首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3274篇
  免费   114篇
  国内免费   9篇
电工技术   200篇
综合类   4篇
化学工业   834篇
金属工艺   106篇
机械仪表   95篇
建筑科学   88篇
能源动力   141篇
轻工业   294篇
水利工程   9篇
石油天然气   7篇
武器工业   2篇
无线电   265篇
一般工业技术   580篇
冶金工业   402篇
原子能技术   95篇
自动化技术   275篇
  2023年   15篇
  2022年   27篇
  2021年   80篇
  2020年   34篇
  2019年   38篇
  2018年   49篇
  2017年   50篇
  2016年   84篇
  2015年   51篇
  2014年   102篇
  2013年   203篇
  2012年   163篇
  2011年   181篇
  2010年   158篇
  2009年   169篇
  2008年   168篇
  2007年   141篇
  2006年   138篇
  2005年   110篇
  2004年   84篇
  2003年   74篇
  2002年   82篇
  2001年   65篇
  2000年   66篇
  1999年   65篇
  1998年   176篇
  1997年   121篇
  1996年   116篇
  1995年   57篇
  1994年   59篇
  1993年   66篇
  1992年   32篇
  1991年   30篇
  1990年   32篇
  1989年   39篇
  1988年   33篇
  1987年   21篇
  1986年   28篇
  1985年   32篇
  1984年   25篇
  1983年   14篇
  1982年   16篇
  1981年   17篇
  1980年   10篇
  1979年   10篇
  1978年   6篇
  1977年   22篇
  1976年   9篇
  1973年   5篇
  1972年   6篇
排序方式: 共有3397条查询结果,搜索用时 328 毫秒
31.
Prognostic factors in esophageal carcinoma treated with irradiation were examined. The prognosis of 111 patients without metastasis who had received more than 60 Gy was analyzed. Significant associations were found between survival rates and tumor length, stage, radioresponse of the primary tumor and the s.c. X-P classification based on barium contrast radiography; superficial type (tumor limited to the surface of the esophageal wall), tumorous type (solid mass without ulceration), Ul-A type (tumor with shallow ulceration with regular margin), Ul-B type (tumor with deep ulceration or irregular ulcer margin), and funneled type (tumor invading the esophageal wall in a scirrhous pattern). In multiple regression analysis, the X-P classification had the strongest correlation with survival and the survival rates of patients with the superficial type, the tumorous type and the s.c. Ul-A type were significantly higher than those of patients with the other tumor types (p < 0.001).  相似文献   
32.
Makoto Kohga 《含能材料》2006,14(6):471-474
1 IntroductionThe ammonium perchlorate ( AP)-based compositepropellant is currently the most widely used one becausethis propellant has good burning characteristics and me-chanical properties. One of the few serious drawbacks ofthe AP-based propellant is that its products of combus-tion, which include HCl, chlorine, and chlorine oxides,cause atmospheric pollution. Increasing concern for aclean atmosphere in recent years has resulted in a com-pelling need for developing a chlorine-free,enviro…  相似文献   
33.
Various aspects of biofilm adaptation to sulfate reduction in horizontal-flow anaerobic immobilized biomass (HAIB) reactors subjected to increasing sulfate concentrations and different COD/sulfate ratios are presented and discussed. Four bench-scale HAIB reactors filled with vegetal carbon (R1 and R2) and polyurethane foam matrices (R3 and R4) were utilized. Influent sulfate concentrations ranging from 500 to 3000 mg/L were applied at COD/sulfate ratios ranging from 5.0 to 1.7. Reactors R1 and R4 were operated with higher sulfate loads than those applied to R2 and R3. For the same COD/sulfate ratio, the highest sulfate reduction efficiency (approximately 80%) was displayed by the vegetal carbon reactor (R2) subjected to low sulfate loads. According to the results of our molecular biology analyses, the different support materials provided different biomass colonization conditions. The lowest diversity of sulfate-reducing bacteria was found in the HAIB filled with polyurethane foam matrices operating with high sulfate loads.  相似文献   
34.
We study dynamics of quantized vortex lattice formation in a rotating Bose-Einstein condensate with a square blue-detuned optical lattice by solving the Gross-Pitaevskii equation. This dynamics depends on the depth of the optical lattice. Vortices tend to form a triangular lattice under the rotation, while an optical lattice likes to pin vortices at their peaks. Such a competition of two effects makes this system more interesting and complicated.  相似文献   
35.
In this paper, we describe two kinds of characteristic nonlinear dynamics in two-component Bose–Einstein condensates. For two overlapping components, we analyzed the collective modes and a variety of nonlinear mode couplings, which were then confirmed by numerical simulation of the time-dependent Gross–Pitaevskii equations. Next, we consider the nonlinear dynamics of two condensates after abruptly turning on the intercomponent coupling strength. For strong intercomponent interactions the out-of-phase density wave of the condensates became unstable, leading to mugtiple domain formation.  相似文献   
36.
An endo-beta-N-acetylglucosaminidase specific for plant glycoprotein oligosaccharides was purified from the culture fluid of a fungus. The Mr of the purified enzyme was 89,000. This enzyme was stable at pH 5.5-7.0, up to 30 degrees C, and showed the highest activity at pH 6.0. Among sugar chains tested, xylose-containing sugar chains (M3X, M3FX, and M2FX) were the most favored substrates. Oligomannose type (M3, M5, and M9) and hybrid type (GNM3) sugar chains were hydrolyzed much more slowly than xylose-containing sugar chains, and a complex type sugar chain (GN2M3) was not hydrolyzed at all by the enzyme. Moreover, the enzyme released sugar chains from native horseradish peroxidase and stem bromelain, which were not hydrolyzed by other endo-beta-N-acetylglucosaminidases (Endo H, D, and F). The enzyme could transfer the xylose-containing sugar chain from bromelain to DNS-Asn-GlcNAc-Fuc.  相似文献   
37.
Neisseria species other than N. meningitidis and N. gonorrhoeae are generally regarded as commensal bacterial flora of the oropharynx, and little is known regarding cases of these non-pathogenic Neisseria species in the lower respiratory tract. We clinically examined respiratory tract infections from which non-pathogenic Neisseria species were isolated by transtracheal aspiration (TTA). The incidence of non-pathogenic Neisseria isolated was 54 (15.7%) out of 344 episodes of respiratory tract infections with isolated microorganisms from TTA, and was 17.6%, 15.8%, 14.3% for pneumonia, acute bronchitis, and chronic lower respiratory tract infection, respectively. All 54 episodes were isolated with other microorganisms such as alpha-Streptococcus spp. (75.9%), Haemophilus influenzae (25.9%) and anaerobics (22.2%). The isolation ratio according to the age group increased at 45 years of age or more, but did not increase with the advance of age. Predisposing factors were identified such as overt aspiration, iatrogenic procedure and heavy smoking. Cases without overt aspiration that had fevers of 38 degrees C or more or hypoxemia of less than PaO2 70 torr when detecting non-pathogenic Neisseria were observed more frequently in the aged than the non-aged. The findings suggest the detection of non-pathogenic Neisseria by TTA is influenced by the host state that the fall of microorganisms from the upper to lower respiratory tract cannot be defended or excluded by mucociliary transportation disorder due to underlying disease and smoking, or deterioration of physical status other than overt or silent aspiration.  相似文献   
38.
39.
40.
Physical optics (PO) is an approximation method for high‐frequency scattering and diffraction problems. But PO fields are inaccurate in the shadow region where the source is screened by the scatter. Two key factors of the error for PO are (i) edge diffraction coefficients and (ii) existence of fictitious penetrating rays. The correction with respect to the former has been extensively investigated by many authors using various ray techniques such as GTD, UTD, and UAT. On the other hand, the latter was identified recently by the authors. This paper proposes novel PO‐based calculation procedures termed PO‐AF and PTD‐AF, where PO and Aperture Field Integration Method (AFIM) are merged with the help of special elementary diffraction coefficients. These can uniformly cover the whole angular region and only the error factor (ii) is removed in PO‐AF while both (i) and (ii) are removed in PTD‐AF. The theoretical backgrounds of PO currents are discussed in terms of field equivalence theorem and visualization of EM waves. Next, new methods are proposed and their validity is numerically demonstrated for 2D scattering problems of a strip, a corner reflector, and a cylinder of circular arc. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 1–10, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20037  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号