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   3323篇
  免费   21篇
  国内免费   2篇
电工技术   12篇
综合类   1篇
化学工业   324篇
金属工艺   92篇
机械仪表   62篇
建筑科学   106篇
矿业工程   10篇
能源动力   50篇
轻工业   174篇
水利工程   26篇
石油天然气   7篇
无线电   134篇
一般工业技术   342篇
冶金工业   1724篇
原子能技术   14篇
自动化技术   268篇
  2021年   14篇
  2020年   14篇
  2019年   18篇
  2018年   27篇
  2017年   21篇
  2016年   31篇
  2015年   24篇
  2014年   26篇
  2013年   91篇
  2012年   61篇
  2011年   81篇
  2010年   59篇
  2009年   51篇
  2008年   64篇
  2007年   75篇
  2006年   79篇
  2005年   55篇
  2004年   66篇
  2003年   65篇
  2002年   74篇
  2001年   45篇
  2000年   48篇
  1999年   97篇
  1998年   454篇
  1997年   288篇
  1996年   191篇
  1995年   129篇
  1994年   114篇
  1993年   120篇
  1992年   35篇
  1991年   26篇
  1990年   43篇
  1989年   38篇
  1988年   46篇
  1987年   47篇
  1986年   44篇
  1985年   37篇
  1984年   37篇
  1983年   38篇
  1982年   36篇
  1981年   37篇
  1980年   26篇
  1979年   21篇
  1978年   28篇
  1977年   44篇
  1976年   94篇
  1975年   23篇
  1974年   17篇
  1973年   20篇
  1972年   19篇
排序方式: 共有3346条查询结果,搜索用时 0 毫秒
991.
Comments on the article by J. R. Haynes (August, 1983) regarding core psychology journals. Haynes originally argues that two APA journals, Journal of Experimental Psychology: Human Perception and Performance and Journal of Experimental Psychology: Human Learning and Memory failed to be included in the citation impact list because of extremely low citation impact for the Journal Citation Report. However, the Journal Citation Report for 1979-1981 is an unreliable source about Journal of Experimental Psychology journals for a number of reasons, including the citation of nonarticles and the conflation of citations for different journals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
PURPOSE: It has recently been reported that CD4+ T-lymphocytes are reduced in advanced colorectal cancer patients. However, it is not clear whether such changes in T-lymphocyte subsets are an early or late event in such patients. The aim of this study was to examine the relationship between these subsets and disease progression in colorectal cancer. METHODS: Flow cytometric analysis of T-lymphocyte subsets was performed in 39 patients who, approximately 12 months previously, had undergone surgery for colorectal cancer. These patients were grouped according to whether they developed a recurrence in the following two years. A group of healthy subjects was studied as controls. RESULTS: There was a significant increase in the median neutrophil count (4.3 vs. 3.7 10(6)/ml) and the median numbers of platelets (282 vs. 216 10(6)/ml) of the recurrence group compared with the control group, respectively (P < 0.05). The median numbers (0.28 vs. 0.73 10(6)/ml) and percentage (29 vs. 38 percent) of CD4+ T-lymphocytes of the recurrence group were significantly reduced compared with that of the control group (P < 0.05). There were also reductions in the median percentage of CD3+ cells (67 vs. 74 percent) and the median numbers of CD4+ T-lymphocytes (0.28 vs. 0.46 10(6)/ml) of the recurrence group compared with the no recurrence group (P < 0.05). CONCLUSIONS: Reduction of CD4+ T-lymphocytes occurs before detectable recurrence of colorectal cancer. Results of the present study are consistent with impaired immunity, as measured by such lymphocyte subset populations, being important in tumor recurrence in colorectal cancer.  相似文献   
993.
OBJECTIVE: To determine whether it is possible to predict the presence of bladder outlet obstruction (BOO) by non-invasive clinical variables in patients with lower urinary tract symptoms (LUTS) suggestive of BOO. PATIENTS AND METHODS: Patients with LUTS suggestive of BOO were entered into a prospective protocol evaluating the International Prostate Symptom Score (IPSS), prostate size, non-invasive uroflow, post-void residual urine volume (PVR) and a pressure flow study. Only patients with a maximum flow rate (Qmax) of < or = 15 mL/s and an IPSS > or = 7 were included. The study comprised 253 patients; the degree of obstruction was correlated to several non-invasive clinical variables. Subsequently nomograms were developed by multiple logistic regression analysis to obtain the probability of BOO in patients with LUTS. RESULTS: Prostate volume, Qmax, PVR and voided volume correlated significantly with the degree of BOO rated according to the linear passive urethral resistance relation (linPURR). In contrast, there was no such correlation for the IPSS and the quality-of-life question of the IPSS. The percentage of patients with BOO defined by a linPURR of 3-6 decreased from 85% in those with a Qmax of 0-5 mL/s to 60% (Qmax 6-10 mL/s) and 44% (Qmax 11-15 mL/s). In parallel, the percentage of patients with BOO increased from 53% of those with a prostate volume of < or = 50 mL, to 79% of those with prostates of 51-100 mL and 75% of those > 100 mL. Based on Qmax, PVR and prostate volume, nomograms were established by multiple logistic regression analysis for the probability of BOO in patients with LUTS. CONCLUSION: The nomograms presented herein should help the clinician to identify patients with LUTS who should undergo pressure flow studies before surgical intervention to detect the presence of obstruction and in whom these studies can be safely spared.  相似文献   
994.
We examined relationships among perceived alcohol availability, drinking location, alcohol consumption, and drinking problems. Subjects were 3,372 adolescent drinkers, ages 16-18, who participated in the Communities Mobilizing for Change on Alcohol Project baseline survey. Mixed-model regression was employed to identify predictors of alcohol consumption and drinking consequences. Perceived alcohol availability was significantly associated with higher levels of alcohol consumption for males. Drinking in a public location with higher levels of alcohol consumption for females. Results underscore the importance of youth alcohol assessibility.  相似文献   
995.
Apoptotic cell changes occurring under certain developmental, physiological, and pathological conditions have been of increasing interest during recent years. Due to occasional difficulties in detecting apoptosis in routinely stained sections, various methods have been developed to facilitate tissue examination. Fragmentation of DNA during the process of apoptosis is a prerequisite for detection in the in situ end-labeling (ISEL) procedure. It is yet unclear whether other mechanisms of cell change that induce DNA fragmentation such as necrosis and postmortem autolysis also show positive staining with the ISEL technique. To investigate whether the ISEL assay visualizes autolytic DNA changes along with apoptotic DNA fragmentation, we tested the technique on brain tissue of mice after different time intervals (0, 6, 12, 24, 48, 72 h) of postmortem delay (PMD) and at 2 different temperatures of postmortem storage (4 degrees C and room temperature (RT)). Our semiquantitative results show that up to 24 h of PMD no prominent difference in labeling is observable at both temperatures. After 48 and 72 h of PMD at RT clusters of labeled cells begin to appear. Clusters of stained cells should therefore not be considered as apoptosis when using the ISEL assay.  相似文献   
996.
997.
Dynamic linking in modern execution environments like .NET is considerably more sophisticated than in the days of C shared libraries on UNIX. One aspect of this sophistication is that .NET assemblies embed type information about dynamically linked resources.This type information implicitly represents compile-time assumptions about the resources available at run-time. However, the resources available at run-time may differ from those available at compile-time. For example, the execution environment on a mobile phone might provide fewer, simpler classes than on a desktop PC. As bytecode cannot adapt to its execution environment, component reuse is restricted and development costs are increased.We have designed and implemented a “flexible” dynamic linking scheme that binds bytecode as late as possible to the assemblies and classes available in a .NET execution environment. We describe the scheme's integration with the .NET linking infrastructure, review important design decisions and report on experiences with the “Rotor” shared source version of .NET.  相似文献   
998.
A software model can be analysed for non-functional requirements by extending it with suitable annotations and transforming it into analysis models for the corresponding non-functional properties. For quantitative performance evaluation, suitable annotations are standardized in the “UML Profile for Modeling and Analysis of Real-Time Embedded systems” (MARTE) and its predecessor, the “UML Profile for Schedulability, Performance and Time”. A range of different performance model types (such as queueing networks, Petri nets, stochastic process algebra) may be used for analysis. In this work, an intermediate “Core Scenario Model” (CSM) is used in the transformation from the source software model to the target performance model. CSM focuses on how the system behaviour uses the system resources. The semantic gap between the software model and the performance model must be bridged by (1) information supplied in the performance annotations, (2) in interpretation of the global behaviour expressed in the CSM and (3) in the process of constructing the performance model. Flexibility is required for specifying sets of alternative cases, for choosing where this bridging information is supplied, and for overriding values. It is also essential to be able to trace the source of values used in a particular performance estimate. The performance model in turn can be used to verify responsiveness and scalability of a software system, to discover architectural limitations at an early stage of development, and to develop efficient performance tests. This paper describes how the semantic gap between software models in UML+MARTE and performance models (based on queueing or Petri nets) can be bridged using transformations based on CSMs, and how the transformation challenges are addressed.  相似文献   
999.
According to several current models of short-term memory, items are retained in order by associating them with positional codes. The models differ as to whether temporal oscillators provide those codes. The authors examined errors in recall of sequences comprising 2 groups of 4 consonants. A critical manipulation was the precise timing of items within the groups, whereby temporal position (time from group onset) and ordinal position (number of items from group onset) were partially unconfounded. Errors that involve items migrating across groups should preserve within-group temporal position according to oscillator models, but should preserve within-group ordinal position according to nonoscillator models. Results from the intergroup errors strongly favored preservation of ordinal rather than temporal position. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
1000.
The rise of new experimental techniques, such as high-throughput combinatorial methods, and the availability of large data sets by means of the Internet have greatly increased the amount of data that must be managed by relatively small projects. Scientific data management systems developed for large projects are often not available, suitable, nor affordable for projects with lesser resources. Increasing numbers of open-source frameworks have made available numerous options for smaller facilities to build for themselves effective and robust data management solutions. We will present considerations of these options and a case study.  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