全文获取类型
收费全文 | 260091篇 |
免费 | 3190篇 |
国内免费 | 823篇 |
专业分类
电工技术 | 5130篇 |
综合类 | 330篇 |
化学工业 | 37219篇 |
金属工艺 | 10252篇 |
机械仪表 | 8486篇 |
建筑科学 | 6103篇 |
矿业工程 | 1076篇 |
能源动力 | 6389篇 |
轻工业 | 22855篇 |
水利工程 | 2561篇 |
石油天然气 | 3908篇 |
武器工业 | 68篇 |
无线电 | 34722篇 |
一般工业技术 | 50068篇 |
冶金工业 | 46543篇 |
原子能技术 | 5418篇 |
自动化技术 | 22976篇 |
出版年
2021年 | 2038篇 |
2019年 | 2032篇 |
2018年 | 3467篇 |
2017年 | 3534篇 |
2016年 | 3728篇 |
2015年 | 2319篇 |
2014年 | 4048篇 |
2013年 | 11283篇 |
2012年 | 6561篇 |
2011年 | 8875篇 |
2010年 | 6982篇 |
2009年 | 7848篇 |
2008年 | 8676篇 |
2007年 | 8616篇 |
2006年 | 7804篇 |
2005年 | 7139篇 |
2004年 | 6885篇 |
2003年 | 6734篇 |
2002年 | 6370篇 |
2001年 | 6470篇 |
2000年 | 6171篇 |
1999年 | 6253篇 |
1998年 | 14246篇 |
1997年 | 10271篇 |
1996年 | 8113篇 |
1995年 | 6413篇 |
1994年 | 5711篇 |
1993年 | 5582篇 |
1992年 | 4551篇 |
1991年 | 4211篇 |
1990年 | 4048篇 |
1989年 | 3779篇 |
1988年 | 3624篇 |
1987年 | 3170篇 |
1986年 | 3065篇 |
1985年 | 3610篇 |
1984年 | 3382篇 |
1983年 | 3031篇 |
1982年 | 2850篇 |
1981年 | 2951篇 |
1980年 | 2760篇 |
1979年 | 2648篇 |
1978年 | 2499篇 |
1977年 | 2947篇 |
1976年 | 3554篇 |
1975年 | 2316篇 |
1974年 | 2312篇 |
1973年 | 2318篇 |
1972年 | 1849篇 |
1971年 | 1745篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Films of electroactive polymers, such as polyaniline (PAN) in its emeraldine base form, and poly(3-alkylthiophene), poly(3-hexylthiophene) (P6TH), poly(3-octylthiophene) (P8TH), and poly(3-dodecylthiophene) (P12TH) can be readily functionalized via thermal or near ultraviolet-light-induced surface graft copolymerization with monomers of polyelectrolyte, polyampholyte and polymeric acids. The monomers used in the present work include dimethyl sulphate quaternized dimethylamino-ethylmethacrylate (DMAEM·C2H6SO4), 3-dimethyl(methacryloyloxyethyl)ammonium propane sulphonate (DMAPS), acrylic acid (AAc) and a sodium salt of styrene sulphonic acid (NaSS). The surface structures and compositions of the electroactive polymer films after functionalization via graft copolymerization were characterized by angle-resolved X-ray photoelectron spectroscopy. Graft copolymerization of poly(3-alkylthiophene) films, but not PAN films, with the hydrophilic monomers readily results in a stratified surface microstructure arising from the migration of the hydrophilic graft chains beneath a thin surface layer which is much richer in the substrate chains. On the other hand, graft copolymerization of PAN films with AAc and NaSS readily gives rise to a self-protonated (and thus conductive) surface structure. 相似文献
942.
This work pertains to output voltage stability of soft adjacent layer biased magnetoresistive heads with abutted permanent magnetic films for domain stabilization. A micromagnetic model has been developed to study the effect of the permanent magnet film microstructure and the micromagnetic properties of the abutted junction interface on head stability. The impact on head stability is analyzed with respect to interfacial ferromagnetic coupling across the junction interface and intergranular exchange coupling in the permanent magnet films among other film properties 相似文献
943.
Minimal inhibition concentrations (MIC) of gentamycin (Ge), neomycin (Neo), rifampicin (Rif), ampicillin (Amp), lincomycin (Lin), erythromycin (Ery), and streptomycin (STM) were determined by the agar dilution technique using 46, 130, 131, 125, 140, 139 and 142 strains of Staphylococcus aureus, respectively. The strains, selected from the collection of the authors' laboratory, were isolated from mammary gland secretions of cows affected with clinical or subclinical mastitis. The following ranges of MIC (micrograms/ml) were assessed for the antibiotics under study: Ge 0.125-0.50, Neo 0.06-0.50, Rif 0.0039-0.030, Amp 0.015-1.00, Lin 0.25-1.00, Ery 0.06-0.25, STM 0.50-64.0. Modal MIC (micrograms/ml) were as follows; Ery 0.125 (86%), Lin 0.5 (71.4%), Rif 0.007 (68.7%), Ge 0.25 (56.5%), STM 1.00 (54.2%), Neo 0.25 (53.8%), Amp 0.06 (41.6%). The order of efficiency expressed in MIC 90 (micrograms/ml) was as follows: Rif (0.015), Ery (0.125), Ge (0.25), Neo (0.25), Amp (0.5), STM (4.0). 相似文献
944.
Flexion-extension moments acting at the L5/S1 level and hip joints were calculated using three different techniques; a pure static analysis, a static analysis including the inertial force of the load, and a dynamic analysis. Ten subjects participated in the study and were asked to lift a box weighing either 50 N or 150 N, using a freestyle technique. The lifts were performed at normal and fast speed. The intra-subject lifting techniques were consistent when lifting the same loads. The moments predicted by the dynamic analysis and the static analysis were the same when holding weights in static postures. When performing the lifts, differences in the peak moments occurred between static and dynamic analyses. These differences were influenced by external load and by lifting speed. Taking the effect of the inertia of load into account in the static analysis resulted in an increase in the moment magnitude, but the predicted moment was still much less than in the dynamic analysis which yielded the largest moment magnitudes. The difference between dynamic and static analysis was greatest when lifting 50 N at fast speed; an 87% increase in L5/S1 moment and a 95% increase in hip moment was observed when replacing the pure static with a dynamic analysis. 相似文献
945.
D Sapoznikov M H Luria Y Mahler M S Gotsman 《Computer methods and programs in biomedicine》1992,39(1-2):75-84
Analysis of heart rate variability (HRV) with Holter monitoring is often difficult due to excessive artifacts and arrhythmias. While short sudden surges are treated successfully by most methods, slow heart rate (HR) variations, nocturnal trapezoidally-shaped HR increases and special types of arrhythmias which are similar to normal HRV fluctuations may distort further time domain and spectral analysis. This paper examines the advantages and disadvantages of different methods for preprocessing of HR data. We have developed the following approach to the analysis of HRV. (1) A combination method based on the absolute difference between HR values and both the last normal HR value and an updated mean is used for removal of artifacts and arrhythmias. This method can detect both sudden surges in HR values as well as longer periods of noise combined with slow normal variations. An additional stage of wild point removal is then optionally applied. (2) Certain special problems such as large T-waves, bigeminal rhythm, slow HR variations and nocturnal trapezoidally-shaped HR increases are also identified. Although none of the algorithms can be applied successfully to all cases, the final computer analysis for preprocessing described in the present study has proved to be superior to the simplified methods which are usually used and provides more suitable data for HRV analysis. 相似文献
946.
A logic language is suitable for specification if it is equipped with features for data abstraction and modularization. In this paper, an effective mechanism to incorporate function and type into logic programming is presented as the means to embed data abstraction mechanism into logic programming. This incorporation is essentially based on Horn clause logic with equality and a polymorphic type system that is an extension of Mycroft and O’Keefe’s system. This paper also presents an implementation based on Warren Abstract Machine (WAM) and shows the performance, along with a comparison with WAM. 相似文献
947.
Recent research suggests that implementing information systems presents considerable difficulties and that many implementations are total or partial failures. This paper argues that what both practitioners and students require are richer and more acceptable models of information systems implementation. Accordingly, case study data concerning the introduction of manufacturing resource planning (MRP II) are used to illustrate five patterns of behaviour (rites) which capture important social actions; and four components of changing psychological orientation. It is argued that appreciation of the rites and psychological developments identified here will support effective change programmes. Guidelines based on our model are provided for practitioners. 相似文献
948.
949.
The authors derive and verify the concept of antenna focusing by a planar 'microstrip reflectarray' antenna. Experimental results from schematically distributed patch radiators with microstrip delay lines are consistent with the simulation results. The advantages and disadvantages of such an antenna are described. The measured overall antenna efficiency is approximately 48% at scan angles up to 30 degrees . These results demonstrate the feasibility of such an antenna.<> 相似文献
950.
Lourtioz J.-M. Chusseau L. Brun E. Hamaide J.-P. Lesterlin D. Leblond F. 《Electronics letters》1992,28(16):1499-1500
Fourier-transform-limited pulses ( Delta tau . Delta nu approximately=0.35) have been obtained from a microwave-modulated DBR laser at 1.56 mu m. The chirp of the gain-switched pulse is compensated for by applying a fraction of the microwave signal to the phase section, thereby creating an instantaneous frequency shift of opposite sign. The generation of short coherent pulses from such a monolithic source can be of great interest for long haul soliton transmission.<> 相似文献