全文获取类型
收费全文 | 410124篇 |
免费 | 4045篇 |
国内免费 | 1246篇 |
专业分类
化学 | 206302篇 |
晶体学 | 6126篇 |
力学 | 20584篇 |
综合类 | 17篇 |
数学 | 64298篇 |
物理学 | 118088篇 |
出版年
2020年 | 2737篇 |
2019年 | 2978篇 |
2018年 | 13522篇 |
2017年 | 13413篇 |
2016年 | 11512篇 |
2015年 | 4378篇 |
2014年 | 6000篇 |
2013年 | 15059篇 |
2012年 | 14392篇 |
2011年 | 23362篇 |
2010年 | 14755篇 |
2009年 | 15209篇 |
2008年 | 18384篇 |
2007年 | 20400篇 |
2006年 | 11624篇 |
2005年 | 11659篇 |
2004年 | 10797篇 |
2003年 | 10333篇 |
2002年 | 9188篇 |
2001年 | 10047篇 |
2000年 | 7762篇 |
1999年 | 5901篇 |
1998年 | 4915篇 |
1997年 | 4756篇 |
1996年 | 4562篇 |
1995年 | 4240篇 |
1994年 | 4085篇 |
1993年 | 3801篇 |
1992年 | 4610篇 |
1991年 | 4637篇 |
1990年 | 4405篇 |
1989年 | 4443篇 |
1988年 | 4410篇 |
1987年 | 4309篇 |
1986年 | 4103篇 |
1985年 | 5283篇 |
1984年 | 5429篇 |
1983年 | 4328篇 |
1982年 | 4584篇 |
1981年 | 4498篇 |
1980年 | 4244篇 |
1979年 | 4682篇 |
1978年 | 4832篇 |
1977年 | 4825篇 |
1976年 | 4680篇 |
1975年 | 4379篇 |
1974年 | 4380篇 |
1973年 | 4330篇 |
1972年 | 2956篇 |
1968年 | 2676篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
YoungJu Choie Olav K. Richter 《Proceedings of the American Mathematical Society》2007,135(8):2309-2315
We determine a class of functions spanned by theta series of higher degree. We give two applications: A simple proof of the inversion formula of such theta series and a classification of skew-holomorphic Jacobi forms.
963.
B. D. Kabulov K. A. Akhundzhanov F. U. Yunusov O. A. Shpigun S. S. Negmatov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(3):354-356
The hydrolytic polycondensation of tetraethoxysilane in the presence of various polymers (polyacrylonitrile, polycaproamide, and chitosan) as templates was performed with the use of the sol-gel technology to obtain nanohybrid composite polymer-silica sorbents-nanofractals. 相似文献
964.
E. Baggio Saitovitch F. J. Litterst I. Souza Azevedo R. B. Scorzelli 《Hyperfine Interactions》1989,50(1-4):529-535
The Mössbauer spectra of YBa2(Cu1?x Fe x )3O7 at room temperature show several doublets attributed to Fe in Cu(1) sites with different oxygen configurations. Here we present a systematic study performed at 4.2 K forx=0.005, 0.01, 0.03, 0.05, 0.10, 0.15. To obtain information about the magnetic ordered state two samples, withx=0.005 andx=0.15, have been studied at 4.2 K underB ext=5 T. The Mössbauer spectra indicate that the iron moments are polarized forx=0.005, while in the ordered state (x=0.15) they have an antiferromagnetic or spin-glass-like arrangement with high anisotropy. 相似文献
965.
In recent years there has emerged significant interest in low pressure radio frequency (rf) glow discharges which are used widely particulary in IC fabrication. Various parameters of the rf glow discharge have been found to be useful for its electrical characterization; however, there is no uniformity and agreement. Extensive experimental investigations on various discharge systems have shown, that the self-bias on the rf driven electrode, the complex conductivity and the breakdown characteristic are preferable parameters of rf discharges. Advantageously the self-bias and the complex conductivity should be presented in dependence on the pressure and the applied rf voltage. The discharge current cannot be measured quite accurately due to currents via leaky capacitors and the deviations from a sinusoidal form of the current due to nonlinearities. 相似文献
966.
Summary High-purity indium was analysed by spark source mass spectrometry, using electrical and photoplate detection. For the calibration of the differences in elemental sensitivity, a standard sample was prepared in which 10 impurities were determined by graphite furnace atomic absorption spectrometry. In this way accuracies of less than 40% were obtained for relatively homogeneous elements at ppm and sub-ppm level. About 40 elements could be determined with detection limits of 10 to 30 ppb. Two pattern recognition methods, principal component analysis and clustering analysis, were applied to obtain information on trace element distribution, which indicated that a number of elements were strongly spatially correlated in the analysed sample.
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
Chemische Analyse und Verteilungsbestimmung von Spurenelementen in Indium-Matrix durch Funkenquellen-Massenspektrometrie
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
967.
This paper reports positive results from an application of one type of group support system (GSS) to a training application. Reviews of the findings of other trials of GSS have been mixed, and inconclusive. We describe the results of a series of seven training sessions in a field-based application of group process support. The subjects were professionals working in various agencies concerned with the welfare of older people. A ‘low-profile’ type of group support system, based on wireless handsets, was used. This design enabled responses from each participant to be input and displayed anonymously. Each session was aimed at stimulating a dialogue focused on the reasons for differences of judgement, as displayed on a single projected feedback screen. Changes of individual judgements were recorded for subsequent analysis and comparison with already known ‘expert judgements’. Frequent changes of judgement were recorded. A significant proportion of these were related to an improvement, which could not be explained as simply the result of conforming behaviour. We propose that the mode of operation and design of a ‘low-profile’ GSS have the potential to create a learning environment by reducing personal anxieties while encouraging group-based learning with focussed conversation. We conclude that this type of GSS design is particularly suited to ‘selective’-type tasks in groups. 相似文献
968.
Hans Weber 《Order》2007,24(4):249-276
We study lattice theoretical properties of lattices of uniformities such as modularity, distributive laws and the existence
of (relative) complements. For this the concepts of permutable uniformities (see Definition 3.1) and independent uniformities
(see Definition 4.1) are important. Moreover, we show that e.g. the lattice of all lattice uniformities on a lattice L is a closed sublattice of the lattice of all uniformities on L. 相似文献
969.
Polyvinyl alcohol (PVA)-based proton conducting polymer electrolytes have been prepared by the solution cast technique. The
conductivity is observed to increase from 10−9 to 10−4 S cm−1 as a result of orthophosphoric acid (H3PO4) addition. The plot of conductivity vs temperature shows that a phase transition occurred at 343 K in the sample PVA-33 wt%
H3PO4. The β-relaxation peak is observed at 313 K. The glass transition temperature of PVA-33 wt% H3PO4 is 343 K. Orthophosphoric acid seems to play a dual role, i.e., as a proton source and as a plasticizer. The ac conductivity
σ
ac = Aω
s was also calculated in the temperature range from 303 to 353 K. The conduction mechanism was inferred by plotting the graph
of s vs T from which the conduction mechanism for sample PVA-17 wt% H3PO4 was inferred to occur by way of the overlapping large polaron tunneling (OLPT) model and the conduction mechanism for the
sample PVA-33 wt% H3PO4 by way of the correlated barrier height (CBH) model. 相似文献
970.
Bernardo Lafuerza-Guillén Donal O’regan Reza Saadati 《Proceedings Mathematical Sciences》2007,117(1):61-70
We introduce the concept of quotient in PN spaces and give some examples. We prove some theorems with regard to the completeness
of a quotient. 相似文献