全文获取类型
收费全文 | 6010篇 |
免费 | 241篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 75篇 |
综合类 | 4篇 |
化学工业 | 968篇 |
金属工艺 | 71篇 |
机械仪表 | 127篇 |
建筑科学 | 229篇 |
矿业工程 | 6篇 |
能源动力 | 125篇 |
轻工业 | 514篇 |
水利工程 | 49篇 |
石油天然气 | 16篇 |
无线电 | 644篇 |
一般工业技术 | 1201篇 |
冶金工业 | 1362篇 |
原子能技术 | 31篇 |
自动化技术 | 832篇 |
出版年
2023年 | 29篇 |
2022年 | 22篇 |
2021年 | 106篇 |
2020年 | 71篇 |
2019年 | 86篇 |
2018年 | 119篇 |
2017年 | 121篇 |
2016年 | 109篇 |
2015年 | 109篇 |
2014年 | 168篇 |
2013年 | 349篇 |
2012年 | 278篇 |
2011年 | 392篇 |
2010年 | 276篇 |
2009年 | 290篇 |
2008年 | 270篇 |
2007年 | 288篇 |
2006年 | 243篇 |
2005年 | 225篇 |
2004年 | 176篇 |
2003年 | 169篇 |
2002年 | 154篇 |
2001年 | 120篇 |
2000年 | 125篇 |
1999年 | 108篇 |
1998年 | 265篇 |
1997年 | 190篇 |
1996年 | 142篇 |
1995年 | 102篇 |
1994年 | 83篇 |
1993年 | 108篇 |
1992年 | 48篇 |
1991年 | 40篇 |
1990年 | 56篇 |
1989年 | 69篇 |
1988年 | 67篇 |
1987年 | 47篇 |
1986年 | 46篇 |
1985年 | 51篇 |
1984年 | 31篇 |
1983年 | 37篇 |
1982年 | 40篇 |
1981年 | 45篇 |
1980年 | 35篇 |
1979年 | 32篇 |
1978年 | 26篇 |
1977年 | 62篇 |
1976年 | 65篇 |
1975年 | 26篇 |
1974年 | 20篇 |
排序方式: 共有6254条查询结果,搜索用时 774 毫秒
51.
52.
P. A. Carter G. Rowley E. J. Fletcher E. A. Hill 《Drug development and industrial pharmacy》1992,18(14):1505-1526
A detailed experimental investigation has been undertaken of the triboelectrification process of the pharmaceutical excipient alpha-lactose monohydrate and selected drugs. Particle charge studies involved the design and construction of an apparatus to incorporate pneumatic powder feed, triboelectric charging via a cyclone separator and simultaneous powder charge (Q) and mass (M) measurements using a modified Faraday well. Preliminary studies showed the charging of the selected materials to be unaffected by relative humidity up to 84%, due to the very low hygroscopicity of the powders. Experiments using lactose size fractions with brass, steel and cellulose contact charging surfaces conducted at different feeder gas pressures, gave net electronegative specific charge values (Q/M) for the metal surfaces, and electropositive values for cellulose. Specific charge increased linearly with gas pressure for the metals, and non-linearly for cellulose. Samples of micronised lactose and beclomethasone dipropionate (BDP) showed more tendency than unmicronised samples to adhere to the contact surface which resulted in more complex charging processes. A novel system to analyse the charge and mass data in further detail was developed, giving relative Q/M values at unit time intervals. It is proposed that this will overcome the limitations of reliance on the final net specific charge value. Preliminary results indicated differences in the charging mechanism for lactose in contact with the two metal surfaces. 相似文献
53.
54.
55.
56.
Ng J.S. Tan C.H. David J.P.R. Hill G. Rees G.J. 《Electron Devices, IEEE Transactions on》2003,50(4):901-905
Electron and hole ionization coefficients in In/sub 0.53/Ga/sub 0.47/As are deduced from mixed carrier avalanche photomultiplication measurements on a series of p-i-n diode layers, eliminating other effects that can lead to an increase in photocurrent with reverse bias. Low field ionization is observed for electrons but not for holes, resulting in a larger ratio of ionization coefficients, even at moderately high electric fields than previously reported. The measured ionization coefficients are marginally lower than those of GaAs for fields above 250 kVcm/sup -1/, supporting reports of slightly higher avalanche breakdown voltages in In/sub 0.53/Ga/sub 0.47/As than in GaAs p-i-n diodes. 相似文献
57.
David P. Cormode Jason J. Davis Paul D. Beer 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(1):32-40
Disulfide and dithiocarbamate functionalized porphyrins have been synthesized and used as protecting ligands for gold nanoparticle
formation either via ligand substitution reactions or by direct synthesis. These nanoparticles have been shown to recognize
anions via changes in the absorbance spectrum of the surface adsorbed porphyrin moieties. Association constants, derived from
quantitative titrations, indicate a remarkable surface enhancement effect where the surface bound porphyrins bind anions much
more strongly than the free receptor in solution. 相似文献
58.
Alexey B. Nadykto Fangqun Yu Jason Herb 《International journal of molecular sciences》2008,9(11):2184-2193
Hydration directly affects the mobility, thermodynamic properties, lifetime and nucleation rates of atmospheric ions. In the present study, the role of ammonia on the formation of hydrogen bonded complexes of the common atmospheric hydrogensulfate (HSO4−) ion with water has been investigated using the Density Functional Theory (DFT). Our findings rule out the stabilizing effect of ammonia on the formation of negatively charged cluster hydrates and show clearly that the conventional (classical) treatment of ionic clusters as presumably more stable compared to neutrals may not be applicable to pre-nucleation clusters. These considerations lead us to conclude that not only quantitative but also qualitative assessment of the relative thermodynamic stability of atmospheric clusters requires a quantum-chemical treatment. 相似文献
59.
The reduction and subsequent reoxidation of isolated vanadate species supported on silica was investigated using temperature-programmed reduction and oxidation, along with in-situ XANES and Raman spectroscopy. Approximately 70–80% of the vanadium was reduced to V3+ after reduction in H2 at temperatures up to 923 K. Upon reduction, the vanadyl oxygen was removed and the three remaining V–O bonds are lengthened by 0.2 Å. The vanadate species are rapidly reoxidized when exposed to O2, with the amount of oxygen uptake matching well with the amount removed during reduction. In-situ Raman spectroscopy during reoxidation in 18O2 showed that significant scrambling occurs between gas phase oxygen and surface oxygen species during the reoxidation of the vanadate species. 相似文献
60.
Knapp Samuel; Gottlieb Michael; Berman Jason; Handelsman Mitchell M. 《Canadian Metallurgical Quarterly》2007,38(1):54
At times the laws under which psychologists function may appear to contradict generally recognized ethical values and/or good clinical care. When these circumstances arise, psychologists must determine if a conflict really exists and, if so, seek solutions that reconcile respect for the law with their ethical values. At times, psychologists may decide to follow the law despite their ethical concerns. At other times, they may determine that a conscientious objection is warranted. The authors recommend options to consider when these situations arise and offer a decision-making process. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献