全文获取类型
收费全文 | 17680篇 |
免费 | 1728篇 |
国内免费 | 823篇 |
专业分类
电工技术 | 1071篇 |
综合类 | 1053篇 |
化学工业 | 2750篇 |
金属工艺 | 975篇 |
机械仪表 | 1160篇 |
建筑科学 | 1207篇 |
矿业工程 | 445篇 |
能源动力 | 520篇 |
轻工业 | 1059篇 |
水利工程 | 405篇 |
石油天然气 | 585篇 |
武器工业 | 146篇 |
无线电 | 2316篇 |
一般工业技术 | 2377篇 |
冶金工业 | 1246篇 |
原子能技术 | 180篇 |
自动化技术 | 2736篇 |
出版年
2024年 | 65篇 |
2023年 | 306篇 |
2022年 | 570篇 |
2021年 | 817篇 |
2020年 | 622篇 |
2019年 | 543篇 |
2018年 | 562篇 |
2017年 | 555篇 |
2016年 | 523篇 |
2015年 | 738篇 |
2014年 | 898篇 |
2013年 | 1173篇 |
2012年 | 1199篇 |
2011年 | 1230篇 |
2010年 | 1048篇 |
2009年 | 1020篇 |
2008年 | 967篇 |
2007年 | 921篇 |
2006年 | 830篇 |
2005年 | 752篇 |
2004年 | 540篇 |
2003年 | 484篇 |
2002年 | 526篇 |
2001年 | 475篇 |
2000年 | 351篇 |
1999年 | 350篇 |
1998年 | 330篇 |
1997年 | 296篇 |
1996年 | 232篇 |
1995年 | 188篇 |
1994年 | 166篇 |
1993年 | 132篇 |
1992年 | 115篇 |
1991年 | 95篇 |
1990年 | 67篇 |
1989年 | 74篇 |
1988年 | 72篇 |
1987年 | 49篇 |
1986年 | 36篇 |
1985年 | 43篇 |
1984年 | 30篇 |
1983年 | 20篇 |
1982年 | 37篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1977年 | 20篇 |
1976年 | 20篇 |
1974年 | 21篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
OBJECTIVE: To examine the relationship between pregnancy incidence and the level of serum E2 during danazol therapy. DESIGN: Danazol was given by 200 mg four times daily for 3 months. Serum E2 level was checked after completing the therapy, but before stopping medication. Patients then were advised to conceive at the appropriate time over a 6-month period. SETTING: Reproductive and Endocrine Laboratory of the Department of Obstetrics and Gynecology, Keelung Chang Gung Memorial Hospital, Keelung, Taiwan. PATIENTS: Infertile women with invasive endometriosis receiving conservative surgery and danazol treatment. INTERVENTIONS: Serum E2 is checked before medication and at the end of danazol therapy, but before stopping medication. MAIN OUTCOME MEASURES: Whether pregnancy is related to the change of serum E2 caused by danazol therapy. RESULTS: There were 24 pregnancies in 38 patients with invasive endometriosis after treatment. Pregnant patients had significantly lower serum E2 levels as compared with the nonpregnant patients. CONCLUSIONS: After conservative surgery for invasive endometriosis associated with infertility, the therapeutic period of danazol treatment could be shortened to 3 months. Because there is significant correlation of fecundability and serum E2 after danazol medication, serum E2 could be a guideline for predicting pregnancy or for prolonging or changing of treatment after danazol therapy. 相似文献
22.
C.H. Chu C.I. Hung Y.H. Wang M.P. Houng 《Photonics Technology Letters, IEEE》1997,9(9):1262-1264
We present a theoretical model for the dark current of bound-to-continuum quantum-well infrared photodetectors (QWIPs), by considering the field-induced mixing effect, tunneling rate and phonon scattering rate between bound and continuum states. Using this model, we can see clearly how these mechanisms significantly influence the Fermi levels of bound and continuum electrons, and thus, the dark current. Nonlinear temperature dependence of the dark current at low temperature is predicted and discussed in detail. The simulated dark currents exhibit good agreement with the experimental results, without use of parameter fitting techniques. 相似文献
23.
First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen 相似文献
24.
Wesley W. Chu Ph.D. Ion T. leong Ph.D. Ricky K. Taira Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):445-477
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach. 相似文献
25.
26.
The effect of thermal oxidation on the residual stress distribution throughout the thickness of heavily-boron-doped (p+ ) silicon films is studied. The deflection of p+ silicon cantilever beams due to residual stress variation throughout the film thickness is studied for as-diffused and thermally oxidized films. Cantilevers of as-diffused p+ silicon films display a positive curvature (or a negative bending moment), signified by bending up of the beams. Thermal oxidation of the films prior to cantilever fabrication by anisotropic etching modifies the residual stresses in the p+ film, specially in the near-surface region (i.e. the top 0.3 to 0.5 μm for the oxidation times used here), and can result in beams with a negative curvature even when the oxide is removed from the p+ silicon cantilever surface subsequent to cantilever fabrication 相似文献
27.
用D72 强酸型阳离子交换树脂催化苯酚与α -甲基苯乙烯的Friedel-Crafts烷基化反应 ,合成对枯基苯酚。考察了苯酚 /α -甲基苯乙烯摩尔比、催化剂用量、反应温度和反应时间对烷基化反应的影响。优化反应条件 :n(苯酚 ) /n(α -甲基苯乙烯 ) =2 0、催化剂用量 5 % (占α -甲基苯乙烯的质量分数 )、反应温度 85℃、反应时间 5h ,对枯基苯酚的产率为 97 0 %。合成产物结构由红外、核磁光谱所证实。实验结果表明 ,D72 强酸型阳离子交换树脂催化剂稳定性高 ,易于回收 ,且可重复利用 ,催化活性在反应时间内 (或经多次使用 )未见明显下降。 相似文献
28.
几种重要的有机氯系阻燃剂 总被引:2,自引:0,他引:2
介绍了氯化石蜡、氯化聚乙烯、四氯邻苯二甲酸酐、四氯双酚A、六氯环戊二烯 及由六氯环戊二烯衍生的几种氯系阻燃剂的生产过程和用途。 相似文献
29.
30.