全文获取类型
收费全文 | 9060篇 |
免费 | 539篇 |
国内免费 | 2880篇 |
专业分类
安全科学 | 755篇 |
废物处理 | 541篇 |
环保管理 | 738篇 |
综合类 | 4761篇 |
基础理论 | 1589篇 |
环境理论 | 3篇 |
污染及防治 | 2834篇 |
评价与监测 | 476篇 |
社会与环境 | 441篇 |
灾害及防治 | 341篇 |
出版年
2024年 | 25篇 |
2023年 | 165篇 |
2022年 | 479篇 |
2021年 | 439篇 |
2020年 | 394篇 |
2019年 | 330篇 |
2018年 | 407篇 |
2017年 | 464篇 |
2016年 | 433篇 |
2015年 | 507篇 |
2014年 | 665篇 |
2013年 | 940篇 |
2012年 | 742篇 |
2011年 | 748篇 |
2010年 | 584篇 |
2009年 | 554篇 |
2008年 | 583篇 |
2007年 | 549篇 |
2006年 | 424篇 |
2005年 | 309篇 |
2004年 | 275篇 |
2003年 | 301篇 |
2002年 | 238篇 |
2001年 | 267篇 |
2000年 | 221篇 |
1999年 | 220篇 |
1998年 | 189篇 |
1997年 | 174篇 |
1996年 | 155篇 |
1995年 | 118篇 |
1994年 | 112篇 |
1993年 | 82篇 |
1992年 | 64篇 |
1991年 | 47篇 |
1990年 | 33篇 |
1989年 | 27篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1972年 | 12篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
The application of a multiple-recapture technique for the study of relatively small fish populations
S. Z. Rafail 《Marine Biology》1972,16(3):253-260
Expressions are given for the estimation of catchability of untagged fish using the type of multiple-recapture experiments suited to relatively small fish populations. in these experiments all captured fish are released after tagging untagged fish. The realistic assumption that fish populations suffer from different causes of mortality during the sampling surveys is adopted here. The catchability estimate for untagged fish is used to evaluate instantaneous fishing mortality, abundance, survival, instantaneous total mortality and instantaneous natural mortality rates of untagged fish. These estimates are free from Types A and B tagging errors, and take into consideration that catchabilities of tagged and untagged fish are different. 相似文献
972.
Is helping a beneficial learning experience for red-cockaded woodpecker (Picoides borealis) helpers?
Several hypotheses have been suggested to explain the evolution and maintenance of helping behavior in cooperatively breeding
birds, one of which we investigated in the red-cockaded woodpecker (Picoides borealis). Helping may provide a learning experience that improves reproductive success once the helper becomes a breeder. We used
data collected from a population of red-cockaded woodpeckers in the Sandhills of North Carolina to compare the reproductive
success of 2-year-old breeders that were helpers at age 1 (helping experience) to those that were floaters or solitary males
at age 1 (no helping experience). Reproductive success of the two groups was similar, indicating that helping provides no
experience useful in reproduction. We reject the learning experience hypothesis as an explanation for the maintenance of helping
behavior in red-cockaded woodpeckers.
Received: 29 July 1996 / Accepted after revision: 27 April 1997 相似文献
973.
汞矿地区人发中甲基汞的气相色谱测定 总被引:6,自引:0,他引:6
本文采用气相色谱法测定人发中甲基汞,对人发的酸度,浸取时间,人发与酸液的比例,以及无机汞存在的影响作了测定和选择,方法的平均回收率96.6%,精确度2.8%,方法可靠性用氢化物原子荧光法核对,结果一致,并对我国某矿区职工,儿童及产妇发样分析结果作了讨论。 相似文献
974.
近中国海域大气微量元素输入量研究 总被引:13,自引:0,他引:13
本文研究了我国近海海域海上气溶胶的微量元素浓度的变化,它的来源、输送,以及某些微量元素沉降于该海域的总沉降量。初步研究估计尘土气溶胶沉降于近海海域的总沉降量为:(15-800)×10^10g/a;大气尘土总沉降量约占输入黄海海域每年泥沙总输入量的1-35%。 相似文献
975.
本文用ESR自旋捕集技术,以4-POBN为捕集剂,研究了吸烟烟气处理的鼠肝微粒体体系中的自由基性质。结果发现,在吸烟烟气处理的鼠肝微粒体中,4-POBN捕集到了自由基信号,这一信号的强度随温育时间的延长及充入烟气的量增加而增强,根据其性质及ESR波谱参数分析,体系中产生了脂类自由基。结果说明,吸烟烟气刺激了鼠肝微粒体的脂质过氧化。 相似文献
976.
Degradation of crude oil by a mixed population of bacteria isolated from sea-surface foams 总被引:4,自引:0,他引:4
A mixed bacteria population (EM4) was isolated from foams formed on the surface of a zone chromically polluted by hydrocarbons (Gulf of Fos, French Mediterranean coast, October 1981). The population was able to degrade crude oil very effectively in the presence of sea water supplemented with nitrogen, phosphorus and iron. The percentage of hydrocarbon degradation was 81% at 30°C, pH 8, and partial oxygen pressure of 100%. After 12 d incubation, 92 and 83% of satured and aromatic compounds (mono-, di- and triaromatics) were degraded, respectively, as well as 63% of polar products and 48.5% of asphaltenes. Maximum degradation was attained at a sodium chloride concentration of between 400 and 800 mM with Population EM4, which is constituted of 8 strains, four of which are weak halophiles. Bacterial growth on hydrocarbons induces the production in the culture medium of surface-active agents which are able to emulsify the substrate. There is high specificity between the nature of the growth substrate and such emulsifying activity, particularly as far as petroleum is concerned: only the culture medium from Population EM4 is able to emulsify petroleum. These surface-active agents contain sugars and lipids (fatty acids, mono- and diglycerides). The foams, which always contain a high concentration of both hydrocarbons (100 to 180 mgl-1) and bacteria that are able to grow on these types of substrates, have a strong emulsifying activity. Our results would seem to demonstrate the importance of biosurfactants in the elimination of hydrocarbons from polluted biotopes. 相似文献
977.
S. Z. Rafail 《Marine Biology》1973,19(4):354-358
The parameter K of the von Bertalanffy equation, as developed by Beverton and Holt (1957), is first estimated by the relation $$\log _e \left( {dL_t /dt} \right) = A - Kt$$ where dLt/dt denotes growth increments per a unit of age, t denotes age, and A is a constant. The K estimate is used to evaluate L∞; $$L_\infty = \left( {e^K \sum\limits_2^n {L_t - \sum\limits_1^{n - 1} {L_t } } } \right)/\left( {n - 1} \right)\left( {e^K - 1} \right)$$ The L∞ estimate is used to estimate t o, and to obtain a better estimate for K; $$\log _e \left( {1 - L_t /L_\infty } \right) = - Kt + Kt_0 $$ The K estimate may be used to obtain another estimate for L∞. Solved examples show that a single iteration is sufficient to obtain fitted equations which are, on the average, as precise as equations fitted by the least squares method shown by Tomlinson and Abramson (1961). This new method can be used, with a slight modification, for the second equation given above, if growth data have unequal age intervals. The variance of K, t o and log e L∞ can be estimated by applying the simple methods used in the case of straight-line relationships. 相似文献
978.
Wang TJ Hu ZY Xie M Zhang Y Xu CK Chao ZH 《Environmental geochemistry and health》2004,26(2-3):169-177
The regional acid deposition model system (RegADMS) was applied to simulate the air sulfur deposition onto different landuse types over China, in which the dry deposition velocities of SO2 and sulfate aerosol (SO4(2-) were estimated by use of a big leaf resistance analogy model and the wet scavenging coefficients were parameterized in terms of precipitation rate. Investigations show that the annual total sulfur deposition over mainland China is 7.24mt (1 mt = 10(6) ton) , in which dry deposition and wet deposition accounts for 56 and 44%, respectively. The sulfur deposition onto agriculture land, grass land, and forest land is 1.09, 3.6 and 1.41 mt, respectively, which sums 6.1 mt and accounts for 84% of the total sulfur deposition. The modeled sulfur deposition was in agreement with the measurement conducted at farmland in Yingtan, a typical read soil region in Jiangxi province of China, during the period of November 1998--October 1999. The total sulfur deposition at the Yingtan site is about 10.3 gm(-2) year(-1) of which 83% is dry deposition. The modeling sulfur deposition at the same site is 8.4 g m(-2) year(-1) Furthermore, the comparison between RegADMS and RAINS-ASIA on modeling regional sulfur deposition shows the consistence of the two models. The correlation coefficient between the simulated sulfur deposition at the medium-large cities reaches 0.72. 相似文献
979.
X.J. Xie W. Ran Q.R. Shen C.Y. Yang J.J. Yang Z.H. Cao 《Environmental geochemistry and health》2004,26(2):237-243
Field experiments were done in two sites, Yixing and Changshu, Jiangsu province, China, to study P movement and leaching in flooded paddy soils. P movement in soil was investigated by using the KH2
32PO4 tracker method, and the amount of P leached from the soil layer in different depths was estimated by measuring P concentrations in the soil solution and saturated hydraulic conductivities in field. Determination was done about one month after P application. There was 46% and 42% of total 32P retained in the 0–5cm layer of soil in the Yixing site and in the Changshu site respectively. The 32P retained in the 25–30 cm layer was only about 1–2% of the total 32P added. Furthermore, 8.01% of 32P in the soil of Yixing site and 16.8% of 32P in the soil of Changshu site was lost from the layer 0–30cm soil. The seasonal amounts of P leached from the top soil layer and from bottom layer are about 4.5–5.8% and 1.6–2.1% of the total P application, respectively. Changes of total P concentrations in soil solutions during rice growth showed that the fertilizer P applied before flooding of the paddy fields suffered a flash leaching loss and a slow leaching loss. We concluded that the fertilizer P could quickly move in the flooded paddy rice field and parts of it can enter into surface water and ground water. Unless the P application is well managed the risk of P loss and consequently environmental pollution exist. 相似文献
980.
Parameters derived from photosynthesis-irradiance (P-I) models, although often empirical in nature, are useful indicators of the photoadaptive state of phytoplankton in culture and in situ. However objective criteria for determining significant changes in P-I curves are rarely provided, because confidence intervals for parameters of non-linear models are not estimated easily. Examination of least-squares residuals in parameter space and Monte Carlo approaches have been used to estimate confidence regions around parameter values, but the computationally intensive nature of these methods has prevented their routine application. We present an alternative method of estimating confidence intervals for parameters of P-I curves that runs quickly on a microcomputer and is easily combined with common parameter-estimation routines. This algorithm was tested using a 3-parameter P-I model and curves describing a wide range of photoadaptive states, with different numbers of observations and different amounts of inherent variability. The method produced results comparable to the Monte Carlo technique. This analysis makes it possible to specify the sample size required to define parameters with acceptable confidence as a function of data variance and photoadaptive state. In most reasonable situations, 25 observations are sufficient. 相似文献