 |
2008年 | 60篇 |
2007年 | 87篇 |
2006年 | 87篇 |
2005年 | 86篇 |
2004年 | 66篇 |
2003年 | 77篇 |
2002年 | 72篇 |
2001年 | 47篇 |
2000年 | 48篇 |
1999年 | 33篇 |
1998年 | 22篇 |
1997年 | 21篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 30篇 |
1993年 | 30篇 |
1992年 | 35篇 |
1991年 | 42篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1986年 | 19篇 |
1985年 | 26篇 |
1984年 | 32篇 |
1983年 | 21篇 |
1982年 | 32篇 |
1981年 | 32篇 |
1980年 | 17篇 |
1979年 | 26篇 |
1978年 | 20篇 |
1977年 | 22篇 |
1976年 | 13篇 |
1975年 | 23篇 |
1974年 | 18篇 |
1973年 | 15篇 |
1972年 | 12篇 |
1971年 | 15篇 |
1968年 | 11篇 |
排序方式: 共有1901条查询结果,搜索用时 15 毫秒
141.
Using an optical technique we generate and detect picosecond shear and quasishear coherent acoustic phonon pulses in the time domain. Thermoelastic and piezoelectric generation are directly achieved by breaking the sample lateral symmetry using crystalline anisotropy. We demonstrate efficient detection in isotropic and anisotropic media with various optical incidence geometries. 相似文献
142.
We report the experimental demonstration of spectral encoding of the polarization state of light by use of multiplexed distributed-feedback lasers in a dye-doped organic thin film by exploiting the pump polarization selectivity of the superimposed resonators. Measurement of the Stokes parameters of the pump light without a priori knowledge of the lasing properties of the structure is discussed. 相似文献
143.
The unprecedented reactivity of Co(4)(CO)(12) with enynes under aqueous conditions, representing the development of a mild and simple aqueous-phase cobalt-catalyzed PK reaction protocol, is described herein. 相似文献
144.
Ding WX Brower DL Terry SD Craig D Prager SC Sarff JS Wright JC 《Physical review letters》2003,90(3):035002
Magnetic field fluctuations (and the associated current perturbation) have been measured in the core of a high-temperature reversed-field pinch using a newly developed fast-polarimetry system. Radial magnetic field fluctuation levels of approximately 1% are measured in standard-reversed-field pinch discharges which increase to approximately 4% during the sawtooth crash (enhanced dynamo). The fluctuation level is reduced fourfold for high-confinement plasmas where the core-resonant tearing modes are suppressed. 相似文献
145.
146.
147.
Hirst AR Smith DK Feiters MC Geurts HP Wright AC 《Journal of the American Chemical Society》2003,125(30):9010-9011
This paper reports the tunability of a two-component gel system based on dendritic l-lysine with a focal point carboxylic acid group and aliphatic diamines. The microscopic structure and macroscopic properties of the gel can be modulated by changing the concentration of the components, altering their molecular structures, or tuning their relative molar ratio. In the latter case, there is a complete change in the morphology of the gel that has a direct impact on its macroscopic properties, specifically its gel-sol transition temperature. 相似文献
148.
Solutions of galactose oxidase stored in air give in 3-4 h a mix of GOase(ox)(Cu(II)-Tyr(*)) and GOase(semi)(Cu(II)-Tyr), as a result of processes involving the formation and decay of the Cu(II)-coordinated tyrosyl radical (Tyr(*)). In this work the two reactions have been studied by UV-vis spectrophotometry and separate rate laws defined. The first involves the "spontaneous" autoreduction of GOase(ox) to GOase(semi), which in air-free conditions is 100% complete. Rate constants (k(red)) are dependent on pH, and previously defined acid dissociation constants pK(1a) = 5.7 (exogenous H(2)O ligand), and pK(2a) = 8.0 (axial H(+)Tyr-495) apply. Values of k(red)(25 degrees C) range from 1.55 x 10(-4) s(-1) (pH 5.5) to 2.69 x 10(-4) s(-1) (pH 8.6), I = 0.100 M (NaCl). No reaction occurs with N(3)(-) or NCS(-) present in amounts sufficient to give >98% binding at the substrate binding (exogenous) site, while CH(3)CO(2)(-) and phosphate (less extensively bound) also inhibit the reaction. From such inhibition studies K(25 degrees C) is 161 M(-1) at pH 6.4 for acetate (previous value 140 M(-)(1)) and 46 M(-1) at pH 7.0 for phosphate. No reaction occurs when the disulfide Cys515-Cys518 (10.2 A from the Cu) is chemically modified with HSPO(3)(2-), and electron transfer via the disulfide and exogenous position is proposed (source of the electron not established). The conversion of GOase(semi) to GOase(ox) only occurs with O(2) present, when a first-order dependence on [O(2)] is observed, giving k(ox)(25 degrees C) = 0.021 M(-1) s(-1) at pH 7.5. This process is unaffected by NCS(-) or N(3)(-) bound at the exogenous site, and a mechanism involving outer-sphere reaction of O(2) to O(2)(-) followed by a fast step O(2) to H(2)O(2) is proposed. As GOase(ox) is formed, autoreduction back to GOase(semi) occurs, and at pH 7.5 with O(2) in large excess (1.13 mM) the maximum conversion to GOase(ox) is 69%. The k(ox) reaction proceeds to completion with >98% N(3)(-) bound at the exogenous site. 相似文献
149.
A new strategy for the combinatorial synthesis of new materials has been developed through the consecutive application of an Ugi 4CC reaction and a ring-opening metathesis polymerization (ROMP) reaction. Norbornenyl aldehydes and carboxylic acids could be used in the Ugi MCR to give highly diverse monomers that were converted to the corresponding polymers by exposure to the second-generation Grubbs' catalyst. These polymers have structural features reminiscent of polypeptides and the process could be extended to the preparation of chiral materials. 相似文献
150.
Let R(t)=P(t)/Q(t) be a quotient of real polynomials. We show that ∫exp(iR(t)) dt/t has a uniform bound with a bound depending only on the degrees of P and Q and not on their coefficients. Also
LP estimates are obtained for certain associated singular integral operators. 相似文献