全文获取类型
收费全文 | 87968篇 |
免费 | 6269篇 |
国内免费 | 2927篇 |
专业分类
电工技术 | 4353篇 |
技术理论 | 9篇 |
综合类 | 4649篇 |
化学工业 | 15519篇 |
金属工艺 | 4455篇 |
机械仪表 | 5233篇 |
建筑科学 | 7029篇 |
矿业工程 | 1985篇 |
能源动力 | 2483篇 |
轻工业 | 4902篇 |
水利工程 | 1448篇 |
石油天然气 | 4540篇 |
武器工业 | 488篇 |
无线电 | 10444篇 |
一般工业技术 | 11308篇 |
冶金工业 | 6117篇 |
原子能技术 | 831篇 |
自动化技术 | 11371篇 |
出版年
2024年 | 324篇 |
2023年 | 1314篇 |
2022年 | 2281篇 |
2021年 | 3113篇 |
2020年 | 2336篇 |
2019年 | 2031篇 |
2018年 | 2256篇 |
2017年 | 2519篇 |
2016年 | 2359篇 |
2015年 | 2943篇 |
2014年 | 4018篇 |
2013年 | 5076篇 |
2012年 | 5244篇 |
2011年 | 5522篇 |
2010年 | 4899篇 |
2009年 | 4716篇 |
2008年 | 4467篇 |
2007年 | 4402篇 |
2006年 | 4649篇 |
2005年 | 4134篇 |
2004年 | 2784篇 |
2003年 | 2501篇 |
2002年 | 2192篇 |
2001年 | 2019篇 |
2000年 | 2282篇 |
1999年 | 2599篇 |
1998年 | 2818篇 |
1997年 | 2122篇 |
1996年 | 1904篇 |
1995年 | 1542篇 |
1994年 | 1281篇 |
1993年 | 958篇 |
1992年 | 669篇 |
1991年 | 566篇 |
1990年 | 435篇 |
1989年 | 391篇 |
1988年 | 338篇 |
1987年 | 200篇 |
1986年 | 178篇 |
1985年 | 125篇 |
1984年 | 99篇 |
1983年 | 66篇 |
1982年 | 64篇 |
1981年 | 59篇 |
1980年 | 54篇 |
1979年 | 32篇 |
1978年 | 17篇 |
1977年 | 59篇 |
1976年 | 121篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
钛容器的特点 总被引:2,自引:1,他引:1
黄嘉琥 《石油化工设备技术》1996,17(5):19-24
根据钛材的化学、物理、力学和工艺性能介绍了钛容器在设计、制造、检验和应用方面的特点。 相似文献
113.
114.
115.
RG Wilde JT Billheimer SJ Germain EA Hausner PC Meunier DA Munzer JK Stoltenborg PJ Gillies DL Burcham SM Huang JD Klaczkiewicz SS Ko RR Wexler 《Canadian Metallurgical Quarterly》1996,4(9):1493-1513
Acyl-CoA:cholesterol acyltransferase (ACAT) is the enzyme largely responsible for intracellular cholesterol esterification. A systemic inhibitor of ACAT is believed to be able to slow or even reverse the atherosclerotic process. Towards that goal, a series of cyclic sulfides, derived from the hetero-Diels-Alder reaction of thioaldehydes with 1,3-dienes, and bearing carboxamide substituents, were prepared and evaluated for in vitro (in several tissues and species) and ex vivo ACAT inhibition. Minor changes in subsequent structure were found to have a significant effect in optimization of the biological activity of this series of compounds. 相似文献
116.
为了不使用任何还原剂而获得聚合物固载高分散零价双金属加氢催化剂,利用金属蒸气法制备了3种不同Pd/Cu质量比的聚合物固载双金属原子簇。透射电镜(TEM)和X衍射(XRD)测定表明,Pd-Cu原子簇粒度很小,平均直径小于3.0nm。X射线光电子能谱(XPS)表明,Pd和Cu均为零价态。Pd-Cu原子簇在异丙叉加氢反应中具有很高的活性和选择性。这些结果提供了令人信服的证据,即金属蒸气法可用于在聚合物孔穴内直接而温和地置入小的零价金属原子簇,而且这样制备的聚合物固载金属原子簇很适合于催化应用。 相似文献
117.
介绍有源声表面波滤波组件的设计思路。报道最新研制的高性能滤波组件,其中心频率40MHz,3dB相对带宽0.8%,阻带抑制优于100dB,矩形系数(Δf100dB/Δf3dB)小于3,输入输出端口电压驻波比接近1。组件体积85mm×35mm×24mm,重量小于115g 相似文献
118.
EJ Velthuis-te Wierik H van den Berg JA Weststrate KH van het Hof C de Graaf 《Canadian Metallurgical Quarterly》1996,50(4):214-219
Plasma levels of fibrinogen, factor VIIc and prothrombin fragment F1 + 2, a marker of thrombin generation in vivo, were studied in 68 subjects with serum total cholesterol (TC) levels between 135 and 349 mg/dl but without clinical evidence of cardiovascular disease and other atherosclerotic risk factors. F1 + 2 plasma levels were directly correlated with TC (p < 0.0004), low-density lipoprotein cholesterol (LDL-C; p < 0.0018) and factor VIIc (p < 0.024). Thirty-five subjects with TC greater than 249 mg/dl (median value of the whole group) showed higher levels of F1 + 2 (p < 0.0001) and fibrinogen (p < 0.0015) than those with TC lower than 249 mg/dl. In subjects with TC > 249 mg/dl and F1 + 2 > 1.2 nM (median value of the whole group), a cholesterol-lowering drug (simvastatin) was able to reduce F1 + 2 (p < 0.009) as well as TC and LDL-C. This study shows a relationship between serum cholesterol and the rate of thrombin generation supporting the hypothesis that a hypercoagulable state may occur in hypercholesterolemic subjects before the onset of clinical evidence of atherosclerotic cardiovascular disease. 相似文献
119.
Through rigorous full-wave analysis, the effective dielectric constant, normalized attenuation constant, characteristic impedance, and radiation pattern of two types of conductor-backed coplanar waveguides are obtained. The analytic results show that the leakage effect is not only controlled by the thickness and dielectric constant of the substrate but also by the slot width. The leakage power transforms to a radiation space wave and a surface wave, the transverse electric field diagrams in the substrate and the far-zone radiation pattern verify the leakage phenomenon. The first structure has the maximum radiation intensity in the endfire direction, while the second one which has more leaky waves radiates into the air, is better served as a radiating device. For both structures under the nonleakage condition, the characteristic impedance is sensitive to the change of the strip width but not the slot width. Using these properties, the nonleaky and leaky circuits can exist on the same circuit board by choosing appropriate circuit dimensions 相似文献
120.
N Nishioka T Kawabata KH Minagawa M Nakamura A Oshima Y Mochizuki 《Canadian Metallurgical Quarterly》1996,43(6):434-445
The purpose of this study was to evaluate the short-term effect of a smoking prevention program for Japanese elementary school-children in the fifth and sixth grades. The program was developed with concepts found in the Know Your Body Program and the conclusions of a National Cancer Institute-convened Expert Advisory Panel, and focused on teaching about the short-term effects of smoking and on resistance to social pressures to smoke. The study was conducted with a quasi-experimental design. An intervention group (52 boys and 54 girls) received three sessions for both the fifth grade in 1992 and the sixth grade in 1993. Moreover, the intervention group received a pre-test before the first session and a post-test after the third session in each grade. A comparison group (102 boys and 91 girls) received the same tests at the same time as the intervention group, but did not receive any program on smoking prevention. The short-term effect of the program were evaluated using the results of the pre-test in the fifth grade and of the post-test in the sixth grade in both groups. The results were as follows: 1) Remarkable short-term effects of the intervention were seen in respect to awareness of the importance of not smoking in girls, and also in the knowledge of the short-term effects of smoking in both sexes. 2) The intervention was not effective with respect to intention to smoke at the age of 20 and self-efficacy of refusing to smoke in both sexes. 3) The short-term effects were not clear in the smoking behavior in both sexes because the rates of ever smokers and of monthly smokers were almost the same for two years between the intervention group and the comparison group. 4) The smoking behaviors of children, their parents and their best friends had little influence on the results of the post-test in the sixth grade. 相似文献