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   29677篇
  免费   2220篇
  国内免费   25篇
电工技术   185篇
综合类   12篇
化学工业   6598篇
金属工艺   569篇
机械仪表   672篇
建筑科学   934篇
矿业工程   58篇
能源动力   609篇
轻工业   5792篇
水利工程   328篇
石油天然气   138篇
武器工业   2篇
无线电   1160篇
一般工业技术   4930篇
冶金工业   5851篇
原子能技术   109篇
自动化技术   3975篇
  2024年   57篇
  2023年   299篇
  2022年   321篇
  2021年   834篇
  2020年   715篇
  2019年   732篇
  2018年   1327篇
  2017年   1284篇
  2016年   1371篇
  2015年   1020篇
  2014年   1300篇
  2013年   2501篇
  2012年   1898篇
  2011年   1757篇
  2010年   1405篇
  2009年   1256篇
  2008年   1279篇
  2007年   1164篇
  2006年   781篇
  2005年   634篇
  2004年   611篇
  2003年   574篇
  2002年   493篇
  2001年   364篇
  2000年   328篇
  1999年   368篇
  1998年   2020篇
  1997年   1302篇
  1996年   818篇
  1995年   451篇
  1994年   346篇
  1993年   371篇
  1992年   117篇
  1991年   96篇
  1990年   82篇
  1989年   81篇
  1988年   103篇
  1987年   94篇
  1986年   86篇
  1985年   102篇
  1984年   79篇
  1983年   61篇
  1982年   68篇
  1981年   87篇
  1980年   84篇
  1979年   49篇
  1977年   142篇
  1976年   267篇
  1975年   52篇
  1973年   55篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
Immunofluorescence microscopic observations indicated that a monoclonal antibody, Vmp 18, raised against the peptide 199-208 of murine interleukin 1 alpha, cross-reacted with an antigenic determinant of Drosophila thorax muscles. Immunoelectron microscopic analysis showed that the gold particles were mainly localized in the Z-line which is the attachment site of thin filaments from adjacent sarcomeres. On the contrary, the antibody failed to mark the Z-line in vertebrate skeletal muscle. A Western blot of total protein extract from Drosophila thorax muscles bound a protein of 43 kDa. Our observations suggest that the Vmp 18 antibody could contribute to clarify the composition of the Z-line in insect's flight muscles.  相似文献   
84.
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program.  相似文献   
85.
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values.  相似文献   
86.
Generation of Technology-Independent Retargetable Analog Blocks   总被引:1,自引:0,他引:1  
This paper introduces a complete methodology for retargeting of analog cells to different sets of specifications. This methodology is technology-independent, thus allowing the migration, from one technology to another, of the circuit under retargeting. Careful integration of the device sizing and layout generation tasks via the incorporation of layout constraints during the sizing process allows to generate fully functional designs in a few minutes. The methodology is illustrated via the retargeting of a fully-differential Miller-compensated two-stage operational amplifier for a new set of specifications and two different technological processes.An erratum to this article can be found at  相似文献   
87.
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ cs and the intergranular transport current densityJ cr are identical if the measurement conditions are similar. A degradation ofJ cs measured in the external field with AC ripple has been observed.  相似文献   
88.
This paper introduces a methodology for symbolic pole/zero extraction based on the formulation of the time-constant matrix of the circuits. This methodology incorporates approximation techniques specifically devoted to achieve an optimum trade-off between accuracy and complexity of the symbolic root expressions. The capability to efficiently handle even large circuits will be demonstrated through several practical circuits.  相似文献   
89.
Conducted a study of client expectations of psychological services in Yucatán, Mexico, under the sponsorship of a grant from the Organization of American States. The Expectations about Counseling–Brief form (EAC-B) questionnaire was translated and administered to 488 subjects across age, sex, and experience with psychological services. Subsequent analyses supported the reliability and robustness of the Spanish EAC-B, with factor structure similar to the EAC-B in English. Some relation was found among age, sex, prior counseling experience, and expectations about counseling. Implications of these data for future research and comparison with U.S. subjects are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
90.
A newly developed method GFFF (Gravitational Field‐Flow Fractionation) and the well known method LALLS (Low Angle Laser Light Scattering) were used to assess starch granule size distribution of ten varieties of spring barley. As a distribution criterion, the ratio of starch granule content larger than 8 μm (type A) and smaller than 8 μm (type B) was chosen. Both methods divided the observed set in a similar way. Varieties Akcent, Forum and Atribut formed a variety set with the highest ratio of large and small starch granules. Varieties Scarlet and Kompakt had intermediate ratios. The remaining five varieties Amulet, Novum, Olbram, Tolar and Krona had the lowest ratios of large and small starch granules. Statistical analysis showed that there was a highly significant correlation between the GFFF and LALLS methods.  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