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   2681篇
  免费   14篇
  国内免费   8篇
电工技术   28篇
化学工业   184篇
金属工艺   83篇
机械仪表   19篇
建筑科学   39篇
矿业工程   1篇
能源动力   49篇
轻工业   87篇
水利工程   12篇
石油天然气   2篇
无线电   195篇
一般工业技术   169篇
冶金工业   1641篇
原子能技术   36篇
自动化技术   158篇
  2021年   9篇
  2020年   8篇
  2019年   18篇
  2018年   12篇
  2017年   8篇
  2016年   11篇
  2014年   14篇
  2013年   64篇
  2012年   27篇
  2011年   57篇
  2010年   35篇
  2009年   52篇
  2008年   50篇
  2007年   62篇
  2006年   52篇
  2005年   54篇
  2004年   38篇
  2003年   37篇
  2002年   29篇
  2001年   20篇
  2000年   28篇
  1999年   69篇
  1998年   400篇
  1997年   270篇
  1996年   186篇
  1995年   121篇
  1994年   89篇
  1993年   89篇
  1992年   30篇
  1991年   30篇
  1990年   42篇
  1989年   64篇
  1988年   60篇
  1987年   40篇
  1986年   42篇
  1985年   60篇
  1984年   21篇
  1983年   24篇
  1982年   25篇
  1981年   20篇
  1980年   38篇
  1979年   15篇
  1978年   19篇
  1977年   53篇
  1976年   95篇
  1975年   15篇
  1974年   7篇
  1973年   9篇
  1972年   11篇
  1954年   6篇
排序方式: 共有2703条查询结果,搜索用时 31 毫秒
21.
Composite metacarpophalangeal joint reconstruction using the toe proximal phalanx and the metacarpal head, with a capsular repair, is an option during free toe transfer procedures for absent fingers. Eleven composite metacarpophalangeal finger joint reconstructions were performed in four patients concurrent with combined second and third toe-to-hand transfer. The average follow-up period was 5 years. Postoperative assessment included range of motion, stability, radiographic changes, and pain. The average range of motion was 52 degrees, average ulnar stress deviation was 14 degrees. No patients complained of pain. Composite metacarpophalangeal joint reconstruction should be considered in free toe-to-hand procedures when metacarpal head articular cartilage is preserved.  相似文献   
22.
The importance of abnormalities of function and epididymis structure in the etiology of male infertility is still not well understood. We studied 52 individuals distributed in five age groups: fetuses, children, adolescents, adults and the elderly. The region of the body of epididymis was obtained by autopsy and immediately fixed by immersion in a solution of 10% buffered formaldehyde, embedded in paraffin and histologically prepared. The samples were observed under an optic microscope. Test-points were counted in 12 random microscopic fields with the M42 test-system. The following stereological parameters were determined: ductal area, volumetric densities (Vv) of the duct, smooth muscle, connective tissue, epithelial duct and blood vessels. The main results distinguished by those whose averages were statistically significant (p < 0.05), showed that the ductal area is 9.7 times greater in the adolescent/adult/elderly group than the children's group. The Vv of the lumen of the epididymis duct occupies 11.7% of the epididymis body in the fetal period, 5.3% in the child and in individuals after puberty this figures reaches more than 15%. The Vv of smooth muscle occupies 28.3% of the body of the epididymis in the fetus and 35.9% in children, but after puberty this figures stays around 22%. The Vv of the connective tissue occupies 26% in prenatal life, 37% in children, and after puberty these figures range from 21 to 27.5%. Comparing the results of the adult group with that of the elderly group there is an increase in the volumetric density of the connective tissue by 18.1%. In conclusion, the epididymal duct area and the Vv of the ductal lumen, smooth muscle and connective tissue were significant comparing the different groups. However, the quantitative relative differences of the duct's epithelium and the blood vessels were not significant comparing these groups. The study of quantitative aspects of the normal human epididymis can increase our knowledge about male fertility.  相似文献   
23.
A processing algorithm for automatically detecting a specific type of ion distribution (called the ion conic distribution) in data obtained from a space-based mass spectrometer has been devised. Automation of this task is necessary due to the sparseness of conic events within the very large databases typical of space plasma instruments. The algorithm used to perform this automated analysis and the methods used to verify the algorithm are described. Initial results on the characterization of the near-Earth space plasma are summarized  相似文献   
24.
The Jade file system, which provides a uniform way to name and access files in an Internet environment, is introduced. Jade is a logical system that integrates a heterogeneous collection of existing file systems in which underlying file systems support different file access protocols. Because of autonomy, Jade is designed under the restriction that the underlying file systems may not be modified. In order to avoid the complexity of maintaining an Internet-wide, global name space, Jade permits each user to define a private name space. Jade's name space supports two features: it allows multiple file systems to be mounted under one directory, and it permits one logical name space to mount other logical name spaces. A prototype of Jade has been implemented to examine and validate its design. The prototype consists of interfaces to the Unix File System, the Sun Network File System, and the File Transfer Protocol. An overview of Jade's design is reported, and the authors' experiences in designing and implementing a large scale file system are reviewed  相似文献   
25.
The emittance of a yttrium-beryllium oxide thermocouple coating was determined by an electrical heating method and by sodium line reversal measurements in the overall temperature range 1465–1830K. The emittance determined by both methods was 0.60. Comparison of emittances measured with different sized thermocouples in one-dimensional flames implied that the appropriate thermocouple heat transfer model was a cylinder in cross flow. Good agreement was obtained between radiation-corrected temperatures measured with silica coated (emittance of 0.22) and yttrium-beryllium oxide coated thermocouples.  相似文献   
26.
Backward priming was investigated under conditions similar to those used in lexical ambiguity research. Ss received prime-target word pairs that were associated either unidirectionally (BABY-STORK) or bidirectionally (BABY-CRY). In Exp 1, targets were presented 500 ms following the onset of visual primes, and Ss made naming or lexical decision responses to the targets. Forward priming was obtained in all conditions, while backward priming occurred only with lexical decision. In Exp 2, primes were presented auditorily, either in isolation or in a sentence. Targets followed the offset of the primes either immediately or after 200 ms. Backward priming occurred with both response tasks, but only when the prime was an isolated word. Backward priming decreased over time with the naming task, but not with lexical decision. These results suggest that the locus of the backward priming effect is different for the 2 response tasks. Results support a context-independent view of lexical access. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
27.
As part of a study of the possible application of polymerisable Langmuir-Blodgett (LB) films as ultra-fine-line e-beam resists, an investigation of the variation of film structure of 22-tricosenoic acid with differing deposition conditions has been made. Unexpected effects with significant implications for deposition speed and resist sensitivity have been observed, and the new techniques for film characterisation developed during the investigation have resulted in a revised model of deposition explaining the observed independence of the disorder causing optical scattering and the macroscopic features observed by polarised microscopy.  相似文献   
28.
29.
30.
ImuVert, a sterile preparation composed primarily of Serratia marcescens membrane vesicles and ribosomes, was significantly inhibitory to murine cytomegalovirus (MCMV) infections in BALB/c mice. Antiviral activity was manifested as increased survivor number and decreased recoverable virus titers in spleens, lungs and salivary glands. Treatments were intraperitoneal (i.p.) beginning 24 h pre, 4 h post- or 24 h post-virus inoculation and then repeated 4 days later. Doses of 5, 16 or 50 micrograms/mouse were effective; 160 micrograms/mouse, which caused host weight loss in toxicity controls, was not inhibitory to the infection. A single i.p. treatment of mice substantially augmented natural killer (NK) cell activity and increased total B-cells, while reducing total T- and T-helper cells. A late (48 h) decline in T-cell function and transient increases in B-cell function were observed in the treated animals. Serum interferon was not induced. Mice pretreated with anti-asialo GM1 antibody to reduce their NK cell populations, then infected with MCMV and treated with ImuVert were protected to the same degree as normal animals. Severe combined immunodeficient mice infected with MCMV and treated with ImuVert were not protected from the infection. These data suggest ImuVert to act by a mechanism other than NK cell activation in preventing MCMV infections.  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