全文获取类型
收费全文 | 4297篇 |
免费 | 33篇 |
国内免费 | 24篇 |
专业分类
安全科学 | 41篇 |
废物处理 | 168篇 |
环保管理 | 146篇 |
综合类 | 1962篇 |
基础理论 | 773篇 |
环境理论 | 5篇 |
污染及防治 | 856篇 |
评价与监测 | 236篇 |
社会与环境 | 152篇 |
灾害及防治 | 15篇 |
出版年
2022年 | 52篇 |
2021年 | 34篇 |
2019年 | 33篇 |
2018年 | 68篇 |
2017年 | 60篇 |
2016年 | 79篇 |
2015年 | 63篇 |
2014年 | 98篇 |
2013年 | 192篇 |
2012年 | 122篇 |
2011年 | 95篇 |
2010年 | 119篇 |
2009年 | 128篇 |
2008年 | 137篇 |
2007年 | 165篇 |
2006年 | 115篇 |
2005年 | 115篇 |
2004年 | 97篇 |
2003年 | 115篇 |
2002年 | 84篇 |
2001年 | 84篇 |
2000年 | 82篇 |
1999年 | 79篇 |
1998年 | 58篇 |
1997年 | 54篇 |
1996年 | 34篇 |
1995年 | 51篇 |
1994年 | 52篇 |
1991年 | 36篇 |
1990年 | 41篇 |
1989年 | 32篇 |
1985年 | 35篇 |
1979年 | 38篇 |
1977年 | 32篇 |
1969年 | 36篇 |
1968年 | 31篇 |
1967年 | 55篇 |
1966年 | 47篇 |
1965年 | 53篇 |
1964年 | 60篇 |
1963年 | 63篇 |
1962年 | 58篇 |
1961年 | 63篇 |
1960年 | 55篇 |
1959年 | 64篇 |
1958年 | 59篇 |
1957年 | 67篇 |
1956年 | 49篇 |
1955年 | 49篇 |
1954年 | 48篇 |
排序方式: 共有4354条查询结果,搜索用时 546 毫秒
231.
232.
Andreas Züttel 《Mitigation and Adaptation Strategies for Global Change》2007,12(3):343-365
Hydrogen storage and transportation or distribution is closely linked together. Hydrogen can be distributed continuously in
pipelines or batch wise by ships, trucks, railway or airplanes. All batch transportation requires a storage system but also
pipelines can be used as pressure storage system. Hydrogen exhibits the highest heating value per weight of all chemical fuels.
Furthermore, hydrogen is regenerative and environment friendly. There are two reasons why hydrogen is not the major fuel of
toady’s energy consumption: First of all, hydrogen is just an energy carrier. And, although it is the most abundant element
in the universe, it has to be produced, since on earth it only occurs in the form of water. This implies that we have to pay
for this energy, which results in a difficult economic task, because since the industrialization we are used to consuming
energy for free. The second difficulty with hydrogen as an energy carrier is the low critical temperature of 33 K, i.e. hydrogen
is a gas at room temperature. For mobile and in many cases also for stationary applications the volumetric and gravimetric
density of hydrogen in a storage system is crucial. Hydrogen can be stored by six different methods and phenomena: high pressure
gas cylinders (up to 800 bar), liquid hydrogen in cryogenic tanks (at 21 K), adsorbed hydrogen on materials with a large specific
surface area (at T < 100 K), absorbed on interstitial sites in a host metal (at ambient pressure and temperature), chemically bond in covalent
and ionic compounds (at ambient pressure), oxidation of reactive metals e.g. Li, Na, Mg, Al, Zn with water. These metals easily
react with water to the corresponding hydroxide and liberate the hydrogen from the water. Finally, the metal hydroxides can
be thermally reduced to the metals in a solar furnace. 相似文献
233.
234.
235.
236.
High-performance permanent magnets 总被引:2,自引:0,他引:2
High-performance permanent magnets (pms) are based on compounds with outstanding intrinsic magnetic properties as well as
on optimized microstructures and alloy compositions. The most powerful pm materials at present are RE–TM intermetallic alloys
which derive their exceptional magnetic properties from the favourable combination of rare earth metals (RE=Nd, Pr, Sm) with
transition metals (TM=Fe, Co), in particular magnets based on (Nd,Pr)2Fe14B and Sm2(Co,Cu,Fe,Zr)17. Their development during the last 20 years has involved a dramatic improvement in their performance by a factor of >15 compared
with conventional ferrite pms therefore contributing positively to the ever-increasing demand for pms in many (including new)
application fields, to the extent that RE–TM pms now account for nearly half of the worldwide market. This review article
first gives a brief introduction to the basics of ferromagnetism to confer an insight into the variety of (permanent) magnets,
their manufacture and application fields. We then examine the rather complex relationship between the microstructure and the
magnetic properties for the two highest-performance and most promising pm materials mentioned. By using numerical micromagnetic
simulations on the basis of the Finite Element technique the correlation can be quantitatively predicted, thus providing a
powerful tool for the further development of optimized high-performance pms. 相似文献
237.
H. Kühne 《Die Naturwissenschaften》1957,44(15):431-431
238.
Model oligo esters of terephthalic acid with 1,2-ethanediol, 1,3-propanediol, and 1,4-butanediol have been investigated with regard to their biodegradability in different biological environments. Well-characterized oligomers with weight-average molar masses of from 600 to 2600 g/mol exhibit biodegradation in aqueous systems, soil, and compost at 60°C. SEC investigations showed a fast biological degradation of the oligomer fraction consisting of 1 or 2 repeating units, independent of the diol component used for polycondensation, while polyester oligomers with degrees of polymerization higher than 2 were stable against microbial attack at room temperature in a time frame of 2 months. At 60°C in a compost environment chemical hydrolysis also degrades chains longer than two repeating units, resulting in enhanced degradability of the oligomers. Metabolization of the monomers and the dimers as well by the microorganisms could be confirmed by comparing SEC measurements and carbon balances in a Sturm test experiment. Based on these results degradation characteristics of potential oligomer intermediates resulting from a primary chain scission from copolyesters consisting of aromatic and aliphatic dicarbonic acids can be predicted depending on their composition. These results will have an evident influence on the evaluation of the biodegradability of commercially interesting copolyesters and lead to new ways of tailor-made designing of new biodegradable materials as well. 相似文献
239.
Phase relations between a circadian rhythm and its zeitgeber within the range of entrainment 总被引:1,自引:0,他引:1
The regular day-night changes in tissues, physiologic functions, and behavior of organisms are based on endogenous rhythmic processes which under constant conditions continue with periods slightly deviating from 24h. These ‘arcadian’ rhythms have properties of self-sustained oscillators. Under natural conditions, circadian rhythms are synchronized (entrained) to 24 h by periodic factors in the environment, the so-called ‘Zeitgebers’. In the laboratory, circadian rhythms can also be entrained to periods other than 24 h within certain limits. Data on the phase relationship between the circadian rhythm and an entraining light-dark cycle for vertebrates, insects, plants, and unicellular organisms are reviewed. 相似文献
240.
The significant processes controlling the fate of particulates are convection an dispersion on one hand, and sedimentation on the other hand. Due to inteparticulated reactions, larger aggregates can be formed from smaller units thus changing the sedimentation characteristics. These phenomena are summarized in a mathematical model whereby hydrodynamic effects as well as the control mechanisms of the dissolved phase are included. A relationship was derived on the basis of energy considerations leading to the formulation of a critical sedimentation velocity of the suspensa, which determines the transport capacity of the flowing system. The sedimentation term is calculated from the above discussed transport capacity, hydro-dynamic parameters and suspending media properties. Aggregation effects are taken into account as an increase of sedimentation velocities of the particles. The equations are solved in a particular computational routine such that the horizontal distribution of suspended solids in a natural system can be describe as function of the above discussed phenomena. The model was tested with in situ-measurements. It was found that the observed processes are described satisfactorily by this model. 相似文献