全文获取类型
收费全文 | 7820篇 |
免费 | 203篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 433篇 |
综合类 | 18篇 |
化学工业 | 1996篇 |
金属工艺 | 188篇 |
机械仪表 | 203篇 |
建筑科学 | 181篇 |
矿业工程 | 5篇 |
能源动力 | 319篇 |
轻工业 | 603篇 |
水利工程 | 28篇 |
石油天然气 | 11篇 |
无线电 | 814篇 |
一般工业技术 | 1437篇 |
冶金工业 | 1028篇 |
原子能技术 | 193篇 |
自动化技术 | 586篇 |
出版年
2023年 | 50篇 |
2022年 | 72篇 |
2021年 | 161篇 |
2020年 | 76篇 |
2019年 | 95篇 |
2018年 | 114篇 |
2017年 | 96篇 |
2016年 | 162篇 |
2015年 | 118篇 |
2014年 | 184篇 |
2013年 | 348篇 |
2012年 | 317篇 |
2011年 | 423篇 |
2010年 | 331篇 |
2009年 | 365篇 |
2008年 | 411篇 |
2007年 | 300篇 |
2006年 | 298篇 |
2005年 | 217篇 |
2004年 | 219篇 |
2003年 | 262篇 |
2002年 | 241篇 |
2001年 | 169篇 |
2000年 | 140篇 |
1999年 | 194篇 |
1998年 | 451篇 |
1997年 | 283篇 |
1996年 | 240篇 |
1995年 | 172篇 |
1994年 | 166篇 |
1993年 | 138篇 |
1992年 | 109篇 |
1991年 | 112篇 |
1990年 | 93篇 |
1989年 | 96篇 |
1988年 | 66篇 |
1987年 | 73篇 |
1986年 | 64篇 |
1985年 | 67篇 |
1984年 | 60篇 |
1983年 | 58篇 |
1982年 | 50篇 |
1981年 | 52篇 |
1980年 | 53篇 |
1979年 | 48篇 |
1978年 | 46篇 |
1977年 | 44篇 |
1976年 | 51篇 |
1975年 | 18篇 |
1973年 | 20篇 |
排序方式: 共有8043条查询结果,搜索用时 15 毫秒
11.
The morphologic changes and signal intensity of the spinal cord on preoperative magnetic resonance images were correlated with postoperative outcomes in 74 patients undergoing decompressive cervical surgery for compressive myelopathy. The transverse area of the spinal cord on T1-weighted images at the level of maximum compression was closely correlated with the severity of myelopathy, duration of disease, and recovery rate as determined by the Japanese Orthopaedic Association score. In patients with ossification of the posterior longitudinal ligament or cervical spondylotic myelopathy, the increased intramedullary T2-weighted magnetic resonance imaging signal at the site of maximal cord compression and duration of disease significantly influenced the rate of recovery. A multiple regression equation was then developed with these three variables to predict surgical outcomes. 相似文献
12.
13.
Masatsune Kato Takaaki Aoki Takashi Noji Yasuhiro Ono Yoji Koike Tomoyuki Hikita Yoshitami Saito 《Journal of Superconductivity and Novel Magnetism》1994,7(1):37-38
We have investigated the relation between the crystal structure and superconductivity in La1.9Bi0.1CuO4+δ , in which the phase separation observed in La2CuO4+δ is suppressed. A phase diagram in theT?δ plane is given for La1.9Bi0.1CuO4+δ with excess oxygen. For very smallδ values, the crystal structure is orthorhombic, and an orthorhombic-tetragonal phase transition occurs markedly atδ ~ 0.03 in the measured temperature range between 13 and 293 K. Superconductivity is observed in the range of 0.04<δ<0.11. This is clear evidence thathigh-T c superconductivity also appears in the tetragonal phase. 相似文献
14.
S Higashiyama M Horikawa K Yamada N Ichino N Nakano T Nakagawa J Miyagawa N Matsushita T Nagatsu N Taniguchi H Ishiguro 《Canadian Metallurgical Quarterly》1997,122(3):675-680
The availability of an analgesic compound devoid of the side effects associated with the commonly used opioid and nonsteroidal antiinflammatory drugs would be useful during the perioperative period. Although adenosine has analgesic and anesthetic-sparing properties, it also produces dose-dependent cardiovascular depression. Inhibitors of adenosine kinase may be able to provide analgesia without producing acute cardiovascular or respiratory depression. This preliminary study investigated the effects of a novel adenosine kinase-inhibiting drug, GP683, on the minimum alveolar anesthetic concentration (MAC) of desflurane in dogs. Seven mongrel dogs were administered one of three different GP683 dose regimens (or the solvent) by intravenous infusion on separate occasions according to a cross-over study design. After determining the baseline desflurane MAC value, GP683 was infused at 75, 150, or 300 microg x kg(-1) x min(-1) for 5 min as a loading dose, followed by 15, 30, or 60 microg x kg(-1) x min(-1) for an additional 85 min to maintain a stable plasma drug level. The desflurane MAC was redetermined 30-90 min after starting the study drug or vehicle infusion, and 30-90 min and 120-180 min after termination of the infusion. Cardiovascular variables and plasma concentrations of GP683 were determined at specific intervals before, during, and after the MAC determinations. The three GP683 dose regimens produced 22%, 31%, and 50% decreases in the desflurane MAC, respectively. In addition, there was good correlation between the decrease in desflurane MAC and the plasma GP683 concentration (r = -0.78). Although the mean arterial pressure (MAP) was decreased up to 25% by the highest infusion rate of GP683, adjustments in the desflurane concentration to an equi-MAC value resulted in normalization of the MAP values. Furthermore, GP683 produced no changes in heart rate. In conclusion, the adenosine kinase-inhibiting drug, GP683, produced dose-dependent decreases in the desflurane MAC of dogs without producing untoward hemodynamic changes. IMPLICATIONS: An investigational drug (GP683) that can increase the levels of an important endogenous substance in the body (adenosine) has been found to decrease the anesthetic requirement in dogs without producing adverse effects on the cardiovascular system. 相似文献
15.
Co-Cinobufotalin Oral Liquor (CCOL) was studied for its ability to inhibit hepatitis B virus DNA replication, HBsAg and HBeAg expression in a HBV-transfected cell line (2.2.15 cell). The result showed that ID50 (the drug concentration that inhibits HBsAg or HBeAg secretion by 50%) was 0.08 mg/ml and 0.07 mg/ml on HBsAg and HBeAg respectively. CD50 (the drug concentration that reduces cell growth by 50%) was 2.5 mg/ml. TI (therapeutic index) was 31.3 and 35.7 respectively. The present data suggest that CCOL could exert a potent antiviral activity against HBV in vitro. Southern blot showed that CCOL inhibited HBV-DNA repication in a dose-dependent manner. 相似文献
16.
Y Tomigahara M Mori K Shiba N Isobe H Kaneko I Nakatsuka H Yamada 《Canadian Metallurgical Quarterly》1994,24(12):1205-1214
1. To examine the metabolic fate of (1RS, trans)- or (1RS, cis)-tetramethrin [3, 4, 5, 6-tetrahydrophthalimidomethyl (1RS, trans)- or (1RS, cis)-chrysanthemate], rat was administered a single oral dose of trans- or cis-[alcohol-14C]tetramethrin at dose levels of 2 or 250 mg/kg. 2. The radiocarbon was almost completely eliminated from rat within 7 days after administration in all groups. 14C-recoveries (expressed as percentages relative to the dosed 14C) in faeces and urine were 38-58 and 42-58% respectively in rat administrated trans-[alcohol-14C]tetramethrin, and in faeces and urine were 66-91 and 9-31% respectively in rat administered cis-[alcohol-14C]tetramethrin. 3. Fourteen metabolites found in excreta were purified by using several chromatographic techniques and identified by spectroanalyses (nmr and MS). Five sulphonate derivatives and three dicarboxylic acid derivatives were found. 4. The main metabolites were sulphonate derivatives in the faeces, and in the urine, alcohols, dicarboxylic acid and reduced metabolites derived from the 3,4,5,6-tetrahydrophthalimide moiety. 相似文献
17.
Takashi Yamazaki Yoichi Takino Ryosuke Matsuoka Susumu Ito 《Electrical Engineering in Japan》1993,113(8):26-36
According to the recent analysis results of temporary ac overvoltage in the ac system connected with a frequency converter station, large-magnitude over-voltages were confirmed to occur under some special system conditions. Most of the station insulators currently used cannot withstand such overvoltages according to an evaluation based on the data obtained earlier. The necessity of tests to be done to evaluate such performance more accurately was recognized. Both power frequency and switching impulse overvoltage flashover tests were made on contaminated insulators by the method well simulating the natural wetting condition. Switching impulse flashover voltage with the waveshape having a long wavefront time of 2 ms can be well correlated with the flashover voltage characteristics of temporary ac overvoltage. Higher flashover voltage characteristics were obtained by a clean fog test method compared with those obtained by equivalent fog test method. 相似文献
18.
Palaeostress reconstruction is the key to quantitative characterization of fractured hydrocarbon reservoirs. In order to calculate the palaeostresses responsible for fault activity, faults in oriented core samples can be analysed and the optimal stresses can then be determined from fault-slip data in a least-squares sense. Many fractured reservoir rocks, however, include faults generated during a number of different tectonic phases. In these cases, the optimal stresses can be determined for subgroups of faults which are considered to be of approximately the same age. The difficulty with this is that criteria for accurate age-dating are often absent, especially from core samples.
Recently, the so-called "multi-inverse" method has been proposed to address this problem. This is a numerical technique for separating palaeostresses within a heterogeneous fault assemblage in the absence of a priori information on the faults'relative ages. In this paper, we apply the method to eighteen faults in two short (9m) cores from an exploration well in Hokkaido, northern Japan. The cores came from a fractured hydrocarbon reservoir and were oriented by correlation with borehole images. Core lithologies included massive Cretaceous basalts in which there was no layering which would show fault offsets; for these samples, we determined the sense of shear by studying asymmetric microstructures on the fault surfaces. The results show that the rocks have experienced six different stress regimes. In general, these are compatible with the tectonic history of the study area as inferred from the regional stratigraphy and from macroscale geological structures.
These results show that the multi-inverse method can be used to extract palaeostress data from cores, thereby providing information which will assist with the exploration of (and production from) fractured hydrocarbon reservoirs. 相似文献
Recently, the so-called "multi-inverse" method has been proposed to address this problem. This is a numerical technique for separating palaeostresses within a heterogeneous fault assemblage in the absence of a priori information on the faults'relative ages. In this paper, we apply the method to eighteen faults in two short (9m) cores from an exploration well in Hokkaido, northern Japan. The cores came from a fractured hydrocarbon reservoir and were oriented by correlation with borehole images. Core lithologies included massive Cretaceous basalts in which there was no layering which would show fault offsets; for these samples, we determined the sense of shear by studying asymmetric microstructures on the fault surfaces. The results show that the rocks have experienced six different stress regimes. In general, these are compatible with the tectonic history of the study area as inferred from the regional stratigraphy and from macroscale geological structures.
These results show that the multi-inverse method can be used to extract palaeostress data from cores, thereby providing information which will assist with the exploration of (and production from) fractured hydrocarbon reservoirs. 相似文献
19.
Yoshida Y. Kawazoe S. Ibuki K. Yamada K. Ochi N. 《Power Delivery, IEEE Transactions on》1992,7(4):1805-1812
The authors present the basic philosophy, construction, design features, and test results of a new fault locating system. This fault locating system helps to shorten the time required for restoration of service after the occurrence of a busbar fault in an air-insulated distribution substation. Recent optical and electronic technologies allow the design of a highly accurate and compact fault locating system which consists of optical current detectors using the Faraday effect and a fault locating processor using a digital data processing technique. The fault location is carried out by discriminating between the directions of zero-sequence currents. Through various tests and field operations, it has been confirmed that the system has sufficient performance for practical applications 相似文献
20.
Takashi Kashiwagi 《Fire Safety Journal》1981,3(3):185-200
Transmittance of external radiation from a CO2 laser through a boundary layer of decomposition products over a vertical sample surface is measured during the ignition period. The results indicate that there is significant absorption of the external radiation for PMMA, and a lesser but still not negligible amount, for red oak. An increase in gas phase temperature over surface temperature is observed over much of the ignition interval. Using the experimentally measured incident flux at the sample surface, surface temperature history was calculated from a model that included re-radiation and convection losses from the surface, endothermic decomposition and conduction into the material. The results confirm the significant effect of gas phase absorption on surface temperature. Steady-state-derived surface regression rate expression was used for PMMA in this model. The results raise questions about the validity of such data for the dynamic heating conditions during the ignition period. Further studies needed to understand the radiative ignition mechanism are identified. 相似文献