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   9651篇
  免费   209篇
  国内免费   7篇
电工技术   91篇
综合类   6篇
化学工业   1436篇
金属工艺   146篇
机械仪表   247篇
建筑科学   413篇
矿业工程   37篇
能源动力   236篇
轻工业   712篇
水利工程   84篇
石油天然气   19篇
武器工业   3篇
无线电   769篇
一般工业技术   1575篇
冶金工业   2964篇
原子能技术   146篇
自动化技术   983篇
  2021年   103篇
  2020年   77篇
  2019年   88篇
  2018年   92篇
  2017年   111篇
  2016年   124篇
  2015年   105篇
  2014年   170篇
  2013年   386篇
  2012年   277篇
  2011年   385篇
  2010年   284篇
  2009年   286篇
  2008年   347篇
  2007年   316篇
  2006年   301篇
  2005年   236篇
  2004年   225篇
  2003年   219篇
  2002年   199篇
  2001年   175篇
  2000年   171篇
  1999年   212篇
  1998年   781篇
  1997年   443篇
  1996年   367篇
  1995年   232篇
  1994年   223篇
  1993年   240篇
  1992年   127篇
  1991年   125篇
  1990年   125篇
  1989年   133篇
  1988年   113篇
  1987年   107篇
  1986年   117篇
  1985年   122篇
  1984年   137篇
  1983年   104篇
  1982年   105篇
  1981年   130篇
  1980年   118篇
  1979年   104篇
  1978年   100篇
  1977年   123篇
  1976年   202篇
  1975年   91篇
  1974年   64篇
  1973年   76篇
  1972年   54篇
排序方式: 共有9867条查询结果,搜索用时 15 毫秒
71.
72.
Memory reallocation is used to construct a run-time data structure for fast/efficient storage of information during collection and analysis. The data structure presented uses dynamic memory but does not require the use of pointers to link nodes of information together. It allows for simple and efficient access to data via array indexing rather than through the use of lists or tree structures and it provides flexibility for competing storage requirements that are determined dynamically. The data structure is developed in the C programming language and a suite of ANSI standard C subroutines that make up a run-time data structure management system is provided.  相似文献   
73.
Electrical characterization of evaporated ZnS:Mn alternating-current thin-film electroluminescent (ACTFEL) devices is accomplished by capacitance-voltage (C-V) analysis. Interpretation of these C-V characteristics is aided by SPICE modeling and by electrical characterization of an ideal ACTFEL device constructed from discrete components, based on a simple equivalent circuit for the ACTFEL device. Various features of the C -V curve are ascribed to equivalent circuit parameters and associated device physics parameters  相似文献   
74.
This article examines factors that may contribute to errors in drug administration. These can range from the omission of a single dose of a non-essential drug to a major overdose resulting in serious harm to a patient. It concludes that a combination of being observant and well-informed can help to prevent errors.  相似文献   
75.
76.
An extremely large database describes genotypes associated with the human cancer phenotype and genotypes of human populations with genetic predisposition to cancer. Aspects of this database are examined from the perspective of risk analysis, and the following conclusions and hypotheses are proposed: (1) The genotypes of human cancer cells are characterized by multiple mutated genes. Each type of cancer is characterized by a set of mutated genes, a subset from a total of more than 80 genes, that varies between tissue types and between different tumors from the same tissue. No single cancer-associated gene nor carcinogenic pathway appears suitable as an overall indicator whose induction serves as a quantitative marker for risk analysis. (2) Genetic defects that predispose human populations to cancer are numerous and diverse, and provide a model for associating cancer rates with induced genetic changes. As these syndromes contribute significantly to the overall cancer rate, risk analysis should include an estimation of the effect of putative carcinogens on individuals with genetic predisposition. (3) Gene activation and inactivation events are observed in the cancer genotype at different frequencies, and the potency of carcinogens to induce these events varies significantly. There is a paradox between the observed frequency for induction of single mutational events in test systems and the frequency of multiple events in a single cancer cell, suggesting events are not independent. Quantitative prediction of cancer risk will depend on identifying rate-limiting events in carcinogenesis. Hyperproliferation and hypermutation may be such events. (4) Four sets of data suggest that hypermutation may be an important carcinogenic process. Current mechanisms of risk analysis do not properly evaluate the potency of putative carcinogens to induce the hypermutable state or to increase mutation in hypermutable cells. (5) High-dose exposure to carcinogens in model systems changes patterns of gene expression and may induce protective effects through delay in cell progression and other processes that affect mutagenesis and toxicity. Paradigms in risk analysis that require extrapolation over wide ranges of exposure levels may be flawed mechanistically and may underestimate carcinogenic effects of test agents at environmental levels. Characteristics of the human cancer genotype suggest that approaches to risk analysis must be broadened to consider the multiplicity of carcinogenic pathways and the relative roles of hyperproliferation and hypermutation. Further, estimation of risk to general human populations must consider effects on hypersusceptible individuals. The extrapolation of effects over wide exposure levels is an imprecise process.  相似文献   
77.
The long‐term consequences of the sale of public sector dwellings to sitting tenants are under‐researched; in particular, the experience of tenant purchasers in the housing market subsequent to purchase is little known. This paper reports research designed to fill this gap in knowledge. Over 200 tenants who had bought their dwelling from the Scottish Special Housing Association and subsequently resold on the open market were traced using the Register fo Sasines and the Land Register and interviewed. Most had made considerable capital gains on resale and had used some of the realised capital to trade up in the housing market. They were, on average, slightly more affluent and younger than sitting tenant purchasers generally; they represented a group of households who were privileged within the public sector through living as tenants in the best stock and who were enabled by the Right to Buy to convert that good luck into hard cash and move into mainstream owner occupation. This good luck compounded the advantaged position vis‐à‐vis other tenants that they enjoyed in the labour market.  相似文献   
78.
79.
80.
Thirteen scenarios were used to measure and compare the perceptions of elder abuse and help-seeking behaviors of African-American, Caucasian American, and Korean-American elderly women. Significant group differences existed in their perceptions of elder abuse with regard to six scenarios, and the Korean-American women were substantially less likely to perceive a given situation as abusive than the other groups. The three groups also showed significant differences in their intended use of formal and informal sources of help in the case of elder abuse.  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