全文获取类型
收费全文 | 603107篇 |
免费 | 8023篇 |
国内免费 | 1871篇 |
专业分类
电工技术 | 10253篇 |
综合类 | 2825篇 |
化学工业 | 88897篇 |
金属工艺 | 24453篇 |
机械仪表 | 18108篇 |
建筑科学 | 14703篇 |
矿业工程 | 2804篇 |
能源动力 | 15572篇 |
轻工业 | 50304篇 |
水利工程 | 6396篇 |
石油天然气 | 9662篇 |
武器工业 | 37篇 |
无线电 | 68585篇 |
一般工业技术 | 116522篇 |
冶金工业 | 105885篇 |
原子能技术 | 10778篇 |
自动化技术 | 67217篇 |
出版年
2022年 | 3165篇 |
2021年 | 4906篇 |
2020年 | 3492篇 |
2019年 | 4574篇 |
2018年 | 21332篇 |
2017年 | 20114篇 |
2016年 | 17316篇 |
2015年 | 6118篇 |
2014年 | 9431篇 |
2013年 | 24222篇 |
2012年 | 17514篇 |
2011年 | 28919篇 |
2010年 | 23449篇 |
2009年 | 22866篇 |
2008年 | 24355篇 |
2007年 | 24970篇 |
2006年 | 15608篇 |
2005年 | 15296篇 |
2004年 | 14616篇 |
2003年 | 14468篇 |
2002年 | 13130篇 |
2001年 | 12913篇 |
2000年 | 12029篇 |
1999年 | 12643篇 |
1998年 | 32858篇 |
1997年 | 22917篇 |
1996年 | 17485篇 |
1995年 | 13042篇 |
1994年 | 11293篇 |
1993年 | 10980篇 |
1992年 | 7922篇 |
1991年 | 7439篇 |
1990年 | 7261篇 |
1989年 | 7013篇 |
1988年 | 6476篇 |
1987年 | 5766篇 |
1986年 | 5655篇 |
1985年 | 6265篇 |
1984年 | 5900篇 |
1983年 | 5170篇 |
1982年 | 4900篇 |
1981年 | 4966篇 |
1980年 | 4705篇 |
1979年 | 4609篇 |
1978年 | 4408篇 |
1977年 | 5334篇 |
1976年 | 6971篇 |
1975年 | 3796篇 |
1974年 | 3550篇 |
1973年 | 3665篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Recent work concerning the interstitial modification of permanent magnet alloys based on rare-earth iron intermetallic compounds is reviewed. The crystal structure of the new materials is discussed, then the thermodynamic and statistical aspects of the low-temperature interstitial modification process are considered. Finally, reaction kinetics and thermal stability of the new compounds are discussed and future prospects assessed. 相似文献
992.
R. H. Howell P. A. Sterne M. J. Fluss J. H. Kaiser K. Kitazawa H. Kojima 《Journal of Superconductivity and Novel Magnetism》1994,7(1):169-173
High-statistics (>4 × 108 counts), room-temperature measurements of the electron-positron momentum density of La2?x Sr x CuO4 have been performed for samples with Sr concentrations of x=0.0, 0.1, 0.13, and 0.2. These spectra have been analyzed in conjunction with theoretical calculations of the electron-positron momentum density. The metallic samples show features consistent with the presence of a Fermi surface, but its evolution with increasing Sr concentration does not follow the predictions of band theory. These results may indicate the effects of electron-electron correlation on the electron momentum distribution in the Cu-O plane. 相似文献
993.
We evaluated the effect of 4-(2-benzylphenoxy)-N-methylbutylamine hydrochloride (bifemelane hydrochloride) on superoxide production by human neutrophils using an MCLA-dependent chemiluminescence assay. Bifemelane hydrochloride dose-dependently inhibited superoxide production by neutrophils stimulated with phorbol myristate acetate, opsonized zymosan, or N-formyl-methionyl-leucyl-phenylalanine, while it had no effect on superoxide production by a hypoxanthine-xanthine oxidase system. These results indicate that bifemelane hydrochloride does not have a scavenging effect, but has an inhibitory effect on superoxide generation by neutrophils. Although this drug is commonly used for treating chronic cerebral infarction, it may also have a protective effect on acute ischemia/reperfusion injury. 相似文献
994.
Aspergillus sydowii MG49 produces a 30-kDa exosplitting xylobiohydrolase during growth on xylan. A specific chemical modification and substrate protection analysis of purified xylanase provided evidence that tryptophan and carboxy and amino groups are present at the catalytic site of this enzyme. Thermal inactivation of the xylanase occurs because of irreversible polymolecular aggregation, which is slower in the presence of glycerol. 相似文献
995.
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
996.
997.
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
998.
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
999.
1000.
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