全文获取类型
收费全文 | 11592篇 |
免费 | 187篇 |
国内免费 | 45篇 |
专业分类
化学 | 6969篇 |
晶体学 | 93篇 |
力学 | 363篇 |
数学 | 1784篇 |
物理学 | 2615篇 |
出版年
2022年 | 148篇 |
2021年 | 172篇 |
2020年 | 157篇 |
2019年 | 150篇 |
2018年 | 148篇 |
2017年 | 126篇 |
2016年 | 201篇 |
2015年 | 197篇 |
2014年 | 205篇 |
2013年 | 669篇 |
2012年 | 430篇 |
2011年 | 527篇 |
2010年 | 381篇 |
2009年 | 325篇 |
2008年 | 487篇 |
2007年 | 446篇 |
2006年 | 439篇 |
2005年 | 389篇 |
2004年 | 396篇 |
2003年 | 332篇 |
2002年 | 324篇 |
2001年 | 199篇 |
2000年 | 198篇 |
1999年 | 162篇 |
1998年 | 129篇 |
1997年 | 147篇 |
1996年 | 178篇 |
1995年 | 134篇 |
1994年 | 130篇 |
1993年 | 162篇 |
1992年 | 162篇 |
1991年 | 173篇 |
1990年 | 122篇 |
1989年 | 128篇 |
1988年 | 134篇 |
1987年 | 188篇 |
1986年 | 150篇 |
1985年 | 208篇 |
1984年 | 194篇 |
1983年 | 151篇 |
1982年 | 178篇 |
1981年 | 184篇 |
1980年 | 180篇 |
1979年 | 183篇 |
1978年 | 172篇 |
1977年 | 166篇 |
1976年 | 145篇 |
1975年 | 163篇 |
1974年 | 133篇 |
1973年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
The determination of the concentration of light elements, such as carbon, nitrogen and oxygen, in e.g. atmospheric aerosol
particles is important to study the chemical behaviour of atmospheric pollution. The knowledge of low-Z element concentrations gives us information on the speciation of nutrients (species having nutritional value for plants)
and toxic heavy metals in the particles. The capability of the conventional energy-dispersive EPMA is strongly limited for
the analysis of low-Z elements, mainly because the Be window in the EDX detector hinders the detection of characteristic X-rays of light elements
such as C, N, O and Na. WDS is suitable for analysis of light elements, but the measurement of beam sensitive microparticles
requires the minimisation of the beam current and the measurement time. A semi-quantitative analytical method based on EPMA
using an ultra-thin window EDX detector was developed. It was found that the matrix and geometric effects that are important
for low-energy X-rays can be reliably evaluated by Monte Carlo calculations. Therefore, the quantification part of the method
contains reverse Monte Carlo calculation done by iterative simulations. The method was standardised and tested by measurements
on single particles with known chemical compositions. Beam-sensitive particles such as ammonium-sulphate and ammonium-nitrate
were analysed using a liquid nitrogen cooled sample stage. The shape and size of the particles, which are important for the
simulations, were determined using a high-magnification secondary electron image. Individual marine aerosol particles collected
over the North Sea by a nine-stage Berner cascade impactor were analysed using this new method. Preliminary results on five
samples and 4500 particles show that the method can be used to study the modification of sea-salt particles in the troposphere. 相似文献
993.
994.
995.
996.
Electrophoretically mediated microanalysis of gentamicin with in-capillary derivatization and UV detection. 总被引:2,自引:0,他引:2
E Kaale E Van Goidsenhoven A Van Schepdael E Roets J Hoogmartens 《Electrophoresis》2001,22(13):2746-2754
This paper describes a system for integration of a one-step-microscale chemical derivatization and analysis by a methodology known as electrophoretically mediated microanalysis (EMMA). Differential electrophoretic mobility between an analyte, reagent, and their product offers EMMA a unique capability to selectively carry out electrophoretic mixing, control product formation, and separation. This system was successfully applied to perform derivatization and separation of the multicomponent aminoglycoside antibiotic gentamicin using 1,2-phthalic dicarboxaldehyde and mercaptoacetic acid as labeling reagents. A multivariate approach based on central composite experimental design was used to optimize the derivative yield. Full automation of the derivatization and analytical procedure, high derivatization efficiency, high sample throughput, and precision are the excellent features of the present method. In addition, this methodology offers short analysis time, as well as selectivity and sensitivity suitable for impurities determination. Separation of gentamicin C1, C1a, C2, C2a, C2b, sisomicin, and several minor components was achieved. For the first time separation and identification of three impurities, namely garamine, 2-deoxystreptamine, and paromamine are described. 相似文献
997.
In this paper, a new fouling measurement method is presented as a pragmatic approach to determine a mixed liquor's fouling propensity. The MBR-VFM (VITO Fouling Measurement) uses a specific measurement protocol consisting of alternating filtration and physical cleaning steps, which enables the calculation of both the reversible and the irreversible fouling resistances. The MBR-VFM principle, set-up and measurement protocol are described as well as the evaluation of the fouling measurement method. Finally, the MBR-VFM was validated by comparing the fouling propensity measured on-line by the MBR-VFM in a lab-scale MBR with the fouling of the MBR membranes themselves. Our experiments indicated that the MBR-VFM can accurately measure fouling and that it can even be detected earlier than can be seen from the on-line filtration data of the lab-scale system itself. Furthermore, the differences measured in reversible and irreversible fouling seemed to be related to the observed impact of physical and chemical cleaning respectively. Therefore, the application of the MBR-VFM as an on-line sensor in an advanced control system, enabling the deployment of the measured fouling data for the control of membrane cleaning, seems feasible and will be tested in the near future. 相似文献
998.
Let P and Q be uniquely completable partial Latin squares. It is an open problem to determine necessary and sufficient conditions so that the completable product P⊗Q is also uniquely completable. So far, only a few specific examples of P have been given such that the completable product of P with itself (P⊗P) does not have a unique completion. In this paper, we find a whole class of such partial Latin squares. 相似文献
999.
Catherine Kealley Margaret Elcombe Arie Van Riessen 《Journal of synchrotron radiation》2008,15(1):86-90
Synchrotron radiation diffraction data were collected from hydroxyapatite–carbon nanotube bioceramic composites to determine the crystallite size and to measure changes in non‐uniform strain. Estimates of crystallite size and strain were determined by line‐profile fitting of discrete peaks and these were compared with a Rietveld whole‐pattern analysis. Overall the two analysis methods produced very similar numbers. In the commercial hydroxyapatite material, one reflection in particular, (0 2 3), has higher crystallite size and lower strain values in comparison with laboratory‐synthesized material. This could indicate preferential crystal growth in the [0 2 3] direction in the commercial material. From the measured strains in the pure material and the composite, there was a degree of bonding between the matrix and strengthening fibres. However, increasing the amount of carbon nanotubes in the composite has increased the strain in the material, which is undesirable for biomedical implant applications. 相似文献
1000.
We present an algebraic multigrid algorithm for fully coupled implicit Runge–Kutta and Boundary Value Method time-discretizations of the div-grad and curl-curl equations. The algorithm uses a blocksmoother and a multigrid hierarchy derived from the hierarchy built by any algebraic multigrid algorithm for the stationary version of the problem. By a theoretical analysis and numerical experiments, we show that the convergence is similar to or better than the convergence of the scalar algebraic multigrid algorithm on which it is based. The algorithm benefits from several possibilities for implementation optimization. This results in a computational complexity which, for a modest number of stages, scales almost linearly as a function of the number of variables. 相似文献