全文获取类型
收费全文 | 6254篇 |
免费 | 318篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 72篇 |
综合类 | 7篇 |
化学工业 | 1209篇 |
金属工艺 | 89篇 |
机械仪表 | 74篇 |
建筑科学 | 504篇 |
矿业工程 | 12篇 |
能源动力 | 283篇 |
轻工业 | 1098篇 |
水利工程 | 58篇 |
石油天然气 | 13篇 |
无线电 | 368篇 |
一般工业技术 | 1026篇 |
冶金工业 | 731篇 |
原子能技术 | 23篇 |
自动化技术 | 1013篇 |
出版年
2023年 | 49篇 |
2022年 | 59篇 |
2021年 | 97篇 |
2020年 | 73篇 |
2019年 | 121篇 |
2018年 | 182篇 |
2017年 | 177篇 |
2016年 | 181篇 |
2015年 | 178篇 |
2014年 | 224篇 |
2013年 | 400篇 |
2012年 | 300篇 |
2011年 | 413篇 |
2010年 | 321篇 |
2009年 | 242篇 |
2008年 | 307篇 |
2007年 | 310篇 |
2006年 | 291篇 |
2005年 | 211篇 |
2004年 | 204篇 |
2003年 | 197篇 |
2002年 | 160篇 |
2001年 | 125篇 |
2000年 | 135篇 |
1999年 | 111篇 |
1998年 | 259篇 |
1997年 | 169篇 |
1996年 | 138篇 |
1995年 | 95篇 |
1994年 | 89篇 |
1993年 | 66篇 |
1992年 | 46篇 |
1991年 | 46篇 |
1990年 | 40篇 |
1989年 | 38篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1986年 | 26篇 |
1985年 | 36篇 |
1984年 | 53篇 |
1983年 | 31篇 |
1982年 | 31篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 29篇 |
1977年 | 35篇 |
1976年 | 47篇 |
1975年 | 19篇 |
1974年 | 22篇 |
1973年 | 25篇 |
排序方式: 共有6580条查询结果,搜索用时 15 毫秒
41.
Summary
We report the synthesis of some new backbone fluorinated
polymers of the poly(phenylenevinylene) type. The new polymers
were characterised by NMR, SEC and X-ray powder diffraction. The
charge carrier mobilities were determined using pulse radiolysis
time resolved microwave conductivity (PR-TRMC) and the carrier
mobilities were compared to the similar non-fluorinated
analogues. The changes in charge carrier mobilities as a
function of molecular substitution pattern is discussed in terms
of other materials properties such as electronic structure and
absorption properties. The major result is that it was found
possible for this type of material to alter the electronic
energy levels by molecular substitution without imparting
significant changes in the magnitude of the charge carrier
mobilities and the optical properties. 相似文献
42.
H.‐G. Boyen G. Kstle K. Zürn T. Herzog F. Weigl P. Ziemann O. Mayer C. Jerome M. Mller J.P. Spatz M.G. Garnier P. Oelhafen 《Advanced functional materials》2003,13(5):359-364
Starting with Co‐salt‐loaded inverse micelles, which form if the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) is dissolved in a selective solvent like toluene and CoCl2 is added to the solution, monomicellar arrays of such micelles exhibiting a significant hexagonal order can be prepared on top of various substrates with tailored intermicellar distances and structure heights. In order to remove the polymer matrix and to finally obtain arrays of pure Co nanoparticles, the micelles are first exposed to an oxygen plasma, followed by a treatment in a hydrogen plasma. Applying in‐situ X‐ray photoelectron spectroscopy, it is demonstrated that: 1) The oxygen plasma completely removes the polymer, though conserving the original order of the micellar array. Furthermore, the resulting nanoparticles are entirely oxidized with a chemical shift of the Co 2p3/2 line pointing to the formation of Co3O4. 2) By the subsequent hydrogen plasma treatment the nanoparticles are fully reduced to metallic Co. 3) By exposing the pure Co nanoparticles for 100 s to various oxygen partial pressures pequation/tex2gif-inf-5.gif, a stepwise oxidation is observed with a still metallic Co core surrounded by an oxide shell. The data allow the extraction of the thickness of the oxide shell as a function of the total exposure to oxygen (pequation/tex2gif-inf-7.gif × time), thus giving the opportunity to control the ferromagnetic–antiferromagnetic composition of an exchange‐biased magnetic system. 相似文献
43.
Per Munk Nielsen Jesper Brask Lene Fjerbaek 《European Journal of Lipid Science and Technology》2008,110(8):692-700
It is well documented in the literature that enzymatic processing of oils and fats for biodiesel is technically feasible. However, with very few exceptions, enzyme technology is not currently used in commercial‐scale biodiesel production. This is mainly due to non‐optimized process design and a lack of available cost‐effective enzymes. The technology to re‐use enzymes has typically proven insufficient for the processes to be competitive. However, literature data documenting the productivity of enzymatic biodiesel together with the development of new immobilization technology indicates that enzyme catalysts can become cost effective compared to chemical processing. This work reviews the enzymatic processing of oils and fats into biodiesel with focus on process design and economy. 相似文献
44.
In most industrialized countries, the end of the Cold War marked a change in focus from preparedness for war to an increasing focus on civil society's own vulnerability and safety. To meet new threats and changing risks, there is also a need for new analytical concepts. Societal safety is a concept developed in Norway during the last decade. It could be defined as: ‘The society's ability to maintain critical social functions, to protect the life and health of the citizens and to meet the citizens' basic requirements in a variety of stress situations’. It aims to be a systematic approach for understanding, mitigating and responding to social problems such as extraordinary stresses and losses, interferences in complex and mutual dependent systems, or lack of trust in vital social institutions. Future threats to society are not limited to specific sectors or areas, but stem from complex interactions amongst economic, technological, social and cultural factors. Thus, the main challenges to improve societal safety will be the ability to coordinate, organize and assign clear roles to different actors at the international, national and local levels. Societal safety has interfaces with other safety‐related areas such as national security, sustainable development, human security and incident management (handling of isolated accidents, common illness and ordinary criminal acts). Societal safety is, however, a sensitive political issue containing dilemmas and value choices that are hardly possible to perceive or solve as pure scientific problems. 相似文献
45.
It is well known that horizontal surfaces of high strength concrete (HSC) are susceptible to cracking in the time before and
during setting. It appears that there are two critical time periods for such cracking: An early period ranging from placing
to an hour or two, and a late period that covers the setting time and early hardening. The latter is considered here. In this
period, the cracking risk may be assessed from the ratio between strain (the volume change) and tensile strain capacity, or
from the ratio between stress generated from the volume change at restraint, and the tensile strength. All these parameters
were measured. It is shown that relatively moderate volume changes of HSC-surfaces caused by drying plus cooling, generate
restraining stress that may exceed the tensile strength, and thus, generate failure. The results indicate that crack risk
assessment from stress/strength is more reliable than using strain/strain capacity. The starting point of tensile strength
evolution of hardened concrete seems to coincide fairly well with the initial setting time. Also, the tensile strain capacity
reaches a low level at this point, but continues descending for another hour or more. 相似文献
46.
J Holst B Lindblad D Bergqvist O Nordfang PB Ostergaard JG Petersen G Nielsen U Hedner 《Canadian Metallurgical Quarterly》1994,71(2):214-219
The aim was to investigate whether a truncated recombinant Tissue Factor Pathway Inhibitor (TFPI1-161), which lacked the third Kunitz-type domain and the basic c-terminal region, had an antithrombotic effect comparable to LMWH in a randomised double-dummy study. The experimental thrombosis was induced in jugular veins, in a total of 40 rabbits by a combination of destruction of the endothelium and restricted blood flow. Group 1: placebo, gr 2: LMWH 60 anti-FXa IU/kg, gr 3-5: 0.1, 1.0 and 10.0 mg/kg TFPI1-161. TFPI1-161 reduced the thrombus weights in all treated groups, significantly in doses of 1.0 and 10.0 mg/kg compared to placebo. The frequency of thrombosis and occlusive thrombosis were also significantly reduced in those doses. The antithrombotic properties of TFPI1-161 (1.0-10.0 mg/kg) measured as thrombus weight, frequency of thrombosis and frequency of occlusive thrombosis was equivalent to the anti-thrombotic properties of LMWH. In the anti-FXa, APTT and PT-assays TFPI1-161 displayed a dose dependent increase of activity. Recombinant-TFPI1-161 did not influence the anti-FIIa-assay. No haemorrhagic side effects were noted. 相似文献
47.
An overall model for maintenance optimization 总被引:1,自引:0,他引:1
This paper presents an approach for identifying the optimal maintenance schedule for the components of a production system. Safety, health and environment objectives, maintenance costs and costs of lost production are all taken into consideration, and maintenance is thus optimized with respect to multiple objectives. Such a global approach to maintenance optimization requires expertise from various fields, e.g., decision theory, risk analysis and reliability and maintenance modelling. Further, a close co-operation between management, maintenance personnel and analysts is required to achieve a successful result. In the past this has been a major obstacle to the extensive use of proper maintenance optimization methods in practice, and techniques to promote the communication between the involved parties of the optimization process is an essential element in the suggested approach. A simple step by step presentation of the required modelling is provided. Contrary to most current methods of RCM (Reliability Centered Maintenance), the approach is based on an analytic model, and therefore gives a sound framework for carrying out a proper maintenance optimization. The approach is also flexible as it can be carried out at various levels of detail, e.g., adopted to available resources and to the managements willingness to give detailed priorities with respect to objectives on safety vs production loss. 相似文献
48.
An executable subset of VDM-SL in an SA/RT framework 总被引:2,自引:2,他引:0
In this article we present the executable specification language IPTES Meta-IV based on the formal specification language VDM-SL. The language has been fitted to work in an SA/RT framework and the article presents how it supports the specification of the data transformation part of SA/RT. Furthermore we present some of the advanced constructs of the language seen as an executable specification language in its own right. Finally we present how an IPTES Meta-IV interpreter is used in combination with a high-level timed Petri net executor to execute SA/RT models. 相似文献
49.
50.
A test chamber has been developed in order to provide a small and simple emission testing facility capable of testing construction products in a climate where the important climatic parameters such as temperature, ventilation rate and air velocity can be varied independently around typical indoor values. The test chamber CLIMPAQ is made of panes of window glass. Other main surface materials are stainless steel and eloxated aluminium. The chamber has a volume of 50.9 litres and is designed to meet the requirements for quantifying air pollution. In this investigation human subjects acted as air pollution judges, and chemical characterization of the air pollution was carried out. Carpet, linoleum, wall paint and seal- ant were tested simultaneously in the CLIMPAQ and in four other chambers ranging from a full-scale chamber of 28 m3 to a field and laboratory emission cell of 3.5· 10?5m3. Product ranking is the same in all chambers for the sensory measurements. Emission rates based on sensory measurements differ for all products less than 100 % except for tests in a 3-litre chamber where emission rates were higher. Chemical measurements differ up to approximately 10 times for the same product in different chambers. Deviations appear to be the result of different environmental parameters in the various chambers. Low air concentrations or high specific ventilation rates seem to increase emissions, while differences in air velocities and sink properties may also be the cause of differences in emission rates. 相似文献