全文获取类型
收费全文 | 3815篇 |
免费 | 210篇 |
国内免费 | 17篇 |
专业分类
化学 | 2954篇 |
晶体学 | 30篇 |
力学 | 86篇 |
数学 | 197篇 |
物理学 | 775篇 |
出版年
2023年 | 20篇 |
2022年 | 31篇 |
2021年 | 67篇 |
2020年 | 60篇 |
2019年 | 79篇 |
2018年 | 50篇 |
2017年 | 50篇 |
2016年 | 133篇 |
2015年 | 117篇 |
2014年 | 153篇 |
2013年 | 271篇 |
2012年 | 322篇 |
2011年 | 325篇 |
2010年 | 219篇 |
2009年 | 165篇 |
2008年 | 282篇 |
2007年 | 253篇 |
2006年 | 244篇 |
2005年 | 223篇 |
2004年 | 164篇 |
2003年 | 169篇 |
2002年 | 194篇 |
2001年 | 75篇 |
2000年 | 62篇 |
1999年 | 41篇 |
1998年 | 42篇 |
1997年 | 26篇 |
1996年 | 32篇 |
1995年 | 33篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有4042条查询结果,搜索用时 31 毫秒
161.
Hee Chul Pak 《Complex Analysis and Operator Theory》2018,12(5):1337-1349
Cauchy’s theorem for analytic functions on complex numbers is extended to analytic functions on the quaternions. For this purpose, we carefully define the notions of differentiation and integration on two or three dimensional manifolds embedded in the quaternions. 相似文献
162.
Choon Ki Ahn 《Nonlinear dynamics》2012,67(1):573-586
In this paper, a new exponential state estimation method is proposed for switched Hopfield neural networks based on passivity
theory. Through available output measurements, the main purpose is to estimate the neuron states such that the estimation
error system is exponentially stable and passive from the control input to the output error. Based on augmented Lyapunov–Krasovskii
functional, Jensen’s inequality, and linear matrix inequality (LMI), a new delay-dependent state estimator for switched Hopfield
neural networks can be achieved by solving LMIs, which can be easily facilitated by using some standard numerical packages.
The unknown gain matrix is determined by solving delay-dependent LMIs. Finally, a numerical example is provided to demonstrate
the effectiveness of the proposed method. 相似文献
163.
Thermal stability of ester linkage in the presence of 1,2,3‐Triazole moiety generated by click reaction 下载免费PDF全文
Kyu Seong Lee So Yeong Park Hong Chul Moon Jin Kon Kim 《Journal of polymer science. Part A, Polymer chemistry》2017,55(3):427-436
The copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC), so‐called “click” reaction, is one of most useful synthetic strategies to connect two polymer chains. 1,2,3‐Triazole ring (TA) produced by the click reaction has good thermal and chemical stability. However, we observed that block copolymers synthesized by the click reaction showed thermal degradation to give homopolymers when they are thermally annealed at high temperature, which is required for obtaining equilibrium microdomain structure. To investigate the origin of thermal instability of block copolymers, we synthesized model polystyrenes (PSs) using systematically designed bi‐functional atom transfer radical polymerization (ATRP) initiators containing TA. PS including both ester and TA groups showed thermal decomposition at relatively low temperature (e.g., 140 °C). MALDI‐TOF analysis clearly demonstrated that the cleavage site is the ester group adjacent to TA. We also found that the bromine group located at the polymer chain end plays an important role in pyrolysis of ester groups at low temperature. The pyrolysis occurs by syn‐elimination of the ester group. This result implies that the phase behavior of block copolymer synthesized by click reaction should be carefully investigated when high temperature thermal annealing is required. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 427–436 相似文献
164.
165.
Efficient and accurate procedure for selecting ground motions matching target response spectrum 总被引:2,自引:0,他引:2
Linear and nonlinear response history analyses have become popular in seismic design and seismic performance evaluation procedures. The accuracy of analysis results depends not only on the accurate analytic models for structures but also on the proper selection of input ground motions. The purpose of this study is to develop a computationally efficient and accurate procedure for selecting ground motions considering the target response spectrum mean and variance, and the correlations between response spectra of different periods. In this procedure, a number of response spectra are simulated equal to the number of ground motions to be selected, using a Monte Carlo simulation. Subsequently, ground motions are selected from a ground motion library to individually match the simulated response spectra, using the proposed selection procedure. This procedure is computationally efficient and accurate in selecting a ground motion that best matches a simulated response spectrum and in determining a scaling factor for the selected ground motion. In order to further improve the selection result, multiple sets of simulated response spectra are considered. The accuracy and efficiency of the proposed procedure are verified with numerical examples. 相似文献
166.
167.
Kim Gun Gyun Lee Jun Young Choi Pyeong Seok Vyas Chirag K. Yang Seung Dae Hur Min Gu Park Jeong Hoon 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(3):1099-1106
Journal of Radioanalytical and Nuclear Chemistry - Accumulation of triphenylphosphonium (TPP) is normally observed in the mitochondria from the extracellular spaces due to the high difference in... 相似文献
168.
169.
Residual determination and risk assessment of buprofezin in plum (Prunus domestica) grown in open‐field conditions following the application of three different formulations 下载免费PDF全文
Md. Humayun Kabir A.M. Abd El‐Aty Sung‐Woo Kim Han Sol Lee Md. Musfiqur Rahman Young‐Jun Lee Hyung Suk Chung Truong Lieu Jeong‐Heui Choi Ho‐Chul Shin Geon‐Jae Im Su Myeong Hong Jae‐Han Shim 《Biomedical chromatography : BMC》2016,30(11):1721-1727
This study was conducted to characterize the residual level and perform a risk assessment on buprofezin formulated as an emulsifiable concentrate, wettable powder, and suspension concentrate over various treatment schedules in plum (Prunus domestica). The samples were extracted with an AOAC quick, easy, cheap, effective, rugged, and safe, ‘QuEChERS’, method after major modifications. As intrinsic interferences were observed in blank plum samples following dispersive‐solid phase extraction (consisting of primary secondary amine and C18 sorbents), amino cartridges were used for solid‐phase extraction. Analysis was carried out using liquid chromatography with diode array detection and confirmed by liquid chromatography–tandem mass spectrometry. The method showed excellent linearity with determination coefficient (R2 = 1) and satisfactory recoveries (at two spiking levels, 0.5 and 2.5 mg/kg) between 90.98 and 94.74% with relative standard deviation (RSD) ≤8%. The limit of quantification (0.05 mg/kg) was considerably lower than the maximum residue limit (2 mg/kg) set by the Codex Alimentarius. Absolute residue levels for emulsifiable concentrates were highest, perhaps owing to the dilution rate and adjuvant. Notably, all formulation residues were lower than the maximum residue limit, and safety data proved that the fruits are safe for consumers. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
170.
Ultrastructural aspects of leaf epicuticular wax structures were investigated in the garden strawberry Fragaria × ananassa by scanning and transmission electron microscopy. Both the adaxial and abaxial surfaces of two cultivars (Maehyang and Red Pearl) were collected and subjected to surface observations and ultrathin sections. The most prominent leaf epicuticular wax structures included membraneous platelets and angular rodlets. Most wax platelets were membraneous, and appeared to protrude from the surface at an acute angle. Angular rodlets were usually bent and had rather distinct facets in the abaxial surface of the two cultivars. Membraneous platelets were predominant on the adaxial surface of Maehyang, whereas the adaxial surface of Red Pearl was characterized by angular rodlets. However, both cultivars possessed angular rodlets on the abaxial surface, simultaneously. The combination of air-drying without vacuum and in-lens imaging of secondary electron signals with a field emission gun could impart the superb resolution at low electron dose with minimal specimen shrinkage. In vertical profiles of the leaf epidermis, epicuticular waxes were observed above the cuticle layer, and measured approximately as 50 nm in thickness. The natural epicuticular waxes were seemingly mixtures of electron-dense microfibrils, and heterogeneous in shape on ultrathin sections. Distinct crystal-like strata could be hardly discernable in the wax structures. These results suggest that the garden strawberry has the nature of syntopism within one plant and polymorphism within the same species in the formation and occurrence of leaf epicuticular waxes. 相似文献