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   265013篇
  免费   4334篇
  国内免费   1823篇
电工技术   5467篇
技术理论   5篇
综合类   1169篇
化学工业   42849篇
金属工艺   11082篇
机械仪表   7820篇
建筑科学   6775篇
矿业工程   1687篇
能源动力   5669篇
轻工业   26066篇
水利工程   2946篇
石油天然气   6011篇
武器工业   243篇
无线电   28042篇
一般工业技术   49718篇
冶金工业   48618篇
原子能技术   5655篇
自动化技术   21348篇
  2021年   2497篇
  2019年   2153篇
  2018年   3423篇
  2017年   3383篇
  2016年   3714篇
  2015年   2824篇
  2014年   4643篇
  2013年   11606篇
  2012年   7784篇
  2011年   10319篇
  2010年   8194篇
  2009年   8758篇
  2008年   9596篇
  2007年   9722篇
  2006年   8535篇
  2005年   7521篇
  2004年   6757篇
  2003年   6310篇
  2002年   6318篇
  2001年   6382篇
  2000年   5981篇
  1999年   5940篇
  1998年   12947篇
  1997年   9614篇
  1996年   7350篇
  1995年   5598篇
  1994年   5141篇
  1993年   5036篇
  1992年   4022篇
  1991年   3792篇
  1990年   3905篇
  1989年   3839篇
  1988年   3604篇
  1987年   3101篇
  1986年   3123篇
  1985年   3511篇
  1984年   3424篇
  1983年   3161篇
  1982年   2787篇
  1981年   2977篇
  1980年   2693篇
  1979年   2933篇
  1978年   2804篇
  1977年   2928篇
  1976年   3764篇
  1975年   2537篇
  1974年   2347篇
  1973年   2391篇
  1972年   2020篇
  1971年   1819篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
We studied the incidence of infection with Helicobacter pylori in Panamanians with chronic dyspepsia, gastric or duodenal ulcer, gastritis or gastric cancer. The histopathology was positive in 54 (81%) of 66 patients; the urea test was positive in 52 (82.5%) of 63 cases; the impromptu was positive in 51 (79.6) of 64 patients; the endoscopic examination was positive in 64 (82.9%) of 77 examinations.  相似文献   
992.
An analysis of the kinetics of gas dissolution in a liquid metal flow is performed. It is shown that due to a high pouring rate and specific surface of the flow, the flow in the arc of molten filler metal, as distinct from the flow of liquid metal during its pouring, leads to intense saturation of the melt with gas.Volgograd Branch of the Novocherkassk Polytechnic Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 4, pp. 414–420, April, 1993.  相似文献   
993.
Examined social skills and social perception of 48 schizophrenia/schizoaffective disorder patients (aged 18–55 yrs) in response to negative affect as a function of family expressed emotion (EE). Ss participated in a role-play test, a social perception test, and a problem-solving discussion with a family member and were assessed on several measures of symptomatology. EE of family members was evaluated with the Camberwell Family Interview. On the role-play test, Ss with less critical relatives became more assertive in response to increased negative affect from a confederate portraying either a family member or friend, but Ss with highly critical relatives did not. Ss with highly critical relatives were also less assertive when confronted with negative affect from a confederate portraying a family member rather than a friend. The behaviors of both relatives and Ss during a family problem-solving interaction were related to the EE dimensions of criticism, emotional overinvolvement, and warmth. Patient gender was also related to family problem solving but was independent of EE. S's ratings of affect on a videotaped social perception task were not related to family EE, and there were few differences in psychopathology between Ss with high and low EE relatives.… (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
994.
OBJECTIVE: To determine the distribution and amount of elastic fibers in the dermis of clinically normal dogs and dogs with dermatoses, particularly solar dermatitis. DESIGN: Skin specimens from 7 anatomic sites were obtained from 19 clinically normal dogs after euthanasia to evaluate the normal distribution of elastic fibers. Biopsy specimens also were obtained from 34 dogs with dermatoses, including 16 with solar dermatitis. Tissue sections were stained with H&E, Verhoeff-van Gieson, and periodic acid-Schiff. ANIMALS: 19 clinically normal dogs and 34 dogs with dermatoses. PROCEDURE: Numbers of elastic fibers were graded subjectively. Comparisons between clinically normal dogs and dogs with dermatoses were made. RESULTS: Normal elastic fibers were present in low numbers in the dermis of adult dogs, regardless of anatomic site or presence or severity of dermatitis. Condensed elastotic material was visualized in only 2 dogs with solar dermatitis. In both dogs, the elastotic material was Verhoeff-van Gieson and periodic acid-Schiff stain positive but was not visible with H&E stain. The most frequent histopathologic finding in the dermis of dogs with solar dermatitis was superficial dermal fibrosis. CONCLUSIONS: The dermis of clinically normal dogs does not contain abundant elastic fibers. Alterations of elastic fibers in dogs with solar dermatitis are rare. Superficial dermal fibrosis may be a better indicator of solar damage.  相似文献   
995.
The magnetic properties of polyethersulfone-matrix composites with 3-19 vol.% polycrystalline nickel filaments (0.4 (im diam) were investigated. These filaments were found to exhibit hysteresis energy loss 10800 J/m3 of nickel and coercive force 16.9 kA/m, compared to corresponding values of 4930 J/m3 and 4.7 kA/m for 2 μ.m diam polycrystalline nickel fibers, 1020 J/m3 and 0.5 kA/m for 20 μm diam polycrystalline nickel fibers, and 1280 J/m3 and 2.3 kA/m for solid polycrystalline nickel.  相似文献   
996.
The genetic relationships between two Finno-Ugric-speaking populations, the Finns and the Finnish Saami (Lapps), were studied by using PCR for six nuclear-DNA marker loci, mitochondrial restriction-site polymorphism, and sequence variation of a 360-bp segment of the mitochondrial control region. The allele frequencies of each of the nuclear-DNA marker loci and the frequencies of mtDNA restriction haplotypes were significantly different between the populations. The Saami showed exceptionally low variation in their mtDNA restriction sites. The 9-bp deletion common in East Asian populations was not observed, nor did the haplotype data fit into the haplogroup categorization of Torroni et al. The average number of nucleotide substitutions from the mtDNA haplotype data indicated that the Finnish Saami may be closer to the Finns than to the other reference populations, whereas nuclear DNA suggested that the Finns are more closely related to the European reference populations than to the Finnish Saami. The similarity of the Finns to the other Europeans was even more pronounced according to the sequence data. We were unable to distinguish between the Finns and either the Swiss or Sardinian reference populations, whereas the Finnish Saami clearly stood apart. The Finnish Saami are distinct from other Circumarctic populations, although two of the lineages found among the Saami showed closer relationship to the Circumarctic than to the European lineages. The sequence data indicated an exceptionally high divergence for the Saami mtDNA control lineages. The distribution of the pairwise nucleotide differences in the Saami suggested that this population has not experienced an expansion similar to what was indicated for the Finns and the reference populations.  相似文献   
997.
998.
999.
This report summarizes the results of a three-day colloquium, held in Minnesota in July 1995, to address issues related to underground space utilization. The colloquium was convened by the Underground Space Center, with major support from the National Science Foundation, Directorate for Engineering, and the Federal Highway Administration.  相似文献   
1000.
Computer-aided simulation for bone surgery   总被引:2,自引:0,他引:2  
A system for evaluating bone deformities using a 3-D model directly recovered from 2-D images and for simulating surgery is described. It derives a 3-D object representation from only two X-ray images. It also offers user-friendly simulation of bone surgery with low-cost hardware and software. The system exhibits satisfactory behavior for reconstructing the bone shape, providing suitable data for the simulation and evaluation of bone surgery. Although the spline interpolation of the bone surface does not produce a realistic 3-D visualization of the tibia, which is used as an example, the reconstruction is useful in solving problems inherent in the pathology considered  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