全文获取类型
收费全文 | 35383篇 |
免费 | 6926篇 |
国内免费 | 5722篇 |
专业分类
化学 | 26412篇 |
晶体学 | 581篇 |
力学 | 2297篇 |
综合类 | 407篇 |
数学 | 4073篇 |
物理学 | 14261篇 |
出版年
2024年 | 29篇 |
2023年 | 622篇 |
2022年 | 913篇 |
2021年 | 1202篇 |
2020年 | 1436篇 |
2019年 | 1494篇 |
2018年 | 1279篇 |
2017年 | 1332篇 |
2016年 | 1737篇 |
2015年 | 1906篇 |
2014年 | 2342篇 |
2013年 | 2931篇 |
2012年 | 3452篇 |
2011年 | 3563篇 |
2010年 | 2656篇 |
2009年 | 2727篇 |
2008年 | 2951篇 |
2007年 | 2457篇 |
2006年 | 2278篇 |
2005年 | 1826篇 |
2004年 | 1369篇 |
2003年 | 1138篇 |
2002年 | 1153篇 |
2001年 | 938篇 |
2000年 | 728篇 |
1999年 | 598篇 |
1998年 | 425篇 |
1997年 | 386篇 |
1996年 | 341篇 |
1995年 | 282篇 |
1994年 | 283篇 |
1993年 | 219篇 |
1992年 | 174篇 |
1991年 | 141篇 |
1990年 | 138篇 |
1989年 | 86篇 |
1988年 | 79篇 |
1987年 | 61篇 |
1986年 | 70篇 |
1985年 | 46篇 |
1984年 | 24篇 |
1983年 | 28篇 |
1982年 | 13篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 19篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1957年 | 8篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Multiresidue determination of 29 pesticide residues in pepper through a modified QuEChERS method and gas chromatography–mass spectrometry 下载免费PDF全文
Min Liu Yan Xie Haichang Li Xingang Meng Yuping Zhang Deyu Hu Kankan Zhang Wei Xue 《Biomedical chromatography : BMC》2016,30(10):1686-1695
This study describes the development and use of a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with gas chromatography with mass spectrometry to determine 29 pesticide residues in green, red and dehydrated red peppers. Pesticides were extracted with acetonitrile (1% acetic acid), partitioned with sodium chloride and purified with primary secondary amino and octadecyl silane in acetone. The QuEChERS extraction conditions were optimized, and the matrix effects that might influence recoveries were evaluated and minimized using matrix‐matched calibration curves. Under the optimized conditions, the calibration curves for 29 pesticides showed good linearity in the concentration range of 0.1–10 μg/mL with determination coefficient R2 > 0.998. The limits of quantification of the 29 pesticides were 0.006–0.06 mg/kg for green pepper, 0.005–0.039 mg/kg for red pepper and 0.014–0.25 mg/kg for dehydrated red pepper. These values are below the suggested regulatory maximum residue limits. The mean recoveries ranged between 70.1 and 110%, and the relative standard deviations were <13%. The developed method was successfully applied to commercial samples. Some samples were found to contain the 29 pesticides with levels below the legal limits. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
992.
993.
The enhanced biological activities of three Zn (II) complexes based on different 1,2,4‐triazole fungicides 下载免费PDF全文
Guo‐yu Ren Jie Li Xu‐zhan Wei Jin‐hua Zhou Biao Yan Zhao‐qi Guo Ying‐hui Ren Xiao‐hong Sun Hai‐xia Ma 《应用有机金属化学》2018,32(9)
In order to screen effective fungicides, three Zn (II) complexes, [Zn L 1 4 (NO3)2]·2H2O·2EtOH ( 1 ), [Zn L 2 4 (NO3)2] ( 2 ), and [Zn L 3 4 (DMF)2](NO3)2 ( 3 ), ( L 1 = paclobutrazol, L 2 = diniconazole, and L 3 = hexaconazole), were synthesized and characterized by elemental analysis, FT‐IR spectroscopy, and single‐crystal XRD. The antifungal activities of these complexes were then evaluated against four selected fungi using the mycelial growth rate method. The resulting data indicate that all the complexes show the enhanced antifungal activities than the corresponding ligand and mixtures. And, the interactions between the metal salt and ligands in the three complexes seem to be synergistic. According to the study of the influence of the structures on the activity, complex 2 with C=C linkage and 2,4‐dichlorophenyl moieties enhances the bioactivity significantly, especially against Wheat gibberellic ( II ). Density functional theory (DFT) calculations were carried out to help explain the enhanced bioactivity of the Zn (II) complexes. Meanwhile, all complexes are excellent grow‐regulators, especially complex 3 . The resulting data show that the complexes based on triazole fungicides have the potential applications in agriculture. 相似文献
994.
Through a two-step vacuum-filtration process, WSe2 and MoS2 nanosheets were sequentially deposited onto a polymeric nanoporous support, forming WSe2/MoS2 bi-layered heterostructure. Highly rectified ion transport phenomenon is observed through the heterogeneous 2D layered membranes. 相似文献
995.
LOCALIZED PATTERNS OF THE CUBIC-QUINTIC SWIFT-HOHENBERG EQUATIONS WITH TWO SYMMETRY-BREAKING TERMS 下载免费PDF全文
Homoclinic snake always refers to the branches of homoclinic orbits \mbox{near} a heteroclinic cycle connecting a hyperbolic or non-hyperbolic equilibrium and a periodic
orbit in a reversible variational system. In this paper, the normal form of a Swift-Hohenberg equation with two different symmetry-breaking terms (non-reversible term and non-k-symmetry term) are investigated by using multiple scale method, and their bifurcation diagrams are initially studied by numerical simulations. Typically, we predict numerically the existence of so-called round-snakes and round-isolas upon particular two symmetric-breaking perturbations. 相似文献
996.
Microstructural evolution and grain refinement mechanism in AZ31 magnesium alloy subjected to sliding friction treatment were investigated by means of transmission electron microscopy. The process of grain refinement was found to involve the following stages: (I) coarse grains were divided into fine twin plates through mechanical twinning; then the twin plates were transformed to lamellae with the accumulation of residual dislocations at the twin boundaries; (II) the lamellae were separated into subgrains with increasing grain boundary misorientation and evolution of high angle boundaries into random boundaries by continuous dynamic recrystallisation (cDRX); (III) the formation of nanograins. The mechanisms for the final stage, the formation of nanograins, can be classified into three types: (i) cDRX; (ii) discontinuous dynamic recrystallisation (dDRX); (iii) a combined mechanism of prior shear-band and subsequent dDRX. Stored strain energy plays an important role in determining deformation mechanisms during plastic deformation. 相似文献
997.
998.
999.
Zhong Ju Liu Wenwen Shi Gui Mei Shi Wei Jiang 《International Journal of Theoretical Physics》2018,57(1):184-194
An array of coupled cavities, each of which contains a triangle-down-level atom, is investigated. An effective Hamiltonian can be achieved under the strong classical driving. We can control the transition between Mott-insulator and superfluid states by the classical driving. The frequency conversion in one site has the same effects of nonlinear in BH hamiltonian which can induce insulator-superfluid states. 相似文献
1000.
Optical Review - Based on the planar optical theory, compact beam expanders are proposed to miniaturize the dimension of an optical system. Both simulated and experimental results have demonstrated... 相似文献