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   35851篇
  免费   2117篇
  国内免费   30篇
电工技术   230篇
综合类   20篇
化学工业   6516篇
金属工艺   611篇
机械仪表   686篇
建筑科学   915篇
矿业工程   72篇
能源动力   552篇
轻工业   5431篇
水利工程   311篇
石油天然气   117篇
武器工业   7篇
无线电   1220篇
一般工业技术   5540篇
冶金工业   11224篇
原子能技术   118篇
自动化技术   4428篇
  2024年   76篇
  2023年   287篇
  2022年   305篇
  2021年   755篇
  2020年   653篇
  2019年   741篇
  2018年   1332篇
  2017年   1298篇
  2016年   1347篇
  2015年   1034篇
  2014年   1214篇
  2013年   2562篇
  2012年   1905篇
  2011年   1738篇
  2010年   1423篇
  2009年   1270篇
  2008年   1231篇
  2007年   1166篇
  2006年   771篇
  2005年   670篇
  2004年   635篇
  2003年   569篇
  2002年   556篇
  2001年   404篇
  2000年   386篇
  1999年   549篇
  1998年   3450篇
  1997年   2245篇
  1996年   1398篇
  1995年   802篇
  1994年   642篇
  1993年   778篇
  1992年   213篇
  1991年   232篇
  1990年   176篇
  1989年   193篇
  1988年   191篇
  1987年   168篇
  1986年   132篇
  1985年   163篇
  1984年   124篇
  1983年   100篇
  1982年   145篇
  1981年   156篇
  1980年   179篇
  1979年   78篇
  1978年   89篇
  1977年   352篇
  1976年   756篇
  1973年   63篇
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
91.
Various influence diagnostics in Multiple Discriminant Analysis can be found in the literature. Almost all of them are based on the overall probability of misclassification. Two case-deletion diagnostics which evaluate the effect of the omission on the linear functions which determine Fisher’s Linear Discriminant Rule are proposed in this paper. Both measures are based on the L 2-norm: The first diagnostic is calculated from the data set and the second diagnostic is calculated in the minimum hypercube which covers it.  相似文献   
92.
Evaluated the effects of intraseptal scopolamine hydrobromide (40 μg) injections on Pavlovian (classical) conditioning, with tones used as the CS and a periorbital electric shock train as the UCS, using New Zealand albino rabbits. Eyeblink (EB) and heart rate (HTR) CRs were concomitantly recorded. Although injections of scopolamine into the medial septum impaired the acquisition of the Pavlovian conditioned eyelid reflex, these injections enhanced the magnitude of accompanying Pavlovian conditioned HTR decelerations. However, scopolamine applied to the lateral septal area had no effect on EB conditioning, relative to the vehicle; like medial injections, scopolamine also enhanced the magnitude of the accompanying HTR decelerations. Results are compatible with those of previous investigations indicating that medial septal dysfunction impairs somatomotor conditioning but leaves autonomic conditioning intact and that septal dysfunction produces a parasympathetic bias of the cardiovascular system. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
93.
The comfort diagrams and the so-called PMV-PPD values are already used today directly and indirectly in a wide field in technical practice, even at a standard level. This theory is known also in Hungary, and the PMV-PPD values have been used by us for the solution of a design problem. The task was to elaborate a calculation method, an index number suitable for the determination of the thermal confort effect in the case of occasional underheating of residential and communal buildings in winter.The results of this work are presented in this paper.  相似文献   
94.
The Mexican petrochemical industry, Morelos S.A. de C.V., is one of the biggest and more important petroleum industries in Mexico and Latin America. It has an activated sludge system to treat its wastewater flow, which is approximately 7,000 m3/d. The wastewater contains volatile organic carbon substances classified as toxics. The old surface aeration system was changed for fine bubble diffusers; however, one major drawback of the new aeration system is that the temperature in the bioreactor has increased due to the compression of the air, which at the compressor exit reaches 85 degrees C. This effect results in the temperature in the bioreactor attaining 32 degrees C during the fall, whereas in the spring and summer, the bioreactor temperature reaches higher values than 40 degrees C. The high temperatures reduce the microorganism activity and cause a higher volatilisation rate of volatile compounds, among other effects, which affect the performance of the biological treatment. This work was performed to obtain a better modelling of the wastewater treatment from the petrochemical industry. The model describes the effect of the temperature on the performance of the biological treatment. The model was obtained from tests that were carried out in laboratory reactors with 14 L capacity, which were operated at different temperatures (from 30 to 45 degrees C), with the same wastewater and conditions as the actual system.  相似文献   
95.
96.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively.  相似文献   
97.
The response of mesoscopic superconductors to an ac magnetic field is investigated both experimentally and with numerical simulations. We study small square samples with dimensions of the order of the penetration depth. We obtain the ac susceptibitity χ=χ′+iχ″ at microwave frequencies as a function of the dc magnetic field H dc. We find that the dissipation, given by x″, has a non monotonous behavior in mesoscopic samples. In the numerical simulations we obtain that the dissipation increases before the penetration of vortices and then it decreases abruptly after vortices have entered, the sample. This is verified experimentally, where we find that χ″ has strong oscillations as a function of H dc in small squares of Pb.  相似文献   
98.
99.
100.
Summary Dynamic light scattering was used to investigate the dynamics of sodium poly(styrene sulfonate) and fully neutralized poly(acrylic acid) gels as a function of the degree of swelling and weight ratio of cross-linking agent. It was shown that the collective diffusion coefficient increases with increasing degree of swelling and that the diffusion coefficient shows stronger concentration dependence than predicted by scaling arguments. For gel samples measured at the swelling equilibrium, the diffusion coefficient increases with increasing gel concentration for both gel systems.  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