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   174219篇
  免费   13955篇
  国内免费   7211篇
电工技术   9887篇
技术理论   14篇
综合类   11009篇
化学工业   29970篇
金属工艺   10108篇
机械仪表   10776篇
建筑科学   14160篇
矿业工程   5110篇
能源动力   4906篇
轻工业   10651篇
水利工程   3224篇
石油天然气   10044篇
武器工业   1538篇
无线电   19305篇
一般工业技术   20784篇
冶金工业   9009篇
原子能技术   2067篇
自动化技术   22823篇
  2024年   729篇
  2023年   2840篇
  2022年   4998篇
  2021年   6951篇
  2020年   5337篇
  2019年   4399篇
  2018年   5120篇
  2017年   5576篇
  2016年   4897篇
  2015年   6630篇
  2014年   8204篇
  2013年   10221篇
  2012年   10938篇
  2011年   11604篇
  2010年   10076篇
  2009年   9835篇
  2008年   9466篇
  2007年   9032篇
  2006年   9510篇
  2005年   8188篇
  2004年   5635篇
  2003年   5002篇
  2002年   4738篇
  2001年   4202篇
  2000年   4303篇
  1999年   4792篇
  1998年   4023篇
  1997年   3372篇
  1996年   3161篇
  1995年   2625篇
  1994年   2066篇
  1993年   1533篇
  1992年   1219篇
  1991年   974篇
  1990年   705篇
  1989年   615篇
  1988年   491篇
  1987年   328篇
  1986年   257篇
  1985年   191篇
  1984年   113篇
  1983年   80篇
  1982年   93篇
  1981年   80篇
  1980年   55篇
  1979年   29篇
  1977年   17篇
  1976年   19篇
  1974年   13篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A new optimization model is discussed for the design of cellular manufacturing systems. It is based on an integer programming formulation that updates some other models by eliminating redundant machine assignment and cost coefficients dependent on cell configuration. To reduce computational burdens, a simplified integer programming model and a decomposition algorithm are proposed. Several computer solutions were performed to evaluate the performance of the new model. The computational results are discussed.  相似文献   
102.
An analytical method is presented for calculating the resonant frequency andQ-factor of a superconducting dielectric disk resonator operating in millimeter-wave regime with whispering-gallery mode. Resonant frequency shift due to the optical generation of quasi-particles in superconducting film is investigated as a function of photon flux. An optically tunable resonant frequency of about 500 MHz is estimated, and good agreement is found between numerical results and experimental ones.  相似文献   
103.
PURPOSE: The purpose of this research is to obtain the tablet coating distribution from weight distributions of uncoated and coated tablets. METHODS: The method of deconvolution with digital smoothing was used to calculate the distribution of coating applied to a tablet population from separate random measurements of individual uncoated and coated tablets. RESULTS: It was demonstrated that the calculated coating weight distribution agrees well with the measured distribution. The effect of the smoothing factor on the solution is illustrated. CONCLUSIONS: This method can be used during development to facilitate process scale-up/optimization. In routine production, the method can assess the reproducibility and consistency of a coating process.  相似文献   
104.
105.
The author presents a personal account of the search for a design procedure for Yagi-Uda antenna arrays yielding a maximum gain, or directivity if element losses are neglected. Results on current distributions in the array are briefly reviewed. The analytical approach used to achieve gain optimization by means spacing and length perturbations is sketched. By using both spacing and length perturbations, it was possible to find the optimized array analytically in a systematic way, some examples having gain increases of nearly 80%. The effects of finite dipole radius and mutual coupling were included in the theoretical treatment  相似文献   
106.
The span-depth ratios of coupling beams to interconnect shear walls are generally small, so that brittle shear failure may occur and lead to reduced ductility. In order to improve the ductility of coupling beams for earthquake loading, a new type of ductile coupling beam is proposed in this paper. Along the middle depth of this beam, a slit through the entire thickness (a narrow hole) near each end and two lateral keyways along the remaining middle part of the span are made. The reductions of the stiffness under service load and the ultimate carrying capacity of the beam due to the weakening mentioned above are small and the ductility is greatly increased. Tests of 4-storey walls interconnected by coupling beams in three different constructions (monolithic beams, beams with a through-slit and new-type beams) indicated that shear walls with the new coupling beams possess the best aseismic behaviours under cyclic loading. The proposed new coupling beam has been used in a high-rise building.  相似文献   
107.
Conventional drying, dehumidification drying, and combined conventional-dehumidification drying of wood were experimentally studied in this article. The results showed that the energy consumption in the dehumidification drying is the least but its drying time is the longest. The energy consumption in the combined drying is more than that in the dehumidification drying but less than that in the conventional drying, and the drying time is half of that in the dehumidification drying. The advantages of the combined conventional and dehumidification drying are discussed from the experiments results.  相似文献   
108.
109.
Two experimental devices were designed and built to determine four coefficients KT KM DM D (or δT = DT / DM occurring in simultaneous heat and mass transfer equations, where,K T and DM are thermal conductivity and moisture diffcusivity respectively, DT ( or δ T is temperature gradient Induced moisture migration coefficient and KM is moisture gradient Induced heat transfer coefficient. Three food materials, i.e. potato, bread dough and bread, were tested. From this study, it was found that the value of 5 was higher for low density food materials, such as bread, than for high density materials, such as potato. The coefficient & measures moisture migration contribution due to temperature gradient within the material. The average values of δ T for potato, bread dough and bread were 0.0014, 0.0059 and 0.0127 per °C, respectively. The contribution of temperature gradient to the overall moisture migration is negligible In high density materials. However, this contribution may be important in the moisture migratlon analysls for low density materials. The moisture gradient induced heat transfer coefficient % as found to be negligible for the materials tested in this study  相似文献   
110.
To investigate the prognostic factors of primary liver cancer (PLC) and improve the long-term results, 1,248 cases of PLC were analysed. Univariate analysis demonstrated that discovery approach, staging of PLC, original gamma-GPT, resection, radical resection, original AFP, tumor size, tumor number, and tumor capsule have very significant effects on prognosis of PLC (all P < 0.001); cirrhosis, HBsAg, local resection, and tumor embolus in portal vein were also significant difference (all P < 0.05); age, sex, original AFP, hepatitis, and differentiation of PLC cells were no significant difference (all P > 0.05). Multivariate analysis demonstrated that original gamma-GPT, radical resection, tumor size, and tumor number were the most significant prognostic factors (all P < 0.001). Some aspects improving long-term survival were discussed.  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