全文获取类型
收费全文 | 150208篇 |
免费 | 37132篇 |
国内免费 | 29210篇 |
专业分类
化学 | 68533篇 |
晶体学 | 1316篇 |
力学 | 6924篇 |
综合类 | 182篇 |
数学 | 13260篇 |
物理学 | 62481篇 |
综合类 | 63854篇 |
出版年
2024年 | 756篇 |
2023年 | 1688篇 |
2022年 | 2330篇 |
2021年 | 2468篇 |
2020年 | 3247篇 |
2019年 | 6169篇 |
2018年 | 6107篇 |
2017年 | 6799篇 |
2016年 | 7697篇 |
2015年 | 7727篇 |
2014年 | 8127篇 |
2013年 | 9726篇 |
2012年 | 10086篇 |
2011年 | 11403篇 |
2010年 | 13917篇 |
2009年 | 13509篇 |
2008年 | 7055篇 |
2007年 | 6422篇 |
2006年 | 5435篇 |
2005年 | 5587篇 |
2004年 | 6572篇 |
2003年 | 5208篇 |
2002年 | 4760篇 |
2001年 | 4476篇 |
2000年 | 3506篇 |
1999年 | 4220篇 |
1998年 | 3631篇 |
1997年 | 3467篇 |
1996年 | 3627篇 |
1995年 | 3847篇 |
1994年 | 3854篇 |
1993年 | 3798篇 |
1992年 | 3332篇 |
1991年 | 3005篇 |
1990年 | 2463篇 |
1989年 | 2478篇 |
1988年 | 2437篇 |
1987年 | 1530篇 |
1986年 | 1492篇 |
1985年 | 1051篇 |
1984年 | 1071篇 |
1982年 | 941篇 |
1981年 | 763篇 |
1980年 | 796篇 |
1979年 | 545篇 |
1978年 | 558篇 |
1977年 | 648篇 |
1976年 | 1063篇 |
1973年 | 447篇 |
1972年 | 540篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Activated carbon fiber (ACF) as extraction fiber for solid-phase microextraction (SPME) and its application for the analysis of banned organochlorine pesticides (OCPs) were investigated. Firstly, ACF was activated by different concentration of zinc chloride, which indicated that ACF activated by 60% zinc chloride had a reasonable specific surface area, pore volume and pore distribution. Secondly, the parameters for the ACF-SPME procedure, the adsorption and desorption conditions, were also optimized when coupled with gas chromatography-mass spectrometry (GC-MS). Thirdly, the ACF-SPME was used to analyze 17 kinds of OCPs in water. The linearity of most pesticides was found to be between 0.2 and 50 microg/l with GC-MS under the selected ion monitoring (SIM) acquisition mode. The limits of detection (LOD) at the sub microg/l were obtained. The work demonstrated here shows that ACF is a promising alternative for the SPME procedure. 相似文献
912.
Vytautas Getautis Albina Stanisauskaite Tadas Malinauskas Jolanta Stumbraite Valentas Gaidelis Vygintas Jankauskas 《Monatshefte für Chemie / Chemical Monthly》2006,23(12):1401-1409
Hydrazones containing 1-phenyl-1,2,3,4-tetrahydroquinoline units were synthesized starting from diphenylamine. These compounds
were found to constitute novel hole transporting materials and were characterized by the time of flight method. The hole drift
mobility in these compounds exceeds 10−6 cm2 V−1 s−1 at an electric field of 106 V cm−1. 相似文献
913.
Mousa Z. Al-Noaimi Raid J. Abdel-Jalil Mustafa M. El-Abadelah Salim F. Haddad Younis N. H. Baqi Wolfgang Voelter 《Monatshefte für Chemie / Chemical Monthly》2006,37(12):745-750
In the presence of RuCl3, N-phenylamidrazone underwent oxidative cyclization into 1,4-dihydro-1-phenyl-1,2,4-benzotriazine, the structure of which is
established by spectral and X-ray diffraction data. 相似文献
914.
Monika Schuster Robert Inführ Claudia Turecek Jürgen Stampfl Franz Varga Robert Liska 《Monatshefte für Chemie / Chemical Monthly》2006,4(4):843-853
To substitute cross-linked photopolymers in rapid prototyping of mold materials and therefore extend the range of materials
which can be casted, organo-soluble photopolymers were developed. Branched bisalkylacrylamides were suitable as base component
for such formulations, due to their high reactivity, good mechanical properties, and excellent solubility of the formed polymers.
These molding materials were used to prepare cellular biocompatible materials which could be used as bone replacement materials.
Biocompatible crosslinkers based on methacrylates from hydrolyzed gelatine or lactic acid ethyleneglycol blockcopolymers and
commercially available reactive diluents are the base components of such a formulation. Biocompatibility was investigated
by osteoblast-like cells. Cellular biocompatible parts were obtained by thermal polymerization in soluble mould materials
prepared by 3D-photoshaping. 相似文献
915.
Ivan Gutman Sabina Gojak Niko Radulovi? Boris Furtula 《Monatshefte für Chemie / Chemical Monthly》2006,46(2):277-284
In a recent work it was demonstrated that in linear hexagonal chains the distribution of π-electrons into rings (as computed
by means of the Randić–Balaban method) is uniform, irrespective of the nature of the terminal fragments. We now establish that an analogous, yet somewhat
more complex, uniformity in the π-electron distribution exists also in double linear hexagonal chains, as well as in some
other benzenoid systems. 相似文献
916.
Wafaa M. Abdou Neven A. Ganoub Amin F. Fahmy Abeer A. Shaddy 《Monatshefte für Chemie / Chemical Monthly》2006,46(10):105-116
Two simple and efficient one-pot procedures for the synthesis of a series of α-branched N-heterocycle-substituted methane-1,1-bisphosphonates
are outlined. In the first method, the parent halosubstrates were reacted with cyanomethylphosphonate followed by reaction
with dialkyl phosphonates to give asymmetrical or symmetrical bisphosphonates (BPs). In the second approach, the same halocompounds were reacted with tetraethyl methyl-1,1-bisphosphonate to give the requisite
BPs. Partial and complete hydrolysis of the prepared BPs were also investigated. The products contain functional groups advantageous for further synthetic modification as structural
units for coupling with the drug. 相似文献
917.
Mohamed Kameche Mohamed Feham 《International Journal of Infrared and Millimeter Waves》2006,27(5):687-705
Simple techniques for determining the broadband small signal equivalent circuit (SSEC) of MESFETs are presented in this paper.
The intrinsic elements are calculated using two-dimensional method from the Y parameters, which are obtained from the Fourier
analysis of the device transient response to voltage-step perturbations at the drain and gate electrodes. Whereas, the parasitic
external elements are determined by simple approximations used in transmission line modeling. In addition, a new technique
is also proposed to determine the source and drain series resistances. A comparison of the SSEC of three different MESFETs
technologies shows that the MESFETs on GaN and 4H-SiC are suitable for high power applications. The method used to determine
the intrinsic elements is validated with simulated data obtained by Monte Carlo method. 相似文献
918.
919.
Sun Shufen 《Acta Mechanica Sinica》1987,3(1):44-51
The coupled model has been developed in this study for moisture transport and beat exchange in soil. The model is driven by
atmospheric conditions measured in a field. The concept that soil has a surface resistance to evaporation is introduced in
order to relate the evaporation from surface with the vapour flux in air. With the use of this concept, the simulation results
agree quite well with the measured data. 相似文献
920.
Model and empirical study on some collaboration networks 总被引:8,自引:0,他引:8
Pei-Pei Zhang Kan Chen Yue He Tao Zhou Bei-Bei Su Yingdi Jin Hui Chang Yue-Ping Zhou Li-Cheng Sun Bing-Hong Wang Da-Ren He 《Physica A》2006,360(2):599-616
In this paper we present an empirical study of a few practical systems described by cooperation networks, and propose a model to understand the results obtained. We study four non-social systems, which are the Bus Route Networks of Beijing and Yangzhou, the Travel Route Network of China, Huai-Yang recipes of Chinese cooked food, and a social system, which is the Collaboration Network of Hollywood Actors. In order to explain the results related to the degree distribution, act-degree distribution and act-size distribution (especially about the degree distribution, which may be better fitted using a stretched exponential distribution (SED)), we suggest a simple model to show a possible evolutionary mechanism for the emergence of such networks. The analytic and numerical results obtained from the model are in good agreement with the empirical results. 相似文献