全文获取类型
收费全文 | 5333篇 |
免费 | 83篇 |
国内免费 | 34篇 |
专业分类
化学 | 2789篇 |
晶体学 | 38篇 |
力学 | 76篇 |
数学 | 470篇 |
物理学 | 1283篇 |
无线电 | 794篇 |
出版年
2019年 | 34篇 |
2017年 | 26篇 |
2016年 | 72篇 |
2015年 | 44篇 |
2014年 | 62篇 |
2013年 | 190篇 |
2012年 | 191篇 |
2011年 | 242篇 |
2010年 | 104篇 |
2009年 | 98篇 |
2008年 | 226篇 |
2007年 | 254篇 |
2006年 | 221篇 |
2005年 | 222篇 |
2004年 | 217篇 |
2003年 | 192篇 |
2002年 | 169篇 |
2001年 | 162篇 |
2000年 | 160篇 |
1999年 | 89篇 |
1998年 | 87篇 |
1997年 | 75篇 |
1996年 | 114篇 |
1995年 | 94篇 |
1994年 | 126篇 |
1993年 | 130篇 |
1992年 | 131篇 |
1991年 | 81篇 |
1990年 | 80篇 |
1989年 | 112篇 |
1988年 | 84篇 |
1987年 | 63篇 |
1986年 | 76篇 |
1985年 | 90篇 |
1984年 | 75篇 |
1983年 | 48篇 |
1982年 | 69篇 |
1981年 | 62篇 |
1980年 | 65篇 |
1979年 | 54篇 |
1978年 | 63篇 |
1977年 | 72篇 |
1976年 | 49篇 |
1975年 | 46篇 |
1974年 | 53篇 |
1973年 | 57篇 |
1972年 | 36篇 |
1971年 | 32篇 |
1970年 | 27篇 |
1968年 | 26篇 |
排序方式: 共有5450条查询结果,搜索用时 15 毫秒
991.
Yoosuf-Aly Z Faraldos JA Miller DJ Allemann RK 《Chemical communications (Cambridge, England)》2012,48(56):7040-7042
The enzyme-guided asymmetric synthesis of (+)-verbenone from geranyl diphosphate in a simple two-step, one pot transformation highlights the potential of chemoenzymatic procedures for the generation of high-value terpenoids. 相似文献
992.
993.
Miller EM Sheps L Lu YJ Case AS McCoy AB Lineberger WC 《The Journal of chemical physics》2012,136(4):044313
Negative-ion photoelectron spectroscopy of ICN(-) (X??(2)Σ(+)) reveals transitions to the ground electronic state (X??(1)Σ(+)) of ICN as well as the first five excited states ((3)Π(2), (3)Π(1), Π(0(-) ) (3), Π(0(+) ) (3), and (1)Π(1)) that make up the ICN A continuum. By starting from the equilibrium geometry of the anion, photoelectron spectroscopy characterizes the electronic structure of ICN at an elongated I-C bond length of 2.65 A?. Because of this bond elongation, the lowest three excited states of ICN ((3)Π(2), (3)Π(1), and Π(0(-) ) (3)) are resolved for the first time in the photoelectron spectrum. In addition, the spectrum has a structured peak that arises from the frequently studied conical intersection between the Π(0(+) ) (3) and (1)Π(1) states. The assignment of the spectrum is aided by MR-SO-CISD calculations of the potential energy surfaces for the anion and neutral ICN electronic states, along with calculations of the vibrational levels supported by these states. Through thermochemical cycles involving spectrally narrow transitions to the excited states of ICN, we determine the electron affinity, EA(ICN), to be 1.34(5) (+0.04∕-0.02) eV and the anion dissociation energy, D(0)(X??(2)Σ(+) I-CN(-)), to be 0.83 (+0.04/-0.02) eV. 相似文献
994.
995.
Fainerman VB Lylyk SV Aksenenko EV Kovalchuk NM Kovalchuk VI Petkov JT Miller R 《Journal of colloid and interface science》2012,377(1):1-6
The complementary drop and bubble profile analysis and maximum bubble pressure tensiometry are used to measure the dynamic surface tension of aqueous SDS solutions in the presence of hardness salts (CaCl(2) and MgCl(2) in the ratio of 2:1 at concentrations of 6 and 40FH). The presence of hardness salts results in an essential increase of the SDS adsorption activity, which indicates the formation of Ca(DS)(2) and Mg(DS)(2) in the SDS solutions. The surface tension isotherms of SDS in presence of Ca(DS)(2) and Mg(DS)(2) are described using the generalised Frumkin model. The presence of hardness salts accelerates the ageing of SDS solutions as compared with the addition of 0.01 M NaCl due to a faster hydrolysis and hence formation of dodecanol. These results are used to estimate the possible concentration of dodecanol in the studied SDS solutions. The buoyant bubble profile method with harmonic surface oscillations is used to measure the dilational rheology of SDS solutions in presence of hardness salts in the frequency range between 0.005 Hz and 0.2 Hz. The visco-elasticity modulus in the presence of hardness salts is higher as compared with its values in the presence of 0.01 M NaCl additions. The ageing of SDS solutions leads to an essential increase of the visco-elastic modulus. 相似文献
996.
Kopreski RP Briggs JB Lin W Jazdzyk M Miller GP 《The Journal of organic chemistry》2012,77(3):1308-1315
Several o-quinodimethane adducts of [60]fullerene were synthesized and their intramolecular aryl CH-fullerene π interactions were studied using variable temperature-NMR (VT-NMR). Evaluation of the rate constants associated with the first-order transition states for cyclohexene boat-to-boat inversions enables quantification of ΔG(?) values for each inversion. A comparison between two constitutional isomers, only one of which is capable of intramolecular CH-π interactions, provides a lower limit of 0.95 kcal/mol for each aryl CH-fullerene π interaction. 相似文献
997.
Summary: The newly developed interactive separation of polyolefins by high temperature liquid chromatography (HTLC) provides new information about the chemical composition distribution of polyolefin elastomers. The technique has the advantage of being quantitative in its separation, and has high resolution for the separation of polyolefins by their chemical composition without influence by cocrystallization. Chemical composition distributions can be determined for individual polymers and blends which contain the full range of comonomer typically present in polyethylene and poylypropylene homopolymers, semi-crystalline copolymers, and amorphous copolymers. HTLC analysis in combination with the other fractionation techniques, such as DSC, TREF, NMR, and xylene fractionation, can be used to estimate the amount of olefin block copolymer present in a block composite produced by chain shuttling catalysis. 相似文献
998.
Miller DE Prasannan CB Villar MT Fenton AW Artigues A 《Journal of the American Society for Mass Spectrometry》2012,23(2):425-429
Hydrogen/deuterium exchange in combination with mass spectrometry (H/D MS) is a sensitive technique for detection of changes
in protein conformation and dynamics. However, wide application of H/D MS has been hindered, in part, by the lack of computational
tools necessary for efficient analysis of the large data sets associated with this technique. We report a novel web-based
application for automatic analysis of H/D MS experimental data. This application relies on the high resolution of mass spectrometers
to extract all isotopic envelopes before correlating these envelopes with individual peptides. Although a fully automatic
analysis is possible, a variety of graphical tools are included to aid in the verification of correlations and rankings of
the isotopic peptide envelopes. As a demonstration, the rate constants for H/D exchange of peptides from rabbit muscle pyruvate
kinase are mapped onto the structure of this protein. 相似文献
999.
As part of a comprehensive review on molecular oxygen spectroscopy, we have measured rotational spectra of isotopic forms of molecular oxygen in its a(1)Δ(g) electronic state with high-resolution terahertz spectroscopy. The data are recorded in close proximity to predicted positions. Due to the high resolution and good signal-to-noise ratio, the fundamental hyperfine parameters eQq and C(I) are determinable for (17)O-substituted species for the first time. A refined nuclear spin orbit coupling constant, a = -211.9328(283) MHz, was determined, and is roughly two orders of magnitude more precise than values determined from near infrared spectroscopy or electron spin resonance studies. Vibrationally excited oxygen in the a(1)Δ(g) electronic state was also observable with small signal levels for many of the rotational transitions. 相似文献
1000.
GA Cranch GA Miller CK Kirkendall 《The Journal of the Acoustical Society of America》2012,132(1):103-114
The interaction between fluid loaded fiber-optic cantilevers and a low frequency acoustic wave is investigated as the basis for an acoustic vector sensor. The displacements of the prototype cantilevers are measured with an integrated fiber laser strain sensor. A theoretical model predicting the frequency dependent shape of acoustically driven planar and cylindrical fiber-optic cantilevers incorporating effects of fluid viscosity is presented. The model demonstrates good agreement with the measured response of two prototype cantilevers, characterized with a vibrating water column, in the regime of Re ≥ 1. The performance of each cantilever geometry is also analyzed. Factors affecting the sensor performance such as fluid viscosity, laser mode profile, and support motion are considered. The planar cantilever is shown to experience the largest acoustically induced force and hence the highest acoustic responsivity. However, the cylindrical cantilever exhibits the smoothest response in water, due to the influence of viscous fluid damping, and is capable of two axis particle velocity measurement. These cantilevers are shown to be capable of achieving acoustic resolutions approaching the lowest sea-state ocean noise. 相似文献