首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   12299篇
  免费   170篇
  国内免费   151篇
安全科学   506篇
废物处理   532篇
环保管理   2662篇
综合类   1358篇
基础理论   3298篇
环境理论   16篇
污染及防治   2804篇
评价与监测   831篇
社会与环境   530篇
灾害及防治   83篇
  2023年   53篇
  2022年   63篇
  2021年   100篇
  2020年   77篇
  2019年   116篇
  2018年   256篇
  2017年   302篇
  2016年   400篇
  2015年   265篇
  2014年   230篇
  2013年   1085篇
  2012年   755篇
  2011年   708篇
  2010年   393篇
  2009年   420篇
  2008年   529篇
  2007年   597篇
  2006年   494篇
  2005年   711篇
  2004年   835篇
  2003年   740篇
  2002年   377篇
  2001年   204篇
  2000年   218篇
  1999年   188篇
  1998年   145篇
  1997年   131篇
  1996年   146篇
  1995年   156篇
  1994年   146篇
  1993年   127篇
  1992年   137篇
  1991年   100篇
  1990年   100篇
  1989年   86篇
  1988年   85篇
  1987年   76篇
  1986年   92篇
  1985年   77篇
  1984年   76篇
  1983年   92篇
  1982年   95篇
  1981年   105篇
  1980年   75篇
  1979年   60篇
  1978年   55篇
  1977年   50篇
  1976年   30篇
  1975年   26篇
  1974年   24篇
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
101.
We report herein a de novo unbalanced chromosome translocation in a fetus resulting from in vitro fertilization technology. Prenatal diagnostic analysis of an amniotic fluid revealed a 46,XX,4p+ karyotype. The origin of the extra material on the short arm of chromosome 4 could not be identified by a variety of banding techniques. However, examination of fetal parts did reveal some dysmorphic features.  相似文献   
102.
Reverse phase HPLC of radioactive globin chains has been compared to classical carboxy methyl cellulose chromatography for the prenatal diagnosis of β thalassaemia. The two methods correlated highly (r = 0.97 p < 0.0005) and provided an identical diagnosis for 40 fetal blood samples of fetuses homozygous or heterozygous for β thalassaemia. The HPLC procedure was much faster and required fewer biochemical steps (no globin preparation). It was at least as accurate and more sensitive than the classical chromatography. A single column can be used for 150 analyses and is always ready to be used. Last but not least it is much less expensive than CMC chromatography.  相似文献   
103.
Mitigation and Adaptation Strategies for Global Change - In Mexico an estimated 4.5 × 106ha are available for farm forestry, while up to 6.1 × 106 ha could be saved from deforestation by...  相似文献   
104.
105.
Although malignant transformation of fetal cervical teratoma is extremely rare, perinatal morbidity is high and usually related to the size of the tumour, which may compromise fetal swallowing and subsequently lead to upper airway obstruction. We present a case in which mid-trimester serial sonography demonstrated markedly rapid early growth of a lesion of this type between 17 and 19 weeks' gestation indicating the aggressive nature of this tumour, assisting parental decision to terminate the pregnancy. Histopathology confirmed grade 3 immaturity of the lesion.  相似文献   
106.
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   
107.
108.
Foreword     
Mitigation and Adaptation Strategies for Global Change -  相似文献   
109.
110.
Stratigraphy, lithology and depositional structures of Liassic red limestone-breccias of the Adnet Formation, including the 'Adnet Scheck', were studied at several outcrops of the Northern Calcareous Alps (NCA) south-east of Salzburg. A four-fold lithostratigraphic division is proposed for the Adnet Formation of the Osterhorn Mountains: the hemipelagic Schmiedwirt (Sinemurian) and Kehlbach (Carixian) members are separated from the pelagic Saubach Member (Toarcian) by a layer of amalgamated breccias (Scheck Member, probably Domerian to early Toarcian). Several other breccia beds occur locally from the base of the Kehlbach Member up to the lower Saubach Member. Although the sediments overlying the Scheck Member breccias are of coeval age, the ages of the underlying strata are very different. This can be explained by submarine Liassic erosion during a period of resedimentation from the middle Carixian until the early Toarcian. At least 10–15?m of partly lithified sediments were eroded by gravity flows. The entire Kehlbach Member and up to two-thirds of the Schmiedwirt Member were removed at Adnet. The breccias originated from submarine debris flows. Repeated flows over a long period and the depositional setting exclude a triggering by sea-level fluctuations. Most probably they arose from tectonically triggered slumps and slides of superficial sediments. The 'Scheck' was initiated on the steep upper slope of the drowned Triassic Adnet reef and flowed to the north-east.The Pliensbachian to early Toarcian period of tectonic activity indicated by the breccias was the most important during the Liassic in the Osterhorn Mountains and other parts of the NCA. From the large-scale regional distribution of the breccias and in accord with published data, a roughly north-east trending strike-slip fault zone is proposed, crossing the NCA south of the Osterhorn block, with a peaking activity during the Pliensbachian to early Toarcian as the cause of the tectonic movements.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号