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   38161篇
  免费   1897篇
  国内免费   51篇
电工技术   245篇
综合类   40篇
化学工业   8746篇
金属工艺   684篇
机械仪表   694篇
建筑科学   1201篇
矿业工程   73篇
能源动力   1120篇
轻工业   6936篇
水利工程   366篇
石油天然气   173篇
武器工业   2篇
无线电   1598篇
一般工业技术   5450篇
冶金工业   7599篇
原子能技术   242篇
自动化技术   4940篇
  2024年   80篇
  2023年   296篇
  2022年   833篇
  2021年   1125篇
  2020年   755篇
  2019年   907篇
  2018年   1240篇
  2017年   1190篇
  2016年   1304篇
  2015年   1052篇
  2014年   1403篇
  2013年   2626篇
  2012年   2127篇
  2011年   2388篇
  2010年   1849篇
  2009年   1835篇
  2008年   1667篇
  2007年   1499篇
  2006年   1166篇
  2005年   999篇
  2004年   952篇
  2003年   828篇
  2002年   770篇
  2001年   531篇
  2000年   529篇
  1999年   581篇
  1998年   2393篇
  1997年   1563篇
  1996年   1101篇
  1995年   597篇
  1994年   514篇
  1993年   542篇
  1992年   214篇
  1991年   181篇
  1990年   167篇
  1989年   196篇
  1988年   163篇
  1987年   149篇
  1986年   128篇
  1985年   170篇
  1984年   122篇
  1983年   90篇
  1982年   106篇
  1981年   130篇
  1980年   108篇
  1979年   71篇
  1978年   59篇
  1977年   185篇
  1976年   341篇
  1975年   49篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The tensile elastic modulus (E), yield stress (σY) and microhardness (MH) of neat and binary and ternary blends of glassy semicrystalline ethylene–vinyl alcohol copolymer (EVOH), a glassy amorphous polyamide and a semicrystalline nylon‐containing ionomer covering a broad range of properties were examined. The tests were carried out on dry and water‐equilibrated samples to produce stiffer and softer materials, respectively. From the results, more accurate linear correlations were found to describe adequately the microhardness, modulus and yield stress of these strongly self‐associated polymers through hydrogen bonding. Copyright © 2003 Society of Chemical Industry  相似文献   
62.
Aggressive behavior induces an adrenocortical stress response, and sudden stressors often precipitate violent behavior. Experiments in rats revealed a fast, mutual, positive feedback between the adrenocortical stress response and a brain mechanism controlling aggression. Stimulation of the aggressive area in the hypothalamus rapidly activated the adrenocortical response, even in the absence of an opponent and fighting. Hypothalamic aggression, in turn, was rapidly facilitated by a corticosterone injection in rats in which the natural adrenocortical stress response was prevented by adrenalectomy. The rapidity of both effects points to a fast, mutual, positive feedback of the controlling mechanisms within the time frame of a single conflict. Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
63.
64.
An Imhoff tank was reconstructed into a 250 m3 UASB reactor in order to treat a malting plant wastewater. The UASB was inoculated with sludge from an anaerobic lagoon used for slaughterhouse wastewater treatment. After two months of operation the reactor achieved full load with an HRT of 17 h, a COD removal higher than 80% and a biogas production of 300 m3/day (77% average methane content), with an organic loading rate of 3.6 kgCOD/m3.d (0.24 kgCOD/kgVSS.d). A yield coefficient of 0.09 gVSS/gCODrem was found from a mass balance. The fat present in the inoculated sludge (48 mg/gSSV) did not affect the start up performance. Sludge from the inoculum with high content of fat (270 mg/gSSV), was separated by flotation in the first week of operation. The COD removal efficiency was scarcely influenced by the reactor operation temperature (17-25 degrees C).  相似文献   
65.
66.
In this study chick embryo optic cups at HH stage 13 of development were analyzed under normal conditions and after inoculation with colchicine for 1, 2, 4, and 8 h. Several changes were seen after these periods of treatment: 1) modifications of the structure, with thicker regions in the cup and a general decrease in the total volume according to the duration of exposure to the drug (about 4 times less than normal, 5,035 x 10(3) microns 3 vs 1,334 x 10(3) microns 3 after 8 h of treatment); 2) enlargement of the ventricular cavity and its closure, due to failure of approximation of retinal and pigmentary layers; 3) failure of lens development, with delay and impairment of pit formation and deformation of all structures; lens volume was less than normal (about 4 times less, 2,148 x 10(3) microns 3 vs 658 x 10(3) microns 3 after 8 h of treatment); 4) a general segregation of the cells making up the structure, principally in the more active proliferating zones. The local alterations found are described.  相似文献   
67.
68.
Data from the past few years have shown that as caffeine metabolizes solely in the liver, caffeine elimination can serve as a liver function test. We have collected data by monitoring 40 persons with liver diseases (11 chronic alcoholic hepatitis, 24 liver cirrhosis, 5 non-cirrhotic liver disease). Eight subjects served as controls. The patients with liver cirrhosis were classified according to the Child--Pugh scoring system. To determine caffeine elimination blood samples were collected before and at 3, 6, 9 and 12 hours after oral administration of 0.2 g caffeine. Fasting serum caffeine concentration and concentration 12 hours after administration, serum clearance, half life, peak concentration and volume of distribution have been compared. The respective values measured in patients with non-cirrhotic liver diseases did not differ significantly from the controls. The disappearance of caffeine was significantly decreased in cirrhotics. Our results demonstrated a good correlation between impairment of caffeine elimination and assessment of severity of liver disease by the Child--Pugh classification. Measuring serum levels in samples taken 12 hours after caffeine administration is a simple and useful method in the diagnosis of liver diseases at cirrhotic stage.  相似文献   
69.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
70.
Identification of Lophius budegassa(black‐bellied angler) and L. piscatorius(angler) (Lophiiformes) was carried out on the amplification of a 486 bp tRNAGlu/cytochrome b segment using the polymerase chain reaction (PCR). Direct DNA sequencing of 6 PCR products was carried out. Six restriction endonucleases (AluI, CfoI, HaeIII, HinfI, Mae, and ScrFI) with different species‐specific restriction fragment length polymorphism (RFLP) were selected. Digestions of PCR products from 30 individuals showed no intraspecific polymorphism. Double digestions (CfoI and HinfI, and HaeIII and ScrFI) were simpler and more rapid than single digestions. This technique is suitable for distinguishing tails of both Lophius species.  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