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   37380篇
  免费   1467篇
  国内免费   59篇
电工技术   386篇
综合类   29篇
化学工业   7329篇
金属工艺   736篇
机械仪表   767篇
建筑科学   2027篇
矿业工程   126篇
能源动力   1099篇
轻工业   3031篇
水利工程   439篇
石油天然气   123篇
武器工业   5篇
无线电   2531篇
一般工业技术   6340篇
冶金工业   6987篇
原子能技术   280篇
自动化技术   6671篇
  2023年   203篇
  2022年   268篇
  2021年   687篇
  2020年   472篇
  2019年   628篇
  2018年   792篇
  2017年   703篇
  2016年   840篇
  2015年   764篇
  2014年   1055篇
  2013年   2445篇
  2012年   1698篇
  2011年   2126篇
  2010年   1678篇
  2009年   1586篇
  2008年   1847篇
  2007年   1813篇
  2006年   1642篇
  2005年   1475篇
  2004年   1208篇
  2003年   1155篇
  2002年   1084篇
  2001年   717篇
  2000年   570篇
  1999年   633篇
  1998年   674篇
  1997年   629篇
  1996年   590篇
  1995年   596篇
  1994年   551篇
  1993年   537篇
  1992年   517篇
  1991年   297篇
  1990年   439篇
  1989年   412篇
  1988年   342篇
  1987年   381篇
  1986年   330篇
  1985年   440篇
  1984年   448篇
  1983年   340篇
  1982年   316篇
  1981年   307篇
  1980年   299篇
  1979年   292篇
  1978年   263篇
  1977年   247篇
  1976年   233篇
  1975年   212篇
  1974年   187篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
111.
The authors highlight several possible ways in which the construction industry could lower present emissions of the greenhouse gas, carbon dioxide. It is an excellent discussion document and is recommended reading.  相似文献   
112.
113.
The purpose of the current study was to describe four models of cognitive deficit and to outline the statistical hypotheses underlying each model. The four models of cognitive deficit were (a) specific deficit; (b) subgroup deficit; (c) a syndrome dissociation model; and (d) a global function dissociation model. Neuropsychological data are analyzed to examine each of these four models in a sample of mild Multiple Sclerosis (MS) patients. The results suggest that for these subjects and tests, the specific deficit model best fits the data. The results are reviewed initially in the context of MS. There follows a consideration of statistical caveats and finally, general applications of the proposed procedures.  相似文献   
114.
Directed delivery and distribution of anaesthetics (novocaine, lidocaine, trimecaine) immobilized on finely dispersed iron powders under the influence of an external magnetic field in body tissues of test animals have been studied. The data of emission spectral analysis relating to concentration of iron in soft and bone tissues of animals influenced by constant and alternating magnetic field on front and reverse sides over a period from 0 to 180 min are given.  相似文献   
115.
Systemised serendipity for producing computer art   总被引:4,自引:0,他引:4  
Serendipity applied to Newton's method, and its derivative the Secant Method, produces unusual and beautiful fractal patterns. Serendipity may be systemised, for example, by the introduction of a perturbation parameter P1, [1] to facilitate searches for interesting pattern variations.  相似文献   
116.
117.
118.
OBJECTIVE: To evaluate aspects of the natural history of AA amyloidosis complicating juvenile rheumatoid arthritis (JRA), and its response to therapy with chlorambucil. METHODS: Scintigraphy and 7-day turnover studies were performed in JRA patients with histologically proven (n = 35) or clinically suspected (n = 30) AA amyloidosis, following intravenous injection of 123I and 125I-labeled serum amyloid P component (SAP). Prospective monitoring studies were performed over 2-3 years in 20 patients with amyloidosis. All but 2 amyloidosis patients were treated with chlorambucil. RESULTS: Positive scanning results were obtained in all patients in whom imaging was performed within 12 years of positive biopsy findings of amyloid and in 5 patients with clinically suspected amyloidosis. Negative scanning results with normal SAP metabolism, indicating regression of amyloid, were obtained in 4 patients whose amyloidosis had been in full clinical remission for more than 12 years. Prospective monitoring studies in patients whose JRA-associated inflammatory activity was in remission demonstrated regression of amyloid in 8 patients and no substantial changes in 8 others; however, in 4 further patients with active inflammation, there was accumulation of amyloid. There was a very poor correlation between the amount of amyloid present at a particular site and the resultant organ dysfunction. CONCLUSION: Radiolabeled SAP scintigraphy and turnover studies are useful complementary tools in the diagnosis, screening, and quantitative monitoring of type AA amyloidosis in JRA. The amyloid deposits may progress and/or regress at different rates in different anatomic sites over short periods.  相似文献   
119.
We consider the problem of generating a large state-space in a distributed fashion. Unlike previously proposed solutions that partition the set of reachable states according to a hashing function provided by the user, we explore heuristic methods that completely automate the process. The first step is an initial random walk through the state space to initialize a search tree, duplicated in each processor. Then, the reachability graph is built in a distributed way, using the search tree to assign each newly found state to classes assigned to the available processors. Furthermore, we explore two remapping criteria that attempt to balance memory usage or future workload, respectively. We show how the cost of computing the global snapshot required for remapping will scale up for system sizes in the foreseeable future. An extensive set of results is presented to support our conclusions that remapping is extremely beneficial.  相似文献   
120.
We have used Path Integral Monte Carlo to study the surface melting of molecular hydrogen. Density profiles perpendicular and parallel to the bare H2 surface are computed showing the formation of a liquid adlayer at 6 K, less than half the bulk melting temperature of para-hydrogen, 13.8 K. To estimate the onset temperature and depth of H2 surface melting we determine the static structure factor within the individual H2-layers for wave vectors in the plane and find no crystalline order down to 3 K in a partially filled H2 adlayer at the free surface. We find quantum effects amplify the melting point depression at the free H2 surface compared to bulk by a factor of five over classical Lennard-Jones solids and find that the zero-point fluctuations of molecules at the surface are much enhanced over their bulk values. We see vacancy formation in the solid before melting.  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