全文获取类型
收费全文 | 1856687篇 |
免费 | 55038篇 |
国内免费 | 22082篇 |
专业分类
电工技术 | 54511篇 |
技术理论 | 45篇 |
综合类 | 31263篇 |
化学工业 | 327545篇 |
金属工艺 | 83205篇 |
机械仪表 | 64287篇 |
建筑科学 | 73926篇 |
矿业工程 | 22953篇 |
能源动力 | 59118篇 |
轻工业 | 140859篇 |
水利工程 | 22075篇 |
石油天然气 | 59057篇 |
武器工业 | 2921篇 |
无线电 | 231387篇 |
一般工业技术 | 321805篇 |
冶金工业 | 187482篇 |
原子能技术 | 37232篇 |
自动化技术 | 214136篇 |
出版年
2022年 | 19768篇 |
2021年 | 28837篇 |
2020年 | 21810篇 |
2019年 | 22628篇 |
2018年 | 24054篇 |
2017年 | 24538篇 |
2016年 | 30452篇 |
2015年 | 30613篇 |
2014年 | 45449篇 |
2013年 | 107173篇 |
2012年 | 57975篇 |
2011年 | 72308篇 |
2010年 | 63391篇 |
2009年 | 70278篇 |
2008年 | 64894篇 |
2007年 | 61269篇 |
2006年 | 64607篇 |
2005年 | 56562篇 |
2004年 | 53268篇 |
2003年 | 51949篇 |
2002年 | 50362篇 |
2001年 | 46422篇 |
2000年 | 44686篇 |
1999年 | 44267篇 |
1998年 | 53334篇 |
1997年 | 46045篇 |
1996年 | 41583篇 |
1995年 | 35900篇 |
1994年 | 33101篇 |
1993年 | 31396篇 |
1992年 | 28361篇 |
1991年 | 25021篇 |
1990年 | 24975篇 |
1989年 | 23843篇 |
1988年 | 22194篇 |
1987年 | 20206篇 |
1986年 | 19553篇 |
1985年 | 22788篇 |
1984年 | 22864篇 |
1983年 | 20695篇 |
1982年 | 19533篇 |
1981年 | 19554篇 |
1980年 | 18173篇 |
1979年 | 18772篇 |
1978年 | 17926篇 |
1977年 | 17996篇 |
1976年 | 19557篇 |
1975年 | 16110篇 |
1974年 | 15647篇 |
1973年 | 15722篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
934.
935.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
936.
In this study, further analysis of the osmotic drying process was conducted to identify the optimum combination of parameters for drying rectangular alumina-gelatin beams. This study was designed to determine the effect of three variables related to the osmotic drying process (osmotic pressure, molecular weight, and immersion time) on the interaction between the liquid desiccant and the submerged alumina-gelatin samples. The water loss from the alumina-gelatin samples was positively correlated with the molecular weight, osmotic pressure, and immersion time. Up to 40% by weight of the initial water content was removed during the osmotic drying process. The samples also experienced solids gain due to the counterflow of solute from the liquid desiccant. The least amount of solids gain resulted from drying for the shortest immersion time at low osmotic pressure and high molecular weight. Evidence of possible interactions between variables was noted for the sintered density metric. Statistical methods were used to form regression equations for the measured responses (water loss, solids gain, bulk density). A verification experiment was conducted to compare the experimental outcomes to the predicted outcomes. The responses were simultaneously optimized to identify the combination of variable settings required to meet specified goals. In order to maximize water loss, minimize solids gain, and maximize bulk density, the ceramic-gelatin object should be immersed for approximately 60?min in an aqueous solution of 100,000?g/mol poly(ethylene oxide) at an osmotic pressure of 2.50?MPa. These values are valid for the range of parameter settings tested and the sample fabrication and drying methods used. 相似文献
937.
Dr. Li Di Prof. Per Artursson Dr. Alex Avdeef Prof. Leslie Z. Benet Prof. J. Brian Houston Dr. Manfred Kansy Edward H. Kerns Prof. Hans Lennernäs Dr. Dennis A. Smith Prof. Kiyohiko Sugano 《ChemMedChem》2020,15(20):1862-1874
Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients. 相似文献
938.
Vu Hoa T. Nguyen Manh B. Vu Tan M. Le Giang H. Pham Trang T. T. Nguyen Trinh Duy Vu Tuan A. 《Topics in Catalysis》2020,63(11-14):1046-1055
Topics in Catalysis - Nano Fe-BTC/graphene oxide (GO) composites were successfully synthesized by hydrothermal treatment with a microwave-assisted method. Samples were characterized by X-ray... 相似文献
939.
940.
Makrina A. Chairopoulou Fabian Kratzer Roland Gross Michael Herrmann Ulrich Teipel 《化学工程与技术》2020,43(5):904-912
Thermogravimetric analysis of a coccolith-containing biogenic broth showed a three-step degradation process. According to this system behavior, the biogenic broth was heated to specific temperatures and characterized in terms of its morphology, surface chemistry, and crystallinity. The elemental and organic composition of the treated samples was also evaluated and compared to the reference material. The presented results were acquired in an effort to exploit pretreatment scenarios for such a biogenic system that would improve and support a separation process. 相似文献