全文获取类型
收费全文 | 182416篇 |
免费 | 16133篇 |
国内免费 | 9185篇 |
专业分类
电工技术 | 12353篇 |
技术理论 | 13篇 |
综合类 | 13242篇 |
化学工业 | 28346篇 |
金属工艺 | 10183篇 |
机械仪表 | 11878篇 |
建筑科学 | 15099篇 |
矿业工程 | 5250篇 |
能源动力 | 5310篇 |
轻工业 | 12598篇 |
水利工程 | 3652篇 |
石油天然气 | 9203篇 |
武器工业 | 1612篇 |
无线电 | 22221篇 |
一般工业技术 | 20583篇 |
冶金工业 | 8310篇 |
原子能技术 | 2162篇 |
自动化技术 | 25719篇 |
出版年
2024年 | 649篇 |
2023年 | 2636篇 |
2022年 | 4979篇 |
2021年 | 6741篇 |
2020年 | 5131篇 |
2019年 | 4170篇 |
2018年 | 4864篇 |
2017年 | 5459篇 |
2016年 | 4841篇 |
2015年 | 6771篇 |
2014年 | 8756篇 |
2013年 | 10498篇 |
2012年 | 11769篇 |
2011年 | 12580篇 |
2010年 | 11414篇 |
2009年 | 11236篇 |
2008年 | 11334篇 |
2007年 | 10505篇 |
2006年 | 10613篇 |
2005年 | 9086篇 |
2004年 | 6689篇 |
2003年 | 6048篇 |
2002年 | 6425篇 |
2001年 | 5754篇 |
2000年 | 4638篇 |
1999年 | 4508篇 |
1998年 | 3490篇 |
1997年 | 3024篇 |
1996年 | 2696篇 |
1995年 | 2255篇 |
1994年 | 1815篇 |
1993年 | 1391篇 |
1992年 | 1100篇 |
1991年 | 847篇 |
1990年 | 669篇 |
1989年 | 563篇 |
1988年 | 421篇 |
1987年 | 316篇 |
1986年 | 223篇 |
1985年 | 174篇 |
1984年 | 102篇 |
1983年 | 79篇 |
1982年 | 98篇 |
1981年 | 71篇 |
1980年 | 55篇 |
1979年 | 45篇 |
1978年 | 26篇 |
1977年 | 25篇 |
1976年 | 40篇 |
1959年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this study, 16 cases of unilateral alveolar cleft with cleft lip and palate were repaired with autografts of cancellous bone (13 cases) or hydroxyapatite (3 cases). The grafts were covered by reflected mucoperiosteal flaps and a mucosal flap from the upper lip. Twelve of the thirteen cases were followed up for 1-5 years. Nine of whom using cancellous bone had bony continuity of the maxilla and 7 cases erupted permanent maxillary canines within the area of autografts. None of the 3 cases using hydroxyapatite erupted a canine tooth. The results showed that autograft was better than hydroxyapatite in terms of maxillary canine eruption. 相似文献
992.
采用表面效应集总模型综合考虑表面费米能级钉扎和表面复合效应,对AlGaAs/GaAsHBT表面效应的影响进行了二维数值模拟。结果表明,表面态的存在对集电极电流几乎不产生影响,但显著增加基极电流,使得电流增益明显下降。同时还发现在台面结构AIGaAs/GaAsHBT中外基区表面复合的集边效应,即外基区表面复合主要发生在发射极台面与外基区的交界处附近,与外基区长度基本无关。模拟还表明基区缓变结构可以减少表面复合,提高电流增益。 相似文献
993.
介绍了X射线荧光光谱仪的基本原理、特点、类型划分及工艺设计等情况,着重叙述了在黑色冶金矿山推广应用的可能性和必要性 相似文献
994.
一种弧焊机器人实时激光扫描视觉系统 总被引:2,自引:0,他引:2
研制了一种小型高精度弧焊机器人实时激光扫描视觉系统,对其各项性能进行了测试,并进行了抗电弧光干扰试验,结果表明,此系统精度高,抗干扰能力强,检测范围宽,能广泛地应秀于机器人和自动化焊接中。 相似文献
995.
J.Z. Wu S.H. Yoo T. Aytug A. Gapud B.W. Kang S. Wu W. Zhou 《Journal of Superconductivity》1998,11(1):169-171
The effect of Na- and Li-doping in Hg-based cuprates has been studied. It has been found that superconductivity can be achieved in samples containing small amount of Na or Li. While little change is found in the crystalline structure, the formed superconducting phase have the onset Tc typically above 140 K and zero-resistance Tc up to 136K. More interestingly, the processing temperature for the doped Hg-1223 can be reduced significantly to near 700 °C which is promising for thin films growth on many technologically compatible substrates. 相似文献
996.
From 1970 to 1992 a total of 63 patients underwent operation for ampullary tumor: 40 pancreatoduodenectomies (PDs), 3 total PDs, 8 ampullectomies, and 12 bypass or exploratory laparotomies. The resectability rate was 68%. There were 9 benign tumors, 1 anaplastic tumor, and 53 adenocarcinomas. According to Martin's classification, there were 7 stage I, 11 stage II, 14 stage III, and 21 stage IV tumors. All patients with stage I, II, and III tumors underwent resection. Patients with stage IV tumors had either resection (n = 11) or bypass (n = 10). The mean duration of hospital stay was 20.6 days. Operative mortality was 12.7% for the whole series and 7.5% after PD (2.5% for the last 10 years). Overall survival was 40% at 5 years (85% for stage I, 65% for stage II, 44% for stage III, and 8% for stage IV). Survival was better for stages I, II, and III after PD than after ampullectomy. For stage IV patients survival was 70% after PD versus 20% after bypass at 1 year and 25% versus 0% after 2 years. In our opinion, PD should be proposed even for benign lesions because two of our patients had to undergo repeat operation (PD) 4 and 22 years later, respectively, for stage IV disease. PD is our choice for all tumors of the ampulla. 相似文献
997.
Lee Y. Wangi Jung-Sheng Wu Sheng-Mao Tseng Chang-Shu Kuo Kuo-Huang Hsieh Wen-Bin Liau Long Y. Chiang 《Journal of Polymer Research》1996,3(1):1-10
Utilization of polyhydroxylated C60 (fullerenols) in a condensation reaction with diisocyanated oligo(tetramethylene oxide) led to the successful fabrication of elastomeric poly (urethane-ether) networks. These polymer networks exhibit interesting thermal behavior at low temperatures, improved tensile strength and elongation at ambient temperatures, and enhanced thermal mechanical stability at high temperatures, as compared with those of the parent linear polyurethane analogues; or with the conventional oligo (tetramethylene oxide)-derived polyurethane elastomers cross-linked by trihydroxylated reagents (1,I,1-trismethylol propane) or tetrahydroxylated reagents (pentaerythritol). The presence of a limited quantity of water molecules in the condensation reaction of fullerenols with diisocyanated prepolymers modified the physical properties of the resulting elastomeric products with a notable increase in tensile strength, modulus, and Ts over those of elasotmers prepared under anhydrous conditions. These water molecules contributed effectively to the increase of the number of cross-linking centers during the reaction. 相似文献
998.
The tail-flick (TF) technique was used to assess the antinociceptive properties of nifedipine (NIF) given intraperitoneally (i.p.). First, the most suitable intensity of the noxious stimulus (temperature of the bulb) has been ascertained and used in the main study. Male Sprague-Dawley rats received NIF, dissolved in dimethyl sulfoxide (DMSO) at the doses of 0.0, 0.5, 2, 5, 10 and 15 mg/kg, or control with no injection. For the main study, the noxious stimulus was limited to 15 sec (cut-off time) and TF latencies were recorded up to 120 min. The antinociceptive response was expressed as the area under the curve for each rat and analyzed by one-way ANOVA. The antinociceptive response to the lower doses of NIF (0.5 and 2 mg/kg) did not differ from control (no injection) and DMSO alone. Significance was found at 5, 10 and 15 mg NIF with no difference among the doses. However, there was an increasing tendency of the mean values from 0.5 to 15 mg NIF resulting in a positive correlation. The correlation coefficient was 0.32483 (p = 0.015) and regression equation Y = (19.37) x dose + 1320. Our data suggest that spinal mechanisms are involved in NIF-induced antinociception. 相似文献
999.
IR LASER BACKSCATTERING FROM AN ARBITRARILY SHAPED DIELECTRIC OBJECT WITH ROUGH SURFACE 总被引:2,自引:0,他引:2
吴振森 《电子科学学刊(英文版)》1993,10(4):298-306
The backscattering of light wave from arbitrarily convex dielectric objects withrough surface is investigated and formulas for calculating the backscattering cross-section of bothcoherent and incoherent fields are obtained.In the infrared wave-band,the influence of the ge-ometry,permittivity and statistical characteristics of the rough surface on LRCS is analyzed,byusing rough sphere and ellipsoids as examples. 相似文献
1000.
掺富勒烯SiO2气凝胶的制备与发光性质研究 总被引:3,自引:0,他引:3
本文利用溶胶-凝胶工艺成功地将富勒烯掺入了SiO2气凝胶的纳米孔洞中,在Ar^+离子激光激发下,观察到了很强的可见光发射,对该现象作了初步的解释。 相似文献