全文获取类型
收费全文 | 417174篇 |
免费 | 6723篇 |
国内免费 | 1405篇 |
专业分类
电工技术 | 7737篇 |
综合类 | 351篇 |
化学工业 | 62923篇 |
金属工艺 | 14399篇 |
机械仪表 | 11998篇 |
建筑科学 | 11895篇 |
矿业工程 | 880篇 |
能源动力 | 11281篇 |
轻工业 | 44161篇 |
水利工程 | 3347篇 |
石油天然气 | 1860篇 |
武器工业 | 13篇 |
无线电 | 55783篇 |
一般工业技术 | 77674篇 |
冶金工业 | 75917篇 |
原子能技术 | 5582篇 |
自动化技术 | 39501篇 |
出版年
2021年 | 2798篇 |
2019年 | 2558篇 |
2018年 | 3968篇 |
2017年 | 4038篇 |
2016年 | 4294篇 |
2015年 | 3552篇 |
2014年 | 5917篇 |
2013年 | 19612篇 |
2012年 | 10497篇 |
2011年 | 15067篇 |
2010年 | 11534篇 |
2009年 | 13100篇 |
2008年 | 14181篇 |
2007年 | 14533篇 |
2006年 | 13001篇 |
2005年 | 12162篇 |
2004年 | 11740篇 |
2003年 | 11404篇 |
2002年 | 11045篇 |
2001年 | 11220篇 |
2000年 | 10348篇 |
1999年 | 10833篇 |
1998年 | 24163篇 |
1997年 | 17702篇 |
1996年 | 13982篇 |
1995年 | 11036篇 |
1994年 | 9839篇 |
1993年 | 9432篇 |
1992年 | 7163篇 |
1991年 | 6816篇 |
1990年 | 6426篇 |
1989年 | 6138篇 |
1988年 | 5882篇 |
1987年 | 4914篇 |
1986年 | 4853篇 |
1985年 | 5999篇 |
1984年 | 5614篇 |
1983年 | 4854篇 |
1982年 | 4524篇 |
1981年 | 4467篇 |
1980年 | 4224篇 |
1979年 | 4092篇 |
1978年 | 3786篇 |
1977年 | 4581篇 |
1976年 | 6122篇 |
1975年 | 3125篇 |
1974年 | 3024篇 |
1973年 | 2901篇 |
1972年 | 2325篇 |
1971年 | 2008篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
JE Myers T Mieczkowski J Perel D Abbondanza TB Cooper JJ Mann 《Canadian Metallurgical Quarterly》1994,35(2):112-120
Serotonergic responsivity was assessed in 20 psychiatric patients by the prolactin response to a fenfluramine challenge test. During the fenfluramine challenge 6 of 20 patients (30%) spontaneously reported psychopathologic reactions that included: increased anxiety/agitation, psychotic symptoms, illusions, mood elevation, and anergia. The time of peak behavioral symptoms (2.5 +/- 0.8 hrs) corresponded closely to the time of peak increase in prolactin levels (3.0 +/- 1.1 hr). Abnormal behavioral responders had statistically significant greater increases in prolactin 1 to 4 hr after fenfluramine when compared to normal responders. Patients who developed an abnormal psychopathologic response to fenfluramine were characterized by higher levels of anxiety and agitation at the time of admission to the hospital but otherwise were not distinguishable on the basis of severity of other psychiatric symptoms. This study suggests that increased serotonergic transmission may trigger anxiety, psychosis, and mood elevation in specific vulnerable individuals, whereas other patients with similar psychiatric illnesses are not affected. 相似文献
992.
Muller-Borer B.J. Erdman D.J. Buchanan J.W. 《IEEE transactions on bio-medical engineering》1994,41(5):445-454
Computer simulations were used to study the role of resistive couplings on flat-wave action potential propagation through a thin sheet of ventricular tissue. Unlike simulations using continuous or periodic structures, this unique electrical model includes random size cells with random spaced longitudinal and lateral connections to simulate the physiologic structure of the tissue. The resolution of the electrical model is ten microns, thus providing a simulated view at the subcellular level. Flat-wave longitudinal propagation was evaluated with an electrical circuit of over 140,000 circuit elements, modeling a 0.25 mm by 5.0 mm sheet of tissue. An electrical circuit of over 84,000 circuit elements, modeling a 0.5 mm by 1.5 mm sheet was used to study flat-wave transverse propagation. Under normal cellular coupling conditions, at the macrostructure level, electrical conduction through the simulated sheets appeared continuous and directional differences in conduction velocity, action potential amplitude and V˙max were observed. However, at the subcellular level (10 μm) unequal action potential delays were measured at the longitudinal and lateral gap junctions and irregular wave-shapes were observed in the propagating signal. Furthermore, when the modeled tissue was homogeneously uncoupled at the gap junctions conduction velocities decreased as the action potential delay between modeled cells increased. The variability in the measured action potential was most significant in areas with fewer lateral gap junctions, i.e., lateral gap junctions between fibers were separated by a distance of 100 μm or more 相似文献
993.
A wideband low-noise pseudomorphic HEMT MMIC variable-gain amplifier has been designed and fabricated. The amplifier has a nominal gain of 13 dB across the band 2-20 GHz, with gain flatness better than ±0.4 dB. The noise figure is less than 3 dB across the band 6-16 GHz. An on-chip temperature-sensing diode is used to provide a linear temperature correction which has been used to reduce the gain variation of the amplifier by a factor of 2 across the temperature range -50°C to +95°C 相似文献
994.
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
995.
996.
J Gurevitch B Sela A Jonas H Golan Y Yahav JH Passwell 《Canadian Metallurgical Quarterly》1993,82(1):119-121
Isolation of Salmonella from the feces of impounded dogs was carried out to make clear the recent microbiological condition of dogs introduced into our facilities. Salmonella was isolated from 10 out of 283 samples (3.5%). Inparticular, during the first week after introduction, Salmonella was isolated from nine out of 74 dogs (12.2%). The isolation rate during the first week after introduction was significantly higher than that for dogs introduced later. No isolates were detected from dogs reared for more than 3 weeks after introduction. This study indicates that impounded dogs had the highest risk of infecting a person with Salmonella during the first week after introduction into our laboratory animal facilities, and that we need to pay attention to this fact when handling them. 相似文献
997.
HM Krumholz Y Wang EM Parent J Mockalis M Petrillo MJ Radford 《Canadian Metallurgical Quarterly》1997,157(19):2242-2247
998.
J. Hong E. S. Lambers C. R. Abernathy S. J. Pearton R. J. Shul W. S. Hobson 《Journal of Electronic Materials》1998,27(3):132-137
Dry etching of InGaP, AlInP, and AlGaP in inductively coupled plasmas (ICP) is reported as a function of plasma chemistry (BCl3 or Cl2, with additives of Ar, N2, or H2), source power, radio frequency chuck power, and pressure. Smooth anisotropic pattern transfer at peak etch rates of 1000–2000Å·min?1 is obtained at low DC self-biases (?100V dc) and pressures (2 mTorr). The etch mechanism is characterized by a trade-off between supplying sufficient active chloride species to the surface to produce a strong chemical enhancement of the etch rate, and the efficient removal of the chlorinated etch products before a thick selvedge layer is formed. Cl2 produces smooth surfaces over a wider range of conditions than does BCl3. 相似文献
999.
L Palazzo B Landi C Cellier G Roseau S Chaussade D Couturier J Barbier 《Canadian Metallurgical Quarterly》1997,29(9):850-853
BACKGROUND AND STUDY AIMS: Granular cell tumors of the esophagus are rare tumors. A definite diagnosis is achieved by endoscopic biopsies in only 50% of cases. Endoscopic ultrasonography (EUS) is the best procedure in the evaluation of upper gastrointestinal tract submucosal tumors. The aim of this study was to describe the endosonographic findings of esophageal granular cell tumors. METHODS: From January 1989 to March 1994, 15 patients with 21 granular cell tumors which had negative biopsies were examined by EUS (Olympus GF UM3 or GF UM20,7,5 and 12 MHz). In five cases, the tumor was also studied with a 20 MHz Olympus miniprobe. The final histological diagnoses were obtained by subsequent endoscopic snare resection in 20 cases and surgically in one case. RESULTS: The endosonographic features (with the GF UM3 or GF UM20) of esophageal granular cell tumors were: a) a tumor size of less than 2 cm in 95% of cases; b) an hypoechoic solid pattern in 100% of cases; c) a tumor arising in the inner layers in 95% (second echo-poor layer n=15; third echo-rich layer n=5). In one case, the endosonographic finding was transmural malignant infiltration of the esophageal wall (histologically confirmed). CONCLUSION: When a granular cell tumor of the esophagus is suspected, EUS can show the inner layer location of the tumor and thus contribute to planning the endoscopic resection or follow up. When the tumor also invades the outer layers, EUS can contribute to planning the surgical resection. 相似文献
1000.