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   3043篇
  免费   187篇
  国内免费   3篇
电工技术   31篇
综合类   6篇
化学工业   794篇
金属工艺   53篇
机械仪表   55篇
建筑科学   121篇
矿业工程   12篇
能源动力   114篇
轻工业   264篇
水利工程   30篇
石油天然气   7篇
武器工业   1篇
无线电   271篇
一般工业技术   545篇
冶金工业   253篇
原子能技术   24篇
自动化技术   652篇
  2024年   6篇
  2023年   48篇
  2022年   149篇
  2021年   144篇
  2020年   94篇
  2019年   89篇
  2018年   113篇
  2017年   92篇
  2016年   112篇
  2015年   98篇
  2014年   129篇
  2013年   219篇
  2012年   165篇
  2011年   262篇
  2010年   171篇
  2009年   155篇
  2008年   201篇
  2007年   141篇
  2006年   127篇
  2005年   77篇
  2004年   61篇
  2003年   59篇
  2002年   53篇
  2001年   41篇
  2000年   38篇
  1999年   32篇
  1998年   87篇
  1997年   60篇
  1996年   42篇
  1995年   33篇
  1994年   24篇
  1993年   21篇
  1992年   8篇
  1991年   6篇
  1990年   5篇
  1989年   6篇
  1988年   9篇
  1987年   3篇
  1985年   5篇
  1983年   2篇
  1982年   7篇
  1981年   2篇
  1980年   8篇
  1979年   2篇
  1978年   3篇
  1977年   4篇
  1976年   7篇
  1975年   6篇
  1970年   2篇
  1968年   2篇
排序方式: 共有3233条查询结果,搜索用时 31 毫秒
981.
Docking models of fructosyl amine oxidase (FAOD) from the marineyeast Pichia N1-1 (N1-1 FAOD) with the substrates fructosylvaline (f-Val) and fructosyl-N-lysine (f-Lys) were producedusing three-dimensional protein model as reported previously(Miura et al., 2006, Biotechnol. Lett., 28, 1895-1900). Theresidues involved in recognition of substrates were proposed,particularly Asn354, which interacts closely with f-Lys, butnot with f-Val. Substitution of Asn354 to histidine and lysinesimultaneously resulted in an increase in activity of f-valand a decrease in activity of f-Lys and thus, increasing thespecificity for f-Val from 13- to 19-fold. In addition to creatingtwo mutant FAODs with great potential for the measurement ofglycated hemoglobin, we have provided the first structural modelof substrate binding with eukaryotic FAOD, which is expectedto contribute to further investigation of FAOD.  相似文献   
982.
Block ramps represent structures that produce high energy dissipation and have a unique characteristic of preserving the ecological balance in a river restoration project. The energy dissipation of a block ramp changes with the tailwater level. In this technical note the relative energy dissipation in submerged flow conditions has been investigated. The experiments were conducted at the Hydraulic Laboratory of the University of Pisa, Pisa, Italy on ramps characterized by different block materials, submergence conditions, and ramp slopes. The study shows that the relative energy loss, varying the hydraulic jump location on the ramp, is essentially a function of the scale roughness, the ramp slope, the ratio between the critical water depth, and the ramp height and the ratio between the ramp length and the reduced length in submerged conditions. The differences in energy dissipation for a submerged hydraulic jump in different bed conditions are also investigated.  相似文献   
983.
Wildfires are a major cause of land degradation in the Mediterranean region due to their frequent recurrence in the same areas. The evaluation of fire risk is therefore of high practical importance, particularly during the summer arid season, when fires are most frequent and harmful. Recent studies have demonstrated that the evaluation of dynamic fire risk can be carried out by the use of remotely sensed images, and specifically of NOAA-AVHRR Normalized Difference Vegetation Index (NDVI) data. This use relies on the sensitivity of the index to vegetation dryness, which is a major predisposing factor for fire occurrence. Several problems, however, remain linked to the spatial variability of the risk in environmentally heterogeneous areas, which requires the application of suitable processing techniques to the low-resolution imagery.The current work reports on the development and testing of different methodologies for estimating dynamic fire risk by the use of NOAA-AVHRR data. The investigation was conducted in Tuscany (Central Italy) using a large archive of fires that occurred in the region and NOAA-AVHRR NDVI data of 16 years (1985-2000). Relying on previous methodological achievements of our group and other research groups, several procedures were tested to extract information related to fire risk from the remotely sensed images. These trials led to define an optimum method which is based on the identification of pixels where the accordance between interyear variations in fire probabilities and NDVI values is maximum. The accuracy of the risk estimates from this optimum method was finally evaluated by a leave-one-out cross-validation strategy. In this way, the performance of the methodology was assessed, together with its potential for operational fire risk monitoring and forecasting in Mediterranean areas.  相似文献   
984.
Starting from three-dimensional (3D) continuum mechanics, a simple one-dimensional model aimed at analyzing the whole static behavior of nonhomogeneous curved beams is proposed. The kinematics is described by four one-dimensional (unknown) functions representing radial, tangential, and out-of-plane displacements of the beam axis, which are due to flexures and extension, and the twist of the cross section due to torsion. The flexural and axial displacements fit with the classical Euler–Bernoulli beam theory of straight beams, and nonuniform torsion is also considered. The relevant elastogeometric parameters have been determined, and the system of governing equilibrium equations is obtained by means of the principle of minimum potential energy. Finally, the general theory is illustrated with examples.  相似文献   
985.
986.
Matita is a new, document-centric, tactic-based interactive theorem prover. This paper focuses on some of the distinctive features of the user interaction with Matita, characterized mostly by the organization of the library as a searchable knowledge base, the emphasis on a high-quality notational rendering, and the complex interplay between syntax, presentation, and semantics. “We are nearly bug-free” – CSC, Oct. 2005.  相似文献   
987.
This paper discusses the integration of structural, functional and control knowledge in manufacturing workcell modeling, simulation and design. After an overview of applications of semantic and object-oriented data models in the manufacturing domain, issues relating to the control synthesis for manufacturing workcells are presented. In particular, a data model encompassing functional and control features, along with application domain structural knowledge, is developed. This model assists in explicitly representing the control aspects of engineering design within an object-oriented database and supports a task-level, functionality-driven, manufacturing workcell design. Since manufacturing workcells consist of a number of elements interacting in a complex manner, workcell control design is one of the most difficult steps in the workcell design procedure. Message passage, commonly used in object-oriented databases, provides no explicit modeling of the database behavior. Hence, it can not serve as a tool for the design of system control. On the other hand, Petrinets (PN) have proven successful in describing complex interaction among active agents. This paper will explore the incorporation of Petri nets as a basis for describing application control knowledge within a structure-function-control data model.  相似文献   
988.
989.
Because there is no difference between derivation rules and view definitions, DOOD systems are the best candidates to support an object-oriented view mechanism. Yet, to combine expressive power (i.e. no restriction on queries defining views), reusability and modeling accuracy (i.e. insertion of views into the generalization hierarchy), and consistency (stability in oid generation) is still an open challenging domain for OO research. This paper is a contribution to improve existing solutions while simplifying the task of users in the view definition process.  相似文献   
990.
We have previously demonstrated that gamma/delta T lymphocytes may participate in the host immune response against lung adenocarcinomas. Here we show that, in about one-fourth of human lung cancers, gamma/delta T cells represented a significant proportion of freshly isolated tumor-infiltrating lymphocytes. Moreover, these cells selectively expand in vitro upon culture in the presence of IL-2, thus suggesting a prior activation in vivo. Finally, when we evaluated the expression of heat shock proteins and of a panel of tumor-associated antigens in lung cancers infiltrated by gamma/delta vs. alpha/beta T cells, we found that the former displayed a distinct antigenic pattern, characterized by over-expression of HSP72 and of the 67-kDa high-affinity laminin receptor, which might account for gamma/delta T-cell recognition.  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