全文获取类型
收费全文 | 3167篇 |
免费 | 743篇 |
国内免费 | 1274篇 |
专业分类
安全科学 | 251篇 |
废物处理 | 151篇 |
环保管理 | 159篇 |
综合类 | 2238篇 |
基础理论 | 1630篇 |
污染及防治 | 500篇 |
评价与监测 | 161篇 |
社会与环境 | 55篇 |
灾害及防治 | 39篇 |
出版年
2024年 | 15篇 |
2023年 | 78篇 |
2022年 | 121篇 |
2021年 | 181篇 |
2020年 | 124篇 |
2019年 | 112篇 |
2018年 | 204篇 |
2017年 | 253篇 |
2016年 | 270篇 |
2015年 | 299篇 |
2014年 | 305篇 |
2013年 | 369篇 |
2012年 | 362篇 |
2011年 | 305篇 |
2010年 | 300篇 |
2009年 | 272篇 |
2008年 | 208篇 |
2007年 | 209篇 |
2006年 | 214篇 |
2005年 | 151篇 |
2004年 | 132篇 |
2003年 | 115篇 |
2002年 | 103篇 |
2001年 | 69篇 |
2000年 | 73篇 |
1999年 | 61篇 |
1998年 | 43篇 |
1997年 | 46篇 |
1996年 | 33篇 |
1995年 | 34篇 |
1994年 | 35篇 |
1993年 | 29篇 |
1992年 | 19篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有5184条查询结果,搜索用时 140 毫秒
991.
Effects of age and sex ratios on offspring recruitment rates in translocated black rhinoceros
下载免费PDF全文
![点击此处可从《Conservation biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jay V. Gedir Peter R. Law Pierre du Preez Wayne L. Linklater 《Conservation biology》2018,32(3):628-637
Success of animal translocations depends on improving postrelease demographic rates toward establishment and subsequent growth of released populations. Short‐term metrics for evaluating translocation success and its drivers, like postrelease survival and fecundity, are unlikely to represent longer‐term outcomes. We used information theory to investigate 25 years of data on black rhinoceros (Diceros bicornis) translocations. We used the offspring recruitment rate (ORR) of translocated females—a metric integrating survival, fecundity, and offspring recruitment at sexual maturity—to detect determinants of success. Our unambiguously best model (AICω = 0.986) predicted that ORR increases with female age at release as a function of lower postrelease adult rhinoceros sex ratio (males:females). Delay of first postrelease reproduction and failure of some females to recruit any calves to sexual maturity most influenced the pattern of ORRs, and the leading causes of recruitment failure were postrelease female death (23% of all females) and failure to calve (24% of surviving females). We recommend translocating older females (≥6 years old) because they do not exhibit the reproductive delay and low ORRs of juveniles (<4 years old) or the higher rates of recruitment failure of juveniles and young adults (4–5.9 years old). Where translocation of juveniles is necessary, they should be released into female‐biased populations, where they have higher ORRs. Our study offers the unique advantage of a long‐term analysis across a large number of replicate populations—a science‐by‐management experiment as a proxy for a manipulative experiment, and a rare opportunity, particularly for a large, critically endangered taxon such as the black rhinoceros. Our findings differ from previous recommendations, reinforce the importance of long‐term data sets and comprehensive metrics of translocation success, and suggest attention be shifted from ecological to social constraints on population growth and species recovery, particularly when translocating species with polygynous breeding systems. 相似文献
992.
采用氟、磷、钾化肥三因素通用旋转组合设计,通过计算机模拟寻优,建立了湘南砂岩红壤玉米-大豆立体栽培模式中玉米施肥量-产量、玉米施肥量-利润数学模型;优选出玉米产量和利润最高的各10套施肥方案;计算出玉米最高产量的施肥量为:尿素750kg/hm2,过磷酸钙1125kg/hm2,氯化钾332kg/hm2,N∶P2O5∶K2O=1∶0.39∶0.58;计算出玉米最佳经济效益施肥量为:尿素712.8kg/hm2,过磷酸钙1125kg/hm2,氯化钾285.2kg/hm2,N∶P2O5∶K2O=1∶0.41∶0.52.玉米与大豆的产量间以及两者的利润间均呈极显著正相关. 相似文献
993.
Simon Holden Sapna Ahuja Amanda Ogilvy-Stuart Helen V. Firth Christoph Lees 《黑龙江环境通报》2007,27(6):566-567
We describe a case of Harlequin Icthyosis where the main 2D and 3D ultrasound findings were digital contractures as opposed to the more commonly described severe facial dysmorphisms. A prenatal finding of distal arthrogryposis can therefore include harlequin icthyosis as a differential diagnosis, where 3D ultrasound may then disclose the facial features more commonly associated with the condition. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
994.
本文以玉山县宅前小流域开发治理规划为例,指出红壤地区小流域治理指导思想和应遵循原则,提出以山顶及坡度≥25°山坡营造防护林,坡度<25°山坡实行等高开垦为水土保持措施;同时兴修水利,建立山地灌溉体系,努力提高劳动者素质,加速区域经济发展,此小流域开发治理将为我国南方未开发的红壤地区充分利用自然资源提出一个典范。 相似文献
995.
996.
实验证明,亚硒酸钠对水稻外植体(成熟胚、幼穗)、愈伤组织和再生绿芽体细胞的生长都有不同程度的抑制作用,其抑制程度依次为再生绿芽>愈伤组织>外植体,但能促进它们的绿苗分化频率,特别在低硒浓度(1mg/L)处理组,并可改变它们的过氧化物酶同工酶的活性。 相似文献
997.
以盘塘红壤实验区为例,在阐明湘北环湖低丘红壤区土壤形成、类型及特性的基础上,提出了综合开发利用该区土壤资源的措施和途径。 相似文献
998.
John E. Kemnitzer Richard A. Gross Stephen P. McCarthy John Liggat David J. Blundell Mike Cox 《Journal of Polymers and the Environment》1995,3(1):37-47
Predominantly syndiotactic poly(-hydroxybutyrate), syn-PHB, of variable syndioregularity (syndyad fractions 0.59, 0.62, 0.64, and 0.71) and molecular weight was prepared by the dibutyltin dimethoxide catalyzed ring opening of racemic-butyrolactone (BL). The crystallization behavior of the syn-PHB polymers was investigated by DSC and X-ray diffraction analyses. DSC of films after melting and annealing showed at least one, and often two distinct melting transitions occuring over a broad (often 40°C) temperature range. These results indicate that syn-PHB chain segments of variable syndioregularity form crystalline regions with very different thermodynamic stabilities. Maximum degrees of crystallinity for melt annealed 0.64- and 0.71-syn-PHB was observed at an annealing temperature (T
c
) of 30°C. AtT
c
values at 45°C and higher, crystallization of relatively lower syndioregular chain segments was apparently excluded to variable degrees dependent onT
c
and sample syndiotactic dyad content. After crystallization of syn-PHB samples at elevated temperatures, ambient temperature annealing resulted in an observed lower temperature melting transition at 50°C. This result showed little to no dependence on syn-PHB syndio-regularity andT
c
. Both solution precipitated 0.62-syn-PHB and 0.71-syn-PHB have WAXS patterns with poorly resolved crystalline reflections superimposed on amorphous haloes indicating low levels of crystallinity (17% and 25%, respectively) and poorly formed crystals. Isothermal crystallization monitored by DSC showed that the syn- and natural origin PHB showed fastest crystallization rates at temperatures between 50°C and 70°C and 60°C and 90°C, respectively. From the dependence of the higher melting transition onT
c
it was determined that the equilibrium melting temperatures for 0.62-syn-PHB (M
n
=83,700 g/mol) and a 0.64-syn-PHB (M
n
=11,900 g/mol) were 157 and 154°C, respectively. An Avrami analysis of syn-PHB yielded results similar to that found for natural origin PHB indicating that crystal growth occurs by a two-dimensional mechanism.Guest Editor: Dr. Graham Swift, Rohm & Haas. 相似文献
999.
本文研究了孔雀绿与磷(砷)酸钼的离子对膜的形成条件。并依此与共存元素分离,进行痕量磷酸根、亚砷酸根和砷酸根的浮膜分光光度法测定。选用硫酸为介质,考察了25种共存离子对测定的影响。拟定了天然水中痕量磷酸根、亚砷酸根和砷酸根的分析方法.操作简便,结果令人满意。 相似文献
1000.