全文获取类型
收费全文 | 157668篇 |
免费 | 2098篇 |
国内免费 | 661篇 |
专业分类
电工技术 | 3176篇 |
综合类 | 192篇 |
化学工业 | 25146篇 |
金属工艺 | 5880篇 |
机械仪表 | 5024篇 |
建筑科学 | 4642篇 |
矿业工程 | 515篇 |
能源动力 | 4037篇 |
轻工业 | 17762篇 |
水利工程 | 1204篇 |
石油天然气 | 627篇 |
武器工业 | 5篇 |
无线电 | 20839篇 |
一般工业技术 | 29860篇 |
冶金工业 | 25337篇 |
原子能技术 | 2385篇 |
自动化技术 | 13796篇 |
出版年
2019年 | 940篇 |
2018年 | 1183篇 |
2017年 | 1234篇 |
2016年 | 1401篇 |
2015年 | 1153篇 |
2014年 | 1935篇 |
2013年 | 6922篇 |
2012年 | 3410篇 |
2011年 | 4942篇 |
2010年 | 3839篇 |
2009年 | 4372篇 |
2008年 | 4932篇 |
2007年 | 5181篇 |
2006年 | 4587篇 |
2005年 | 4296篇 |
2004年 | 4180篇 |
2003年 | 4049篇 |
2002年 | 4079篇 |
2001年 | 4098篇 |
2000年 | 3834篇 |
1999年 | 3783篇 |
1998年 | 6889篇 |
1997年 | 5418篇 |
1996年 | 4606篇 |
1995年 | 3825篇 |
1994年 | 3458篇 |
1993年 | 3285篇 |
1992年 | 2874篇 |
1991年 | 2731篇 |
1990年 | 2694篇 |
1989年 | 2681篇 |
1988年 | 2517篇 |
1987年 | 2229篇 |
1986年 | 2168篇 |
1985年 | 2610篇 |
1984年 | 2377篇 |
1983年 | 2242篇 |
1982年 | 2128篇 |
1981年 | 2047篇 |
1980年 | 1909篇 |
1979年 | 1902篇 |
1978年 | 1804篇 |
1977年 | 2126篇 |
1976年 | 2627篇 |
1975年 | 1603篇 |
1974年 | 1454篇 |
1973年 | 1469篇 |
1972年 | 1221篇 |
1971年 | 1124篇 |
1970年 | 957篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
We report here observational results demonstrating that a three-station network of properly distributed VLBI observatories can routinely determine UT1 with a formal standard error of ±0.05 ms of time, in an observing period of 24 h. We also report the results of a three-month series of daily observing sessions of only 1-h duration with a single interferometer, which produced estimates of UT1 with standard errors of ±0.1 ms. The UT1 values obtained from the 1-h observing sessions track smoothly between the points of the 24-h time series, and the combined time series shows that it is not unusual for UT1 to vary by 1-2 ms in periods of several days. Preliminary results of reprocessing the 24-h observing sessions in 2-h segments suggest that variations of 0.4 ms may occur on time scales of only 6-8 h. 相似文献
102.
Ahn Jaeshin Stromsmoe Keith A. Lawson Ronald P. W. 《Industrial Electronics, IEEE Transactions on》1985,(4):405-409
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films. 相似文献
103.
Poly(vinyl alcohol) is crosslinked in dilute solution (c=0.1 wt%) with glutaraldehyde. The reaction product is characterized by viscometry and gel permeation chromatography (g.p.c.). The intrinsic viscosity decreases with increasing degree of crosslinking and does not depend on temperature. G.p.c. reveals that the reaction product is not homogeneous, but consists of a mixture of particles with different sizes, possibly both intra- and intermolecularly crosslinked molecules. The intramolecularly crosslinked molecules are smaller in size than the initial polymer molecules and their size depends on the degree of crosslinking. They possess a narrow particle size distribution even if the initial polymer sample had a broad molecular weight distribution. 相似文献
104.
W Seilmeier H Wieser H D Belitz 《Zeitschrift für Lebensmittel-Untersuchung und -Forschung》1987,185(6):487-489
Reduced glutenin is separated by gel permeation high-performance liquid chromatography into three major and five minor fractions, which significantly differ in their amino acid compositions. By reversed-phase high performance liquid chromatography, about 20 glutenin components are obtained. These can be classified into three groups according to their amino acid compositions: a hydrophilic group with relatively high values of Glx and Phe, a more hydrophobic group with a high content of Gly, and a strongly hydrophobic group with higher values of Val and Leu. Groups 1, 2 and 3 contain middle-, high- and low-molecular-weight (MMW-, HMW-, LMW-) subunits respectively. 相似文献
105.
106.
Nichols M.A. Siegel H.J. Dietz H.G. Quong R.W. Nation W.G. 《Parallel and Distributed Systems, IEEE Transactions on》1991,2(3):290-303
Efficient data layout is an important aspect of the compilation process. A model for the creation of perfect memory maps for large-scale parallel machines capable of user-controlled partitionable single-instruction-multiple data/single-program-multiple data (SIMD/SPMD) operation is developed. The term perfect implies that no memory fragmentation occurs and ensures that the memory map size is kept to a minimum. A major constraint on solving this problem is based on the single program nature of both the SIMD and SPMD modes of parallelism. It is assumed that all processors within the same submachine used identical addresses to access corresponding data items in each of their local memories. Necessary and sufficient conditions are derived for being able to create perfect memory maps, and results are applied to several partitionable interconnection networks 相似文献
107.
Arthur W. Westerberg 《Computers & Chemical Engineering》1985,9(5):421-429
The last dozen years have produced almost 50 English language articles on the synthesis of separation systems [1]. Most work has considered separating a single relatively ideal mixture into sharply split, usually pure-component products using systems of single-feed, two-product distillation columns. Of late, the work has considered heat-integrating these columns to reduce energy consumption. Present research will very likely produce valuable results for nonsharp separations.Earlier approaches developed both algorithmic- and heuristic-based tree search algorithms for discovering the better systems of non-heat-integrated columns. New results permit the design of heat-integrated systems.The paper highlights the above developments. 相似文献
108.
P.W. Hawkes 《Ultramicroscopy》1985,17(2):151-156
Modifications of solid water and their transitions are described as they relate to cryo electron microscopy. In particular, the various amorphous states (amorphous polymorphs) as they exist below 100 K are extensively investigated. The “high-density” midification exhibits a lower viscosity than the “low-density” form. Differences are also observed in the mechanism of void formation due to electron irradiation: in the high-density form, voids are formed — not, however, in the low-density form. Together with the reaction to radiation damage, the physical properties of amorphous solid water are discussed with respect to embedding of organic specimens. Finally, the conditions and pitfalls associated with preparation of thin and entirely vitrified ice layers by shock-freezing are described. 相似文献
109.
R. Breil T. Fries J. Garnaes J. Haycocks D. Hüser J. Joergensen W. Kautek L. Koenders N. Kofod K. R. Koops R. Korntner B. Lindner W. Mirand A. Neubauer J. Peltonen G. B. Picotto M. Pisani H. Rothe M. Sahre M. Stedman G. Wilkening 《Precision Engineering》2002,26(3)
Comparison measurements on reference standards are reported in which 13 partners with different instruments took part. A set of prototype standards which had been produced and calibrated within a European project were used for the measurements. Here, results of measurements on a 240 nm step height standard and a two-dimensional lateral standard with a nominal pitch of 1 μm are reported. 相似文献
110.