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   1970篇
  免费   22篇
电工技术   11篇
化学工业   125篇
金属工艺   10篇
机械仪表   17篇
建筑科学   46篇
矿业工程   2篇
能源动力   24篇
轻工业   117篇
水利工程   10篇
石油天然气   4篇
无线电   129篇
一般工业技术   157篇
冶金工业   1175篇
原子能技术   10篇
自动化技术   155篇
  2021年   7篇
  2019年   6篇
  2018年   12篇
  2017年   18篇
  2016年   9篇
  2015年   13篇
  2014年   16篇
  2013年   58篇
  2012年   20篇
  2011年   47篇
  2010年   34篇
  2009年   25篇
  2008年   35篇
  2007年   29篇
  2006年   37篇
  2005年   32篇
  2004年   46篇
  2003年   34篇
  2002年   30篇
  2001年   27篇
  2000年   20篇
  1999年   54篇
  1998年   318篇
  1997年   187篇
  1996年   138篇
  1995年   93篇
  1994年   68篇
  1993年   84篇
  1992年   41篇
  1991年   24篇
  1990年   17篇
  1989年   25篇
  1988年   19篇
  1987年   21篇
  1986年   19篇
  1985年   34篇
  1984年   12篇
  1983年   18篇
  1982年   16篇
  1981年   23篇
  1980年   17篇
  1979年   22篇
  1978年   11篇
  1977年   42篇
  1976年   59篇
  1975年   8篇
  1973年   10篇
  1972年   6篇
  1968年   5篇
  1967年   6篇
排序方式: 共有1992条查询结果,搜索用时 15 毫秒
141.
The changes in neighbourhood income inequality noted in Gregory and Hunter (1995) indicate that significant changes in the nature of Australian cities have occurred since the mid-1970s. This paper seeks to establish that the regional dimension of income inequality is becoming a more important component of overall inequality. Furthermore, low status and high status areas are becoming increasingly homogenous with more low income households living together in low status neighbourhoods and higher income households living elsewhere. The inadequacies of the regional income data currently available means that it is difficult to explore changes in social welfare in any detail.  相似文献   
142.
We introduce and investigate a natural extension of Dung's well-known model of argument systems in which attacks are associated with a weight, indicating the relative strength of the attack. A key concept in our framework is the notion of an inconsistency budget, which characterises how much inconsistency we are prepared to tolerate: given an inconsistency budget β, we would be prepared to disregard attacks up to a total weight of β. The key advantage of this approach is that it permits a much finer grained level of analysis of argument systems than unweighted systems, and gives useful solutions when conventional (unweighted) argument systems have none. We begin by reviewing Dung's abstract argument systems, and motivating weights on attacks (as opposed to the alternative possibility, which is to attach weights to arguments). We then present the framework of weighted argument systems. We investigate solutions for weighted argument systems and the complexity of computing such solutions, focussing in particular on weighted variations of grounded extensions. Finally, we relate our work to the most relevant examples of argumentation frameworks that incorporate strengths.  相似文献   
143.
AB SCIEX公司最新发布全新的高分辨液相色谱质谱联用系统——TripleTOF5600是在享有盛名的API 5500三重四极杆系统和QSTAR Elite(QqTOF)系统这两个技术平台的基础上开发出来的。TripleTOF 5600高分辨液相色谱质谱联用系统能够对复杂的蛋白质组学样品进行高通量分析,并能同时提供高质量的定性和定量结果。为评估这款仪器的性能,设计基于纳升液相色谱和TripleTOF 5600联用系统的一系列实验。首先,应用这一拥有高分辨率、高灵敏度和高质量准确度的系统对酵母细胞裂解物的胰酶消化产物进行分析。实验中采用每秒最多采集50幅串联质谱谱图的信息相关采集模式,单次LC-MS/MS实验就鉴定10179条独特肽段和1174种蛋白(at 1%global false discoveryrate)。而实际达到平均每秒34幅串联谱图的采集速度是在单次实验获得如此优异的鉴定结果的决定性因素。此外,也对一组含有5种已知蛋白以及部分重同位素标记肽段的样品进行分析,以检验TripleTOF 5600的定量能力。实验中这5种蛋白质都获得很高的序列覆盖率,其中进样量仅有100amol的Peroxiredoxin 1蛋白的序列覆盖率也高达53%。而测试中得到肽段的平均质量偏差仅为1.7 ppm,展示TripleTOF 5600的高质量准确度和稳定性。此外还获得高度准确的定量结果,充分证明TripleTOF 5600能够提供三重四极杆系统级别的定量结果。  相似文献   
144.
145.
The northern Great Plains of North America has millions of small wetlands, and these are often dispersed through cultivated fields. We investigated relationship between pesticide occurrence and precipitation in selected wetlands in a 30.4 x 10(4) km2 area of the Great Plains with relatively uniform farming practices and 1,777,600 wetlands (southern Saskatchewan, Canada). By early July after pesticides have been applied to crops, the mean number of pesticides detected in wetlands ranged from 1.8 in regions with little precipitation (< 21 mm rain during the previous 15 days) to 3.2 in regions under higher rainfall (> 90 mm). The proportion of wetlands in which at least one pesticide exceeded Canadian guidelines for the protection of aquatic life increased from 0% to 60% over this same precipitation range. The maximum number of pesticides detected in a single wetland was six. Concentration of lindane in wetlands increased with increasing precipitation. Using geographic information on rainfall, wetland densities, area seeded to crops, and region specific relationships between pesticides and precipitation, we estimated the number of wetlands in Saskatchewan with elevated levels of pesticides. In early July, during 3 of the 6 years, the number of wetlands subjected to pesticide levels that exceeded guidelines for the protection of aquatic life was significant, ranging from 152,000 to 424,000 wetlands or 9-24%, respectively, of the total. Lindane and triallate exceeded the guidelines most frequently.  相似文献   
146.
Budding yeast cells divide asymmetrically, giving rise to a mother and its daughter. Mother cells have a limited division potential, called their lifespan, which ends in proliferation-arrest and lysis. In this report we mutate telomerase in Saccharomyces cerevisiae to shorten telomeres and show that, rather than shortening lifespan, this leads to a significant extension in lifespan. This extension requires the product of the SIR3 gene, an essential component of the silencing machinery which binds to telomeres. In contrast, longer telomeres in a genotypically wild-type strain lead to a decrease in lifespan. These findings suggest that the length of telomeres dictates the lifespan by regulating the amount of the silencing machinery available to nontelomeric locations in the yeast genome.  相似文献   
147.
Based on data from 4 independent studies reported by R. Vineberg and E. N. Taylor (1972) with a total sample size of 1,474, path analysis was used to examine the causal impact of job experience on job knowledge, performance capability as measured by job sample tests, and supervisory ratings of job performance. Findings support the conclusion that (1) when mean job experience is 2–3 yrs, there is substantial variance in job experience and (2) when the jobs are of an intermediate complexity level, job experience has a substantial direct impact on job knowledge and a smaller direct impact on performance capabilities as assessed by job sample measures. Job experience also has a substantial indirect effect on work sample performance through its effect on job knowledge, which, in turn, was found to be the strongest determinant of work sample performance. The pattern and magnitude of causal effects of general mental ability were similar to those of job experience. The effect of job knowledge on supervisory ratings was several times stronger than the effect of job sample performance, confirming the findings of J. E. Hunter (1983). When job experience was held constant, the direct impact of ability on the acquisition of job knowledge increased substantially, and this, in turn, increased the indirect effect of ability on job sample performance. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
148.
149.
D Parry  A Hextall  VP Robinson  NR Banner  MH Yacoub 《Canadian Metallurgical Quarterly》1996,51(11):1162-4; discussion 1164-5
Successful pregnancy in a single lung transplant recipient has not been reported previously. The long term effect of pregnancy on graft function and management of deteriorating pulmonary function is not defined. This case describes the management, outcome, and problems encountered when a single lung transplant recipient developed a progressive deterioration in pulmonary function during pregnancy, attributed to accelerated obliterative bronchiolitis.  相似文献   
150.
OBJECTIVE AND IMPORTANCE: We report a case of a posterior fossa neuroepithelial tumor with unusual clinical presentation, magnetic resonance imaging appearance, and morphological features. CLINICAL PRESENTATION: This 66-year-old man presented with a history of gait ataxia, dizziness, and tinnitus and was found to have a large tumor in the posterior fossa and cerebellopontine angle. INTERVENTION: Gross total excision of the tumor was accomplished. Histologically, the most unique features were macrovesicular accumulations of lipid, giving the tumor (at least focally) an appearance virtually identical to that of mature adipose tissue. Evidence of biphasic neuronal and glial differentiation was noted by immunohistochemistry and electron microscopy. CONCLUSION: A literature review is presented. Diagnostically, this neoplasm seems to fit in a unique group of rarely described, lipomatous neuroectodermal tumors that show divergent neuronal and glial differentiation.  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