全文获取类型
收费全文 | 309950篇 |
免费 | 4606篇 |
国内免费 | 1331篇 |
专业分类
电工技术 | 5284篇 |
综合类 | 586篇 |
化学工业 | 47154篇 |
金属工艺 | 11886篇 |
机械仪表 | 9150篇 |
建筑科学 | 8116篇 |
矿业工程 | 1742篇 |
能源动力 | 7693篇 |
轻工业 | 26241篇 |
水利工程 | 3253篇 |
石油天然气 | 5849篇 |
武器工业 | 44篇 |
无线电 | 35823篇 |
一般工业技术 | 63260篇 |
冶金工业 | 53856篇 |
原子能技术 | 7767篇 |
自动化技术 | 28183篇 |
出版年
2021年 | 2930篇 |
2020年 | 2269篇 |
2019年 | 2705篇 |
2018年 | 4537篇 |
2017年 | 4617篇 |
2016年 | 4979篇 |
2015年 | 3412篇 |
2014年 | 5473篇 |
2013年 | 14245篇 |
2012年 | 8615篇 |
2011年 | 11647篇 |
2010年 | 9043篇 |
2009年 | 10200篇 |
2008年 | 10678篇 |
2007年 | 10582篇 |
2006年 | 9009篇 |
2005年 | 8204篇 |
2004年 | 7986篇 |
2003年 | 7722篇 |
2002年 | 7466篇 |
2001年 | 7405篇 |
2000年 | 6974篇 |
1999年 | 7256篇 |
1998年 | 17042篇 |
1997年 | 12150篇 |
1996年 | 9386篇 |
1995年 | 7234篇 |
1994年 | 6373篇 |
1993年 | 6378篇 |
1992年 | 4631篇 |
1991年 | 4409篇 |
1990年 | 4261篇 |
1989年 | 4233篇 |
1988年 | 3925篇 |
1987年 | 3559篇 |
1986年 | 3543篇 |
1985年 | 3987篇 |
1984年 | 3711篇 |
1983年 | 3403篇 |
1982年 | 3187篇 |
1981年 | 3243篇 |
1980年 | 3186篇 |
1979年 | 2987篇 |
1978年 | 3022篇 |
1977年 | 3306篇 |
1976年 | 4292篇 |
1975年 | 2559篇 |
1974年 | 2500篇 |
1973年 | 2511篇 |
1972年 | 2096篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Mastrapasqua M. Luryi S. Belenky G.L. Garbinski P.A. Cho A.Y. Sivco D.L. 《Electron Devices, IEEE Transactions on》1993,40(8):1371-1377
A monolithic multiterminal logic device that functions both optically and electrically as an ORNAND gate, is demonstrated for the first time. The device, based on the real-space transfer of hot electrons into a complementary collector layer, has been implemented in an InGaAs/InAlAs/InGaAs heterostructure grown by molecular beam epitaxy. Excellent performance is obtained at room temperature. The collector current and the optical output power both exhibit the OR and the NAND functions of any two of the three input terminals, these functions being interchangeable by the voltage on the third terminal 相似文献
142.
143.
S. Bismo P. Duverneuil L. Pibouleau S. Domenech J. -P. Couderc 《Materials and Manufacturing Processes》1995,10(2):241-266
This paper presents the results of our work on a new type of CVD reactor, annular reactor. This equipment is able to deposit pure silicon and also in-situ phosphorus doped silicon on a large number of substrates 相似文献
144.
Rats were trained to discriminate between ethanol (1.0 g/kg; 10% v/v) and saline under a fixed ratio 10 schedule of sweetened milk reinforcement. Both diazepam [nonselective, full benzodiazepine (BZ) receptors agonist] and bretazenil (nonselective, partial BZ receptor agonist) produced dose-dependent ethanol-appropriate responding (>75%). Neither diazepam nor bretazenil affected the response rate at the doses producing maximal generalisation from ethanol. In contrast, zolpidem (full BZ1 receptor agonist) and abecarnil (full BZ1/full or partial BZ2 receptor agonist) produced only moderate (<50%) ethanol-appropriate responding when tested up to doses that markedly decreased the overall response rate. These results suggest that: 1) there are no major differences between full and partial, nonselective BZ receptor agonists in their ability to substitute for 1.0 g/kg dose of ethanol; 2) stimulation of BZ1 receptors alone is not sufficient to produce ethanol-like discriminative stimulus effects in the rat. 相似文献
145.
We report a comprehensive crosstalk investigation of a packaged InGaAsP/InP 4×4 semiconductor optical amplifier gate switch matrix, experimentally as well as theoretically. For a fully loaded switch with the same wavelength on all four inputs, all possible switching combinations are analyzed, thus yielding realistic crosstalk figures. Coherent and incoherent crosstalk phenomena are identified, and a switch crosstalk less than -40 dB has been measured 相似文献
146.
Kang W.P. Wisitsora-at A. Davidson J.L. Kerns D.V. 《Electron Device Letters, IEEE》1998,19(10):379-381
A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp2 content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters 相似文献
147.
Effect of oral administration of fenvalerate, a pyrethroid insecticide was studied in different behavioral paradigms in mice. Fenvalerate at 15, 30 and 45 mg/kg dose increased start latency, decreased ambulation and rearing in open-field, increased immobility in tail-suspension test and attenuated haloperidol-induced catalepsy in a dose-dependent manner. The time-course of data shows that these effects of fenvalerate may sustain up to several hours of its oral administration. The study indicates that pyrethroids can cause adverse behavioral effects even after a very low-level exposure. Although, it is difficult to extrapolate these findings directly to behavioral changes in man, they indicate that subtle behavioral dysfunction also occur in humans at exposures which do not cause acute toxicity. 相似文献
148.
149.
An investigation has been carried out into the possibility of in situ formation of MoS2 within porous anodic films on aluminium, to improve subsequent tribological behaviour, by re-anodizing in thiomolybdate electrolyte. Acidification of thiomolybdate was employed to simulate the conditions for formation of the sulphide at the anodic film/electrolyte interface, followed by appropriate vacuum heat treatments to study possible temperature effects on the sulphide due to either friction or Joule heating during anodizing. The products of both acidification and heat treatment, characterized by X-ray powder diffraction and scanning electron microscopy, were compared with those formed by direct thermal decomposition of ammonium tetrathiomolybdate crystals. The precipitate formed by acidification was mainly amorphous molybdenum trisulphide (MoS3), which on heat treatment at 450 and 850°C yielded 3R-MoS2. 3R-MoS2 also formed by the thermal decomposition of thiomolybdate crystals. Thermogravimetric and differential thermal analyses showed that the decomposition of MoS3 to MoS2 occurred in the range 220–370°C and revealed the sequence of reaction steps. The findings suggest that mainly amorphous MoS3 is formed as a consequence of changes in the pH of the film/electrolyte interface during re-anodizing but the product is relatively easily transformed to crystalline MoS2 on moderate heating which may occur during wear processes. 相似文献
150.
The cytosolic chaperonin containing TCP-1 (CCT) is known to keep fold cytoskeletal proteins and is involved in the proper organization of the cytoskeleton. These studies are based on the assumption that growth responses linked to structural rearrangement of the plant cytoskeleton include the action of CCT and the need for newly synthesized tubulin. The presence of the alpha- and epsilon-subunits of CCT was investigated in soluble fractions of protein extracts from maize mesocotyls and coleoptiles at distinct growth stages. The CCT-subunits, tubulins and actin decreased in the coleoptile in response to far-red light. In addition, independent from light treatment, the amount of CCT epsilon abundance declined with age in coleoptiles and mesocotyls between 2 and 4.5 days after sowing. In contrast to CCT epsilon, no significant light regulation of CCT alpha was found in the mesocotyl. In two day old, light-grown rapidly elongating coleoptiles part of the CCT alpha subunit and the bulk of actin and tubulin was found shifted into fractions of high molecular weight complexes when compared to slowly elongating, dark grown coleoptiles. In 4.5 day old, etiolated and elongating coleoptiles, part of both CCT-subunits and cytoskeleton proteins were found in fractions of high molecular weight. A complete disappearance of these polypeptides was observed in old far-red irradiated growth-arrested coleoptiles. CCT epsilon was found to be colocalized to microtubular structures and to the nucleus. We conclude from our data that abundance of CCT-subunits in soluble extracts is dependent on age and light treatment, but independent from the growth stage of mesocotyl and coleoptile. 相似文献