全文获取类型
收费全文 | 4208篇 |
免费 | 54篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 18篇 |
综合类 | 1篇 |
化学工业 | 375篇 |
金属工艺 | 30篇 |
机械仪表 | 80篇 |
建筑科学 | 119篇 |
矿业工程 | 2篇 |
能源动力 | 64篇 |
轻工业 | 229篇 |
水利工程 | 14篇 |
石油天然气 | 3篇 |
无线电 | 304篇 |
一般工业技术 | 403篇 |
冶金工业 | 2293篇 |
原子能技术 | 29篇 |
自动化技术 | 301篇 |
出版年
2021年 | 21篇 |
2019年 | 29篇 |
2018年 | 27篇 |
2017年 | 26篇 |
2016年 | 34篇 |
2015年 | 23篇 |
2014年 | 32篇 |
2013年 | 108篇 |
2012年 | 64篇 |
2011年 | 88篇 |
2010年 | 66篇 |
2009年 | 60篇 |
2008年 | 93篇 |
2007年 | 86篇 |
2006年 | 75篇 |
2005年 | 73篇 |
2004年 | 57篇 |
2003年 | 62篇 |
2002年 | 72篇 |
2001年 | 60篇 |
2000年 | 63篇 |
1999年 | 118篇 |
1998年 | 662篇 |
1997年 | 375篇 |
1996年 | 285篇 |
1995年 | 156篇 |
1994年 | 148篇 |
1993年 | 157篇 |
1992年 | 49篇 |
1991年 | 51篇 |
1990年 | 47篇 |
1989年 | 54篇 |
1988年 | 69篇 |
1987年 | 52篇 |
1986年 | 42篇 |
1985年 | 52篇 |
1984年 | 41篇 |
1983年 | 31篇 |
1982年 | 45篇 |
1981年 | 54篇 |
1980年 | 44篇 |
1979年 | 30篇 |
1978年 | 36篇 |
1977年 | 93篇 |
1976年 | 130篇 |
1975年 | 33篇 |
1974年 | 29篇 |
1973年 | 17篇 |
1971年 | 19篇 |
1970年 | 20篇 |
排序方式: 共有4265条查询结果,搜索用时 15 毫秒
21.
Although the tissue solvent and bactericidal properties of sodium hypochlorite are well known, the effective shelf-life of prepared sodium hypochlorite solutions is not known. The stability of sodium hypochlorite is adversely affected by exposure to high temperature, light, air, and the presence of organic and inorganic contaminants. The purpose of this study was to investigate the variables of storage conditions and time on the tissue-dissolving capacity of three different concentrations of sodium hypochlorite. Fresh frozen human umbilical cord was used as the tissue sample for this experiment. Tissue samples were dissolved at time intervals ranging from 1 day to 10 wk in 5.25%, 2.62%, and 1.0% solutions of sodium hypochlorite. The tissue-dissolving ability of 5.25% sodium hypochlorite remains stable for at least 10 wk. The tissue-dissolving ability of 2.62% and 1.0% sodium hypochlorite remains relatively stable for 1 wk after mixing, then exhibits a significant decrease in tissue-dissolving ability at 2 wk and beyond. 相似文献
22.
23.
A.J. Roberts 《Computer Physics Communications》1997,100(3):215-230
I describe a method, particularly suitable to implementation by computer algebra, for the derivation of low-dimensional models of dynamical systems. The method is systematic and is based upon centre manifold theory. Computer code for the algorithm is relatively simple, robust and flexible. The method is applied to two examples: one a straightforward pitchwork bifurcation, and one being the dynamics of thin fluid films. 相似文献
24.
National and regional corporate spatial structure 总被引:3,自引:0,他引:3
Much is known about the macro-impacts of business activities on national and regional economies; however, comparatively little
is known at the micro level about the impact spatial agglomeration of corporate wealth and performance has on urban systems.
This paper reports on a collaborative research project between the Australian Housing and Urban Research Institute and Dun
and Bradstreet, an international financial credit agency, to analyse the spatial implications of corporate structure in metropolitan
regions. This paper analyses spatial patterns of medium to large businesses in three Australian State capital cities at the
postcode level in order to assess the agglomeration of corporate capital, sales, and performance. The research indicates that
ratio analysis can provide a useful insight into the competitiveness of metropolitan regions and the control corporate headquarters
have over decision making and investment processes. The findings of this research are of special interest to capital markets,
business and urban researchers in the Asia Pacific Region.
Received: September 1997/Accepted: September 2001 相似文献
25.
AF Minnick MJ Roberts WB Young RM Kleinpell RJ Marcantonio 《Canadian Metallurgical Quarterly》1997,35(4):399-409
OBJECTIVES: Market forces make it essential to know what policies and actions influence patients' reports of hospital services. No studies have examined the role of patient characteristics, labor quality and staff characteristics, nonlabor resources, managerial practices, and employee attitudes within a single investigation. METHODS: The authors collected, simultaneously, data about labor, management and service processes, nonlabor resources, and employee attitudes on 117 nonintensive medical-surgical inpatient units in 17 hospitals selected from a pool of 69 institutions within a metropolitan area by a stratified random sample. Of the 2,595 patients who agreed to participate, 2,051 (79%) completed telephone interviews regarding their experiences with physical care, education, and pain management services within 26 days of hospital discharge. RESULTS: A significant amount of variation in patients' service reports was explained (adjusted R2 = 0.41 physical care, 0.35 pain management, 0.44 education). Although the predictors varied for each service report, patient characteristics, especially those related to personal resources, had a large explanatory role. A labor assignment pattern that could explain why earlier studies found labor quality and staff characteristics to have only a weak role in the prediction of patients' service reports was noted. CONCLUSIONS: The results related to patient characteristics may indicate opportunities to improve care by confronting service design strategies that erroneously rely on a homogeneous patient population. Measurement challenges identified by this study must be addressed to determine the role of labor quantity and staff characteristics. 相似文献
26.
Neil Roberts Silas Barbosa Lance D. Blumhardt Ron A. Kawoski Richard H. T. Edwards 《Magma (New York, N.Y.)》1994,2(3):375-378
Point counting represents a convenient and efficient technique for estimating the area of transects through multiple sclerosis (MS) lesions on magnetic resonance (MR) images obtained for sections through the brain. When sectioning has been performed according to the Cavalieri method, unbiased estimates of the total volume of MR-visible MS plaques can be obtained with a precision of 3–5% in 5–10 min. 相似文献
27.
28.
Ingram M. Roberts 《Lipids》1985,20(4):243-247
A rapid, sensitive and convenient fluorescent assay was developed to screen for lipase activity. The non-fluorescent substrate,
4-methylumbelliferyl butyrate (4-MUB), solubilized in either liposomal dispersions or bile salt/lecithin mixed micelles, is
hydrolyzed to butyric acid and the highly fluorescent compound, 4-methylumbelliferone (4-MU). Assays are run at 37 C for 10
min, terminated, and the changes in fluorescence quantitated with a Turner III fluorometer. Both lingual and pancreatic lipases
exhibit activity against this artificial substrate. The assay has several advantages: nmoles 4 MU/ml/hr are measured allowing
the detection of very low lipolytic activity; multiple samples may be simultaneously assayed, and only a brief incubation
period is required. 相似文献
29.
Standards which eliminate ambiguity in reporting nonlinear phenomena, especially in the increasingly complex realm of biaxial crystals, are proposed. In order to restore uniformity to the designation of crystallographic axes and crystal tensor properties, adoption of IEEE/ANSI Std. 176, with a small but much needed modification for crystal class mm2, is recommended. For the reporting of nonlinear interaction characteristics, other frames are proposed which result in simpler rules than heretofore given for categorizing phase-matching loci, and for characterizing eigenmode polarizations, double refraction, effective nonlinear coupling, and first- and second-order acceptance bandwidths (angular, spectral, thermal) along these loci. Similarities as well as differences between biaxial and uniaxial crystals are emphasized 相似文献
30.