全文获取类型
收费全文 | 2467篇 |
免费 | 122篇 |
国内免费 | 421篇 |
专业分类
安全科学 | 145篇 |
废物处理 | 107篇 |
环保管理 | 224篇 |
综合类 | 967篇 |
基础理论 | 533篇 |
环境理论 | 1篇 |
污染及防治 | 658篇 |
评价与监测 | 182篇 |
社会与环境 | 141篇 |
灾害及防治 | 52篇 |
出版年
2024年 | 4篇 |
2023年 | 44篇 |
2022年 | 108篇 |
2021年 | 102篇 |
2020年 | 86篇 |
2019年 | 74篇 |
2018年 | 95篇 |
2017年 | 114篇 |
2016年 | 122篇 |
2015年 | 126篇 |
2014年 | 154篇 |
2013年 | 241篇 |
2012年 | 218篇 |
2011年 | 233篇 |
2010年 | 207篇 |
2009年 | 180篇 |
2008年 | 187篇 |
2007年 | 193篇 |
2006年 | 168篇 |
2005年 | 83篇 |
2004年 | 59篇 |
2003年 | 43篇 |
2002年 | 41篇 |
2001年 | 24篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 13篇 |
1996年 | 3篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3010条查询结果,搜索用时 62 毫秒
941.
Aurora M. Castilla Stefan Van Dongen Anthony Herrel Amadeu Francesch Juan Martínez de Aragón Jim Malone Juan José Negro 《Die Naturwissenschaften》2010,97(2):143-151
We compared membrane thickness of fully developed eggs with those of non-developed eggs in different endangered falcon taxa.
To our knowledge, membrane thickness variation during development has never been examined before in falcons or any other wild
bird. Yet, the egg membrane constitutes an important protective barrier for the developing embryo. Because eggshell thinning
is a general process that occurs during bird development, caused by calcium uptake by the embryo, eggs are expected to be
less protected and vulnerable to breakage near the end of development. Thus, egg membranes could play an important protective
role in the later stages of development by getting relatively thicker. We used linear mixed models to explore the variation
in membrane thickness (n = 378 eggs) in relation to developmental stage, taxon, female age, mass and identity (73 females), egg-laying sequence (105
clutches) and the study zone. Our results are consistent with the prediction that egg membranes are thicker in fully developed
eggs than in non-developed eggs, suggesting that the increase in membrane thickness during development may compensate for
eggshell thinning. In addition, our data shown that thicker membranes are associated with larger, heavier and relatively wider
eggs, as well as with eggs that had thinner eggshells. Egg-laying sequence, female age and the study zone did not explain
the observed variation of membrane thickness in the falcon taxa studied. As we provide quantitative data on membrane thickness
variation during development in falcons not subjected to contamination or food limitation (i.e. bred under captive conditions),
our data may be used as a reference for studies on eggs from natural populations. Considering the large variation in membrane
thickness and the multiple factors affecting on it and its importance in the protection of the embryo, we encourage other
researchers to include measurements on membranes in studies exploring eggshell thickness variation. 相似文献
942.
Kol-Maimon H Levi-Zada A Franco JC Dunkelblum E Protasov A Eliyaho M Mendel Z 《Die Naturwissenschaften》2010,97(12):1047-1057
The vine mealybug (VM) females collected in Israel produce two sex pheromone compounds: lavandulyl senecioate (LS) and (S)-lavandulyl isovalerate (LI). The males display ambiguous behavior to LI: repulsion in the vineyard and attraction of laboratory-reared
males. We addressed the question of individual male behavior, i.e., do males respond to both LS and LI, or might they display
a distinct response to each of the two pheromone compounds. We compared male pherotype frequencies between wild-caught and
laboratory-reared populations. Then, we examined the relationship between pherotype composition and male capture rates in
pheromone traps. Finally, we addressed the heredity of the pherotypes. The Israeli VM populations contain nine different male
pherotypes, as defined according to the male behavior to pheromone compounds. The studied Portuguese populations included
five of the nine pherotypes; none of the Portuguese males were attracted to LI. It seems that the high frequency of males
that were attracted to LI is related to dense VM populations. It is hypothesized that selection for the male pherotypes, I
males, those that respond to LI, occur under high-density rearing conditions. This may result from shorter development times
of males and females that produce more I male pherotypes. The lower relative frequency of trapping of males in LI-baited traps
than expected from the percentage determined in a Petri dish arena suggests that males that respond solely to LS (S males)
are better fliers. The results also suggest that the pherotype trait is inherited by both sexes of the VM. 相似文献
943.
944.
The traditional locomotive diesels are usually designed for the performance of rated condition and much fuel will be consumed. A new plunger piston matching parts of fuel injection pump and injector nozzle matching parts were designed. The experimental results of fuel injection pump test and diesel engine show that the fuel consumption rate can be decreased a lot in the most of the working conditions. The forced lubrication is adopted for the new injector nozzle matching parts, which can reduce failure rate and increase service life. The design has been patented by Chinese State Patent Office. 相似文献
945.
纳米TiO_2的溶胶-微波法合成及其光催化性能研究 总被引:1,自引:0,他引:1
以钛酸四正丁酯为原料,采用溶胶-凝胶法、溶胶-水热法及溶胶-微波法三种方法合成出纳米TiO2,借助XRD、UV-Vis吸收光谱等测试手段对其进行了表征,并以甲基橙为模型污染物,考察了样品的光催化性能。物相分析表明,所得样品均为锐钛矿相TiO2,与其它两种方法相比,溶胶-微波法合成的样品衍射峰明显宽化,强度明显降低,说明该法合成出纳米TiO2粒径较小;UV-Vis吸收光谱表明,溶胶-微波法合成的样品在可见光区和紫外光区对光均呈现更强的吸收,说明该法合成的粉末对光具有更高的利用率。光催化实验表明,溶胶-微波法合成样品的光催化活性高于另两种方法,紫外灯连续照射5h,甲基橙溶液脱色率为99.06%。此外,将该样品用于延安卷烟厂蒸叶车间废水的光催化氧化处理,效果较好,太阳光照射3d后COD去除率为77.4%。 相似文献
946.
947.
948.
949.
沘江两岸耕地土壤重金属径流迁移模拟研究 总被引:1,自引:0,他引:1
为研究重金属污染土壤在暴雨径流条件下是否存在水环境风险,对亚洲最大铅锌矿所在地,即沘江两岸耕地土壤中重金属元素As、Zn、Cd、Pb累积状况进行系统调查,并选择上游、中游、下游污染程度不同的3个代表性供试土壤,通过人工模拟降雨方法,研究不同坡度(5°、15°和25°)和不同降雨强度(30 mm/h和60 mm/h)下沘江流域耕地土壤中重金属元素As、Zn、Cd、Pb随地表径流迁移流失的环境风险.结果表明:1)沘江两岸耕地土壤重金属累积存在不同程度的污染,流域内中风险组As、Zn、Pb、Cd的含量超标率分别为7.69%~85.71%、7.69%~100%、23.08%~46.67%和38.46%~60%,高风险组Pb和Cd的含量超标率分别为53.33%~71.43%和40%~100%,流域不同位置耕地土壤中重金属As、Zn、Cd、Pb平均累积量从大到小表现为上游、中游、下游;2)模拟研究结果显示,沘江流域耕地土壤的地表径流水中出现不同程度重金属污染,上游耕地土壤的径流中As、Zn、Cd、Pb均被检出,中游耕地土壤的径流中Zn、Cd、Pb被检出,下游耕地土壤的径流中只有Cd被检出,其中Cd和Pb质量浓度在地表水Ⅳ-劣V类之间波动,径流中As和Zn质量浓度均未超过I类水质标准;3)地表径流水中As、Zn、Cd、Pb的质量浓度和迁移量都随着坡度和降雨强度的增加而增大.沘江两岸耕地土壤中存在重金属污染,土壤污染程度、降雨强度和坡度都可能对研究区域耕地土壤重金属径流迁移造成影响. 相似文献
950.
Glucocorticosteroids (GCs) of the hypothalam–pituitary–adrenal axis play a role in association with both stressful events
and daily life processes. However, relatively little is known about the role of GCs in relation to daily and seasonal life
processes in animals in the wild. In this paper, we present data on basal levels of plasma corticosterone CORT in chicks of
a pelagic seabird, the thin-billed prion, Pachyptila belcheri, during two predictable changes in demands, the daily activity pattern and the preparation for fledging. By comparing chicks
fed recently with unfed chicks, we test how GC levels are modified according to nutritional condition. In accordance with
their nocturnal feeding rhythm, chicks had a clear daily rhythm with increased CORT secretion at night, but CORT levels during
the active phase were also highly elevated in unfed chicks compared with fed chicks. Close to fledging, chicks rapidly increased
basal CORT levels, and again unfed chicks had higher levels than fed chicks, although the age effect here was stronger than
the effect of recent feeding. The present data thus support the hypothesis that GC levels are adjusted to life stages with
predictable changes in demands, but food availability and/or internal energy stores also affect the level to which GCs increase. 相似文献