全文获取类型
收费全文 | 33453篇 |
免费 | 675篇 |
国内免费 | 1487篇 |
专业分类
安全科学 | 1161篇 |
废物处理 | 1255篇 |
环保管理 | 4395篇 |
综合类 | 7005篇 |
基础理论 | 9232篇 |
环境理论 | 21篇 |
污染及防治 | 8806篇 |
评价与监测 | 2007篇 |
社会与环境 | 1414篇 |
灾害及防治 | 319篇 |
出版年
2023年 | 196篇 |
2022年 | 375篇 |
2021年 | 365篇 |
2020年 | 339篇 |
2019年 | 363篇 |
2018年 | 560篇 |
2017年 | 577篇 |
2016年 | 736篇 |
2015年 | 679篇 |
2014年 | 967篇 |
2013年 | 2543篇 |
2012年 | 1203篇 |
2011年 | 1604篇 |
2010年 | 1327篇 |
2009年 | 1348篇 |
2008年 | 1541篇 |
2007年 | 1588篇 |
2006年 | 1416篇 |
2005年 | 1191篇 |
2004年 | 1118篇 |
2003年 | 1090篇 |
2002年 | 1044篇 |
2001年 | 1324篇 |
2000年 | 953篇 |
1999年 | 623篇 |
1998年 | 504篇 |
1997年 | 493篇 |
1996年 | 505篇 |
1995年 | 528篇 |
1994年 | 470篇 |
1993年 | 422篇 |
1992年 | 447篇 |
1991年 | 384篇 |
1990年 | 392篇 |
1989年 | 419篇 |
1988年 | 350篇 |
1987年 | 305篇 |
1986年 | 280篇 |
1985年 | 312篇 |
1984年 | 288篇 |
1983年 | 323篇 |
1982年 | 323篇 |
1981年 | 275篇 |
1980年 | 244篇 |
1979年 | 271篇 |
1978年 | 229篇 |
1977年 | 195篇 |
1976年 | 201篇 |
1975年 | 192篇 |
1972年 | 199篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
531.
A pleural effusion associated with congenital pulmonary lymphangiectasia was detected in a fetus in utero but was absent at the time of delivery. The pleural effusion was unilateral although the disease involved both lungs. In this case there was an association between polyhydramnios and congenital pulmonary lymphangiectasia. 相似文献
532.
533.
In Acromyrmex octospinosus leaf-cutting ants the metapleural glands produce an array of antibiotic compounds that serve as a general defence against unwanted microbes on the cuticle. Leaf-cutting ants also grow mutualistic Pseudonocardiaceae bacteria on their cuticle that produce antibiotics controlling a microfungal parasite of their fungus gardens. Interaction between this bacterium and gland secretion therefore seems unavoidable. We document the typical development of bacterial growth on the cuticle of young major workers, show that growth starts a few days after eclosion, and that the maximal cover is reached after 2–3 weeks and gradually declines when workers mature. Experimental closure of the metapleural glands had no effect on the initial exponential growth phase of the bacterium, but significantly reduced the cover during the decline phase. The age-dependent abundance of the bacterium and its partial dependence on metapleural gland secretion support the hypothesis that the abundance of this mutualist is actively regulated. 相似文献
534.
With the advent of more stringent controls on wastewater treatment, sewage sludge production in Europe and many parts of the world is increasing. With this increase comes the problem of sludge disposal, and recycling to land arguably offers an economically and environmentally sustainable option. However, a major limitation of sewage sludge reuse is the potential release of heavy metals from the sludge and heavy metal accumulation to toxic levels in topsoils. The properties of the sludge play a crucial role in determining the initial release and subsequent availability of heavy metals in amended soils. Bioavailable forms of heavy metals in recently amended soils are most likely to be those that are bioavailable in the sewage sludge. In this paper, published research on the importance of sewage sludge characteristics on metal release and bioavailability will be reviewed and contrasted with original research. A selection of sludges from around Australia has been collected for this purpose. Through the use of incubation studies, isotope dilution techniques, ion-selective electrode measurements and 13C-NMR spectroscopy, the importance of a range of sludge properties on heavy metal behaviour in sludges and sludge-amended soils is addressed. 相似文献
535.
R Burt M.A WilsonT.J Keck B.D Dougherty D.E StromJ.A Lindahl 《Advances in Environmental Research》2003,8(1):51-67
Long-term copper smelting in the Anaconda and Deer Lodge Valley area of Montana has resulted in an extensive area of trace element contamination. Aerial extent of contamination is generally established, but total analysis of soils does not correlate to relative degree of impact on vegetation growth. Three pedons (Beaverell, Cetrack and Judco) were analyzed by routine soil characterization methods, aqua regia microwave digestion, sequential chemical extraction, and X-ray diffraction analysis with the objective of providing a better understanding of chemical forms and potential reactivity of selected trace elements (Cd, Co, Cr, Cu, Hg, Mn, Ni, P, Pb). Surface horizons of soils are more acidic than subsoils, with pH for all horizons ranging from 4.0 to 8.7. Beaverell is the most contaminated in the upper 20 cm with the sum of total extractable (SUMTE) trace elements by microwave digestion ranging from 1836 to 3605 mg kg−1, largest H2O-soluble (WS) and exchangeable (EX) fractions (e.g. 1.6 and 9.3%, respectively), and smallest residual (RES) fraction (e.g. 14.3%). Cetrack has greater SUMTE elements than Judco, though a lower WS+EX fraction due to the effects of alkaline pH, carbonates and high P. Oxide (OX), organic matter/sulfide (OM/S), and RES fractions predominate over WS, EX, and specially-sorbed/carbonate-bound fractions (SS/CAR) for all horizons. Copper, Zn, Pb and Cd are elevated in surface over subsurface horizons in these latter fractions, indicating these elements were anthropogenic additions. X-ray data indicate that Pb, Cu, Cr and Cd partially exists as both OX and sulfide mineral forms. 相似文献
536.
537.
Gamergates (i.e. mated reproductive workers) are mostly known from ant species within the Ponerinae. We report here the discovery of gamergates in two species of the subfamily Myrmicinae. Until now, mated reproductive females in colonies of myrmicine species have been considered morphologically distinct from the worker caste. However, in two species of the myrmicine Metapone (Metapone madagascarica and a newly discovered, not yet described Metapone species) all workers have six ovarioles and a spermatheca; and some of them are mated. There are no morphological differences between mated and non-mated workers. Field observations and laboratory studies indicate that colonies of the Metapone species can reproduce with gamergates only. 相似文献
538.
矿区生态系统健康内涵及评价指标体系研究 总被引:1,自引:0,他引:1
结合生态系统健康理论及矿区发展特点,探讨了矿区生态系统健康内涵、阐述了矿区生态系统健康评价目的和评价指标体系的设置思想,构建了矿区生态系统健康评价指标体系。 相似文献
539.
11种有机磷农药对海洋微藻致毒效应的研究 总被引:17,自引:0,他引:17
通过研究不同盐度条件下11种有机磷农药对扁藻的相对增长率和叶绿素a含量的影响,得到了S=30和S=20时的半数有效浓度,并比较其大小。盐度作为环境因子,影响到有机磷农药的毒性。研究发现,遥有机磷农药在低浓度时出现一定限度的促生长作用;容易进攻细胞膜的有机磷农药对扁藻的致毒性相对较强;此外,有机磷农药的毒性大小与其结构密切相关含有苯环结构的有机磷农药毒性大小不含有苯 有机磷农药的毒性。 相似文献
540.
J. Caspar Rüegg 《Die Naturwissenschaften》1998,85(12):575-582
2+ concentrations tropomyosin is located at the edge of the thin filament, thereby interfering with the formation of strong
actin-myosin linkages (blocked state). An increase in Ca2+ activity causes an azimuthal shift of tropomyosin around the filament (by about 30°), thereby increasing the probability
of low-force crossbridge interaction, a process which by cooperative effects induces further tropomyosin movement (by an additional
10°) which results in the open state of the filament characterized by forceful crossbridge interaction. (This mechanism may
be analogous to that in ligand-gated ion channels, where ligand binding increases the open probability of the pore.) The extent
of activation then depends on the free Ca2+ concentration and on the calcium sensitivity of the thin filament that may be affected by protein phosphorylation, crossbridge
attachment, the troponin isoform composition of the filament, and novel calcium-sensitizing drugs that act on the contractile
or regulatory proteins and thus increase the force of the heart. 相似文献