全文获取类型
收费全文 | 922篇 |
免费 | 16篇 |
国内免费 | 9篇 |
专业分类
化学 | 564篇 |
晶体学 | 7篇 |
力学 | 26篇 |
数学 | 112篇 |
物理学 | 238篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 27篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 94篇 |
2012年 | 41篇 |
2011年 | 41篇 |
2010年 | 39篇 |
2009年 | 27篇 |
2008年 | 45篇 |
2007年 | 40篇 |
2006年 | 51篇 |
2005年 | 37篇 |
2004年 | 25篇 |
2003年 | 21篇 |
2002年 | 25篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1973年 | 8篇 |
1970年 | 6篇 |
排序方式: 共有947条查询结果,搜索用时 31 毫秒
101.
It is proposed to construct a spallation neutron source (SNS) at Centre for Advanced Technology (CAT) based on a 1 GeV proton
synchrotron with 100 MeV H− LINAC as injector. Additionally, the LINAC can form the first 100 MeV part of a 1 GeV proton LINAC to be built in future
for accelerator driven system (ADS) applications. We are exploring a configuration of the 100 MeV LINAC which will consist
of an H− ion source, a 4–6 MeV RFQ followed either by a 20 MeV drift tube LINAC (DTL) and 100 MeV separated function drift tube LINAC
(SDTL) or a coupled cavity drift tube LINAC (CCDTL) structure. In this paper, we present the results of our preliminary physics
design studies of the RFQ-SDTL, RFQ-CCDTL and RFQ-DTL-SDTL configurations. The design of the 4.5 MeV RFQ is discussed along
with the matching sections between the RFQ-SDTL/DTL and RFQ-CCDTL. The choice of the accelerator configuration and that of
various parameters of the individual accelerator structures under consideration are discussed. The design objectives are to
arrive at a configuration which eases heat removal for CW operation and which is less prone to halo formation in order to
reduce the beam loss at higher energies. 相似文献
102.
One‐Pot Cannizzaro Cascade Synthesis of ortho‐Fused Cycloocta‐2,5‐dien‐1‐ones from 2‐Bromo(hetero)aryl Aldehydes
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Laurence Burroughs Lee Eccleshare John Ritchie Omkar Kulkarni Prof. Dr. Barry Lygo Prof. Dr. Simon Woodward Dr. William Lewis 《Angewandte Chemie (International ed. in English)》2015,54(36):10648-10651
An intramolecular Cannizzaro‐type hydride transfer to an in situ prepared allene enables the synthesis of ortho‐fused 4‐substituted cycloocta‐2,5‐dien‐1‐ones with unprecedented technical ease for an eight‐ring carboannulation. Various derivatives could be obtained from commercially available (hetero)aryl aldehydes, trimethylsilylacetylene, and simple propargyl chlorides in good yields. 相似文献
103.
104.
New test method for obtaining softening response of unnotched concrete specimen under uniaxial tension 总被引:4,自引:0,他引:4
A new method was developed to obtain the complete stress-deformation response of an unnotched concrete specimen. This method
employs a digitally controlled closed-loop testing machine and five control channels: stroke LVDT and four LVDTs mounted on
the specimen. The test portion of the specimen was fully spanned by these four LVDTs. The outputs of these control channels
and the load cell were monitored during the test by a computer equipped with LabTech's Notebook software. A ‘C’ language program
was written to enable quick switching of the mode of control from one LVDT to another. The problem of uncertainty in the location
of the major crack was tackled by the said LVDT arrangement and the computer program. It was demonstrated that it is always
possible to obtain stable post-peak response provided one ensures that at any time during the test, the feedback used is the
LVDT that exhibits, at that time, the largest slope of the response-time curve. An acoustic emission (AE) measurement system
of six channels was also used in the experiments. Monitoring of signals from the AE transducers provided valuable information
which helped in making the decision to switch control. 相似文献
105.
A. Sengupta M. J. Kulkarni S. V. Godbole 《Journal of Radioanalytical and Nuclear Chemistry》2011,289(3):961-965
DHOA (Di-n-hexyl-octanamide) is one of the alternative extractants to TBP (tri-n-butyl phosphate) known for the extraction of uranium from moderate nitric acid medium without significant extraction of the fission products. Analytical application of DHOA was explored to develop a methodology for determination of trace metallic constituents in uranium based nuclear materials. This involved the separation of uranium matrix by 1.1 M DHOA-dodecane followed by the analysis of the raffinate for trace constituents by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). A systematic study showed that four contacts of 1.1 M DHOA-dodecane were required for quantitative extraction of U from 4 M HNO3 feed for the sample size of 1 g in 10 mL. The feasibility of using DHOA for extraction of U from trace metallic constituents in U based fuel materials without losing trace quantities of analytes of interest was studied by using synthetic samples after appropriate spiking of common impurities and critical elements at their required specification limits (common elements—5 ppm, critical elements—1 ppm). A systematic study was carried out to compare the analytical performance of DHOA with TBP, which revealed that DHOA could successfully be employed for the determination of 19 trace constituents with lower estimation limits of 5 ppm for common impurities and 1 ppm for critical elements. 相似文献
106.
Kim KC Kulkarni AD Johnson JK Sholl DS 《Physical chemistry chemical physics : PCCP》2011,13(48):21520-21529
First principles calculations have played a useful role in screening mixtures of complex metal hydrides to find systems suitable for H(2) storage applications. Standard methods for this task efficiently identify the lowest energy reaction mechanisms among all possible reactions involving collections of materials for which DFT calculations have been performed. The resulting mechanism can potentially differ from physical reality due to inaccuracies in the DFT functionals used, or due to other approximations made in estimating reaction free energies. We introduce an efficient method to probe the robustness of DFT-based predictions that relies on identifying reactions that are metastable relative to the lowest energy reaction path predicted with DFT. An important conclusion of our calculations is that in many examples DFT cannot unambiguously predict a single reaction mechanism for a well defined metal hydride mixture because two or more mechanisms have reaction energies that differ by a small amount. Our approach is illustrated by analyzing a series of single step reactions identified in our recent work that examined reactions with a large database of solids [Kim et al., Phys. Chem. Chem. Phys. 2011, 13, 7218]. 相似文献
107.
Niederdraenk F Seufert K Stahl A Bhalerao-Panajkar RS Marathe S Kulkarni SK Neder RB Kumpf C 《Physical chemistry chemical physics : PCCP》2011,13(2):498-505
The detailed structural characterization of nanoparticles is a very important issue since it enables a precise understanding of their electronic, optical and magnetic properties. Here we introduce a new method for modeling the structure of very small particles by means of powder X-ray diffraction. Using thioglycerol-capped ZnO nanoparticles with a diameter of less than 3 nm as an example we demonstrate that our ensemble modeling method is superior to standard XRD methods like, e.g., Rietveld refinement. Besides fundamental properties (size, anisotropic shape and atomic structure) more sophisticated properties like imperfections in the lattice, a size distribution as well as strain and relaxation effects in the particles and-in particular-at their surface (surface relaxation effects) can be obtained. Ensemble properties, i.e., distributions of the particle size and other properties, can also be investigated which makes this method superior to imaging techniques like (high resolution) transmission electron microscopy or atomic force microscopy, in particular for very small nanoparticles. For the particles under study an excellent agreement of calculated and experimental X-ray diffraction patterns could be obtained with an ensemble of anisotropic polyhedral particles of three dominant sizes, wurtzite structure and a significant relaxation of Zn atoms close to the surface. 相似文献
108.
Spray formation in ambient atmosphere from gas-centered swirl coaxial atomizers is described by carrying out experiments in
a spray test facility. The atomizer discharges a circular air jet and an axisymmetric swirling water sheet from its coaxially
arranged inner and outer orifices. A high-speed digital imaging system along with a backlight illumination arrangement is
employed to record the details of liquid sheet breakup and spray development. Spray regimes exhibiting different sheet breakup
mechanisms are identified and their characteristic features presented. The identified spray regimes are wave-assisted sheet
breakup, perforated sheet breakup, segmented sheet breakup, and pulsation spray regime. In the regime of wave-assisted sheet
breakup, the sheet breakup shows features similar to the breakup of two-dimensional planar air-blasted liquid sheets. At high
air-to-liquid momentum ratios, the interaction process between the axisymmetric swirling liquid sheet and the circular air
jet develops spray processes which are more specific to the atomizer studied here. The spray exhibits a periodic ejection
of liquid masses whose features are dominantly controlled by the central air jet. 相似文献
109.
Anant D. Kulkarni Dhurba Rai Libero J. Bartolotti Rajeev K. Pathak 《Journal of Molecular Structure》2007,824(1-3):32-38
Methyl hydrogen peroxide (MHP) exhibits a tendency to form a stable dimer by hydrogen-bonding. Ab initio theoretical investigations on methyl hydrogen peroxide dimer (MHPD) carried out herein lead to several energetically stable structures that have a direct bearing on the reactivity of the monomer in terms of its molecular electrostatic potential (MESP). To gauge the role played by the electron-correlation in lending stability to MHP and its dimer, we employ the density functional theory (DFT) (as implemented by B3LYP-functional), and subsequently second order Møller-Plesset (MP2) perturbation theory, using the basis sets 6-31G(d, p) and 6-311++G(2d, 2p). Simulated infra-red vibrational spectra lead to spectral intensity redistribution upon dimerization. Energetically the lowest MHPD is endowed with inversion symmetry and has two hydrogen bonds, while three other structures emerge: one energetically very close with two H-bonds, and the two others, with three H-bonds each, yet higher by about 2 kcal mol−1. 相似文献
110.
Mukesh Chopra Manish Bhardwaj Muralidhar Kulkarni Asok De R. K. Sinha 《Fiber and Integrated Optics》2002,21(4):253-268
We present the design of a 3-dimensional (3-D) noncoherent optical hybrid network. We also report the design of a new family of 3-D codes for fiber optic hybrid networks. We show that the hybrid network allows for shorter bit times and a higher number of users, given a set chip rate, compared to previously conceived networks. These newly designed hybrid single-pulse-per-row (HSPR) codes have very low autocorrelation side-lobes and very small cross-correlation peaks. We compare the performance of our hybrid model using our codes with the Optical Orthogonal Codes (OOCs) and Temporal/Spatial (T/S) codes and show that the new network can support a greater number of users and higher data rates than those using OOCs and T/S codes. 相似文献