全文获取类型
收费全文 | 41279篇 |
免费 | 3370篇 |
国内免费 | 2039篇 |
专业分类
电工技术 | 719篇 |
综合类 | 1600篇 |
化学工业 | 12744篇 |
金属工艺 | 3275篇 |
机械仪表 | 1923篇 |
建筑科学 | 959篇 |
矿业工程 | 517篇 |
能源动力 | 1776篇 |
轻工业 | 4300篇 |
水利工程 | 109篇 |
石油天然气 | 990篇 |
武器工业 | 156篇 |
无线电 | 3939篇 |
一般工业技术 | 9524篇 |
冶金工业 | 1851篇 |
原子能技术 | 1519篇 |
自动化技术 | 787篇 |
出版年
2024年 | 126篇 |
2023年 | 800篇 |
2022年 | 1098篇 |
2021年 | 1415篇 |
2020年 | 1328篇 |
2019年 | 1202篇 |
2018年 | 1184篇 |
2017年 | 1438篇 |
2016年 | 1462篇 |
2015年 | 1456篇 |
2014年 | 2096篇 |
2013年 | 2696篇 |
2012年 | 2596篇 |
2011年 | 3554篇 |
2010年 | 2394篇 |
2009年 | 2625篇 |
2008年 | 2250篇 |
2007年 | 2402篇 |
2006年 | 2039篇 |
2005年 | 1675篇 |
2004年 | 1606篇 |
2003年 | 1491篇 |
2002年 | 1263篇 |
2001年 | 846篇 |
2000年 | 764篇 |
1999年 | 684篇 |
1998年 | 576篇 |
1997年 | 481篇 |
1996年 | 459篇 |
1995年 | 366篇 |
1994年 | 376篇 |
1993年 | 298篇 |
1992年 | 319篇 |
1991年 | 273篇 |
1990年 | 201篇 |
1989年 | 148篇 |
1988年 | 113篇 |
1987年 | 95篇 |
1986年 | 85篇 |
1985年 | 89篇 |
1984年 | 84篇 |
1983年 | 55篇 |
1982年 | 72篇 |
1981年 | 32篇 |
1980年 | 16篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1976年 | 12篇 |
1975年 | 10篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Cs-K混合蒸气中Cs(8D)+K(4S)碰撞能量转移 总被引:3,自引:3,他引:0
在Cs-K混合蒸气中,两步激发Cs原子到8D态,观察了Cs(8D) K(4S)→Cs(5D) K(4P)碰撞能量合并逆过程(REP,reverse energy pooling)。应用双调制技术探测K(4P)原子发射的荧光,基态K原子密度用光学吸收方法测量。得到了REP速率系数,讨论了其它过程对速率系数的影响. 相似文献
63.
In order to investigate the reduction mechanism of thioglycolic acid (TG) on the keratin fibers, cross-sectional samples of white human hair treated with TG were prepared. The heterogeneous reaction between TG and keratin fibers involving the diffusion of TG into human hair was analyzed at the molecular level using microspectrophotometry and FT-Raman spectroscopy. The diffusion of TG into human hair clearly increased by increasing the treatment time and by raising pH. The TG relative concentration and the disconnected relative concentration of disulfide (–SS–) groups at various depths of the hair samples with pH 9.0 were in good agreement, indicating that the reaction rate (the disconnection of –SS– groups) was faster than the diffusion rate of TG into human hair. From these experiments, we demonstrated that TG diffuses gradually beyond the cuticle region, and toward the inside of the cortex region along with the disconnection of –SS– groups. 相似文献
64.
We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ?4 ps long pulses of 565 nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76 MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (<4 ps). We suggest that the transient IRAV absorption is due to secondary polarons formation following exciton dissociation. 相似文献
65.
介绍用已知年龄和烧结温度的古陶片穆斯堡尔超精细参数与年龄和烧结温度的实验关系曲线作基础,应用计算机模拟程序,自动求出未知陶片的年龄和最高烧结温度的方法。 相似文献
66.
S V Bhat 《Bulletin of Materials Science》1994,17(7):1271-1285
When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT
c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon
can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even
in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination
of material parameters of interest such asJ
c andH
c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The
details of these aspects are discussed. 相似文献
67.
油田污水中咪唑啉缓蚀剂浓度检测技术研究 总被引:5,自引:0,他引:5
研究评价了油田污水中咪唑啉缓蚀剂浓度检测的七种方法 ,其中紫外光分析法和显色反应法适合于低浓度咪唑啉缓蚀剂检测 ,且方法简便、速度快、成本低 ,检测浓度范围 2~ 5 0mg/L。 相似文献
68.
69.
软X射线不仅能引起红细胞表面电荷的变化,同时也能导致淋巴细胞和血小板表面电荷下降,表现为照射后它们的电泳率下降。低剂量范围内,这种电荷的变化是暂时性的,照后4小时降到最低点,24小时后恢复到对照的水平。细胞电泳率的下降与辐射剂量相关。淋巴细胞是一个复杂的细胞群,正常状态下,按细胞在电场中泳动速度的快慢,可分为两个组分:快峰为T细胞,慢峰为B细胞。软X射线照射以后,T和B细胞的电泳率皆减慢,频数分布峰值下降,离散度加大。血小板成分单一,电泳率较一致。 从照射浓集的血小板再加回自身血浆中电泳率的下降较照射血浆再加到血小板中的电泳率下降大得多;受照射的血小板在磷酸缓冲液中电泳率下降较在血浆悬液中严重得多;2000 rad照后,悬浮于血浆中的血小板电泳率能恢复,而悬浮于磷酸缓冲液中则不能恢复,三个方面来看,血浆中可能存在抗辐射因子。超氧化物岐化酶能有效地预防血小板电泳率的下降,从而可阻止血小板的凝聚。 相似文献
70.
TeMxMo1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N2. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb4Mo10O31 and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene. 相似文献