全文获取类型
收费全文 | 43082篇 |
免费 | 4158篇 |
国内免费 | 2450篇 |
专业分类
电工技术 | 1916篇 |
技术理论 | 2篇 |
综合类 | 3042篇 |
化学工业 | 10000篇 |
金属工艺 | 1535篇 |
机械仪表 | 2375篇 |
建筑科学 | 2169篇 |
矿业工程 | 1120篇 |
能源动力 | 1359篇 |
轻工业 | 6747篇 |
水利工程 | 1686篇 |
石油天然气 | 2266篇 |
武器工业 | 355篇 |
无线电 | 3636篇 |
一般工业技术 | 4537篇 |
冶金工业 | 1867篇 |
原子能技术 | 1048篇 |
自动化技术 | 4030篇 |
出版年
2024年 | 193篇 |
2023年 | 653篇 |
2022年 | 1060篇 |
2021年 | 1445篇 |
2020年 | 1564篇 |
2019年 | 1536篇 |
2018年 | 1409篇 |
2017年 | 1623篇 |
2016年 | 1783篇 |
2015年 | 1719篇 |
2014年 | 2612篇 |
2013年 | 2903篇 |
2012年 | 3193篇 |
2011年 | 3166篇 |
2010年 | 2241篇 |
2009年 | 2324篇 |
2008年 | 2059篇 |
2007年 | 2554篇 |
2006年 | 2362篇 |
2005年 | 2032篇 |
2004年 | 1653篇 |
2003年 | 1519篇 |
2002年 | 1308篇 |
2001年 | 1110篇 |
2000年 | 969篇 |
1999年 | 865篇 |
1998年 | 662篇 |
1997年 | 570篇 |
1996年 | 426篇 |
1995年 | 415篇 |
1994年 | 313篇 |
1993年 | 276篇 |
1992年 | 241篇 |
1991年 | 148篇 |
1990年 | 114篇 |
1989年 | 101篇 |
1988年 | 90篇 |
1987年 | 54篇 |
1986年 | 50篇 |
1985年 | 63篇 |
1984年 | 54篇 |
1983年 | 37篇 |
1982年 | 30篇 |
1981年 | 26篇 |
1980年 | 28篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1976年 | 10篇 |
1964年 | 20篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Sang Cheol Lee Won Kook Lee 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,55(3):251-261
The extraction of penicillin G from simulated media was performed by water/oil/water (w/o/w) emulsion liquid membranes (ELMs) and studied under various operational conditions in a batch system. The degree of extraction achieved was between 80% and 95% under specific conditions. A concentration of greater than nine times the initial concentration of penicillin G in the external phase was obtained in the internal phase. The pH of the internal aqueous solution, containing a basic salt, was theoretically calculated on the basis of the amount of penicillin G transported into the internal phase. The calculated results agreed with the experimental data well and were used to select a suitable type and concentration of a basic salt in the internal phase to give a pH within the range 5 to 8 where penicillin G was stable after the termination of extraction. The extraction of penicillin G was successfully performed by the ELM process with sodium carbonate in the internal phase. 相似文献
52.
Ching-Yeh Shiau 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,54(1):7-12
The understanding of the permeation rate of metal ions through liquid membranes is important for the design of such systems. In this paper, the permeation rates of copper ions through liquid surfactant membranes, including interfacial reaction rates and the diffusion rate of the copper ion, were analyzed using a model based on a mobilized hollow spherical globule configuration. The analysis shows that the extracting reaction is dominant at the external interface of the membrane and the stripping reaction is dominant at the internal interface; this means the reactions at both interfaces are not in equilibrium during the course of extraction. It also shows that the extraction rate, the diffusion rate and the stripping rate are not of equal value, especially at the early stage of the run. 相似文献
53.
Mario J. Pires Joaquim M. S. Cabral 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,61(3):219-224
Recombinant cytochrome b5 was extracted into the reversed micelle phase of an anionic surfactant (AOT) in octane and back-extracted to a final aqueous phase. The extraction of the protein was controlled by an electrostatic mechanism, since it was dependent on the global charge of the protein. This was directly demonstrated by experiments with native and mutant cytochromes obtained by site directed mutagenesis. The back-extraction of cytochrome b5 to a fresh aqueous phase was decreased by factors that reduced the size of the water pool of the organic phase, such as high salt concentrations (1–2 mol dm?3 NaCl) and low temperatures (4°C), probably because of an increase in a favourable interaction of this protein with the surfactant at closer distances. 相似文献
54.
The main problems in estimating the uncertainty due to the presence of impurities in the material: the absence in the documents of a unique definition of the quantity being measured – the fixed point temperature, the lack of agreed methods of realizing the fixed points and the insufficient justification of the equations used for the estimate, are analyzed. The results of a measurement of the melting point of gallium are presented, which differ in the conditions in which they were realized – with one and two liquid-solid interfaces and different solidification conditions, are presented. The reasons for the considerable difference between the values of the temperatures obtained in these experiments are discussed. 相似文献
55.
This research focused on the syllable as a processing unit in handwriting. Participants wrote, in uppercase letters, words that had been visually presented. The interletter intervals provide information on the timing of motor production. In Experiment 1, French participants wrote words that shared the initial letters but had different syllable boundaries. In Experiment 2, French- and Spanish-speaking participants wrote cognates and pseudowords with a letter sequence that was always intrasyllabic in French and intersyllabic in Spanish. In Experiment 3, French-Spanish bilinguals wrote the cognates and pseudowords with the same type of sequences. In the 3 experiments, the critical interletter intervals were longer between syllables than within syllables, indicating that word syllable structure constrains motor production both in French and Spanish. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
56.
57.
We have developed a Zimm-type viscometer specially designed for the simultaneous measurements of the structure factor and the viscosity of hyperswollen lyotropic liquid crystals under a very weak shear. We have investigated the shear effects on the layer undulation fluctuation in the lamellar structure and the transition from the anisotropic lamellar to the isotropic sponge phase. We have found a significant difference in the rheological properties between the lamellar and the sponge phase: The former exhibits non-Newtonian flow behavior, while the latter exhibits Newtonian behavior.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A. 相似文献
58.
Precusors to the YBa2 Cu3 O7-δ material were prepared by both the oxalate precipitation method and conventional ceramic processing. Second-phase grains were observed to develop on the exposed fracture surface during annealing at 500° to 600°C in an ambient atmosphere. The second-phase grains were identified to be BaCO3 using EDX and XRD. The liquid phase, which was formed because of local chemical inhomogeneity in the Y-Ba-Cu-O system, contributed to the formation of second-phase grains as a source of Ba. 相似文献
59.
系统介绍了舞钢开发的针状铁素体型X70宽厚板的设计思路、工艺特点和实物水平;采用电炉 炉外精炼 连铸 TMCP工艺生产的X70宽厚板满足西气东输专用技术条件的要求,并批量应用在西气东输主干线工程中。 相似文献
60.
Yun Zhang Xirong Huang Yuezhong Li 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1230-1235
BACKGROUND: [bmim][PF6] is a hydrophobic ionic liquid which could be considered as an environmentally friendly solvent for biocatalysis. In pure [bmim][PF6], however, alcohol dehydrogenase from yeast (YADH) has no catalytic activity. The aim of the present work was (1) to quantitatively study the negative effect of [bmim][PF6] on the catalytic activity of YADH and the related mechanism and (2) to made an attempt to lessen the negative effect of [bmim][PF6] on YADH by microemulsifying [bmim][PF6]. RESULTS: The activity of YADH in the homogeneous solution formed by H2O, CH3CH2OH and [bmim][PF6] decreased rapidly with the increase of the molar fraction of [bmim][PF6]. The inhibitory effect of [bmim][PF6] on YADH was probably caused by the competition of the imidazole group of [bmim][PF6] with the coenzyme NAD+ for the binding sites on YADH. In a water‐in‐[bmim][PF6] microemulsion, YADH was catalytically active due to the formation of the interfacial membrane of the nonionic surfactant TritonX‐100, which separated YADH from [bmim][PF6] and avoided the direct inactivation of [bmim][PF6] on YADH. Under optimal conditions, the activity of YADH was as high as 51 µmol L?1 min?1. CONCLUSION: [bmim][PF6] was an inhibitor of YADH and its negative effect on YADH could be lessened by its microemulsification. Copyright © 2008 Society of Chemical Industry 相似文献