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   202315篇
  免费   11550篇
  国内免费   117篇
林业   8089篇
农学   6796篇
基础科学   1464篇
  24073篇
综合类   34275篇
农作物   7542篇
水产渔业   10385篇
畜牧兽医   104904篇
园艺   2596篇
植物保护   13858篇
  2018年   2813篇
  2017年   3164篇
  2016年   2938篇
  2015年   2540篇
  2014年   3107篇
  2013年   7987篇
  2012年   5676篇
  2011年   7014篇
  2010年   4526篇
  2009年   4487篇
  2008年   6883篇
  2007年   6478篇
  2006年   6340篇
  2005年   5673篇
  2004年   5536篇
  2003年   5509篇
  2002年   5238篇
  2001年   6540篇
  2000年   6313篇
  1999年   5001篇
  1998年   1966篇
  1997年   2055篇
  1996年   1919篇
  1995年   2372篇
  1994年   2149篇
  1993年   2060篇
  1992年   4238篇
  1991年   4424篇
  1990年   4427篇
  1989年   4397篇
  1988年   4008篇
  1987年   4088篇
  1986年   4153篇
  1985年   4014篇
  1984年   3350篇
  1983年   2962篇
  1982年   2062篇
  1981年   1898篇
  1979年   3034篇
  1978年   2461篇
  1977年   2087篇
  1976年   1953篇
  1975年   2126篇
  1974年   2699篇
  1973年   2697篇
  1972年   2606篇
  1971年   2402篇
  1970年   2268篇
  1969年   2138篇
  1967年   1878篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
41.
Landscape Ecology - Forest landscapes at the boreal–temperate ecotone have been extensively altered. Reducing the gap between current and presettlement forest conditions through...  相似文献   
42.
43.
44.
45.
46.
Abstract

The insecticidal efficacy of microwave irradiation against the at 12, 24, 48 and 72?h following exposure to microwave irradiations (100, 300?W) and the progeny production was assessed 45?days later. Linearly increasing irradiation power range (100, 200 and 300?W) was set up for determining mortality tendency. An increase of insect mortality caused by higher irradiation period and times elapsed after treatment has become evident commencing from 12?h after the treatment, which has significantly decreased at later elapsed time after treatment. The irradiation periods inducing the highest mortality at the examined powers were at 10?min and at 100?W power (72?h: 64.93%) and at 4.5?min. and at 300?W power (12?h: 87.01). In addition, a complete suppression of progeny production was achieved by 4.5?min treatment at 300?W power. Lognormal-type mortality process was caused by the linearly increased irradiation range. The properly chosen microwave irradiation can be used for management of Sitophilus granarius larval and adult developmental stages. This treatment could provide an effective and friendly environmental treatment technique in Integrated Pest Management (IPM) program.  相似文献   
47.
48.
The present study aimed to determine the ideal ratios of digestible essential amino acids (EAAs) for pacu (Piaractus mesopotamicus) juveniles by the amino acid (AA) deletion method. A completely randomized design which consisted of 11 treatments and three replicates each was used. The treatments included a control diet (CD) containing 55% of nonpurified natural ingredients and 45% of purified synthetic amino acids and ingredients, and other ten isonitrogenous and isoenergetic EAA limiting diets (LDs), each being deficient in 44.4 ± 0.02% of the respective EAA. Pacu juveniles with initial average body weight of 6.22 ± 0.09 g were distributed among 33 fiber glass tanks. Fish were fed with semipurified and extruded diets for 113 days two times a day until apparent satiation. The ideal ratio of each dietary EAA was calculated on the basis of the relationship between body N retention and amount of EAA deleted from the respective EAA LD. Based on the AA deletion method, the ideal ratios of digestible EAAs for pacu juveniles, relative to lysine requirement of 100% were estimated as: methionine 14.6%, threonine 35.0%, tryptophan 6.6%, arginine 62.8%, histidine 13.6%, isoleucine 26.3%, leucine 43.7%, phenylalanine 27.2%, and valine 35.8%.  相似文献   
49.
A large, firm, multi-cystic mammary gland mass grew slowly over 4 y in a 12-y-old, female Finn–Shetland cross sheep. A diagnosis of epithelial malignancy was suspected following fine-needle aspiration cytology at 30 mo after initial observation. The sheep was euthanized when the flock was downsized 18 mo later. A field postmortem examination revealed a large mammary mass, but an absence of metastases to internal organs. Imprint cytology of the mammary tissue supported a benign proliferative process. Histologically, mammary tissue was obliterated by cystic, tubular, and papillary adenomatous arrangements of mammary epithelium, with an anaplastic component, consistent with mammary carcinoma arising in an adenoma. IHC showed strong nuclear positivity to the antibody against progesterone receptor and minimal positivity to the antibody against estrogen receptor alpha expression. Intrinsic subtyping for basal or luminal epithelial origin was attempted through adaptation of companion animal IHC classification panels; high- and low-molecular-weight cytokeratins (CK5, CK8, CK18) failed to stain, but p63 expression for basal epithelium was positive.  相似文献   
50.
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