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   1323篇
  免费   73篇
  国内免费   4篇
电工技术   22篇
综合类   1篇
化学工业   497篇
金属工艺   33篇
机械仪表   42篇
建筑科学   27篇
矿业工程   1篇
能源动力   42篇
轻工业   117篇
水利工程   7篇
石油天然气   3篇
无线电   72篇
一般工业技术   246篇
冶金工业   59篇
原子能技术   10篇
自动化技术   221篇
  2023年   12篇
  2022年   47篇
  2021年   73篇
  2020年   33篇
  2019年   42篇
  2018年   56篇
  2017年   35篇
  2016年   69篇
  2015年   51篇
  2014年   78篇
  2013年   116篇
  2012年   70篇
  2011年   125篇
  2010年   75篇
  2009年   54篇
  2008年   58篇
  2007年   62篇
  2006年   41篇
  2005年   42篇
  2004年   30篇
  2003年   19篇
  2002年   16篇
  2001年   15篇
  2000年   11篇
  1999年   11篇
  1998年   16篇
  1997年   21篇
  1996年   11篇
  1995年   8篇
  1994年   9篇
  1993年   8篇
  1992年   3篇
  1991年   5篇
  1989年   3篇
  1987年   3篇
  1986年   4篇
  1985年   6篇
  1984年   5篇
  1983年   5篇
  1981年   2篇
  1980年   6篇
  1979年   4篇
  1977年   5篇
  1976年   8篇
  1975年   4篇
  1974年   2篇
  1973年   3篇
  1970年   3篇
  1969年   3篇
  1965年   2篇
排序方式: 共有1400条查询结果,搜索用时 281 毫秒
11.
A new analytical method has been developed for the determination of the reactive lysine content of soya bean protein. The method is based on the reaction of the free basic groups of the protein with 1-phenylazo-2 naphthol-6,8 disulphonic acid. With regard to the stoichiometry of the procedure, it has been proved, contrary to earlier reports, that the basic amino acids, histidine, arginine and lysine, each combine with one mole of the dye. After acylation with propionic anhydride lysine alone loses its dye reactivity. The usefulness of the proposed method has been demonstrated by the determination of the reactive lysine content of several untreated, heat-treated and acid-treated soya bean samples. The results show that heat damage of about 5% in reactive lysine content can be measured in 1·5 h with good reproducibility.  相似文献   
12.
13.
We investigate (quasi)copulas as possible truth functions of fuzzy conjunction which is not necessarily associative and present some axiom systems for such fuzzy logics. In particular, we study an expansion of Łukasiewicz (infinite valued propositional) logic by a new connective interpreted as an arbitrary quasicopula (and also by a new connective interpreted as the residuum of the copula). Main results concern standard completeness.  相似文献   
14.
cABL is a protooncogene, activated in a subset of human leukemias, whose protein product is a nonreceptor tyrosine kinase of unknown function. cABL has a complex structure that includes several domains and motifs found in proteins implicated in signal transduction pathways. An approach to elucidate cABL function is to identify proteins that interact directly with cABL and that may serve as regulators or effectors of its activity. To this end, a protein-interaction screen of a phage expression library was undertaken to identify proteins that interact with specific domains of cABL. An SH3-domain-containing protein has been identified that interacts with sequences in the cABL carboxyl terminus. The cDNA encoding ALP1 (amphiphysin-like protein 1) was isolated from a 16-day mouse embryo. ALP1 has high homology to BIN1, a recently cloned myc-interacting protein, and also shows significant homology to amphiphysin, a neuronal protein cloned from human and chicken. The amino terminus has homology to two yeast proteins, Rvs167 and Rvs161, which are involved in cell entry into stationary phase and cytoskeletal organization. ALP1 binds cABL in vitro and in vivo. Expression of ALP1 results in morphological transformation of NIH 3T3 fibroblasts in a cABL-dependent manner. The properties of ALP1 suggest that it may be involved in possible cytoskeletal functions of the cABL kinase. Additionally, these results provide further evidence for the importance of the cABL carboxyl terminus and its binding proteins in the regulation of cABL function.  相似文献   
15.
The focus of this article is on the creation of a collection of sentences manually annotated with respect to their sentence structure. We show that the concept of linear segments—linguistically motivated units, which may be easily detected automatically—serves as a good basis for the identification of clauses in Czech. The segment annotation captures such relationships as subordination, coordination, apposition and parenthesis; based on segmentation charts, individual clauses forming a complex sentence are identified. The annotation of a sentence structure enriches a dependency-based framework with explicit syntactic information on relations among complex units like clauses. We have gathered a collection of 3,444 sentences from the Prague Dependency Treebank, which were annotated with respect to their sentence structure (these sentences comprise 10,746 segments forming 6,341 clauses). The main purpose of the project is to gain a development data—promising results for Czech NLP tools (as a dependency parser or a machine translation system for related languages) that adopt an idea of clause segmentation have been already reported. The collection of sentences with annotated sentence structure provides the possibility of further improvement of such tools.  相似文献   
16.
Cytokinins are a class of phytohormones, signalling molecules specific to plants. They act as regulators of diverse physiological processes in complex signalling pathways. It is necessary for plants to continuously regulate cytokinin distribution among different organs, tissues, cells, and compartments. Such regulatory mechanisms include cytokinin biosynthesis, metabolic conversions and degradation, as well as cytokinin membrane transport. In our review, we aim to provide a thorough picture of the latter. We begin by summarizing cytokinin structures and physicochemical properties. Then, we revise the elementary thermodynamic and kinetic aspects of cytokinin membrane transport. Next, we review which membrane-bound carrier proteins and protein families recognize cytokinins as their substrates. Namely, we discuss the families of “equilibrative nucleoside transporters” and “purine permeases”, which translocate diverse purine-related compounds, and proteins AtPUP14, AtABCG14, AtAZG1, and AtAZG2, which are specific to cytokinins. We also address long-distance cytokinin transport. Putting all these pieces together, we finally discuss cytokinin distribution as a net result of these processes, diverse in their physicochemical nature but acting together to promote plant fitness.  相似文献   
17.
Ceramics joints are applied for producing products that should be made in a general shapes and dimensions for more advantageous usage. The article presents the research work related to ceramic joint quality evaluation, the thermal-structural analysis of ceramic joining and ceramic bond design and implementation. The role of ceramic material in the electronics industry and motivation for joining ceramics is described in the introduction. The requirements and methods for improving the quality of joints are summarized. Also, the results of simulations of pressure sensor cooling after removal from the oven during joining are discussed. The experimental results are evaluated by using a t-test before and after process cooling modification. Important directions for future research are summarized, with emphasis on the statistical determination of poor connection, and how the interface of modification of joint technology and process setting affects results and parameters that have been achieved.  相似文献   
18.
The Contractibility problem takes as input two graphs G and H, and the task is to decide whether H can be obtained from G by a sequence of edge contractions. The Induced Minor and Induced Topological Minor problems are similar, but the first allows both edge contractions and vertex deletions, whereas the latter allows only vertex deletions and vertex dissolutions. All three problems are NP-complete, even for certain fixed graphs H. We show that these problems can be solved in polynomial time for every fixed H when the input graph G is chordal. Our results can be considered tight, since these problems are known to be W[1]-hard on chordal graphs when parameterized by the size of H. To solve Contractibility and Induced Minor, we define and use a generalization of the classic Disjoint Paths problem, where we require the vertices of each of the k paths to be chosen from a specified set. We prove that this variant is NP-complete even when k=2, but that it is polynomial-time solvable on chordal graphs for every fixed k. Our algorithm for Induced Topological Minor is based on another generalization of Disjoint Paths called Induced Disjoint Paths, where the vertices from different paths may no longer be adjacent. We show that this problem, which is known to be NP-complete when k=2, can be solved in polynomial time on chordal graphs even when k is part of the input. Our results fit into the general framework of graph containment problems, where the aim is to decide whether a graph can be modified into another graph by a sequence of specified graph operations. Allowing combinations of the four well-known operations edge deletion, edge contraction, vertex deletion, and vertex dissolution results in the following ten containment relations: (induced) minor, (induced) topological minor, (induced) subgraph, (induced) spanning subgraph, dissolution, and contraction. Our results, combined with existing results, settle the complexity of each of the ten corresponding containment problems on chordal graphs.  相似文献   
19.
The capability of following a moving target in an environment with obstacles is required as a basic and necessary function for realizing an autonomous unmanned surface vehicle (USV). Many target following scenarios involve a follower and target vehicles that may have different maneuvering capabilities. Moreover, the follower vehicle may not have prior information about the intended motion of the target boat. This paper presents a trajectory planning and tracking approach for following a differentially constrained target vehicle operating in an obstacle field. The developed approach includes a novel algorithm for computing a desired pose and surge speed in the vicinity of the target boat, jointly defined as a motion goal, and tightly integrates it with trajectory planning and tracking components of the entire system. The trajectory planner generates a dynamically feasible, collision-free trajectory to allow the USV to safely reach the computed motion goal. Trajectory planning needs to be sufficiently fast and yet produce dynamically feasible and short trajectories due to the moving target. This required speeding up the planning by searching for trajectories through a hybrid, pose-position state space using a multi-resolution control action set. The search in the velocity space is decoupled from the search for a trajectory in the pose space. Therefore, the underlying trajectory tracking controller computes desired surge speed for each segment of the trajectory and ensures that the USV maintains it. We have carried out simulation as well as experimental studies to demonstrate the effectiveness of the developed approach.  相似文献   
20.
Summary Measurements of autocorrelation functions extending over a broad time range are reported for a sample of polystyrene in ethyl acetate as a function of temperature between –44°C (-temperature) and 70°C. The corresponding spectra of decay times are obtained by two mathematical methods. The existence of three dynamic processes is shown and their temperature and angular behaviour is studied.  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