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   2041篇
  免费   88篇
  国内免费   1篇
电工技术   34篇
综合类   14篇
化学工业   636篇
金属工艺   28篇
机械仪表   32篇
建筑科学   136篇
矿业工程   9篇
能源动力   56篇
轻工业   124篇
水利工程   4篇
石油天然气   2篇
无线电   127篇
一般工业技术   357篇
冶金工业   191篇
原子能技术   11篇
自动化技术   369篇
  2023年   18篇
  2022年   20篇
  2021年   37篇
  2020年   45篇
  2019年   36篇
  2018年   50篇
  2017年   25篇
  2016年   47篇
  2015年   41篇
  2014年   81篇
  2013年   111篇
  2012年   97篇
  2011年   163篇
  2010年   106篇
  2009年   92篇
  2008年   98篇
  2007年   93篇
  2006年   88篇
  2005年   55篇
  2004年   60篇
  2003年   51篇
  2002年   63篇
  2001年   40篇
  2000年   38篇
  1999年   42篇
  1998年   68篇
  1997年   64篇
  1996年   34篇
  1995年   32篇
  1994年   26篇
  1993年   26篇
  1992年   21篇
  1991年   13篇
  1990年   21篇
  1989年   14篇
  1988年   14篇
  1987年   12篇
  1985年   9篇
  1984年   13篇
  1983年   10篇
  1982年   11篇
  1981年   13篇
  1980年   12篇
  1979年   9篇
  1978年   8篇
  1977年   9篇
  1976年   21篇
  1975年   10篇
  1974年   8篇
  1970年   6篇
排序方式: 共有2130条查询结果,搜索用时 187 毫秒
1.
2.
Financial theory creates a puzzle. Some authors argue that high-risk entrepreneurs choose debt contracts instead of equity contracts since risky but high returns are of relatively more value for a loan-financed firm. Conversely, authors who focus explicitly on start-up finance predict that entrepreneurs are the more likely to seek equity-like venture capital contracts, the more risky their projects are. Our paper is an initial step towards resolving this puzzle empirically. We present microeconometric evidence on the determinants of debt and equity financing in young and innovative SMEs. We pay special attention to the role of risk for the choice of the method of financing. Since risk is not directly observable we use different indicators for financial and project risk. It turns out that our data generally confirms the hypothesis that the probability that a young high-tech firm receives equity financing is an increasing function of the financial risk. With regard to the intrinsic project risk, our results are less conclusive, as some of our indicators of a risky project are found to have a negative effect on the likelihood to be financed by private equity.  相似文献   
3.
Approximately 80% of the international transport of goods is carried on by means of ships. A large portion of the transport capacity is represented by Roll-on-Roll-off (RoRo) ships. Especially in Europe this is a relevant potential for the RoRo segment. Consequently, the design and construction of RoRo ships plays an increasing role for German shipyards and their suppliers. In order to make the loading and unloading procedure of trailer economically more competitive, ship owners would like to improve the lashing of trailers on the ship. On the basis of a multibody system formalism, a software tool has been developed which allows for an optimization of the loading of trailers on RoRo ships. Commemorative Contribution.  相似文献   
4.
Consistent modeling of capacitances and transit times of GaAs-based HBTs   总被引:1,自引:0,他引:1  
This paper investigates how time delays and capacitances observed under small-signal conditions can be consistently accounted for in heterojunction bipolar transistor (HBT) large-signal models. The approach starts at the circuit level by mapping the large-signal equivalent circuit (which consists of charge and current sources) to the well-known small-signal circuit (which consists of capacitances, transit-time, and resistances). It is shown that and how bias dependent charge sources at either pn-junction impact transit-time, base-collector capacitance, and their mutual dependence. It is demonstrated for the example of a GaAs-based HBT that the interrelation of the elements is observed in measurements as predicted. The results of the investigation enhance understanding of HBT model characteristics and provide a criterion to check model consistency.  相似文献   
5.
Dynamic complexity investigates the required effort to maintain knowledge about a property of a structure under changing operations. This article introduces a refined notion of dynamic problems which takes the initial structure into account. It develops the basic structural complexity notions accordingly. It also shows that the dynamic version of the LOGCFL-complete problem D2LREACH(acyclic) can be maintained with first-order updates.  相似文献   
6.
We present a method based on extended linear real quantifier elimination for multiple object semilinear motion planning, i.e. finding collision-free trajectories for several robots in a time dependent environment. For practical applicability the method is limited to polygonal objects and linear trajectories. It can, however, deal with situations involving even non-convex objects.  相似文献   
7.
Das Autobahnmautgesetz zeichnet sich durch eine strenge Zweckbindung für die Mautdaten aus. Diese dürfen ausschlie?lich für die Zwecke des Mautgesetzes erhoben und verarbeitet werden. Diese Vorgabe hat das LG Magdeburg in einem Beschluss richtungsweisend auch für die Verbindungsdaten der GSM-Kommunikation best?tigt.  相似文献   
8.
This paper presents a detailed analysis of the stressing mechanisms for highly rugged low-noise GaN monolithic-microwave integrated-circuit amplifiers operated at extremely high input powers. As an example, a low-noise amplifier (LNA) operating in the 3-7-GHz frequency band is used. A noise figure (NF) below 2.3 dB is measured from 3.5 to 7 GHz with NF<1.8 dB between 5-7 GHz. This device survived 33 dBm of available RF input power for 16 h without any change in low-noise performance. The stress mechanisms at high input powers are identified by systematic measurements of an LNA and a single high electron-mobility transistor in the frequency and time domains. It is shown that the gate dc current, which occurs due to self-biasing, is the most critical factor regarding survivability. A series resistance in the gate dc feed can reduce this gate current by feedback, and may be used to improve LNA ruggedness  相似文献   
9.
We prove several essential fractal properties, such as positivity, finiteness or local infinity, of Hausdorff and packing measures of radial Julia sets for large subclasses of entire and meromorphic functions considered in our previous work: çGeometric thermodynamical formalism and real analyticity for meromorphic functions of finite order'. Most of the results proven are shown to be optimal.  相似文献   
10.
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