全文获取类型
收费全文 | 704330篇 |
免费 | 9163篇 |
国内免费 | 2106篇 |
专业分类
电工技术 | 12993篇 |
综合类 | 671篇 |
化学工业 | 105328篇 |
金属工艺 | 26707篇 |
机械仪表 | 20458篇 |
建筑科学 | 17379篇 |
矿业工程 | 2942篇 |
能源动力 | 19773篇 |
轻工业 | 61414篇 |
水利工程 | 6798篇 |
石油天然气 | 11415篇 |
武器工业 | 45篇 |
无线电 | 83404篇 |
一般工业技术 | 137175篇 |
冶金工业 | 136482篇 |
原子能技术 | 13872篇 |
自动化技术 | 58743篇 |
出版年
2022年 | 4170篇 |
2021年 | 6384篇 |
2020年 | 4665篇 |
2019年 | 5898篇 |
2018年 | 10047篇 |
2017年 | 9863篇 |
2016年 | 10359篇 |
2015年 | 7115篇 |
2014年 | 11932篇 |
2013年 | 32576篇 |
2012年 | 18855篇 |
2011年 | 26075篇 |
2010年 | 20636篇 |
2009年 | 23290篇 |
2008年 | 23924篇 |
2007年 | 23500篇 |
2006年 | 20653篇 |
2005年 | 18566篇 |
2004年 | 17961篇 |
2003年 | 17839篇 |
2002年 | 16892篇 |
2001年 | 17272篇 |
2000年 | 16019篇 |
1999年 | 16973篇 |
1998年 | 43434篇 |
1997年 | 30405篇 |
1996年 | 23339篇 |
1995年 | 17588篇 |
1994年 | 15367篇 |
1993年 | 15150篇 |
1992年 | 10899篇 |
1991年 | 10360篇 |
1990年 | 10107篇 |
1989年 | 9678篇 |
1988年 | 9120篇 |
1987年 | 8027篇 |
1986年 | 7874篇 |
1985年 | 8718篇 |
1984年 | 8137篇 |
1983年 | 7388篇 |
1982年 | 6920篇 |
1981年 | 6893篇 |
1980年 | 6632篇 |
1979年 | 6379篇 |
1978年 | 6047篇 |
1977年 | 7351篇 |
1976年 | 9736篇 |
1975年 | 5149篇 |
1974年 | 4904篇 |
1973年 | 4947篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The effect of spreading code length on the BER performance of an asynchronous DS-CDMA system is studied by means of Monte Carlo simulation. The probability of the crosscorrelation value between segments of long sequences is also discussed. Results indicate that the system performance with very long codes is ~1 dB worse compared to that of short CDMA codes 相似文献
993.
994.
An electroimpact compaction method recently developed for powder consolidation is described In terms of the basic principles of electric discharge and dynamic compaction processes. The influence of processing parameters, microstructural characteristics and mechanical properties of preforms obtained are discussed. Mathematical models for the mechanics of compaction, electrical resistance, discharge current variations and comparisons with experimental results are presented. The best set of properties are obtained when electrical discharge is applied to cause interparticle fusion at the instant when dynamic compaction pressure attains its peak level. 相似文献
995.
N. Balchev D. Kovacheva V. Lovchinov K. Konstantinov K. Petrov 《Journal of Superconductivity》1993,6(1):49-54
The preparation conditions, phase composition, and superconducting properties of Bi-Pb-Sr-Ca-Cu oxide materials from different nominal compositions have been investigated. Nearly single-phase samples from Bi2Pb0.4Sr2Ca3Cu4O
y
, as well as from the proposed compositions Bi1.8Pb0.4Sr2Ca3Cu4O
y
and Bi1.8Pb0.4Sr2Ca2.5Cu3.5O
y
were obtained by a solid-state reaction in air. Samples with the third nominal composition showed the best superconducting properties (T
on=111 K and zero resistance atT
0=103 K). A possible mechanism for the 2223 phase formation in the three investigated compositions has been discussed. 相似文献
996.
A. M. Rabasco I. Caraballo M. Fern ndez-Ar valo 《Drug development and industrial pharmacy》1993,19(14):1673-1691
A high-performance liquid chromatographic (HPLC) assay has been developed for thimerosal and some of its degradation products: thiosalicylic and 2,2'-dithiosalicylic acids. Using this method, the influence of formulation factors as: isotonic agent, initial concentration, addition of tromethamine, pH and container material, over thimerosal stability was studied. 相似文献
997.
998.
EH Eddes AM Masclee HG Gooszen M Fr?lich CB Lamers 《Canadian Metallurgical Quarterly》1997,174(4):387-392
Two mobilizable cloning vectors, designated pABW1 and pAWB2, were constructed basing on the E. coli vector pBGS18 and oriT originating from RK2. In pABW2 the kanamycin resistance gene was replaced by a novel tetracycline resistance cassette derived from Tn1721. Both vectors, specific for E. coli, allow to perform the cloning steps in E. coli and then to efficiently transfer the constructs by conjugation to the host of choice. A vector which cannot propagate in the given host can be applied for identification of the host specific plasmid replicator regions. With the use of pABW2 we defined the minimal replicator region of pTAV202-a mini-derivative of the large pTAV1 plasmid of P. versutus. We also proved that RepC' encoded on this fragment is the principal initiator replication protein and that oriV is located along its coding sequence. 相似文献
999.
1000.
Gader P.D. Mohamed M. Jung-Hsien Chiang 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》1997,27(1):158-164
An off-line handwritten word recognition system is described. Images of handwritten words are matched to lexicons of candidate strings. A word image is segmented into primitives. The best match between sequences of unions of primitives and a lexicon string is found using dynamic programming. Neural networks assign match scores between characters and segments. Two particularly unique features are that neural networks assign confidence that pairs of segments are compatible with character confidence assignments and that this confidence is integrated into the dynamic programming. Experimental results are provided on data from the U.S. Postal Service. 相似文献