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931.
通过电化学活化和硅烷偶联剂在石英谐振器的金电极表面修饰对氮氧化物(NOx)敏感的金属酞菁化合物,制成压电气体传感器.探讨了不同敏感材料对NOx的响应灵敏度、检出限及载气流速、温度和干扰气体等对传感器的响应和回复特性的影响.结果表明:酞菁铅最敏感;其适宜的载气流速为40 mL/min,温度范围为10~40 ℃;在9.55×10-4~1.91 mg/m3质量浓度范围内,有良好的线性响应关系;用于大气中NOx的测定,有较好的可靠性和准确性.使用寿命约300次. 相似文献
932.
Alex J. Cannon Paul H. Whitfield 《Journal of the American Water Resources Association》2001,37(1):73-89
ABSTRACT: Transient events in water chemistry in small coastal watersheds, particularly pH depressions, are largely driven by inputs of precipitation. While the response of each watershed depends upon both the nature of the precipitation event and the season of the year, how the response changes over time can provide insight into landscape changes. Neural network models for an urban watershed and a rural‐suburban watershed were developed in an attempt to detect changes in system response resulting from changes in the landscape. Separate models for describing pH depressions for wet season and dry season conditions were developed for a seven year period at each watershed. The neural network models allowed separation of the effects of precipitation variations and changes in watershed response. The ability to detect trends in pH depression magnitudes was improved by analyzing neural network residuals rather than the raw data. Examination of sensitivity plots of the models indicated how the neural networks were affected by different inputs. There were large differences in effects between seasons in the rural‐suburban watershed whereas effects in the urban watershed were consistent between seasons. During the study period, the urban watershed showed no change in pH depression response, while the rural‐suburban watershed showed a significant increase in the magnitude of pH depressions, likely the result of increased urbanization. 相似文献
933.
Collective detection concerns the idea that all members of a socially feeding group are alerted to an attack as long as at
least one group member detects it. We found that collective detection in mixed flocks of emberizid sparrows is limited markedly
by relatively small degrees of visual and spatial separation between foragers. These limits on collective detection appear
to influence the degree to which flock members lower their vigilance with increasing group size (the group size effect). Specifically,
the decrease in collective detection with increasing visual and spatial isolation between foragers is accompanied by a concomitant
decrease in the strength of the vigilance group size effect. Explanations for the vigilance-related effects of such separation
based upon a bird’s ability to monitor the vigilance behavior of flockmates can be ruled out for our experimental system.
Our results also shed light on the issue of whether the vigilance group size effect is influenced more by collective detection
or the simple dilution of risk with increasing group size. We argue that collective detection is not only an important determinant
of the group size effect, but also that the phenomena of collective detection and risk dilution are interdependent.
Received: 25 July 1995/Accepted after revision: 17 December 1995 相似文献
934.
935.
有害气体的扩散吸收和无动力检测技术 总被引:4,自引:0,他引:4
系统地论述了有害气体的扩散吸收和无动力检测技术的原理,介绍了无动力检测器的组成结构、技术指标及应用范围,综述了无动力检测技术的发展状况和趋势,为此项技术的应用提供了科学依据 相似文献
936.
937.
机动车排污检测/维修体系的改进和提高,实施检测/维修制度是在用车辆排污治理最有效、最合理、最经济的办法。本文就如何确定适合本地的检测标准、改进检测方法、提高维修技术及完善管理体系等有关方面作初步探讨。 相似文献
938.
介绍了Z比分数的构成,评价标准和运用Z比分数时应注意的问题。通过实例运用,指出正确选择指定值和变动性度量是实验室能力验证达标的关键。 相似文献
939.
为了解渗滤液污染土壤的复电阻率特性及其与海水入侵所造成的电特性差异,指导海滨场地的污染探测,设计了黏土和砂土两种土壤,在水饱和情况下通入不同浓度的渗滤液,测量复电阻率的幅值和相位响应;在砂土中通入与渗滤液电阻率相同的模拟海水,对比海水入侵与渗滤液污染所造成的相位差异.结果表明:受渗滤液污染土壤的复电阻率变化明显,0.1 Hz下被2%渗滤液(渗滤液体积占溶液总体积比例为2%)污染的土壤中,与背景值相比,黏土的幅值和相位分别降低了78%和70%,砂土的幅值和相位分别降低了66%和33%,且渗滤液浓度越高,幅值和相位的值就越小;而对于电阻率背景值较低的土壤(如海水入侵场地或地下水-海水交错带区域),通入渗滤液后,其复电阻率参数没有明显变化.对比海水入侵与渗滤液污染,受渗滤液污染较轻的土壤的相位略高于海水入侵污染土壤,而当渗滤液浓度较高时,二者几乎没有区别.研究显示,正常条件下,复电阻率法对渗滤液污染的反映灵敏,有较好的指示意义,其参数变化主要与孔隙水中金属离子的含量和双电层极化有关;而在天然低电阻率背景条件下,渗滤液污染引起的电阻率变化很小,但相位变化较为明显,这种相位的变化有可能被识别出来. 相似文献
940.