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   1713篇
  免费   94篇
  国内免费   4篇
  2023年   21篇
  2022年   23篇
  2021年   110篇
  2020年   41篇
  2019年   58篇
  2018年   79篇
  2017年   54篇
  2016年   57篇
  2015年   80篇
  2014年   105篇
  2013年   122篇
  2012年   117篇
  2011年   126篇
  2010年   49篇
  2009年   48篇
  2008年   70篇
  2007年   58篇
  2006年   71篇
  2005年   47篇
  2004年   29篇
  2003年   35篇
  2002年   27篇
  2001年   30篇
  2000年   29篇
  1999年   28篇
  1998年   8篇
  1997年   8篇
  1995年   4篇
  1994年   18篇
  1993年   10篇
  1992年   17篇
  1991年   16篇
  1990年   20篇
  1989年   18篇
  1988年   12篇
  1987年   17篇
  1986年   14篇
  1985年   21篇
  1984年   12篇
  1983年   9篇
  1982年   9篇
  1981年   7篇
  1979年   6篇
  1977年   7篇
  1976年   5篇
  1974年   8篇
  1973年   6篇
  1972年   8篇
  1971年   8篇
  1970年   7篇
排序方式: 共有1811条查询结果,搜索用时 15 毫秒
41.
  1. Ongoing intensification and fragmentation of European agricultural landscapes dramatically reduce biodiversity and associated functions. Enhancing perennial noncrop areas holds great potential to support ecosystem services such as ant‐mediated pest control.
  2. To study the potential of newly established grassland strips to enhance ant diversity and associated functions, we used hand collection data and predation experiments to investigate differences in (a) ant community composition and (b) biocontrol‐related functional traits, and (c) natural pest control across habitats in cereal fields, old grasslands, and new grassland transects of three years of age.
  3. Ant species diversity was similar between new and old grasslands, but significantly higher in new grasslands than in surrounding cereal fields. Contrary, ant community composition of new grasslands was more similar to cereal fields and distinct from the species pool of old grasslands. The functional trait space covered by the ant communities showed the same distribution between old and new grasslands. Pest control did not differ significantly between habitat types and therefore could not be linked to the prevalence of functional ant traits related to biocontrol services in new grasslands.
  4. Our findings not only show trends of convergence between old and new grasslands, but also indicate that enhancing ant diversity through new grasslands takes longer than three years to provide comparable biodiversity and functionality.
  5. Synthesis and applications: Newly established grasslands can increase ant species richness and abundance and provide a consistent amount of biocontrol services in agroecosystems. However, three years after their establishment, new grasslands were still dominated by common agrobiont ant species and lacked habitat specialists present in old grasslands, which require a constant supply of food resources and long colony establishment times. New grasslands represent a promising measure for enhancing agricultural landscapes but must be preserved in the longer term to promote biodiversity and resilience of associated ecosystem services.
  相似文献   
42.
OBJECTIVE--To determine the efficiency of tuberculosis contact tracing in South Glamorgan 1987-9. DESIGN--Review of records of contact tracing clinic and of data from the Mycobacterium Reference Unit. The clinic''s practice was compared with 1983 British Thoracic Society''s recommendations. SETTING--Health authority tuberculosis control programme. MAIN OUTCOME MEASURES--Proportion of contacts screened, follow up attendance rates, number of secondary cases detected, and quality of record keeping. RESULTS--101 index patients and 611 contacts were identified. 596 (97.5%) contacts were screened, of whom 139 should not have been. Of 356 contacts requiring a Heaf test, 237 were tested, seven refused the test, and 112 had chest radiography without a Heaf test. 95 contacts were unnecessarily tested. 87 contacts had chest radiography unnecessarily and seven should have had radiography but did not. 34 contacts were given follow up appointments inappropriately and seven were overlooked for follow up. Tuberculosis was diagnosed in five asymptomatic contacts, all at initial screening and all close contacts of index patients with pulmonary disease. CONCLUSION--Inadequacy of data, non-adherence to contact tracing guidelines, and failure to define the term highly infectious index case resulted in many contacts being unnecessarily screened or followed up. IMPLICATIONS--The efficiency of tracing contacts would be improved by specifying smear results and ethnic origin of the index case on the notification form, clearly classifying contacts as close or causal, and clearly defining the term highly infectious.  相似文献   
43.
International Journal of Peptide Research and Therapeutics - Piwi interacting RNA (piRNA) molecules belong to a largest class of small non coding RNA molecules which are originally discovered in...  相似文献   
44.
45.
The human epidermal growth factor (HER2) is a transmembrane receptor that is highly expressed in breast cancer and in different other cancers. Therefore, it is of interest to identify the new HER2 inhibitors from a selected 300 compounds in the ZINC database. The top two hit compounds (ZINC000014780728 (-11.0 kcal/mol) and ZINC000014762512 (-10.8 kcal/mol)) showed a high affinity with HER2 relative to the reference compound (lapatinib (-10.2 kcal/mol)) for further consideration.  相似文献   
46.
Beta-catenin is linked with colorectal cancer (CRC). Therefore, it is of interest to design and develop novel compounds to combat CRC. Hence, we document compounds (chlorogenic acid, gallic acid, protocatechuic acid, quercetin and vanillic acid) from Lycopersicon esculentum with optimal binding features for further consideration.  相似文献   
47.
Plant and Soil - Success in agronomic biofortification of maize and wheat is highly variable. This study aimed to elucidate the differences in uptake and translocation of foliar-applied zinc (Zn)...  相似文献   
48.
49.
50.
Doklady Biochemistry and Biophysics - Abutilon indicum Linn (A. indicum) is native to tropical and subtropical zones and traditionally used in ulcer, diabetes, piles, jaundice, gonorrhoea and...  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