全文获取类型
收费全文 | 3878篇 |
免费 | 141篇 |
国内免费 | 47篇 |
专业分类
化学 | 2534篇 |
晶体学 | 34篇 |
力学 | 139篇 |
综合类 | 2篇 |
数学 | 597篇 |
物理学 | 760篇 |
出版年
2023年 | 23篇 |
2022年 | 29篇 |
2021年 | 49篇 |
2020年 | 49篇 |
2019年 | 45篇 |
2018年 | 44篇 |
2017年 | 21篇 |
2016年 | 75篇 |
2015年 | 71篇 |
2014年 | 98篇 |
2013年 | 202篇 |
2012年 | 254篇 |
2011年 | 269篇 |
2010年 | 141篇 |
2009年 | 145篇 |
2008年 | 234篇 |
2007年 | 229篇 |
2006年 | 224篇 |
2005年 | 197篇 |
2004年 | 176篇 |
2003年 | 155篇 |
2002年 | 113篇 |
2001年 | 95篇 |
2000年 | 99篇 |
1999年 | 58篇 |
1998年 | 57篇 |
1997年 | 37篇 |
1996年 | 76篇 |
1995年 | 52篇 |
1994年 | 50篇 |
1993年 | 46篇 |
1992年 | 43篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1985年 | 49篇 |
1984年 | 29篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 38篇 |
1980年 | 31篇 |
1979年 | 26篇 |
1978年 | 31篇 |
1977年 | 27篇 |
1976年 | 21篇 |
1975年 | 25篇 |
1974年 | 37篇 |
1973年 | 21篇 |
排序方式: 共有4066条查询结果,搜索用时 187 毫秒
141.
Binhang Yan Pengcheng Xu Xuan Li Cliff Yi Guo Yong Jin Yi Cheng 《Plasma Chemistry and Plasma Processing》2012,32(6):1203-1214
Liquid hydrocarbons including n-hexane, cyclohexane and toluene are pyrolyzed in H2/Ar plasma to investigate the effects of feedstock properties and key operating conditions (e.g., the feedstock specific input power and residence time) on the reaction performance. The experiments verify that the non-aromatic hydrocarbons show better chemical reactivity than partially aromatic substances. Meanwhile, the straight-chain alkanes and cycloalkanes have better yields of ethylene during the pyrolysis. The results also demonstrate that the pyrolysis reactions are almost completed within the first 0.8?ms in Ar/H2 plasma independent of the feed substances (i.e., liquid hydrocarbons), where the increased feedstock specific input power enhances the reactant conversions and correspondingly raises the yields of acetylene. At a feedstock specific input power of 4.7?×?104?kJ/kg, the n-hexane conversion is over 90?% and the yield of acetylene reaches 70?%. In addition, when using n-hexane as the feedstock, very little coke is formed during the course of reaction. Comprehensive comparisons of the current experiments with the data reported in the literature are made to point out the key influencing factors, i.e., the effective mass ratio of C/H (R C/H) in the gaseous phase and the quench temperature. Both two factors would need to be enhanced in order to get a better performance. Finally, the improvements on the specific energy requirement of this process are discussed. 相似文献
142.
Synthetic organic chemists are continually looking for milder, more specific methods of effecting given transformations, and one such problem which recently arose in our laboratory involved ester cleavage. In particular, we sought a specific, wild, non-hydrolytic method for effecting teh ester - acid transformation under conditions which other acid or base sensitive functional groups would survive. 相似文献
143.
A k-regular bipartite graph is said to be 2-factor hamiltonian if each of its 2-factor is hamiltonian. It is well known that if a k-regular bipartite graph is 2-factor hamiltonian, then k?Q3. In this paper, we give a new proof of this fact. 相似文献
144.
In this study, cultural, economic as well as certain crucial demographic factors are considered as the determinants for projecting the average family size in rural India. We use the Analytic Hierarchy Process to analyze influences of the factors which enter implicitly in a rural couple's decision‐making to determine the number of children they want to have as time goes by. We did not attempt to make distinctions among the regional differences in rural India. The outcome projected in our analysis compares favorably with the results of other demographic studies. 相似文献
145.
Although divalent organophosphinyl radicals have been frequently postulated as intermediates in many organochosphorous reactions, very few of them have been identified by e.s.r. By low temperature trapping of products from the photolysis of gaseous tetraphenyl-diphospine in a flow system, Schmidt and coworkers2 have observed an e.s.r. signal of a single broad and asymmetric line centered at about g = 2.009 and have assigned this to the diphenylphosphinyl radical. We have reinvestigated the photolysis of this compound by flash photolysis and by e.s.r. at low temperatures, the preliminary e.s.r. results will be reported here. 相似文献
146.
The production of track-spots in CR-39 detectors for alpha particles and the subsequent optical counting of the detectors are often influenced by foreign substances deposited on the surface of the detectors. The removal of these substances can be achieved using chemicals for pre-irradiation treatment. Two methods of pre-irradiation treatment were studied in the present experiments. One of them involves the dipping of the detectors in ethanol. In the other method, the detectors were treated in 6N KOH etchant prior to exposure. It was found that prolonged treatment could only produce a reduction in the track density of less than 20%. 相似文献
147.
The purpose of this paper is to construct two superimposed optimization methods for solving the mixed equilibrium problem and variational inclusion. We show that the proposed superimposed methods converge strongly to a solution of some optimization problem. Note that our methods do not involve any projection. 相似文献
148.
Symmetrical and cyclic alkyl trithiocarbonates were synthesized by reacting CS2 and 33% aqueous NaOH with alkyl hal-ides under phase transfer catalysis conditions 相似文献
149.
Denis C. K. Wong 《Mathematics in Computer Science》2016,10(2):223-227
In this paper, we construct some families of binary linear and nonlinear codes by using various bipartite graphs. Furthermore, we also determine some conditions for the constructed binary linear code to be a maximum distance separable code. 相似文献
150.
Bis‐clickable Mesoporous Silica Nanoparticles: Straightforward Preparation of Light‐Actuated Nanomachines for Controlled Drug Delivery with Active Targeting
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Achraf Noureddine Dr. Magali Gary‐Bobo Dr. Laure Lichon Dr. Marcel Garcia Prof. Jeffrey I. Zink Dr. Michel Wong Chi Man Dr. Xavier Cattoën 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9624-9630
Bis(clickable) mesoporous silica nanospheres (ca. 100 nm) were obtained by the co‐condensation of TEOS with variable amounts (2–5 % each) of two clickable organosilanes in the presence of CTAB. Such nanoparticles could be easily functionalized with two independent functions using the copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction to transform them into nanomachines bearing cancer cell targeting ligands with the ability to deliver drugs on‐demand. The active targeting was made possible after anchoring folic acid by CuAAC click reaction, whereas the controlled delivery was performed by clicked azobenzene fragments. Indeed, the azobenzene groups are able to obstruct the pores of the nanoparticles in the dark whereas upon irradiation in the UV or in the blue range, their trans‐to‐cis photoisomerization provokes disorder in the pores, enabling the delivery of the cargo molecules. The on‐command delivery was proven in solution by dye release experiments, and in vitro by doxorubicin delivery. The added value of the folic acid ligand was clearly evidenced by the difference of cell killing induced by doxorubicin‐loaded nanoparticles under blue irradiation, depending on whether the particles featured the clicked folic acid ligand or not. 相似文献