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   5821篇
  免费   321篇
  国内免费   5篇
电工技术   76篇
综合类   13篇
化学工业   1494篇
金属工艺   138篇
机械仪表   115篇
建筑科学   402篇
矿业工程   29篇
能源动力   146篇
轻工业   451篇
水利工程   50篇
石油天然气   8篇
无线电   450篇
一般工业技术   1231篇
冶金工业   249篇
原子能技术   37篇
自动化技术   1258篇
  2024年   11篇
  2023年   102篇
  2022年   140篇
  2021年   229篇
  2020年   150篇
  2019年   128篇
  2018年   190篇
  2017年   165篇
  2016年   248篇
  2015年   242篇
  2014年   301篇
  2013年   400篇
  2012年   379篇
  2011年   462篇
  2010年   356篇
  2009年   340篇
  2008年   341篇
  2007年   317篇
  2006年   240篇
  2005年   211篇
  2004年   159篇
  2003年   149篇
  2002年   126篇
  2001年   81篇
  2000年   78篇
  1999年   66篇
  1998年   76篇
  1997年   46篇
  1996年   49篇
  1995年   57篇
  1994年   34篇
  1993年   33篇
  1992年   29篇
  1991年   20篇
  1990年   18篇
  1989年   18篇
  1988年   15篇
  1987年   13篇
  1986年   8篇
  1985年   5篇
  1984年   23篇
  1983年   9篇
  1982年   9篇
  1981年   7篇
  1980年   7篇
  1979年   5篇
  1978年   6篇
  1976年   9篇
  1975年   6篇
  1974年   5篇
排序方式: 共有6147条查询结果,搜索用时 15 毫秒
101.
In this paper, we present and compare formulations for the inventory routing problem (IRP) where the demand of customers has to be served, over a discrete time horizon, by capacitated vehicles starting and ending their routes at a depot. The objective of the IRP is the minimization of the sum of inventory and transportation costs. The formulations include known and new mathematical programming formulations. Valid inequalities are also presented. The formulations are tested on a large set of benchmark instances. One of the most significant conclusions is that the formulations that use vehicle‐indexed variables are superior to the more compact, aggregate formulations.  相似文献   
102.
The synthesis of nanoparticles from noble metals has received high attention from researchers due to their unique properties and their wide range of applications. Silver nanoparticles (AgNPs), in particular, show a remarkable inhibitory effect against microorganisms and viruses. Various methods have been developed to obtain AgNPs, however the stability of such nanostructures over time is still challenging. Researchers attempt to obtain particular shapes and sizes in order to tailor AgNPs properties for specific areas, such as biochemistry, biology, agriculture, electronics, medicine, and industry. The aim of this study was to design AgNPs with improved antimicrobial characteristics and stability. Two different wet chemical routes were considered: synthesis being performed (i) reduction method at room temperatures and (ii) solvothermal method at high temperature. Here, we show that the antimicrobial properties of the obtained AgNPs, are influenced by their synthesis route, which impact on the size and shape of the structures. This work analyses and compares the antimicrobial properties of the obtained AgNPs, based on their structure, sizes and morphologies which are influenced, in turn, not only by the type or quantities of precursors used but also by the temperature of the reaction. Generally, AgNPs obtained by solvothermal, at raised temperature, registered better antimicrobial activity as compared to NPs obtained by reduction method at room temperature.  相似文献   
103.
Alterations in mitochondrial function are an important control variable in the progression of metabolic dysfunction-associated fatty liver disease (MAFLD), while also noted by increased de novo lipogenesis (DNL) and hepatic insulin resistance. We hypothesized that the organization and function of a mitochondrial electron transport chain (ETC) in this pathologic condition is a consequence of shifted substrate availability. We addressed this question using a transgenic mouse model with increased hepatic insulin resistance and DNL due to constitutively active human SREBP-1c. The abundance of ETC complex subunits and components of key metabolic pathways are regulated in the liver of these animals. Further omics approaches combined with functional assays in isolated liver mitochondria and primary hepatocytes revealed that the SREBP-1c-forced fatty liver induced a substrate limitation for oxidative phosphorylation, inducing enhanced complex II activity. The observed increased expression of mitochondrial genes may have indicated a counteraction. In conclusion, a shift of available substrates directed toward activated DNL results in increased electron flows, mainly through complex II, to compensate for the increased energy demand of the cell. The reorganization of key compounds in energy metabolism observed in the SREBP-1c animal model might explain the initial increase in mitochondrial function observed in the early stages of human MAFLD.  相似文献   
104.
The Role of Donor-Acceptor Complexes in Cationic Polymerisations. The Interaction of Halide Ions with Organic aπ-Acceptors The anions of salts of the type Kat+X (Kat+  Li+, Na+, Et4N+; X  Cl, Br, I) form donor-acceptor complexes with organic a π-acceptors. The long-wave charge-transfer absorption show a bathochrome shift with higher periodic numbers of X and increasing electron affinity of the acceptors Acc. Strong acceptors form radical ions very rapidly with X  I and slowly with X  Br. Cl. The interactions in the system Kat+X → Acc are influenced by solvents in a very complex way. As acceptors they interact preferably with the halide ion X and, hence, reduce its donicity for the competing acceptor Acc. As donors they change the dissociation of the ion pair Kat+X by solvation of the cation Kat+ and influence in that indirect way also the donicity of X for the acceptor Acc.  相似文献   
105.
OCT1 and OCT2 are polyspecific membrane transporters that are involved in hepatic and renal drug clearance in humans and mice. In this study, we cloned dog OCT1 and OCT2 and compared their function to the human and mouse orthologs. We used liver and kidney RNA to clone dog OCT1 and OCT2. The cloned and the publicly available RNA-Seq sequences differed from the annotated exon-intron structure of OCT1 in the dog genome CanFam3.1. An additional exon between exons 2 and 3 was identified and confirmed by sequencing in six additional dog breeds. Next, dog OCT1 and OCT2 were stably overexpressed in HEK293 cells and the transport kinetics of five drugs were analyzed. We observed strong differences in the transport kinetics between dog and human orthologs. Dog OCT1 transported fenoterol with 12.9-fold higher capacity but 14.3-fold lower affinity (higher KM) than human OCT1. Human OCT1 transported ipratropium with 5.2-fold higher capacity but 8.4-fold lower affinity than dog OCT1. Compared to human OCT2, dog OCT2 showed 10-fold lower transport of fenoterol and butylscopolamine. In conclusion, the functional characterization of dog OCT1 and OCT2 reported here may have implications when using dogs as pre-clinical models as well as for drug therapy in dogs.  相似文献   
106.
(1) Objective: Considering that current knowledge of mechanisms involved in the molecular pathogenesis of Social Anxiety Disorder (SAD) is limited, we conducted a systematic review to evaluate cumulative data obtained by Proton Magnetic Resonance Spectroscopic (1H MRS) studies. (2) Methods: A computer-based literature search of Medline, EMBASE, PsycInfo, and ProQuest was performed. Only cross-sectional studies using 1H MRS techniques in participants with SAD and healthy controls (HCs) were selected. (3) Results: The search generated eight studies. The results indicated regional abnormalities in the ‘fear neurocircuitry’ in patients with SAD. The implicated regions included the anterior cingulate cortex (ACC), dorsomedial prefrontal cortex (dmPFC), dorsolateral prefrontal cortex (dlPFC), insula, occipital cortex (OC), as well as the subcortical regions, including the thalamus, caudate, and the putamen. (4) Conclusions: The evidence derived from eight studies suggests that possible pathophysiological mechanisms of SAD include impairments in the integrity and function of neurons and glial cells, including disturbances in energy metabolism, maintenance of phospholipid membranes, dysregulations of second messenger systems, and excitatory/inhibitory neurocircuitry. Conducting more cross-sectional studies with larger sample sizes is warranted given the limited evidence in this area of research.  相似文献   
107.
We present a detailed account of a translation from probabilistic call-by-value programs with procedures to Rabin’s probabilistic automata. The translation is fully abstract in that programs exhibit the same computational behaviour if and only if the corresponding automata are language-equivalent. Since probabilistic language equivalence is decidable, we can apply the translation to analyse the behaviour of probabilistic programs and protocols. We illustrate our approach on a number of case studies.  相似文献   
108.
The paper gives a summary of the existing results about algorithmic analysis of probabilistic pushdown automata and their subclasses.  相似文献   
109.
110.
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