全文获取类型
收费全文 | 2232篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 9篇 |
综合类 | 2篇 |
化学工业 | 147篇 |
金属工艺 | 25篇 |
机械仪表 | 31篇 |
建筑科学 | 40篇 |
矿业工程 | 9篇 |
能源动力 | 24篇 |
轻工业 | 107篇 |
水利工程 | 4篇 |
石油天然气 | 8篇 |
无线电 | 211篇 |
一般工业技术 | 166篇 |
冶金工业 | 1304篇 |
原子能技术 | 7篇 |
自动化技术 | 150篇 |
出版年
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 20篇 |
2017年 | 16篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 20篇 |
2013年 | 45篇 |
2012年 | 42篇 |
2011年 | 42篇 |
2010年 | 34篇 |
2009年 | 42篇 |
2008年 | 36篇 |
2007年 | 32篇 |
2006年 | 44篇 |
2005年 | 38篇 |
2004年 | 33篇 |
2003年 | 29篇 |
2002年 | 32篇 |
2001年 | 29篇 |
2000年 | 50篇 |
1999年 | 66篇 |
1998年 | 374篇 |
1997年 | 208篇 |
1996年 | 140篇 |
1995年 | 107篇 |
1994年 | 82篇 |
1993年 | 86篇 |
1992年 | 35篇 |
1991年 | 30篇 |
1990年 | 42篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1987年 | 32篇 |
1986年 | 26篇 |
1985年 | 35篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 31篇 |
1976年 | 92篇 |
1975年 | 7篇 |
1974年 | 16篇 |
1973年 | 6篇 |
1971年 | 6篇 |
排序方式: 共有2244条查询结果,搜索用时 0 毫秒
71.
Many materials, upon fracturing, emit electrons (exo-electrons) by a process called fracto-emission. For a substance or mixture that can deflagrate or detonate upon impact or friction, these exo-electrons may contribute to the initiation of deflagration or detonation. Some materials, such as p-type semiconductors, can absorb exo-electrons and, as used as additives, can reduce the impact or friction sensitivity of propellants or explosives. It was found that the addition of 1% p-type silicon powder did decrease the impact sensitivity of a propellant consisting of ammonium perchlorate in a polybutadiene matrix, but did not reduce the impact sensitivity of powdered cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX), and pentaerythritol trinitrate (PETN). 相似文献
72.
Damage development during instrumented falling weight impact (IFWIM) testing of poly(methyl methacrylate) (PMMA) is recorded using short pulse photography. The first visible damage is cracking on application of the peak force. Finite element analysis predicts the deformation and state of stress throughout the specimen until the first point of failure is reached. A variation in the specimen geometry produces a significant change in initial failure energy, while the maximum tensile stress is approximately constant. The proposed failure criterion is the attainment of a critical time-dependent value of tensile stress. © 1992 John Wiley & Sons, Inc. 相似文献
73.
Incorporation of [14C] from acetoacetate, D(-)- and L(+)-3-hydroxybutyrate, glucose, glutamine, acetate and palmitate in cellular lipids were
studied in cultures in human diploid fibroblasts (HDF). The results showed that acetoacetate was 2–10 times more effective
as a lipogenic precursor than was either D- or L-3-hydroxybutyrate. Its extent of incorporation into lipids was 2- to 8-fold
more than the other precursors examined under conditions when the overall rates of nonsaponifiable and saponi-fiable lipogenesis
as measured by3H2O incorporation were essentially unchanged. Acetoacetate supported both saponifiable and nonsaponifiable lipid syntheses with
half-saturation values (Km app.) of 185 μM and 30 μM, respectively. Glucose stimulated acetoacetate incorporation into lipids whereas, conversely, acetoacetate
inhibited [14C] glucose incorporation into lipids. The presence of low density lipoproteins (LDL) cholesterol (@40 μg cholesterol/mL) inhibited
the incorporation of [14C] from acetoacetate 56% into nonsaponifiable lipids; the inhibition was consistently higher (75%) when [14C] glucose or glutamine were the precrusors. The loss of 3-hydroxy-3-methyl-glutaryl CoA (HMG CoA) reductase activity upon
addition of LDL-cholesterol was greater than the suppression of [14C] incorporation from acetoacetate or glucose into nonsaponifiable lipids. In the presence of glucose, [14C] acetoacetate was incorporated into 3-βOH sterols (digitonin precipitable). 7.7±1.1 times more effectively than was [14C] glucose. The results suggest that HDF would be a suitable model to investigate the effects of various precrusors of HMG
CoA on the rate of cholesterol biosynthesis. 相似文献
74.
Siddhartha Gaur T. R. Rao T. B. Reed P. D. Grover 《Petroleum Science and Technology》1992,10(9):1461-1499
The Reactivity of corn cob char in CO2 has been studied on a thermogravimetric balance to develop a rate equation for the design of biomass gasifiers operating on corn cob char. Experiments in the range of 650-1000°C were conducted with cylindrical shaped pellets of 1 cm diameter having L/D=l. The average porosity of the pellets was 0.5. It was observed that the rate of the CO2/char reaction decreased with increase in temperature from 650-750°C and then increased with temperature upto 1000°C.
The data obtained at temperatures 750°C and above has been used to determine a rate equation for char gasification. It has been found that the reaction proceeds according to the Sharp Interface Model (SIM) with a first order chemical reaction as the rate controlling step. The activation energy is found to be 40 Kcal/mole with frequency factor being 1.2 × 107 mm/sec. Analysis of the data obtained for the decreasing reaction rate regime (650-750°C) indicates that the change in the ash structure result in this kind of behavior. 相似文献
The data obtained at temperatures 750°C and above has been used to determine a rate equation for char gasification. It has been found that the reaction proceeds according to the Sharp Interface Model (SIM) with a first order chemical reaction as the rate controlling step. The activation energy is found to be 40 Kcal/mole with frequency factor being 1.2 × 107 mm/sec. Analysis of the data obtained for the decreasing reaction rate regime (650-750°C) indicates that the change in the ash structure result in this kind of behavior. 相似文献
75.
76.
Kihong Lee Sebastian F. Maehrlein Xinjue Zhong Daniele Meggiolaro Jake C. Russell Douglas A. Reed Bonnie Choi Filippo De Angelis Xavier Roy Xiaoyang Zhu 《Advanced materials (Deerfield Beach, Fla.)》2019,31(36)
The coupling of phonons to electrons and other phonons plays a defining role in material properties, such as charge and energy transport, light emission, and superconductivity. In atomic solids, phonons are delocalized over the 3D lattice, in contrast to molecular solids where localized vibrations dominate. Here, a hierarchical semiconductor that expands the phonon space by combining localized 0D modes with delocalized 2D and 3D modes is described. This material consists of superatomic building blocks (Re6Se8) covalently linked into 2D sheets that are stacked into a layered van der Waals lattice. Using transient reflectance spectroscopy, three types of coherent phonons are identified: localized 0D breathing modes of isolated superatom, 2D synchronized twisting of superatoms in layers, and 3D acoustic interlayer deformation. These phonons are coupled to the electronic degrees of freedom to varying extents. The presence of local phonon modes in an extended crystal opens the door to controlling material properties from hierarchical phonon engineering. 相似文献
77.
Jess D Reed Girma Gebre‐Mariam Christopher J Robinson Jean Hanson Agnes Odenyo Paul M Treichel 《Journal of the science of food and agriculture》2001,81(15):1481-1486
Acacia angustissima has potential in agroforestry systems for forage production in tropical environments. However, feeding trials indicate that the leaves are potentially toxic. Signs of toxicity in sheep are similar to those presented by sheep fed flatpea (Lathyrus sylvestris) hay which contains a high concentration of the non‐protein amino acid 2,4‐diaminobutanoic acid (DABA). Cation exchange chromatography, high‐performance liquid chromatography (HPLC) and NMR were used to isolate and identify the non‐protein amino acid in A angustissima leaves. A quantitative HPLC method was used to determine the content of the non‐protein amino acid in leaves from 20 accessions. The non‐protein amino acid was identified as 4‐N‐acetyl‐2,4‐diaminobutanoic acid (ADAB), previously reported to occur in seeds. The average and range in ADAB content were 16.8 and 10.6–25.4 mg g?1 respectively. This content of ADAB is higher than the levels of DABA in flatpea hay that are toxic to sheep. © 2001 Society of Chemical Industry 相似文献
78.
Rotational and functional motor behavioral changes were studied in five MPTP lesioned chronic hemiparkinsonian Macaca nemestrina monkeys after i.m. pramipexole, a predominant D2 subfamily agonist. Pramipexole induced contraversive rotations in a dose-dependent manner with an optimal dose of 56 microg/kg for approximately 2 to 4 hr after injection. Three different rating scales were used to determine drug-induced functional improvement. They included a monkey parkinsonism rating scale, volitional responses to fruit presentations, and number of hand movements that appeared volitional. A dose of 56 microg/kg of pramipexole produced functional improvements on hand disability, and on a parkinsonian rating scale for monkeys in a dose-dependent manner from 32 to 100 microg/kg. These doses produced an increase in significant hand movements in the affected (contralateral) as well as in the normal (ipsilateral) hand to the side of the brain lesion compared with 5% dextrose in water vehicle control. With a dose of 100 microg/kg, the therapeutic effects of pramipexole on hand movements were less than with 56 microg/kg, due to side effects such as scratching. 相似文献
79.
80.